the geology and genesis of the central zone alkalic copper-gold porphyry deposit, galore creek ...

387 Pages·2010·12.38 MB·English

by  Janina Micko

THE GEOLOGY AND GENESIS OF THE CENTRAL ZONE
ALKALIC COPPER-GOLD PORPHYRY DEPOSIT,
GALORE CREEK DISTRICT,
NORTHWESTERN BRITISH COLUMBIA, CANADA

by

Janina Micko

MSci, The University of Birmingham, 2005

A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF
THE REQUIREMENTS FOR THE DEGREE OF

DOCTOR OF PHILOSOPHY

in

The Faculty of Graduate Studies

(Geological Sciences)

THE UNIVERSITY OF BRITISH COLUMBIA
(Vancouver)

December, 2010

© Janina Micko, 2010
ABSTRACT
Located in the Late Triassic Galore Creek alkalic Cu-Au porphyry district in
northwestern British Columbia, the Central Zone deposit represents the end-member of the
silica-undersaturated class of alkalic porphyry systems. The deposit is hosted by volcano-
sedimentary rocks of the Middle to Upper Triassic Stuhini Group that were intruded by a
syenite-monzonite complex and hydrothermal breccias. Post-mineral tilt (45 to 60° W-SW)
provides an opportunity to examine a vertically extensive depth range of the system, and the
impact of host rocks and a redox control on the precipitation of sulfide and silicate alteration
minerals.
Early mineralization associated with potassic alteration is dominated by gold-bearing
chalcopyrite + bornite (Cu:Au ~ 2:1). A second gold-poor mineralization event is associated
with calc-potassic alteration and dramatically changes the Cu:Au ratio (5:1) in the core of the
Central Zone. In general, greatest Cu-Au concentrations overlap lithological contacts
characterized by contrasting ferromagnesian mineral content, thus forming redox gradients.
Sulfur isotopic compositions emphasize the importance of fO conditions in ore
2
deposition. Sulfides in highly mineralized centers are characterized by moderately negative
δ34S values (-10.66‰ to -7.84‰), whereas sulfides deposited distally show highly negative
sulfide
δ34S values (-17.13‰ to -4.03‰). These data suggest that the interaction of sulfate-rich
sulfide
(SO 2- ) fluids with varying amounts of Fe2+-bearing minerals in host rocks increased
4 (aq)
H S/SO 2- leading to formation of reduced S, and precipitation of sulfide minerals.
2 4
Trace elements such as V and As in host rocks and Eu2+ in hydrothermal garnet reflect
the same redox influence. Vanadium and As are soluble under highly oxidizing conditions. The

shift in oxidation state facilitates their incorporation in alteration minerals. Thus, highest V
(>700ppm) and As (>40ppm) concentrations form halos distally to the redox gradients and ore
ii
bodies. Hydrothermal garnets near lithologic contacts contain excess Eu2+. In contrast to V and
As, Eu2+ is soluble in reduced fO conditions and precipitates close to the redox gradient.
2
This study demonstrates that redox is the dominant control on ore deposition in the
Central Zone. Recognizing redox changes may provide a valuable guide for future exploration
in the Galore Creek district and perhaps other alkalic Cu-Au porphyry systems worldwide.
iii
PREFACE
This thesis consists of four manuscripts that have been prepared for future publication in
peer-reviewed international journals:
Chapter 2 represent the first manuscript of which I am the lead author. Richard Tosdal,
Claire Chamberlain, and Kirstie Simpson are the co-authors and initiators of the overall research
project. As the lead author, I conducted field work, collected samples, and carried out all
analytical studies. The latter was supported by Mati Raudsepp. In addition, I designed the bulk
of the text, figures, and tables. All three co-authors provided technical advice and suggestions
both in the field and during manuscript preparation. Richard Tosdal and Thomas Bissig, another
member of the research group, contributed to revisions of the manuscript. The reference for the
manuscript will be as follows:

Micko, J., Tosdal, R.M., Chamberlain, C.M., and Simpson, K.A., Lithological description and
interpretation of the host-rocks of the Central Zone deposit, Galore Creek alkalic copper-
gold porphyry district, northwestern British Columbia, Canada.

Chapter 3 has been submitted for a peer-review international journal. I am the lead
author, whereas Richard Tosdal, Thomas Bissig, Claire Chamberlain, and Kirstie Simpson are
the co-authors. As the lead author, I conducted field work, collected samples, and carried out the
dominant portion of analytical studies. The latter was supported by Mati Raudsepp. Richard
Tosdal conducted a geochronological analysis (SHRIMP-RG) of titanite samples, interpreted the
acquired data, and designed the associated text, figure, and table. I produced the remainder and
bulk of the text, figures, and tables. All three co-authors provided technical advice and
suggestions both in the field and during manuscript preparation. Richard Tosdal and Thomas
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Bissig contributed to revisions of the manuscript. The reference for the manuscript will be as
follows:

Micko, J., Tosdal, R.M., Bissig, T., Chamberlain, C.M., and Simpson, K.A., (in review),
Hydrothermal alteration and mineralization of the Central Zone deposit, Galore Creek
alkalic copper-gold porphyry district, northwestern British Columbia, Canada.

Chapter 4 is intended for submission to a peer-reviewed international journal. I am the
lead author, whereas Scott Halley, Richard Tosdal, and Thomas Bissig are the co-authors. As the
first author I aided in design of the overall study and collected the required samples. The
analysis of samples was carried out by two commercial labs, ALS Chemex, Canada, and the
Univeristy of Tasmania, Australia. The study addresses two individual research aspects. I was
responsible for the bulk of the interpretation of S-isotopic data, whereas Scott Halley and
Richard Tosdal supported the interpretation and figure design of the whole rock geochemical
data. I was also responsible for the correlation of the two studies and their results as well as the
bulk of the text, most figures, and tables. All co-authors provided technical advice and
suggestions during manuscript preparation. Richard Tosdal and Thomas Bissig contributed to
revisions of the manuscript. The reference for the manuscript will be as follows:

Micko, J., Halley, S., Tosdal, R.M., and Bissig, T., Whole rock and isotope geochemistry of the
Central Zone deposit, Galore Creek alkalic copper-gold porphyry district, northwestern
British Columbia, Canada: international journal to be determined.

A version of chapter 5 will be submitted for a peer-reviewed international journal. I am
the primary author, whereas Shaun Barker, Greg Dipple, and Adam Kent are the co-authors. I
collected the required samples and conducted most of the analytical research. Mati Raudsepp
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aided in the EMP analysis of samples and Adam Kent supported the LA-ICP-MS study. I was
responsible for much of the interpretation of acquired data; however, I received significant
assistance from Gregory Dipple and Shaun Barker. I designed the bulk of the text, figures, and
tables. All three co-authors provided technical advice and suggestions during manuscript
preparation. Greg Dipple and Shaun Barker contributed to revisions of the manuscript. The
reference for the manuscript will be as follows:

Micko, J., Barker, S.L.L., Dipple, G.M., and Kent, A., Oscillatory zoning in garnets as a record
for hydrothermal system evolution and brecciation in the Central Zone deposit, Galore
Creek alkalic copper-gold porphyry district, northwestern British Columbia, Canada:
Journal to be announced.
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TABLE OF CONTENTS
ABSTRACT……………………………………………………………………………………...ii
PREFACE……………………………………………………………………………………….iv
TABLE OF CONTENTS………………………………………………………………………vii
LIST OF TABLES…………………………………………………………………………….xiii
LIST OF FIGURES…………………………………………………………………………….xv
LIST OF ABBREVIATIONS AND SYMBOLS…………………………………………....xxiv
ACKNOWLEDGMENTS…………………………………………………………………....xxvi
DEDICATION……………………………………………………………………………....xxviii

1 Introduction ........................................................................................................................... 1
1.1 Objectives ........................................................................................................................ 1
1.2 Project background and support ...................................................................................... 1
1.3 District overview ............................................................................................................. 3
1.4 Alkalic porphyry deposits ................................................................................................ 4
1.4.1 Geologic characteristics............................................................................................ 4
1.4.2 The Cadia district ..................................................................................................... 7
1.4.3 Significance for exploration ..................................................................................... 9
1.5 Previous research ........................................................................................................... 10
1.6 Overview of the dissertation .......................................................................................... 12
1.7 References ...................................................................................................................... 14

2 Lithological description and interpretation of the host-rocks of the Central Zone
deposit, Galore Creek alkalic copper-gold porphyry district, northwestern British
Columbia, Canada ...................................................................................................................... 17
vii
2.1 Introduction .................................................................................................................... 17
2.2 Regional geology ........................................................................................................... 20
2.3 District geology ............................................................................................................. 20
2.4 Methodology .................................................................................................................. 22
2.5 Rock units of the Central Zone ...................................................................................... 24
2.5.1 Supracrustal host-rocks .......................................................................................... 24
2.5.2 The Central Zone intrusive complex (CZIC) ......................................................... 33
2.5.3 Breccia complexes .................................................................................................. 38
2.6 Breccia development in the Central Zone ..................................................................... 50
2.6.1 Matrix bearing breccia ............................................................................................ 50
2.6.2 Cement-bearing breccias ........................................................................................ 51
2.6.3 Mechanisms for brecciation in the CZ ................................................................... 52
2.7 Conclusions.................................................................................................................... 53
2.8 References ...................................................................................................................... 54

3 Hydrothermal alteration and mineralization of the Central Zone deposit, Galore
Creek alkalic copper-gold porphyry district, northwestern British Columbia, Canada..... 58
3.1 Introduction .................................................................................................................... 58
3.2 Regional geology and tectonic setting ........................................................................... 62
3.3 District geology ............................................................................................................. 63
3.4 Central Zone geology .................................................................................................... 65
3.4.1 Supracrustal hostrocks ............................................................................................ 67
3.4.2 The Central Zone intrusive complex ...................................................................... 70
3.4.3 Breccias .................................................................................................................. 71
3.5 Hydrothermal alteration ................................................................................................. 73
3.5.1 Hydrothermal paragenesis of the North Gold Lens (NGL) .................................... 74
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3.5.2 Hydrothermal paragenesis of the Central Replacement Zone (CRZ) .................... 85
3.5.3 Hydrothermal paragenesis of the South Gold Lens (SGL) .................................... 91
3.5.4 Summary of the hydrothermal paragenesis ............................................................ 96
3.5.5 Age of Hydrothermal Alteration .......................................................................... 100
3.6 Discussion .................................................................................................................... 104
3.6.1 Tilting of the hydrothermal system ...................................................................... 104
3.6.2 Timing of hydrothermal alteration ....................................................................... 105
3.6.3 Hydrothermal evolution........................................................................................ 107
3.6.4 The Central zone — An end-member alkalic porphyry Cu-Au deposit ............... 114
3.7 The hydrothermal model – a summary ........................................................................ 115
3.8 References .................................................................................................................... 117

4 Whole rock and isotope geochemistry of the Central Zone deposit, Galore Creek
alkalic copper-gold porphyry district, northwestern British Columbia, Canada .............. 123
4.1 Introduction .................................................................................................................. 123
4.2 Geological setting ........................................................................................................ 127
4.3 Central Zone geology .................................................................................................. 128
4.3.1 North Gold Lens - geology ................................................................................... 129
4.3.2 Central Replacement Zone-geology ..................................................................... 134
4.4 Methodology ................................................................................................................ 136
4.5 Sulfur isotope distribution ........................................................................................... 139
4.5.1 North Gold Lens ................................................................................................... 141
4.5.2 Central Replacement Zone ................................................................................... 145
4.5.3 Geothermometric analysis .................................................................................... 149
4.6 Lithogeochemistry ....................................................................................................... 152
4.6.1 Variations in primary igneous chemistry ............................................................. 152
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4.6.2 Variations in immobile elements due to alteration ............................................... 159
4.6.3 Variations in alkali elements due to alteration ..................................................... 163
4.6.4 Pathfinder element distribution ............................................................................ 167
4.7 Discussion .................................................................................................................... 177
4.8 Conclusions and exploration implications ................................................................... 185
4.9 References .................................................................................................................... 188

5 Oscillatory zoning in garnets as a record for hydrothermal system evolution and
brecciation in the Central Zone deposit, Galore Creek alkalic copper-gold porphyry
district, northwestern British Columbia, Canada ................................................................. 195
5.1 Introduction .................................................................................................................. 195
5.2 Regional and local geology ......................................................................................... 198
5.3 Methodology ................................................................................................................ 199
5.4 Mineral stratigraphy ..................................................................................................... 200
5.4.1 Destructive events and marker bands ................................................................... 205
5.4.2 Garnet growth zones ............................................................................................. 208
5.4.3 Petrographic summary and interpretations ........................................................... 211
5.5 Compositional analysis ................................................................................................ 213
5.5.1 EMP analysis ........................................................................................................ 214
5.5.2 LA-ICP-MS analysis ............................................................................................ 217
5.6 Discussion .................................................................................................................... 224
5.7 Conclusions and implication........................................................................................ 227
5.8 References .................................................................................................................... 231

6 Conclusions ........................................................................................................................ 235
6.1 The geology and genesis of the Central Zone deposit ................................................. 235
x