The Southwest Zone breccia-centered silica-undersaturated alkalic porphyry Cu-Au deposit ...

181 Pages·2009·7.04 MB·English

The Southwest Zone breccia-centered silica-undersaturated
alkalic porphyry Cu-Au deposit, Galore Creek, B.C:
Magmatic-hydrothermal evolution and zonation, and a
hydrothermal biotite perspective
by
Kevin Byrne
BA. (Hons.) Mod Geology, Trinity College, Dublin, 2004
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR
THE DEGREE OF
MASTER OF SCIENCE
in
THE FACULTY OF GRADUATE STUDIES
(Geological Sciences)
THE UNIVERSITY OF BRITISH COLUMBIA
(Vancouver)
April, 2009
© Kevin Byrne 2009
ABSTRACT
Situated in northwest B.C Canada, the Southwest Zone Cu-Au breccia-centered
deposit is one oftwelve mineralized centers in the Galore Creek alkalic porphyry district.
Formed in an island arc-setting outboard ofancestral North America in the lateTriassic,
deposits inthe Galore Creek district have a combined measured and indicated resource of
785.7 Mt at 0.52 per cent Cu, 0.29 g/t Au and 4.87g/t Ag. Mineralisation in the
Southwest Zone is centered in narrowhydrothermally cementedbreccias.
Composite dikes of megacrystic orthoclase-phyric syenite and megacrystic
orthoclase and plagioclase-phyric monzonite are cut by polylithic, poorly sorted pebble-
cobble clast size matrix-rich breccias. Hydrothermally cemented breccias, characterised
by the cement (infill) assemblage phlogopite ± K-feldspar ± magnetite ± anhydrite ±
diopside ± suiphide, overprint the western contact between matrix-bearing breccias and
megacrystic porphyries. Coeval with cemented breccia formation, intrusions of biotite
phyric monzodiorite occur at the matrix-bearing breccia-wall rock contact and in the
matrix-bearing breccias. Biotite-phyric monzodiorite and the principal cemented breccia
domains are co-spatial and syn-Cu-Au.
Drilling has outlined a zone of >0.3% hypogene Cu approximately 20-lOOm
thick, 500m wide and 400m in length that strikes l0O, dips 45-60°S, and has a semi-
ellipsoidal morphology. This mineralisation is coincident with potassic (stage D)
alteration and infill. Cu-poor, diopside-dominated (calc-[potassic]) alteration formed
contemporaneously with, and locally flanks, potassic-D infill. Sulphide minerals are
zoned from a core ofchalcopyrite-bomite, to chalcopyrite>pyrite, to pyrite>chalcopyrite
out to pyrite only. Garnet-bearing peripheral propylitic alteration overlaps with a pyrite
and Au-halo and locally overprints potassic and calc-Q,otassic) assemblages.
Based on electron microprobe analysis, systematic spatial variations in Ti-content
and F3/2Fee of infill biotite are evident. Increases in Ti-contents and F372F1ee overlap
with positive gradients in Cu concentration, taken with interpreted alteration reactions,
this suggest Cu-deposition is caused by decreasing102 coupled with an increase in pH at
420-475°C. Low l2Oo/gJHQFH), determined from infill biotite, distinguish potassic
fluids in the Southwest Zone, and other alkalic porphyry deposits, from fluids in calc
alkalic systems and reflects the contrasting magmatic composition.
11
TABLE OF CONTENTS
ABSTRACT I
.
TABLE OF CONTENTS iii
LIST OF TABLES vi
LIST OF FIGURES vii
ACKNOWLEDGMENTS xi
CHAPTER 1: OVERVIEW I
1.1 Rationale for Study I
1.2 Thesis organization 2
1.3 Regional Geological Setting 3
1.4 Galore Creek District 5
1.4.1 Geography 5
1.4.2 Exploration History 5
1.4.3 SupracrustalRocks 5
1.4.4 Igneous Rocks 8
1.4.5 HydrothermallyAlteredandMineralized Centers 11
1.4.6 StructuralHistory 11
1.4.7 SouthwestZone 12
1.5 Breccias 15
1.5.1 Approach andNomenclature 15
1.5.2 Fragmentation MechanismsandBreccia Classification 15
1.5.3 PrincipalBreccia Fades Characteristics 17
1.6 Biotite 22
1.6.1 Crystal-chemistry 22
1.6.2 Normalization Schemes forMicroprobe Data 24
1.6.3 Mechanisms ofTi AlandFe3+ Incorporation 25
1.7 Biotite in the Porphyry Environment 27
1.7.1 Example Studies 27
1.7.2 Geothermometry 29
1.7.3 Oxygen FugacityEstimates 31
1.7.4 Halogen and WaterFugacityEstimates 31
1.8 Research Objectives 32
1.9 Study Methodology 33
1.10 References 35
111
CHAPTER 2: MAGMATIC-HYDROTHERMAL EVOLUTION AND ZONATION
OF A BRECCIA CENTERED CU-AU ALKALIC PORPHYRY: SOUTHWEST
ZONE, GALORE CREEK 43
2.1 Introduction 43
2.2 Exploration History 46
2.3 Regional Geological Setting 46
2.4 District Geology 47
2.5 Rock types of the SouthwestZone 51
2.5.1 Coherentrocks 52
2.5.2 Clastic rocks 60
2.5.3 Rockparagenesis 67
2.6 Structural controls on rock distribution 68
2.7 Alteration 69
2.7.1 K-feldspar± biotite ± hematite dusting(potassic-A and-B)-Stage-1 70
2.7.2 Phlogopite ± chlorite ± magnetite (potassic-C)-Stage-1 70
2.7.3 Phlogopite ± magnetite ± K-feldspar(potassic-D)-Stage-2 70
2.7.4 Diopside ± magnetite ±phiogopite (calcic-fpotassicD-Stage-2 72
2.7.5 K-feldspar-anhydrite (waningpotassic)-Stage-2 76
2.7.6 Sericite ± anhydrite (phyllic)-Stage-3 76
2.7.7 Garnet± chlorite (calcic)-Stage-3 77
2.7.8 Chlorite ± epidote ± calcite ±pyrite (propyiltic)-Stage-4 79
2.7.9 K-feldspar± Fe-carbonate (carbonate-potassic)-Stage-4 80
2.7.10 Quartz (quartz veins)-Stage-4 81
2.8 Sulphide minerals 82
2.8.1 Potassic-D and calcic-fpotassicJ-Stage-2 82
2.8.2 Late-stage K-feldspar± Fe-carbonate-Stage-4 84
2.9 Structural controls on alteration and mineralisation 84
2.9.1 Pre tosyn Stage 2 and3 84
2.9.2 Post-Stage 2 and3 85
2.10 Oxygen and hydrogen isotope data 86
2.11 Metals Zoning 88
2.11.1 Copper, Goldand Silver 88
2.11.2 LeadandZinc 90
2.11.3 Molybdenum 91
2.12 Discussion and Genetic Interpretation 92
2.12.1 Clastic rocks 92
2.12.2 Isotopic composition ofhydrothermalfluids 95
2.12.3 Alteration zoning (Stages 2 and3) 98
2.12.4 Metaltransport, deposition andzoning 103
2.12.5 Palaeo-geometryanddepositmodel 111
2.13 Conclusions 116
iv
2.14 References .118
CHAPTER 3: COMPOSITION OF BIOTITE FROM THE SOUTHWEST ZONE
ALKALIC PORPHYRY CU-AU DEPOSIT, GALORE CREEK, BC, CANADA:
EVALUATION OF HYDROTHERMAL FLUID CHEMISTRY 124
3.1 Introduction 124
3.2 Geological framework 126
Regional: 126
District: 127
Deposit: 129
3.3 Biotite types classification 131
3.4 Analytical procedures and sample methodology 137
3.5 Normalization of microprobe data and estimation of F3e 139
3.6 Biotite composition by type 142
3.7 Spatial variation in Ti and F3e 145
3.8 Biotite halogen chemistry 150
3.9 Hydrothermal fluid halogen fugacity ratio estimates 153
3.10 Comparison offugacity ratios with other porphyry systems 155
3.11 Discussion 158
3.11.1 Significance ofgradients in infilbiotite chemistry 158
3.11.2 Halogen chemistry 160
3.12 Conclusions 161
3.13 References 162
CHAPTER 4: CONCLUSIONS 167
4.1 Recommendations for future work (and other conjectures) 168
4.2 References 170
APPENDICIES A-D on disc I in sleeve and is also available at
http:llwww.mdru.ubc.ca
V
LIST OF TABLES
TABLE 1.1 Summary of Galore Creek intrusive rocks (Enns, et. al., 1995) 10
TABLE 1.2 Average conserved element ratios from Galore Creek intrusive rocks (Enns, et. al.,
1995) 10
TABLE 1.3 Genetic classes and associated fragmentation processes, adapted from Sillitoe
(1985), Davies (2002) and Davies et al (2008b) 20
TABLE 1.4 Common porphyry-system breccia facies and theirdescriptive criteria adapted from
Seedorifet al. 2005, Sillitoe (1985), and Davies (2002) 21
TABLE 1.5 Substitution mechanismsforT4,i A3l and F3e in biotite 26
TABLE 2.1 List ofabbreviations used in figures and tables 45
TABLE 2.2 Summary ofSouthwestZone coherent rocks 53
TABLE 2.3 Summary of Southwest Zone clastic rocks 61
TABLE 2.4 Paragenetic stages of coherentand clastic rocks in the SouthwestZone 67
TABLE 2.5 Stable isotope results for Stage 2 infill phlogopite and phyllic stage sericite 86
TABLE 3.1 Hydrothermal apatite compositions from vein samples in the SouthwestZone 137
TABLE 3.2 Southwest Zone biotite data distribution 138
TABLE 3.3 Substitution mechanismsforT4,i A3l and F3e in biotite 140
TABLE 3.4 Biotite Thomson-space components 141
TABLE 3.5 Representative biotite compositions from the SouthwestZone by textural type 143
TABLE 3.6 Titanium, F3eand F3/e F2evalues for infill biotite 146
vi
LIST OF FIGURES
FIG. 1.1 Map of British Columbia showing the location of the accreted Quesnellia and Stikinia
ocean arc terranes, major alkalic Cu-Au porphyry deposits and alkalic intrusive centers,
morphogeological belts and Galore Creek 4
FIG. 1.2 A. Major tectono-stratigraphic elements and the location of the Galore Creek district,
Eskay Creek, Red Chris, Schaft Creek and Copper Canyon in the Stikinia terrane 6
FIG. 1.3 Simplified geological and alteration-mineralisation map ofthe Galore Creek district 14
FIG. 1.4 Ferromagnesian biotitewith labeled structural sites 23
FIG. 1.5 Biotite composition trends in an idealized porphyry alteration model 29
FIG. 2.1 Map of British Columbia showing the location of the accreted Quesnellia and Stikinia
ocean arc terranes, major alkalic Cu-Au porphyry deposits and alkalic intrusive centers,
morphogeological belts and Galore Creek 44
FIG. 2.2 A. Major tectono-stratigraphic elements and the location of the Galore Creek district,
Eskay Creek, Red Chris, Schaft Creek and Copper Canyon in the Stikinia terrane 47
FIG. 2.3 Simplified geological, and alteration and mineralisation map of the Galore Creek district
illustrating the location of mineralized centers and major structural features 49
FIG. 2.4 Photographs of the Galore Creek valley, looking A south, and B north with labeled
mineralized centers 50
FIG. 2.5 Simplified bedrock geology plan map and Cu-grade distribution in the Southwest Zone.
Location ofsection line A-A’ (6333650N) and B-B’ (350030E) indicated with black lines 52
FIG. 2.6 Sequence ofcoherent and clastic rock emplacement in the Southwest Zone 54
FIG. 2.7 Photographs ofcoherent rocks in the SouthwestZone 56
FIG. 2.8 Distribution of clastic facies and simplified coherent units along cross section 6333650N,
line A-A’ 57
FIG. 2.9 Distribution of clastic facies and simplified coherent units along cross section 350030E
along line B-B’ 58
FIG. 2.10 Photographs ofdiagnostic features in biotite-phyric monzodiorite dike and dikelet facies
59
FIG. 2.11 Photographs ofdiagnosticfeatures in matrix-bearing breccias 63
FIG. 2.12 Photographs of cemented breccia facies in the Southwest Zone: MC-BX and CM-BX
65
FIG. 2.13 Photographs of monolith in-situ cement dominated breccias (C-BX) 66
FIG. 2.14 Post-cemented breccia facies coherent units 68
vii
FIG. 2.15 Paragenetic stages of coherent and clastic rocks, and alteration and mineralisation
facies in the Southwest Zone 69
FIG. 2.16 Photographs of Stage 2 and phyllic alteration and infill 73
FIG. 2.17 Distribution and abundances of potassic-D and calcic-(potassic) and waning potassic
hydrothermal minerals (Stage 1) and the> 0.3% Cu shell along section lines A-A’ and B-B’ 75
FIG. 2.18 Photographs and photomicrographs of Stage 3 and 4 alteration facies and veins 78
FIG. 2.19 Distribution and abundances of Stage 3 calcic and propylitic alteration minerals on
section lines A-A’ and B-B’ 79
FIG. 2.20 Distribution of late-stage carbonate-potassic veins and alteration, hydrothermal quartz
and Au intercepts> 3 g/t along section B-B’ 81
FIG. 2.21 Photomicrographs ofsulphide and oxide mineralisation in the Southwest Zone 82
FIG. 2.22 Pattern of Stage 2 and 3 sulphide mineral distribution along section lines A-A’ and B-B’.
83
FIG. 2.23 Mineral 6018 and 6D values from the Southwest Zone 87
FIG. 2.24 A. Copper grade shells and hydrothermal diopside along sectionsA-A’ and B-B’ 89
FIG. 2.25 A. Lead, > 0.3 % Cu and > 0.1 g/t Au grade shells and distribution of moderately
intense propylitic alteration along sections A-A’ and B-B’ 91
FIG. 2.26 A. Calculated isotopic compositions ofwater in equilibrium with infill phlogopite and, B.
sericite from the Southwest Zone, with fluid compositions associated with potassic and phyllic
alteration in other porphyry systems also shown 96
FIG. 2.27 A-C. Activity-activity diagrams showing stability of silicate minerals at 350°C, 500 bars
pressure, modified from Beane and Titley, (1981) and Beane, (1982) 99
FIG. 2.28 Log pH diagram at 350°C showing solubility contours for Cu and Au and the
f(o2) —
stability fields of minerals in the Cu-Fe-C-System (redrafted and modified from Huston et al.,
1993) 108
FIG. 2.29 Log temperature diagram for solubility ofAu as chloride and bisulfide complexes
f(02) —
in the porphyry Cu environment (redrafted and modified from Huston and Large, 1989 and Jones,
1992) 110
FIG. 2.30 Stylized perspective projections of joined sections A-A’ and B-B’ in approximated
palaeo-geometry (-60° tilt). A. Outline of cemented breccia domains projected beyond current
erosion surfaces. B. Domains of intense potassic-D alteration comprising and calcic-(potassic)
veins and alteration 112
FIG. 2.31 A-E. Time-integrated cartoons illustrating the evolution of the Southwest Zone breccia
complex and paragenesis ofStage 1- early Stage 2 alteration events 113
vii’
FIG. 2.32 Time-integrated alteration and mineralisation schematic in estimated palaeo-geometry.
A. Incipient stage 2 alteration; potassic-D and calcic-(potassic) alteration and infill form
contemporaneously. B. Alteration and Cu distribution at the end of stage 2 and start of stage 3.
Minor phyllic alteration develops in fractures zones at upper levels in the system. C. Distribution
of propylitic alteration facies, Au-halo, and Cu, Zn and Pb contours at the end ofstage 3 114
FIG. 3.1 Map of British Columbia and the Canadian Cordillera showing the location of the
accreted Quesnellia and Stikinia ocean arc terranes, morphogeological belts and Galore Creek
126
FIG. 3.2 Regional scale geology of Galore Creek showing the location of Copper Canyon alkalic
porphyry Cu-Au occurrence 128
FIG. 3.3 Simplified geological map and location of mineralised centers in the Galore Creek
District 129
FIG. 3.4 Simplified geology along cross sections 6333650N (A-A’) and 350030E (B-B’) 131
FIG. 3.5 Photomicrographs least altered igneous and secondary biotite 133
FIG. 3.6 Infill biotite vein in megacrystic orthoclase-phyricsyenites 134
FIG. 3.7 A. Plane light and B. polarized photomicrographs ofone side ofan infill biotite vein... 135
FIG. 3.8 Back scattered electron images of infill biotite 136
FIG. 3.9 XMg versus atoms per formulae unit AI(total), Si, Fe(total) F3Ie F2,e Ti, Cl, XF, Mn, and Ba
for least-altered, secondary and infill biotite in polished thin sections from the Southwest Zone.
142
FIG. 3.10 Compositional variation ofthe clusterof infill biotite grains indicated in figure 3.6A. .145
FIG. 3.11 Ti % (norm) values of infill biotite, distribution of calc-silicate alteration and infill, and Cu
concentrations on cross sections 6333650N (A-A’) and 350030E (B-B’) in the Southwest Zone.
147
FIG. 3.12 F3e I F2e of infill biotite, distribution of calc-silicate alteration and infill, and Cu
concentrations on cross sections 6333650N (A-A’) and 350030E (B-B’) in the Southwest Zone.
148
FIG. 3.13 A. Ti vs. F3Ie F2e and B. Ti vs. Si. All data in atoms per formula unit and normalized
to scheme-B 149
FIG. 3.14 A. XFe versus log (XF/XOH) of infill biotite grains with 4 or more spot analysis per
sample 151
FIG. 3.15 Reliable infill biotite data and the slope ofa line (in red) calculated from equation (24) in
Zhu and Sverjensky (1992) at 420°C 153
fluid
FIG. 3.16 A. XFe versus lo XF/XoH) and calculated log (fH2oIfHF) B. XMg versus log (XFIXCI)
and calculated log (fHFIfHCI) UI of repesentitive infill biotite anlayses 154
FIG. 3.17 A. L2Oo/fgH(fFH) versus l2Oo/fgH(CfHI), and B. log(fHF/fHCl) versus l2Oo/gfH(fCHl)
ratios for potassic fluids in the Southwest Zone. Also shown are the fugacity values determined
forother porphyry Cu systems (Selby and Nesbit, 2000; Twelker, 2007; Kroll et al., 2002) 155
ix
FIG. 3.18 Comparison of secondary and least altered igneous biotite from the Southwest Zone
and from Mo, W and Cu porphyry deposit types, modified after Brimhall and Ague (1988) 157
FIG. 3.19 Log pH diagram at 350°C showing solubility contours for Cu and the stability
f(o2) —
fields of minerals in the Cu-Fe-O-System, modified from Huston et al. (1993) 159
x