1 AN ABSTRACT OF THE THESIS OF Alexander K Raab for the degree of Master of Science in Geology presented on August 27, Title: Geology of the Cerro Neg...
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AN ABSTRACT OF THE THESIS OF Alexander K Raab for the degree of Master of Science in Geology presented on August
27, 2001. Title: Geology of the Cerro Negro Norte Fe-Oxide (Cu-Au) District, Coastal Cordillera, Northern Chile.
Abstract A roved: Redacted for privacy
John H. Dilles
The intrusion-related Cerro Negro Norte Fe-oxide (Cu-Au) deposit is hosted in andesites and diorites of the early to middle Cretaceous Coastal Cordilleran arc of northern Chile. Tabular and irregularly shaped magnetite orebodies are localized on splays and fractures of the regional NNE striking Atacama Fault Zone. Production from
this district was 100 MT @ 65 wt. % Fe. Early Na-Ca alteration assemblages associated with magnetite ± apatite ± pyrite ± chalcopyrite ore include actinolite, marialitic scapolite, oligoclase, titanite, and epidote. Na-Ca alteration is extensive (> 4 km2 in area), locally pervasive in the district,
and is locally associated with granodiorite dike emplacement. The alkali-rich alteration and sulfide poor mineralization at CNN is characterized by metasomatic exchange of major, minor, and trace elements (added Fe, Na, Ca, Cl, P, Rare Earth Elements) between andesitic and diorite host rocks and halite-saturated saline hydrothermal fluids preserved as inclusions. Intrusion-heated fluids converge along the Atacama Fault Zone, and dikes, and may have been derived either from seawater or evaporitic water trapped in sedimentary rocks of the protoarc.
Younger, cross-cutting hydrothermal assemblages such as tourmaline-quartzsericite (± breccias), associated with granodiorite dikes, and chlorite-calcite-tourmalinequartz assemblages are related to pyrite ± chalcopyrite ± hematite and Cu-Au mineralization. Supergene minerals include goethite, Cu-carbonates and Cu-oxide. Later carbonate (dolomite) alteration is also localized along northeast-striking faults.
Inferred Cu-Au estimates are 1 MT @ lg/T Au and 0.25 wt. % Cu. Late alteration assemblages may contain a component of magmatic saline fluids generated by observed monzodiorite-granodiorite dikes and pluton emplacement. Massive magnetite ore and associated Na-Ca alteration assemblages were
deposited at high temperatures ( 500 to 600° C), with igneous intrusions providing heat but not necessarily fluids and metals. Later moderate to low temperature Cu-Au mineralization (sulfide + oxide) replaces magnetite, and records the transition to more brittle faulting, with NW ± re-activated NNE structural control, and a greater proportion of magmatic fluids, sulfur (834Spy= -1 %o), and metals.
C) Copyright by Alexander K. Raab August 27, 2001 All Rights Reserved
Geology of the Cerro Negro Norte Fe-Oxide (Cu-Au) District, Coastal Cordillera, Northern Chile by Alexander K. Raab
A THESIS submitted to
Oregon State University
in partial fulfillment of the requirements for the degree of Master of Science
Presented August 27, 2001 Commencement June 2002
Master of Science thesis of Alexander K. Raab presented on August 27, 2001
APPROVED: Redacted for privacy
Major Professor, representing Geology Redacted for privacy
Chair of Department of Geosciences Redacted for privacy
I understand that my thesis will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my thesis to any reader upon request.
Redacted for privacy
Alexander K. Raab, Author
ACKNOWLEDGEMENTS I would like to thank my committee, and in particular, Dr. John H. Di lles for support
and guidance throughout my masters program at Oregon State University. John was always available to meet with me and discuss or explain questions regarding classes, thesis research, fieldwork, and industry opportunities. His connections with industry and academia, as well as excellent mentoring in the field as an economic exploration field geologist were very beneficial during my academic career. Cy Field provided assistance in accomplishing sulfur isotope work, and was always available to discuss both project work and adventures in South America. I would also like to thank all of the other Geoscience and several Oceanography professors with whom I was in close contact during my three years at OSU. They always made time for work and play and were open and accommodating as friends and mentors. I appreciated the comradery in the department between different professors and students and enjoyed all the scholastic and social events we shared.
Portions of this project were funded by Dr. John Dilles, who always worked hard to provide me with continuous Teaching Assistantships and Research Assistantships. Other portions of the project were funded Cyrus Field. Two grants received from the Society of Economic Geologists, and one grant from the Geological Society of America also provided funds for portions of my fieldwork and laboratory analysis costs. I would like to acknowledge Compania Minera Pacifica and all their geologists for allowing access to and providing time to tour and discuss many of the Chilean Fe-oxide deposits. Geologists from the Chilean Servicia Nacional de Geologia
y Mineria, and other companies also provided valuable information and expertise. I wish to thank all of my close friends at OSU, in the U.S.A., Chile, and other parts of the world for their support, encouragement, and friendship over the past three years; their companionship has been a big part of my success in this project. Finally, to my parents and sister who have been there through all the "thick and thin" that life brings, appreciate their continuing love, support and encouragement through this and many other of my endeavors. Appropriately, this degree is dedicated to my family.
TABLE OF CONTENTS Rage
CHAPTER 1: INTRODUCTION AND PURPOSE 1.1 INTRODUCTION AND PURPOSE 1.2 FE-OXIDE-CU-AU-U-REE DEPOSITS AND THEIR ORIGIN( WORLD WIDE)
CHAPTER 2: FE-OXIDE DEPOSITS OF THE CHILEAN IRON BELT 2.1 PAST STUDIES IN THE CHILEAN IRON BELT
2.2 RECONNAISSANCE STUDIES IN THE CHILEAN IRON BELT
NORTHERN CHILEAN IRON BELT 22.214.171.124 CERRO IMAN (Fe) 126.96.36.199 EL SALVADOR (Cu-Au) 188.8.131.52 LA LUNAR (Fe) 184.108.40.206 LA LUNAR (Au) 220.127.116.11 AUGUSTINA (Fe)
.17 .17 .23 ..24 ..25 25
2.2.2 SOUTHERN CHILEAN IRON BELT 18.104.22.168 El ROMERAL (Fe) 22.214.171.124 LOS COLORADOS (Fe) 126.96.36.199 EL ALGARROBO (Fe)
.27 27 .29 33
2.2.3 MANTO VERDE, PUNTA DEL COBRE, AND LA CANDELARIA 188.8.131.52 MANTO VERDE (Cu, Au) 184.108.40.206 PUNTA DEL COBRE DISTRICT 220.127.116.11 LA TIGRESA (Cu-Au) 18.104.22.168 LA CANDALARIA (Cu-Fe-Au)
...33 .35 ..41
TABLE OF CONTENTS (CONTINUED) Page
CHAPTER 3: METHODOLOGY OF CERRO NEGRO NORTE FIELD AND LABORATORY STUDIES 3.1 FIELD MAPPING
3.3 ELECTRON MICROPROBE
3.5 SULFUR ISOTOPES
3.6 U/PB GEOCHRONOLOGY
CHAPTER 4: REGIONAL GEOLOGY OF THE COASTAL CORDILLERA, AND GEOLOGY OF THE CERRO NEGRO DISTRICT 4.1 REGIONAL GEOLOGY OF THE COASTAL CORDILLERA
CHAPTER 7: MINERALIZATION OF THE CERRO NEGRONORTE DISTRICT 7.1 FE-OXIDE (MAGNETITE + HEMATITE) MINERALIZATION..
7.2 SULFIDE (PYRITE AND CHALCOPYRITE) AND SULFATES (BARITE AND GYPSUM) MINERALIZATION
7.3 CU-AU MINERALIZATION
TABLE OF CONTENTS (CONTINUED) Page
CHAPTER 8: GEOCHEMISTRY OF THE CERRO NEGRO NORTE DISTRICT 8.1 INTRODUCTION
8.2 MAJOR OXIDES
8.3 TRACE ELEMENTS
8.4 GEOCHEMISTRY OF CU AND AU IN THE HYDROTHERMAL SYSTEM .157 8.5 RARE EARTH ELEMENTS
CHAPTER 9: SULFUR ISOTOPES OF THE CERRO NEGRO NORTE DISTRICT 9.1 INTRODUCTION
CHAPTER 10: U/PB GEOCHRONOLOGY OF THE CERRO NEGRO NORTE DISTRICT 10.1 INTRODUCTION
10.2 U/PB DATES ON TITANITE FROM EARLY SCAPOLITE-BEARING NA-CA ALTERATION AT CERRO NEGRO NORTE 171 CHAPTER 11: SUMMARY AND CONCLUSIONS ON THE CERRO NEGRO NORTE DISTRICT 11.1 SUMMARY
TABLE OF CONTENTS (CONTINUED) Page REFERENCES
LIST OF FIGURES Figure
la. Location Map of some of the larger Fe-oxide deposits of the Chilean Iron Belt (CM)
lb. Location Map of the Atacama Fault Zone (AFZ) in the Coastal Cordilleran arc of northern Chile
2a. Schematic geologic summary of field observations at some Fe-oxide deposits in the northern CIB 18 2b. Schematic details of massive magnetite ores from field observations at some Fe-oxide deposits in the northern CIB
3a. Generalized geology and E-W cross section of the Cerro Iman Fe-oxide deposit
3b. West side of mylonitized zone at Cerro Iman
3c. View looking south-southwest over the Cerro Iman magnetite mine pit
4a. Augustina magnetite Fe-oxide deposit
4b. Augustina mine
5a. Bedrock geology of the El Romeral Fe-oxide massive magnetite deposit, near La Serena, Chile
5b. View looking north over the north pit at El Romeral
5c. South end of the main northern El Romeral pit floor
6a. View looking east across the "B" pit to the "east" pit at Los Colorados
6b. Looking northeast at a post-mineral dike cutting massive magnetite in the east ore body pit floor at Los Colorados
7a. Sample of massive magnetite with elongate crystal habit from the El Algarrobo Fe-oxide deposit
7b. Pit floor of the "C" pit at the El Algarrobo Fe-oxide mine owned and operated by CMP
LIST OF FIGURES (CONTINUED) Figure
8a. Generalized distribution of geologic units across the central part of the Manto Verde deposit
8b. Generalized distribution of hydrothermal alteration across the central part of the Manto Verde deposit
8c. Generalized distribution of Fe-Cu-Au mineralization across the central part of the Manto Verde deposit
8d. View to the north from the main pit at Manto Verde
8e. View of Manto Russo on the Manto Verde property
8f. Sample MR 1 from the Manto Russo area
8g. Samples from Manto Verde
9a. View looking north over the Cerro Negro Norte District
9b. View looking south-southeast over the Cerro Negro Norte District
10a. Western ridge line to the west of Cerro Negro Norte District
10b. Magmatic hydrothermal breccia with magnetite clasts (CNN 4)
11 a. View looking to the south over Sector Augusta at Cerro Negro Norte
11b. View looking southeast to the northern slopes of Sector Augusta at Cerro Negro Norte
12a. View looking NW from the west edge of the Abanderada pit
12b. Augusta area at Cerro Negro Norte
13a. Sector Veta Central at Cerro Negro Norte
13b. View looking to the east-northeast at the north end of the Abanderada pit
LIST OF FIGURES (CONTINUED) Figure
14a. View to the NE from the east rim of Abanderada pit..
14b. View looking ENE from the Abanderada ramp
14c. Abanderada pit floor at Cerro Negro Norte
14d. View looking NNE from the east rim of the Abanderada pit, at Cerro Negro Norte
14e. View looking NE from the eastern rim of the Abanderada pit at Cerro Negro Norte
19a. CNN 102, 103 at Cerro Negro Norte located west of the Abanderada pit
19b. CNN 78 to the west of the Abanderada pit
20a. CNN 19 sample from the Sector Abanderada
20b. Abanderada magnetite with plagioclase veinlets dump sample
21a-d. Photomicrographs of various plagioclase analyzed by electron microprobe
22. Feldspar ternary plot of samples from Cerro Negro Norte
23a-d. Photomicrographs of various tourmaline and quartz crystal habits
23e-f. Photomicrographs of sericite alteration after plagioclase associated with tourmaline-quartz alteration
24a. Late pegmatite/aplite dikes or sills
24b. Abanderada pit wall at 4+90 m, sample CNN 63
24c. Abanderada dump pegmatite veins
24d. Abanderada pit sample of massive pegmatite float
24e. Sector Cata Alfaro at Cerro Negro Norte 24f-i. Tourmaline thin section scans and photomicrographs
LIST OF FIGURES (CONTINUED) Figure
25. Variation plots comparing the Fe number to major oxides of Na, Ca, Ti, and Al in tourmaline
26a-d. Photomicrographs of various chlorite + calcite + sulfide alteration and mineralization
27a. View to the SE from within the Abanderada pit at sample CNN 67
27b. Liesegang goethite + carbonate veining along east side of the Abanderada pit
27c-d. Photomicrographs of carbonate alteration and barite mineralization
27e. Dolomite or carbonate veins cut through massive magnetite altered to hematite in the Abanderada
28a. Magnetite vein (CNR 13) located south of Cerro Negro Sur
28b-e. Magnetite mineralization in thin section scans and photomicrographs
28f. Scattergraph comparing molar Cl /(Cl +F) versus molar Cl /(Cl +F +OH) of apatite at Cerro Negro Norte
29a. Abanderada pit, near sample CNN 55
29b. Abanderada pit at 4+30 m, near sample CNN 59A
29c. Late quartz + sulfide veining in Abanderada dump sample
29d. Early Na-Ca cut by late quartz + sulfide veining in Abanderada pit at 3+50 m (dump pile)
29e-g. Late quartz + sulfide veins in thin section scans
30a-d. Photomicrographs of various sulfide replacement of magnetite, and late quartz + calcite + sulfide veining....
31a. Abanderada pit at 4+84 m
31b. Abanderada pit, near sample CNN 13
LIST OF FIGURES (CONTINUED) Figure
31c. Thin section scan of CNN120
32a. Backscatter image of CNS 7 from the Augusta Sector 32b. Photomicrograph of CNS 7 from the Augusta Sector
33. Variation diagrams for SiO2 wt. % vs major oxide wt. %
34a-b. Spider diagrams showing chemical gains and losses of major oxides (A) and trace elements (B) for three main types of alteration at Cerro Negro Norte
35. Log variation diagrams for SiO2 wt. % versus trace elements in ppm (Au in ppb)
36. Isocon diagrams for Fe-oxide-Cu-Au mineralized samples from the Abanderada Sector at Cerro Negro Norte
36a. Variation digrams comparing Cu and Au in early Fe-rich (magnetite) and late S-rich (sulfide) mineralization events
37. REE spider plots comparing trends for unaltered and altered andesite and diorites both distal and proximal to the massive magnetite Fe ore bodies at Cerro Negro Norte ..160 38. Distribution of 834S values from pyrite, chalcopyrite, and barite from Cerro Negro Norte
39a. Sample CNN 115 at Cerro Negro Norte
800 m west of the Augusta Sector 172
39b. Backscatter image of CNN 115
39c. Photomicrograph of CNR 2B (2.5X) x-polar
U versus 207Pb/235U plot for the crystallization age of titanite
41. Schematic model of igneous-driven circulation of evaporitic fluids showing alteration zoning in mafic and felsic systems
42. Schematic geologic plan view and cross section of the Cerro Negro Norte District
LIST OF TABLES Table 1.
Table of hydrothermal mineral assemblages, associated vein assemblages, and relict minerals
2. U/Pb age determinations for titanite from the CNN District
LIST OF APPENDICES Appendix
A1.1 Petrography description of samples; includes descriptions of lithology, alteration, veining and mineralization from polished and unpolished thin sections. Appendix indicates which samples have been analyzed by electron microprobe, sulfur isotopes, geochemistry, photomicrographs, and thin section scans 196 A2.1 List of 30 computer-scanned thin sections; includes a list of unpolished
long thin sections which have been scanned and illustrated. See CD-ROM for scanned images, petrography descriptions can be found in appendix A1.1 1
A3.1 List of 46 photomicrographs; includes a list of samples with both
transmitted and reflected light photographs of groundmass, phenocrysts, textures, mineral assemblages, alteration and lithology from the Cerro Negro Norte District. See CD-ROM for photomicrographs
B1.1 List of sample numbers from the Cerro Negro Norte District and
microscope coordinates of minerals which have been analyzed by Electron Microprobe 235
B1.2 List of all elements analyzed by Electron Microprobe for specific minerals found in CNN samples
B2.1 Electron Microprobe Chemical Analyses of Scapolite
B2.2 Electron Microprobe Chemical Analyses of Feldspar
B2.3 Electron Microprobe Chemical Analyses of Amphibole
B2.4 Electron Microprobe Chemical Analyses of Pyroxene
B2.5 Electron Microprobe Chemical Analyses of Apatite
B2.6 Electron Microprobe Chemical Analyses of Titanite / Rutile B2.7 Electron Microprobe Chemical Analyses of Tourmaline
B2.8 Electron Microprobe Chemical Analyses of Sulfides
B2.9 Electron Microprobe Chemical Analyses of Barite
LIST OF APPENDICES (CONTINUED) Appendix
B2.10 Electron Microprobe Chemical Analyses of Mica (Sericite, Chlorite) B2.11 Electron Microprobe chemical analyses of Magnetite / Hematite
C1.1 List of 17 samples analyzed for geochemical whole rock analyses including; ten major oxides and forty trace elements. A description of the
sample's dominant lithology, alteration assemblages, and mineralization is included ...263
C1.2 Geochemical elemental detection limits analyzed by ICP, INAA, ICP-MS and XRF .264
C2.1 Geochemical analyses of whole rock for major and trace element content, Cerro Negro Norte samples .265 C3.1 Rare Earth Elements normalized to chondrite
C3.2.1 Major Oxides normalized to TiO2
C3.2.2 Trace elements normalized to TiO2
C3.3.1 Elemental gains and losses calculated in % for major oxides normalized to TiO2 for unaltered versus altered andesite from Cerro Negro Norte
C3.3.2 Elemental gains and losses calculated in % for trace elements normalized to TiO2 for unaltered versus altered andesite from Cerro Negro Norte 269 D1.1 Sulfur isotope appendix; includes a list of samples, sulfide or sulfate
mineral separates, purities, mineral assemblages, paragenetic association, and 834S %.2, values
E1.1 CNN District Field Photograph appendix; includes a list of 84 photographs, with short descriptions from the Cerro Negro Norte District. See CD ROM for illustrated photos ..271 E2.1 CIB Field Photograph appendix; includes a list of 32 photographs of various active and inactive mines and prospects from the Chilean Iron Belt from 26° 32° S latitude. See CD-ROM for illustrated photos .273
LIST OF PLATES (POCKET) Plate 1.
Plate #1 Cerro Negro Norte District Geology, 1:10,000 scale
2. Plate #2 Cerro Negro Norte District Alteration 1:10,000 scale 3.
Plate #3 Cerro Negro Norte District Mineralization 1:10,000 scale
6. Plate #3 Abanderada Sector, Mineralization, 1:1000 scale 7. Plate #7 Cerro Negro Norte District Topography and Sample Locations,
CD-ROM (POCKET) 1.
Appendix A2.1 30 computer-scanned and illustrated unpolished long thin sections from the Cerro Negro Norte District.
2. Appendix A3.1 46 photomicrographs of selected samples from the Cerro Negro Norte District. 3. Appendix E1.1 84 illustrated photographs from the Cerro Negro Norte District. 4. Appendix E2.1 32 illustrated photographs from the Chilean Iron Belt (CIB).
Geology of the Cerro Negro Norte Fe-Oxide (Cu-Au) District, Coastal Cordillera, Northern Chile
CHAPTER1: INTRODUCTION AND PURPOSE
1.1 Introduction and Purpose The major igneous-related Fe-oxide (Cu-Au) deposits of the Chilean Iron Belt (CIB) are located in the Cordilleran Coastal Range of northern Chile between 26° and 32° S
latitude. These deposits are hosted in late Cretaceous rocks of the Jurassic to Late Cretaceous magmatic arc and back-arc rocks of the Chilean Coastal Cordillera (Brown et al., 1993; Grocott et al., 1994), which include andesitic volcanic rocks, plutonic rocks ranging in composition from diorite to granite (Arevalo, 1995; Bookstrom, 1977; Vivallo, 1995), and marine sedimentary rocks deposited in shallow water (Tilling, 1962; Marschik and Fontbote, 1996). All of these deposits are closely spatially related to the Atacama Fault Zone (AFZ), and subsidiary faults. The AFZ, located between La Serena, Chile (29.75° S) and Iquique, Chile (20.5° S) is a 1000 km long, trench-parallel,
subduction-related fault zone, trending sub-parallel to the Jurassic-Cretaceous magmatic arc. Early ductile extension along the AFZ is possibly responsible for the emplacement of N-S linear trending plutonic complexes and Fe-oxide (magnetite) mineralization, along an eastward dipping ramp fault (Grocott et al., 1994).
A later brittle motion with a transtensional left-lateral strike-slip character along the AFZ and possibly related NNW-striking transpressional left-lateral strike-slip faults
are often the locus of Fe-oxide deposits with Cu and Au mineralization. The transition to the later brittle faulting, according to Grocott et al. (1994) was a result of cooling and eastward migration of the arc during the Late Cretaceous. The Fe-oxide deposits of the CIB are dominantly massive magnetite bodies that form as irregular elongate to tabular ore bodies up to several hundred meters long and wide and usually more than one hundred meters deep. The Fe-oxide ore bodies often lie immediately adjacent to or very close to, the NNE-striking AFZ and are often closely spatially associated with diorite to granodiorite intrusions.
The magnetite ore bodies throughout the CIB vary in size from several tens to 400 MT, with from
100 MT common for some of the larger mined deposits. Grades range
50 to 100 weight percent total Fe-oxide. The mineralogy of the ores is magnetite
± hematite ± apatite ± pyrite ± chalcopyrite. Sulfide mineralization is typically very sparse and does not exceed a few volume percent total. Gangue minerals in the Fe-oxide ore are actinolite ± quartz ± tourmaline ± calcite. Cu and Au grades vary, but are generally low and most often are not directly associated with the magnetite ore. However, locally sulfides do replace magnetite. Average Cu and Au tonnage is usually 1 MT at an average grade of 1g/T Au, and 0.25 wt. % Cu.
Characterization of the similarities and differences of the Fe-oxide (Cu-Au-Rare Earth Elements) deposits of the CIB in terms of geology, mineralization, and structural controls may help to create a time-space model for these types of deposits. The working hypothesis of this study is that the Cerro Negro Norte Fe-oxide (Cu-Au) District and other Chilean Fe-oxide deposits form as the direct result of igneous-driven circulation of hydrothermal saline fluids derived from either evaporitic or sedimentary basin brines,
or possibly sea-water, which produces Fe and Na-Ca metasomatism along the NNEstriking Atacama Fault Zone. A secondary hypothesis is that Cu-Au mineralization was later and is the result of magmatic, or a mixing of magmatic and connate source fluids controlled by secondary NW-striking faults in the district, which leads to particular interest in the timing and spatial association of Fe-oxide and Cu-Au mineralization. The purpose of this study is to determine the geologic environment of ore formation and alteration at the Cerro Negro Norte Fe-oxide (magnetite) deposit, and thereby possibly evaluate whether or not the source and pathways of the mineralizing hydrothermal fluids are non-magmatic versus magmatic.
1.2 Fe-Oxide-Cu-Au-U-REE Deposits and their Origin (Worldwide) Fe-oxide mineralization with variable enrichment in Cu, Au, U, and REEs, which range in age from Proterozoic through Mesozoic, occurs in both end-member felsic and mafic volcanic and intrusive rocks. The mafic to intermediate deposits tend to be associated with orogenic and continental-margin (extensional) settings, whereas the felsic end-members are associated with anorogenic or back-arc settings (Barton et al., 1996). Common traits between these two end-members are the Fe mineralization, low sulfide to oxide ratios, sparse base metals except Cu, REE (deposit / igneous rock) enrichment, saline fluids, early high-temperature magnetite-apatite-scapolite to late low temperature, low-pH assemblages such as hematite-mica ± quartz ± sulfide ± REE ± phosphate.
Barton and Johnson (1997) and Johnson and Barton (2000a) have worked in the Great Basin on the Humbolt Mafic Complex and the felsic Cortez Mountains, in
western Nevada. Both of these areas are related to the Jurassic arc and back-arc region
of western North America. Similarities exist between these two complexes and the Feoxide deposits of Chile. At the Humbolt and Cortez Mountains complexes there is extensive high temperature proximal and deeper sodic-calcic alteration and shallower depth distal potassic alteration (albite ± scapolite ± hornblende), with extensive mass transfer of Na, K, Ca, Fe, Mg, P, Cu, Zn, Pb and REE's. Barton and Johnson (1996) have proposed hydrothermal fluids are evaporitic brines with high Cl/S ratios; therefore, only least soluble chalcophile elements (Cu) form sulfides with other elements forming oxides or oxysalts (Fe, U, REEs) or metals (Au). The fluids (SO4 > H2S) have too little
sulfur to precipitate sulfide minerals at high temperatures, along the flow path from the source rocks toward the intrusives resulting in the removal of Pb and Zn from the system and sparse Fe sulfide precipitation. With decreasing temperature fluids become more oxidizing and sulfidizing and hematite ± Cu-Fe sulfides precipitate (Barton and Johnson, 1996). These characteristics are seen clearly at the El Romeral deposit, CIB, Chile, where in the main ore body sulfur content is low in the main ore body and pyrite accompanied by traces of hypogene chalcopyrite are the most common sulfides. Apatite from El Romeral contains minor CO2 and abundant Cl as determined by chemical tests
with nitric acid and silver nitrate, respectively (Bookstrom, 1977). An early scapolite alteration and a late chlorite ± carbonate alteration typify the mafic systems, whereas the felsic systems have an early sodic (albitic)-potassic and late silicic-sericitic alteration (Barton and Johnson, 1996). Hitzman et al. (1992) demonstrate that many Proterozoic deposits worldwide have the sodic-potassic alteration patterns that dominate the deep parts of the deposits and are consistent with high-temperature (400° C)
hydrothermal fluids. Prograde heating fluids produce Na-metasomatism and retrograde cooling fluids produce more distal shallow K-metasomatism (Barton and Johnson, 1996; Di lles and Einaudi, 1992).
Work on the Proterozoic age Olympic Dam deposit, in Australia, by Haynes et al. (1995) suggest a fluid-mixing model for ore genesis. Mineral associations and their zonation, fluid inclusion and isotopic data have indicated a hot source fluid of either magmatic origin or deep meteoric origin that has mixed with cooler meteoric water. Fluid inclusion salinity data suggest a source fluid, which originated as saline ground water or playa lake water associated with the felsic and mafic volcanic rocks in the area. Fe-oxide deposits without economic Cu ± U may be a result of the absence of contemporaneous oxidized saline ground water, or a depositional temperature, which is too high. Modeling at the Olympic Dam (Cu-Au-U) deposit suggests that an oxidized saline ground water transported Cu, Au, U and S042 and then mixed with hotter water carrying Fe, F, Ba and CO2 (Haynes et al., 1995).
Work on the Pliocene-Pleistocene El Laco District also brings new evidence for a saline fluid source involved in the genesis of Fe-oxide deposits (Rhodes et al., 1997). Scapolite and diopside metasomatism of host rock andesites preceded magnetite mineralization, which was followed by silicic and argillic alteration. Fluid inclusions taken from the diopsidic alteration are extremely saline and indicate high
homoginization or trapping temperatures that may be bimodal (710° 750° C and 810°820° C). Primary fluid inclusions from apatite yielded homogenization temperatures of 250°- 350° C, with salinities between 0.02 59 weight percent NaCl. The 5180 %o
values, from diopside alteration, apatite, and quartz relative to typical igneous rock
suggest oxygen exchange with an isotopically heavy fluid. Ore may have been deposited by a mixture of magmatic-hydrothermal fluid, which was generated as magmatic water from calc-alkaline magma at depth, with evaporitic rocks or with evaporite-derived fluids. Such fluids would be capable of mobilizing large amounts of iron (Rhodes et al., 1997).
Carten (1986), Dilles and Einaudi (1992) and Dilles et al. (1995, 2000) have worked on Na-Ca altered porphyry copper deposits, extensively in the Yerington District of Nevada, where moderate fluid/rock ratios produce extensive sodic/calcic alteration both peripheral and below the ore zones at 3-5 km paleodepth. The causative fluids originated as high-salinity, alkali-chloride formation waters, which flowed up a temperature gradient (prograde fluid path) produced by the batholith intrusion (Dilles et al., 1995). These heated fluids (400° C) result in the addition of Na, Ca, and the removal of Fe and K (sodic-calcic alteration). These fluids may have produced Fe deposits upon cooling, in outflow zones, for example the Pumpkin Hollow deposit (200 MT of Fe) (Dilles and Proffett, 1995; Dilles et al., 2000). The alteration of the quartz monzodiorite-granite at Yerington includes plagioclase, actinolite, epidote and titanite. Middle Triassic diorites and granites near Yerington also have sodic-calcic alteration. Cretaceous-aged plutons in the western margin of the Great Basin rarely exhibit sodic alteration due to their spatial relation to the limits of the Jurassic evaporite sequences of the Early Mesozoic marine province. Early workers on these Cretaceous magnetite-apatite ore bodies of the CIB invoked a magmatic origin via "immiscible Fe-oxide melt". This interpretation was based on textural similarities to those Fe-oxide deposits of the Kiruna type, Proterozoic
in age, in northern Sweden and the El Laco District, Pliocene-Pleistocene in age, located in the high Andes of northern Chile, in which lava flow structures and "columnar" magnetite have been reported (Park, 1961; Espinoza, 1997; Henriquez et al., 1997; Travisany et al., 1995). Later studies by other workers cited evidence for a magmatic-hydrothermal origin based on replacement textures in the host rocks; metasomatic chemical change of rock composition; geologic mapping of dikes, veins, and veinlets associated with the magnetite ore bodies; and fluid inclusion work (Bookstrom, 1977; Sheets et al., 1997, Rhodes, 1997).
The deposits of the CIB are composed of massive magnetite ± hematite ± apatite ore bodies in igneous and metamorphic rocks along the Atacama Fault Zone. They form an important variety of the general class of Fe-oxide-Cu-Au-U-REE deposits. The magmatic-hydrothermal hypothesis origin of many Fe-oxide deposits that contain economically important amounts of Cu, Au, U, and REEs is recent and has led to considerable debate. On the basis of fluid-inclusion (salinity), and stable oxygen isotope data, Rhodes et al. (2000) have suggested an evaporitic brine source fluid for the El Laco District of northern Chile. Barton et al. (1991) confirm similar conclusions for Feoxide deposits in the Great Basin of the western United States citing mass-balance relationships, extensive sodic-calcic alteration, and isotope analysis. Similarities exist between both Proterozoic and Phanerozoic age Fe-oxide (Cu-Au-U-REE) deposits in both tectonically extensional and continental-arc settings as well as non-orogenic settings. These deposits are generally associated with evaporite sequences and arid latitudes globally, especially during the Mesozoic (Barton and Johnson, 1996).
The Fe-oxide deposits in the Chilean Iron Belt have not yet been studied extensively enough to determine whether or not a non-magmatic evaporitic source fluid model is plausible. The Chilean Iron Belt provides an excellent opportunity to study both the genesis of igneous-related Fe-oxide deposits and to evaluate the economic potential with regard to Cu, Au, U and REEs. This study documents the distribution and mineralogy of hydrothermal
alteration, the relative age and spatial relation of ores and altered rocks to faults and plutons, and geochemical characteristics of alteration, in the Cerro Negro Norte District (CNN),
45 km north of Copiapo, Chile. Key questions focus on the enrichment of Cu
and Au at many of these deposits, the timing of Cu-Au versus Fe-oxide mineralization, and do Cu-Au forming fluids differ from Fe-oxide forming fluids? The maps, mineral assemblages, and chemical data presented here help to resolve the pressuretemperature-time-space conditions of alteration, which in turn helps to determine the
source and flow patterns of fluids. Investigation of hydrothermal alteration types, namely sodic-calcic and actinolite-rich alteration, and calculation of the volume of alteration, away from the main igneous intrusions is important. The volume of sodic alteration from saline fluids generated by magmatic-hydrothermal sources is generally small, whereas that of alteration from non-magmatic sources is usually very extensive (Battles and Barton, 1995; Dilles et al., 1995). The proximity of the alteration to igneous intrusions, and relationships between alteration and structural conduits for hydrothermal fluids is also important. Alteration associated with fluids derived from magmatic sources tends to be proximal to the intrusions unlike non-magmatic sources, which can affect areas at a great distance from the intrusives and associated ore bodies.
Careful identification of mineral assemblages both proximal and distal to the igneous intrusions and ore bodies is necessary in order to determine fluid flow paths. Brine circulation from evaporitic sources on the downwelling or lateral path toward a heat source typically produces sodic or calcic alteration (Carten, 1986). When temperatures are high, alteration produces scapolite-albite-actinolite assemblages, and fluid enrichment in Fe, K, Ca, and REEs; such fluids may produce magnetite-apatite mineralization hosted by the igneous rocks (Barton and Johnson., 1996). Based on schematic models of igneous-driven circulation of evaporitic fluids, when fluids are cooling on the upwelling path, sodic alteration continues if fluid-rock ratios are high. Hydrolytic alteration may form biotite-quartz alteration assemblages in felsic rocks and may form chlorite in mafic rocks as a response to cooling and precipitation of certain metals from chloride complexes (Barton and Johnson, 1996). With decreasing temperature hematite ± copper-iron sulfides and REEs precipitate as fluids become more oxidizing and sulfidizing.
Sulfur-bearing minerals can be paragenetically defined and located in veins, and if the S042/ H2S ratio of fluids can be estimated, sulfur isotope studies (34S / 32S) could be used to determine the source of the sulfur. Enrichment of 34S (6345 > 5 %o) typically
indicates sulfur originating in sedimentary or evaporitic sequences (evaporite 634S =16 to 20 %o) whereas, 634S = 0 ± 5 %o indicates a magmatic origin (Ohmoto and Rye,
1979). The origin of the sulfur in turn may lead to an understanding of the source of hydrothermal fluids in the system. Much research work has recently been devoted to developing geologic models for igneous-related Fe-oxide (Cu-Au-U-REE) mineralization. Such deposits are
economically important, and have been the focus of exploration in the past 20 years. Olympic Dam, one of the world's largest Cu, REE deposits, in south-central Australia; and the Candelaria Cu deposit in northern Chile, exemplify the importance of this study.
CHAPTER 2: FE-OXIDE DEPOSITS OF THE CHILEAN IRON BELT
2.1 Past Studies in the Chilean Iron Belt The Chilean Iron Belt (CIB) (Ruiz, 1965) is a narrow north-south trending belt of magnetite-apatite ore deposits, approximately 30 km wide and 600 km long between 26° S and 32° S latitude, along the eastern side of the Coastal Cordillera of Chile (Figure
la). The CIB contains large deposits (>100 Mt) and up to forty iron ore deposits, of which as many as seven are of economic importance (Menard, 1995). The Chilean Iron Belt continues to be mined as an important source of iron, with new mines coming into production as late as 1996 at Los Colorados. These Fe-oxide deposits are dominantly early Cretaceous in age and are associated with the Jurassic-Cretaceous arc that includes intermediate to mafic volcanic rocks and intrusive plutonic centers affected by extensive actinolite (sodic-calcic) and albite (sodic) alteration (Barton and Johnson, 1996). The El Romeral deposit, one of the larger deposits in the CIB is hosted in schists, quartzites and phyllites of late Paleozoic age, an andesite porphyry, and the Romeral diorite pluton of Early Cretaceous age. The magnetite ores are also Early Cretaceous, but crosscut the diorite pluton (Bookstrom, 1977). Many deposits in the C113, including El Romeral (Bookstrom, 1977), El
Algarrobo (Menard, 1995), and Cerro Iman (Vivallo et al., 1994b) are located along the strike-slip Atacama Fault system or splays, which runs approximately 1000 km, along
the length of northern Chile (Figure lb). The ore bodies often lie immediately adjacent to steeply dipping faults. The spatial proximity of mineralization to faults suggests that
X` --.\ al
t% C0(11:4211;011 itIlor
LIMIT OF THE CHILEAN' 26°
0 Manta. Blanco'
ERRO NEGRO NORTE 100 Ne
CERRO IMAN 100
COPIAPO PUNTA DEL COBRE
Z wZ Escondidci (Cut
BOODERON CHANA LOS COLORADOS
4 0 Mt
o 0Vt 0
\El Salvador II (Cu) 8
28' Magnetite deposits (with actinolik and apatite)
Chanar (F.) Loa Colorado. F.)
Underlined deposib introit that they were sidled as part at thit study
+ ApaliR deposits (tad apatite and magnetite)
/// LA SERENA
FIG. 1. a) Location map of some of the larger Fe-oxide deposits of the Chilean Iron Belt (CIB). Tonnage and whether deposits were visited as part of this study are indicated. Modified after Bookstrom, 1977. b) Location map of the Atacama Fault Zone (AFZ) in the Coastal Cordilleran arc of northern Chile. Spatial distribution of Fe and Cu districts located along the AFZ is shown. Modified after Vila et al., 1996.
fluids may have migrated along faults. Recent work and proposed hypotheses on the genesis of Fe-oxide (Cu-Au-REE) and other related deposits that may have been formed by hydrothermal non-magmatic fluids or a mixture of magmatic and non-magmatic fluids include: (1) the El Laco District in northern Chile (Rhodes et al., 1997, 2000); (2) the Cerro Negro Norte deposit north of Copiapo, Chile (Vivallo et al., 1995a); (3) the Punta del Cobre District, and the Candelaria deposit (Marschik and Fontbote, 1995, 1996); (4) the Olympic Dam Deposit of south-central Australia, (Oreskes and Einaudi, 1990, 1991; Haynes et al., 1995); (5) Proterozoic iron oxide deposits world wide (Hitzman et al.,1992); (6) Fe-oxide deposits of the Great Basin and world wide (Johnson and Barton, 1997, 2000a, b); and (7) Sodium-Calcium alteration by nonmagmatic saline fluids in porphyry Cu deposits (Dilles et al., 1995, 2000). Many of the magnetite iron deposits in the Chilean Iron Belt are found close to diorite intrusions into volcanic-sedimentary sequences along the lower Cretaceous arcaxis and along north-south striking faults of the stike-slip Atacama Fault Zone (AFZ) (Bonson et al., 1997). At the El Romeral Deposit, just north of La Serena, the main ore body is found between two lobes of the Romeral diorite pluton, which crystallized prior to ore deposition, and is immediately adjacent to the left-lateral Romeral fault, which was moving concurrently with ore deposition (Bookstrom, 1977). The Romeral Fault probably represents the southern end of the Atacama Fault Zone. Massive replacement magnetite-apatite ore as well as cross cutting magnetite-apatite veins pervade the Romeral diorite. Alteration around the ore bodies contains magnetite, actinolite, marialitic scapolite, plagioclase, tourmaline, diopside, clinozoisite, titanite, chloroapatite, pyrite, chlorite, micas and clays. The ores were formed hydrothermally
and are associated with abundant hydrothermal actinolite, especially along the Romeral fault, at temperatures between 4750-550° C, based on phase petrology (Bookstrom, 1977).
At Cerro Negro Norte, actinolite-altered rocks have been strongly enriched metasomatically in Ca, Mg, Fe, P, F, Cl, V, Au, and B, and depleted in La, Ce, Nd, Sm, Na, K, Ti, Sr, Zr, Zn, and Hf (Vivallo et al., 1995a). Albitized rocks are characterized by a high Na/K ratio and with the exception of Si and Na, they are depleted in all major elements. The elements Zr, S, V, Zn and Au display a distinct enrichment. Tourmalinerich rocks have a strong B enrichment and moderate increase in volatile content, Zr, S, V and As. Cross-cutting relationships of different mineral assemblages and host rock chemical composition suggest a hydrothermal solution initially characterized by high contents of Ca, Mg, Fe, Na, P, F, Cl, and CO2, which produced a proximal actinolite
with local albite-rich alteration zone and more distal tourmaline and silicification halos around the orebodies. Preliminary fluid inclusion studies indicate the presence of two types of fluid inclusions in the genesis of the ore bodies in the district (Vivallo et al., 1995a). One type corresponds to high temperature (>450°C) inclusions with high
salinity and without evidence of boiling, and the second is a later fluid inclusion with much lower temperature, rich in gases and moderate salinity (Vivallo et al., 1995a). Lledo (1998a) also did a fluid inclusion study in the district and found that quartz + magnetite? ± tourmaline veins from two Fe-oxide deposits including Adrianitas to the south of Cerro Negro Norte, indicate coexisting two and three phase fluid inclusions with both low and high salinities. The average homogenization temperature being 336° C, with an approximate salinity of 28 wt. % equivalent NaCl.
Similarities exist between the Chilean Iron Belt and the Punta del Cobre Belt, part of the Chilean Iron Belt, located south of Copiapo, Chile. Cu-Au (Fe-oxide), Co, Cu-Ag-(Co), and Au-Ag-Cu deposits (Lledo, 1998a) in the Punta del Cobre belt were formed in middle Cretaceous time and are associated with granitic plutons emplaced into shallow marine sequences from the Andean back-arc basin (Marschik and Fontbote, 1996). The principal alteration includes Ca-amphibole ± biotite ± sericite ± chlorite ± epidote ± quartz ± calcite associated with contact metamorphism. This alteration is superimposed on early sodic metasomatism and local potassic alteration. Alkali metasomatism is spatially related to the Cu (Fe-oxide) mineralization. The alteration pattern and fluid inclusions indicate saline fluids and high temperatures (400 ° 500° C), which are inferred (Marschik et al., 1997) to be related to the granitic
intrusions of the Copiapo batholith (Tilling, 1962) in the district. The La Candelaria (Cu-Fe-oxide) world class mine has estimated minable reserves of 366 Mt at 1.08 % Cu, 0.26 g/T Au, and 5g/T Ag (Ryan et al., 1995), taken at a 0.4 % Cu cut-off grade (Jenkins et al., 1998). Lledo (1998a) did fluid inclusion studies on calcite and quartz from three different types of deposits (Au-Cu, Fe-Au-Cu, and Fe) in the Punta del Cobre belt and found that the average homogenization temperatures were 311°C, with a salinity of 27 wt. % equivalent NaCl.
2.2 Reconnaissance Studies in the Chilean Iron Belt The Chilean Iron Belt includes numerous Fe-oxide deposits, which produced or
are producing >100 Mt of magnetite ore. Most of the larger deposits lie further to the south of the Cerro Negro Norte and Cerro Iman deposits, at latitudes between Vallenar
(28.5° S) and La Serena (30° S), Chile (Figure 1 a). Compania Minera Pacifica (CMP)
currently produces Fe-oxide magnetite ore from the El Romeral, El Algarrobo, and Los Colorados mines by open pit operations. CMP was willing and very helpful in allowing access and mine visits to these three mines. El Romeral was first studied in the late 40's, exploration began in the middle 50's and production by Bethlehem Steel started in the early sixties, as it did at the El Algarrobo, Cerro Iman and Cerro Negro Norte deposits. Both the El Romeral and El Algarrobo deposits were put back into operation in the 1990's. The Los Colorados deposit started production in 1995 (Leonardo Vergara, CMP, personal communication).
Reconnaissance geologic investigations reported below are based on 1 day or less of fieldwork per deposit. This work in the Chilean Iron Belt (CIB) extended as far north as the MantoVerde deposit
60 km to the north of Cerro Negro Norte and as far
south as the El Romeral Fe-oxide deposit (Bookstrom, 1977, 1995)
20 km north of La
Others Fe-oxide deposits include: Los Colorados Fe-oxide (CMP), El Algarrobo Fe-oxide (Menard, 1995), the Plieto Melon District (Travisany et al., 1995, CMP), Cerro Iman Fe-oxide (Vivallo et al., 1994b, 1997, Espinoza et al., 1994), the Punto del Cobre District (Marschik and Fontbote, 1996, Marschik et al. 1997), including La Candelaria Fe-Oxide (Cu-Au) deposit (Ryan et al., 1995), and the Manto Verde Feoxide (Cu) deposit (Vila et al., 1996, Minera Mantos Blancos). Several other smaller Fe-oxide and Fe-oxide (Cu, Au) prospects and abandoned workings were visited. The objective was to investigate some of the geology, alteration and mineralization in other parts of the Chilean Iron Belt, with the hopes of using some regional styles to compare
with the Cerro Negro Norte District. All of the above-mentioned deposits are spatially
associated with the Atacama Fault Zone (AFZ) and subsidiary faults (Figure lb). The deposits vary with respect to types of Fe-oxide mineralization either magnetite, or hematite, and whether or not there is Cu and Au mineralization present. Compania Minera Pacifica, based in La Serena, Chile, owns eighty percent of the Fe-oxide (magnetite) deposits in the Chilean Fe Belt. CMP was nationalized in 1971, and has since been privatized.
2.2.1 Northern Chilean Iron Belt The Cerro Iman (Fe), El Salvador (Cu-Au), La Lunar (Fe), La Lunar (Au), Fortuna (Fe), and Augustina (Fe) deposits and workings represent the northern portion of the CIB. They are all within 25 km to the south of the Cerro Negro Norte District, northwest of Copiapo, Chile. An overview schematic summary of the structure, geology, and mineralization (Figure 2a) and a schematic of the details of massive magnetite ore (Figure 2b) are compiled from observations seen in the field and characterize the Fe-oxide deposits near the CNN District.
22.214.171.124 CERRO IMAN (Fe)
The Cerro Iman (Fe-oxide) deposit was mined in the early 1960's by Bethlehem Steel and is located
25 km to the south of the Cerro Negro Norte District. Cerro Iman
(Raab, Dilles, field notes, 2000) lies
15 km to the northwest of Copiapo, Chile. In
1961 the production at Cerro 'man was
310,500 tons, with average grades of 65 % Fe.
The irregular and tabular ore bodies oriented 340° and dipping 90°, as well as 030° and
LATE NORMAL FAULT THAT RE-OPENS AND REACTIVATES OLD STRIKE SLIP AFZ
ATACAMA FAULT ZONE (CI)
LATE VUGGY QUARTZ+SULFIDES+AU(?)
MYLONITIZED DIORITE -GRANODIORITE WITH MYLONITE FOLIATION CUT BY ACTINOLITE, EPIDOTE + ALBITE VEINLETS
MONZODIORITE- DIORITE DIKES (CNN) WITH ACTINOLITE + CHLORITE + EPIDOTE ALTERATION ZONES OF STRONG FE-CARBONATE ALTERATION + SULFIDE, ASSOCIATED PYRITE+ACTINOLITE +CHALCOPYRITE VEINLETS CUT MAGNETITE ORE
LATE DIORITEQUARTZ MONZODIORITE
RHYOLITE? DIKE (CL)
DIKES (FOR) WI FRESH
WITH ALBITE? + SERICITE +PYRITE MINERALIZATION
HORNBLENDE OR WEAK CHLORITE + EPIDOTE CUTTING MAGNETITE
MAGNETITE+APATITE DIKES-VEINS (VERY EARLY) MASSIVE ACTINOLITE PODS OR ZONES WITH 1 cm CRYSTALS (EARLY) ALTERED TO CHLORITE (LATE)
HAIRLINE MAGNETIT E VEINLETS (<1-3 mm)
FIG. 2b. Schematic details of massive magnetite ores from field observations at some Fe-oxide deposits in the northern CIB.
dipping 80° W were mined by open pit with a final size of 800 meters long, 400 meters wide, and 200 meters deep (Lledo, 1998a). A total of five hand samples were collected, however no petrography or analysis has been done. On the west side of the pit a quartz, albite, epidote, rutile, magnetite (hematite) mineralized diorite is in contact with the andesite and is locally weakly mylonitized and altered to actinolite, with crosscutting actinolite veins. Later albite ± epidote veins crosscut actinolite. Local magnetite + quartz clots and later cutting magnetite veins are present. A large mylonitized fault zone strikes
030° and dips 80° E. The fault lies
between the above rocks and the ore body (Figure 3a). Locally massive quartz float is found, and is associated with the fault. Massive quartz is brecciated of infilled with specularite (hematite) and goethite veins, a strong goethite staining and remnant sulfide? boxworks are still visible. A granodiorite dike striking 340° contains chloritealtered mafics and cuts the albite ± quartz altered mylonitized zone. Further to the west 20 meters a diorite intrusion is also intensely mylonitized and is strongly altered to plagioclase (albite?), actinolite, sphene, hematite, ± magnetite, ± chrysacolla. The mylonitized diorite is crosscut by undeformed albite and/or quartz veinlets with pyrite ± chalcopyrite, which indicates that sodic alteration postdates faulting and mylonite (Figure 3b). On the southwest side of the open pit, dike-like irregular lobate magnetite bodies oriented 220° cut an andesite host rock (Figure 3c).
On the south side of the open pit a fine grained actinolized diorite is cut by albite? veinlets. Small magnetite veinlets crosscut and off set the albite veinlets. Actinolite ± chlorite veins also re-open magnetite veinlets and actinolite is commonly a selvage to the magnetite veins. The albite veinlets also cut the magnetite veins and
v v X
v v v
1Fe A A
Unconsolidated Quaternary Andesite
Actinolitized, brecciated in part Igneous breccia
IxI GranitOid I+I I
Aplite Grey Mylonite
1.0"1 Dike Quartz-Tourmaline vien (+ epidote) Magnetite+hematite quartz+Cu-oxide vein
FIG. 3a. Generalized geology and E-W cross section of the Cerro Iman Fe-oxide deposit. Notice the 500 m wide mylonite zone, part of the Atacama Fault Zone, to the west of the deposit. Modified after Vivallo, 1994.
FIG. 3b. West side of mylonitized zone at Cerro Iman. Albite, actinolite, titanite altered granodiorile to diorite with very fine hairline fractures. Late Cuoxides, probably after chalcopyrite. Albite veins crosscut the host and are undisturbed by mylonitization suggesting albite alteration postdates faulting.
FIG. 3c. View looking south-southwest over the Cerro Iman magnetite mine pit Scabs of massive magnetite can be seen on the west side of the pit Cerro Iman is located 15 km northwest of Copiapo, Chile. The mine is 30 km due south of Cerro Negro Norte and was one of the larger producers of magnetite ore from the Chilean Iron Belt which runs north-south along the Atacama Fault Zone, in the Chilean Coastal Cordillera.
indicate that magnetite mineralization and albite alteration is closely temporally related. Massive magnetite with sub-horizontal planar veins of gypsum is cut by quartz + actinolite + epidote + pyrite veins. Larger magnetite veins strike
035° and cut the
Bedrock on the east-side of the pit is a fine-grained mafic diorite? Massive magnetite ore is cut by epidote and actinolite veins and later quartz + pyrite ± chalcopyrite with actinolite selvages. Possible remnant igneous pyroxene is totally altered to actinolite. Also, on the east-side of the pit, an albite + actinolite ± epidoteveined granodiorite porphyry dike striking
330° cuts the host diorite, and is likely the
same dike observed on the west side of the pit. Biotite in the porphyry dike is altered to chlorite.
126.96.36.199 EL SALVADOR (Cu-Au) The El Salvador (Raab, Dilles, field notes, 2000) piquero or prospect is located just north of the Cerro Iman. Six hand samples were collected, however no petrography or analysis has been done. The prospect is hosted in biotite, quartz monzodiorite to granodiorite with epidote in fractures. Mineralization consists of disseminated magnetite, altered to hematite and trace pyrite. The vein striking 062° and dips 72° NW,
and has been partially mined out. Numerous stopes where the vein was drifted into can be followed up the hill to the north for
800 to 1000 meters. At the bottom of the hill,
in the lowest adit, a specularite veinlet strikes 065° and dips 62° NW and has an albite +
chlorite selvage. Following the vein to the north, specular hematite + magnetite veins with selvages of quartz, epidote, K-spar, and Cu-oxides, + jarosite staining are present.
Supergene mineralization consisting of open-space veins with botryoidal quartz overgrows Cu-oxide associated the hematite + gypsum veinlets. On the west-side of the vein, the monzodiorite is weakly Na-Ca altered to albite and actinolite, and contains small epidote veinlets. The vein itself contains quartz, sericite, specular hematite, and jarosite, the latter of which fills a pyrite boxwork. Small pickings to the east of the main vein are hosted in the same monzodiorite. Mafic sites are altered to chlorite. The Na-Ca altered host has strongly bleached joint sets that strike 323° and dip 70° W. Less altered monzodiorite forms a halo around the altered rock, and is cut by 1 cm wide albite
veinlets. Approximately 50 meters to the northwest is another mined vein that strikes 065° and dips 70° NW. To the east of the lowest adit another magnetite vein strikes 042° and dips 68° NW.
188.8.131.52 LA LUNAR (Fe) The La Lunar (Raab, Dilles, field notes, 2000) magnetite deposit is located 15 km to the northwest of Cerro Iman. Seven hand samples were collected, however, no petrography or analysis has been done. This deposit was mined as a small open-pit, with shafts > 50 meters deep and stopes for underground operation. The main magnetite body trends 065° and dips 75° NW and a second trends
037°. The host rock is an
actinolite-altered plagioclase phyric andesite. The andesite is cut by actinolite stringers, epidote veinlets, carbonate veinlets and small magnetite + apatite veins, which strike parallel to the main magnetite body. Additional magnetite + granular apatite + epidote veins 1-5 cm wide, strike 030°, and dip 80° NW and cut the andesite host. The massive
magnetite ore is cut by epidote veins. On the west edge of the ore body the andesite is
cut by magnetite + apatite veinlets and crosscut by albite veinlets with magnetite selvages. At the west entrance to the pit, carbonate + quartz ± magnetite or goethite veins striking 050° and dipping 87°N fill joint sets. The ore dump outside the mine contains magnetite-veined andesite which is cut by quartz + pyrite + goethite veins.
184.108.40.206 LA LUNAR (Au) The La Lunar Au piquero (Raab, Dilles, field notes, 2000) to the north of the main magnetite ore body is a vein < 1 meter wide containing quartz + limonite + hematite + chlorite + actinolite ± magnetite + visible gold, with a selvage of magnetite 10 meters wide cutting a fine grained diorite host. The vein strikes 310° and dips 77°
NW and produces an average grade of 140 to 600 grams/tonne or 5 to 20 ounces per tonne Au (field communication with local miner). About 100 meters wet of both the magnetite ore body and quartz vein lies a quartz porphyry dike with an aplitic border phase. Sheeted quartz veins in the dike strike 330° and cut the magnetite body running parallel to the quartz vein. Quartz + sulfide veins cut north-south trending actinolite, magnetite, and albite (?) veins. 220.127.116.11 AUGUSTINA (Fe)
The Augustina (Raab, Dilles, field notes, 2000) workings follow an irregular tabular-shaped magnetite ore body
100 meters long by 50 meters wide striking 082°
and dipping 59° S (Figure 4a). Small 5-25 cm wide magnetite veins cut strongly
actinolite altered, andesite host (Figure 4b). Secondary workings follow a 8 m wide hornblende diorite-granodiorite porphyry striking 345° and dipping 77°E, which clearly
cuts and post-dates the magnetite ore body. Magnetite veins snake through the andesite
FIG. 4a. Augustina magnetite Fe-oxide deposit. Strong actinolization of andesite host with 5-25 cm wide magnetite veins cutting host. Both magnetite and actinolite are very course grained. Magnetite veins trend through rock at 330 but form irregular pods or bodies. Plagioclase from host is altered to epidote.
FIG. 4b. Augustina mine. Strongly actinolite altered andesite host with magnetite veinlets 5 cm wide cutting host, and large pods of actinolite.
330°. Coarse- grained actinolite, pods of octahedral magnetite, and veins crosscut
the magnetite ore and andesite host.
2.2.2 Southern Chilean Iron Belt Production of massive magnetite ore was in progress in 2000 at El Romeral, El
Algarrobo, and Los Colorados. Los Colorados is the largest Fe-oxide deposit ( 400 MT) currently being mined, and El Romeral (-200 MT) is the second largest operation. Los Colorados is a 50/50 joint venture between CMP and Mitsubishi plus private investors. El Algarrobo is scheduled to close in 2002 (personal communication, Leonardo Vergara, CMP, 2000). Total magnetite ore production for all of CMP operations totals
800 MT to date. These three mines are all located in the southern
portion of the CIB, near La Serena and Vallenar, respectively.
18.104.22.168 El ROMERAL (Fe) The El Romeral deposit (Raab, Barton, Marschik, field notes, 2000) is located
20 km north of La Serena, Chile. A half-day mine visit was made possible by CMP's head of exploration. Seventeen hand samples were collected, however, no petrography or analysis has been done. El Romeral is one of a few Fe-oxide magnetite deposits to be studied in some detail (Bookstrom, 1977; Vivallo, 1994c). This
220 MT Fe-oxide
deposit is hosted in a pendant of andesites and metamorphosed sedimentary rocks, between two lobes of a diorite intrusion along the Atacama Fault Zone (El Romeral Fault) (Figure 5a). The deposit has several zones of varied alteration and mineralization. There is a boundary between high-grade and low-grade magnetite ore delineated by
FIG. 5a. Bedrock geology of the El Romeral Fe-oxide massive magnetite deposit, near La Serena, Chile. From Bookstrom, 1977.
depth and spatial proximity to the Romeral fault. A large silicified area located in the northeast side of the main pit at the 100 meter level contains massive magnetite, with lesser actinolite, quartz, epidote, chlorite, pyrite ± chalcopyrite mineralization. This zone produces the highest Cu and Au assays. On the west side of the pit the contact of the magnetite ore body and a granodiorite dike is visible. The west side of the ore body is bounded by the actinolized Romeral diorite, which contains abundant hydrothermal actinolite. At the northern end of the main pit, soft, high-grade magnetite ore ( 70 wt.
% Fe) is intruded by a 15-meter-wide diorite dike (Figure 5b). Three textures of magnetite ore are present at Romeral and include massive, disseminated, brecciated. The total wt. % Fe is > 58, 57-40, and 40-30, respectively. Average grades are 51 wt. % Fe and the cutoff is 30 wt. % (personal communication, Mario Rojo, CMP, 2000). This low grade (S 32% Fe) magnetite ore and magnetite-replaced diorite is cut by biotite + pyrite ± chalcopyrite veins, where the hydrothermal biotite has been altered to chlorite. Epidote veinlets also cut the diorite. To the north of the main pit, a cataclastic biotite schist has foliation striking
330° and pyrite + chalcopyrite veins cut the foliation
obliquely. Diorite dikes locally called andesite with pyritic border zones cut the weakly
foliated schist. Locally, sericite + pyrophyllite(?) + titanite ± sulfide-altered zones and epidote veins are present. Diorite dikes intrude the magnetite ore body in the middle of the pit (Figure 5c).
22.214.171.124 LOS COLORADOS (Fe)
The Los Colorados (Raab, Barton, Marschik, field notes, 2000) Feoxide deposit is located
50 km northwest of Vallenar, Chile. Ten hand samples were
::, . tio ,;,*..'
111.- 4% 30"... , . ',Aa e. Ci".....,.. i
FIG. 5b. View looking north over the north pit at El Romeral. On the west side of the pit the actinolized western diorite intrusion. In the middle, a massive magnetite ore body (A) is bounded by a mylonite zone to the west. A granodiorite dike (B) is visible cutting the diorite on the west side of the pit. On the east side of the pit is a silicified zone (C) of the eastern diorite intrusion. Notice the bench faliure on the east side due to water saturation and unstability in a zone of strong clay alteration associated with the silicified
FIG. 5c. South end of the main northern El Romeral pit floor Massive magnetite high grade "soft ore" is crosscut by diorite dikes (pale). Just above at the 100 m level the silicified zone of massve magnetite with actinolite and sulfides including pyrite + chalcopyrite + epidote + quartz + chlorite comprise a zone of the highest Cu and Au assays in sulfide seen in Figure 5b. .
collected, however, no petrography or analysis has been done. This joint venture between CMP, Mitsubishi, and MC Inversions went into iron pellet production in 1995, and produces 700,000 tons annually. The estimated geological resource is and reserves are 245,251,000 T averaging
48 wt. % Fe (personal communication,
Roberto Elqueta, CMP, 2000). The ore is transported 110 km by private train to the pellet plant in Huasco, Chile. The deposit consists of three separate, sub-vertical magnetite-apatite ore bodies that are
500 meters wide by 600 meters long by 550 meters deep. The ore bodies are
hosted in the 2000 m thick Bandurrias Formation, which locally consists of intermediate to silicic lavas and tuffs, as well as younger diorite-tonalite intrusions. Pichon (1981) reported ages using the K/Ar method of rocks in the Los Colorados District. The ages range from 111 Ma for the host andesite; 110 Ma for a post-mineral dike; and 108 Ma for a diorite.
Three pits (north, south and east) presently mine three magnetite bodies (Figure 6a). These ore bodies are localized along faults striking 050° and along the
striking Atacama Fault Zone. The tabular shaped, vertically orientated main ore body is left-laterally offset
200-300 meters by the NW-striking Los Colorados fault. The
central part of the deposit is a silicified meta-andesite breccia cemented by quartz, pyrite, ± chalcopyrite, which cuts the magnetite bodies, presumably along the Los Colorados fault. The east ore body is hosted in an actinolized ± scapolite (?) volcanic breccia (?) with specular hematite. A vuggy, strongly actinolite-altered brecciated dike (Figure 6b) containing disseminated sulfides cuts the massive magnetite body. The contact zone has pyrite ± chalcopyrite. Actinolite + magnetite + apatite veins crosscut
FIG 6a. View looking east across the "B" pit to the "east" pit at Los Colorados. This deposit consists of three pits (N, S, E). The magnetite - apatite ore bodies are 500 X 600 m, subvertical and dike -lice bodies hosted in a 2000 m thick section of the volcanic and sedimentary Bandurrias and Chanarcillo Formations. Diorites and tonalites intrude these formations locally. Emplacement ofmagnetite was controlled by the NE- striking AFZ. The ore bodies are cut by the NW-striking Los Colorados fault. A left-lateral displacement of -- 200 -300 m offets the NE trending ore bodies emplaced along the AFZ. The central part of this deposit consists of a hydrothen-nal silicified breccia with clasts of meta-andesites and is mineralized with pyrite and chalcopyrite.
FIG 6b. Looking northeast at a post-mineral dike cutting massive magnetite in the "east" ore body pit floor at Los Colorados. Chalcopyrite and pyrite mineralization is present near the dike contact
the magnetite. The magnetite ore has local zones of octahedral crystals of magnetite (lodestone). Local shear or tensional fractures in the diorite intrusion are chloritized and contain sulfides. Both epidote veinlets and quartz + specular hematite + sulfide veins also cut the diorite. The quartz veinlets are inferred to post-date epidote, although no crosscutting relationship was seen.
126.96.36.199 EL ALGARROBO (Fe) The El Algarrobo (Raab, Barton, Marschik, field notes, 2000) Fe-oxide deposit is located
30 km southwest of Vallenar, Chile. Four hand samples were collected,
however, no petrography or analysis has been done. A very brief one-hour tour of operations and a mine visit was made possible by CMP. Mine life at El Algarrobo is projected to end in 2002. At the 860 m level in pit C high-grade coarse-grained magnetite (Figure 7a) + apatite + pyrite ± chalcopyrite is currently being mined. Carbonate ± quartz veins cut sulfide veinlets. A diorite dike striking 015° at the north end of pit C has pyrite ± chalcopyrite mineralization, and is cut by actinolite veinlets altered to chlorite (Figure 7b). Some sulfide veinlets are cut by later (?) carbonate + K-
feldspar + quartz veinlets. Massive magnetite ± hematite is spatially associated 10-20 meters from the Totoritos fault, which is part of the Atacama Fault Zone.
2.2.3 Manto Verde, Punta del Cobre, and La Candelaria The Manto Verde deposit is owned and currently operated by Compania Minera Mantos Blancos, Chile. La Candelaria is also currently in operation and is owned and operated by Phelps Dodge Chile. These two deposits represent the Cu (-Fe)-Au deposits
FIG. 7a. Sample of massive magnetite with elongate crystal habit from the El Algarobbo Fe-oxide deposit.
FIG. 7b. Pit floor of the "C" pit at the El Algarobbo Fe-oxide mine owned and operated by CMP. Equigranular diorite dike trending NE cuts massive high-grade magnetite ore. Pyrite and chalcopyrite mineralization is associated with the dike, and actinolite veins have been altered to chlorite.
in which hematite is the major Fe-oxide and Cu-Au mineralization is the economic ore reserve.
The historic Punta del Cobre District host a variety of deposits, with mineralization of Cu, Au, Ag, Co, and Fe. Most are associated with the Copiapo and/or Los Lirios plutons, which intrude marine sedimentary rocks of the Punta del Cobre Formation (Marschik, 1997).
188.8.131.52 MANTO VERDE (Cu-Au) The Manto Verde deposit (Raab, Barton, Marschik, field notes, 2000) is located
110 km NNW of Copiapo, Chile, and
60 km due north of the Cerro Negro Norte
district. Seventeen hand samples were collected from the Manto Verde District, however no petrography or analysis has been done. This Cu-hematite (Fe-oxide) deposit is hosted in Early Cretaceous, east-dipping Bandurrias Formation andesite volcanic rocks, and in diorite dikes. The Manto Verde deposit lies parallel to the Manto Verde Fault (MVF), which forms a northwest-striking splay between the central and eastern strands, of the Atacama Fault Zone (Segmento Salado). The eastern flank of the AFZ trends 045° and has left-lateral offset, and the MVF strikes 335° and dips 50° E (Vila et
al., 1996). To the east of the deposit, a chlorite altered and silicified diorite pluton is dated at 124-127 Ma (Vila et al., 1996). The footwall mineralization along the MVF is the "Manto Verde" tectonic breccia, with glassy limonite pitch after chalcopyrite. The hanging-wall "Manto Atacama" hydrothermal breccia is
100 m wide and
mineralization is dominantly specularite which infills as the matrix. Oxide mineralization extends to
250 meters depth and overlies an 80 m wide zone of
chalcopyrite and pyrite, with supergene enrichment of bornite and chalcocite at the hypogene ore contact
750 meters above sea level. The ore is
5 vol. % sulfides,
contains anomalous U and trace REE's (personal communication, Borris Castillo, 2000).
"Manto Verde" is
2100 meters long and between 4 to 60 meters wide and is
divided into southern, northern and central zones. Malachite, chrysacolla, atacamite, pyrite, and chalcopyrite mineralization is disseminated and forms the breccia matrix. Grade ranges from 0.80-1.06 wt. % Cu. Calcite + sulfide veins cut the breccia and postdate main mineralization (Figure 8a).
The "Manto Atacama" is
1700 meters long and between 30 to 60 meters wide.
Above 850 meters above sea level, it has a specularite matrix hydrothermal breccia with brochantite, chrysacolla, and atacamite mineralization, and between 850 and 750 meters above sea level it has covellite, chalcocite and bornite supergene (?) mineralization. Grade averages 1.1 wt. % Cu. A transitional zone, approximately 1500 meters long and 20 to130 m wide ranges from andesite to hydrothermal breccia, and mineralization includes brochantite, chrysacolla, and atacamite. Grade averages 0.48 wt. % Cu. See Figure 8g for mineralized samples from Manto Verde. Post-mineral diorite dikes cut the transition zone to the east of the high-grade "mantos" (Figure 8a). Northwest trending granitic dikes intrude the cataclastic breccias. However, although the exact relation to mineralization is not known, it is thought that these dikes may be the source of mineralization (personal communication, Borris Castillo and William Robles, 2000). Two different diorite bodies cut the mineralization and bound the MVF to the east and west. K-feldspar, chlorite, ± quartz alteration is district-wide
MANTO VERDE FAULT
t 50 LEVEL 0 (895 m.a.s.1.
MOINTE AIA DOM *IMO WADE IMCCCIA MMITO
FIG. 8. Generalized distribution of a) geologic units, b) hydrothermal alteration, c) Fe-Cu-Au mineralization across the central part of the Manto Verde deposit. Mineralization is spatially associated with the NW striking Manto Verde Fault. Figure after Vila et al., 1996.
and is cut by zones of younger quartz + sericite alteration localized near the MVF (Figure 8b). K/Ar dates on sericite from a localized alteration zone along the MVF produced ages ranging from 116-121 Ma (Vila et al., 1996). Manto Verde geologists have developed a paragenesis of the whole deposit as follows: 1) diorite intrusion and coevel andesite volcanism, 2) cataclastic deformation of andesite, 3) intrusion of granite dikes, 4a) ductile sinistral faulting and mylonitization along the MVF, 4b) Fe-Cu-Au mineralization coevel with faulting (Figure 8c), 5) post mineralization andesitic dikes, 6) and late post mineralization east-side-down, dip-slip brittle movement on the MVF. As of January 1999, the strip ratio was 1: 4 at Manto Verde and total production was 20,500T/day @ 0.52 wt. % Cu (Compania Mantos Blancos, William Castillo, 1999). Estimates of 115 MT of ore total are accessible by open pit, with total reserves at 200 MT. The district has 250 MT inferred oxides. The final pit floor is planned to be at 780 meters above sea level.
Approximately 13 km to the south of the Manto Verde deposit, the Franco deposit has a Fe-oxide (magnetite) resource of 25 MT, and between the Manto Verde and Franco deposits, the Manto Cristo deposit also has a Fe-oxide (magnetite) resource of 25 MT (personal communication, Borris Castillo, 2000). The Manto Cristo deposit is a magnetite ore body, which strikes roughly NE along the eastern splay of the AFZ. Along the eastern flank of the AFZ, and
7 km to the north of the Manto Verde
deposit lies the Santa Clara prospect. The Santa Clara prospect is an actinolite-apatitemagnetite body with later specularite, calcite, siderite veining. To the northwest of the Santa Clara deposit, the western diorite pluton hosting the Santa Clara deposit is cut by magnetite veinlets and also crosscut by later oxide after sulfide veinlets. Locally,
FIG. 8d. View to the north from the main pit at Manto Verde. On the right side of the photo the eastern flank of the AFZ strikes to the NE. In the distance, the Santa Clara magnetite deposit, and in the foreground, two smaller magnetite deposits with local small Cu piqueros along side can be seen. To the west, the light colored rock is the western diorite pluton cropping out.
FIG. 8e. View of Manto Russo on the Manto Verde property. This manto has speculurite hematite veins with sulfide and Cuoxide mineralization, which cuts massive magnetite. This area is known as Manto Verde Sur and produced 120 tonnes at 0.5% Cu.
FIG. 8f. Sample MR1 from the Manto Russo area. Manto Russo is a tectonic/ hydrothermal diorite?/andesite breccia cemented by speculurite (hematite) and Cu-oxides.
FIG. 8g. Samples from Manto Verde. Cu-oxides include atacamite, broncantite and chrysocolla associated with magnetite mineralization to the south and hematite mineralization to the north.
specularite veinlets and K-feldspar alteration are present. Two other small magnetite bodies, with Cu workings are located between Santa Clara and Manto Verde (Figure 8d).
The Manto Russo prospect lies along the MVF to the northeast of Manto Verde (Figure 8e), and has been mined in small workings. The Manto Russo prospect is a magnetite ore body with a late tectonic/ hydrothermal diorite (?)/andesite breccia cemented by specularite + Cu-oxides ± chalcopyrite (Figure 8f).
184.108.40.206 PUNTA DEL COBRE DISTRICT
The Punta del Cobre District (PDC) is located 15 km to the south of Copiapo, Chile. It includes Candelaria Norte, Candelaria Sur and Candelaria Este. Tilling (1962) worked in the Punta del Cobre District, which has had substantial production. Numerous small Cu-Au mines, prospects, and small workings situated just outside the 2.5 km wide contact zone of the Copiapo batholith (Jenkins et al., 1998) are still being mined. The style of mineralization in this district differs from the Fe-oxide deposits in the Cerro Iman and Cerro Negro Norte districts. The most obvious difference between the Punta del Cobre District and the Cerro Negro Norte and Cerro Iman districts is the type of Fe-oxide and Cu-Au mineralization. The deposits of the Punta del Cobre District typically have hematite-rich rather than magnetite-rich Fe-oxide mineralization and have ubiquitous presence of Cu and Au. The district produced >12 Mt of Fe-oxide (CuAu) ores from mantos, veins and breccias. Average grades of ores produced from the PDC district as a whole were
1.1 to 2 % Cu, 0.2 to 0.6 g/T Au, and 2 to 8 g/T Ag
(Marschick, 1997). Some similarities exist between PDC and other CIB deposits, such
as actinolite and scapolite alteration. An abbreviated visit to this district only enabled us to make very general observations. To that end, refer to publications on Candelaria (Ryan et al., 1995), and the Punta del Cobre District (Marschik and Fontbote, 1996; Marschik et al., 1997a, b, c, 2000).
220.127.116.11 LA TIGRESA (Cu-Au) The La Tigresa piquero (Raab, Di lles, Marschik, Barton, field notes, 2000) is located
8 km to the northeast of the Candelaria Fe-oxide (Cu-Au) deposit. Four hand
samples were collected, however, no petrography or analysis has been done. The prospect is hosted in the (Kmd) Cretaceous hornblende, biotite (?) diorite to
monzodiorite porphyry (Arevalo, 1995), cut by magnetite + actinolite veins and later quartz + magnetite + chalcopyrite ± pyrite veins. Felsic dikes, 0.25 meters wide composed of equigranular 2 mm grain size K-feldspar, quartz, plagioclase, biotite (?) cut the diorite. The hornblende tonalite to diorite Los Lirios pluton just to the east of the prospect hosts a strongly albitized, sericite, rutile, specular hematite, goethite, hematite stained piquero or workings. Diorite to andesite (?) dikes
75 to100 meters to the
southeast of La Tigresa, cut the Los Lirios intrusion and strike
108°. Locally, Na-Ca
alteration with albite and actinolite is present.
18.104.22.168 LA CANDELARIA (Cu-Fe-Au) The Candelaria mine, (Raab, Dilles, Marschik, Barton, field notes, 2000) is located
20 km to the south of Copiapo, Chile and is owned and operated by Phelps
Dodge. A mine visit was not possible, however, a very short visit to exposures west of
the Ojancos shear zone on the east side of the deposit was possible. Three hand samples were collected, however, no petrography or analysis has been done. The country rock is a sheared monzodiorite containing plagioclase, K-feldspar, biotite, quartz, ± chalcopyrite. Magnetite veins striking between 080° and 140° and dipping 90° cut the
host rock. Later quartz + magnetite + chalcopyrite veins with hydrothermal biotite selvages, and scapolite + actinolite veins also cut the host monzodiorite. The Ojancos shear zone is a foliated rock that is
30 meters wide, strikes 033 ° and dips 73 ° E.
Andesite dikes cut the shear zone, as does a muscovite vein
10 to 20 cm wide, striking
330°. The shear zone may represent a possible border phase on the margin of the San Gregareous monzodiorite intrusion. To the NNE of the Candelaria deposit the Ojos del Salado deposit (Cu) owned and operated by Phelps Dodge is hosted in the Punta del Cobre and Charnacillo Formations, which are composed of marine sedimentary and volcaniclastic rocks. The mine is spatially associated with a large dacitic dome nicknamed "Albitiforo" and is sodically altered as the name suggests.
CHAPTER 3: METHODOLOGY OF CERRO NEGRO NORTE FIELD AND LABORATORY STUDIES
3.1 Field Mapping One and a half months of fieldwork were completed during 1999 and 2000. Mapping of the district at a scale of 1:10,000 covered roughly 4 km2, and pit bench mapping of the Abanderada Sector at a scale of 1:1000 covered a total of approximately 750 linear meters on the pit floor. A total of 250 samples were collected, 75 from the Abanderada pit, and the others from the rest of the district. Field mapping was carried out with limited topographic control, as CMP's district topography base at 1:1000 scale was unavailable to the author. Aerial photographs at a scale of 1:10,000 and topographic maps at a scale of 1:10,000 adjusted from 1:50,000 scale were used in conjunction with a hand held Garmin 38 GPS to field map. The accuracy of field mapping on a district scale is ± 35 meters, and within the Abanderada pit is ± 10 meters. Detailed "bench" mapping of mineralization and alteration in the Abanderada pit and the district as a whole was carried out using a slightly modified version of the "Anaconda Method" (Einaudi, 1997). This method of mapping was developed in the 1960's by Anaconda geologists working on Cu porphyry deposits, namely the El Salvador deposit at El Salvador, Chile, and at Yerington, Nevada. Alteration and ore minerals, both hypogene and supergene, have been mapped using color pencil line codes, where different colors represent different minerals. Vein assemblages, some with measured orientation, and selvages are mapped in the same color scheme, with one color representing one mineral. On the bench maps of the Abanderada pit, mineralized
veins are mapped on the "rock side" of the bench face and selvages are mapped on what is termed the "air side". These veins are plotted with the true orientation measured facing the bench or pit wall. When using a compass in close proximity to massive magnetite, as was the case in the Abanderada pit, there are often local magnetic field perturbations. This problem was most often solved by both moving away from the outcroppings slightly and sighting from a short distance or by using the body or hands to "protect" the compass from local magnetic influence. Occasionally, it was impossible to get a precise bearing or strike and only generalized trend could be obtained. Crosscutting and offsetting relationships are also plotted directly onto the maps. Alteration and mineralization features are plotted on the rock side, and disseminated mineralization or stockwork veining, etc. is distinguished by either small dots or crosscutting squiggly lines (Plates #2, #3 Abanderada Sector). The overall type of alteration is plotted on the airside and distinguishes partial or fully altered igneous minerals, with dash and solid lines respectively. The inner column on the airside represents the predominant alteration mineral replacing igneous mafic minerals and the outer column represents the prominent alteration mineral replacing igneous felsic mineral alteration.
Alteration limit lines, which delineate relative boundaries of certain minerals or mineral assemblages, can be found on both the district and Abanderada pit alteration maps. These different colors represent different mineral assemblages, and the colors found on the maps represent the six major types of alteration in the district and also correspond to various other aspects of the project, such as the geochemical analyses. Disseminated, brecciated or massive mineralization and alteration are distinguished by
different symbols as mentioned above. Faulting both (inferred and observed), shear zones, sample locations, adits, stopes, etc. are also plotted on all maps. See Plates #1#3 of the Abanderada pit and Plates #1- #3 of the Cerro Negro Norte District for detailed explanation in the legends.
3.2 Petrography Petrography and minor ore microscopy were done on a total of 242 thin sections from the Cerro Negro Norte District. Billets were cut at Oregon State University, and the thin sections were prepared at the University of Oregon Thin Section Lab. A total of 101 polished sections and 141 unpolished sections including 30 long thin sections were prepared. Short descriptions of the samples include lithology, mineralization, textures, alteration assemblages, and veining (Appendix A1.1.1). This appendix also indicates whether the sample was analyzed with electron microprobe, for whole rock geochemical analyses, for sulfur isotopes, and/or by U/Pb dating techniques. See Appendix A2.1.1 for a list of illustrated computer scanned images of the thin sections found on the CD-ROM. The petrography was done on a Nikon AFX-DX microscope outfitted with transmitted and reflected light capabilities, and typical 2.5X, 10X, 20X, and 40X objectives and a 12.5X objective lens. The same microscope was used to take photomicrographs (Appendix E1.1.1) of selected samples also found on the CD-ROM.
3.3 Electron Microprobe Major and minor element geochemistry analyses were performed on seventeen samples from the Cerro Negro Norte District, using the CAMECA SX-50 electron
microprobe at Oregon State University, under the direction of manager Professor Roger L. Neilson. Different minerals from major alteration assemblages and mineralization were analyzed for compositional purposes, and at times for identification of unknowns. Analyses were performed using a beam current between 30-50 nA, an accelerating
voltage of 15 kV, and a defocused (3-51m) beam. Multiple standards were used for elemental analyses in roughly sixteen different mineral phases (Appendices B1.1B11.1). These standards include Smithsonian (USNM) (Jarosewich et al., 1980), and Astamec standards for major, minor, trace, and metal elements, Asar standards for
Uranium, Drake standards for REE's (Drake and Well, 1972), and Jack Rice's standards from the University of Oregon for fluorine. Count times vary between 10-40 seconds for standards. Major and minor element analyses were counted for 10-20 seconds. Elements with low concentration, for example REE's, were counted for 200 seconds, and U was counted for 300 seconds.
3.4 Geochemistry Lithogeochemical whole rock analyses were performed on seventeen samples from the Cerro Negro Norte District (Appendix C1.1.1-C3.3.2). The samples were selected to characterize certain alteration and mineralization assemblages in order to determine elemental gains and losses. Actlabs-Skyline in Tucson, Arizona, prepared the samples and Activation Laboratories in Ontario, Canada, performed the analyses. Preparation includes crushing to minus 10 mesh, splitting, and pulverization to minus 150 mesh. An original sample size of
1 kg and a final split size of
5-10 grams was
used for analysis. Contamination due to pulverization with hardened steel can be up to
0.2 wt. % Fe, 200 ppm Cr, and trace Ni, Si, Mn, and C. The analysis package (Total IDENT Code 4E-expl.) (Act labs, 2000) includes both lithium metaborate/ tetraborate
fusion and total acid digestion. Inductively Coupled PlasmaMass Spectrometry (ICPMS), Instrumental Neutron Activation Analysis (INAA), and X-ray Diffraction (XRF) technologies are used to analyze 48 elements including majors, minors, trace, REE's, and metals. See Appendix C1.2 for Act labs published details concerning detection limits
3.5 Sulfur Isotopes Sulfur isotope analyses (15) were performed on twelve samples from Cerro Negro Norte District. See Appendix D1.1 for sample information. Pyrite, chalcopyrite (sulfide) and barite (sulfate) were hand picked from the samples by the author and pulverized to <140 mesh equivalent (< 0.1 mm diameter) in a ceramic mortar and pestle. The powders (most > 97 % pure) were sent to Professor Edward M. Ripley in the Department of Geology at Indiana University for sulfur extraction and analysis. Sample size is
1 milligram for pyrite,
1.5 milligrams for chalcopyrite, and 4 milligrams
for barite. The standard used for the analyses is Bingham pyrite (634S = +1.21 %o) and was provided by Professor Cyrus W. Field at Oregon State University. 6345 = +0.8 %o
was obtained for the standard when analyzed for this study. The fully automated continuous flow Elemental Analyzer System is coupled to a conventional isotope ratio mass spectrometer. The combustion chamber combusts the sulfide and sulfate samples at 1010° C and the evolved SO2 gas is cleansed of CO2 and H2O in a scrubber column.
The purified SO2 gas is then fed by continuous flow into a gas chromatograph column
and ultimately into a mass spectrometer for the isotope ratio analyses. Analytical uncertainty is probably between ± 0.2 and 0.4 %o for the analyzed samples, based on replicates of lab standards.
3.6 U/Pb Geochronology Geochronology using U-Pb dating techniques were performed on one titanite sample from the Cerro Negro Norte District. The purpose of this dating was to see if a reasonable age for titanite associated with early high temperature Na-Ca alteration assemblages could be extracted. Sample preparation included initial crushing of the samples with a steel sledge. Titanite was hand picked for large pieces < 4 mm in size. The samples were then ultrasonically washed to separate titanite from other minerals. Light crushing in an agate mortar and pestle and subsequent sieving to >60 mesh equivalent and -60 +100 mesh equivalent followed. Samples were then hand picked again to retrieve pure (99-100%) titanite grains, and ultrasonically washed a second time. Sample size is
5-10 milligrams. The titanite samples were analyzed by Electron
Microprobe and were found to contain uranium ranging from less than the detection limit (40 ppm) to
400 ppm, but most of the analyses have a 200-400 ppm detection
limit. The samples were sent to Professor Mark Martin in the Department of Earth, Atmospheric, and Planetary Sciences at the Massachusetts Institute of Technology (MIT) in Cambridge, Massachusetts, where chemical dissolution and U/Pb separation via ion exchange resins and mass spectrometer analyses were performed.
CHAPTER 4: REGIONAL GEOLOGY OF THE COASTAL CORDILLERA, AND GEOLOGY OF THE CERRO NEGRO NORTE DISTRICT
4.1 Regional Geology of the Coastal Cordillera The Coastal Cordillera of northern Chile is composed of magmatic and volcanic arc rocks of Mesozoic age. During the Jurassic to Early Cretaceous the magmatic arc was built on basement rocks, which include upper Paleozoic meta-sedimentary rocks and granite intrusions of Permo-Triassic age. These rocks are exposed in a broad band to the west of the Atacama Fault Zone (AFZ), along the present coastline of northern Chile (Brown et al., 1993a, b). The formation of the magmatic arc was accompanied by
the development of a backarc basin 75 km to the east of the arc. Between 25°- 27° S latitude, lower Jurassic shallow water limestones of the Pan de Azucar Formation are overlain by conglomerates of the Posada de los Hidalgo Formation, and volcaniclastic sedimentary sequences of the La Negra Formation (Grocott et al., 1994). Late Jurassic to Early Cretaceous andesitic volcanic rocks and breccias of the informal Sierra Indiana unit (Arevalo, 1995) and Late Jurassic volcanic and sedimentary rocks of the Bandurrias Formation are exposed further to the east of the La Negra Formation. The Cerro Negro Norte Fe-oxide deposit is hosted in the Sierra Indiana andesites. South of 27.5° S latitude, near Copiapo, Chile, volcanics of the Punta del Cobre Belt and overlying marine sedimentary rocks of the Charnacillo Group are Early Cretaceous in age (Marschik and Fontbote, 1996), and overlie the Bandurrias Formation. This area is characterized as an interface between the volcanic arc and a backarc basin to the east.
During the middle Cretaceous as the volcanic arc moved eastward, the arcbackarc pair was replaced by a single eastward moving terrestrial arc. The Late
Cretaceous Cerrillos Formation is composed of 4500 meters of continental sedimentary rocks, andesite volcanic rocks and volcaniclastic breccias (Marschik and Fontbote, 1996). The La Candelaria (Cu-Au-Fe-oxide) deposit is hosted in the Punta del Cobre Belt. Middle Jurassic through Early Cretaceous age plutons and dikes which range in composition from mafic to felsic crop out in a north-south linear pattern parallel to the northern Chilean continental margin, throughout the Mesozoic arc. Several studies (Brown et al., 1993a) and field relationships (Marschik and Fontbote, 1996) indicate that the general composition of intrusive rocks becomes more felsic as they young to the east across the arc and that more felsic phases tend to intrude the more mafic rocks. The methods of emplacement are still a subject of debate. Grocott et al. (1994) suggest that the emplacement of plutonic rocks of the arc has been controlled by, but not completely restricted to, ductile extensional deformation along the Atacama Fault Zone (AFZ). Both intrusive and volcanic rocks of the Mesozoic arc get progressively younger to the east.
4.2 Geology of the CNN District The Cerro Negro Norte District lies between UTM 7003000N and 700100N and UTM 366000E and 367500E. The district is located approximately 45 km to the north of the city of Copiapo, Chile and is accessible by the Pan-American highway (Ruta 1) and gravel roads. The Cerro Negro Norte District is an abandoned district, which was
mined in the early to middle 1960's, and consists of five sectors of large magnetite Feoxide ore bodies (Figure 9a,b). In order from largest to smallest open pit these include Abanderada, Augusta, Beduino, Veta Central and Cata Alfaro (Acosta and Vicencio, 1985). There are also numerous other smaller workings in the district. All the irregular lobate and/or tabular or dike-like magnetite ore bodies are hosted dominantly in andesites of the informal Sierra Indiana Formation (Ksi) of late Jurassic to early Cretaceous age (Arevalo, 1995; Llego, 1998b).
The Ksi is composed of andesitic lavas and breccias (Arevalo, 1995), which represent a roof pendant of volcanic rocks intruded by granitoids. The absolute age of the andesites is not known, but they are thought to be correlative to the Bandurrias Formation to the south, which limits the minimum age to the later part of the lower Cretaceous (112 Ma). Locally, the ore bodies are hosted in diorite to quartz diorite intrusions, which bound the andesitic rocks to the west and east. Approximately 1.5-2 km to the east of the CNN District, a relatively homogeneous monzonite-monzodiorite pluton (Sierra Blanca, about 50 km2 in area) bounds the district on the east. These
monzonite-monzodiorite rocks have been dated at 112 ± 3 Ma by the K/Ar method on biotite, just north of the CNN District (Arevalo, 1995). The andesites and intrusive rocks are likely close in age. Andesitic rock is often found as small pockets of outcrop surrounded by intrusive rock. Granodiorite intrusions and dikes often cut andesitic rocks and diorite-quartz diorite intrusions within the district. Locally, outside the CNN District, these granitoids also intrude the Sierra Indiana andesite rocks, and other earlier monzodiorite to diorite rocks. Arevalo (1995) has mapped the intrusive rocks on the west side of the CNN District as a granodiorite (Kg) of the Sierra Pajas Blanas. The
FIG. 9a. View looking north over the Cerro Negro Norte District. In the foreground is Sector Beduino, and just behind to the north, Sector Augusta. The Abanderada pit is hidden behind the hill in the center of the photo, but lies just behind it. Sector Cata Alfaro is on the far northern ridge line. Notice the contact of the light colored western diorite pluton and the darker andesite to the east at the top of the photograph.
FIG. 9b.View looking south-southeast over the Cerro Negro Norte District. Photograph shot from sample CNN 82. In the foreground the southern end of the Abanderada pit and to the south the quartz + tourmaline altered andesites and hydrothermal breccia (hills) of the Augusta Sector. The valley to the east (left side of photograph) of Cerro Negro Norte District is filled with Tertiary-Quaternary gravels.
granodiorite has been dated outside the CNN District, by the K/Ar method on biotite, and yields an age of 103 ± 5 Ma (Arevalo, 1995). As will be discussed in this chapter and the geochronology chapter, the author has mapped the western plutons in the CNN District as diorites to quartz diorites with local intrusions and dikes of monzodiorite to granodiorite composition. Early Na alteration of these rocks yielded an age (this study) similar to that of the Sierra Blanca pluton immediately to the east of CNN. Another quartz monzodiorite to granodiorite pluton
8 km to west of the district has been dated
at between 122 ± 3 and 107 ± 3 Ma on recrystallized biotite (Arevalo, 1995). Mylonitic rocks to the south of the CNN District, near Cerro Iman, have yielded a minimum age of 114 ± 4 Ma, by whole rock K/Ar method (Arevalo, 1995). See Geology Plate # 1 of the CNN District and Appendix A1.1 for more detailed descriptions of the lithology.
4.2.1 Andesite Acosta and Vicencio (1985) describes the andesites in the Augusta sector as both meta-andesites and chloritic andesites, and mapped a north-south mylonite zone to the east of the Veta Central and Abanderada sectors. Mapping by the author (District Geology Plate # 1) indicates that andesitic rock crops out in the central part of the CNN District and forms a north-south linear unit
300 meters to 1 km wide and 2+ km long.
The andesitic rock, which hosts almost all of the large magnetite ore bodies in the district, is bounded to the west by a diorite to quartz diorite intrusion. The eastern part of the district is tourmaline-quartz-sericite-chlorite-altered andesites and locally other intrusive rocks, as well as hydrothermal quartz-tourmaline breccias. The andesite lavas crop out as sub-horizontal dipping flows. The flows vary in thickness from 25-50 m.
Locally, flow tops and/or bottoms are still visible, especially in the open pits in the district. The breccia zones are typically < 50 m2 wide and crop out as steeply dipping
zones of andesitic protolith rock cemented which tourmaline and quartz. The exact contacts between the andesitic rock and intrusive rocks to the west are often hard to delineate, due to strong alteration, and similar rock compositions with minor textural differences. To the north of the Abanderada sector, the contact between andesite and the quartz diorite intrusive rocks to the west is obscured by a north-south trending zone of strong silicification along a fault that separates the two rock types. To the southwest of the Abanderada sector the contact is covered by tailings removed from Abanderada pit. In the eastern part of the district, mineralogy and color delineate the andesitic rock with tourmaline-quartz alteration.
The andesites are most often green in color, typically contain 5-10 vol. % and locally up to 25 vol. % euhedral lath-shaped to subhedral plagioclase phenocrysts, most often albite twinned, and with variable amounts of alteration, which will be discussed in Chapter 6. The plagioclase phenocrysts vary in size between 0.5 to 3 mm in size. Most
of the mafic phenocrysts, which include pyroxene ± hornblende in freshest rocks, have been mostly altered to actinolite. Euhedral igneous clinopyroxene phenocrysts range in size from < 0.25 to 0.5 mm, and hornblend is often up to 2.5 mm in size. The percentage of mafic phenocrysts is typically 5-10 %. The groundmass consists dominantly of fine-grained plagioclase ± quartz ± pyroxene.
Variable amounts of scapolite, albite, epidote, titanite, quartz, tourmaline, chlorite, calcite, and sericite of hydrothermal origin are also present in the andesites and will be discussed in terms of alteration assemblages in Chapter 6. Magnetite is present
in andesite in the form of disseminated to massive mineralization, from 1 to 99 total wt. % Fe-oxide and will be discussed in Chapter 7.
4.2.2 Diorite-Quartz Diorite The main ore bodies and host andesites are bounded to the west by diorite to quartz diorite intrusions. Locally, a more tonalitic composition predominates. Mapping by the author (District Geology Plate # 1) was limited to the western ridgeline (Figure
10a) at UTM 036600E. The diorite-quartz diorite intrusion also crops out in a linear N-S trending body and covers
1 km2 area. The diorites typically are equigranular and
have up to 50-75 vol. % subhedral to euhedral plagioclase, with oscillatory concentric zoning and albite twinning. Quartz is typically anhedral and varies from 5-10 vol. %, and locally up to 15-20 vol. %. Locally, where rock is little altered, amphiboles and pyroxenes are still present, however, most often mafics are altered to actinolite and range up to 35 vol. %. Epidote is common in the intrusive rocks and varies between 2 and 10 vol. %.
Titanite is common, locally up to 5 vol. %, and where hydrothermal titanite is added, up to 10 vol. % in the diorite to quartz diorite intrusions, particularly to the southwest of the Abanderada sector. Large zones of Na, and Na-Ca alteration are present also to the west of the Abanderada sector and will be discussed in Chapter 6. Titanite from this diorite to quartz diorite intrusion, as mentioned earlier, was dated by U/Pb methods as part of this study and is discussed in Chapter 10. Within the diorite intrusions, zones
25-75 m2, of quartz diorite porphyry that
encloses magnetite breccia clasts "magnetite breccia" (Figure 10b) are present to the
FIG. 10a. Western ridge line to the west of Cerro Negro Norte District View looking south to the Cerro Negro Sur prospect. Mapping did not extend to the west of this ridgeline, which is a diorite-quartz diorite pluton, cut by NE trending granodiorite dikes. The end of the ridge is the Solitario vein prospect The Cerro Negro Sur prospect is the dark high point along the ridge, and has not been exploited. See FIG.12a for a close-up look at the western pluton with granodiorite dikes.
FIG. 10b. Magmatic hydrothermal breccia with magnetite clasts (CNN 4). Sample is from Abanderada Sector, southwest of the main pit 800 m, just above the old town site (camp). Note 34 cm diameter magnetite clasts (dark) enclosed in a matrix ofNaplagioclase (albite?) + epidote + sericite(?) altered quartz diorite breccia.The magmatic hydrothermal breccia is in contact with a Caaltered porphyry dike, with pyroxenes altered to actinolite and plagioclase altered to epidote + calcite and trace titanite (?). The NaCa alteration and the sericite + epidote suggest that the emplacement of the magmatic hydrothermal breccia was probably closely associated with magnetite (Fe-oxide) mineralization and circulation of hydrothermal brines producing sodic alteration.
west and southwest of the Abanderada sector. The magmatic-hydrothermal breccias are found associated with the diorite to quartz diorites, often where the western intrusive rocks are spatially close to contacts of earlier andesites. The matrix of the breccia is the same composition as the host quartz diorite, however, it is typically strongly bleached and Na-Ca altered, with albite ± chlorite veinlets crosscutting it. Plagioclase up to (70 vol. %), is moderately altered to sericite. Actinolite is often replaced by chlorite. Quartz, locally up tol5 vol. % with fluid inclusions 121.1m in diameter, contains solid halite up
to 7.5i.im in diameter ± hematite flakes. Tourmaline ( 3 vol. %) has a bladed radiating to clotty habit. The angular to rounded magnetite breccia fragments are composed of an
agglomeration of many very fine- grained euhedral cubic magnetite grains (10m) ±
anhedral clots up to lmm in size as seen in thin section. The magnetite replaces the host and is locally altered to hematite. Because older, equigranular diorite is brecciated and mineralized with magnetite, and the breccias are closely associated with porphyry dike intrusions, the diorite to quartz diorite intrusions and hydrothermal Fe-oxide mineralization are closely temporally associated. These zones of breccia are also extensively Na-Ca altered and will be further discussed in Chapter 6.
4.2.3 Hydrothermally Altered Andesites, Diorites and Breccias On the eastern limits of the CNN District, the Beduino and Augusta sectors are bounded by tourmaline + quartz ± sericite ± chlorite altered andesites and diorite intrusions (Figure 11a). These rocks have the same basic protolith mineralogy as the andesitic and dioritic rock discussed above, and are further discussed as an alteration
FIG. lla View looking to the south over Sector Augusta at Cerro Negro Norte. The Augusta pit is visable in the center of the photo, and the Beduino pit is just south of that To the east a small hill is in the foreground before the Tertiary-Quatemary valley behind it This hill is dominantly a tourmaline + quartz altered andesite with tourmaline + quartz hydrothermal breccia outcrops associated with quartz veining and some felsic dikes. The road on the right side of the photograph is the main N-S road through the CNN District.
FIG. 11b. View looking southeast to the northern slopes of Sector Augusta at Cerro Negro Norte. Photograph taken from the top of Sector Veta Central. The eastern rose colored rock (left) is a tourmaline + quartz altered andesite and hydrothermal quartz tourmaline breccia seen along the entire eastern margin of the Cerro Negro Norte District The green-brown rock to the west (right) is the chlorite-altered meta-andesite host rock of the Augusta magnetite ore body.
assemblage in Chapters 6.5 and 6.6. The hydrothermal "contact" with andesitic rock to the west is delineated by the presence of ubiquitous tourmaline and quartz veining and alteration, and this limit is used here as a spatial, and temporal reference for the geology of the CNN District. Zones of hydrothermal quartz-tourmaline altered breccias about 50-100 m2 crop out on the eastern flank of the district and are spatially associated with
the tourmaline-quartz altered andesites and intrusive rocks, often near the contact of these rocks with the chlorite-altered andesitic rocks or near faults. Locally, these breccia zones are also closely spatially associated with granodiorite dikes and/or irregular intrusions, which crosscut and may possibly post-date the tourmaline-quartz altered rocks. The tourmaline + quartz ± sericite ± chlorite altered andesites and/or diorite intrusions form a zone about
100-250 meters wide by 1 km long and are irregularly
shaped, but also crop out in a linear N-S striking manner. These tourmaline-quartz altered rocks are bounded to the east by Quaternary gravels and to the west by andesites (Figure 11 b). See Geology Plate #1 of CNN District.
4.2.4 Monzodiorite-Granodiorite Intrusions and Dikes Throughout the district, north to northeast striking monzodiorite to granodiorite porphyry dikes, dikelets, and irregular shaped intrusions intrude the diorite to quartz diorite intrusive bodies (Figure 12a), as well as magnetite (Figure 12b; 24a, Chapter 6.5) and andesitic rocks. Crosscutting relationships mapped in the field suggest that the granodiorite dikes and intrusions post-date the andesitic and dioritic rocks. Tourmalinequartz altered andesite and dioritic rocks are also cut by granodiorite dikes, but local zones of moderate tourmaline + quartz ± sericite ± chlorite alteration of granodiorite
FIG. 12a. View looking NW from the west edge of the Abanderada pit. Small amphibole granodiorite porphyry dikelets or apotheses which intrude pyroxene quartz diorite to diorite. The quartz diorite host is Na-Ca altered with actinolite + scapolite + titanite + epidote(?) altered and scapolite + actinolite veined. See samples CNN 83, 84. Andesite crops out on the ridge line. The trend on these dikelets and veins is to the NE. The high point on the horizon is an andesite.
FIG. 12b. Augusta area at Cerro Negro Norte. Magnetite outcrop, near CNS 2, 5 x 10 m wide. Part of a quartz vein trending NW with vuggy quartz and hematite. The magnetite has breccia clasts of plagioclase, quartz , Kfeldspar(?) granodiorite, which have been altered to clays + calcite. Magnetite vein and later quartz-tourmaline veins cut andesite host.
dikes and intrusions suggest a close temporal relationship between dike intrusions and this alteration. Acosta and Vicencio (1985) also mapped a granodiorite intrusion
meters to the northeast of the Augusta sector. The quartz monzodiorite and granodiorite typically are equigranular to porphyritic with
50-60 vol. % anhedral-subhedral
plagioclase, 25-30 vol. % anhedral quartz, 5-10 vol. % K-feldspar with albite rims, 5 vol. % mafics including hornblend and pyroxenes altered to actinolite ± tourmaline ± sericite and chlorite as discussed in Chapter 6.
4.2.5 Post-mineral Andesite-Microdiorite Dikes Post-mineralization andesite dikes are also present throughout the district. The Veta Central sector pit has four north-northeast striking andesite dikes (Figure 13a), and the Abanderada sector pit has one major east-west striking dike (Figure 13b). These dikes likely intruded along zones of weakness during reactivation of the major N-S, and later NW striking faults. The andesite dikes post-date the Fe mineralization, and also cut diorite and andesitic rocks to the west and southwest of the Abanderada sector (Plate # 1, CNN District). In both these areas the dikes cut massive magnetite ore or andesite
with disseminated magnetite mineralization. Typically, the dikes are
0.5 to1.0 meters
wide. The andesitic dike that cuts across the northern end of the Abanderada pit is intruded along an east-west striking fault and may be temporally associated with pyrite
+ chalcopyrite mineralization. The post-mineral andesite (microdiorite) dikes in the Veta Central sector have a plagioclase-rich groundmass that is generally fine-grained, and locally equigranular, with plagioclase ± pyroxene ± amphibole phenocrysts. The dikes are moderately to very strongly altered to assemblages with actinolite, epidote,
FIG. 13a. Sector Veta Central at Cerro Negro Norte. Mew looking NE at two 5-10 m-wide adits, between adits are three post-mineral andesite-microdiorite dikes. These dikes strike to the NE and dip steeply between 80 degrees to the NW and vertical. All the dikes are moderately to strongly altered to chlorite after actinolite and calcite + epidote + clay + sericite after plagioclase. The edges of the dikes are generally goethite + clay + brecciated magnetite. Locally, pyroxenes are only slightly altered to actinolite. Hematite veinlets cut dikes and later quartz + calcite + Cu-carbonates cut dikes, magnetite + carbonate andesite host rock and massive magnetite. Limonite + goethite + hematite + clay is locally pervasive. The massive magnetite has 3 vol. % disseminated Fe-Cu sulfides. Cucarbonates and oxides are from supergene processes.
FIG.13b. View looking to the east-northeast at the north end of the Abanderada pit. The photograph taken from 25 m above the pit floor. The andesite porphyry dike 1.2 m wide with copper staining to the left of the main adit cuts magnetite replaced andesite and massive magnetite. The andesite dike strikes east, and is in contact with a structure(?), or zone of weakness 70 cm wide also striking east-northeast.
chlorite, calcite, sericite and clay, with up to 2 % disseminated magnetite often altered to hematite. The alteration assemblages will be further discussed in Chapter 6.
4.2.6 Mylonites Several small mylonite zones not wider than 50 m are present in the district, however, major mylonitic zones are not present. The minor zones are located to the south on the western flanks of the district, and north of the Abanderada pit (CNN District Geology, Plate # 2), as well as to the east of the Abanderada pit as mapped by Acosta and Vicencio in1985 (Vivallo et al., 1995b). The mylonite zone in the southwestern portion of the district is within
50 meters of the diorite contact with
andesite, and the mylonite zone in the northern part of the district lies directly on the same contact, where mylonites deform andesitic rock at this location. The relative age of mylonite to the andesite and diorite intrusions was not determined via direct crosscutting relations in the field. However, the mylonite zone to the south is surrounded by diorite and is cut by a granodiorite dike, suggesting that timing of deformation pre-dates diorite intrusions, as well as granodiorite intrusions. In thin section, the mylonites have actinolite-rich mineralogy, with local alternating bands from 0.1- 4 mm wide of coarse
and fine-grained actinolite. Locally scapolite + actinolite + titanite veinlets left-laterally offset and cut magnetite veinlets, which cut across pyroxene (moderately altered to actinolite)-scapolite banded mylonites. These alteration assemblages and veining relationships suggest that the mylonites were likely in place before early stages of NaCa alteration associated with Fe-oxide mineralization.
CHAPTER 5: REGIONAL STRUCTURE OF THE COASTAL CORDILLERA, AND STRUCTURE OF THE CERRO NEGRO NORTE DISTRICT
5.1 Regional Structure of the Coastal Cordillera The Atacama Fault Zone (AFZ) is the dominant fault of northern Chile, where it cuts intrusive and volcanic rocks of the Coastal Cordillera of northern Chile. The AFZ is a north-northeast-striking, sinistral, trench-parallel, wrench system that is related to the oblique subduction of the Aluk (Phoenix) plate during the Jurassic to Early Cretaceous, and is possibly the controlling mechanism for pluton emplacement in the arc (Scheuber and Andriessen, 1990).
This complex discontinuous fault system extends for over 1000 km from La Serena to Iquique, Chile. Between La Serena and Copiapo, the AFZ is an anastomosing north-northeast-striking fault zone composed of multiple faults. Between Copiapo and Taltal, the El Salado Segment of the AFZ is composed of three separate (western, central, and eastern) north-striking faults. The Paposo and Salar del Carmen Segments lie between Taltal and Antofagasta and Antofagasta and Iquique, respectively (Brown et
al., 1993b). All three segments display a concave to the west orientation (Figure lb). In the El Salado Segment, Brown et al. (1993b) have suggested that the western fault experienced ductile dip-slip deformation and the central and eastern faults have had ductile strike-slip motion. It has been proposed (Brown et al., 1993a; Grocott et al., 1994) that ductile deformation probably initiated as an extensional break away fault on
the forearc sliver of the overriding South American plate during Jurassic to Early
Cretaceous time. Grocott et al. (1994) proposed that the shallow-angle, dip-slip, downto-the-east fault either enabled pluton emplacement along dilational jogs, or volcanism during periods of decreased or increased subduction rates relative to convergence rates. Ductile deformation produced large mylonite zones from a few meters up to 2 km wide seen along the AFZ from its southern terminus near La Serena to Iquique. In the northern CIB, at Cerro Iman, mylonites < 1 km wide bound the deposit on the west side. Amphibolite facies metamorphism is generally developed on the western boundary of the AFZ as a result of higher temperatures related to magma emplacement. Later, lower temperature, greenschist facies alteration is recognized to the east of the AFZ. During the Late Cretaceous, the Jurassic to Early Cretaceous arc was abandoned and arc activity moved to the east, probably as a result of more rapid westward movement of the South American Plate. This was likely the result of the initiation of sea floor spreading in the South Atlantic (Brown et al., 1993a). Application of4°Ar/39Ar age
dating techniques and mapped kinematic indicators, and cross-cutting relationships of mylonites and intrusions, both deformed and undeformed, along the AFZ has shown that this fault system has experienced both ductile as well as brittle deformation. Age dates suggest that a change from ductile to a brittle strike-slip deformation
are similar in age ( 130 Ma), however, strike-slip deformation likely post-date the extensional normal faulting. The magmatic activity peaked between 130 Ma and 120 Ma and with the culmination of volcanic activity, brittle deformation began (121 ± 3 to117 ± 3 Ma K/Ar on sericite) due to cooling on the AFZ (Vila et al., 1996). This late brittle deformation is associated with sericite alteration at Manto Verde.
Work done on the El Salado Segment of the AFZ, near the Manto Verde mine, suggests that brittle deformation overprints earlier ductile deformation, along the western, central and eastern faults. These faults are interpreted to bound asymetrical sidewall ripout slabs due to the sticking on the principal strand of the AFZ (Brown et al., 1993b; Vila et al., 1996).
In addition to the main faults composing the AFZ, smaller, northwest-striking sinistral strike-slip faults and shear zones have been recognized in field studies as well as on Landsat TM imagery (Bonson et al., 1997; Taylor et al., 1998). The majority of work on the northwest-striking fractures has been via Landsat imagery, and only minimal field mapping of these shear zones has been done. Taylor et al. (1998) suggested that these NW-striking structures merge into the NNE striking faults of the AFZ and represent a crustal scale left-lateral transpressional duplex. The duplex forming as a result of the detachment of the forearc sliver during increased convergence rates, more oblique convergence, and reduction in subduction angle, due to the eastward migration of the magmatic arc during the Late Cretaceous. It has been noted that these northwest-striking shear zones range from kilometer scale faults to joints and microfractures (Bonson et al., 1997), and amount of offset has not been determined on many of the faults (Taylor et al., 1998). Evidence that these shears cut and displace portions of the AFZ or sole into faults of the AFZ suggest that they may be part of the original AFZ and simply represent reactivation after Early Cretaceous time.
5.2 Structure of the Cerro Negro Norte District The majority of the Fe-oxide deposits in the CIB are associated with the main trace of the Atacama Fault Zone (AFZ) and subsidiary faults comprising the AFZ as a
whole. Faulting in the Cerro Negro Norte District is not as obvious as it is in several other deposits such as Cerro Iman (Vivallo et al., 1994b) or El Romeral (Bookstrom, 1977), where large mylonitic zones either bound or are poorly exposed close to the
magnetite ore bodies. Mylonite zones, which are clear and can be several 10's to 100's of meters wide in these districts, are poorly exposed in the Cerro Negro Norte District. Quaternary sediments cover much of the eastern part of the CNN District. Arevalo (1995) mapped two north-south striking faults, which cross the whole CNN District and merge into the same fault to the north of the district. These faults define a contact between the Sierra Indiana andesites on the east and intrusive rocks of monzodiorite to diorite composition on the west side of the district.
Mylonite is poorly exposed in the CNN District as mentioned above. This, as seen from observed field relationships is due to 1) lack of major structure associated with the AFZ, in the District and 2) mylonite, which had developed has been removed by igneous intrusions. Mylonites are spatially associated with early magnetite ore deposition.
Small discontinuous zones of mylonite, obvious slickensides, and smaller shear zones often with mineralization can be used to infer two general sets of faulting in the district, both proximal and distal to the main ore bodies. Field observations by the author (Plate # 1 CNN District and Abanderada Sector), previous mapping by Acosta and Vicencio (1985) and CMP geologists (1997) suggest an early NNE-striking ductile
system, which is likely associated with magnetite ore deposition, and a later subsidiary NNW-striking ± re-activated NNE-striking brittle system associated with later quartz + sulfide mineralization. Pit floor bench mapping in the Abanderada sector at a 1:1000 scale (Plates # 1-3, Abanderada Sector), and the CNN District at 1:10,000 scale (Plates # 1-3, CNN District) show plotted fault traces in blue.
5.2.1 NNE-Striking Ductile Faulting In the southwest part of the CNN District at sample CNN 117 a small mylonite zone at the edge of the mapped area crops out. This banded mylonite is a strongly altered actinolite + scapolite-bearing pyroxene andesite and crops out as a pendant completely included in the western diorite to quartz diorite intrusion, which defines the western limit of the district. Within the Abanderada pit, diorite dikes or intrusions and post-mineral (magnetite) monzodiorite to granodiorite dikes, which define the pit wall on the southwest side of the pit were likely emplaced along zones of weakness during early ductile faulting (Plate #1, Abanderada Sector). Trace amounts of mylonite deformed andesitic rock is found in the Abanderada pit. However, when found it is closely spatially associated with massive magnetite mineralization, which either cuts the mylonite fabric or the deformed rock is found undisturbed, with no mineralization. This indicates that ductile deformation is closely associated in time with magnetite mineralization and may be coevel or slightly pre-date magnetite mineralization. On the east side of the pit, on the surface above the eastern high-wall an irregularly shaped diorite intrusion
50 m long crops out (Figure 14a). This diorite intrusion was likely
intruded into the main trace of the AFZ, along a zone of weakness, resulting in the cutting out of the mylonitic zones locally. This fault is mapped as the dominant NE striking fault in the CNN district (Vivallo, 1998), and likely bounds the Abanderada ore body on the southeast side. Four hundred meters due east of the Abanderada sector a mylonite zone approximately 100 meters wide has been mapped by previous workers (Vivallo et al., 1995a). The author did not map this area and therefore the mylonite zone was not
witnessed. This zone is
500 meters long and defines a contact between andesites and
intrusive rocks to the east of the Veta Central and Abanderada sectors. Acosta and Vicencio (1985), Villagran (1997) and Vivallo et al. (1995a) mapped a 2.2 km long north-south striking fault that loosely defines the eastern limit of the Cerro Negro Norte District. This fault lies within 100 meters to the east of the Fe-oxide bodies in Veta Central, Augusta, and Beduino sectors, and effectively defines a contact between amphibole and feldspar-bearing meta-andesites and tourmaline, chlorite altered metaandesites in the Augusta sector of the district. The author did not do any detailed mapping on the eastern limit of the district in this project, except in the Augusta and Veta Central sectors, where northwest-striking structures discussed in the following section were mapped. Whether all these small segments are part of one larger structure or are just small expressions of early ductile NNE faulting is not clear. Regardless, these observed faults, shears, zones of alteration, mylonite zones, comprise the early NNE striking faults in the Abanderada Sector and the western portion of the CNN District.
FIG. 14a. View to the NE from the east rim of Abanderada pit. Massive magnetite scab 3 m wide can be seen in contact with the carbonate + Fe-oxide altered zone, which deliniates the NE-striking fault through the Abanderada pit. The same relation of massive magnetite juxtaposed by the fault against carbonate-altered rock is seen at the southern end of the pit as well.
FIG. 14b. View looking ENE from the Abanderada ramp. In the center of the photo is a hematized outcrop of massive magnetite in contact with the locally brecciated carbonate + Fe-oxidized liesegang altered host rock. The scabby hematite outcrop has gently plunging slickensides. The outcrop has Cuoxides present, as well as strong clay and epidote alteration.
5.2.2 NNE-Striking Strike-Slip Brittle Faulting Two discrete faults striking north and northeast and cross the CNN district from south to north and represent the major expression of brittle strike-slip faulting, which locally re-activates earlier zones of weakness. Along the eastern pit-wall in the Abanderada pit, horizontal to sub-horizontal strike-slip slickensides are visible on local scabs of hematized magnetite ore (Figure 14b). Intense clay, sericite, carbonate, and quartz-altered host rock, magnetite breccia zones 5-50 meter wide, five meter wide quartz veins, and zones of intense massive carbonate veining which cut through hematized ore define the eastern pit wall. The eastern pit wall also defines the eastern edge of the magnetite ore body, and represents a fault plane over (Figure 14c). The fault strikes to the northeast at
125 meters distance
035 ° and the fault plane dips sub-
vertically or steeply to the WNW. Within the pit on the east side, intense clay, sericite, quartz and carbonate altered andesite, abut the massive magnetite ore body. Several northeast-striking shear zones or small fault spays are visible on the southwest wall of the pit near the entrance. These small structures have late barite + quartz + hematite mineralization and likely were also zones of weakness that were re-activated. Remnant scabs of hematized ore are separated from the intrusive monzodiorite dikes discussed above by the small fault splays. Horizontal slickensides are present in this intensely altered zone, and on outcrops of hematized magnetite ore, which indicates brittle strikeslip movement after magnetite mineralization.
At the northern end of the Abanderada pit (between samples CNN 60 and 61) a 10 meter wide zone of small shears striking northeast and dipping variably from vertical to 71° NW may define the northernmost trace of this fault in the lower parts of the pit.
FIG. 14c. Abanderada pit floor at Cerro Negro Norte. The view is looking NE along the trend of carbonate + goethite + Fe-oxide alteration, and fault trace of the NE-striking fault, which deliniates the eastern margin of the Abanderada magnetite ore body. Notice the magnetite scabs from the main orebody left behind on the eastern high walls of the pit. The magnetite and carbonate alteration seem to be separated only by the smooth planar fault surface.
FIG. 14d. View looking NNE from the east rim of the Abanderada pit, at Cerro Negro Norte. Massive magnetite ore body can be seen on the west side of the pit. On the north end of the pit a possible splay of the NE fault, which deliniates the eastern limit of the magnetite ore body, and is in contact with the carbonate altered zone. The light colored rock (right) is diorite.
On higher levels of the pit the extracted magnetite ore body (Figure 14d) is delineated by the surface expression of the pit (Plates # 1-3, CNN District). The ore body was likely bounded to the east by an early ductile NNE-striking fault. However, observed brittle features, such as slickensides indicates a more brittle faulting regime which has been superimposed on the older magnetite mineralization and andesitic rock host (Figure 14e). Exposure is covered by mine dumps immediately to the north and northeast of the pit. Approximately 500 meters to the northeast, near sample CNR 22, where mine dumps no longer cover the surface, a northeast-striking sub-vertically dipping fault cuts the tourmaline-quartz altered andesites. This surface expression may represent the re-activation of the northernmost part of the NE striking fault that defines the eastern limit of the Abanderada ore body.
One hundred meters to the west of the Abanderada pit a large zone of tourmaline-quartz altered andesites, intense quartz veining, silicification, multiple small workings in adits and numerous stopes follow underground workings for Cu-Au mineralization. These workings and mineralization follow along a north to northeaststriking andesite/diorite contact that probably represent a re-activated fault trace, which dips to the northwest at 83°. Large linear zones of massive actinolite + scapolite ± quartz form north trending dike-like bodies, that follow the andesite/diorite contact to the north. It is not possible to trace the fault to the south, due to mine dump cover. However, several adits and stopes in the mine dumps may indicate the fault trace. An adit at sample CNN 85 and 86 has been dug to follow late mineralization at the intersection of the north-striking 83° NW dipping re-activated fault and/or andesite/diorite contact discussed above and a NW-striking, 77° SW dipping fault.
FIG. 14e. View looking NE from the eastern rim of the Abanderada pit at Cerro Negro Norte. View follows a 040 degree bearing along the probable fault trace through the northern end of this sector. Massive magnetite, and strongly actinolitealtered andesite in the center of the photo are offset on either side of a small fault trace (dark rock) that runs through the center of the outcrop, bounding magnetite body to east.
About 500 meters to the southwest along the projected trend of this inferred fault an adit at sample CNN 119 has been dug at the intersection of a northeast-striking fault dipping 76° to the southeast and a northwest-striking fault dipping 34° to the west.
5.2.3 WNW-Striking Dip-Slip Shear Zones and Faults A secondary and later set of faults and/or shear zones cut across the Cerro Negro Norte District and strike dominantly to the WNW. These faults often have Fe and Fe-Cu sulfide and/or supergene Cu-oxide mineralization associated with them. They typically have very little observed offset (< 1 m). In the Abanderada sector near the northern end of the pit (Plates # 1-3, Abanderada Sector), at sample CNN 53 a massive pyrite, chalcopyrite, vein (Figure 15a) follows a northwest trend cutting across the magnetite ore body (CNN 59). This small fault dips to the southwest between 54 ° and vertical. A post-mineral andesite dike cuts through the northernmost part of the pit and follows a small structure striking east-west to northwest and dips at
74° NE. Locally, intense
supergene Cu-carbonate and Cu-oxide mineralization at samples CNN 56 and 57 is localized along this fault and the andesite dike. Two adits at the northeastern end of the Abanderada pit and magnetite ore body follow Cu-Au mineralization associated with quartz-tourmaline alteration and at least one of these two fault zones. This zone was delineated by Acosta and Vicencio (1985), as one of the four zones in the Abanderada sector for a potential Cu-Au target. The west side of Abanderada pit has several westnorthwest striking faults or shear zones that cut massive magnetite and magnetitereplaced andesite. Pyrite ± chalcopyrite often fills these shear zones (Figure 15b). At
FIG. 15a. Abanderada pit 25 m above pit floor (sample CNN 53). Small 60 cm wide vein and 351N structure. This late vein is quartz + actinolite + magnetite + epidote + plagioclase(?) + pyrite + chalcopyrite + Cu-oxides. Sulfide ratios for pyrite:chalcopyrite are 2:1. This zone of mineralization and alteration is at the intersection of the NW-striking structure and the NE-striking fault and andesite dike at the northern end of the Abanderada pit.
FIG. 15b. Abanderada pit wall at 3+24 m (CNN 41). A masive pyrite + chalcopyrite irregular vein. The vein strikes 355 degrees and is 20 cm wide with an actinolite selvage 9 cm wide. Strong actinolite alteration locally patchy. Plagioclase + quartz + K-feldspar + pyrite + chalcopyrite veinlets stockwork the massive magnetite outcrop.
sample CNN 26 a porphyritic quartz + plagioclase ± K-feldspar dike/quartz vein follows a west-striking normal fault that downdrops the magnetite ore body to the north (Figure 15c). Fe-Cu sulfide and oxidized Fe (jarosite), and Cu-oxide mineralization is present along this fault, and farther to the west just outside the pit, Acosta delineated another potential Cu-Au target. At sample CNN 35 a small northwest-striking structure cuts the disseminated magnetite andesite and massive magnetite, and has speculurite and Cu-oxide mineralization. Northwest-striking fault zones with Cu-oxide mineralization were also mapped in the Veta Central and Augusta sectors (Plates # 1-3, CNN District). At the northern end of the Veta Central pit a total of four post-mineral dikes cut the magnetite ore bodies and trend to the northeast. These dikes act as a trap for locally intense Cu-oxide mineralization, which is probably associated with a small northwest striking structure that cuts through the northern high-wall of the pit. In the Augusta sector, the author has mapped only one major northwest trending structure with no lateral offset, however Acosta and Vicencio (1985), Vivallo et al. (1995a), and Villagran (1997) have mapped four northwest-striking faults with left-lateral dip-slip movement, which offsets the earlier NNE trending fault in the district. About 150 meters to the east of the main pit in the Augusta sector, large zones of tourmaline-quartz breccia and tourmaline-quartz-altered andesites are in contact with chlorite-altered andesites along a well defined fault contact at sample CNS 4. Previous workers have mapped three other northwest-striking faults, which terminate at or in the tourmalinequartz hydrothermal breccias and tourmaline-quartz-sericite altered andesitic rocks ± diorites that define the eastern limit of the district.
FIG. 15c. View looking to the west across the Abanderada pit from the eastern pit rim, at Cerro Negro Norte. The outcrop 5 m wide at the bottom may be a porphyritic plagioclase + quartz + K-feldspar(?) dike with quartz + pyrite + chalcopyrite + Cu-oxides + sericite(?) veining, with chlorite selvages, and openspace quartz veining possibly along a WNW-striking fault. It appears to cut the massive magnetite ore body to the north and may downdrop it to the north. The magnetite has disseminated sulfides 3 % total (Py> Cp) and is also quartz + pyrite + chalcopyrite + calcite-veined, with supergene Cu-carbonates.
CHAPTER 6: ALTERATION OF THE CERRO NEGRO NORTE DISTRICT
6.1 Introduction Alteration in the Cerro Negro Norte District is widespread (in the
mapped in current project) and locally very intense both proximal and distal to the magnetite (Fe-oxide) ore bodies. There are six dominant alteration assemblages; some are more pervasive than others are. Spatial (Table 1) and temporal (Figure 16) variations, as well as overprinting of multiple assemblages, are common in the district, and therefore there are variable mineral associations within each of the main types of alteration. Table 1 provides a mineralogical compilation derived from more than two hundred-forty thin sections and simplifies six dominant types of alteration. Also included in Table 1 is typical open-space vein fill, Fe-oxide and sulfide mineralization discussed in Chapter 7, as well as relict minerals both igneous or hydrothermal, and dominant host rock and their spatial association to the magnetite ore bodies. Figure 16 is a paragenetic summary of all the alteration minerals associated with the six dominant alteration assemblages. Illustrated thin section scans from the Abanderada pit, and field photos from the whole district are on the CD-ROM found in the pocket at the back of the thesis text. Plates # 2 and 3 of the Abanderada pit at 1:1000 scale also show mapped crosscutting vein relationships, and alteration. Plate #2 of the CNN District shows the spatial association and relative extent of different alteration assemblages.
TABLE 1. Table of Hydrothermal Mineral Assemblages, associated Vein Assemblages, and Relict Minerals Alteration Type/ Relative Temporal Association
Tm + Qtz + Plag +Act + Cal + Ser + Ti + Py + Cp ± Mt ± Scap ± Ept ± K-spar
Hm, Qtz, Plag/Ser/Act /Py/Cp/ChVBio(?)//Tm
Mt, Hm, Py, ± Cp
I Px, Plag
Andesite / Prox & Dist Diorite/ Prox & Dist
Tm + Qtz(Chalcedony) + Ser
Cal / ±Chl/ ±Tm/ ±Hm
I Plag H Act, Mt, Ti
Andesite / Prox & Dist Diorite/ Prox & Dist
H Mt, Ti
Andesite / Prox & Dist Diorite/ Prox & Dist
//Cal ± Qtz, Chl, Tm Cal + Chl + Rut + Hm
Qtz/Hm/±Ser/Rut Hm + Qtz + Plag + Hm + Ser
Chl + Ab + Scap + Ser + Ept + Cal + Ti ± Rut
I Px, Hbl, Plag
Andesite / Prox
Chl + Cal ± Act ± Ept ± Mt
Mt//Hm, Cal, Cal/Qtz
I Px, Hbl, Plag
Andesite / Prox
Chl + Cal + Tm + Hm + Ser ± Ept
I Px, Hbl, Plag
Andesite / Prox
Cal + Chl ± Ser ± Rut ± Tm
Hm + Cp
H Act, Mt, ± Scap, Ti
Andesite / Prox & Dist
Ser + Qtz + Tm + Hm
Andesite / Prox
Ser + Cal + Qtz + Ept + Hm + Rut
I Px, Hbl, Plag H Mt I Px, Hbl, Plag H Mt
Act + Chl + Ser + Tm ± Rut ± Ept ± Cal ± Py ± Hm
Cal, Qtz/Tm/K-spar /Py/±Cp/±Chl
I Plag, (Px) H Act, Ti
Andesite / Prox Breccia / Prox
Scap + Act + Chl + Ti + Ept + Cal ± Qtz
Hm/Cal/ Sid?, Cal//Cp ± Py
I Plag H Act, Scap
Andesite / Prox & Dist Diorite/ Dist
Propylitic (?) (E-M)
Act + Chl + Plag + Ab + Ept + Cal + Ser + Mt ± Py
I Px, Hbl, Plag
Andesite / Prox & Dist Diorite / Prox & Dist
Clay ± Goeth ± Jar + Hm +
H Mt, Hm, Py, Cp
Andesite / Prox & Dist Diorite / Prox & Dist
Hm, Goeth, Jar, Cv
Andesite / Prox
Actinolite Scapolite Titanite Actinolite Na Plagioclase Epidote Tourmaline
-------------- ----- ------ ---- ---
Pyrite................---...... .... ..
Chalcopyrite Chlorite Calcite Siderite Rutile
---..... .... ............
Carbonate (Dolomite) Barite
o 0 20
a) .6 ci);
ii CO :-0¶ (7) a) ..,_, 73
c a0 SC a) 0 t) -o
FIG. 16. Paragenesis of newly-formed, hydrothermal silicate alteration and hypogene ore ), sparse (--- ---), rare mineralization at Cerro Negro Norte. Abundant and common ( (-- --), and trace (- - - -) amounts present.
Alteration mineralogy can be divided into two general sequences: 1) early, NaCa (± Ca) assemblages with scapolite, Na-plagioclase, actinolite, and magnetite as essential minerals, associated with diorite dikes and quartz diorite porphyry intrusions; 2) late, hydrolytic and carbonate alteration with essential minerals (tourmaline, sericite, chlorite, pyrite, ± chalcopyrite, carbonates), post-dating and associated with pegmatite dikes and other quartz-bearing intrusions.
6.2 Terminology Terminology used within the text, figures, and appendices are based on field note shorthand. Abbreviations for minerals and other terminology used throughout the thesis are defined in Table 1.
Various symbols are used to identify multiple mineral "associations" that may or may not represent stable mineral assemblages found in equilibrium. These symbols are defined as follows: 1) (+ or ±) is used to indicate minerals that are associated and may be part of an assemblage listed in order from the greatest to least in abundance; 2) (/) is often used to separate multiple minerals in veins, which may form assemblages; 3) (//) is used to indicate the separation of vein minerals and selvage minerals. An example of the terminology is as follows: (act/±scap//act) is a vein with abundant actinolite and lesser scapolite, with a vein selvage of actinolite.
"Relict" minerals are defined as either igneous or hydrothermal minerals. Igneous relict minerals are those, which have not been completely hydrothermally altered or are still locally unaltered. Hydrothermal relict minerals are those minerals
which formed during early high temperature alteration, which have been further altered or replaced, during later, lower temperature, hydrolytic or carbonate alteration.
6.3 Actinolite-Rich Calcic Alteration Among the six basic alteration assemblages, the earliest three are Na-Ca varieties. Among these, an early calcic (Ca) assemblage is most recognizable and is characterized by actinolite-rich alteration. Actinolite is likely the dominant mineral in the district and probably the earliest to form as seen by cross-cutting vein relationships. Actinolite is found associated with both early plagioclase and/or scapolite-bearing NaCa alteration assemblages discussed in the following sections, albeit not in massive form and/or monomineralic veins as it is found within the magnetite ore bodies and andesitic rocks, which host the ore bodies. Actinolite-rich calcic alteration is defined, as a separate assemblage on the basis of: 1) abundance, where actinolite is the dominant alteration mineral such as mentioned above; and 2) where actinolite pervasively replaces igneous mafic minerals (pyroxene, hornblend), but Na alteration of felsic minerals is minimal (Ca alteration >> Na alterations). Actinolite is paragenetically long lived (Table 1). Actinolite is dominantly present proximal to the ore bodies, and is also found commonly on parting plains and shear zones within the massive magnetite ore body and surrounding magnetite mineralized host andesite (Viva llo et al., 1994c, 1995a), but is also present distal to the
main ore bodies in diorites and andesitic rock. Strong actinolite alteration of the western diorite is distinguishable by the light green color of the rock when associated with more sodic alteration. Actinolite alteration covers an area
2 km2 (Plate # 2, CNN District
Alteration), and is associated with marialitic scapolite and Na-plagioclase in more NaCa assemblages discussed in the following sections. Actinolite replaces most igneous mafic minerals, including pyroxene and hornblende throughout the district. Local zones of massive actinolite amphibolite ± scapolite crop out to the north of the Abanderada sector in dike-like or massive veins possibly associated with a mylonitic zone, which lies on the fault/contact of andesitic rocks and the western diorite pluton. See Plate # 1 of the CNN District and samples CNN 89 and CNN 99 (Figure 17a). Actinolite is locally pervasive within the massive magnetite ore bodies, and is found most often as veins from hairline up to tens of centimeters wide, which cut the massive magnetite (Figure 17b). Large pods of actinolite up to 0.25 m wide can be found within the ore body. The timing of actinolite-rich calcic alteration and magnetite mineralization is likely synchronous in time. Cross-cutting vein relationships and mineral associations observed in the field and in thin section indicate that massive magnetite is often cut by actinolite veins only, and magnetite veins often cut massive actinolite alteration. Andesitic rock proximal to the ore bodies are dominantly actinolite altered with associated pervasive magnetite mineralization preferentially replacing the groundmass. Locally, actinolite veins may also have magnetite forming as a selvage. Often the large pods of actinolite are locally either partially or completely altered to chlorite and are locally associated with later alteration assemblages, including minerals such as calcite, quartz, and tourmaline. Earlier formed actinolite veins are often re-opened by later veining, which include minerals such as scapolite ± plagioclase ± quartz ± sulfides (Figure 17c-d). In thin section it is clear that strong calcic actinolite
FIG. 17a. Sample CNN 89, NW of the Abanderada pit at Cerro Negro Norte. Massive actinolite + quartz + apatite + pyroxene + scapolite(?) dike or massive vein 75-100 m long and 15 m wide trending NNE, and cutting diorite host rock. The actinolite crystals are up to 20 cm long.
FIG. 17b. Abanderada pit wall at 3+50 m. Actinolite veins 20 cm wide cut massive magnetite ore and andesite host with magnetite mineralization. Locally, large pods of actinolite, rather than veins, and cleavage planes with actinolite can be seen.
FIG. 17c. Early Na-Ca and late pegmatite veins in the Abanderada pit near sample CNN 54A. Massive magnetite with early scapolite (S) or Na-plagioclase(?) vein cut by actinolite vein. Late quartz + K-feldspar + plagioclase + pyrite + chalcopyrite pegmatitic (P) veinlet with tourmaline selvage cutting actinolite (A) vein. However, later pegmatitic veins also re-open older actinolite veins and follow along selvages.
FIG. 17d. Early Na-Ca and late sulfide veins in the Abanderada pit. Andesite host with 2 cm wide actinolite veinlets. Early actinolite veins cut andesite host. Note later cross-cutting and re-opening of actinolite veins with quartz + albite + pyrite + chalcopyrite veinlets 0.5 cm wide. Additional albite + actinolite + sulfide veinlets form a stockwork in the andesite host.
wide X 8 cm long, e-f) actinolite veins cutting magnetite + actinolite + scapolite replaced andesite, and in turn cut by scapolite + plagioclase veins. Late quartz + pyrite + chalcopyrite viens may re-open and crosscut earlier veins. g) Photomicrograph of CNN 47 (10X) x-polar, fibrous habit actinolite vein, with cross-cutting plagioclase(?) vein, re-opened by quartz + sulfide (opaque) veinlet. h) Photomicrograph of CNN 24 (2.5X) x-polar, euhedral habit actinolite vein, cutting magnetite. Trace chalcopyrite after(?) magnetite.
alteration gets cut and offset by later ore Na assemblages, such as scapolite and plagioclase. These later veins seem to follow local zones of weakness and either cut through the center or along the edges of early actinolite veins (Figure 17e-f). Actinolite often forms small millimeter wide selvages and is found as trace to a few % vein fill for most of the later veining and overprinting alteration assemblages. Actinolite often displays an elongate fibrous habit with crystals aligned and as coarse-grained crystals (Figure 17g-h).
Electron microprobe analysis of the actinolite ± hornblende indicate compositions which range from ferroactinolite to actinolite with Fe/(Fe + Mg) numbers of (0.54-0.51) and (0.47-0.27), respectively. Molar Cl/(Cl + F) range from 0.1 - 0.6. The actinolite analyzed from the Cerro Negro District is Fe-Mg-Ca-Al rich and depleted in Na (Appendix B2.3).
6.4 Scapolite-Bearing Sodic-Calcic Alteration Early sodic-calcic (Na-Ca) assemblages include rocks with both scapolite and actinolite. The assemblage is characterized as having abundant scapolite alteration and equal or lesser amounts of actinolite alteration. This assemblage is found proximal to the Fe-oxide bodies in massive form after plagioclase and mafics (Figure 18a), or locally as veins. Distally, the assemblage is common in veins as well as in disseminated replacements. In the CNN District, scapolite bearing Na-Ca alteration covers a
area in the southwestern part of the district, and is confined mostly to quartz diorite (Figure 18b), however, locally andesitic rocks display the same assemblage in the southern part of the district, near the Augusta and Beduino Sectors. The scapolite-rich
FIG. 18a. Massive scapolite + actinolite alteration on Abanderada pit floor. Scapolite (S) + actinolite (A) + pyrite in massive magnetite (M).
FIG. 18b. Sample CNN 114 at Cerro Negro Norte 800 m to the NW of Sector Augusta. Outcrop is a moderately actinolite-altered quartz diorite. Scapolite + plagioclase + titanite + quartz + epidote veining cuts host. A strong chlorite + carbonate alteration overprints the host, and actinolite is completely absent in strong quartz and scapolite altered zones. Titanite is stable 5 vol. % in strongly altered outcrop.
alteration is spatially associated with the andesite/diorite contact on the west side of the district (Plate # 2, CNN District). Johnson et al. (2000) reports similar scapolite-rich assemblages in the Humbolt Mafic Complex (HMC), in west-central Nevada, which are commonly spatially concentrated near plutonic-volcanic contacts, along structurally complex zones, or dike swarms. At the Buena Vista Fe-oxide (magnetite) deposit located in the HMC, massive intense scapolite alteration from deeper proximal exposures is present. Scarce magnetite mineralization, and the alteration of most mafics to actinolite + chlorite at the Buena Vista mine is similar to the scapolite alteration at Cerro Negro Norte. This Na-Ca assemblage commonly has titanite + epidote ± magnetite ± calcite ± apatite also associated with it (Table # 1). Relict igneous clinopyroxene is locally present in areas with less actinolite alteration. The scapolite analyzed by electron microprobe is enriched in Na, Cl, and Al relative to Ca -CO3 end-member meionite (Ca4A16Si6O24CO3). CO3 content was
estimated from microprobe data on the basis of all the anions analyzed (Cl and F) summing to 1. CO3 was calculated by subtracting the sum of analyzed anions from a total of 1. Chlorine averages 3.75 wt. %, and molar Cl /(Cl + F) is nearly 1. All the scapolite is chlorine-rich and marialite (Na4A13Si9O24C1) -rich, ranging from
approximately 73-78 mol % marialite as given by 100*Na/(Na+Ca) (Figure 18c) (Appendix B2.1). Scapolite distal to the magnetite ore bodies is slightly more enriched in chlorine. Bookstrom (1977) estimated the scapolite associated with actinolite alteration at the El Romeral deposit Cl-rich in composition and approximately marialite95-meionite5.
Molar 100* Na/(Na+Ca) vs CIACI+F+CO3+SO4) of Scapolite 78 .r CS
0 z z
CNN 02 CNN 12-1 CNN 114 CNR 2B
FIG. 18c. Scattergraph of molar 100* Na/(Na+Ca) versus molar C1/(Cl+F+CO3+SO4) for scapolite from Cerro Negro Norte. CO3 was estimated by subtracting the total analyzed anions from 1 (Appendix B2.1). Samples CNN 02, and CNN 12-1 are from the Abanderada pit and samples CNN 114, and CNR 2B are distal to the Abanderada pit. All the scapolite samples from the Cerro Negro Norte District are chlorine and sodium-rich (marialite-rich) scapolites.
3.5 cm wide X 8 cm long. Scapolite + actinolite + titanite veining in early scapolite-bearing Na-Ca
alteration. Early actinolite viens with scapolite selvages locally are cut and offset by scapolite + plagioclase veins (E), and scapolite veins have actinolite + magnetite selvages (D). Magnetite + actinolite veins often crosscut actinolite alteration, as well as scapolite veinlets. Magnetite mineralization (veinlets) are temporally very close in time with scapolite-bearing Na-Ca alteration and may slightly predate plagioclase-bearing Na-Ca alteration.
0 6 mm FIG. 18f-g. Scapolite photomicrographs. 0 CNN 12 (2.5X) x-polar, massive scapolite (Scap) crystals, and partially scapolite-altered plagioclase associated with actinolite within Abanderala magnetite ore body. g) CNN 114 (10X) x-polar, scapolite veining with aligned fine- grained fibrous crystals in the interior of vein, and coarser-grained subhedral crystals on the selvages.
Petrographic analyses indicate scapolite occurs as both massive replacements of plagioclase and extensive veining (Figure 18d-e) in host rocks, which have sodic-calcic alteration. The scapolite-bearing Na-Ca alteration as seen in cross-cutting relationships in the field and thin section, suggest scapolite veins and veinlets are the same age, and/or locally may slightly post-date actinolite + magnetite veins and veinlets discussed earlier. Scapolite veins often have actinolite + magnetite selvages and locally scapolite veinlets with no selvage cut and offset actinolite veins. Magnetite ± actinolite veins also crosscut scapolite veinlets. These relationships indicate a close temporal relationship between magnetite mineralization and early Na-Ca alteration. Often, replacement scapolite is found on the rims of euhedral plagioclase phenocrysts in andesites. Scapolite is also common as anhedral grains replacing plagioclase in groundmass. Scapolite veins display euhedral grains up to 5 mm long and 1 mm wide and are commonly spatially associated with titanite. Scapolite also commonly forms a massive feathery texture, which is composed of aligned sub-millimeter sized euhedral to subhedral individual grains. Photomicrographs CNN 12-1 and CNN 114 (Figure 18f-g) display typical scapolite alteration, from massive replacement proximal to the ore body, to veins and replacement more distal. See Appendix B2.1 for microprobe analyses.
6.5 Plagioclase-Bearing Sodic-Calcic Alteration Another Na-Ca assemblage is dominated by actinolite and sodic plagioclase and is found mainly distal to the ore bodies in locally pervasively altered diorites, granodiorite dikes, and in some cases in andesites. However, albite veining is also locally present in magnetite-replaced andesite and massive magnetite in the Abanderada
ore body. Na-plagioclase is not found as massive replacement but rather in local pockets of strongly bleached rock, or more commonly as discrete zones several 10's of m2 associated with zones of weakness, either along structures, or intrusive contacts. It is found locally replacing igneous plagioclase in andesites proximal to the magnetite ore bodies. The total area that has been affected by variable degrees of Na-plagioclasebearing alteration is
0.5 km2 (Plate # 2, CNN District Geology), and is located to the
west of the Abanderada pit, hosted mainly in the dioritic rocks. This Na-Ca assemblage (Table # 1) is composed dominantly of Na-plagioclase and actinolite, that are commonly associated with epidote + magnetite ± calcite ± titanite. Pyroxene, ± hornblende is locally present as relict igneous phenocrysts, where alteration is weaker. To the west and southwest of the Abanderada pit, a porphyritic igneous breccia of quartz diorite to monzodiorite composition is strongly Na ± Ca altered and albitized plagioclase is present. Albite + epidote veins and bleached white outcrops trend NNE and crosscut earlier calcic alteration assemblages, and may be spatially/temporally associated with granodiorite porphyry dikes (Figure 19a-b). Epidote ± scapolite ± quartz is common in veins of this alteration assemblage distal to ore bodies, normally associated with diorite intrusions, as well as locally within the Abanderada pit (Figure 20a-b). To the east side of the district, not mapped by the author, Vivallo et al. (1997) has mapped another Na-altered albite-rich zone with associated quartz. The timing of this alteration relative to quartz-tourmaline alteration is unclear. Johnson et al. (2000) mentions that Na alteration is restricted in distribution and is found at distal and at shallow levels in the HMC in west-central Nevada. Spatial and temporal similarities
FIG. 19a. CNN 102, 103 at Cerro Negro Norte located west of the Abanderada pit Clasts of magnetite + actinolite are found in the Na-plagioclase altered igneous breccia of porphyritic quartz dioritemonzodiorite composition. Plagioclase + quartz + actinolite veinlets cut earlier actinolite, magnetite, and scapolite veins with actinolite + magnetite selvages. The granodiorite dikes are chlorite + sericite + epidote(?) + calcite altered after plagioclase and actinolite.
FIG. 19b. CNN 78 to the west of the Abanderada pit. Granodiorite porphyry with magnetite altered to hematite + actinolite breccia fragments. The plagioclase is altered to albite + epidote + calcite, and has hairline fractures with magnetite + actinolite + epidote, with local titanite. These small dike like pods of breccia strong actinolite alteration forming dike selvages.The quartz diorite host rock has Naplagioclase + epidote altered plagioclase and locally actinolite after pyroxene. Note the plagioclase + quartz veins cutting earlier magnetite + actinolite veinlets.
FIG. 20a. CNN 19 sample from Sector Abanderada. Monzodiaite porphyry dike with magnetite clasts up to 7 cm in length. This dike is in contact with massive magnetite and a quartz diorite dike-like intrusion parallel to the maganetite ore body along the east side of the pit ti ending 030 degress. Na-plagioclase alteration is locally pervasive found in veinlets, and clots as seen in lower right hand corner.
FIG. 20b. Abanderada magnetite with plagioclase veinlets dump sample. Contact of massive magnetite and moderately magnetite replaced andesite at the top left side of sample. Plagioclase + scapolite(?) + actinolite veins cut host rock, and early magnetite veinlets. Later quartz + tourmaline veins 1-2 mm wide cut everything.
between sodic plagioclase alteration found at CNN and sodic plagioclase alteration assemblages found associated with Fe-oxide deposits around the Great Basin of the U.S. as described by Johnson et al. (2000a, b); Carten (1986); and Dilles and Einaudi, (1992) are striking. The scapolite-bearing Na-Ca assemblage is sporadically overprinted by Naplagioclase (oligoclase) assemblages. Replacement of feldspar phenocrysts by sodic plagioclase, replacement of groundmass plagioclase in andesites by Na plagioclase ± quartz, and Na-plagioclase + epidote + actinolite veining is common in the CNN District (Plate # 2, CNN District), and locally in the Abanderada pit (Plate # 2, Abanderada Sector). In the Augusta Sector, Na-plagioclase alteration is spatially associated with tourmaline-quartz hydrothermal breccias in contact with the andesitic rocks, which host the magnetite ore body. Electron microprobe analyses on various plagioclase feldspars from the district indicate plagioclase associated with scapolite + actinolite alteration is andesine, whereas plagioclase associated with late tourmaline, quartz + sericite is albite or oligioclase. Included are igneous plagioclase from the western diorite, granodiorite dikes, plagioclase from altered andesites proximal to the Abanderada ore body, as well as from the tourmaline-quartz-sericite-chlorite altered andesites and hydrothermal breccias immediately to the east of the Augusta sector (Appendix B2.2). Vivallo et al. (1995a) reports that albite-altered rocks compared to unaltered andesite rocks from the CNN district, display relatively little change in Na, but do show depletion in Ca, Mg, Fe, and K. Feldspar samples from scapolite-actinolite altered andesites (CNN 02 and CNN 121), within the Abanderada pit, range in composition between An24 and
(oligoclase), and are between 3 and 5.3 mol % K-feldspar (Or). CNN 78 is a sample
containing igneous euhedral plagioclase phenocrysts with clear oscillatory zoning from a granodiorite dike to the west of the Abanderada pit cutting the western diorite. A microprobe traverse from rim to core indicates a sodic (An35) core. The composition of the rim range from An22 to An35, whereas the core
ranges from An37 to An45, and is dominantly andesine in composition (Appendix B2.2).
This igneous plagioclase phenocryst can be compared to the igneous oscillatory-zoned igneous plagioclase from sample CNN 103-3, and the sodically altered igneous plagioclase in samples and 103-3 and 108. These samples are from bleached variably sodically altered andesites and granodiorite dikes, respectively to the west of the Abanderada ore body; plagioclase ranges from An22 toAn49, indicating an oligoclase to
andesine composition (Figure 21a). The samples mentioned above have less than 1.7 mol % Or. Plagioclase in andesites is often altered to epidote, and when in close proximity to granodiorite-monzodiorite dikes, which intrude the andesite, such as
sample CNN 76B (Figure 21b). Samples CNS 03, and 09A are from the Augusta Sector. The groundmass plagioclase analyzed from these samples range in composition from Ani to An12. Feldspars from sample CNS 09A are locally potassic (up to 77 mol %
Or) in composition possibly due to tourmaline + sericite alteration (Figure 21c). CNR 14A from a diorite-granodiorite dike in the southern part of the district display the strongest Na-plagioclase alteration with associated rutile after titanite ± carbonate
(Figure 21d). Compositions are < lmol % An (Figure 22). Plagioclase in igneous rocks typically range between A1136_50, Na-Ca altered plagioclase associated with scapolite
typically range between An24-27, and plagioclase associated with tourmaline + quartz +
wwwisa% 0.6 nun
FIG. 21a-d. Photomicrographs of various plagioclase analyzed by electron microprobe. a) CNN 103 (2.5X) x-polar: Plagioclase phenocrysts from igneous breccia , locally with Na-plagioclase rims, and groundmass strongly Na-altered. b) CNN 76B (10X) x-polar: Plagioclase phenocryst from andesite host, locally altered to epidote. c) CNS 9A (10X) x-polar: Plagioclase phenocrysts and groundmass Na-altered, locally potassic when associated with quartz-tourmaline breccias, and possible granodiorite dikes. d) CNR 14A (10X) x-polar: Plagioclase in groundmass and phenocrysts from granodiorite dike with strong Na-plagioclase alteration + calcite + epidote (?), and associated rutile after titanite.
Tm +Ser +Chl
Plag + K-spar +
0 Tm + Ser
Sec + Cal
Flag + Cal +
Tm + Rut + Qtz
CNN 103-3 Andesite Act + Plag = igneous zoned
CNN 108 Granodiorite Na -Flag +Act
0An FIG. 22. Feldspar ternary plot of samples from Cerro Negro Norte. Feldspar compositions from microprobe analyses are plotted above. The apices indicate anorthite (An), albite (Ab), and orthoclase (Or). Multiple dots of the same color indicate either different feldspar grais in the same sample, or multiple zones within one grain, in the same sample. Feldspar end-member compositions range approximately betweenAnO - An50.
sericite alteration is typically albite or orthoclase. See Plate # 2, CNN District for distribution and extent of plagioclase-bearing Na-Ca alteration.
6.6 Tourmaline-Quartz-Sericite Alteration To the east of the Abanderada ore body and to the east of the Augusta sector, a tourmaline-quartz-sericite hydrothermal breccia and tourmaline-quartz-sericite-chlorite altered andesitic rock ± diorite display a texture-destructive and protolith- destructive
pervasive alteration. These tourmaline-quartz-altered rocks define the eastern limits of outcrop in the district, and cover
0.5 km2. Granodiorite dikes crosscut and post-date
this alteration near UTM 0367100E and 7001000N and are orientated NNE (Plate # 1, District Geology). Vivallo (1995a) notes that the tourmaline-quartz breccia is often spatially associated with porphyritic felsic intrusives. The tourmaline + quartz alteration is temporally later than the early Na-Ca assemblages, and is often found overprinting the earlier assemblages.
Tourmaline forms in various habits including massive optically zoned euhedral grains (Figure 23a), disseminated very fine-grained euhedral grains in groundmass (Figure 23b), radiating subhedral to anhedral fibrous interstitial grains and as anhedral clots (Figure 23c), and many times as stockwork veins and veinlets. The quartz is usually anhedral and forms in clusters as interlocking grains, in veins and veinlets, and also as euhedral "dogtooth habit" in open space veins, or as fibrous chalcedony (Figure 23a, d). Much of the quartz contains fluid inclusions, that are often < 5 1.tm in diameter and very irregularly shaped. However, those fluid inclusions > 5 1.1M generally are Type II fluid inclusions with multiple solids containing
FIG. 23a-d. Photomicrographs of various tourmaline and quartz crystal habits. a) CNN 66-2 (10X) x-polar: zoned euhedral cubic stubby basal crystals, with anhedral quartz containing fluid inclusions. b) CNN 53-3 (20X) x-polar: fine- grained euhedral grains overprinting earlier plagioclase. c) CNN 46A(10X) x-polar: anhedral clots overprinting K-feldspar phenocrysts in a quartz + plagioclase + K-feldspar vein. d) CNS 15A (10X) x-polar: Fibrous radiating supergene chalcedony low temperature (< 200 degrees C) often found with quartz-tourmaline altered andesitic rocks and probably post-date tourmaline-quartz breccias from the Augusta Sector.
halite salt crystals up to 101.1m in size and often hematite flakes as well as other
unidentified pleochroic minerals. The tourmaline-quartz assemblage includes sericite, which most often replaces plagioclase phenocrysts (Figure 23e-f) or the groundmass of the protolith, but also forms as very fine-grained radiating masses associated with quartz in small veinlets, and as overprinting anhedral fibrous grains. Titanite is locally altered to rutile, especially near zones of intense brecciation and/or granodiorite dikelets. Pyrite ± chalcopyrite is associated with quartz, tourmaline and sericite as disseminated grains usually no greater than 2-3 vol. % or as vein fill with quartz and tourmaline. In oxidized rock jarosite after pyrite and earthy hematite ± goethite fills vugs in the rocks. Hematite is the dominant hypogene Fe-oxide in this alteration assemblage and magnetite is rarely stable, but can be present, usually in veins as relicts from early alteration.
Granodioritic pegmatite and aplitic dikes and sills consisting of medium to coarse-grained (4-6mm in size) quartz + tourmaline + plagioclase ± K-feldspar + pyrite ± chalcopyrite ± sericite ± chlorite are locally present in the Cerro Negro Norte District and are most likely associated with the tourmaline-quartz altered andesites and diorites as well as the tourmaline-quartz breccias. These aplitic dikes (Samples CNN 46, and 63) can be found proximal to and cutting massive magnetite and actinolite, scapolite, titanite, albite, epidote-altered andesites in the Abanderada pit (Figure 24a-b), and in the Veta Central pit. Massive tourmaline up to 30 vol. % often forms as anhedral overprinting masses with no crystal habit, and as selvages on quartz + plagioclase + Kfeldspar + sulfide veins or in massive form (Figure 24c-d). Small granodiorite dikes and/or quartz + plagioclase + tourmaline veins with graphic textures intrude and cut the
FIG. 23e-f. Photomicrographs of sericite alteration after plagioclase associated with tourmaline-quartz alteration. e) CNS 13A (10X) x-polar: Plagioclase phenocryst in upper right hand corner moderately altered to sericite, sample is associated with strong chlorite alteration after actinolite f) CNN 75 (40X) x-polar: Plagioclase phenocryst altered to sericite, quartz + hematite veining cuts the original host rock.
FIG. 24a. Late pegmatite/aplite dikes or sills. These (subhorizontal) plagioclase + quartz + K-feldspar + tourmaline dikelets 3.5cm wide cut massive magnetite and strongly magnetite-replaced andesite host. Individual feldspar crystals are 1.5 cm wide as compared to 2-3 mm wide in other dikes.
FIG. 24b. Abanderada pit wall at 4+90, sample CNN 63. Massive magnetite at bottom of photograph is in contact with a sub-horizontal pegmatitic dike altered to quartz + albite + clay + sericite + actinolite + hematite + goethitite A quartz breccia vein (border zone) is between the dike and the massive magnetite altered to hematite, near the red pencil. .
FIG. 24c. Abanderada dump pegmatite veins. Left sample: 1cm wide actinolite veins cutting magnetite replaced andesite. Late plagioclase + quartz + K-feldspar with tourmaline + quartz selvages (- 2.5 cm /12.5 mm wide) pegmatitic vein cuts host andesitic rock. Right sample: plagioclase + quartz + K-feldspar + actinolite + calcite + epidote + pyrite + chalcopyrite + tourmaline veins 1 cm wide cut actinolite veined, magnetite replaced, andesite host.
FIG. 24d. Abanderada pit sample of massive pegmatite float. Sample of pegmatite quartz + K-feldspar + plagioclase + tourmaline + actinolite + pyrite + chalcopyrite. Pegmatite cuts an actinolized andesite host. Locally actinolite has altered to chlorite.
massive magnetite ore bodies strongly altered to hematite, as well as the andesite host in the Cata Alfaro Sector (Figure 24e). Plagioclase forms 0.8 mm euhedral lath-shaped grains locally altered to sericite which fill in around larger framework grains. The framework is composed of 2-3 mm anhedral grains of plagioclase locally strongly altered to sericite, and anhedral quartz up to 6 mm in size. Plagioclase and quartz display an intergrown texture. K-feldspar is generally interstitial to the quartz and plagioclase.
Sulfide mineralization is common in this assemblage, and massive pyrite fills in around other silicate minerals in a mosaic texture (Figure 24f-i). Pyrite, chalcopyrite and magnetite are often spatially associated. Chalcopyrite may have replaced magnetite or is included in magnetite, and it is generally found with a hematite-altered rim. In larger veins tourmaline forms optically concentrically zoned subhedral grains up to 4mm in size, and is found both as vein fill and most often forms the vein selvage. Anhedral quartz is up to 4 mm in size and often has undulose extinction, and plagioclase typically has a subhedral to euhedral habit. Tourmaline was analyzed by microprobe from both pegmatitic quartz + tourmaline + plagioclase ± K-feldspar dikes (CNN 46) cutting magnetite-replaced andesites and massive magnetite ore in the Abanderada pit, and from tourmaline-quartz altered andesites and tourmaline-quartz breccias (CNS 03, CNS 09) in the Augusta
sector (Appendix 2.7). The A1203 content is about the same ( 23-26.5 wt. %) in both tourmaline-quartz altered rocks and the pegmatite veins from the Abanderada sector. In contrast FeO is diminished by half from
24-27 wt. % in tourmaline from the aplitic
veins in the Abanderada sector, but only
12-13 wt. % in samples from the tourmaline-
FIG. 24e. Sector Cata Alfaro at Cerro Negro Norte. Quartz + plagioclase + tourmaline horizontally oriented graphic- textured dike 15 cm wide cuts massive magnetite strongly altered to hematite. Quartz + calcite + Fe-oxides + Cu-carbonate alteration and in veins cut andesite(?) host rock in the area. The massive magnetite bodies trend to the northeast.
FIG. 24f-i. Tourmaline thin section scans and photomicrographs. Thin sections are 3.5 cm wide cm X 8 cm long, and photomicrographs are labled. f) Massive tourmaline alteration with quartz + plagioclase + K-feldspar + actinolite + pyrite + chalcopyrite vein with possible zoned tourmaline selvages. g) same type of alteration and veining as F, notice sulfides along selvages. h) CNN 46 (2.5X) x-polar, dark mineral is tourmaline, notice mosaic texture of tourmaline. i) CNR 11 (10X) x-polar, quartz vein cutting tourmaline, later quartz + tourmaline vein cuts quartz.
TiO2 vs FeO /(FeO +MgO) in Tourmaline
Na02 vs FeO /(FeO +MgO) in Tourmaline 3.0
2.5 2.0 -
CNS 03 e CNS 09A
° 1.0 i--:
CNN 46 CNS 03 CNS 09A
FeO /(FeO +MgO)
A1203 vs Fe0/(Fe0+Mg0) in Tourmaline
CaO vs Fe0/(Fe0+Mg0) in Tourmaline
ci FeO /(FeO +MgO)
o 1.5 o 1.0 -
CNN 46 CNS 03 CNS 09A
M 25 -
CNN 46 CNS 03 CNS 09A
< 24 -
FeO /(FeO +MgO)
FIG. 25. Variation plots comparing the Fe number to major oxides of Na, Ca, Ti, and Al in tourmaline. Notice that samples CNS 03, CNS 09A, which are tourmaline-quartz altered andesite and breccia samples from the Augusta Sector are depleted in Fe compared to CNN 46A from the Abanderada Sector. Fe content of tourmaline is higher where massive magnetite ore is present.
quartz altered andesites from the Augusta sector. The samples from the Augusta sector
(CNS 03 and CNS 09) therefore are depleted in FeO, and enriched in Mg (-9 wt. %),
CaO, and TiO2 ( 2 wt. %) relative to aplite samples. Na2O remained the same in both areas at
2 wt. % (Figure 25). The tourmaline-quartz samples from the Augusta sector
are proximal to the Augusta magnetite ore body, however, they do not cut the massive magnetite ore body or magnetite replaced andesite, as is the case in sample CNN 46. Where magnetite is present in host rock (Abanderada pit), Fe-content of tourmaline is generally higher.
6.7 Chlorite-Carbonate-Quartz-Sericite Alteration The fifth type of alteration is a late chlorite-quartz-sericite-calcite alteration that is found dominantly proximal and locally distal to the magnetite ore bodies and magnetite replaced andesites in the Abanderada, Augusta and Beduino sectors. The most pervasive chlorite alteration is spatially associated with the tourmaline-quartz altered andesitic rocks to the east of the main ore bodies defining the eastern limit of the CNN District, discussed in the previous section. This type of alteration may represent a later lower temperature phase, distal to the tourmaline + quartz + sericite alteration or simply more strongly altered zones near structures, which are present in the eastern portion of the district. Here, the extent of alteration is
0.5 km2 (Plate # 2, CNN
District), however, chlorite is found throughout the district, mostly as replacement of actinolite in the massive magnetite ore bodies (Plate # 2, Abanderada Sector), mentioned above. Typically, plagioclase found in this assemblage is altered to or replaced by calcite + sericite ± epidote, with relict albite. Locally, chlorite + quartz +
calcite + sericite + rutile veins are present in proximal zones where they crosscut the massive magnetite and earlier alteration assemblages. Sulfides (pyrite ± chalcopyrite) are commonly associated with calcite and quartz + calcite veins (Figure 26a-c). The chlorite often replaces actinolite in andesitic and intrusive rocks as well (Figure 23e, previous section). Chlorite forms as large anhedral radiating masses or clots and as interstitial masses in groundmass or simply as replacements of individual actinolite grains (Figure 26d). See Appendix B2.10 for chemical analysis of chlorite. Johnson and Barton (2000a) mentions that chlorite + carbonate alteration is found distal to and grading out from albitic assemblages, and overprints Na-Ca assemblages in the Humbolt mafic complex of west-central Nevada. This assemblage is often widespread and pervasive near structures and favorable lithologic contacts at shallow levels, and dominantly fracture controlled at depth. In the CNN District the distribution pattern is similar.
Stockwork veinlets and veins of calcite + chlorite are also common and often have supergene Cu-carbonates associated. Quartz forms zoned or banded euhedral grains growing into open space, or as radiating masses of chalcedony (Figure 23d, previous section). Quartz veinlets contain poorly formed fluid inclusions. Stockwork calcite veins and very fine-grained replacement of plagioclase from the earlier quartztourmaline alteration is common in this assemblage. Rutile replaces hydrothermal titanite and is locally spatially associated with calcite in thin section. The Cl + F analyses are near or below detection limits of the microprobe (Appendix 2.6). Fe-oxide mineralization as in the tourmaline-quartz-sericite altered rocks described above is dominantly hematite. Epidote is found locally as clusters of anhedral grains and in veins
FIG. 26a-d. Photomicrographs of various chlorite + calcite + sulfide alteration and mineralization. a) CNN 27-1 (10X) x-polar: Quartz + calcite + pyrite vein with chalcedony selvage re-opens early actinolite vein in magnetite replaced andesite host. b) CNR 26A (10X) x-polar: Calcite vein cutting epidote + calcite altered andesite. c) CNN 31 (2.5X) x-polar: Calcite + quartz + pyrite vein cutting magnetite replaced scapolite + actinolitealtered andesite. d) CNN 48- 1(10X) x-polar: Interstitial chlorite replacement of actinolite near pyrite grain.
with chlorite. Sulfides are entirely oxidized, near the surface, where jarosite + goethite are pervasive, locally forming a light brown staining.
6.8 Carbonate (Dolomite) Alteration The last type of hypogene alteration is the carbonate alteration assemblage, which is proximal to the ore body in the Abanderada sector. A zone
200 meter long
100 m wide of dolomite crops out in the pit, and along the eastern highwall of the
pit (Figure 27a). The carbonate alteration in the pit is undoubtedly spatially related to the north-south striking fault, defining the eastern side of the Abanderada ore body. Calcite ± goethite ± hematite veins are the dominant veining along the eastern side of the pit, cutting a sericite + chlorite + quartz + clay altered zone (Figure 27b). The carbonate alteration crops out in massive bodies and also in veins that cut the massive magnetite ore, which is strongly altered to hematite forming a "zebra" striped outcrop. In thin section the dolomite veins are up to 2 mm wide and form colliform and banded textures, with anhedral and euhedral grain centers (Figure 27c). Barite veins and pockets of barite are common in brecciated magnetite (altered to hematite) scabs, which abut the intense carbonate alteration in the Abanderada pit (Plate #2, Abanderada Sector). The veins of barite + quartz are cut by later hematite veins (Figure 27d). Earlier quartz veinlets cut and offset magnetite ore and are in turn cut and offset by carbonate veins. Johnson et al. (2000a, b) indicates that quartz + barite + sulfide veins are common in this type of carbonate assemblage at shallow levels in the Humbolt mafic complex. Barite + quartz + hematite ± calcite veins are found distal to the massive magnetite ore bodies, in the western part of the CNN District cutting quartz diorite.
FIG. 27a. View to the SE from within the Abanderada pit at sample CNN 67. Contact between the magnetite ore body and massive carbonate alteration. View up three benches from the pit floor on a landslide of carbonate (CNN14). The carbonate alteration and magnetite body contact trends 130 and dips 50 degrees to the SW. The magnetite has disseminated sulfides (Pyrite:Chalcopyrite = 3:1).
FIG. 27b. Liesegang goethite + carbonate veining along east side of the Abanderada pit. Possibly an altered diorite body or andesite? Magnetite has been altered to goethite and plagioclase has been altered to clays. This carbonate alteration is supergene and may be associated with a fault/ shear zone striking 040 degrees along the east side of the pit.
FIG. 27c-d. Photomicrographs of carbonate alteration and barite mineralization. c) CNN 14 (2.5X) x-polar: Colliform banded carbonate cutting massive magnetite, magnetite is altered to hematite. d) CNN 08 (10X) x-polar: Barite cut by a hematite quartz vein. Barite may be associated with late carbonate alteration at shallow levels in the system, followed by local supergene mineralization.
Calcite veins always cuts and often offsets all other earlier alteration types in the district as well as overprints all earlier alteration assemblages (Figure 27e). Calcite alteration and carbonate veins district-wide are common with sulfide mineralization and later supergene minerals often associated. In zones of very strong carbonate alteration, chalcedony, and supergene minerals including goethite, hematite, covellite, and Cucarbonates, such as malachite are associated with the alteration, presumably within 200
m of the surface. A 250 m by 300 m zone of carbonate "flooding" alteration is present to the north of the Abanderada sector in the Cato Alfaro sector (Plate # 2, CNN District), and is spatially very close to the tourmaline-quartz-sericite-chlorite-calcite alteration in the northeast part of the CNN district.
FIG 27e. Dolomite or carbonate veins cut through massive magnetite altered to hematite in the Abanderada pit. Disseminated actinolite + pyrite + chalcopyrite + epidote and tourmaline also present in the hematite.
CHAPTER 7: MINERALIZATION OF THE CERRO NEGRO NORTE DISTRICT
7.1 Fe-Oxide (Magnetite + Hematite) Mineralization Fe-oxide magnetite + hematite ± chloroapatite ore bodies in the Cerro Negro
Norte District have produced
100 Mt of Fe ore in total. The ore bodies consist of
massive magnetite up to 99 wt. % total Fe203, and varying degrees of magnetite replaced andesites up to 55 wt. % Fe203. The average grade during production in 1962 was reported to be 65 wt. % Fe203. Airborne magnetic surveys in 1967 delineated four major ore bodies including the Abanderada, Veta Central, Augusta and Beduino massive ore bodies (Compania Minera Pacifica, 2000). Tres Clotes and Cata Alfaro are two smaller sectors with minor workings. The Abanderada ore body is 150 m wide, by
400 m long by
100 m deep, and is the largest of the open pits in the district. The
Abanderada pit was the most important producing pit during exploration in the district,
during the sixties (Vivallo et al., 1997-98). The Veta Central workings are long by
150 m wide by
50 m deep, and the Augusta and Beduino orebodies are
125 m long by 125 m wide by 50 m deep. The smaller workings throughout the district consist of pits < 50 m long and up to a few tens of meters wide. Fe-oxide mineralization in the Cerro Negro Norte District is extensive and forms dominantly as large ore bodies of massive magnetite, which are located in the central part of the district, and define a N-S trending zone
2.5 km long and 0.5 km wide
(Plate # 1, CNN District). The magnetite ore bodies have variable orientation and shape. Although most of the high-grade ore in the Abanderada pit has been exploited, textures,
basic morphology and general orientation of the ore body are still discernible. Locally, the magnetite is replaced by hematite along late hydrothermal conduits. The ore bodies are most often vertical to sub-vertical and elongated NNE. Along the eastern side of the Abanderada pit, small scabs of brecciated magnetite altered to hematite ore are in contact with intensely carbonate + sericite ± sericite altered wall rock. The NNE striking contacts are abrupt and dip from
85° to vertical. Small,
irregularly shaped bodies of massive ore, between 10 and 25 m wide crop out at higher levels of the pit like pendants within massive carbonate altered host rock (Figure 14a, Chapter 5.2.1). In the northeastern part of the pit, massive magnetite lines the pit walls. Locally, small zones of brecciated magnetite are in contact with the massive magnetite. Veins of magnetite up to 1 meter wide, striking 030° with variable dips are associated with zones of massive quartz veining and brecciation along the side of the pit. The northern part of the Abanderada pit was mined out following two vertical, NNEtrending tabular massive magnetite bodies, which likely indicate fluid flow paths and zones of weakness such as faults or shear zones (Figure 14c, Chapter 5.2.1). The western side of the Abanderada pit is dominantly massive magnetite in gradational contact into host andesite rock with disseminated magnetite mineralization. The massive magnetite has varying textural characteristics ranging from a very fine grained to coarse-grained euhedral cubic habit. The ore body here is irregularly shaped, but the magnetite-replaced andesitic host rock is oriented subhorizontal, and is locally extensively fractured subhorizontally. Later WNW striking faults dipping
down-drop portions of massive magnetite and/or strongly mineralized andesites to the north (Figure 15c, Chapter 5.2.2). Vivallo (1997-98) mentions that these fractures form
a radial pattern oriented parallel to the roof of the magnetite body defining a dome-like ore body, but the author has not recognized such textures. To the north of CNN 25 and 26 (Plate # 3, Abanderada Sector), in the Abanderada pit, massive magnetite is cut by pyrite ± chalcopyrite-bearing quartz + calcite veins and/or NW-striking shear zones with massive pyrite + chalcopyrite sulfide mineralization, or locally by simple disseminated sulfides. The massive magnetite ore in this zone varies locally from very fine-grained to coarse grained. (See geochemistry analysis in Appendices C1.1-C2.1). The Veta Central pit also displays sub-vertical ore bodies that range from irregular to tabular in shape, and are often fractured by sub-horizontal fractures. The magnetite bodies grade from massive magnetite ore to varying degrees of disseminated magnetite mineralized andesite host and wall rocks over a few meters distance. The magnetite-replaced andesite host rocks in the Veta Central sector display a layered or stratified morphology, presumably from original andesitic flows. Vivallo (1997-98) notes that magnetite bodies in this sector are interbedded with the stratified volcanic rocks. However, the author did not see clear evidence for stratified magnetite lavas. On the northeast side of the Veta Central pit, massive magnetite is in contact with an altered intrusive rock containing 15 volume % disseminated magnetite. This contact strikes 055° and dips 81° to the northwest.
Magnetite mineralization is not confined to the four massive ore bodies in the district. Immediately to the west of the Abanderada pit, an irregularly shaped dike-like body of magnetite strikes wide on the surface and
045° and dips 33° ESE. The magnetite body is 30-35 m
300 m long. It loosely follows and is spatially close to a
contact of diorite and andesitic rock inferred to be a fault with intense quartz + sulfide
mineralization discussed in the following section. Two other irregular magnetite bodies or veins strike approximately NNE between the edge of the Abanderada pit and the previously mentioned magnetite body. (Plate # 3, CNN District). Magnetite veins from centimeters to several meters wide, and locally altered to hematite are found throughout the district and further to the south. To the northwest of the Augusta Sector small NNE-trending stopes following magnetite ore bodies, which are several meters wide by 50 to 100 m long. To the west, north and northwest of the Abanderada sector hematite + quartz ± calcite ± Cu-oxides are common. The veins strike from NNE to NW and are normally no longer than several 10's of meters long (Figure 28a).
Near the Solitaria piquero,
1 km to the south of Cerro Negro Sur (outside of
CNN District plates), a hematite + quartz + Cu-oxides + Cu-carbonates + calcite + goethite + earthy hematite vein was prospected and/or mined presumably for Cu ± Au(?). In thin section, the hematite breccia is cemented with quartz + Cu-carbonates ± tourmaline(?) (Figure 28b). The vein is between 0.5-2 m wide and strikes 320°-335 °, and dips 87° to the SW. Other hematite veins
5 cm wide crosscut the vein, strike 024°,
and dip vertically.
The Cata Alfaro Sector, at the northern end of the CNN district has massive and
brecciated magnetite in steeply dipping irregular to tabular bodies or veins 10's of meters wide by 50-75 m long (Figure 24e, Chapter 6.6). These ore bodies have been altered to hematite, and in thin section the hematite has a grain size
2 mm long, and a
bladed habit (speculurite). The workings in this area follow both NNE-and NWtrending hematite ore bodies with quartz + calcite ± tourmaline + supergene
FIG. 28a. Magnetite vein (CNR 13) located south of Cerro Negro Sur. The vein is south of the Solitario magnetite + Cu-oxide vein and is 1.5-2 m wide striking NW over ridge line for 20 m. The vein has massive pods of calcite and possibly apatite, with minor quartz + Cu-oxides. The host andesite(?) rock is altered to scapolite + epidote after plagioclase. Later alteration includes chlorite after actinolite, with sericite + calcite after scapolite. Scapolite + calcite + titanite veins cut host rock, and latest calcite + epidote veins cut everything.
mineralization including Cu-oxides + Cu-carbonates + goethite, which characterize the sector (Plate # 3, CNN District). Large inclusions of quartz and calcite up to several meters wide in diameter are also included in the Fe-oxide ore (Viva llo et al., 1997-98).
Disseminated Fe-oxide mineralization is common in the district, dominantly in host andesitic rocks, but also in the diorite, monzonite-granodiorite dikes. Most of the mineralization is magnetite, which is locally altered to hematite. Modal rock percentages of magnetite range from 1 % to 5 vol. % distal to the orebodies and is probably the original igneous rock content, such as in the western diorite, and closer to the large massive magnetite orebodies modal percentages of magnetite are near 10 vol. % added magnetite. Andesitic wall rock, within the pits and closely spatially associated with massive ore bodies can have from 30 % up to 75 vol. % modal magnetite (Plate # 3, Abanderada Sector). Occasionally, the disseminated magnetite has a cubic habit, however most of the magnetite seen in thin section forms in small clots < 2 mm in size, often as a replacement texture in groundmass, or veinlets (Figure 28c-e). The matrix of the igneous breccia containing the magnetite clasts mentioned previously in Chapter 4.2.2 has a quartz diorite composition. These breccia zones are most often spatially associated with monzodiorite to granodiorite porphyry dikes and/or intrusions that intrude andesite and equigranular diorite. The breccia zones crop out both in the Abanderada pit district (Plates # 1, # 3, Abanderada Sector), and in several other locations, on the western side of the CNN district (Plate # 1, CNN District). The breccias, which have been strongly Na-Ca altered, commonly have up to 10 % disseminated magnetite mineralization, as well as 3-5 cm wide angular clasts of magnetite. In thin section, the clasts are composed of clots of anhedral to euhedral cubic
FP Ia. g -waltz .4- Act
c as Firt.P I a 0 (7)
FIG. 28b-e. Magnetite mineralization in thin section scans and photomicr 9 . phs. Thin sections are 3.5 cm wide X 8 cm long. b) CNR 4 (10X) x-polar: Hematite breccia cemented with quartz + tourmaline + Cu- carbonates. c) CNN 28 (10X) x-polar: Massive magnetite cut by quartz + plagioclase vein altered to sericite. d-e) In thin section, magnetite can be seen replacing
groundmass as in D, or cross-cutting host rock in veinlets, and as selvages. Magnetite veinlets are cut by scapolite + plagioclase veinlets.
Molar C1/(Cl+F) vs C1/(Cl+F+OH) in Apatite
FIG. 28f. Scattergraph comparing molar C1/(Cl+F) versus molar C1/(Cl+F+OH) of apatite at Cerro Negro Norte. Five points analyzed from two separate apatite grains closely spatially and temporally associated with early massive magnetite mineralization. Sample CNN 36A is from the Abanderada pit, at Cerro Negro Norte.
grains of magnetite, from lmm to 10 pm in size, which have been locally altered to hematite. On the southwest side of the Abanderada pit (Plate # 1, Abanderada Sector) a similar igneous breccia with magnetite clasts is spatially associated with monzodiorite to granodiorite dikes, which crop out parallel to the magnetite orebody along a NEstriking zone of weakness or faulting.
Apatite is paragenetically related in time, as well as spatially associated to magnetite mineralization at CNN. The apatite analyzed (Appendix B2.5) has molar C1 /(C1 + F) values
0.55 and average 2.25 wt. % chlorine (Figure 28f).
7.2 Sulfides (Pyrite and Chalcopyrite) and Sulfates (Barite and Gypsum) Mineralization Sulfide mineralization as a whole in the Cerro Negro Norte District is sparse, and is often associated with late quartz and carbonate veining, as well as with pegmatitic quartz, plagioclase, tourmaline, K-feldspar veins, both proximal and distal to the massive magnetite bodies. However, pyrite ± chalcopyrite is also present as replacement of magnetite within the massive Fe-oxide ore. Supergene Cu-carbonates, Cu-oxides, and goethite are associated with late quartz and carbonate veins distal to the ore bodies and as disseminated mineralization in local zones proximal to small NWstriking structures or shears, and along andesite dikes, which cut the massive magnetite ore.
Within the Abanderada pit, pyrite ± chalcopyrite veining is dominantly controlled by small shear zones or faults which strike to the northwest (Figure 15a-b, Chapter 5.2.2). Several samples from within the Abanderada pit, along WNW-striking
faults and shears, as well as proximal to the pit, along NE-striking fault zones have elevated Au, Cu, Cr, Co, and V values. Pyrite + chalcopyrite in a volume ratio of (5:1) + epidote mineralization forms veins, which are in contact with a 70 cm wide fault zone, striking 108° and dipping 74 ° NNE at the northern end of the Abanderada pit (Figure
29a). The edge of a 1 meter wide post magnetite andesite dike near sample CNN 55 (Figure 14b, Chapter 4.2.5). (Plate # 3, Abanderada Sector) is sheared by this later fault, which cuts massive magnetite ore and is spatially related to a zone of quartz + tourmaline + K-feldspar + epidote + chlorite + calcite + actinolite + pyrite + chalcopyrite with supergene Cu-carbonate at the north end of the Abanderada ore body. The mineralization locally occurs in stockwork veinlets and veins (10-12)/m2 in area, as well as in clots 2-4 cm2 in area. Pyrite + chalcopyrite up to 10% of the rock,
with ratios from 1:1 to 5:1 (pyrite:chalcopyrite) are spatially associated with epidote ± calcite. Acosta and Vicencio (1995) delineated this as the fourth zone for Cu-Au potential previously discussed above. Along the northeast side of the pit massive magnetite ore is cut by NW trending structures (Plate # 3, Abanderada Sector), striking 130° and dipping 65° SW. These small faults and shears host up to 25 modal % sulfides
1:2 to1:3) (Figure 29b). Cu-oxides and carbonates cement
brecciated magnetite. Pyrite ± chalcopyrite is most common along the western side of the Abanderada pit. Pyrite + chalcopyrite sulfides + quartz + carbonate veins 1 cm and veinlets 1 mm wide strike to the northwest and locally reopen older actinolite + albite veins as seen in the field (Figure 29c-d) and thin section (Figure 29e-g), and/or filling NW trending shear zones. (See Figure 17d-g, Chapter 6.3). Overall sulfide of the rock,
FIG. 29a. Abanderada pit, near sample CNN 55. Fault gouge 70 cm wide with clay + sericite + limonite + hematite clasts up to 0.5 cm wide. The NE-striking structure has multiple alteration haloes including: 1) 3 cm wide zone of epidote + actinolite + pyrite + chalcopyrite (pyrite:chalcopyrite = 5:1); 2) 3 cm wide zone of albite + quartz(?) + sulfides stringers, and 3) 3 cm wide zone of epidote + Fe-oddes. The structure is bounded to the east by an andesite dike 1 m wide weakly actinolite-altered and crosscut by albite + eptidote veinlets.
FIG. 29b. Abanderada pit at 4+30 m, near sample CNN 59A. Plagioclase + quartz with tourmaline + actinolite + pyrite + chalcopyrite selvages cut massive magnetite. Magnetite breccia is cemented by sulfides and actinolite and cut by chalcopyrite + pyrite (chalcopyrite:pyrite = 3:1) veinlets 1 mm wide. Cuoxide staining is present, and a NW-striking 10 cm wide fault bounds the breccia. The area around the fault is 25 % sulfides.
FIG.29c. Late quartz + sulfide veining in Abanderada dump sample. Pyrite + actinolite vein cuts and offsets earlier plagioclase veins in a magnetite replaced andesite.
FIG. 29d. Early Na-Ca cut by late quartz + sulfide veining in the Abanderada pit at 3+50m (dump pile). Early actinolite veins 2 cm wide are re-opened and crosscut by 0.5 cm wide plagioclase + quartz + pyrite + chalcopyrite veinlets. Other plagioclase + actinolite + sulfide veinlets cut the magnetite mineralized andesite host.
FIG. 29e-g. Late quartz + sulfide veins in thin section scans. Thin sections are 3.5 cm wide X 8 cm long. All the thin sections show late quartz + calcite + pyrite + chalcopyrite + actinolite veins re-opening plagioclase or scapolite + actinolite veins and cutting massive magnetite replaced andesites (E, F), and massive magnetite mineralization (G). Pyrite and chalcopyrite is often associated with late quartz + calcite as vein fill.
in outcrop ranges from trace to 4 % and is either disseminated or in veins
3 mm to 2
cm wide, often crosscutting earlier magnetite veins.
Thin section and microprobe analyses of magnetite ore samples from the Abanderada pit indicate that sulfide (pyrite ± chalcopyrite) mineralization in massive magnetite + apatite ores may have replaced and/or cross cut magnetite (Figure 30a) with local subsequent supergene covellite after chalcopyrite. Sulfide ± Au veinlets crosscutting the same massive magnetite-apatite-actinolite ore consists of massive pyrite with inclusions of chalcopyrite altered to supergene covellite and Au-bearing supergene covellite (Appendix B2.8) (Figure 30b). Calcite + sulfides clearly cut massive magnetite ore, magnetite stringers, and scapolite + quartz veins, as well as fill in interstitial to magnetite (Figure 30c-d).
Supergene earthy goethite is pervasive in the southeast wall of the Abanderada pit, associated with earthy hematite and quartz veining in an intensely clay ± sericite + chlorite + carbonate altered host (Figure 27b, Chapter 6.7). The goethite is likely derived from the oxidation of siderite and/or pyrite mineralization associated with carbonate alteration.
Brecciated magnetite bodies, cut by slickensides and massive quartz veins (Plate # 3, Abanderada Sector) up to 10 m wide (Figure 31a), and quartz + hematite veinlets are also common along the eastern side of the Abanderada pit. Massive quartz is cut by quartz + hematite stringers and veinlets (Figure 31b). Tectonically brecciated magnetite, mostly altered to hematite is found as angular clasts cemented by quartz + goethite ± calcite ± oxidized sulfides (Figure 31c).
FIG. 30a-d. Photomicrographs of various sulfide replacement of magnetite, and late quartz + calcite + sulfide veining. a) CNN 36A (10X) x-polar: Massive magnetite + apatite ore with chalcopyrite. b) CNN 36A (20X) x-polar: Late sulfide veins with chalcopyrite inclusions in pyrite and supergene Au-bearing covellite after chalcopyrite. c) CNN 22 (2.5X) x-polar: Pyrite vein cuts and offsets earlier scapolite + quartz vein in massive magnetite. d) CNN 01A (10X) x-polar: Calcite + actinolite + chlorite + pyrite vein cuts massive magnetite.
FIG. 31a. Abanderada pit at 4+84 m. View looking northeast along the possible irregular trend of a quartz vein from CNN 13. On the left side of the photo massive magnetite altered to hematite is in contact with the vein.
FIG. 31b. Abanderada pit, near sample CNN 13. Quartz + hematite + calcite breccia. Quartz + magnetite altered to hematite + goethite(?) Goethite veins 2-10 cm wide fill fractures shears in the breccia . Quartz + calcite + goethite 0.4-0.8 mm wide cut host. Hairline fractures of carbonate + goethite(?).
FIG. 31c. Thin section scan of CNN 120. (3.5 cm wide X 8 cm long). Sheared massive magnetite breccia altered to hematite, with quartz + plagioclase(?) + calcite + goethite veins.
175 microns FIG. 32a. Backscatter image of CNS 7 from the Augusta Sector. Hematite with inclusions of gypsum and associated rutile after titanite(?) veining. These minerals are spatially and temporally associated with sulfide mineralization seen in FIG. 32a and with tourmaline-quartz alteration in the Augusta Sector. The gypsum is probably a weathering product.
FIG 32b. Photomicrograph of CNS 7 from the Augusta Sector. Sulfide veins are associated with tourmaline + quartz breccias and consist of dominantly pyrite + chalcopyrite. Pyrite has inclusions of chalcopyrite, pyrrhotite and magnetite. Chalcopyrite is often altered to supergene covellite.
Sulfates are also present at the entrance to the Abanderada pit and distal to the ore body. Quartz + barite + earthy hematite veins strike NNE cutting brecciated magnetite in the pit (Plate # 3, Abanderada Sector), and veins with the same mineralogy ± Cu-oxide strike NW cutting through the western quartz diorite intrusion to the southwest of the Abanderada sector (Plate # 3, CNN District). Pods of massive barite ± gypsum up to tens of centimeters wide are also locally present in earthy hematite altered ore near the entrance to the Abanderada pit. Additional information on the presence of barite associated with late carbonate alteration is provided in Chapter 6.7. Thin section and microprobe analyses of sample CNS 7, from the Augusta Sector indicate gypsum is locally present as inclusions in hematite (Figure 32a), and is also spatially associated with pyrite, pyrrhotite, and chalcopyrite sulfide vein mineralization (Figure 32b), (Appendix B2.8).
7.3 Cu-Au Mineralization Compania Minera Pacifica (CMP) recognized the potential for possible economic Cu-Au reserves in the CNN District and started a campaign in 1985 to map out potential targets. Acosta and Vicencio (1985) delineated four zones of Cu-Au mineralization in the Abanderada sector. A total of 550,000 tons with an average grade of 1.45g/T Au and 0.24 wt.% Cu is estimated. Three of these zones are to the west of the Abanderada pit, where abundant quartz-calcite-Cu-carbonate veins occur along a NNE trending fault zone, and/or contact between andesite and diorite. Acosta and Vicencio (1985) estimated a total potential of 440,000 Tons at an average of 1.45g/T Au and 0.21 wt. % Cu within these
three zones. One of the zones lies near the intersection of a NNE-striking re-activated(?) fault with an E-W-striking fault. This zone has Fe-Cu sulfide and Cu-oxide supergene mineralization and was calculated to contain around 160,000 tons at 2.38g/T Au and 0.23 wt. % Cu. These zones have been prospected as there are numerous stopes following veins. Intense goethite oxidation, and Cu-oxide mineralization including malachite and chrysacolla, as well as calcite is associated. The fourth zone is on the north end of the Abanderada sector in a zone of chlorite-calcite-quartz-tourmaline altered andesite and has a calculated estimated 110,000 tons at 1.23g/T Au and 0.23 wt. % Cu.
The Augusta sector contains an estimate of 900,000 tons with average grade at 0.41g/T Au and 0.27 wt. % Cu. Four holes were drilled in the Augusta sector in 1997 with variable Au and Cu results (Villagran, 1997). Three of the four drill targets were inclined
50° 60° to the east to target intensely quartz-tourmaline-sericite altered
breccias with sulfide mineralization, and northwest striking faults. The fourth hole was inclined west to target tourmaline breccia and the main Augusta magnetite ore body at depth as well as host chlorite-and tourmaline-altered meta-andesites. Vivallo et al. (1995b) states that gold in the CNN District is concentrated in magnetite ore and in pyrite rather than andesite host rocks and actinolite-altered rocks. The average Au values are higher in pyrite-bearing magnetite ore samples, compared to those that lack pyrite. Au in brecciated magnetite also has a high average concentration. Vivallo et al., (1995b) considered that brecciated magnetite is hydrothermal and massive magnetite is of magmatic origin. Vivallo et al. (1995b) also analyzed Au from both magnetite and pyrite separates taken from the same sample and then compared
them to the whole rock massive magnetite. The results indicate that Au concentration is
usually higher (.100 ppb Au) in pyrite, versus lower
00 ppb Au) concentrations in
magnetite separations. They postulated that late hydrothermal activity may have remobilized Au from the massive magnetite ores and redistributed it with an increased activity of S in the system.
The data of this study suggest that Au-Cu mineralization is dominantly associated with late pyrite ± chalcopyrite veins and associated tourmaline-quartz-calcite alteration. Isochon diagrams (after Baumgartner and Olson, 1995), from mineralized samples of the Abanderada Sector indicate samples with strong sulfide vein mineralization (Chapter 8.3), and associated late alteration types, along late faults(?) and shear zones are enriched in S, Au, Co, and V relative to samples of massive magnetite ore, with sparse sulfides. Cu is enriched (up to
1 wt. %) in all samples with
Fe-oxide mineralization, however Cu-Au totals are higher in late sulfide rich veining,
which cut magnetite ore as described in Chapter 8.3-8.4 concerning the geochemistry of trace elements.
CHAPTER 8: GEOCHEMISTRY OF THE CERRO NEGRO NORTE DISTRICT
8.1 Introduction In order to characterize the different alteration assemblages in terms of whole
rock gains and losses of major, minor and trace elements, geochemical analyses of representative samples from the Cerro Negro Norte District were performed. Samples representing six major alteration assemblages in both host andesites and diorites were chosen to represent the alteration both proximal and distal to the massive magnetite ore bodies. Gains and losses correlate with changes in mineralogy and indicate the geochemical environment during hydrothermal alteration. Mineralized samples include massive Fe-oxide, as well as Cu-Fe sulfides from both the Abanderada pit and to the west of the pit along faults and shear zones. Alteration is extensive throughout the district and within the project area there is very little rock that has escaped alteration. Three samples were chosen to represent the unaltered andesitic and dioritic host rocks to which altered samples could be compared. Appendix C1.1 gives a detailed explanation of samples that were chosen to represent the six major alteration assemblages discussed in Chapter 6, within different rocks from the CNN District. Samples (CNN 92, CNN 54A, CNN 77A), which represent unaltered rock in the district where chosen due to the lack of intense alteration. These three "fresh" samples have igneous mafic and felsic minerals, which have not been completely hydrothermally altered, however, minor Na-Ca alteration and minor magnetite is present. See Appendices C1.2-C3.3.2 for all analytical data, including detection limits for chemistry,
whole rock chemical compositions, normalization calculations, and chemical gains and losses.
8.2 Major Oxides On the basis of silica and alumina, the unaltered samples indicate a high Al basaltic andesite to high Al andesite whole rock composition. Figure 33 shows variation scatter plots of the major oxides including Al, Ti, Fe, Ca, Na, K, Mn, Mg, P, and LOI plotted against Si for all the samples including unaltered and altered as well as mineralized and unmineralized samples. Obvious major oxide trends characterize the different alteration assemblages. The plots indicate that within a certain type of alteration assemblage, spatial variation (proximal versus distal) with reference to the magnetite ore bodies has minimal effect on the major oxides. The plots also indicate
that the variation between andesites and diorites is minimal. Calcic and sodic-calcic assemblages including actinolite, scapolite, albite, titanite, and epidote as the dominant mineralogy are generally enriched in alkalis (Na and K). Ca is locally enriched especially in scapolite-bearing assemblages. Na-Ca assemblages are similar or slightly depleted in Fe (Figure 33, plots C, F, G, and H). Albite alteration displays the strongest enrichment in Na2O. Scapolite + actinolite alteration displays an enrichment in CaO, 1(20, MgO, and locally P205. Tourmaline-quartz-sericite alteration displays an overall
depletion in CaO, Na2O, enrichment in Fe, and a relative enrichment in MgO, and K20 compared to plagioclase-bearing sodic alteration. TiO2 is relatively immobile in all the
alteration types in the district. Therefore, all the major oxides were normalized to TiO2
(Appendix C3.2.1) See Appendix C1.1 for an explanation on which samples represent
0 CNN 3
3102 vs A1203
3102 vs CaO
CNN 40 CNN 54A
x CM 86
A CNN 91A
u 10 4o
z CNN 120 CNS 14
Si02 wt %
3102 vs TiO2
3102 vs Na20
Si02 wt %
02 rot %
3102 vs Fa203
3102 vs K20
40 SiO2 wt %
Si02 wt %
Si02 wt %
FIG. 33. Variation diagrams for Si02 wt. % vs major oxides wt. %. Colors and shapes indicate alteration assemblages and rock type respectively. Black is fresh "unaltered" rock, Orange is scapolite-actinolite-titanite, Yellow is albite-actinolite-epidote, Purple is tourmaline-quartz, Brown is early magnetite mineralization, Red is strongly Fe-oxideCu-(Au) mineralized samples, and Pink is carbonate altered. Squares are distal andesites, diamonds are proximal andesites, triangles are distal diorites, and crosses are proximal diorites. See Appendix C1.1 for spatial and descriptive data, and Appendix C2.1 for analytical data on all samples. Sample locations are on 1:1000 Abanderada pit and 1:10,000 CNN District maps.
3102 vs P201
SKY2 vs IMO craa 3
CNN 12 CNN 14
CNN 54A CNN 58
0 1.0 -
CNN 91A 0.5
CtI 120 MS 14
3K12 vs 111.0
3102 vs LOI
40 3102 wt
FIG. 33. (Continued)
40 8102 w1%
the scapolite-actinolite-titanite bearing (Na-Ca), plagioclase-actinolite-epidote bearing (Na-Ca), and tourmaline-quartz-sericite acidic alteration assemblages, as well as the sample considered to be unaltered andesite.
A spider diagram (Figure 34, plot A) was plotted to graphically display gains and losses of the major oxides of three different dominant alteration assemblages and compare them to one another, and to determine the percent change (Appendix C3.3.1) from an "unaltered" andesitic protolith. Scapolite-bearing sodic-calcic altered andesite in the district displays an increase (25-50%) in SiO2, MnO, MgO, CaO, and Na2O. Minor losses of less than 5% in A1203, K2O, and FeO, and a significant loss (75%) in
P2O5 characterize this assemblage. Plagioclase-bearing Na-Ca altered andesite displays an overall depletion in all the major oxides, except Na2O and P2O5. The alteration shows slight loss in SiO2, a moderate loss (40%) in A1203, and CaO, and a strong loss (80%) of FeO, MnO, and K2O. A gain (50%) in Na2O and a gain (40%) in P2O5
characterize this assemblage. Finally, the tourmaline-quartz altered andesites are characterized by a strong increase (-80%) in SiO2, MgO and LOI, and a moderate increase (30%) in A1203. All the remaining oxides (Fe, Mn, Ca, Na, K, and P) in this
type of alteration have been depleted compared to the unaltered protolith. Fe-oxide (magnetite, hematite) and Fe-Cu sulfide mineralized samples from within the Abanderada pit and just west of the main ore body along a re-activated N-S striking fault and andesite/ diorite intrusive contact were analyzed. The samples are depleted in all the major oxides as expected, except for Fe, local Ca and volatiles associated with late carbonate alteration. Phosphorous has generally remained the same for mineralized and unmineralized samples. One exception (CNN 53) is a massive
Spider Diagram showing Gains and Losses of Major Oxides in altered Andesites at Cerro Negro Norte
100 80 60 40 20 0 -20 -40 -60 -80
=2 E (7) 00
(CNR 2A/CNN 92) (CNN 3/CNN 92) (CNR 31A/CNN92)
0 0 V
Spider Diagram showing Gains and Losses of Trace Elements in altered Andesites at Cerro Negro Norte 900
(CNR 2A/CNN 92) o (CNN 3/CNN 92) (CNR 31A/CNN92)
V) V) Q Trace Elements
FIG. 34. Spider diagrams showing chemical gains and losses of major oxides (A), and trace elements (B) for three main types of alteration at Cerro Negro Norte. Orange is scapolite-bearing Na-Ca alteration, yellow is plagioclase-bearing Na-Ca alteration, and purple is hydrothermal tourmaline -quartz alteration. The protolith is a distal andesite (CNN 92), numbers in parenthesis are (altered/fresh) pairs. The samples are normalized to TiO2 by dividing raw value by wt. % TiO2 . See Appendix C1.1 for spatial and petrographical data, C2.1 for analytical data, C3.2.1 and C3.2.2 for normalization calculations, and C3.3.1 - C3.3.2 for gains and losses calculations.See Figure 33 for variation diagrams, and Figure 37 for REE spider diagram plots for these samples. Sample locations can be seen on 1:10,000 scale District maps.
magnetite + apatite ore with pervasive sulfide veining ± tourmaline + quartz alteration and displays a slight increase in P, and K. CNN 53 represent a mixed early Fe-oxide (magnetite) mineralization and late tourmaline-quartz alteration with Fe-Cu sulfide mineralization. A second exception (CNN 86) has late sulfide-bearing mineralization associated with tourmaline-quartz alteration and also displays a slight increase in P, K, and Mn. Isocon diagrams (Figure 36) are plotted assuming a constant elemental composition and have both major oxides and trace elements plotted logarithmically with the unaltered andesite on the X-axis and the mineralized sample plotted on the Y-axis.
8.3 Trace Elements Trace elements are plotted in Figure 35 against SiO2 weight % in log variation
diagrams for all the mineralized and unmineralized Cerro Negro Norte samples. Trace elements from the Cerro Negro Norte District were then also normalized to TiO2, as
were the major oxides (Appendix C3.2.2). Figure 34 (plot B) shows gains and losses of scapolite-bearing Na-Ca, plagioclase-bearing Na-Ca, and tourmaline-quartz-sericite altered andesites with respect to a unaltered andesite for the trace elements in a spider diagram. Calculated percent change from unaltered to altered andesites normalized to TiO2 is given in Appendix C3.3.2. The scapolite-bearing sodic-calcic altered andesites
are strongly (.100%) enriched in Au, Cu, Ni, Cr, Sb, As and Y. These andesites are only slightly (<100%) enriched in Ag, Sc, and Th, and depleted in Zn, Co, V, Sr and Ba. Zr, Hf and U are immobile and/or unchanged. The plagioclase-bearing sodic-calcic
FIG. 35. Log variation diagrams for Si02 wt. % versus trace elements in ppm (Au in ppb). Samples colors and shapes indicate various alteration assemblages and rock type respectively. Black is fresh "unaltered" rock, Orange is scapolite-actinolite-titanite, Yellow is albite-actinolite-epidote, Purple is tourmaline-quartz, Brown is early magnetite mineralization, Red is strongly Fe-Oxide-Cu-(Au) mineralized samples, and Pink is carbonate altered. Squares are distal andesites, diamonds are proximal andesites, triangles are distal diorites, and crosses are proximal diorites. See Appendix C1.1 for spatial and petrographic data, and C2.1 for analytial data. Sample locations can be seen on 1:1000 Abanderada pit maps and 1:10,000 scale District maps.
altered andesites are characterized by strong enrichment (?..100%) in Ag, Ni, Zr, Hf, Th
and U, with slight enrichment in Y. Strong depletions include Cu, Zn, Cr, Co and Ba, with minor depletions in V, Sb, Sc, As and Sr. The tourmaline + quartz altered andesite is strongly (>_1 00%) enriched in Cr, As and Zr. Slight gains (<100%) include Au, Ag,
Ni, V, Sb, Sc and Hf. Slight depletions in Cu, Zn, Co, Sr, Y and Ba. Th and U are immobile and/or unchanged. Overall losses from all the altered andesites include Zn, Co, Sr and Ba. Overall gains were Au, Ag and Ni. Although Zr, Hf, Th and U showed minor gains and losses with respect to unaltered andesites, these elements are relatively immobile and/or unchanged with respect to the three alteration assemblages. Mineralized samples from within the Abanderada pit were plotted against a "unaltered" host-rock andesite (CNN 54A) on a logarithmically scaled isocon diagram assuming a constant elemental composition (Figure 36). Overall enrichment in trace elements of the early Fe-oxide (magnetite) mineralized samples (plots A-C) include S, Au, Cu, Co, V, Ni. Late sulfide-bearing ± Cu-carbonate mineralization, associated with tourmaline-quartz alteration localized on shears or faults, that crosscut early magnetite mineralization (plots D-F) show an overall general enrichment in all trace elements relative to those samples that have early Fe-oxide mineralization. Additional trace element geochemistry on samples CNN 12, a scapolite bearing Na-Ca altered andesite from the Abanderada pit, and CNN 114, a scapolite-titanite bearing Na-Ca altered diorite to the west of the Abanderada pit, had bromine concentrations of 173 and 216 ppm respectively (Appendix C2.1).
FIG. 36. Isocon diagrams for Fe-oxide-Cu-Au mineralized samples from the Abanderada Sector at Cerro Negro Norte. See Baumgartner and Olsen (1995) for text on least square isocon method. Major oxide and trace element gains and losses on a constant element basis are compared between "unaltered" proximal andesite (CNN 54A) and early Fe-oxide (magnetite), as well as late sulfide rich mineralized samples from the Abanderada Sector at CNN. Sample CNN 9 is massive magnetite, sample CNN 14 is massive magnetite altered to hematite and intensely carbonate veined and sample CNN 40 is massive magnetite with trace Fe-Cu sulfides. Samples CNN 53, CNN 56 and CNN 86 are massive sulfide ± Cu-carbonate veins that are localized on faults that crosscut early massive magnetite mineralization and are associated with variable tourmaline-quartz alteration. See Appendix C1.1 for spatial and petrographic data, and C2.1 for chemical compositions.
Isocon Diagram for unaltered andesite vs early magnetite mineralized andesite at Cerro Negro Norte
8 00 0 Log CNN 54A
Isocon Diagram for unaltered andesite vs late hematitecarbonate mineralized andesite at Cerro Negro Norte 1000.00 100.00 10.00
0 O 0
O O O
0 O O O
Log CNN MA
Isocon Diagram for unaltered andesite vs early magnetite + trace sulfide mineralized andesite at Cerro Negro Norte 1000.00 100.00
0 Log CNN MA
Isocon Diagram for unaltered andesite vs early magnetite + late sulfide mineralized andesite at Cerro 51 *A203 1102 Negro Norte l00000 100.00 co
O O O
Log CNN 54A
Isocon Diagram for unaltered andesite vs early magnetite + late sulfide mineralized andesite at Cerro Negro Norte 1000.00 100.00 10.00 1.00
0 O 0
O 0 O
Log CNN 54A
Isocon Diagram for unaltered andesite vs late sulfide mineralized andesite at Cerro Negro Norte 1000.00 100.00 cow
Log CNN MA
FIG. 36 (Continued)
8.4 Geochemistry of Cu and Au in the Hydrothermal System Six mineralized samples (CNN 9, 40, 53, 56 and 86), discussed in the previous
section were used to test whether or not Cu and Au are part of the earlier Fe-rich, Spoor magnetite mineralization event, or the younger Fe-poor, S-rich pyrite-chalcopyrite mineralization event associated with tourmaline-quartz alteration. Figure 36a contains a series of plots comparing Fe to Cu and Au (plots A and B, respectively), as well as sulfur to Cu and Au (plots C and D, respectively). Plots A and C indicate that Cu seems to be associated with the late S-rich mineralization event, however, one massive
magnetite sample (CNN 40) with trace pyrite and chalcopyite has
1 wt.% Cu. Plots
Band D indicate Au may be associated with the early magnetite mineralization, however, this is based on one sample (CNN 40), which also has high Cu values, and the fact that Au in early magnetite mineralized samples are enriched in Au (>50ppb). Au associated with the younger S-rich mineralization in the form of tourmaline-quartzpyrite-chalcopyrite veins cutting massive magnetite is elevated also, and ranges between 90 and 610 ppb (Appendix C2.1).
Plot E compares Cu to Au in all the mineralized samples and indicates that Au/Cu ratios are higher in magnetite ores than in sulfide rich ores, where ratios are lower. Good correlation between Au and Cu in the S-rich mineralized samples versus the magnetite ore samples, where it is difficult to establish a trend may suggest a genetic link between Au and Cu in the later mineralization event.
Overall observations from limited data suggest Au and Cu totals are higher in the late sulfide mineralization event. It is noted that some tourmaline-quartz-sulfide
Fe verus Cu in early Fe-rich, S -poor (magnetite) and in late Fe-poor, sulfur-rich (sulfide) events 50000 45000 40000 35000
Chei 9 ea* CNN 14 early CNN 40 early CNN 53 late CNN 56 late CNN 86 late
a 20000 (3 15000 10000
8 verus Cu in late Ps -poor, 3-rich (sulfide) and in early Fe-rich, S-poor (magnetite) events 50000 45000 40000 35000
CNN 53 late
CNN 88 late
C11 56 late
CNN 9 early CNN 14 ealy
CNN 40 early
Fe203 (wt. %)
Fe verus Au in early Fe-rich, S-poor (magnetite) and in late Fe-poor, sulfur-rich (sulfide) events
S verus Au in late Fe-poor, 8-rich (sulfide) and in early Fe-rich, S-poor (Inegnallle) events
CM 19 early
CNN 14 early CNN 40 early CNN 53 late CNN 56 late *CNN NI late
S (wt. %)
800 400 200
CNN 53 late
MI 56 late
27 woo. el
C NI late
CM 9 early
CNN 14 early CNN 40 early
F6203 (wt. 1/4)
3 (wt. 1/4)
Cu versus Au in early Fe-rich, S-poor (magnetite) and in late Fe-poor, sulfur-rich (sulfide) events 1200
CM 19 early
C1*1 14 early
CNN 40 early
CNN 53 late C101 56 late
CNN 86 late
FIG. 36a. Variation diagrams comparing Cu and Au in early Fe-rich (magnetite) and late S-rich (sulfide) mineralization events. Plots A and B compare Cu vesus Fe and Au versus Fe, respectively of mineralized samples. Plots C and D compare Cu versus S and Au versus S, respectively of mineralized samples. Black samples (CNN 9, 14 and 40) represent early Fe-rich, S-poor (magnetite) mineralization. Red samples (CNN 53, 56 and 86) represent late S-rich, Fe-poor (sulfide) mineralization. An explanation of the samples is in Figure 35 caption, and in Appendix C1.1. Chemical compositions are in Appendix C2.1.
alteration which cuts earlier magnetite mineralization generally has higher Au ± Cu
values, versus that alteration which does not cut magnetite ores (CNN 53, 56 versus CNN 86). It seems possible that Au and Cu may have been deposited in the early magnetite event. Higher Au/Cu ratios in the Fe-rich ores could suggest a leaching of Cu from early magnetite ores, whereas Au would less inclined to leach. Higher Au and Cu values in late sulfide rich veins, which cut massive magnetite suggest a possible remobilization and reconcentration of these metals into the veins during the latter Srich, Fe-poor event.
8.5 Rare Earth Elements Rare earth element (REE) analytical data are in Appendix C2.1. REE's were normalized to chondrite (Cl) using values from Sun and Mc Donough (1982) and element/chondrite ratios are in Appendix C3.1. REE spider plots (Figure 37), compare a suite of eight rare earth elements representing unaltered and altered andesites and diorites from the Cerro Negro District. See Appendix C1.1 for compositional and spatial information on specific samples. Plot A shows three samples (same as in previous sections) that represent unaltered andesite and diorite both distal, and proximal to the magnetite ore body in the Abanderada Sector. The REE trends among "unaltered" rocks are almost identical within an order of magnitude. Plots B-D compare similar types of alteration assemblages in different types of host rock. Scapolite-bearing sodic-calcic alteration in plot B shows variation between altered samples that are distal as compared to those proximal to the Abanderada pit. CNN 12 is an andesite sample proximal to the
Fe-oxide mineralization, and is enriched in the light rare earth's, such as La, and Ce,
FIG. 37. REE spider plots comparing trends for unaltered and altered andesite and diorites both distal and proximal to the massive magnetite Fe ore bodies at Cerro Negro Norte. Cl Chondrite concentrations are taken from Sun and Mc Donough, 1982. The color indicates type of alteration and can be compared to the alteration maps. Plots A through E show trends for the dominant types of alteration and include andesites and diorites. The boxes indicate distal andesites, diamonds are proximal andesites, triangles are distal diorites and crosses are proximal diorites. Plots H and I compare trends of "unaltered" rock versus three dominant alteration assemblages to both andesite and diorite respectively, distal to the massive Fe ore bodies. See Appendix C1.1 for descriptive and spatial information, Appendix C2.1 for chemical compositions and C3.1 for sample/chondrite ratios.
"Unaltered" rocks from Cerro Negro Norte
Magnetite-Scapolite-Actinolite-Pyrite (after Mag) altered rocks from Cerro Negro Norte
- IN- ON 92 - 41-CNN 64A - a- C914 77A
Sulfide Mineralization along faults and shear zones from Cerro Negro Norte
- -CNN 56 100
-0 -C189 98
0- CNN 53
CN4 114 o CNR 2A
Comparison of distal diorites with differing alteration types from Cerro Negro Norte
o CM 3
Albite-Actinoltte-Epidote altered rocks from Cerro Negro Norte
Scapolite-Actinolite-Magnetite-Titanite-Pyrite altered rocks from Cerro Negro Norte
a CM 120
Imo U 100
Tourmaline-Quartz-Sericite-Sulfide altered rocks from Cerro Negro Norte
Comparison of distal andesites with differing alteration types from Cerro Negro Norte
-8- CNN 92 (Unhand
1000 CNR 2A (Scap-ActMag-Ti-
Carbonate- Hematite -Cu Carbonate altered rocks from Cerro Negro Norte 10003
a. 10 If
= CM! 141
CNR 31* (Tm-00Ser-Chl-
and depleted in the heavy rare earth elements, such as Sm, Eu, Yb, and Lu. An identical reversed trend is seen in both distal intrusive rocks (CNN 114), as well as distal andesitic rock (CNR 2A). The plagioclase-bearing Na-Ca altered samples in plot C show slight variations between different rock types in LREE's including La, Ce, as well as Nd, and Sm. Plot D shows no variation in tourmaline-quartz altered rocks or in their spatial proximity to the massive Fe-oxide ore bodies. Plot I is a comparison of distal andesites with three different types of alteration compared to an unaltered andesite. Relative to the unaltered andesite, the plagioclase-bearing Na-Ca altered andesite shows
an overall slight enrichment in all the REE's, particularly in the light REE's, whereas the scapolite-bearing Na-Ca altered andesites show no change except a slight depletion in La, and Ce. The tourmaline-quartz altered andesite display an overall depletion in
most rare earth elements, except LREE's, that remained immobile. In plot H the same trend holds true for tourmaline + quartz altered diorite, however both plagioclase and scapolite-bearing Na-Ca altered diorites have been enriched slightly in light rare earth's La, Ce, Nd, and Sm.
Fe-oxide (magnetite) and Fe-Cu sulfide mineralized samples from the Abanderada pit were split into three categories. Plot E (Figure 37) is a hematite sample after massive magnetite (CNN 14) from the Abanderada pit with late carbonate
alteration and veining. All the REE's are depleted in this sample with Sm and Eu depleted near an order of magnitude. The second category is early massive magnetite ore with slight Na-Ca alteration ± sulfides after magnetite. These samples (CNN 9 and CNN 40) are depleted in all rare earth elements (Figure 37, plot F). Nd, Sm, Eu, and
HREE's are depleted by a factor of 10, and the LREE's (La, Ce) are depleted by slightly
less than a factor of 10. The third type of mineralization is massive Fe-Cu sulfide mineralization, which is late compared to Fe-oxide magnetite mineralization, and
contains associated tourmaline + quartz + carbonate alteration (CNN 53, 56, and 86). This mineralization is focused on NW striking shears and re-activated N-S striking re-
activated faults. Plot G shows a variable enrichment in light REE's, and a variable depletion in the heavy REE's. LREE's are locally enriched by a factor of 10 compared to the altered samples. HREE's (Yb, Lu) are locally depleted. CNN 53 and CNN 56 have Tb present, unlike any of the other samples.
Johnson et al. (2000a) reports a large Na addition with alteration at both shallow and deeper levels resulting in conversion of igneous plagioclase to Na plagioclase and scapolite within the Humbolt mafic complex (HMC) in western Nevada. Loss of Fe accompanies a gain in Na, and metals such as Cu, Zn, Pb, Co, and Ni are removed during Na-Ca alteration at deep levels. In sulfur poor environments (HMC) siderophile elements and the most chalcophile elements precipitate. Fe + apatite mineralization is precipitated at shallower levels in upflow zones near igneous intrusive bodies. Cu and minor Co are present in sulfide bearing mineralization at shallow distal settings. More soluble chalcophile elements like Zn and Pb are lost from the system. At Cerro Negro Norte, Vivallo et al., (1995a) reported REE data similar to this study for unaltered diorite-quartz diorite rock from the western intrusion, (distal to the magnetite ore bodies) as well as unaltered andesitic rock. A slight enrichment in
LREE's and depletion in HREE's from both tourmaline + quartz altered rocks and Feoxide mineralized rocks with minor Na-Ca alteration also compare well with past work.
CHAPTER 9: SULFUR ISOTOPES OF THE CERRO NEGRO NORTE DISTRICT
9.1 Introduction Sulfur isotope analyses were performed on a total of 12 samples. Pyrite and chalcopyrite associated with both paragenetically early Fe-oxide mineralization and later tourmaline-quartz-sulfide veining were analyzed from samples from within the Abanderada pit. Two paragenetically late barite samples, one from within the Abanderada pit and the other from a NW-striking quartz + barite + hematite ± Cucarbonate vein to the southwest of the Abanderada pit were analyzed. Appendix D1.1 shows samples analyzed, sample purities, type of sulfide and/or sulfate analyzed, relative paragenetic timing, 8 34S %o values, and mineral assemblage from which sulfide
and/or sulfates were taken. The distribution of sulfur isotope values of pyrite, chalcopyrite, and barite from analyzed CNN samples are shown in Figure 38.
9.2 Sulfides Sulfur isotopic compositions of sulfides range from -3.6 to +1.0 %o. The isotopic
values for pyrite samples that are paragenetically associated with early Fe-oxide (magnetite) ± apatite mineralization range from +0.1 to +0.4 %o (average +0.2 %o, n =
2). Pyrite and chalcopyrite associated with later tourmaline-quartz-chlorite-calcite alteration and found most commonly in veins, range from -3.6 to -0.4 %o (average -1.4
%o, n = 9). Pyrite isotopic values are between 3.6 %o and 0.4 %o (average 1.5 %o, n =
7). Chalcopyrite isotopic values are between 1.2 %o and 1.0 %o (average 1.1 %o,
Pyrite Chalcopyrite Barite
Early, n=3 Late, n=
I II -4
634S values Figure 38. Distribution of 8345 values from pyrite, chalcopyrite, and barite from Cerro Negro Norte.
n = 2). Pyrite from sample CNN 49 has a value of +1.0 %o. This sample represents early
Fe-oxide mineralization ± chalcopyrite. Late quartz + tourmaline + pyrite veins cut the early magnetite mineralization. Ohmoto and Rye (1979) summarized equations for temperature dependency of sulfur isotope fractionation in pairs of co-existing sulfide mineral pairs. Assuming that pyrite and chalcopyrite formed in equilibrium during late mineralization, a potentially useful isotopic geothermometer can be provided, using the equation from Omoto and Rye (1979, Table 10-2, p.518): T °K = 0.67 ± 0.04 x 10 3 / A112, where A = 8 34S pyrite - 8 34S chalcopyrite. Only two samples including CNN 41 and
CNN 46A provided sufficient chalcopyrite to analyze. The difference in per mil between pyrite and chalcopyrite in both these samples was 0.1 %o, and did not yield a
geologically reasonable isotopic temperature. However, samples CNN 41 (chalcopyrite = -1.0 %o), and CNN 42 (pyrite = -0.4 %o) are spatially close to one another and have
the same basic mineralogy, however CNN 41 has trace pyrrhotite. These two samples, if considered a pyrite-chalcopyrite pair, yield A = 0.6, and give a more reasonable depositional temperature of 590 ± 52° C, however, chalcopyrite breaks down incongruently around 550° C. At high temperatures between
450-700° C, as can be
assumed from Fe-oxide magnetite mineralization, sulfur is initially SO2 dominant, and oxidation state is less than the hematite/magnetite buffer. As the temperature decreases during cooling, an increase in 8 34SH2s results from the conversion of SO2 to H2S. At
temperatures < 450° C, H2S makes up the majority of 8 34S bulk solution and may cross
the hematite/magnetite buffer. Pyrite and chalcopyrite replacement of magnetite in many of the samples from CNN, may be the result of fluid cooling and crossing the SO2! H2S buffer at about 590 ± 40° C.
9.3 Sulfates Two sulfate samples of barite, one from a quartz-barite-hematite vein in the Abanderada pit (Figure 27d, Chapter 6.7), and one from a distal quartz-barite-hematitecalcite vein, to the west of the Abanderada Sector, were analyzed. The barite samples yielded 8 34S values of +8.6, and +8.5 %o, respectively. CNN 110 is a vein sample distal
to the Abanderada pit, and contains quartz, and massive barite, cemented with hematitegoethite-carbonate ± trace sulfide(?). The host is massive magnetite breccia with open space quartz, and local chalcedony (indicating a lower temperature than quartz), carbonates, hematite, goethite, epidote, sericite, and Cu-carbonate. Since fresh sulfide was not present in this sample, a sulfate-sulfide pair was not available. Ohmoto and Rye (1979) indicate that at temperatures below 350° C, which this sample likely represents, it is difficult to obtain realistic isotopic temperature estimates from the sulfate-sulfide pairs, as a consequence either of non-contemporaneous deposition of these minerals or the slower rates of isotopic equilibribration. Other sulfates such as gypsum are present in the CNN District. In the Abanderada sector, large pods of gypsum are found close to the massive barite veins. Gypsum is also found included in magnetite from the Augusta Sector, such as
represented by andesite in sample CNS 7, which is a hydrothermal assemblage of tourmaline-quartz-sericite that contains pyrite mineralization, with inclusions of chalcopyrite, pyrrhotite, and magnetite (Figure 32a-b, Chapter 7.2). The magnetite is altered to hematite locally and has gypsum included. Gypsum cannot form above 100°C, and most (if not all) gypsum in hydrothermal deposits is supergene in origin
either from the oxidation and leaching of hydrothermal hypogene sulfides or from the hydration of hydrothermal hypogene sulfates such as anhydrite.
9.4 Discussion Ohmoto and Rye (1979) state 8 34S values for sulfides and sulfates from many porphyry copper deposits range between -3 and +1 %o and between +8 and +15 %o,
respectively. In comparison, sulfur isotopes from pyrite and chalcopyrite from the Punta del Cobre Belt range from -0.7 %o to +3.1 %o (Marschik et al., 1997, 2000). Ullrich and
Clark (1999) suggest an evaporitic origin for sulfur, based on sulfur isotope measurements up +7.5 %o. Sulfur isotope measurements made on pyrite, chalcopyrite
and chalcocite from the Productura Fe-oxide Cu-U-Au-REE) prospect, between the El Algarrobo and Los Colorados Fe-oxide mines, range from -8.2 %o to +1.2 %o, and do
not support evaporites as a source of sulfur (Fox, 2000). Slightly heavier isotopic values for both sulfides and sulfates may indicate an evaporitic source for at least some of the sulfur. The 8 34S values obtained from late sulfide mineralization in the CNN district suggest there may be some similarities in sulfur source between Fe-oxide deposits and porphyries. At minimum it would appear from the 8 34S data for sulfides (-3.6 to +1.0 %o) that the source of sulfur was primarily
magmatic. Moreover, the data for sulfates (barite, +8.5 and +8.6 %o) are compatible
with a magmatic source of sulfur ( 0 ± 3 %o; Ohmoto and Rye, 1979), assuming incomplete isotopic equilibration as a result of low temperature deposition, and they preclude a major component of isotopically heavy sulfur from an evaporite or connate source.
Recent work on Re-Os isotopes and comparisons of calculated initial 1870s/1880s of ore minerals from the Candelaria deposit, in the Punta del Cobre Belt, and from magnetite-apatite ores typical of the Chilean Iron Belt (CNN District), suggest a distinct difference in their genesis (Marthur et al., 2001). Hydrothermal magnetite and sulfides from the Candelaria deposit yield calculated initial 1870s/1880s of 0.36 ± 0.1, similar to that of magmatic magnetite found in nearby granitoid plutons. In contrast, calculated initial 1870s/1880s from massive magnetite ores from the CNN District are 7.59 ± 0.72,
suggesting that magnetite ores acquired a radiogenic 1870s signature from a non-
CHAPTER 10: U/PB GEOCHRONOLOGY OF THE CERRO NEGRO NORTE DISTRICT
Exact radiometric age determinations of the mineralization and alteration of Chilean Fe-oxide deposits in and near the Cerro Negro Norte District have not been accomplished to date. Ages that range from 119 and 103 Ma have been determined for granitoid plutons, which bound small enclaves of andesitic rock assigned to the informal Sierra Indiana Formation (Ksi) (Lledo, 1998a). The Fe-oxide bodies at CNN are dominantly hosted in the Sierra Indiana Formation. The age of intrusions in the CNN district are poorly defined, and on the basis of relative ages seen outside the district a range in age of 103 to 112 Ma can be inferred (Vivallo et al., 1997-98). Arevalo (1995) dated biotite by K/Ar methods from small granodiorite plutons (Kg) that crop out near Fe-oxide deposits such as Cerro Iman, and Adrianitas, which are within 20 km of CNN, and determined a minimum age of 103 ± 5 Ma. Mylonitic rocks have also been dated in several places, outside the CNN district, where Fe-oxide mineralization both predates and postdates the formation of mylonites (Lledo, 1998a). Zentilli dated mylonitic rocks containing biotite by K/Ar methods and determined a minimum age of 104 ± 3 Ma for deformation along the Atacama Fault Zone (Lledo, 1998a). The age of Fe-oxide mineralization has been restricted to relative age relationships inferred by crosscutting relationships with the intrusive rock and deformational characteristics of massive magnetite bodies in the field (Lledo, 1998a).
The Punta del Cobre Belt lies
50 km to the southeast of the Cerro Negro Norte
district. Tilling (1962) mapped numerous plutonic complexes in this district, which intrude the marine sediments of the Chanarcillo group. These plutonic rocks have been dated at 116-119 Ma (K/Ar on biotite, Arevalo, 1995). Potassic alteration in the western portion of the Punta del Cobre District overprints an earlier hydrothermal Na alteration assemblage. An Ar/Ar date on biotite, taken from the potassically altered host rock in the district produced an age of 114.9 ± 0.5 Ma (Marschik and Fontbote, 1996).
10.2 U/Pb Dates on Titanite from Early Scapolite-Bearing Na-Ca Alteration at Cerro Negro Norte Four fractions of titanite from a single sample (CNN 115) from the Cerro Negro Norte District were selected to determine the absolute age of early scapolite bearing NaCa alteration assemblage, which commonly includes titanite. The four titanite fractions were all taken from sample CNN 115 (Figure 39a), from the western diorite intrusion, located in the southwestern part of the district. The titanite formed as small clots and is associated with scapolite + actinolite + plagioclase veining (Figure 39b-c). Locally, in zones of intense plagioclase + scapolite ± quartz alteration, actinolite is not present and titanite remains stable. The 206FD//238 U dates for the titanite samples range between 111.7 and 117.9 Ma
(Table # 2). Three of the four fractions analyzed were concordant and one was discordant. A 206Pb/238U versus 207Pb/235U plot indicate the age of crystallization of
titanite, associated with early scapolite-bearing Na-Ca assemblages is 116 ± 4 Ma (Figure 40). Common lead corrections from rocks in the CNN District were not applied
FIG 39a. Sample CNN 115 at Cerro Nego Norte 800 m west of the Augusta Sector. Host is a quartz diorite-granodiorite with scapolite + plagioclase + titanite + epidote + quartz veining with actinolite selvages. "Breccia" like fragments of actinolite, from intense scapolite + titanite veining. In strongly altered areas actinolite is absent and titanite 5-10 vol. % is stable. The plagioclase is partly altered to epidote, clay, and carbonate. Zones up to 10 m wide are scapolite + quartz altered. Locally scapolite + quartz(?) veins are cut by scapolite veins with actinolite + epidote selvages.
265 microns FIG. 39b. Backscatter image of CNN 115. Titanite forms anhedral grains or clots associated with actinolite + scapolite + magnetite in diorite from the western intrusion in the SW part of the CNN District.
FIG. 39c. Photomicrograph of CNR 2B (2.5X) x-polar: Titanite + scapolite vein cutting actinolite altered andesite in the SW part of the CNN District.
TABLE 2. U/Pb Age Determinations for Titanite from the CNN District. Concentration
Error-2 sigma (%) Age (Ma) Sample Weight U Pb Pb 206 Pb 208 Pb 206 Pb 207 Pb 207 Pb 207 Pb 206 Pb Fractions (ug) (ppm) (ppm) (pg) 204 Pb 206 Pb 238 U % err 235 U % err 206 Pb % err 238 U 235 U (a) (b) (c) (d) (e) (f) CNN-115 s2 38 35 1 21 92 0.108 0.01846 (.89) 0.12259 (3.11) 0.04817 (2.82) 117.9 117.4 s4 53 17 1 47 41 0.471 0.01813 (.97) 0.12113 (7.16) 0.04846 (6.75) 115.8 116.1 s3 45 36 1 23 95 0.321 0.01747 (.82) 0.11480 (4.47) 0.04766 (4.16) 111.7 110.4 sl 50 41 2 42 76 0.408 0.01829 (.59) 0.11444 (3.67) 0.04537 (3.46) 116.9 110.0 (a) (#) signifies the number of sphene crystals in analysis. (b) Sample weights are estimated by using a video monitor and are known to within 40%. (c) Total common-Pb in analyses. (d) Measured ratio corrected for spike and fractionation only. (e) Radiogenic Pb. (f) Corrected for fractionation, spike, blank, and initial common Pb. Mass fractionation correction of 0.15%/amu f 0.04%/amu (atomic mass unit) was applied to single-collector Daly analyses and 0.12%/amu ± 0.04% for dynamic Faraday-Daly analyses. Total procedural blank for Pb ranged from 0.65 to 3.7 pg and < 1.0 pg for U. Blank isotopic composition: 206Pb/204Pb = 19.10 ± 0.1, 207Pb/204Pb =15.71 ± 0.1, 208Pb/204Pb= 38.65 ± 0.1. Corr. coef. = correlation coefficient. Age calculations are based on the decay constants of Steiger and Jager (1977). Common-Pb corrections were calculated by using the model of Stacey and Kramers (1975) and the interpreted age of the sample.
Note:Isotopic ratios, concentrations, and corrections are included. Analyses done by Mark Martin (MIT, 2001)
207 Pb corr. 206 Pb coef. 107.8 121.6 82.4 -35.6
0.46 0.48 0.45 0.41
20703 / 235u 0.1085
FIG. 40. 206Pb/238U versus 207Pb/235U plot for the crystallization age of titanite. The plot shows an age date of 116 +/- 4 Ma for the four seperates from CNN 115. Three of the four samples were concordant.
to these dates, as there are no phases containing lead in the CNN District, however a standard common Pb correction was calculated using the model of Stacey and Kramer (1975), and the interpreted age of the samples.
CHAPTER 11: SUMMARY AND CONCLUSIONS ON THE CERRO NEGRO NORTE DISTRICT
11.1 Summary The hydrothermal Fe-oxide (Cu, Au) deposit at Cerro Negro Norte typifies the magnetite ± apatite, sulfide-poor ore deposits found throughout the Chilean Iron Belt. Cerro Negro Norte is hosted in a pendant of basaltic-andesites of the Sierra Indiana Formation surrounded by plutons of intermediate composition (52
64 wt. % Si02),
including diorite to quartz diorite and monzodiorite-granodiorite. The host rocks in the district are intensely altered and within the study area virtually no rock was left unaltered. Relatively voluminous Na-Ca assemblages dominate the alteration in the district Actinolite is associated with Na-plagioclase to albite, marialitic scapolite, titanite, and epidote. Actinolite replaces most mafic minerals including pyroxene and hornblende in andesitic and intrusive rocks, and is pervasive proximal to and within the massive ore body, as well as distal to the ore bodies in andesitic and granatoid rocks. Na-plagioclase or albite, and marialitic scapolite are common replacements of igneous plagioclase distal to the massive magnetite bodies. Carbonate alteration is localized along late NNE-striking faults and is closely spatially associated proximal to massive magnetite ore. Chlorite-carbonate-quartz-sericite alteration and tourmaline-quartzsericite alteration, locally associated with hydrothermal breccias are superimposed on much of the earlier alteration in the district, and are associated with late granodiorite to monzodiorite dikes and intrusive bodies.
Early massive Fe-oxide mineralization and associated Na-Ca alteration at Cerro Negro Norte evoke a model whereby external saline fluids possibly derived from seawater or evaporites where driven by igneous intrusions, leaching chemical constituents from host rocks by these saline fluids between
and resulting in
Fe-oxide mineralization along fluid flow paths (Figure 41). These fluid flow paths may have been NNE-striking ductile fault splays of the Atacama Fault Zone, and likely served as upwelling zones for fluids, whereas andesitic rock served as a sufficient chemical trap for magnetite mineralization. The magnetite mineralization formed as a metosomatic replacement of the andesitic rocks. Geochemical analyses on chlorine-rich scapolite-bearing Na-Ca altered andesite from the Abanderada pit, and scapolite-titanite bearing Na-Ca altered diorite to the west
of the Abanderada pit both have bromine concentrations of 173 and 216 ppm respectively.
The Cerro Negro Norte District lies at
latitude and its position has not
changed since Early Cretaceous time. An arid paleo-environment (Barton and Johnson, 1996),
near the Coastal Cordilleran arc would have been suitable for paleo-evaporite
formation, with external brine circulation driven by heat from igneous intrusions. To the south of the Cerro Negro Norte District, the Chanarcillo Group and the Bandurrias Formation have been interpreted as marine sedimentary and volcanic and sedimentary rocks respectively, of a near shore environment on the edge of the Coastal Cordilleran volcanic arc.
Massive magnetite ± apatite ore is localized on NNE-striking faults of the Atacama Fault Zone, forming tabular vertically oriented or dike-like bodies. Apatite
%,.evaporite evapont ,;0.07
clastic evaporite~:. X#0,%;
%r'1 %tip/ / / / 4
Alteration & Mineralization
late (I lower-T) oxidesulfide mineralization
late (I lower-T) Na(-K) alteration
oxidized skam (high-T & low-7)
Mt-Ap(-Am) II early (I high-T) oxide mineralization Scp-Hbl-Px
early (/ high-7) sodic alteration
FIG. 41. Schematic model of igneous-driven circulation of evaporitic fluids showing alteration zoning in mafic and felsic systems (from Barton and Johnson, 1996)
associated with early Fe-oxidation magnetite mineralization is chlorine-rich, averaging 2.25 weight percent chlorine. Later Cu-Au sulfide mineralization is localized by WNWstriking faults and reactivated NNE-striking faults. The Cu-Au mineralization is temporally later than the Fe-oxide mineralization and is commonly associated with sericite-chlorite-carbonate alteration and tourmaline-quartz hydrothermal breccias. Na-Ca altered rocks relative to fresh rock have gained Si, Na, Ca, and variable Mg and Mn and have lost Al, K, and Fe. Metals such as Cu, Cr, Co, Zn, and V are
typically depleted. A slight enrichment in REE's, especially LREE typify the Na-Ca assemblages. Later tourmaline-quartz altered rocks are characterized by gains relative to fresh rock in Si, Al, Mg, and volatiles. Metals such as Cr, Au, Ag, Ni, V, Sb, as well as Zr, and As are enriched. An overall depletion in REE characterizes the tourmalinequartz altered rocks in the district. Massive magnetite ores are depleted relative to fresh rock in all constituents except Fe, (and locally Ca and volatiles), and trace metals Co, Cr, Ni, V ± Au, and Ag.
REE's are overall depleted, particularly in HREE for Fe-oxide mineralized samples. Sulfide mineralization associated with tourmaline-quartz alteration is characterized by enrichment in S, Fe, K, P, volatiles, Au, Cu, Ag, Ni, V, As, and U. Sulfide mineralized samples associated with Fe-oxide mineralization show similar depletion in REE, as do tourmaline-quartz altered rocks, however late sulfide mineralization distal to Fe-oxide mineralization is characterized by an overall enrichment of over an order of magnitude, in all REE's. Sulfur isotope results at Cerro Negro Norte suggest a magmatic fluid component for sulfur associated with late Cu-Au mineralization. Fluid inclusions are saline and
typically have solid halite crystals ± hematite, and other solids. Sulfides associated with early Fe-oxide mineralization are slightly isotopically heavier than those associated with later mineralization, and sulfates are isotopically heavy near 8345 = 8.6 %o. The absence
of isotopically heavy sulfur and a difference in values from early and later sulfides may be due to depositional disequillibrium, or may reflect a system that initially had an evaporitic sulfur source with a later increasing magmatic sulfur source.
11.2 Conclusions The geologic history of the Cerro Negro Norte District is complex and can be simplified by separating the geology, structure, alteration mineralogy, and mineralization into two separate igneous events; an early event (1-5 below), and a late event (6-10 below). The history of the Cerro Negro Norte District is as follows: 1.
Deposition of Late Jurassic-Early Cretaceous volcanic rocks of the Sierra Indiana Formation in an arc-backarc(?) environment.
2. Early high temperature (400° C- 550° C) Na-Ca alteration of andesites.
Alteration characterized by scapolite-actinolite-titanite assemblage (U/Pb on titanite = 116±4 Ma, this study). Coevel mylonitization of andesitic rocks ± magnetite-scapolite-actinolite altered rock, along the ductile, NNE-striking Atacama Fault Zone (AFZ). 3.
Emplacement of dike-like Fe-oxide (magnetite) ore bodies, possibly in tensional openings, and steeply dipping quartz diorite to monzodiorite dikes parallel to the magnetite ore bodies, controlled by the early NNE-
striking Atacama Fault Zone, Ductile deformation continued during early magnetite mineralization. 4. Emplacement of western quartz diorite pluton into strands of the
Atacama Fault Zone, probably to the west of the Cerro Negro Norte andesite pendant, suggested by the presence of small mylonite pendants surrounded by quartz diorite. 5.
Continued Na-Ca alteration, locally characterized by a Na-plagioclaseactinolite-epidote assemblage. Alteration associated with NE trending granodiorite porphyry dikes, which intrude western quartz diorite pluton. Coevel igneous breccias containing magnetite clasts, are spatially associated. The porphyry dikes and breccias suggest an upper limit depth
1-2 km for alteration.
6. E-W or WNW-striking brittle shear zones, locally associated with granodiorite and andesite-microdiorite dikes, have little offset and cut magnetite ore bodies and host rocks. Shears have sulfide-rich pyritechalcopyrite mineralization, and associated chlorite-sericite-calcite alteration. 7. Pegmatite sills ± dikes cut magnetite ore and host rocks and are likely
associated with hydrothermal tourmaline-quartz breccias in the eastern part of the CNN District suggesting that alteration has a lower limit
depth of S 6 km, and temperatures < 350° C. Hypogene mineralization consists of moderate amounts of pyrite + chalcopyrite ± specular
hematite. Continued locally intense chlorite-sericite-calcite alteration suggest a low pH, hydrolytic fluid. 8.
Coevel(?) emplacement of Sierra Blancas pluton to the east of the Cerro Negro Norte District(?).
Reactivated NE-striking, steeply NW dipping brittle strike-slip fractures and faults, with very small displacement, cut massive magnetite ore along old ductile structures and magnetite ore bodies. These fractures and faults localize veins of barite-carbonate-quartz ± sulfide and are associated with alteration of magnetite to hematite.
10. Supergene alteration and weathering produce Cu-carbonates, gypsum,
goethite, and local jarosite localized along any zones of weakness, such as WNW-striking shears, and NE-striking brittle fractures and faults. In summary it is clear that two separate igneous events are present in the Cerro
Negro Norte District. These two events are associated with two different styles of faulting and include their own characteristic alteration and mineralization. Figure 42 is a schematic cartoon model of the Cerro Negro Norte District and includes major igneous intrusions, structure, magnetite ore bodies, sulfide-rich zones, and generalized alteration.
Inferred source regions for non-magmatic fluids which may have contributed to Na-Ca alteration and magnetite mineralization are not shown on the cross section, but would have come laterally from a distance being heated and driven by the emplacement of the western quartz diorite pluton and utilizing the early Atacama Fault Zone as a conduit. These hypersaline hydrothermal fluids are sodium saturated and chlorine-rich
as evidenced by solid halite crystals (>26 wt. % NaC1) in fluid inclusions found in NaCa altered igneous breccias. At deeper levels in the system Na would be added, due to the increasing temperature near the igneous intrusions. Field mapping relationships suggests that early sodic-calcic alteration was coevel with ductile deformation at least initially, before the western pluton was fully emplaced into the fault zone. In contrast, low pH, lower temperature(<350° C) fluids producing late hydrothermally altered tourmaline-quartz andesites and breccias, hydrolytic chloritesericite-quartz alteration assemblages and sulfur-rich mineralization are of magmatic origin as indicated by sulfur isotope values (-3.6 to +1 %o). These fluids were perhaps related to the younger (112± 3 Ma) granodiorite-monzodiorite pluton (Sierra Blancas) to the east of the CNN District and are localized along late brittle shear zones and minor
NNW-striking and NNE-striking re-activated faults with little offset. Cu and Au totals are high in rock associated with this younger alteration and sulfur-rich mineralization, and may have been remobilized from the earlier Fe-oxide mineralization event.
FIG. 42. Schematic geologic plan view and cross section of the Cerro Negro Norte District. Figure not to scale. Plan map and cross section showing the temporal and spatial relationship of the two major igneous intrusion events at CNN. Associated structure, alteration and mineralization of both the early and later events are shown. The early scapolite-Na-plagioclase-actinolite Na-Ca altered portion of the district (west) is outlined in yellow, and is associated with Fe-rich, S-poor mineralization. The later tourmaline-quartz-sericite-chloritecalcite altered portion of the district (east) is outlined in purple and is associated with Fe-poor, S-rich mineralization.
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APPENDIX A1.1 Sample # : Petrography, Descriptions of Litho logy, Alteration, Veining, and Mineralization. CNN Ol -1LS: Thin-section Scan, Groundmass is Actinolite with fibrous habit anhedral up to 1 mm long locally strongly altered to Chlorite, early Scapolite veins up to 5 mm wide anhedral to subhedral 5.4 mm in size, later Pyrite or Pyrrhotite? subhedral to anhedral massive habit/ Calcite anhedral/ Sphene//Calcite/ Epidote/Chlorite vein 1-8 mm wide, latest Calcite veinlets cut main vein .2 mm wide, late Carbonate and/ or Calcite overprint on much of groundmass with associated Epidote 3 % and Chlorite, later Goethite/ Fe-oxide stain associated with Calcite overgrowth, Magnetite disseminated subhedral-anhedral 3-5 %. CNN 01A: Photomicrograph, Sulfides and oxides are anhedral, late Pyrite vein with Plagioclase/ Actinolite/ Calcite //Quartz? (Chalcedony) associated with Pyrite (8 mm // 80 lam) and cuts massive Magnetite, stringers of Magnetite as well, Actinolite crystals up to 1.2mm overgrow Pyrite in vein or Pyrite is interstitial and Actinolite has Magnetite selvage, Pyrite cuts Magnetite and fills in around Magnetite, Actinolite moderately-strongly altered to Chlorite, Actinolite altered to Chlorite along grain boundaries and fractures through Magnetite, Magnetite crystals with Pyrite, Chalcopyrite or other Cu Sulfide or Pyrrhotite inclusions and Magnetite is altered to Hematite around inclusion inclusions are 101.1m, supergene Covellite or Chalcocite? locally after Chalcopyrite. CNN 01B-1: Photomicrograph, Massive Magnetite with clotty and disseminated texture, Actinolite fibrous sub-anhedral .2-.6 mm long in crosscutting .4-.8 mm wide veinlets and interstitial to Magnetite, Scapolite anhedral feathery to blocky habit up to 4 mm wide + Plagioclase?/ ± Actinolite / Pyrite anhedral blebs veins 4-5 mm wide cut Actinolite and Magnetite, late Calcite/ Carbonate veinlets 40 µm - .15 mm wide cut Magnetite and Actinolite host and Scapolite/ Plagioclase veins, these Cal veinlets may be the source of the Pyrite found in the Scapolite/Plagioclase veins due to the close spatial proximity to crosscutting Calcite/ Carbonate veinlets. CNN 01B-2: Photomicrograph, 1.2-2 mm long Actinolite crystals to very fine-grained locally moderately-strongly altered to Chlorite veins up to .75 mm wide, Actinolite stringers and veinlets crosscut Actinolized host, Magnetite and Actinolite host may be coeval or Magnetite is early, Scapolite/ Actinolite veins with Actinolite crystals up to 2 mm long, late Scapolite veins .4-4 mm wide cut and locally offset both earlier Actinolite veins and host, Scapolite in vein is .4-1.2 mm and has subhedral to poikylitic anhedral bladed and feathery habit, very late Carbonate (Calcite) veinlets 25 j.im wide with anhedral Calcite grains cut both earlier Actinolite, Scapolite veins and the host, Magnetite is anhedral aggregates and stringer like with local alteration to Hematite. CNN O1 C: Magnetite disseminated dotty anhedral habit, Scapolite ± Actinolite groundmass, some Scapolite veining with anhedral Tourmaline grains up to 2 mm wide (on selvage?), Calcite veinlets 80 [tm mostly plucked out cuts groundmass, Magnetite weakly altered to Hematite on Calcite vein selvage, Carbonate overgrowth, Tourmaline may be associated spatially with Carbonate veining, but Calcite veinlets cut Tourmaline crystals, Chalcopyrite anhedral after Magnetite on selvages of Calcite veinlets and locally in the rest of host, Pyrite sub-anhedral possibly after Magnetite, but looks like overgrowth?
CNN 02: See Microprobe Data, Plagioclase and Scapolite pegmatic texture anhedral grains .4-4 mm in size, Plagioclase moderately altered to Scapolite ± Epidote ± Sericite ± Calcite?, Actinolite disseminated throughout .25 mm anhedral fibrous habit most often associated with Magnetite locally moderately to strongly altered to Chlorite, Magnetite 10 % as stockworking veinlets and intergranular associated with Actinolite mostly strongly altered to bladed habit Hematite also disseminated as anhedral clots and masses mostly intergranular and as stringers, small Goethite ± Calcite? stringers cut everything. CNN 02A: Vein? Quartz subhedral-anhedral with small 20-40 pm fluid inclusions with 10 % vapor bubbles 3 mm in size/ Plagioclase moderately altered to Sericite ± K-feldspar subhedral 3-4 mm in size/K-feldspar// Tourmaline 4-5 mm long anhedral grains, local Goethite stringers, groundmass Magnetite massive to granular anhedral grains S 20 pm, Scapolite feathery anhedral habit, Tourmaline anhedral grains ratty overgrowing Scapolite, Amphibole anhedral grains up to 8mm long in possible vein with up to 2 mm wide Plagioclase CNN 03: Photomicrograph, See Geochemistry, Phenocrysts: Plagioclase 2-4 mm long and 1-1.5 mm wide sub-euhedral habit strongly-moderately altered to Epidote ± Chlorite ± Sericite? and locally Calcite, Pyroxenes twinned anhedral .5-1 mm in size mostly strongly altered to Actinolite, groundmass: Plagioclase .6-1 mm wide grains all anhedral mostly strongly altered to Calcite ± Epidote ± Clays, ± Actinolite, Magnetite disseminated anhedral 1 %, Na- altered ? or local Carbonate overgrowth, trace Sphene? CNN 04-1: Quartz Diorite, Quartz 20 % anhedral .4-.6 mm, Plagioclase pockets 4-8 mm wide with weak moderately altered to Sericite ± anhedral intergrown Clays? Plagioclase phenocrysts .2 -1.75 mm in size, Plagioclase 75 % phenocrysts .2- .8 mm in size anhedral-subhedral in rest of rock moderately-strongly altered to Sericite & Clay? ± Epidote, Magnetite 3-4 % anhedral-subhedral grains 40 pm- .2 mm in size, Actinolite 5 % intergrown and associated with disseminated Magnetite mostly anhedral fibrous .5 mm, Epidote 2-3 % anhedral grains after Plagioclase or in clots. CNN 04-2:Quartz diorite-monzodiorite, Quartz 15 % anhedral generally interstitial to large Plagioclase crystals and associated with magnetite and Actinolite which are also interstitial, Fluid inclusions in Quartz up to 12 gm with salt (Halite) solids 7.5 pm in size and possible Hematite flakes 4 pm in size, Plagioclase 70 % anhedral to subhedral crystals with Albite twinning still visible 1 mm moderately to strongly altered to Sericite ± other Clays?, Actinolite 9 % fibrous anhedral habit mm in size locally unaltered moderately to strongly altered to Chlorite, Tourmaline 3% bladed radiating prismatic euhedral to subhedral and anhedral grain and dotty habit 1.6 mm long, Magnetite 3 % cubic euhedral to anhedral grains and clots 1 mm to 10 pm in size clots comprised of small anhedral grains looks like a Magnetite breccia with clots up to 6 mm in size and replaces host altered moderately to strongly to Hematite locally, Fe-Oxide and Goethite? staining locally associated with altered Magnetite, local Calcite 3 % in clots and overprint mostly Plagioclase. CNN 07: Quartz/ Hematite/ Barite breccia, Quartz 60 % euhedral to anhedral grains locally mm in size with local ratty Fluid inclusions up to 5 pm with multiple solids 1 pm in size, Barite 40 % up to 16 mm long and 2 mm wide subhedral to euhedral
grains bladed habit, Quartz and Barite comprise framework and size of grains generally 1 mm in size, groundmass is Quartz anhedral grains .8 mm to .1 mm and mostly smaller 80 pm in size with pockets of Chalcedony with radiating fibrous grain habit interlocking anhedral grains .2 mm locally Chalcedony in vugs in Quartz and Barite grains, Sericite .2 mm fibrous anhedral grains overprint associated with Quartz all interstitial to framework grains, local trace Calcite?, Tourmaline 5 % locally overprint very fine-grained 5_ 10 pm euhedral grains, Hematite after Magnetite also interstitial with strong Fe-Oxide staining mostly in cross cutting veinlets 40 pm wide. CNN 08: Photomicrograph, See Microprobe Data & Sulfur Isotope Data, 10 mm long 3.75 mm wide euhedral to subhedral Barite, interstitial Magnetite strongly altered to Hematite and anhedral Quartz 40 prn, late Hematite veinlets cut optically continuous Barite crystals. CNN 09: See Geochemistry, Veins of Pyrite 1.75-4+ mm wide cut Actinolite and Scapolite host 1-2 %, Pyrite looks like it is after Magnetite, inclusions of Magnetite in Pyrite, but also looks like Magnetite could be veining through Pyrite locally, Pyrite 30 % sub-anhedral, Magnetite 70 % massive anhedral. CNN 10: Andesite, 10 % phenocrysts: Plagioclase 90 % up to 5 mm long locally Albite twinned mostly between .8- 1.2 mm long anhedral to subhedral laths weakly to strongly altered to Calcite and Sericite and other Clays ± Chlorite?, Actinolite 3 % maybe after euhedral Hornblend 4 mm long and 2 mm fibrous anhedral grains, Pyroxene 7 % anhedral to subhedral 1-2.5 mm in size weak to moderately altered to Amphibole ± Actinolite, 90 % groundmass: Plagioclase 50 % anhedral to subhedral laths .15 mm in size mostly weakly to moderately altered to Calcite ± Clays, Actinolite 50 % fibrous anhedral grains .2 mm strongly altered to Chlorite, strong Calcite overprint mostly in clots 1 mm in size also late Calcite very fine- grained / Quartz anhedral .1 mm in size veins .2-.8 mm wide cut host, Calcite and Actinolite and Chlorite all spatially associated with and after Plagioclase and Hornblend phenocrysts. CNN 11: Intergranular vein? Scapolite long bladed up to 2 mm long subhedral crystals/ Actinolite huge 2-3 mm long and wide anhedral grains locally weakly altered to Chlorite possibly after other Amphiboles?/ Plagioclase anhedral 2-3 mm wide and long locally moderately altered to Clays? and Sericite/ Chalcopyrite dotty embayed anhedral disseminated 2 %, Magnetite dotty anhedral with interstitial Actinolite, Tourmaline anhedral 2-3 mm wide with Actinolite growing around rims. CNN 12-1: Photomicrograph, See Microprobe, Sulfur Isotope & Geochemistry Data, Actinolite anhedral to subhedral crystals up to 4 mm long, Scapolite anhedral to subhedral crystals up to 4 mm long and .8 mm wide, local Calcite possibly after Plagioclase, local Chlorite altered Actinolite, Pyrite 2-3 % closely spatially associated and included in long prismatic Scapolite grains but also randomly disseminated cubic euhedral to anhedral may have inclusions of silicates and Chalcopyrite which have been plucked out, trace Hematite. CNN 12-2: See CNN12-1, Actinolite 5+ mm long anhedral fibrous habit locally moderately altered to Chlorite mostly unaltered average size 1.5 mm, Scapolite up to 8+ mm long and 2+ mm wide anhedral to subhedral crystals some small .2 mm size
grains also locally after Plagioclase and locally weakly to moderately altered to Calcite ± Sericite, radiating .4 mm Chlorite grains, poikalytic anhedral Calcite up to 4 mm in size surround average size 1 mm Chlorite interstitial to large Scapolite crystals, Pyrite .8 mm in size cubic to anhedral habit disseminated and included in Scapolite and actinolite. CNN 13: Hematite Quartz breccia, Quartz 90 % euhedral anhedral open-space crystals to very fine-grained interlocking rounded grains doubly terminated no fluid inclusions seen 4 mm 20 pm, Calcite 10 % anhedral fills in between Quartz and Magnetite altered to Hematite in veins poikalitic texture, single Quartz grains up to 4mm in size, Quartz 1.75-2 mm wide euhedral crystals / Magnetite altered to Hematite vein, Hematite angular breccia habit and Quartz grain often included in Hematite, Actinolite? trace amounts scattered fibrous habit, Calcite/Quartz anhedral/ ± Actinolite/ ± Goethite veins .4-.8 mm wide cuts Magnetite altered to Hematite, hairline fractures 1011m of Goethite? ± Calcite. CNN 14: Photomicrograph, See Geochemistry, Magnetite massive with Calcite/ Carbonate veins cutting zebra veining, Magnetite mostly altered mod-strongly to Hematite ± Goethite, Calcite veins .4-2 mm wide edges of vein open space growth colliform and banded texture, centers of veins have anhedral Calcite grains 40 p.m- 1 mm in size, Calcite veinlets offset and cut each-other, earlier Quartz vein .2mm wide with anhedral Quartz cut and offset Magnetite and in turn are cut and offset by Calcite veins. Covellite 1-2 % on Calcite vein selvage and in Calcite veins. CNN 15-1: Magnetite massive locally altered to Hematite around later veins, Quartz (crystals .4 mm anhedral) veins .5 - .8 mm wide cut Magnetite, groundmass of host is also anhedral and feathery habit Quartz ± Scapolite, later Magnetite with trace 1 % Chalcopyrite locally veinlets .2-.4 mm wide also cut Scapolite veins and host, green Cu Carbonates or Oxides (green and blue fibrous, blocky, prismatic and associated with Magnetite). CNN 15-2: Blasted breccia?, Host: Actinolite anhedral .4 mm long, Quartz anhedral .2 mm wide locally .8 mm wide in clusters or veinlets, Magnetite semi-massive locally altered to Hematite ± Goethite, some .7 mm wide Quartz veinlets suggest the Quartz may be late. CNN 17: Equigranular Diorite, Plagioclase 70 % S 2 mm subhedral -anhedral moderately- strongly altered to Micas and Clays and locally altered to Scapolite in trace amounts, Actinolite 20 % interstitial and anhedral .8 mm in length and locally altered to Chlorite, Epidote 5 % anhedral mostly after Plagioclase, disseminated Magnetite .2mm cubic & euhedral-anhedral habit. CNN 17A-1: Equigranular Diorite slightly more altered than CNN 17, Plagioclase 55 % subhedral to mostly anhedral moderately- strongly altered to Micas, Clays ± Scapolite, Actinolite 15 % locally weakly altered to Chlorite or Epidote, locally twinned and altered or associated with Scapolite? or Tremolite? 5 1.5 mm long and bladed habit, Epidote 20 % locally after Plagioclase, ± mafics (Actinolite), Magnetite 5 % anhedral disseminated dotty and single grains, Sphene 3 % associated with Epidote and Actinolite. CNN 17A-2: Equigranular Diorite, Plagioclase 70 % anhedral to subhedral average size .4-1.2 mm also as small as .1mm and up to 3.5 mm long moderately to strongly altered to Sericite ± other Clays ± Epidote? ± Scapolite?, Amphiboles 15 % 120° cleavage anhedral
to locally subhedral .4-.8 mm in size mostly strongly to moderately altered to Actinolite locally only weakly altered, Pyroxene? 5 % locally also altered to Amphibole, Sphene 2 % anhedral clots up to 2 mm in size interstitial to Plagioclase and Amphibole, Actinolite 5 % after mafics locally strongly altered to Chlorite fibrous anhedral bladed, Calcite 3 %? interstitial and in clots sub prismatic habit associated with Titanite. CNN 18: Equigranular? Diorite? or porphyry Andesite Dike?, strongly altered, Actinolite 20 % locally twinned anhedral and fibrous locally strongly altered to Chlorite ± Epidote and moderately throughout 1 mm 95 % and 5 % 2 mm, Plagioclase ( Albite?) 70 % very strongly altered to Micas Clays ± Scapolite ± Epidote locally up to 4+mm long most between .4-.8mm long anhedral to subhedral and local reaction rims and concentric zonation, strongly altered Plagioclase veinlets possibly associated with local Goethite stringers which cut host, Epidote 5 % anhedral mostly after Plagioclase, Magnetite 5-7 % anhedral disseminated and in clusters. CNN 19: Equigranular Diorite, strongly altered, Plagioclase 60 % 1 mm long strongly altered to Micas (Sericite) Clays and locally to Scapolite? 5 %, Actinolite 25 % .5 mm locally up to 1 mm long bladed and fibrous habit locally moderatelystrongly altered to Chlorite, Epidote 5 %, Sphene trace, Magnetite 10 % disseminated and in angular anhedral grained clusters which represent breccia, but may not be 8-10 mm wide, Goethite stained Muscovite? in altered Plagioclase around the large breccia Magnetite clusters. CNN 20-1: good Quartz/ Carbonate alteration, Plagioclase 40 % 3 mm anhedral framework mostly unaltered but locally some are altered to Carbonate, Carbonate 20 % subhedral? alteration covers Plagioclase and Quartz, Quartz 40 % Chalcedony feathery radiating fine-grained crystal texture in groundmass low temp alteration or supergene .4 mm, Magnetite stringers of disseminated anhedral Magnetite grains. CNN 20-2: Andesite?, Plagioclase phenocrysts subhedral-anhedral locally concentrically zoned very strongly altered to Sericite ± Calcite, overall Goethite /Carbonate ? ? /Actinolite? /± Clay? Overprint very hard to tell what type of alteration of groundmass, Goethite stingers 40 1-1,M cut host, Magnetite 15 % disseminated anhedral to euhedral cubic very fine- grained 10 µm in groundmass, Magnetite 5 % .1mm everywhere else, Magnetite locally in clots and clasts with stringers. CNN 21: Magnetite 60-70 % replacing Actinolite ± Scapolite altered host, Carbonate (Calcite) veins 12+mm wide cut Magnetite host grains are anhedral average .4-.8 mm wide // selvages are Hematite altered after Magnetite mineralized host, 1.2 mm wide Carbonate veinlets with bladed feathery or dog-tooth habit. CNN 22: Photomicrograph, Quartz anhedral grains 40 pm- .4 mm wide/ Scapolite?/ ± Actinolite/ ± Apatite? vein .2 mm wide cuts massive Magnetite, Quartz, Scapolite + Plagioclase?, Actinolite groundmass interstitial to massive Magnetite, local Plagioclase veinlets, Pyrite/ Actinolite vein .8 mm wide (possible conjugate vein) cuts and offsets Quartz/ Scapolite/ ± Actinolite vein, Pyrite stringers 20-40 pm wide, local Goethite / FeOxide staining. Chip sample taken. CNN 23: Actinolite anhedral locally twinned lath shaped habit .2 3 mm long, Plagioclase anhedral .8-1 mm in width intergrown and overgrows Actinolite in host, Plagioclase vein 3 mm wide grains up to 3 mm wide anhedral-subhedral moderately-
strongly altered to Sericite ± Clays?, Magnetite massive brecciated locally altered to Hematite with interstitial Plagioclase ± Scapolite? ± Actinolite anhedral grains average size .1 mm CNN 24: Photomicrograph, Magnetite massive, cut by 1-1 5 mm wide Actinolite vein anhedral-subhedral lmm wide grains, Scapolite 1-1.5 mm wide anhedral / Actinolite anhedral interstitial to Scapolite / Chalcopyrite ± Pyrite anhedral trace-1 % vein 3 mm wide, Chalcopyrite and Pyrite locally found in clots after? Magnetite with associated supergene Covellite or Chalcocite, local Goethite / Fe-oxide stained veins. CNN 25: Plagioclase subhedral to euhedral laths Albite twinned locally grains form radiating masses from 2 mm to .2 mm long unaltered to weakly Sericite altered could be a possible vein? 3.6 mm wide or could be selvage of Calcite vein? with anhedral to subhedral Calcite, fine-grained Plagioclase euhedral to anhedral 40 pm to .2 mm in size with radial grains associated with fibrous anhedral Chlorite, all grains comprise interlocking texture, fine-grained anhedral 20 pm in size Calcite overprint interlocking Plagioclase and Chlorite grains, interstitial anhedral Quartz grains and locally subhedral to euhedral up to 3 mm Quartz grains associated with edge of Calcite overprint, Calcite anhedral to subhedral grains average size 1.2 mm overprints Plagioclase and Chlorite and Quartz may be a secondary Calcite/Carbonate overprint, later Calcite/ Goethite?/ Feoxide liesigang fronts and stockwork veinlets cut and overprint all earlier alteration. CNN 26: Quartz anhedral to euhedral bladed and radiating habit undulose extinction up to 4 mm in size with few ratty Fluid inclusions and little solid salts, two possible events of Calcite overprint, first gray birefringence clear in plain light subhedral to anhedral clots overgrow Quartz, later anhedral high birefringent Calcite ± Sericite? Or other Clays veining cuts original, late Calcite overprint stringers and veinlets with 40 µm anhedral fibrous grains to euhedral grains 1 mm in size form dotty habit, local Fe-Oxide and Goethite? stain associated with Calcite, Sphene 3 % in large anhedral to euhedral diamond shaped grains .25 mm in size with very high birefringent colors and pleochroism visible. CNN 27-1: Photomicrograph, magnetite massive, cut by Actinolite vein very finegrained fibrous habit 4-5 mm wide, later Quartz anhedral .4-1 mm wide banded around edges/ Calcite anhedral .4-1 mm wide // Pyrite discontinuous anhedral grains 40-80 ptm wide locally cubic pyritahedrons vein cuts into Actinolite vein path, Calcite/ Pyrite vein 1-4 mm wide where it cuts into earlier Actinolite vein, Magnetite breccia on selvage of Calcite vein, trace-1 % local grains of Pyrite in or after Magnetite up to .75 mm wide also in Calcite/Quartz veins, Chalcopyrite trace anhedral clots. CNN 27-2: Magnetite massive brecciated and veined by fine-grained Actinolite ± Amphiboles 4-5 mm wide, later 1.5-2 mm wide veins of Quartz anhedral banded 5.2.4 mm wide grains ± feathery Chalcedony?/ Calcite anhedral .2-.5 mm wide also interstitial very fine-grained cuts but no offset of earlier Actinolite vein and runs parallel to Actinolite vein path, Quartz/Pyrite ± Chalcopyrite stringers crosscut Magnetite, Pyrite anhedral 3-5 mm long and wide with Quartz and Actinolite inclusions in Actinolite vein, but closely spatially associated with crosscutting Quartz/ Calcite veins. CNN 27-3: Magnetite massive cut by finegrained fibrous Actinolite vein up to 8 mm wide, cut by later Quartz anhedral .4-.5 mm wide / Calcite interstitial anhedral-subhedral grains ± Scapolite??/ Pyrite/ ± Chalcopyrite veins and stringers from .2-2 mm wide,
disseminated and stringers of Pyrite/ ± Chalcopyrite associated with Quartz/ Calcite veining and up to 5 mm long clots of anhedral- subhedral Pyrite associated with Quartz/ Calcite veins. CNN 28: Photomicrograph Magnetite massive overgrows Actinolite locally subhedral 2 mm long and wide mostly anhedral fibrous, & Plagioclase altered groundmass, Quartz some Fluid inclusions with cubic Halite solids/ Plagioclase interstitial anhedral .2-.4 mm strongly altered to Sericite / ± Actinolite / ± Chalcopyrite anhedral grains 1 % with Pyrite up to 1 mm wide in vein 7 mm wide has intergranular and equigranular texture, some stringers also .4 mm wide with trace Chalcopyrite, late Goethite stringers cut Quartz/ Plagioclase/ Actinolite/ Sulfide? vein and Magnetite, remnant Plagioclase? CNN 29: Quartz / Pyrite / Chalcopyrite with supergene bladed Covellite after Chalcopyrite vein and in clots cut Magnetite host, anhedral- subhedral Pyrite cut by late Quartz ± dotty Scapolite stringers, late? Actinolite anhedral and fibrous, Plagioclase anhedral and disseminated, Quartz part of groundmass with small fluid inclusions, Scapolite part of groundmass anhedral-subhedral and anhedral interstitial to massive Magnetite, ± Epidote, Pyrite stringers 50 pm wide with a dotty texture and habit, locally Actinolite /± Quartz /± Pyrite veinlets and stringers, possible coeval Quartz and Pyrite and earlier Pyrite? Structure with Cu Carbonates + Carbonates and powdery white precipitate? CNN 30: Granodiorite pegmatitic vein in host andesite, Host: Plagioclase moderatelystrongly altered to Sericite, Actinolite anhedral fibrous average size 6 mm strongly altered to Chlorite locally up to 3.5 mm and very weakly altered, Magnetite 2 % disseminated and dotty locally .4mm subhedral grains, Quartz/ Plagioclase / ± Kfeldspar// Tourmaline/ Epidote trace pegmatic veins cut host, Plagioclase 45 % in vein anhedral up to 6 mm in size moderately altered to Sericite ± Clays?, Quartz 50 % in vein anhedral up to 5 mm in size minor type II fluid inclusions with solids, Tourmaline 5 % anhedral intergrown with Quartz and Plagioclase 50 pm and up to 1 mm near selvage, late Goethite/ Hematite stringers .1 mm wide cut host and earlier veins, Quartz stringers 40 p,m wide cut everything, Fluid inclusions. CNN 31: Photomicrograph, Magnetite massive overgrows Actinolite & Scapolite groundmass, vein 14 mm wide Calcite subhedral up to 4 mm wide avg. 1 mm / Quartz .2.4 mm anhedral intergrown grains/ Pyrite 25 % clots and massive anhedral grains .3-.5 mm wide in vein and on selvage/ ± Chalcopyrite trace anhedral, can't tell if Calcite or Pyrite is selvage, very fine-grained anhedral Calcite & Quartz on selvage. CNN 32: Groundmass is Actinolite locally 2 mm long anhedral bladed, mostly mm long fine-grained, ± Scapolite, disseminated Magnetite anhedral dotty blebs 50 %, local Sphene crystals up to 1.2 mm wide anhedral aggregate habit & up to 7 % of slide some boats possibly associated with veining, .4-.8 mm wide Plagioclase/ ± Scapolite/ ± Quartz // Actinolite locally twinned and have Pyroxene form near selvage ± Apatite?? found along and spatially associated with selvage. CNN 33: Magnetite massive, 4-6mm wide vein of Actinolite anhedral fibrous and granular habit from .4 mm to 2.5 mm long/ Scapolite avg. size .5 mm wide up to 1 mm wide anhedral, stringers of Actinolite/ Scapolite also, late Calcite stringers 40- 80 p,m wide with grains of anhedral lmm long, 10 % Pyrite ± trace Chalcopyrite in veins.
CNN 34: Magnetite massive with Actinolite fine-grained & Scapolite anhedral ± Plagioclase? groundmass, vein 1.5- 2 mm wide Quartz anhedral 5.4 mm in size locally very fine-grained and sometimes feathery/ Pyrite up to 2 mm long anhedral-subhedral mostly on selvage 50 % of vein/ Hematite. CNN 35: Massive Magnetite with interstitial Actinolite ± 2 % Scapolite in anhedral clots, 1-2 % Pyrite .8 mm wide surrounded or included by Actinolite, late open-space? Vein 23 mm wide?, Calcite euhedral- subhedral 1.2-1 6 mm wide, Quartz euhedral to subhedral .8- 1.2 mm long low temp Chalcedony with feathery radial habit locally small stringers branch out from main vein, re-mobilized Magnetite altered to Hematite long bladed Speculurite with high relief, No associated sulfides. CNN 36: See Microprobe Data, Actinolite massive anhedral-euhedral locally finegrained 2-5 mm in length fibrous bladed twinned, locally cut and offset by Magnetite stringers sometimes discontinuous, Magnetite disseminated to massive replacement grows around Actinolite grains and into crystals causing embayed and anhedral Actinolite grains, Pyroxene phenocrysts locally weakly altered to Actinolite, Magnetite late stringers 80 pin cut and offset twinned Actinolite, local anhedral Scapolite with Actinolite groundmass 2-3 % in clots and clusters. CNN 36A: Photomicrograph, See Microprobe Data, Magnetite massive with 2 % subhedral Pyrite ± Chalcopyrite, and Apatite, Apatite anhedral to subhedral relatively intergrown and equigranular 2 mm in size/ Pyrite anhedral up to 4 mm in size with Chalcopyrite inclusions 40 pm to .2 mm in size with supergene Covellite rims / Covellite 10 % of vein/ Chalcopyrite/ ± Actinolite, locally anhedral fibrous avg, size .4 mm up to 2 mm veining. CNN 37LS: Thin-section Scan, Earlier Scapolite ± Apatite ± Pyrite // Actinolite ± Magnetite vein 2- 2.5 mm wide cut and offset by later Calcite vein 1.75-2 mm wide. 40 pm, Quartz .1 mm wide selvage of Calcite vein. Looks like Calcite vein with grains up to 2 mm wide may be late after Scapolite ± Quartz veinlets or Scapolite ± Quartz veinlets late after Calcite vein, Scapolite ± Quartz veinlets also cut through the middle of the Calcite vein. Calcite stringers through Scapolite and Actinolite host, Actinolite has nice twins and are up to 4 mm long, Magnetite disseminated with fine-grained Actinolite groundmass, Magnetite 20 % clotty anhedral-subhedral. CNN 38LS: Thin-section Scan, See Sulfur Isotope Data, Massive Magnetite with stringers and veinlets of Apatite/ Actinolite / Pyrite/ ± Chalcopyrite, sulfide is dotty in stringers, ± Pyrite disseminated in Magnetite. Chip sample taken. CNN 39-1LS: Thin-section Scan, Poikylitic Apatite, Pyrite and Chalcopyrite anhedral and ratty most often associated with fine grained Actinolite and Magnetite, Magnetite veinlets cut groundmass, Scapolite? + Apatite ± Plagioclase anhedral groundmass with interstitial Actinolite, possible Carbonate? Alteration locally. CNN 39-2LS: Thin-section Scan, Sphene trace 1 %, poikylitic Scapolite overgrowing Plagioclase altered to Sericite, groundmass is Plagioclase ± K-feldspar? (crossplaid), Quartz and twinned Actinolite, Scapolite/ Plagioclase/± Sphene // Actinolite ± Sphene ± Pyrite cuts Magnetite and Actinolite host, Actinolite stringers cut Magnetite, Magnetite stringers cut Scapolite/ Plagioclase veins.
CNN 40: See Geochemistry, Chip sample across massive magnetite with pods of Actinolite, individual crystals up to 7 cm long, Actinolite/ Pyrite/ Chalcopyrite veins, Cu oxides (Chrysacolla) on shear and cleavage planes. CNN 41LS: Thin-section Scan, See Sulfur Isotope Data, Sections of unaltered Actinolite mm length with associated Pyrite/ Chalcopyrite, Plagioclase anhedral subhedral, Scapolite ± Quartz? veining with associated Pyrite, Chalcopyrite ± Pyrrhotite??, much of groundmass Actinolite is altered to Chlorite, Chlorite veinlets up to lmm wide, Plagioclase moderately to strongly altered to Sericite ± Epidote, Magnetite associated with mafics in groundmass, Scapolite veinlets 1mm wide cut Magnetite/Actinolite groundmass and are cut by Actinolite stringers, Scapolite may be replacing Plagioclase or it may be Plagioclase/ Scapolite ± Apatite stock-working. CNN 42: See Sulfur Isotope Data, Quartz vein 2-5 mm wide, Quartz crystals anhedral .41.2 mm wide with included Tourmaline crystals long slender cylinders, associated Pyrite 5 % up to 1.2 mm wide pyritehedrons and Chalcopyrite 1 % anhedral and interstitial, ± Plagioclase or K-feldspar?, Actinolite trace, late Calcite stringers cut (look at again). CNN 43LS: Thin-section Scan, Actinolite and Amphibole altered to Chlorite and massive Magnetite replacement, Calcite and Epidote clots in Plagioclase 50 %, altered to Sericite, Calcite altered Plagioclase and Scapolite stockwork veinlets and veins 2mm in width. CNN 44LS: Thin-section Scan, Epidote/ Actinolite/ Quartz?! Pyrite veinlets lmm wide cut host, 40- 80 inn wide Actinolite stringers and veins up to 1.5 mm wide, Scapolite ± Quartz/ Plagioclase ± Epidote stockwork veinlets .5mmm wide, 20 wm wide stringers of Actinolite => Chlorite cut and offset by local Actinolite => Chlorite, Mass Scapolite veins 2+ mm wide Scapolite is .1 mm wide and displays feathery texture. CNN 45LS: Thin-section Scan, Groundmass massive Magnetite with Plagioclase ± Scapolite & Actinolite ± Epidote or Chlorite??, 4-4.5 mm wide Albite? Euhedralsubhedral mm wide strongly moderately altered to Clays? or Sericite / Scapolite poikylitic may be after Plagioclase / ± Epidote // selvage same assemblage smaller mm in size anhedral grains ± Epidote? & Actinolite, this earlier vein has been re-opened by a younger locally discontinuous Actinolite/ Pyrite veinlet .4 mm average width, this veinlet cuts optically continuous Plagioclase phenocrysts in older vein, Pyrite anhedral and dotty and fills in around grain boundaries, Actinolite locally altered to Chlorite, Pyrite not 100 % sure whether associated with Actinolite veinlet or with original earlier Plagioclase/ Scapolite vein, but is spatially close to Actinolite, these two veins are cut by Calcite ± Scapolite vein sub-anhedral crystals with .2 mm width, local Calcite stringers and later? veinlets. CNN46: Photomicrograph, See Microprobe Data, Granodiorite pegmatite, Plagioclase groundmass or fill in mostly large crystal framework .8 mm long euhedral laths locally weakly to moderately altered to Sericite?, Plagioclase framework 2-3 mm in size anhedral locally strongly altered to Sericite? around Quartz, Quartz up to 6 mm anhedralsubhedral, texture of Plagioclase and Quartz intergrown?, ± K-feldspar?, Tourmaline 30 % anhedral massive but ratty eaten up to 4 mm long, Chalcopyrite anhedral possibly after Magnetite and with alteration rim of Hematite where included in Magnetite, Pyrite massive anhedral 4-6 mm long mosaic texture as if filled in around other silicates, Epidote 1-2 %, Magnetite/Pyrite/ Chalcopyrite spatially associated.
CNN46ALS: Thin-section Scan, See Sulfur Isotope Data, Andesite, groundmass: equigranular Plagioclase subhedral 70 %, Actinolite, ± Scapolite 5 % anhedral up to 1.5 mm wide, Plagioclase 2 mm weakly-moderately altered to K-feldspar? Clays/ Micas, Magnetite 20% disseminated and dotty .4 mm anhedral, Tourmaline 5 %, veins .4-5mm wide Plagioclase 2 mm wide subhedral/ Quartz anhedral! Tourmaline sub-anhedral/ ± Actinolite/ Pyrite anhedral/ ± Chalcopyrite // Tourmaline ratty aggregate with no crystal habit. CNN46BLS: Thin-section Scan, Concentrically zoned Tourmaline subhedral 4 mm habit also anhedral and dotty, Quartz anhedral undulose extinction up to 4mm wide / Plagioclase up to 4 mm sub-euhedral / K-feldspar / Tourmaline // Tourmaline? (12 mini/ 4 mm), Pyrite ± Chalcopyrite disseminated and associated with Magnetite, veins Plagioclase anhedral-subhedral/ Tourmaline anhedral- euhedral aggregate/ Actinolite fibrous 50 p.m wide /± Epidote?, groundmass massive Magnetite replacement ± Actinolite, Plagioclase ± Scapolite. CNN 47LS: Thin-section Scan, Photomicrograph, 16- 18 mm wide massive Actinolite vein with fibrous bladed Actinolite up to 2+ mm long // selvage non-existent or Plagioclase altered?, vein cuts host of Plagioclase altered moderately-strongly to Sericite?, Actinolite, Magnetite ± Sphene breccia, Actinolite vein reopened by Magnetite? vein (looks like more massive Magnetite ± Plagioclase than host but may be more richly replaced Magnetite area, .4- .5 mm wide Plagioclase vein Plagioclase weaklystrongly altered to Micas ± Scapolite? Strongly when in contact with Actinolite vein, Plagioclase vein cuts and offsets the massive Actinolite and possible secondary Magnetite veins, 1 mm wide Plagioclase weakly altered to Scapolite?/ Quartz?! + Pyrite/ ± Chalcopyrite cuts Actinolite vein and host. CNN 48-1LS: Thin-section Scan, See Sulfur Isotope Data, 6 mm wide Actinolite 2 mm long blades ± Tremolite? locally weakly altered to Chlorite vein cuts host which is disseminated to massive Magnetite 60 % with Actinolite, Plagioclase, ± Scapolite, Scapolite/ Plagioclase veins? or 2-2.5 mm wide selvage to Actinolite veins (found on contact of host and vein), Scapolite in veins or selvage are anhedral and poikylitic 1-1.5 mm wide, Plagioclase in veins or selvage .4 mm wide, later Scapolite veins 4 mm wide cut Actinolite veins Actinolite has bladed habit up to 2+ mm long also have poikylitic texture and are anhedral, associated Pyrite either as stringers that crosscut or are part of Scapolite? vein, anhedral blebs of re-mobilized Actinolite? also, large clots of Pyrite also associated with 4+ mm wide Scapolite with feathery habit veins which may be after Plagioclase/ Scapolite veins on selvage of Actinolite vein, Plagioclase 4+ mm wide anhedral to subhedral locally altered to Sericite/ Scapolite 4-5 mm wide anhedral // disseminated Magnetite selvage (?//.1 mm) cuts and offsets Actinolite and earlier Scapolite/Plagioclase veins by 2 mm distance. CNN 48-2LS: Thin-section Scan, Host intensely Actinolite altered, disseminated Magnetite anhedral grains and clots 20 %, local Scapolite in host, late Quartz veins 2 mm wide with Flincs: vapor less than 20 % with possible small salt crystals, crosscutting stock-working Scapolite veins and veinlets with anhedral grains 1 mm wide bladed habit, very late feathery fine-grained Scapolite ± Quartz veinlets .4 mm wide crosscut and offset all stock-working smaller earlier Scapolite veins and host, Pyrite/ ± Chalcopyrite stringers associated with Quartz ± Scapolite veins (vein fill and selvage).
CNN 49: See Sulfur Isotope Data, Massive Magnetite with interstitial Tourmaline, Actinolite, Plagioclase?, ± Scapolite 2-3 % and Chalcopyrite 1 % with inclusions of Actinolite, sub-anhedral dotty to massive Pyrite up to 2mm wide, K-feldspar? anhedral, Pyrite/ ± Chalcopyrite anhedral clots and blebs/ Quartz/ Plagioclase anhedral to subhedral 5_ .4 mm in size/ Actinolite anhedral no crystal habit mottled / ± Epidote?/ Tourmaline vein 2 mm wide, and mylonite foliations. CNN 5OLS: Thin-section Scan, Host is Scapolite anhedral clusters of 2 mm sized grains unaltered, Actinolite fibrous bladed crystals up to 2 mm long, coated by pistachio green Epidote anhedral grains 1 mm in size, disseminated Pyrite dotty texture 2 % dominantly in host associated with Magnetite, Plagioclase? associated with Scapolite unaltered?, Magnetite veins up to 1.75- 2 mm wide associated with Scapolite ± Plagioclase veins and alone, disseminated Magnetite 15 % and in stringers .5-1 mm wide crosscut host, Plagioclase veins 2- 4 mm wide cut host grains weakly altered to Micas, Magnetite stringers cut these veins also, Possible late Carbonate? Alteration with epidote alteration. CNN 51LS: Thin-section Scan, Groundmass Plagioclase twined ± Scapolite? 15 %, Actinolite 10 %, Magnetite semi massive 70 % and disseminated, Pyroxene twinned with inclined extinction 5 %, vein 4 mm wide of Plagioclase 2 mm wide/ Amphibole 4+ mm long /± Actinolite/± Scapolite poikylitic 2 mm wide, vein .4 mm wide twinned Pyroxene weak- moderately altered to120° cleaved Amphibole/ ± Actinolite/ Plagioclase anhedral. CNN 52LS: Thin-section Scan, Granular anhedral Quartz, subhedral Plagioclase, Epidote granular, Quartz? veinlets cut host, Epidote veinlets and stringers, Actinolite/Epidote veinlets, late Quartz veinlets and stringers, Magnetite 10 % disseminated associated with Quartz and Plagioclase?, fault breccia offset in right or left lateral sense. 2nd Sample is Actinolized Magnetite replaced andesite host with Actinolite/Quartz/Plagioclase/Pyrite/± Chalcopyrite/Tourmaline/Chlorite veins CNN 53: See Geochemistry, Chip sample across 30 cm wide structure and vein trending 351 ° /V. Magnetite + Actinolite + Pyrite + Chalcopyrite (2:1) + Quartz + Epidote ± Carbonate ± Cu Carbonates ± Clay. CNN 54A: Photomicrograph, See Microprobe & Geochemistry Data, Plagioclase (Albite), massive Actinolite after Pyroxene, some Pyroxenes have mottled and altered to Amphibole (Actinolite) alteration, Magnetite 3-5 % disseminated, Plagioclase and Actinolite in old Pyroxene sites? CNN 55-1: Massive Actinolite, Plagioclase phenocrysts, Pyroxene altered to Actinolite ± Plagioclase?, Pyroxene with oscillatory (concentric) zoning, Epidote?, Actinolite veins, Plagioclase /Calcite/Chlorite ± Actinolite selvage. CNN 55-2: Andesite, Pyroxene locally altered to Actinolite and Plagioclase phenocrysts altered to Calcite or Sericite, twinned Pyroxene, Actinolite + Plagioclase ± Quartz? matrix, Actinolite veinlets cut host. CNN 56: See Geochemistry, Chip sample across 3 m2 area, Brecciated massive Magnetite with Calcite +Cu-carbonates + Pyrite + Chalcopyrite + Actinolite + Quartz ± Scapolite? + Epidote + Gypsum interstitial. 10 % sulfides. Veins with same assemblage as above and Tourmaline selvages.
CNN 57: 40 cm wide channel sample across brecciated Magnetite locally altered to Hematite in fault gouge, Jarosite + Goethite + Sericite ± Clays + 2-5 % disseminated Pyrite + Chalcopyrite ± Actinolite ± Epidote ± Chlorite ± Albite? CNN 58: Massive Tourmaline locally .2mm long anhedral aggregate grains ± Epidote? and Chlorite groundmass, Magnetite veins and stringers cut Tourmaline and Chlorite groundmass, late Hematite/ Goethite/ Clay (Sericite) Muscovite fibrous habit ± Kfeldspar vein .6mm wide cut the Magnetite and Chlorite, locally Scapolite .4mm in size anhedral grains, possibly clots also but slide is plucked. CNN 59: Chip sample across structure, Very fine grained Tourmaline + Pyrite ± Chalcopyrite ± Actinolite ± Chlorite ± Scapolite? Sample is dominately fine grained Tourmaline, see CNN 59A. Chalcopyrite on many shear planes. CNN 59A: Local 3 % clots of anhedral Pyrite ± trace Epidote, disseminated and .2 mm wide stringers of Magnetite anhedral grains replace groundmass of fine-grained host of Tourmaline, Actinolite, Plagioclase anhedral and strongly altered to Sericite ± Clays, Tourmaline??, local Pyroxenes? altered to Amphiboles or Actinolite locally twinned .4 mm up to 5 mm long by 2 mm wide, Actinolite veinlets .2 mm wide cut Magnetite stringers host and Actinolized and disseminated Magnetite, late 2 mm wide veins with massive sub-anhedral Plagioclase 95 % 4-6 mm long and 2 mm wide crystals locally moderately-strongly altered to Clay ± Sericite/ ± Actinolite 4 % anhedral 50 µm in clusters/ ± Pyrite 1 % anhedral// discontinuous Tourmaline selvage, Plagioclase stringers and veinlets .2 mm wide (locally loaded with Apatite euhedral-subhedral long prismatic) cut Pyroxenes, host, larger Plagioclase veins, Magnetite and Magnetite stringers. CNN 60: Possible Andesite, Plagioclase moderately-strongly altered to Clays or Sericite, Actinolite, ± Epidote, ± Tourmaline, ± Scapolite host, locally massive to strongly disseminated Magnetite anhedral and local veinlets up to .4 mm wide, replacement Magnetite associated with more of the groundmass than Plagioclase phenocrysts, Plagioclase phenocrysts .8 mm sub-anhedral strongly altered to Clays ± Sericite, late 1.2-1.6 mm wide vein Plagioclase anhedral crystals strongly altered to Clays and possibly Scapolite ± Sericite / ± Actinolite/ ± Pyrite 1 % anhedral/ Chalcopyrite 1 %/ ± Chlorite 1 % / ± Biotite?, local Chalcopyrite/ Pyrite trace-1 % in groundmass, discontinuous Actinolite stringers .1-.2 mm wide, .8-1.2 mm wide veinlets of Plagioclase strongly altered to Clays and Sericite ± Scapolite ± Carbonates? CNN 61: large sub-euhedral Quartz with Magnetite locally as matrix, clots of mediumfine grained Quartz, Magnetite and Goethite stringers, 1 mmQuartz vein with dog-tooth texture & very small inclusions // Magnetite selvage. CNN 61A: same as CNN 61, trace Actinolite, Magnetite veinlets altered to Hematite locally. CNN 62-2: Euhedral doubly terminated Quartz 4 mm wide some growth zones, interstitial Magnetite locally altered to Hematite ± Goethite in wormy stringy dendritic? Texture, locally Actinolite on grain boundaries, late Carbonate stringers fill in fractures through Quartz and groundmass?, possible trace Tourmaline?, interstitial low temp and open space dog-tooth Quartz and microcrystalline feathery bladed Quartz some aggregates , ± Calcite, Quartz has local ratty Fluid inclusions.
CNN 63: Undulose Quartz, Actinolite, fine grained Magnetite altered to Hematite, Magnetite and Actinolite stringers, Clays, Sericite, strongly altered rind to pegmatite Quartz + Plagioclase + K-feldspar ± Tourmaline veins CNN 64: Quartz + Sericite ± Actinolite, Quartz with needle Rutile? inclusions (pleochroic), open space veins with clotty fine-grained Quartz. CNN 65LS: Thin-section Scan, Very strongly altered, euhedral- anhedral .8-2 mm locally up to 4 mm Tourmaline (zone = 20 mm wide), anhedral Scapolite, Actinolite moderately to strongly altered to Chlorite, disseminated Magnetite ratty dotty anhedralsubhedral cubit habit 20 % with Chlorite & 50 % with Tourmaline, Sphene 3-4 % nice boats, texture is blasted bubbly, botroydal, mirmykitic, local Quartz and Epidote. CNN 66-1: Calite (&/or?), Chlorite stringers?, Quartz with fine needles of Rutile?, Actinolite, Disseminated Magnetite 40 %, Mass Magnetite veins cut by Chlorite, Quartz, Actinolite, Hematite, ± Plagioclase? CNN 66-2: Photomicrograph, late? Magnetite stringers anhedral aggregates 40 wn- .2 mm wide// Chlorite selvage (dark blue min associated with Chlorite, could be Covellite? or Chlorite), latest vein Quartz interstitial around Plagioclase sub-euhedral .8 mm long/ Plagioclase moderately altered to Calcite up to 5 mm long sub- anhedral/ Scapolite after Plagioclase locally poikylitic/ K-feldspar?/ ± Calcite after Plagioclase/ Chlorite //Tourmaline zoned 2 mm wide subhedral along selvage. CNN 66-3LS: Thin-section Scan, Rutile? in groundmass and in vein with Quartz, starburst habit Chalcedony and Chlorite?, Plagioclase/ Scapolite vein cut and offset by Calcite?/ Plagioclase/ ± Quartz// Actinolite altered to Chlorite vein, Magnetite 60-70 % replacing disseminated Pyroxene altered to Amphibole, possible Tourmaline??, possible Scapolite?? trace 2 %, Quartz veins, Hematite. CNN 67: Stringers & disseminated Magnetite 35-40 %, random orientated Magnetite// Actinolite & Epidote veinlets (.4 mm// 05 mm), late open space vein (Quartz? 2 mm) cuts Magnetite // Actinolite veins, Plagioclase Phenos altered, Quartz ± Actinolite veinlets cut, but don't offset Magnetite// Actinolite veins, timing?, pistachio green plain light epidote, Quartz in matrix. CNN 68LS: Thin-section Scan, Plagioclase laths, Magnetite 35 % disseminated, host cut by Plagioclase/ ± Quartz?/ ± Calcite veins anhedral crystals, Magnetite veinlets cut disseminated Magnetite and Plagioclase groundmass split and offset optically uniform crystals, fine-grained Actinolite veinlets with Plagioclase selvages may cut through Magnetite veins, Plagioclase veins, local Hematite oxidation after Magnetite. CNN 69: massive Magnetite with discontinuous stringers .1-.4 mm wide of Scapolite ± Quartz which is also in clusters 1.2- 4 mm long, Quartz and Scapolite are anhedral crystals .8 mm wide. CNN 70: Plagioclase altered to Clays ± Quartz?, ± Sphene, Scapolite poikylitic overgrowing Plagioclase, Calcite // medium sized anhedral Scapolite ± Quartz, Actinolite, Biotite scabby ± Chlorite, ± Epidote (4 mm//.75 mm), Magnetite disseminated locally 30 %, Plagioclase altered Actinolite? Or Clay, Magnetite replaces in groundmass rather than Plagioclase phenocrysts, .5mm Actinolite veinlets, hairline Quartz veinlets, hairline Magnetite veinlets. CNN 71: Scapolite 4-5 mm, Actinolite, Epidote, ± Quartz, ± trace Apatite?, ± trace Calcite?, Actinolite stringers & interstitial to Scapolite.
CNN 72: Quartz, Sericite, Fe-oxide? fine-grained altered rock, trace Scapolite??, Magnetite locally banded altered to Hematite, surrounded by Quartz, Goethite or Magnetite stringers with Fe-oxidized selvages, 1 mm wide Magnetite & Quartz vein cuts Fe-oxidized, Clay (Sericite?) altered host. CNN 73: Quartz, (?) phenos altered to Clay (Sericite?), disseminated Hematite & alteration rims on Magnetite, Barite tabular white colorless in plain light, 1st order blackwhite cross polar, trace Actinolite, minor Magnetite veinlets, banded white Quartz rich and Fe-oxidized zones (liesigang). CNN 74: Clotty aggregate Quartz, Actinolite, Clays and Magnetite replacement, Magnetite altered to Hematite, some remnant phenocrysts?, Quartz, Actinolite ± Rutile?, Rutile? associated with Quartz veins often, Chlorite rims on clay altered phenocrysts, Generally Quartz with Hematite/Magnetite/Clay matrix ± Actinolite, 1.5-2 mm wide Magnetite veinlets & stringers. CNN 75: Photomicrograph, Plagioclase ± Clay, Magnetite /Goethite stringers, Sericite after Plagioclase, Actinolite, bleached, .25 mm Magnetite/Quartz vein, Magnetite altered to Hematite vein may follow earlier Quartz vein, anhedral Quartz with Magnetite altered to Hematite covering. CNN 76: Quartz Diorite, Plagioclase 65 % => altered rims (clay) on phenocrysts, euhedral subhedral equigranular crystals, some phenos look fractured and have Quartz fill, Epidote 10 % after Plagioclase sometimes? Associated locally with anhedral Quartz veinlets, Quartz 20 % suhedral- anhedral, Actinolite 5 % locally disseminated, Calcite trace, Plagioclase ± Quartz veins large irregular anhedral Plagioclase & small anhedral Quartz grains .8-1 mm wide no selvage, Epidote stringers cut Plagioclase veins, Magnetite 2-3 % disseminated, but often associated with altered Pyroxene? => Epidote? CNN 76A: Photomicrograph, Tourmaline 55 % rectangular and basal stubby, Quartz 30 % anhedral medium-small sized grains, Plagioclase trace-5 % unaltered sub-anhedral, ± K-feldspar?, Epidote 5 % granular anhedral medium grained, Magnetite altered to Hematite trace- 5 %, Fluid inclusions in Quartz vapor bubbles 15-20 % Na crystals & Hematite flakes. CNN 76B: Photomicrograph, Andesite?, Phenocrysts: Plagioclase moderately-strongly altered to Epidote ± Calcite in cores, local Scapolite? in interstitial clots ± Clay± Sericite after Plagioclase, Plagioclase euhedral- subhedral 2 mm- 4 mm long probably Albite (ML method 12°, 13°, 10°), local Calcite, Carbonate? and Fe oxide Jarosite (brownorange) ± Chlorite, twinned Actinolite phenocrysts after Pyroxenes 2 mm long subhedral-anhedral locally Chlorite altered, trace Magnetite cubic habit most .2 mm wide associated with Plagioclase phenos, groundmass .25 mm long Plagioclase strongly altered & Actinolite all sub-anhedral, Sphene 1 % boats. CNN 77: Equigranular Granodiorite or Quartz Diorite, Quartz 12 % anhedral average of .4 mm wide, Plagioclase 65 % 5 1.2-2 mm carlsbad simple and Albite twinned and concentrically zoned weak-moderately altered to Epidote & or Clays ± Sericite locally (ML method 10°), Actinolite 20 % anhedral locally twinned .8 mm with associated local aggregates of anhedral Magnetite 3 % some cubic habit, local Magnetite stringers 40 i.tm wide, discontinuous Quartz stringers .4mm wide.
CNN 77A: See Geochemistry, Diorite Quartz Diorite, Plagioclase locally moderately altered on rims to Epidote or Clays ± Magnetite, Epidote 5-10 %, Magnetite 5 % preferentially replaces where Epidote and Clays are after Plagioclase, Quartz 10 %, Plagioclase 80 %, possibly more K-feldspar? (Granodiorite), .80 mm wide Epidote vein, and replaces twinned Plagioclase like a weak coating. CNN 78: See Microprobe Data, Equigranular Granodiorite?, Quartz 20 % anhedral .4-1.2 mm wide, white 8mm wide bands of mod-strongly Clay, Sericite ± Carbonate altered Plagioclase, relatively less Quartz in white bands, Plagioclase euhedral-subhedral 1.6 mm wide and long, Actinolite twinned anhedral 1.2 mm wide mostly .8 mm long, Epidote 2-3 % locally, Sphene 2 % ± Magnetite after Plagioclase?, Magnetite 3 % anhedral aggregates associated dominantly with Actinolite. CNN 78A: Fine grained euhedral Quartz/ Plagioclase groundmass looks like intergrown grain boundaries, possibly re-crytallized, K-spar 10 % mostly unaltered, Plagioclase 50 % generally unaltered, Pyroxene ? altered to Actinolite 5 % with Epidote on rims, Epidote 15 % in rock and in veins, Epidote ± Actinolite hard to tell difference (50/50) in vein, looks like Epidote after Actinolite/ Magnetite in .80 mm wide vein, Quartz/Plagioclase inter-growth or K-feldspar tartan crosshatch 20 %, Magnetite associated with stringers of Epidote and Actinolite 1-2 %. CNN 78B: massive Actinolite 65 %, Quartz ± Plagioclase matrix or stock-working 30 %, brecciated Actinolite?, small .05- .1 mm wide discontinuous Magnetite stringers, & disseminated 3 %, interstitial Quartz, Plagioclase 2-5 %, Epidote trace- 3 %, Very fine grained Actinolite? and Quartz ± clay altered Plagioclase on white part of slide. CNN 79LS: Thin-section Scan, Sphene 5 % associated with Actinolite euhedral subhedral blades 2mm long in veins 1-2 mm wide, Magnetite anhedral associated with Actinolite veins, Actinolite stringers crosscut whole rock, host Plagioclase rich subhedral phenos 50 % .4-2 mm wide, Mafics altered to Actinolite, in groundmass Plagioclase 50 % anhedral 40 1.1M, ± Scapolite?, some altered Pyroxenes? weakly - moderately altered to Actinolite twinned in veinlets lmm wide, Magnetite stringers. CNN 79A: Plagioclase moderately- strongly Clay altered, mafics altered to Actinolite, hairline stringers of Magnetite, some veinlets have Actinolite selvages, disseminated dotty Magnetite associated dominantly with mafics, Interstitial small Quartz grains intergrown make up groundmass. CNN 80: Strongly altered Andesite? Fine-grained groundmass: mafics altered to Actinolite, Quartz, Plagioclase, disseminated Magnetite 20 % in groundmass dominantly, Phenocrysts: Plagioclase strong-moderately altered to ?, .1mm wide Actinolite veinlets with selvages Quartz ± Actinolite. CNN 81: Na altered Plagioclase (ML method 15°, 14°, 8° = 85-95 % Ab, 05-15 % An), .4 mm wide Magnetite/ Actinolite veinlets, Magnetite stringers, medium-grained Quartz? or Scapolite glomerocrysts 7 %, Plagioclase altered to Albite 75 %, equigranular subanhedral Albite, disseminated anhedral Actinolite 15 %, Magnetite 3 %, Epidote trace 2 %, Sphene 2 %. CNN 82LS: Thin-section Scan, Very fine-grained white plain light Plagioclase ± Quartz, x-nicol white-blue K-feldspar? white-yellow Plagioclase ± Quartz, Magnetite disseminated trace 1 %, Actinolite patchy, Plagioclase with alteration rims, Kspar/Plagioclase? cheeseboard, Actinolite/ Magnetite veins and Actinolite/ ± Magnetite
veinlets cut host, Magnetite cubic disseminated in Actinolite vein?, Magnetite stringers discontinuous cut optically continuous crystals in groundmass. CNN 83: Porphyritic Granodiorite, Phenocrysts 50 % of rock: Scapolite 20 %, Plagioclase 70 % weak Sericite or Clay altered locally concentric zoning and Albite twinned, ± Apatite? Quartz 5-10 %, mafics strongly altered to Actinolite 5 %, groundmass 50 % of rock Scapolite 88 %, Plagioclase 10 %, dotty Magnetite and Actinolite disseminated 2 %, Amphibole? CNN 84: Diorite, equigranular, Pyroxene unaltered to weak-moderately altered to Actinolite could be secondary?, Magnetite most often associated with Actinolite, hairline Magnetite/Actinolite veinlets, Quartz altered cores of Plagioclase? with Albite concentric rims?, Plagioclase 50 %, Pyroxene/ or Actinolite 40 %, Quartz 10 %, K-feldspar trace? CNN 84ALS: Thin-section Scan, Actinolized massive host very fine-grained 90 % 40 lam 10 % larger, locally 10 % Epidote and Scapolite, Scapolite vein 1.5 mm wide bladed anhedral .4-1 mm wide crystals / ± Actinolite // Actinolite, Sphene, Magnetite, ± Epidote locally?, fine-grained Scapolite veinlets 1 mm wide cut host and other larger veins, larger and earlier Actinolite/Scapolite veins up to 12-14 mm wide, Scapolite and Actinolite 8 mm long locally very fine-grained and feathery habit, Sphene up to 7 % mostly in selvages of Scapolite veins but also locally disseminated in host, later Scapolite stringers 40 i_tm wide with Epidote? or Actinolite? Selvage grains 5 i_tm wide cut early veins and host, latest Quartz/ K-feldspar/ Tourmalie veins, possible local Carbonate alteration. CNN 85: Quartz groundmass with Apatite? locally, Actinolite stringers, Tourmaline clusters with Quartz & fine-grained Tourmaline in groundmass, Magnetite altered to Hematite stringers & veins probably using same Quartz vein path, euhedral dog-tooth course-grained Quartz with fine-grained anhedral Quartz selvage. Chip sample across 1.2 m of fault gouge and andesite host. Fault shows dip slip and strike slip motion. Quartz + Hematite + Goethite + Jarosite + Sericite + Clays ± Pitch? CNN 86: See Geochemistry, Chip sample taken across 30 cm of NW trending shears (320°/77° SW), Hematite + Calcite + CuOxides and Carbonates + Goethite ± Jarosite ± Pitch? Quartz!! Tourmaline veining CNN 87: Massive Quartz vein with Cu-carbonates ± Oxides?, Magnetite altered to Hematite Quartz breccia, euhedral Tourmaline up to 1 cm long, Fluid inclusions 15 tm with 20 % vapor (secondary?) ± solids Halite up to 5µm and Hematite up to 3 i.tm, many ratty fluid inclusion trains also, offset Fluid Inclusion train at (x = 6.8 and y = 47.7), late hairline fractures S 30 pnl with Cu Carbonate stringers, Magnetite breccia with Cu oxides ± Carbonates Goethite and Magnetite altered to Hematite, local Carbonate stringers with Cu Carbonates, Quartz breccia cemented with Hematite and Carbonate angular Quartz fragments 1.2mm wide. Spongy and vuggy Sericite ± earthy Goethite ± Jarosite ± Clays. CNN 88: Strongly altered, Amphiboles 120° cleavage, Actinolite with Quartz ± Plagioclase clots ± Apatite? CNN 88A: 1.5-2 mm wide Scapolite / Quartz? vein, lmm glomerocrysts of anhedral Scapolite with feathery habit & Plagioclase?, Scapolite replaces Plagioclase, Epidote?, Pyroxene locally in clusters moderately-strongly altered to Actinolite locally twinned, pervasive Actinolite altered rock with late Quartz/ Scapolite veining.
CNN 89-1: Actinolite locally altered to Chlorite 4+ mm long euhedral-subhedral, Scapolite locally crystals look recrystallized and may be associated with Quartz or could just be recrystallized anhedral Quartz, small clusters of Apatite? CNN 89-2: Massive anhedral Quartz grains intergrown, Apatite?, massive Amphibole (Actinolite), ± Pyroxene, Scapolite? CNN 90A: Plagioclase 15 % weakly altered to Clays?, Quartz 60 % anhedral and intergrown, Actinolite 25 % fibrous moderately-strongly altered Pyroxene's, Calcite 2 %, Actinolite/Magnetite ± Chlorite .5-1 mm wide crosscutting, Quartz // Magnetite ± Actinolite veins, or Quartz following older Magnetite //Actinolite or Magnetite/Actinolite veins. CNN 90B: Equigranular Diorite, strongly Actinolite 35 % altered anhedral grains locally moderately-strongly altered to Chlorite, Plagioclase 60 % strongly altered to Sericite ± Clays also stock-working stringers and veinlets locally altered to Epidote 5 % ± Calcite, Magnetite associated with Epidote and moderately-strongly altered to Hematite. CNN 90C: Andesite, Pyroxene up to .4 mm wide anhedral-subhedral weakly altered, ± Epidote, very fine-grained Actinolite, Scapolite feathery habit, Plagioclase?, Hairline fractures with Quartz. CNN 91: Photomicrograph, Diorite-Quartz Diorite, equigranular, Plagioclase 70 % mostly weakly altered to clays in centers of phenocrysts, alteration halos concentric zoning possibly Albite?, Quartz 5 %, mafics moderately-strongly altered to Actinolite 20 %, Epidote 5 %, trace globs of Magnetite associated with Epidote. CNN 91A: Photomicrograph, See Geochemistry, Plagioclase altered to Epidote, Seriite?, Albite? mostly strongly bleached, some Pyroxene moderately-strongly altered to Actinolite, random dotty disseminated Magnetite 7 %, Actinolite locally altered to Chlorite, Albite or fresh unaltered Plagioclase? Overgrowing an Amphibole (not Actinolite) texture looks recrystallized, Amphiboles present generally unaltered maybe after Pyroxene? CNN 92: Photomicrograph, See Geochemistry, Andesite, 40 % Phenocrysts: Plagioclase 80 % sub-euhedral phenocrysts mostly unaltered normal, Albite twinned and locally concentrically zoned, locally altered to Chlorite? ± Clays and Sericite ± Epidote mm wide, Tourmaline 1 %, Pyroxenes 20 % moderately-strongly altered to Actinolite .4-2-3 mm wide and anhedral, 60 % Groundmass: Actinolite 50 %, Plagioclase 50%, Magnetite disseminated and associated with groundmass dominantly anhedral-euhedral aggregates also cubic habit .2 mm wide. CNN 93: Actinolite 95 %, 4 .1 mm wide alternating bands of fine and course-grained Actinolite, 5 % Scapolite??, mylonite. CNN 94: Andesite strongly altered?, Plagioclase 55 % Clay or Sericite altered, mafics 20 % moderately-strongly altered to Actinolite, locally twinned, Quartz? 12-15 % possibly K-spar after Plagioclase?, Magnetite 10 % anhedral-subhedral disseminated and dominantly associated with Actinolite, but not all the time, Epidote trace, zone of stronger Plagioclase alteration with much smaller Magnetite only 1-2 %, higher Quartz %, possible silica flooding?, Quartz stringers. CNN 94A:Quartz 55 %, Plagioclase 40 % moderately altered to Sericite, Tourmaline 5%.
CNN 95-1: (Veta Central), Andesite post-mineral dike, Plagioclase in groundmass and 5 % phenos weak to moderately altered to Clays, Chlorite 5-10% after Actinolite?, Actinolite after all mafics up to .04 mm wide, Magnetite 10 % very fine .005 mm cubic disseminated. CNN 95-2: (Veta Central), Andesite post-mineral dike strongly altered, Calcite 20% in groundmass & in vein 4-5 mm wide; 3 mm Goethite stained ± Magnetite altered to Hematite selvage// Quartz .2mm, Calcite veinlets .05 mm wide, Chlorite 20 %, possibly secondary Quartz veins after Calcite or visa versa or Quartz/Calcite together, Plagioclase altered to Calcite, Chlorite?, ± Epidote rims, shreddy Magnetite locally altered to Hematite 5-7 %, very little Actinolite left altered to chlorite. CNN 95A: (Veta Central), Actinolite altered to Chlorite locally in phenocrysts, disseminated Magnetite 30 % not associated with Chlorite, Plagioclase altered to Sericite Clay in core of phenos; in groundmass Plagioclase moderately-strongly altered to Clay ± Albite? CNN 95B: (Veta Central), fine-grained andesite, Calcite/ Chlorite veinlets (open space), huge clusters of secondary Calcite (late) with Chlorite, Plagioclase? altered to Chlorite, Calcite, ± Epidote, minor Actinolite mafics gone except for very fine Actinolite with Plagioclase in groundmass. CNN 95C: (Veta Central), Moderately altered Andesite Dike, equigranular, Plagioclase locally altered to Epidote others strongly altered to Clays and Sericite, Pyroxene's locally moderately altered to Actinolite, Calcite 20 %, Chlorite 20 %, Epidote 5 %, Actinolite 20 %, Plagioclase 35 %, Epidote/Chlorite/Calcite clusters, disseminated shreddy Magnetite altered to Hematite 2 %. CNN 96: (Veta Central), Andesite, equigranular, large Actinolite with twins probably after Pyroxene?, Epidote 2-3 %, Plagioclase strongly altered to Sericite ± Epidote bleached, Magnetite 20 % very fine-grained disseminated locally larger .2 .4 mm cubic habit, Chlorite moderate alteration, localized Calcite 2-3 %. CNN 97: (Veta Central), Fine-grained Actinolite ± Chloritoid? 1.2-2.4 mm wide 45 %, Plagioclase 30 % strong-moderately Clay? Altered, disseminated Magnetite 25% cubic euhedral-subhedral, glomerocrysts of Quartz .4mm, late Quartz veinlets .1mm wide, Chlorite trace-2 %, equigranular Actinolite ± Epidote? and Chloritoid, Tourmaline CNN 98-1: Carbonate/ Quartz/ Plagioclase/ Chlorite/ ± Actinolite, spotty Magnetite ± Epidote// Chlorite// Magnetite ± Quartz vein or pervasive alteration, cuts host composed of very fine-grained Actinolite? (like CNN 97), Plagioclase?, Carbonate, ± Chlorite, ± Epidote, Quartz. CNN 98-2LS: Thin-section Scan, 90° cleavage dotty Pyroxenes altered to Amphiboles which could be primary, or primary Pyroxene altered to mottled Amphibole pink-brown to light pink-brown, massive Actinolite parallel extinction possibly Tremolite ± Chlorite?, Magnetite/ Actinolite vein discontinuous, Magnetite 10 % disseminated near vein in selvage, groundmass with Actinolite + Scapolite ± Quartz?.
CNN 99: Actinolite twinned massive 5-6 mm and less cementing breccia fragments of dominantly Quartz ± Plagioclase and local Amphibole with associated sub-cubic euhedral-subhedral Magnetite, Pyroxene locally moderately-strongly altered to Actinolite, breccia fragments are finer-grained than both course and fine-grained Actinolite cementing breccia fragments, breccia fragments have glomerocrysts of Quartz, Plagioclase phenocrysts with Quartz. CNN 100-1: Quartz diorite or Granodiorite, Excellent offset by hairline Actinolite veinlets of Actinolite grain in a 4-5 mm wide Actinolite vein, Actinolite crystals up to 3-4 mm wide, Actinolite/ Amphibole veins cut equigranular Plagioclase, Quartz, K-feldspar host, late Quartz veins .5-.8 mm wide cut Actinolite veins, Magnetite ± Quartz veinlets cut Actinolite veins and may be same time as Quartz veinlets?, Plagioclase phenocrysts: Albite? rims, K-feldspar phenos with Albite? rims. CNN 100-2: Equigranular Diorite or Granodiorite?, Plagioclase 50 % concentrically zoned reaction rims altered to Albite? With possibly some Calcite & Clays, Quartz 40 %? Some 2 mm large anhedral phenos may be K-feldspar, K-feldspar 5 % or more, Pyroxene altered moderately-strongly Actinolite 5 %, hairline Carbonate or Actinolite veinlets? and later Quartz veinlets cut earlier veinlets. CNN 101: Massive Magnetite with inclusions of Chalcopyrite 1-2 % anhedral, cut by 4-6 mm wide vein of Calcite grains anhedral- subhedral 2mm long and wide/ Pyrite 1 % ± Chalcopyrite anhedral aggregates .15 mm, along selvage Magnetite altered to Hematite, some local .2 mm wide Calcite veinlets, later .4-.8 mm wide vein of Quartz .4-.8 mm in size anhedral/ Carbonate /± Actinolite/ ± Chlorite/ Pyrite pitted and .4-1.6 mm long ± Chalcopyrite anhedral grains, cut into earlier Carbonate vein and run along edge or selvage of Carbonate vein, could be same vein? CNN 102: Similar to CNN78, equigranular Granodiorite, Quartz anhedral with Fluid inclusions mm in size Halite solids up to 40 pm and 20 % vapor, Plagioclase anhedral moderately-strongly altered to Carbonate ± Sericite 2.5 mm, Actinolite moderately altered to Chlorite anhedral 1.6mm long, vein 2-3 mm wide of Plagioclase anhedral average 1 mm in size moderately altered to Sericite and Carbonate(Calcite), disseminated ratty clots of anhedral Magnetite 2 % locally altered to Hematite and locally euhedral cubic Magnetite associated with Actinolite, local Actinolite stringers 40 1..tm wide, check Plagioclase vein texture. CNN 103-1LS: Thin-section Scan, K-feldspar? and Scapolite?// Actinolite local Magnetite 5 % vein cuts K-spar & Plagioclase host, possible that Magnetite veins used K-feldspar/ Scapolite vein path or visa versa , Magnetite veinlets discontinuous. CNN 103-2: Quartz Diorite- Quartz Monzodiorite, anhedral < .4 mm granular Quartz groundmass, Plagioclase .4 mm phenocrysts, mottled Actinolite ± Epidote + Magnetite veins and stringers, local Quartz and K-feldspar phenos .4-.5 mm, clusters of Quartz, possible Calcite alteration. CNN 103-3: Photomicrograph, See Microprobe Data, Andesite, (Porphyritic Granodiorite?), Quartz!! Actinolite vein .8 mm wide cuts and offsets Actinolite vein .2mm wide, silicified Quartz alteration?, fine-grained Quartz ± K-feldspar groundmass 40pm, Plagioclase phenos .1-.2 mm concentrically zoned; normally and simple twinning moderately altered to Calcite? (same as CNN 106), Quartz, K-feldspar.
CNN 104: Quartz/ Hematite vein, local K-spar, anhedral-euhedral Quartz most have reaction rims radiating euhedral bladed or feathery overgrowths could be recrystallized chalcedony? possible supergene alteration, Quartz has ratty inclusions fluid inclusions near original Quartz grain and overgrowth boundary, high liquid/ vapor ratios in main grains, Actinolite trace, massive interstitial Hematite after Calcite? Locally in spicual habit, anhedral K-feldspar? 2-3 %. CNN 105LS: Thin-section Scan, K-feldspar carlsbad twinned, Clinopyroxene, Actinolite huge, Plagioclase twinned, Actinolite// K-feldspar veins, yellow white plain light Kfeldspar/Actinolite//K-feldspar veinlets. CNN 106: Silicified Andesite or porphyritic Quartz Diorite (same as CNN103-3?), very fine-grained anhedral Quartz/Plagioclase groundmass, Plagioclase phenos .2-.4 mm moderately- strongly Clay altered with Albite reaction rims?, Actinolite veinlets .2 mm wide offset and cut by Magnetite veinlets & stringers, Magnetite veinlets may follow some earlier Actinolite veinlets or just have Actinolite selvage, Actinolite patchy & stringers with associated Magnetite, Epidote trace. CNN 106A:Granodiorite, relatively equigranular no phenocrysts/ groundmass distinction, Quartz/ Plagioclase intrusive cuts earlier Andesite? Host: Quartz 20 % anhedral .4 mm wide, Plagioclase 80 % anhedral 5_ 2 mm in length .4-.8 mm wide locally moderatelystrongly altered to Sericite ± Carbonate others relatively unaltered, late open-space probably plucked stringers and veins of Epidote 40 1.1M -.2 mm wide, interstitial Epidote 2 % ± Hematite & Goethite and in hairline fractures in Plagioclase, Andesite: Plagioclase anhedral phenos strongly altered to Clays? Sericite & Carbonates 1.2 mm in size groundmass is Actinolite fine-grained locally up to .8 mm long ± Epidote trace, Magnetite 2 % disseminated anhedral lam locally subhedral larger, local zones of Scapolite? Between Andesite and Granodiorite. CNN 108: Photomicrograph, See Microprobe Data, Granodiorite?, equigranular S 1.5 mm, Plagioclase 75 % weak-moderate Albite? rims, Quartz 10 %, K-feldspar 5 %, mafics Amphibole or Pyroxene altered to Actinolite 10 %, dotty Magnetite 1-2 %, Intrusive cuts andesite host, hairline Carbonate veinlets .4 mm wide// Carbonate 2-3 mm selvage, possibly cuts Magnetite!! Actinolite veinlet replacing all Plagioclase & K-spar, mafics in selvage moderately-weakly altered to Actinolite or not altered possible secondary Pyroxene and Amphibole? CNN 109B: Equigranular Carbonate & Quartz, Quartz 25 % anhedral .4-.8 mm, Plagioclase altered to Carbonate 75 % anhedral 1.2 mm, Quartz? +Magnetite? Stringers, Actinolite trace. CNN 110-1: Massive Magnetite breccia with anhedral Quartz 75 % of cement with growth zones no fluid inclusions, Quartz fills voids fractures and stringers, Cu Carbonates Malachite & chrysocolla? possible supergene covellite, Epidote 3 %, very fine-grained Clays ± Sericite (Muscovite) and Carbonates 10 %, Goethite and Hematite 5 % normally along edge of Magnetite ± Chlorite possibly after Actinolite?, Quartz low temp radial and feathery bladed Chalcedony.
CNN 110-2: See Sulfur Isotope Data, massive Barite/ Quartz vein, Quartz 4 mm wide anhedral-subhedral, massive cubic 5 mm Barite xtals with hairline fractures containing Magnetite altered to Hematite and Quartz, all fractures and around larger grains .4 mm Quartz grains cemented with Magnetite altered to Hematite, Goethite ± sulfide? (Chalcopyrite? + Pyrite trace boxwork?) and Carbonates. CNN 111: Porphyritic Diorite or Andesite?, Carbonate ± trace Quartz vein .2 -.3 mm wide Carbonate selvage cut host, Actinolite locally strong-moderately altered to Chlorite 5 %, Plagioclase 80% equigranular .4mm groundmass moderately-strongly altered to Calcite or other Carbonates, large Plagioclase phenos, weak-moderately altered to Carbonate ± 2-4mm, Quartz 1 % phenocrysts. CNN 112: Diorite equigranular .2-.5 mm Plagioclase locally altered to Calcite ± Sericite 90 %, interstitial Clay ± Carbonate fibrous or Actinolite 2-3 %, brown Goethite ? or stained brown Carbonates, zero mafics left, ± Quartz 2-3 %, discontinuous shreddy Carbonate ± Goethite Fe-oxide veinlets .1- 1 mm wide, ± K-feldspar? CNN 113: Andesite Dike, .2-.8 mm wide Chlorite vein reopened by 40-80 pm wide Calcite vein or vein/selvage relationship, Chlorite has small alteration rims high birefringence on edge of feathery grains, fine-grained groundmass 100 pm of Plagioclase & Actinolite, Actinolite locally altered to Chlorite, disseminated Magnetite 57 % 15 pm wide cubic habit, Quartz/ Carbonate/ ± Magnetite altered to Hematite .8mm wide veins cut host composed of 2 mm wide Quartz 1 % and Plagioclase phenos, weakstrong Calcite altered, most large mafics (Pyroxene ?) phenocrysts altered to Chlorite. CNN 114: Photomicrograph, See Microprobe Data & Geochemistry, possibly original Diorite, Sphene 5% anhedral clots mostly associated with Scapolite, Scapolite 60 % possible veining zone poikylitic anhedral euhedral blades to feathery habit 3mm long bladed habit zone 12 mm wide probably late after Actinolite host, Plagioclase 10 % anhedral 2+ mm long and wide altered to clays ± Sericite?, Actinolite 30 % anhedral often twinned locally up to 3 mm long, Magnetite 3 % .8 mm wide anhedral clots locally altered to Hematite ± opaque min?, white Clay ? alteration. CNN 115: See Microprobe Data, See U/Pb dates on titanite, Granodiorite? to quartz diorite, Sphene 5 % high relief very high birefringence, Actinolite 20 %, Plagioclase 30 % subhedral altered to Carbonate, Quartz 45 % intergrown anhedral grains, Carbonate alteration interstitial to Quartz and Plagioclase, in strong silica altered Quartz/ Plagioclase area Actinolite is gone and Sphene is stable. CNN 116: Granodiorite? to quartz diorite, Brittle shears may have used older Scapolite veins or could be coeval brittle shears cut but don't offset the Scapolite veins could be offset Scapolite veins, Magnetite 3 % dotty, Sphene 3 % local clusters or clots in vein, Scapolite anhedral S .2 mm in feathery habit undulose extinction, Scapolite veins 1.5 2 mm wide, Epidote?/ Actinolite veinlets 40 pm cuts Scapolite veins, small 40 50 pm Scapolite// Actinolite? hairline veinlets cut larger Scapolite ± Quartz veins, Plagioclase phenos 2mm strongly altered to Clays, Epidote locally, Calcite, Scapolite 20 %, Pyroxene strongly-moderately altered to Actinolite with local twinning still visible, Pyroxene texture completely swiss cheese very ragged edges, locally Scapolite overgrows Actinolite which has granular texture, possible Epidote with Actinolite color masking.
CNN 116A: Granodiorite, equigranular, Scapolite 15 %interstitial to Plagioclase, Quartz 10 % anhedral grains, Plagioclase 60 % 1.5-3 mm euhedral- anhedral moderately altered to Sericite concentric zoning; normal and Albite twinned, 3 mm, mafics 5 % Pyroxene altered to Actinolite mostly altered around rims anhedral-subhedral with some local twinning ± Epidote trace, Magnetite 2-3 % associated with Actinolite, discontinuous Magnetite/Actinolite veinlets. CNN 117: Photomicrograph, Mylonite, banded, Scapolite anhedral crystals, Pyroxene moderately-strongly altered to Actinolite locally twinned, hairline Scapolite?/ or Quartz? /Actinolite/ ± Sphene veinlets possible left lateral offset cuts Magnetite hairline veinlets. CNN 118-1: Diorite to monzodiorite, equigranular, Plagioclase 65 % altered to Clay ± Calcite which is moderate- strong Scapolite 10 %, ± Quartz anhedral interstitial, Scapolite vein lmm -.2 mm with fine-grained 40 pm feathery habit, mafics 15 % Actinolite anhedral with ratty edges, Magnetite trace dotty, Sphene 5 % and Epidote? on selvage of Scapolite veinlets, associated Magnetite. CNN 118-2: Microprobe?, Brown pink in plain light high birefringence high relief Sphene in vein, Magnetite associated with Actinolite, Carbonate, Magnetite & S 2 mm wide (uniaxial -) Scapolite, cut by feathery Scapolite ± Quartz? ± Clay/ Albite? vein .4-2 mm wide and veinlets 40 pm, equigranular anhedral Plagioclase altered to Carbonates ± Clays, Quartz anhedral, Actinolite disseminated and fibrous, Actinolite ± Epidote veinlets .1mm wide cut Scapolite veins, Fluid inclusions in Quartz with Hematite flakes may suggest higher Na waters. CNN 119LS: Thin-section Scan, Plagioclase, Actinolite, ± K-feldsparspar carlsbad, Magnetite 3 % disseminated, late hairline Magnetite veinlets. CNN 119ALS: Thin-section Scan, Plagioclase altered rock, late Hematite veins cut optically continuous Plagioclase phenos. CNN 119B: Plagioclase anhedral interlocking grains average .8 mm in size strongly altered to Sericite ± Clay ± Epidote, Actinolite 2 % interstitial, Magnetite vein massive 45 mm wide moderately-strongly altered to Hematite // Quartz selvage .8-1.2 mm wide euhedral-anhedral Quartz from .4-1.2 mm long larger grains, much fine-grained 40 pm along host Plagioclase contact and local stock-working of larger crystals up to .8 mm wide. CNN 120: See Geochemstry, Diorite equigranular, Plagioclase 80 % altered to NaPlagioclase? anhedral to subhedral .8-1.2 mm in length moderately-strongly altered to Sericite ±Clays? and Carbonate, Epidote 3 % interstitial anhedral aggregate, Actinolite 10 % interstitial anhedral 5_ .5 mm locally strongly altered to Chlorite, Magnetite 5 % mostly anhedral to locally euhedral cubic disseminated 5_ .2mm strongly altered to Hematite locally along cleavage plains associated with Actinolite ± larger clots 1.2 mm wide, Calcite 2-3 % local anhedral grains with Epidote rims. CNN 120ALS: Thin-section Scan, Massive Magnetite breccia altered to Hematite by fluids, mottled Hematite textures, Hematite breccia fragments surrounded by fine- grained secondthird order pleochroic blues and greens, Plagioclase twinned, Quartz veins cut Magnetite breccia, local Quartz veins stained by Hematite, Plagioclase ± Quartz/Calcite anhedral grains close packed grains in veins 3 mm wide, acicular bladed xtals light brown/ green in plane light redbrown to blue x-nicol altered to Plagioclase? or some Amphibole, Calcite with growth zones.
CNR 01: Strongly Actinolized Andesite host, Plagioclase 78 % lmm in size anhedral to subhedral moderately altered to Scapolite and Clays, Plagioclase moderately to strongly altered to Scapolite in later Plagioclase veinlets 2 mm wide semi aligned grains subhedral to anhedral cut through earlier Actinolite, Calcite clots and stringers cover Actinolite host, Actinolite 20 % anhedral fibrous 1 mm in size, K-feldspar trace-1 % Magnetite 2 % disseminated anhedral and in discontinuous veinlets. CNR 01A: Massive Scapolite veining 90 % grains anhedral to subhedral from 10 pin to .4 mm in size mostly aligned prismatic habit also anhedral grains, Sphene 6 % anhedral aggregates average size .1 mm up to .5 mm could have some Calcite associated, Epidote trace anhedral grains, Actinolite 4 % anhedral grains .2 mm locally weakly altered to Chlorite, 80 pm wide stockwork veinlets of Hematite/Calcite? with 5 p.m wide selvages of Fe-Oxides, Magnetite 2 % disseminated anhedral to euhedral cubic habit. CNR 02: Quartz anhedral 2 mm in size local ratty Fluid inclusions 8-10 pm with some salts, host overprinted by very fine-grained anhedral Quartz and Calcite, Calcite anhedral to euhedral zoned grains up to 2 mm in size / ± Goethite // ± Quartz veins 4-6 mm wide cut all, Quartz veinlets .8 mm wide also cut fine - grained Quartz and Calcite, Magnetite altered strongly to Hematite in Quartz veins and in clots up to 1.6 mm in size. CNR 02ALS: Thin-section Scan, See Geochemistry, Groundmass Actinolite anhedral and Scapolite anhedral average size 50 pm, Actinolite vein 4 mm wide massive to subhedral grain habit with 20 % hydrothermal euhedral-subhedral massive Sphene cut host, associated Magnetite anhedral some locally altered to Hematite, Sphene stringers 40-50 pm wide cut Actinolite vein along with other Actinolite stringers, Actinolite vein cut and offset by Plagioclase sub-anhedral ± Scapolite?/ Actinolite subhedral // Calcite up to lmm wide veinlets and stringers, Plagioclase veinlets also reopen some older Actinolite veins and run between Actinolite veins and host, older Actinolite veins offset and cut by younger smaller Actinolite and Magnetite veins and veinlets. CNR 02B: Photomicrograph, See Microprobe Data, and U-Pb Date on Sphene, Scapolite 80 % .5 mm wide anhedral stubby prismatic feathery and bladed habit locally 1.2 mm long, Quartz? 10 % intergrown and interstitial to Scapolite, Actinolite 5 % .5 mm long fibrous blades, Sphene 5 % anhedral locally single xtals 5+ mm long & 1.75 mm wide high temperature 550-600° C, very fine-grained feathery wisps of Scapolite, local Magnetite stringers .01 mm wide. CNR 02C: Equigranular Diorite? With crystals up to 2 mm completely altered to Plagioclase? Plagioclase moderately-strongly altered to Sericite ± Clays, early? irregular stock-work veining .4-1mm in width Actinolite locally weakly- moderately altered to Chlorite/ Magnetite, Epidote clots and stringers random throughout, late vein lmm wide colorless in plain light low Fe content Actinolite + Epidote cut earlier Actinolite/Magnetite veins Epidote locally on selvages, local Scapolite on selvage of later Actinolite/ Epidote veining, some Plagioclase ± Scapolite stringers or Scapolite after Plagioclase. CNR 03: Photomicrograph, Quartz/ Plagioclase/ Tourmaline hydrothermal breccia?, Quartz anhedral .2mm 1mm wide strained ratty Fluid inclusions 5-35 pm wide some may have solid salts locally growth zones are visible Chalcedony low temperature Quartz also, Plagioclase anhedral S 1.2 mm long, Tourmaline very fine-grained anhedral to euhedral prismatic habit in contact with Quartz, Tourmaline stock-working veinlets
overprinted by Quartz?, Tourmaline and later Quartz ? cut by Goethite? veinlets 20pm wide, later Magnetite/ Quartz veins .6mm wide cut Tourmaline Quartz altered host, latest Calcite/ ± Chlorite?/ ± Tourmaline/ ± Hematite/ ± Cu Carbonates// Calcite ( 1.2 mm // 50 pm) vein cuts everything, Quartz (Chalcedony) veinlets follow one side of the Calcite vein. CNR 03 A: Hammered, strongly altered Scapolite, Actinolite, Carbonate?, ± Epidote, disseminated Magnetite 10 % anhedral dotty, vein 2 4mm wide Scapolite? & Sphene 5 % much has been plucked out of slide?, local Magnetite stringers. CNR 04: Photomicrograph, Quartz with 3pm wide fluid inclusions with solid Halite xtals 2.5 pm wide and Hematite flecs almost all Quartz has fluid inclusions 75% volume Halite, Quartz anhedral-subhedral 40 pm 2 mm long strained extinction / Tourmaline euhedral- anhedral largest grains S .15 mm most very fine-grained as selvage and in vein with Quartz vein 2-4 mm wide, Magnetite massive associated with Quartz veining altered to Hematite near Quartz/Tourmaline vein, jade green Cu Oxide or Carbonate, Cuprite or Malachite in voids and stringers in Magnetite breccia also on Quartz rims with Goethite, Plagioclase?? anhedral grains 1- 1.5 mm wide altered to Sericite?? or it could be fibrous could be Tourmaline or Actinolite also?? CNR 05: Strongly altered Andesite, Plagioclase phenocrysts and groundmass often undistinguishable, very strong Sericite ± other Clay ± Calcite alteration, Tourmaline overprint anhedral aggregates and fibrous habit in veinlets up to 50 pm wide, Plagioclase phenocrysts? 2-3 % anhedral grains .4mm in size very strongly altered to Sericite, Actinolite anhedral fibrous average size .1mm, Magnetite 10 % disseminated anhedral to euhedral cubic habit average size 25-50 JAM in size moderately altered to Hematite. CNR 06: Photomicrograph, Magnetite massive, with Carbonate or Sericite or possible Tourmaline clots fibrous mineral with green Cu Carbonate or Oxides overgrowing it same as CNR-14 or 04? possible Clay or Carbonate alteration?, massive Quartz anhedral .2 mm grains inter-growing and crosscutting Magnetite some radiating fibrous low temp Quartz Chalcedony, ± Tourmaline subhedral, Plagioclase, ± Covellite? Bluish supergene interstitial to Chalcedony, Hematite/Calcite // Tourmaline/ Quartz ± Covellite vein (.2mmll .6-.8 mm / .8-1.2 mm wide) cuts Quartz, in vein Calcite has radiating openspace xtals, inner selvage Tourmaline anhedral to subhedral up to .2 mm-.4 mm, outer selvage Quartz anhedral grains to massive .4-.6mm, Hematite ± Goethite stringers and stock-working 40-80 pm wide. CNR 07: Strongly altered Andesite?, cannot distinguish phenocrysts from groundmass, Plagioclase 50 % anhedral to subhedral .8 mm grain size moderately to strongly altered to Scapolite ± other Clays, Actinolite 50 % anhedral fibrous .4mm in size weakly to strongly altered to Chlorite, Sphene 2 % anhedral grains and local discontinuous veinlets .2 mm wide, local clusters of anhedral Quartz, ± K-feldspar, and anhedral to euhedral Tourmaline .2 mm grain size, late Scapolite / Plagioclase vein .8-2 mm wide, Scapolite after Plagioclase grains prismatic euhedral to anhedral 5 1.2 mm in size average size .2-.4 mm probably later than Actinolite and Magnetite replacement., b/c vein cuts alteration locally Fe-Oxide and Hematite stained, latest? Very fine-grained Tourmaline? or calcite? veinlets 40 pm -.12 mm wide. Magnetite 10 % locally altered to Hematite especially in Calcite/Carbonate or Tourmaline? veins, stringers and anhedral dotty replacement.
CNR 08: Andesite, trachytic textured, 2 % phenocrysts: Plagioclase 100 % .4-2 mm in size moderately altered to Sericite ± other Clays ± Calcite, 98 % groundmass: Plagioclase 100% < .25 mm average in size subhedral to anhedral laths all equigranular with domains of alignment trachytic texture moderately to strongly altered to Clays ± Calcite ± Sericite Chlorite, dotty spots of Calcite and Fe-Oxide staining, Magnetite 10 % locally altered to Hematite anhedral grains .2 mm in size, Quartz anhedral/ Hematite bladed habit/ Calcite/ ± Fe-Oxides veinlets .1-.4 mm wide with Calcite and Fe-Oxide altered Plagioclase groundmass selvages 1-4 mm wide cut Andesite. CNR 09: Strongly Actinolized, Actinolite 3.2 mm to 40pm in size anhedral fibrous locally very weakly altered to Chlorite, very fine-grained trace Actinolite in Scapolite veins cut the large grain size Actinolite alteration, Sphene 5 % diamond shaped euhedral boat habit 1 mm in size associated with Scapolite in Scapolite/ Sphene stringers and veinlets .2 mm wide, Scapolite veins 5 2 mm wide grains anhedral fibrous to euhedral prismatic up to 2mm long with associated Sphene, Magnetite 4 % anhedral grains and clots .4 mm in size compose discontinuous stockwork stringers that cut across Actinolized host. CNR 10: See CNR 9, Actinolite anhedral to subhedral locally twinned .8mm in size unaltered to locally weakly altered to Chlorite fibrous to anhedral grain habit, Scapolite veining and stockwork up to 8 mm wide aligned grains subhedral prismatic to radiating and anhedral habit average size .2- .4 mm most .8 mm some local very fine-grained 10- 20 µm in size intergranular and semi aligned grains, Sphene 3-4 % associated with Scapolite veining anhedral clots, large Calcite altered patches up to 6 mm long and 2 mm wide of very fine grain size, Magnetite 3 % disseminated 5_ .1 mm in size. CNR 11: Photomicrograph, Magnetite massive breccia locally strongly altered to Hematite ± Goethite, stock-working veins .2-.8 mm wide Quartz/ Tourmaline/ Cu Carbonate/ Carbonate/ ± Hematite// Tourmaline, Quartz in vein has banded growth zoned open-space xtals up to .6 mm & low temp radiating fibrous Chalcedony, Carbonate very fine-grained radiating open-space clusters associated with very fine-grained Quartz Hematite ± Goethite intergrown anhedral grains, Tourmaline in vein acicular radiating and in clots with Cu Carbonates and sometimes on selvage, some Tourmaline in clots cut by 40 p.m Quartz stringers. CNR 12: Andesite?, Phenos: Plagioclase most 1-1.5 mm up to 3 mm in size anhedral strongly altered to Clay & Sericite ± Epidote ± Scapolite ± Carbonate, locally Actinolite xtals up to 4 mm long most .2-.4 mm wide moderately-strongly altered to Chlorite, Groundmass: Tourmaline anhedral to subhedral fine-grained granular to overgrowing, Actinolite trace mostly altered to Chlorite, Magnetite 15 % disseminated subhedral to cubic euhedral habit 25 pm- .4 mm, Actinolite altered to Chlorite/ Scapolite?/ Hematite/ ± Goethite/ ± Carbonate(?) veinlet 50 Rm wide. CNR 13: Plagioclase huge anhedral crystals flood? Locally moderately to strongly Sericite altered and locally strongly altered to Scapolite, Actinolite anhedral moderately to strongly Chlorite altered, Scapolite/ Calcite / ± Sphene veinlets .25 mm wide cut Plagioclase and Actinolite host, locally Sphene 5 % usually in veinlets but also anhedral clots in rest of rock associated with Calcite and Scapolite, latest Calcite/ ± Epidote? veinlets .5mm wide and overprinting Actinolite.
CNR 14: Andesite, phenos 50 % of rock: Plagioclase 85 % 4 mm long mostly strongly altered to Sericite ± Clay ± Scapolite? some grain boundaries altered to Carbonates?, local Calcite ± Chlorite after Plagioclase, Pyroxenes 15 % twinned; groundmass 50 %: Plagioclase 60 % 40 ptm, Actinolite 30 % moderately altered to Chlorite, Sphene 10 % anhedral aggregates, disseminated Magnetite 5 % 20 [tm locally subhedral euhedral cubic habit up to .4 mm also anhedral clots. CNR 14A: Photomicrograph, See Microprobe Data, 75 groundmass: Plagioclase 100 % anhedral to euhedral 75 [tm in size unaltered to weakly altered to Na plagioclase, 25 % phenocrysts: Plagioclase 100 % .4-4 mm long majority unaltered locally weakly altered to Calcite along twinning planes ± Sericite and Clays, Magnetite 2 % disseminated anhedral .2 mm in size mostly all moderately altered to Hematite, local clots of anhedral Quartz and Fe rich cubic habit Rutile? most often associated with Calcite, late Calcite stockwork stringers 50 [tm wide veinlets cut through host, dotty Calcite ± Goethite? Overprint all of host. CNR 14C: Massive Plagioclase 75 % altered locally to Scapolite?.2mm long feathery habit in groundmass, Plagioclase phenos 25 % generally unaltered 5 1.2 mm in size anhedral- euhedral, Carbonate ± Goethite? stockwork stringers, Quartz clots 5-10 % anhedral grains and in veins, associated cubic very high birefringence and pleochroic Tourmaline and Rutile? .2-.3mm wide. CNR 15A: Andesite, Phenocrysts: Plagioclase 100 % locally 4 mm normally between 2.6 mm euhedral to subhedral Albite and simple twinned Michel Levy method = 10° 15° 12° indicates Albite > 90 % for volcanics unaltered to weakly altered to Calcite ± fibrous yellow Clays? or possibly Calcite?, Groundmass: Plagioclase laths average size .25 mm euhedral to anhedral unaltered to weakly altered to Calcite 20 % ± Epidote? clear in plain light bubbly blocky associated mineral may be altered to Dolomite? Also associated brown/green granular Rutile? Mineral overgrows and associated with Clays and Epidote possible Sauserrite?, Magnetite 20 % euhedral cubic to subhedral locally altered to Hematite average size 25 [tm. CNR 15B: Andesite? Phenos 30 %: Plagioclase 100 % euhedral to anhedral .8- 2 mm locally 4 mm weakly to moderately altered to Calcite and Clays ± Chlorite, Groundmass 70 %: Plagioclase 100 % anhedral euhedral .1-.6 mm in size, Epidote 5 % in clots of anhedral grains, late Chlorite ± other Clays 25 % anhedral wispy grains interstitial to Plagioclase grains and after Plagioclase, latest Calcite 15 % clots and grains overgrow and interstitial and 10 [tin wide stringers cut through Chlorite alteration and host, Magnetite 2 % anhedral clots to anhedral to cubic grains locally altered to Hematite and Goethite also locally staining the Clays. CNR 16: Magnetite breccia altered to Hematite, Quartz anhedral 5_ .8 mm average .4 mm, stock-working Quartz/ Goethite veins .4 mm wide, Magnetite altered to Hematite on vein selvages and fill in Magnetite breccia. CNR 17: Diorite? or Andesite, Plagioclase 80 % equigranular minus a couple larger phenos anhedral to euhedral laths weakly to strongly altered to Calcite ± Clays ± Scapolite, Chlorite 20 % interstitial after Actinolite?, Clays and Calcite 20 % clots and interstitial throughout rock, Magnetite 4 % moderately altered to Hematite ± Goethite anhedral to euhedral cubic habit 60 p,m wide, late Calcite/ Quartz/ Specular Hematite// Goethite vein (.4mm// .8mm), later Goethite ± Carbonate veinlets .2mm wide cut
Calcite/Quartz/ Hematite vein, latest crosscutting open-space or plucked Calcite? .2mm wide vein very fine-grained Calcite on selvage offset and cut Goethite stringers. CNR 18: Hydrothermal Sphene 3-5 % anhedral grains up to .6 mm long & possibly after Pyroxene's?, clots and mosaic of strong Actinolite ± other Amphiboles? alteration very weakly altered to Chlorite subhedral laths to anhedral grains up to 2 mm long average size .8mm, Plagioclase .8 1 mm long anhedral interlocking grains and in clots weakly altered to Scapolite??, Scapolite ± Plagioclase?? vein 1 mm wide, Scapolite feathery cross hatch texture in vein and also floods whole rock leaving Actinolite & Amphibole & Sphene islands or clots, Magnetite 2 % disseminated anhedral blebby locally altered to Hematite. CNR 19: Magnetite massive strongly altered to Hematite ± Goethite, Quartz normally wispy feathery and anhedral to subhedral 5 mm in size locally Quartz radiating concentrically banded growth zones on grains undulose extinction anhedral small ratty Fluid inclusions, looks like Hematite ± Goethite overgrows Quartz because Quartz is included in Hematite, Goethite has very fine needle like habit, possible later Quartz veining cut Hematite, small pockets clusters of Quartz grains 80 µm wide on selvages with associated Sericite with the granular Tourmaline clusters near Hematite-Quartz boundaries, Quartz stringers 80 pm wide cut into Hematite. CNR 20-1: Strongly altered Andesite, Tourmaline overprint, Plagioclase anhedral to subhedral .4mm in size unaltered to weakly altered to Scapolite? ± Sericite, Tourmaline anhedral .5 mm in size, late Hematite/Calcite /± other Fe-Oxides /± Tourmaline vein 2 mm wide cuts Andesite and Tourmaline, locally Hematite after Magnetite veinlets also cut Andesite and Tourmaline overprint. CNR 20-2: Same as CNR20-1, but original Andesite host in better condition, Andesite, Plagioclase phenocrysts locally moderately altered to Sericite and Scapolite some locally unaltered anhedral to subhedral 1.2 mm in size, groundmass unaltered to weakly altered, stockwork overprint of Tourmaline anhedral grains and fibrous grains .15 mm in size, Magnetite mostly altered to Hematite, Calcite with growth zones/ Hematite!! Tourmaline (.2-.3 mm // .3 mm locally) veins, veinlets and stringers. CNR 20A-1:Equigranular intrusive Quartz Diorite, Plagioclase 60 % anhedral to euhedral laths unaltered to moderately altered to Sericite ± Clays?, Quartz 40 % anhedral 1 mm in size, Magnetite stringers 10gm wide altered to Goethite and Hematite, Tourmaline anhedral overgrowth 1.2 mm in size. CNR 20A-2: Quartz Diorite, same as CNN 20A-1, little stronger alteration of Plagioclase to Sericite ± Clays, no Tourmaline alteration, Plagioclase 60 % anhedral to euhedral, Quartz 40 % anhedral, Magnetite trace anhedral almost all altered to Hematite + Goethite. CNR 20B: Andesite overprinted by Quartz + Tourmaline breccia, Plagioclase phenocrysts 1.5 mm in size subhedral weakly to moderately altered to Clays?, groundmass interlocking anhedral to subhedral Plagioclase .2 mm in size, Andesite overprinted by stockwork Tourmaline clots and veins up to 2 mm wide, Magnetite altered to Hematite < .1 mm in size anhedral interstitial and also in discontinuous stringers, Quartz anhedral grains forming in clusters grain size 1.6 mm Fluid inclusions locally in Quartz up to 15 pm with Halite and Hematite, Pyrite trace anhedral to subhedral, Calcite ± Goethite locally interstitial.
CNR 21: Andesite, 20 % phenocrysts: Plagioclase 100 % anhedral .4-1.6 mm in size moderately altered to Sericite and other Clays, 80 % groundmass: Plagioclase 100 % interlocking anhedral grains 50 µm -.2 mm in size unaltered to moderately altered to Scapolite??, Tourmaline overprint anhedral grains .6 mm also locally .1mm forms in clusters and as singular grains and discontinuous small stringers, Magnetite 2 % as anhedral clots moderately to strongly altered to Hematite, late very fine-grained Calcite?/Carbonate stringers and Tourmaline with associated Hematite ± Fe-Oxides. CNR 21A: Intrusive Quartz Diorite, Quartz 10-12 % anhedral .2-2 mm in width intergrowing and interlocking between Plagioclase, Plagioclase 80 % .2-5 mm in length locally unaltered and moderately-strongly altered to Carbonate ± Clays?, Magnetite 2 % anhedral dotty, Tourmaline overgrowing host 1.2 mm in size average size .2 mm anhedral mostly fine-grained, Hematite/ Goethite vein .2-.8 mm wide cuts earlier Tourmaline overgrowth. CNR 22: Plagioclase phenocrysts 25 % 1-2 mm long anhedral moderately altered to Sericite ± Epidote trace ± Clays(?), Groundmass 75 % Quartz and Plagioclase anhedral 40 gm interlocking grains, Magnetite anhedral to subhedral cubic habit disseminated grains .2 mm & dotty up to 2 mm in size, Tourmaline overprint very fine-grained up to 50gm stock-working veinlets up to .2 mm wide, Magnetite stringers 40 gm wide cut Tourmaline and Quartz or may coevel with Tourmaline, associated Goethite alteration with Magnetite stringers, late Quartz veinlets .2mm wide cut everything. CNR 24: Same Quartz Diorite as CNN 20A-1 and CNN 20A-2, but Plagioclase anhedral is strongly altered to Sericite ± Carbonate?, Epidote 1-2 % anhedral dotty grains 50 pm in size, Tourmaline 1-2 % locally completely eaten grains up to lmm in length looks like it is late and overgrows the Quartz Plagioclase Diorite, Hematite/ Goethite 20 pm wide stringers cut Quartz Diorite. CNR 24A: Quartz/ Tourmaline/ Hematite breccia, framework breccia grains: Quartz anhedral .2-7mm in size mostly ratty Fluid inclusions 10 gm in size with solid salts ± Hematite flakes 2 5 pm in size, Tourmaline 1.6-2 mm in size anhedral grains, matrix: Hematite and Fe-Oxide stained Plagioclase, late Hematite veins cut breccia .1-.4 mm wide, breccia Quartz fragments and matrix fragments incorporated in veins, veinlets and stringers as little as 2.5 pm cut singular Quartz grains, local trace Actinolite? ± Calcite? or Sericite? Chip sample taken. CNR 25: Strongly altered Andesite, Plagioclase remnant crystals anhedral to subhedral .5mm in size moderately altered to Sericite make up groundmass, completely overprinted with Fe Oxides and Hematite to make red, Magnetite 35 % disseminated strongly altered to Hematite forms as massive clots with grains forming an interlocking texture also euhedral cubic habit, local disseminated Tourmaline, late Tourmaline vein .25 mm wide radiating anhedral crystal habit, cut by latest Quartz vein .25 mm wide with feathery wispy (Chalcedony) habit. CNR 26: Andesite? or Diorite moderately equigranular, 40 % phenocrysts: Plagioclase .2 - 1.6 mm average size .8 mm anhedral to euhedral moderately to strongly altered to Sericite ± other Clays, 60 % groundmass: Plagioclase? 50 % average size 50 75 gm interlocking anhedral grains, Actinolite 50 % anhedral fibrous habit 2mm average size locally weakly altered to Chlorite, local Sphene 2 % anhedral grains and clots, late stockwork Tourmaline veins 1.2mm wide with radiating prismatic euhedral grain
masses locally clots and clusters of euhedral to anhedral Tourmaline .2 mm in size, later Plagioclase anhedral strongly Sericite altered grains vein .2- 1 mm wide cut and offset Tourmaline veins, latest Hematite veinlets 50 pm .15 mm wide cuts everything, Magnetite 15 % massive clots and anhedral grains replace much of host associated mostly with groundmass but also with phenocrysts. CNR 26A: Photomicrograph, Complete Calcite and Epidote (Clinozoisite) alteration and overprint of Andesite?, remnant Actinolite and Plagioclase phenocrysts overprinted with Calcite rhombs and massive Calcite, Epidote anhedral to euhedral with perfect crystal habit as overprint and in stockwork veinlets from.2 mm up to 1.6 mm wide, Magnetite forms as anhedral clots and shards mostly moderately to strongly altered to Hematite associated mostly with Calcite flooding of host often forms rims around Calcite rhombs and disseminated also 50 µm - .8 mm in size, very late Calcite veinlets 50 pm wide cuts everything. CNR 27: See Microprobe Data, Quartz with small Fluid inclusions? .8-1 mm equigranular anhedral grains, Magnetite veinlets 40 pm - .4 mm wide with a local density of 20/ 4 mm of rock riddle Quartz also massive Magnetite overgrows everything?, late Cu Carbonate veins .4-.6 mm wide cut host and offset Magnetite veinlets, later Quartz/ Carbonate + Cu Carbonate veinlets .4 mm wide, local Goethite staining along veins is this possibly Tourmaline? CNR 28: Quartz/ Calcite veining, Quartz radiating fibrous Chalcedony and anhedral grains up to .8 mm wide no Fluid inclusions seen, Calcite disseminated very fine grained anhedral intergranular and interstitial to Quartz Calcite overprinting Quartz and as selvages (fine-grained) on Calcite/ Quartz veinlets with grain size up to 1 mm. CNR 29: Massive Hematite long bladed rectangular habit 2 mm long, Quartz anhedral with clear possible included Tourmaline grains in clots locally 5 .2 mm wide, Quartz veinlets .1-.15 mm and up to 3 mm wide, local Goethite staining in veins and veinlets. CNR 30: Andesite, Plagioclase phenocrysts anhedral 5. 1 mm long very strongly altered to Calcite ± Carbonates + Sericite + Epidote and Clays, Groundmass Plag .1-.3 mm in size very strongly altered to same as phenocrysts, Hematite 1 % bladed often associated with Calcite, green/brown bubbly Rutile? After Sphene? spatially near Clay and Calcite. CNR 31:_Granodiorite? to Quartz Diorite equigranular, Plagioclase 50 % anhedralsubhedral _5_ 1.2mm wide moderately altered to Sericite & Clays? simple and Albite twinning 10° angles from Michael Levy method, Quartz 25% anhedral 5_ 2mm, Pyroxene's 5 % parallel extinction sub- anhedral, K-feldspar? 15 %, Actinolite 5 % locally interstitial, micro 5 2 pm discontinuous stringers. CNR 31 A: See Geochemistry, Quartz anhedral grains 1.2 mm some local fine-grained feathery chalcedony 5_ 40 pm in size, Actinolite relict locally strongly altered to Chlorite, Scapolite, Sericite, Tourmaline anhedral very fine-grained to radiating crystals up to .4 mm long overprint and stockwork entire rock locally up to 1 mm wide. CNR 32 A: Andesite? fine-grained rock, overprinted with Carbonate?/ Calcite ± Clays fibrous habit and very fine-grained 5_ .4 mm, Tourmaline 5-7 % up to 1.5 mm in size anhedral to subhedral, secondary overprint of Hematite and other Fe-Oxides, Quartz locally 2-3 % anhedral grains, subhedral high relief biaxial mineral possibly Calcite? altered Plagioclase up to 1.5 mm in size subhedral to anhedral, local Epidote? 2 % or Tourmaline? or Calcite? in clusters of anhedral grains yellow brown, remnant Plagioclase
phenocrysts strongly altered to Sericite ± Clays?, discontinuous Plagioclase veinlets up to 70 pm wide Plagioclase euhedral grain size 15 pm. CNS 01: Andesite, phenocrysts: Plagioclase 100% anhedral to subhedral 1.6-.2 mm in size moderately to strongly altered to Clays? ± Sericite locally, groundmass: Plagioclase 100 % ± Quartz?, interlocking anhedral grains average size 5 50 pm, disseminated Tourmaline 20 % .15 mm anhedral to subhedral aggregates overprint Andesite, Magnetite 15 % disseminated anhedral to euhedral cubic habit .2 mm to 5 pm in size locally clots up to 1.2 mm, Plagioclase 1.5 mm anhedral interlocking strongly altered to Sericite/ Tourmaline anhedral grains .5-4 mm in size/ ± Hematite/ ± Chlorite anhedral radiating masses vein from 2-4 mm wide cut Andesite, local clots .2-.8 mm in size of Hematite + Chlorite + Tourmaline ± Epidote? in veins. CNS 01A: Andesite host cut by Quartz Diorite, Andesite has 10 % phenocrysts: Plagioclase 80 % up to 2mmm in size weakly to strongly altered to Sericite ± Clays, Actinolite 20 % average size 1 mm strongly altered to Chlorite, 90 % groundmass: Plagioclase 95 % 15- 75 pm unaltered to weakly altered to Sericite, Actinolite 5 % anhedral to subhedral grains locally fibrous and up to .25 mm strongly altered to Chlorite local patches of Chlorite ± other Clay alteration 2mm wide, Andesite cut by pegmatic Quartz/ Plagioclase /Tourmaline dikelet or vein (Quartz Diorite equigranular 16mm wide), Quartz 20 % anhedral .4-.8 mm wide grains, Plagioclase 75 % euhedral to subhedral 2 mm long moderately altered to Sericite ± Clays, Tourmaline 5 % anhedral .4-1.2 mm in size on selvages also disseminated .2 mm in size throughout andesite, Magnetite 6 % 10 pm -.1 mm anhedral to euhedral cubic locally altered to Hematite. CNS 02: Andesite? Phenocrysts: Plagioclase 93 % anhedral- euhedral .4 2 mm in length weakly-moderately altered to Sericite and Scapolite, Scapolite 5% anhedral grains .4- .6 mm in size clusters locally, Actinolite 2 % strongly altered to Chlorite, Groundmass: Plagioclase 5_ .1 mm in size weakly altered to unaltered interlocking anhedral grains, Chlorite veinlets 5..2mm wide & discontinuous stockwork veinlets, Tourmaline stringers 50- 60 pm anhedral-subhedral grains up to 20 pm & Tourmaline veins 1+ mm wide, Magnetite 15% disseminated anhedral to euhedral average size 25 1.1M, youngest Calcite veinlets 50 pm wide fine-grained cut Chlorite and host. CNS 03: See Microprobe Data, Andesite?, Phenocrysts: Plagioclase 20 % between 1.75 1 mm long subhedral mostly moderate-strongly altered to Clays & Sericite, Actinolite? 2 % strongly altered to Chlorite .4mm long, Groundmass: Plagioclase 30 % anhedral subhedral avg. 5 50 pm, Quartz 50 % anhedral intergrown, Tourmaline 35 % overgrows rock anhedral grains .2 mm in size, Quartz veinlet 80 pm wide with Tourmaline selvage .4 mm wide, Magnetite 5 % 5 .2 mm anhedral disseminated throughout altered to Hematite, possible trace Covellite? CNS 03 A-1: Andesite ?, same as CNS 3, Magnetite trace .6mm in size disseminated grains anhedral, Phenocrysts: Plagioclase 20 % 2mm long moderately-strongly altered to Sericite ± Clays, Actinolite 3 % 5_ 1 mm mostly strongly altered to Chlorite some unaltered, Groundmass: Plagioclase 50 % .5 mm long lined up trachytic texture locally, Quartz 50 % 5_ .25 mm in size anhedral grains, late Tourmaline 25 % 5.2 mm in size overprinting.
CNS 03 A-2: Quartz, Tourmaline altered Andesite?, Phenocrysts 25 %: Plagioclase 80 % 1.5 mm in size anhedral to subhedral moderate-strongly altered to Sericite, Quartz anhedral S .6 mm in size, Groundmass: Plagioclase 85 % 50 pm very fine-grained anhedral-subhedral, Quartz 15 % .15 mm in size anhedral, Tourmaline 35 % .8 mm in size anhedral overgrowing. CNS 03 B-1: Andesite?, Plagioclase phenocrysts 40 % avg. 1 mm in size subhedral weak moderately altered to Clay ± Sericite, Groundmass: Plagioclase 95 % .1 mm -50 µm interlocking anhedral subhedral intergrown all weakly altered, Quartz 5 % anhedral, stock-working Tourmaline veining .2 4 mm wide, Chlorite 3% associated with Tourmaline maybe after Actinolite, Quartz clots up to 1 mm in size associated with Tourmaline stock-working and veining. CNS 03 B-2: Andesite? Phenocrysts 20 %: Plagioclase 95 % 1.5 mm euhedral to anhedral unaltered to weakly altered to Sericite ± Clays?, Actinolite 5% anhedral fibrous moderately altered to Chlorite, Groundmass 80 %: Plagioclase interlocking 50 [tm anhedral & euhedral laths unaltered to weakly altered to Sericite? ± Scapolite interstitial and hard to tell, Tourmaline late veinlets and stringers .2- 1.2mm wide stock-working radiating habit and anhedral granular. CNS 04: Porphyritic Andesite, Phenocrysts 60 %: Plagioclase 95 % 1.5 mm euhedral subhedral mostly moderately-strongly altered to highly birefringent Sericite ± Clays, Actinolite 5 % anhedral fibrous clots .4 mm wide not really phenocrysts, Groundmass 40 %: Plagioclase 80 % .1 mm subhedral-anhedral moderately-strongly altered, Magnetite anhedral to sub-cubic disseminated 50 % large .4 mm 50 % small .30 Actinolite weakly altered to Chlorite/ ± Quartz/ Epidote/ Sericite? or Tourmaline vein .3-.4 mm wide. CNS 05: Andesite, 40 % phenocrysts: Plagioclase 100 % .2-1.6mm in size anhedral to subhedral unaltered to moderately altered to Clays ± Sericite?, 60 % groundmass: Plagioclase 100 % anhedral interlocking grains average size 10 [tm .15 mm unaltered to weakly altered, Tourmaline overprint and stockwork veinlets very fine-grained anhedral aggregate and radiating anhedral fibrous to euhedral columnar habit of grains also dotty masses with anhedral grains S .1mm in size veinlets .2 mm wide, Quartz anhedral 5.4 mm in size locally fibrous low temperature Chalcedony normally in clusters spatially associate with Tourmaline overprint, Quartz + Tourmaline alteration overprints Andesite completely possibly two events of Tourmaline first is course-grained stockwork and later is very fine-grained Tourmaline, late Hematite veinlets .25 mm wide cut Tourmaline overprint and latest or coevel with Hematite veinlets; Tourmaline veinlets .15 mm wide cut Hematite veinlets, also Hematite/ Tourmaline veinlets. CNS 05A: Andesite, Phenocrysts: Plagioclase .4-.8 mm in size sub-anhedral moderatelystrongly altered to Sericite ± Clays? locally only weakly altered, Quartz clusters interlocking anhedral grains and veinlets .4-.6 mm wide vein with .4-.2 mm grain size, Groundmass: anhedral Quartz 50 µm and subhedral Plagioclase 50 µm all interlocking and intergrown, Magnetite trace locally altered to Hematite, Epidote? anhedral blocky grains / Chlorite fibrous grains stock-working very fine- grained veining 1.2-.4 mm wide, some Actinolite altered to Chlorite, Tourmaline ± Rutile + Jarosite. CNS 06: Quartz 95 % anhedral between 80 µm .2 mm locally .4 mm, Magnetite trace altered to Hematite and Goethite associated with veining only, Tourmaline locally zoned
< .2 mm- .4 mm anhedral to subhedral/ ± Chlorite/ Sericite anhedral fine-gained/ Tourmaline?/ ± Jarosite? / ± Rutile trace anhedral fine-grained stock-worked veining up to 1 mm wide. CNS 06A: Andesite, 25 % phenocrysts: Plagioclase 100 % anhedral to subhedral 1.2 mm in size weakly to strongly altered to Clays ± Sericite, 75 groundmass: Plagioclase 80 % 5 50 pm in size anhedral to subhedral laths and interlocking grains, Actinolite 18 % anhedral fibrous grains average size 50 pm -.1 mm in size often clotty texture moderately to strongly altered to Chlorite, Tourmaline 2 % locally anhedral 1.6 mm grains, Magnetite 5 % strongly altered to Hematite locally disseminated shard-like bladed habit often associated with late Carbonate/ Calcite/ ± Chlorite/ ± Hematite overprint and discontinuous stockwork veinlets and veins from 50 pm -.8 mm wide, edge of Calcite + Carbonate overprint has colliform texture and Calcite grows in zoned habit with radiating masses also rhomb shaped habit into open space? Associated Quartz 1.5 mm in size, locally clots of Calcite overprint throughout also. CNS 07: Photomicrograph, See Microprobe data, Andesite, Plagioclase phenocrysts .2 mm - 1.6 mm in size often in clusters anhedral to euhedral laths unaltered to weakly altered to Sericite ± Clays, groundmass interlocking anhedral grains of Plagioclase 60 pm, locally interlocking anhedral to subhedral Plagioclase grains 20 pm in size with associated clusters of .25 mm size anhedral Quartz, mosaic Tourmaline? overprint ± Actinolite, Sericite ± Clays ± Chlorite is dominant alteration in stronger altered areas and has a very fine-grained fibrous habit forming stockwork and stringers, clots of Jarosite + Epidote? Associated with Actinolite and Sericite and sulfide/ Quartz veins, Calcite locally also, Magnetite 1 % disseminated and altered to Hematite, late Quartz anhedral .2 mm in size/ Plagioclase/ Calcite/ Pyrite anhedral 1.2 mm in size/ Chalcopyrite vein .4.8 mm wide cut through host, Chalcopyrite and Pyrrhotite included in Pyrite, Gypsum inclusions in Magnetite closely spatially associated with the sulfides. CNS 08: Andesite, 45 % phenocrysts: Plagioclase phenocrysts 100 % moderately altered to Sericite subhedral to euhedral .5-2 mm wide with local reaction rims, 55 % groundmass: Plagioclase 60 %, Scapolite 5 %, Actinolite 10 % locally altered to Chlorite, Tourmaline 20 % anhedral 1.2 mm wide mostly associated with groundmass and cubic to anhedral Magnetite 20 % up to .4 mm in groundmass, trace Sphene. CNS 08 A: Andesite, 40 % phenocrysts: Plagioclase 100 % < 2 mm average size 1.6 mm anhedral to subhedral weakly to strongly altered to Sericite ± Clays, 60 % groundmass: Plagioclase 95 % interlocking anhedral grains average size .1mm locally altered to anhedral clots of Scapolite, Actinolite 5 % anhedral fibrous habit .2-.4 mm moderately altered to Chlorite locally, Tourmaline anhedral to subhedral grains .4mm in size mostly in clusters also stockwork veinlets .16mm wide and also disseminated single grains, late Calcite rind on rock with colliform texture anhedral Calcite overprints host Andesite and Tourmaline, trace Sphene. CNS 08 B: Andesite?, 75 % phenocrysts: Plagioclase 95 % .4-2 mm in length euhedral subhedral laths weak- moderate altered to Sericite ± Scapolite? Trace, Scapolite trace anhedral, Amphiboles 5 % remnant anhedral locally altered to Actinolite, Groundmass 25 %: Plagioclase 78 % anhedral- subhedral grains .4 mm weakly altered to Sericite locally unaltered, Scapolite? 2% anhedral, Chlorite 20 % anhedral fibrous interstitial, slide split in half by Tourmaline vein .2-.4 mm wide anhedral grains .2 mm average
80 pm, on one side clotty and stock-working Tourmaline overgrowth anhedral grains .2 mm in size on other side of vein, Carbonate? ± Goethite overgrowth cant tell if Carbonate and Goethite overgrowth is earlier or later than Tourmaline and Magnetite, Chlorite associated with Carbonate and Magnetite only on Tourmaline side anhedral to euhedral cubic .2-.4 mm in size no Chlorite or Carbonate ± Goethite, late Calcite ± Quartz trace veinlet - .2mm wide cuts Tourmaline vein. CNS 09: Andesite, 60 % phenocrysts: Plagioclase 100 % euhedral to anhedral Albite twinned weakly to moderately altered to Sericite ± Clays ± Scapolite (Micheal Levy method on Plagioclase 10o 9°, 100, 40 % groundmass: Plagioclase 60 % anhedral interlocking moderately altered, Actinolite 40 % anhedral fibrous habit moderately to strongly altered to Chlorite, Magnetite 3 % 50 pm -.4 mm in size disseminated clots anhedral to euhedral cubic grains mostly associated with groundmass, anhedral clots of Scapolite 1 % probably after Plagioclase, Tourmaline 5 % anhedral to subhedral grains disseminated and in clusters .2 mm in size locally up to .4 mm and local discontinuous veinlets up to .2 mm wide. CNS 09 A: Photomicrograph, See Microprobe Data, probably Andesite, Phenocrysts: Plagioclase 100 % anhedral 2mm long moderately- strongly altered to Sericite ± Scapolite and possible Carbonate, Groundmass: Plagioclase 75 % 30 pm wide, Tourmaline 25 % disseminated anhedral aggregates - average .2mm wide, Biotite? 2% anhedral, Actinolite 5 % interstitial locally altered to Chlorite, Epidote trace, Magnetite 3 % disseminated anhedral with weak-moderate altered to Hematite along cleavage and mottled. CNS 10: Strongly altered Andesite, 20 % phenocrysts: Plagioclase 100 % anhedral very strongly altered to Sericite ± other Clays ± Scapolite, 80 % groundmass: Plagioclase 80 % interlocking anhedral grains moderately altered to Scapolite ± Clays, Actinolite 10 % anhedral fibrous majority strongly altered to Chlorite, Scapolite 10% probably after Plagioclase in clusters and anhedral grains, Magnetite 10 % disseminated anhedral clots up to .4 mm and single grains -50 pm, local clusters of anhedral Quartz 70 mm in size, very strong Tourmaline overprint disseminated anhedral fibrous aggregates to euhedral prismatic columnar habit spatially associated with groundmass mostly, local patches of Calcite locally after Plagioclase, late Quartz anhedral/ Tourmaline anhedral fibrous veins -50 pm wide cut Andesite host. CNS 11: Andesite or Diorite Porphyry?, 20 % phenocrysts: Plagioclase 95 % subhedral to anhedral most between 4-8 mm long moderately to strongly altered to Epidote + Sericite ± Scapolite ± other Clays and Chlorite, Epidote after Plagioclase anhedral to subhedral 1.6mm, Sericite after Plagioclase fibrous habit, Amphibole? 5 % twinned up to .8 mm altered to Actinolite, 80 % groundmass: Plagioclase 60 % anhedral interlocking grains .15 mm in size moderately altered to Sericite ± other Clays, Actinolite 40 % anhedral fibrous mostly moderately to strongly altered to Chlorite, local Sphene 5 % anhedral clots and grains, Magnetite 10 % anhedral clots to euhedral cubic grains from 10 pm -.6 mm in size usually associated with groundmass, local clots of Chlorite radial fibrous masses. CNS 12: Andesite, Phenocrysts 50 %: Plagioclase 100 % anhedral- euhedral .2-1.2 mm in size unaltered to weakly altered to Sericite ± Scapolite?, Groundmass 50 %: Plagioclase 100 % anhedral grains completely intergrown average size 10 pm no obvious
alteration possibly secondary? Albite, Tourmaline overgrowth dotty and stock-working veining most in radiating habit, some grains anhedral- euhedral habit .2 mm locally, Magnetite strongly altered to Hematite associated most often with Tourmaline and disseminated light dusting and interstitial to Tourmaline. CNS 12 A: Andesite, 25 % phenocrysts: Plagioclase 100 % anhedral to euhedral .2- lmm in size weakly to moderately altered to Sericite ± other Clays locally found in clusters, 75 % groundmass: Plagioclase .4 mm euhedral to anhedral unaltered to moderately altered to Sericite ± Clays clots, Tourmaline disseminated clusters stringers stockworked and massive habit with grain sizes from .2 mm to 6+ mm in size euhedral to anhedral in irregular masses and in radiating masses, Magnetite 3 % disseminated altered strongly to Hematite anhedral grains .4mm in size, stringers of Goethite ± Hematite 50 IAM wide cut Andesite, latest Calcite// Goethite (801.1m // 15 ) veinlets cut Fe-Oxide veinlets. CNS 12 B: Andesite, Phenocrysts: Plagioclase 100 % anhedral euhedral 1 mm average size .6mm mostly moderately-strongly altered to Clay? ± Carbonate?, Groundmass: Plagioclase 100 % anhedral interlocking possibly slightly altered to Scapolite very difficult to see with strong Tourmaline overgrowth and seems groundmass has grown together solid, Tourmaline anhedral and Magnetite overgrowth 80 % of host mostly confined to smaller grain size groundmass and less in Plagioclase phenocrysts locally sub-trachytic texture, Magnetite anhedral habit 30-50 CNS 13: Andesite, 10 % phenocrysts: Plagioclase 100% .8-4 m in size locally unaltered mostly moderately to strongly altered to Chlorite maybe after Scapolite ± other Clays Sericite Calcite and trace Epidote, ML method on Plagioclase phenocrysts 13°, 14°, 15°, 15° indicate a Plagioclase from high temperature Ab 70/An 30, 90 % groundmass: Plagioclase 80 % anhedral to euhedral laths unaltered to moderately altered to Scapolite locally .8mm in size, Actinolite 20 % strongly altered to Chlorite anhedral grains fibrous S .4mm in size, local Calcite overprint. CNS 13 A: Photomicrograph, Diorite or Andesite? Relatively equigranular but has Plagioclase phenocrysts, Phenocrysts: Plagioclase locally up to 5mm long by 1.5 mm wide normally 1.5mm in size sub-anhedral moderately-strongly altered to Epidote .25 mm Calcite anhedral .25 mm clots ± Sericite ± Scapolite, Actinolite .2 mm anhedral fibrous strongly altered to Chlorite ± Tremolite?, local possible altered Pyroxene 7 % twinned 1.75 mm in size, Magnetite 4 % disseminated 40 pm local chunks up to .2mm locally altered to blood red Hematite. CNS 13 B: Andesite- Diorite?, Phenocrysts: Plagioclase locally up to 4-5 mm long strongly altered to Epidote subhedral habit, rest of phenocrysts subhedral to euhedral .51.5 mm in length generally unaltered or very weakly altered to Sericite ± Clays? hard to distinguish groundmass from smaller phenocrysts, Groundmass: Plagioclase unaltered anhedral to euhedral, Chlorite 25 % interstitial to Plagioclase groundmass, Sphene 2-3 % anhedral grains, Sphene and Chlorite may be associated and are spatially close, Magnetite 4 % anhedral to euhedral cubic habit .1- 10 µm in size locally altered to Hematite especially on grain boundaries.
CNS 14: See Geochemistry, Quartz intergrown and interlocking average size .2 mm anhedral very few ratty Fluid inclusions sometimes in clusters of larger grain size, mosaic overprint of stock-working veining Tourmaline average size of grain .1-.2 mm columnar prismatic & fibrous radiating light rusty brown/green subhedral- euhedral Jarosite and Goethite filling vugs. CNS 15: Andesite, 10 % phenocrysts: Plagioclase 100 % .4-2 mm long and wide anhedral to subhedral weakly to moderately altered to Sericite, 90 % groundmass: Plagioclase 70 % euhedral to subhedral .2-.8 mm in size unaltered to moderately altered to Sericite + Clays, Actinolite 30 % strongly altered to Chlorite throughout some pockets of strong Chlorite alteration, Magnetite 3 % altered to Hematite (specular) bladed habit and in anhedral clots, Jarosite 2-3 % in clusters in vugs after sulfide. CNS 16: Hematite + Goethite + Jarosite breccia.
Petrography done in transmitted and reflected light on a Nikon AFX-DX microscope. Red colored sample numbers indicate staining for K-feldspar. See Appendix A2.1 for Thin Section Scans; See Appendix A3.1 for Photomicrographs; See Appendix B1.1.1-B2.11.1for Microprobe Analysis; See Appendix C1.1-C3.3.2 for Whole Rock Geochemistry Analysis; See Appendix D1.1 for Sulfur Isotope Analysis; See Appendix E3.1 for field photographs; See Abanderada pit bench maps @ 1:1000 and Cerro Negro Norte District maps @ 1:10,000 scale.
CNR 21A X CNR 22 X CNR 24 CNR 24A CNR 25 X CNR 26 CNR 26A CNR 27 CNR 28 CNR 29 X CNR 30 X CNR 31 CNR 31 A CNR 32 A
X X X X
CNR 01 CNR 01A
X X X X X X X X X X X X
T Sec poll
CNS 01 CNS 01A CNS 02 CNS 03 CNS 03 A-1 CNS 03 A-2 CNS 03 B-1 CNS 03 B-2 CNS 04 CNS 05 CNS 05A CNS 06 CNS 06A CNS 07 CNS 08 CNS 08 A CNS 08 B CNS 09 CNS 09 A CNS 10 CNS 11 CNS 12 CNS 12 A CNS 12 B CNS 13 CNS 13 A CNS 13 B CNS 14 CNS 15 CNS 15 A
Total: 242 samples
X X X X X
X X X X X
101 Polished 141 Thin Sec
X X X X X X
X X X X X X X X X X X X X
X X X
APPENDIX A2.1 Thin Section Scans (See CD ROM for Computer scans) See Appendix A1.1 for Thin Section Sample Descriptions; See Appendices B1.1.1 B2.11.1 for Microprobe Analysis; See Appendices C1.1-C2.1 for Whole Rock Geochemistry Analysis; See Appendix D1.1 for Sulfur Isotope Analysis. See Abanderada pit bench maps @ 1:1000 and Cerro Negro Norte District maps @ 1:10,000 scale.
Scale: All photos are scans of -2.25cm wide X -6.5cm long thin sections. Crosscutting vein relationships are illustrated on Scans.
1) CNN 1-1LS: See Appendix A1.1 for Thin Section Descriptions 2) CNN 37LS: See Appendix A1.1 for Thin Section Descriptions 3) CNN 38LS: See Appendix A1.1 for Thin Section Descriptions 4) CNN 39-1LS: See Appendix A1.1 for Thin Section Descriptions 5) CNN 39-2LS: See Appendix A1.1 for Thin Section Descriptions 6) CNN 41LS: See Appendix A1.1 for Thin Section Descriptions 7) CNN 43LS: See Appendix A1.1 for Thin Section Descriptions 8) CNN 44LS: See Appendix A1.1 for Thin Section Descriptions 9) CNN 45LS: See Appendix A1.1 for Thin Section Descriptions 10) CNN 46ALS: See Appendix A1.1 for Thin Section Descriptions 11) CNN 46BLS: See Appendix A1.1 for Thin Section Descriptions 12) CNN 47LS: See Appendix A1.1 for Thin Section Descriptions 13) CNN 48-1LS: See Appendix A1.1 for Thin Section Descriptions 14) CNN 48-2LS: See Appendix A1.1 for Thin Section Descriptions 15) CNN 5OLS: See Appendix A1.1 for Thin Section Descriptions 16) CNN 51LS: See Appendix A1.1 for Thin Section Descriptions 17) CNN 52LS: See Appendix A1.1 for Thin Section Descriptions 18) CNN 53-1LS: See Appendix A1.1 for Thin Section Descriptions 19) CNN 65LS: See Appendix A1.1 for Thin Section Descriptions 20) CNN 66-3LS: See Appendix A1.1 for Thin Section Descriptions 21) CNN 68LS: See Appendix A1.1 for Thin Section Descriptions 22) CNN 84ALS: See Appendix A1.1 for Thin Section Descriptions 23) CNN 79LS: See Appendix A1.1 for Thin Section Descriptions 24) CNN 82LS: See Appendix A1.1 for Thin Section Descriptions 25) CNN 103-1LS: See Appendix A1.1 for Thin Section Descriptions 26) CNN 105LS: See Appendix A1.1 for Thin Section Descriptions 27) CNN 119LS: See Appendix A1.1 for Thin Section Descriptions 28) CNN 119ALS: See Appendix A1.1 for Thin Section Descriptions 29) CNN 120ALS: See Appendix A1.1 for Thin Section Descriptions 30) CNR 2ALS: See Appendix A1.1 for Thin Section Descriptions
APPENDIX A3.1 Photomicrographs (See CD ROM for Photomicrographs) See Appendix A1.1 for Thin Section Sample Descriptions; See Appendices B1.1.1B2.11.1 for Microprobe Analysis; See Appendices C1.1-C2.1 for Whole Rock Geochemistry Analysis; See Appendix D1.1 for Sulfur Isotope Analysis. See Abanderada pit bench maps @ 1:1000 and Cerro Negro Norte District maps @ 1:10,000 scale. Scale (photo width): 2.5X 4.8mm; 10X 1.2mm; 20X .6mm; 40X .3mm. 1) CNN 1A: (10X) 50% Reflected and 50% Transmitted light, X-polar Plag altered to cal/act/ ± chl/py vein cuts mt, mt .4 mm 2) CNN 1B-1: (2.5X) 50% Reflected and 50% Transmitted light, X-polar Scap/act vein 4 mm wide, pyrite in scap/plag/act vein. 3) CNN 1B-2: (2.5X) 50% Reflected and 50% Transmitted light, X-polar Scap/ ± act vein 1.2 mm wide cuts act vein. 4) CNN 3: (10X) 100% Transmitted light, X-polar Plag phenocryst altered .8 mm wide. 5) CNN 3: (2.5X) 100% Transmitted light, X-polar Pxn 1.6 mm wide altered to act, plag altered to cal ± Na plag ± ser. 6) CNN 8: (10X) 100% Transmitted light, X-polar Barite cut by qtz/hm vein, large qtz crystal .1 mm long. 7) CNN 12-1: (2.5X) 100% Transmitted light, X-polar Act altered to chl, scap, pyritohedron, rounded scap grain 1 mm. 8) CNN 14: (2.5X) 100% Transmitted light, X-polar Carbonate veined hm, width of hm ' .8 mm wide. 9) CNN 22: (2.5X), 50% Reflected and 50% Transmitted light, X-polar Py vein 1 mm wide cuts mag replaced host and earlier qtz?/scap vein. 10) CNN 24: (2.5X), 50% Reflected and 50% Transmitted light, X-polar Act vein 1 6 mm wide cuts mag, cp ± cov? after mag. 11) CNN 27-1: (10X), 50% Reflected and 50% Transmitted light, X-polar Qtz /cal/py / /chalcedony vein re-opens earlier act vein in mag host, py .5 mm wide. 12) CNN 28: (10X), 100% Transmitted light, X-polar Qtz w flincs/plag altered to sericite vein cuts mag, .1 mm wide plag (remnant). 13) CNN 31: (2.5X), 50% Reflected and 50% Transmitted light, X-polar Cal/qz/py vein cuts mag replaced scap + act host, py grain 1 mm wide. 14) CNN 36A: (20X), 100% Reflected light, X-polar Cp + pyr inclusion in pyrite. 15) CNN 36A: (10X), 50% Reflected and 50% Transmitted light, X-polar Chloroapatite + mt, cp with cv alteration .25 mm long. 16) CNN 46: (2.5X), 100% Transmitted light, X-polar Cp/py/tm/qtz vein, qtz vein ' 1.5 mm long. 17) CNN 46: (10X), 100% Transmitted light, X-polar K-spar, tm, qtz, K-spar carlsbad twin .3 mm wide 18) CNN 47: (2.5X), 100% Transmitted light, X-polar Act vein cut mt and cut by plag vein altered to ser + cal ± scap. 19) CNN 47: (2.5X), 100% Transmitted light, X-polar Act vein ' .1mm wide cut by qtz/py/plag vein. 20) CNN 48A: (10X), 50% Reflected and 50% Transmitted light, X-polar Pyrite grain included by act altered to chl, .8 mm pyrite grain. 21) CNN 48A: (2.5X), 50% Reflected and 50% Transmitted light, X-polar Py, hm, chl, act , amph andesite.
22) CNN 53: (10X), 50% Reflected and 50% Transmitted light, X-polar Mt breccia cemented by py + tm ± cal, cal vein .15 mm wide. 23) CNN 53-3: (20X), 100% Transmitted light, X-polar Tm overprint of plag phenocryst altered to Na-plag. 24) CNN 54A: (10X), 100% Transmitted light, X-polar Cpx and plag weakly altered to Na-plag + albite?± ser. 25) CNN 54A: (2.5X), 100% Transmitted light, X-polar Px altered to act, plag phenocryst 1 mm wide altered to Na-plag. 26) CNN 66-2: (10X), 100% Transmitted light, X-polar Qtz/chl/tm cuts cal altered plag host, chl in middle of photo .1 mm wide. 27) CNN 75: (40X), 100% Transmitted light, X-polar Plag strongly altered to ser ± clay with hm/goe/qtz veinlets 75 pm. 28) CNN 76A: (40X), 100% Transmitted light, Plain-light Fluid inclusion 10 µm in qtz with halite crystal and hm flakes, tm 29) CNN 76B: (10X), 100% Transmitted light, X-polar Plag phenocryst 1mm wide altered to ept, ser ± alb - Na-plag, cal overprint 30) CNN 91A: (10X), 100% Transmitted light, X-polar Plag phenocryst rim altered to alb ± ept cores, amph altered to act, act altered to chl. 31) CNN 92: (2.5X), 100% Transmitted light, X-polar Andesite, plag rims altered to Na-plag, px 1 mm wide. 32) CNN 103-3: (2.5X), 100% Transmitted light, X-polar Porphyry granodiorite to qtz diorite, plag 2 mm long. 33) CNN 108: (2.5X), 100% Transmitted light, X-polar Granodiorite, plag phenocryst 1.2 mm long. 34) CNN 108: (2.5X), 100% Transmitted light, X-polar Granodiorite-andesite contact. 35) CNN 114: (10X), 100% Transmitted light, X-polar Scap vein cuts act altered diorite?, titanite .25 mm long associated with scap. 36) CNN 117: (10X), 100% Transmitted light, X-polar Mylonite, act after pxn, scap after plag, cut by late qtz?/scap left lateral offset. 37) CNR 2B: (2.5X), 100% Transmitted light, X-polar Scap/ti .3 mm wide cuts act altered host. 38) CNR 3: (10X), 100% Transmitted light, X-polar Tm-qtz altered, late tm/qtz/hm veins cut by qtz/chl/cal/Cu-carb//qtz veins. 39) CNR 4: (10X), 50% Reflected and 50% Transmitted light, X-polar Hm breccia cemented with qtz-tm-Cu-carbs, hm frags .5 mm wide. 40) CNR 11: (10X), 100% Transmitted light, X-polar Tm-qtz altered, qtz vein .5 mm wide, qtz/Cu-carb/tm//tm veins cut tm-qtz alteration. 41) CNR 14A: (10X), 100% Transmitted light, X-polar Plag andesite relatively unaltered, Plag phenocryst cut by cal + rut veins 701.1m. 42) CNR 26A: (10X), 100% Transmitted light, X-polar Cal vein .1 mm wide cuts ept (clinozoisite)-cal altered andesite. 43) CNS 7: (40X), 100% Reflected light, X-polar Py with pyr + cp + cov + mag inclusions. 44) CNS 9A: (10X), 100% Transmitted light, X-polar Plag altered to ser ± cal, act altered to chl, qtz intersticial, tm-qtz overprint. 45) CNS 13A: (10X), 100% Transmitted light, X-polar Plag .2 mm wide altered to ser ± ept, act altered to chl ± trem?, mt altered to hm. 46) CNS 15A: (10X), 100% Transmitted light, X-polar Hm breccia with goeth ± jar?/ hm ± tm, qtz veins cut.
APPENDIX B.1.1 Sample Coordinates for Microprobe Scope X
CNN 02 CNN 02 CNN 02 CNN 02 CNN 02
Scapolite Plagioclase Scapolite after Plag Scapolite Plagioclase
Plagioclase Rim Plagioclase Zone Plagioclase Core Plagioclase Zoned Plag Rim Plagioclase Core Calcite altered Plag
CNN 108 CNN 108 CNN 108 CNN 108 CNN 108
Act altered Pxn? Actinolite? Actinolite Plagioclase Rim Plagioclase Core
CNN 114 CNN 114 CNN 114 CNN 114 CNN 114 CNN 114
10.2 10.5 3
3.7 3.7 3.5
10.5 10.8 11.8 12.2
18.7 18.4 18.5 18.2
18.7 17.3 1.4 1.8 1.7 2.7
0.2 18.7 17.3 17.7 18.9
54.6 52.3 52.5 51.5 51
APPENDIX B1.2 List of Elements for Microprobe Mineral Analysis MINERAL Element/L Element #2 Element #a Element Element #5 Element #6 Element #7 Element #8 Element #9 Element #10 Flement #11 Element #12 ElementY1a Element ta4
Scapolite Plagioclase Sericite Chlorite Tourmaline Amphibole Pyroxene Titanite Rutile Apatite Barite Pyrite Chalcopyrite Pyrrhotite Magnetite Hematite Si Ti Al Fe Mn Mg
Ca Na K F
Si Al Fe Mg Ca Na K
Si Ti Al Fe Mn Mg
Si Ti Al
Fe Mn Mg Ca Na
Si Ti Al Fe Mn Mg Ca Na K S CI F
Si Ti Al Fe Mn Mg Ca Na K
Si Ti Al Fe Mn Mg Ca Na K
Si Ti Al Fe Mn Mg Ca
Si Ti Al Fe Mn Mg
Ce Sm Yb U
Ce Sm Yb U
Sr Na P S CI F
Al Fe Mn Mg Ca
Sr Pb Ba S K
Fe Co Cu Zn Mo Aq Pb
Fe Co Cu Zn
Co Cu Zn
Mo Aq Pb
Mo Aq Pb
Th U _.
Si S Fe
Si Ti Al.
Si Ti Al.
Fe Mn Mg Zn Ca
Fe Mn Mg Zn Ca
§§§§§§§g 666.666doidV gg
§§§§§§Wa dde6ddcidc,i6V gg
r§§§§§inl 000.0.4 Nr
0) de1 ddtdciNd12 gg
Wg5§§12F2g gE 4.4. 666666dc46;
ingnEFIFI ,0(10000N0,1 00001.. N
c.i'§§g§§Mg4 ciddcd 6-Egq
AWg§n-W1 ri§§§ docid
8.888G,_,862; 26d66666,66d Op d
88888Sto-R,Tv;8; ciddcidoicird6686: 6
...§:i§§§W'a nEil ,^:88238°,2,1Mt: 0 p,.......0,1 .000..200.0-0-2 .....'i.
m§§§wq nggg§ deidciddcqdm
Sq:884s',3tgge32; S .6466.6doideidodS
o 5 .-
.134 3Nx 2 E (56. apRImm/32225wiro2
Chlorine vs Fluorine in Scapolite 0.15 0
CNN 02 CNN 12-1 CNN 114 CNR 2B
c 0.10 ._ 0 0.05 LC)
Chlorine wt.% Scattergraph comparing chlorine to fluorine weight percent of scapolite from Cerro Negro Norte. Notice that early paragenetic scapolite has considerably rich chlorine compositions compared to fluorine regardless of spatial association around the deposit.
APEENDDLI12.2 Cerro_Negro Norte Feldspar Microprobe Data Lahti No X Y SIO2 A1202
-8494 28719 Standard 50.73 30.66 0.42 0.15 13.43 3.58
2.330 1.660 0.016 0.010
Number of Ions based on 80 2.964
K Total Cat
2.952 1.059 0.004 0.000 0.024 0.808 0.152 4.999
mol% Ab mol% An mole% Or
81.674 2.662 15.664
82.124 2.480 15.396
Fe Mg Ca Na
2.952 1.058 0.005 0.000 0.025 0.810 0.150 5.000
2.331 1.658 0.014 0.011
2.338 1.656 0.017
0.663 0.320 0.007 5.003
0.653 0.312 0.007 4.993
0.000 0.253 0.729 4.995
0.319 0.007 5.003
82.248 2.488 15.264
32.305 66.997 0.698
32.064 67.226 0.710
32.313 67.008 0.679
25.774 0.000 74.226
0.247 0.743 5.004
2.984 1.024 0.005 0.001
0.000 0.247 0.732 4.993 25.225 0.000 74.775
2.599 1.317 0.005 0.000 0.347 0.895 0.053 5.216
68.629 27.602 3.769
69.159 26.771 4.070
68.150 26.590 5.260
2.602 1.312 0.016 0.001 0.351 0.872
0.015 0.000 0.341 0.873 0.067 5.209
1.293 0.020 0.001 0.327 0.902
1.267 0.002 0.003 0.296 0.893 0.039 5.166
0.044 5.207 70.871
72.727 24.137 3.136
2.768 1.233 0.004 0.000 0.226 0.761
2.640 1.365 0.008 0.000 0.351 0.621
76.302 22.655 1.043
63.306 35.807 0.887
CNN78. Area 1.1 CNN78. Area 1,2 C N N78. Area 1.3 CNN78. Area 1.4 CNN78. Area 1.5 CNN78. Area 1.6 CNN78. Area 1.7 CNN78. Area 1.8 CNN78. Area 1.9 C N N78. Area 1.1Q CNN78. Area 1.11 CNN78. Area 1.12 CNN78. Area 1.1Q 10
-10959 18242 Na Plag (rim) 62.84 23.74 0.10 0.00 4.78
Plot of Na/(Na+Ca) vesus C1/(Cl+F) in amphiboles from Cerro Negro Norte. Trends seem to be generally similar between samples, but may vary slightly between points in various samples or various points on same grain. Sample CNN 54A is an unaltered andesite sample.
APPENDIX B2.4 Cerro Negro Norte Pyroxene Microprobe Data Label No X Y
Variation plots comparing Fe number to major oxides of Ti, Na. Ca. and Al. CNN 36 is a massive magnetite replaced andesite and CNN 54A is a relatively unaltered andesite. Both samples are from the Abanderada Sector. See Geochemical data for CNN 54A.
APPENDIX B2.5 Cerro Negro Norte Apatite Microprobe Data Label No X Y MgO CaO SrO Na2O P2O5
Note: Elements and compounds colored RED were analized by a TOTAL DIGESTION ICP method, elements colored BLUE were method. anallzed by a FUSION ICP method, and elements colored 81 ORANGE were analzed by a