Syenite-hosted gold mineralization and hydrothermal alteration at the Young

188 Pages·2012·15.39 MB·English

Syenite-hosted gold mineralization and
hydrothermal alteration at the Young-
Davidson deposit, Matachewan, Ontario

by

Ryan D. Martin

A thesis
presented to the University of Waterloo
in fulfillment of the
thesis requirement for the degree of
Master of Science
in
Earth Sciences

Waterloo, Ontario, Canada, 2012

© Ryan D. Martin 2012
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AUTHOR'S DECLARATION
I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, including any
required final revisions, as accepted by my examiners.

___________________________, Ryan D. Martin

I understand that my thesis may be made electronically available to the public.

___________________________, Ryan D. Martin

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Abstract
The syenite-hosted Young-Davidson (YD) gold deposit is located at the western extension of the
Cadillac-Larder-Lake deformation zone (CLLDZ), southwest of Kirkland Lake, in the southern
Abitibi greenstone belt, Canada. Gold is predominantly hosted by syenite, and to a lesser extent by
Timiskaming sedimentary rocks and mafic volcanic rocks in veins and/or small pervasively altered
shear zones related to the CLLDZ. Historical gold production was mainly from quartz veins and
disseminated pyrite hosted in altered syenite. Recent drilling by AuRico Gold Corporation (formerly
Northgate Minerals Co.) has expanded the underground resource to 14.6 million tonnes (measured
and indicated) at an average grade of 2.03 g/t Au and an underground reserve of 39.1 million tonnes
(proven and probable) at an average grade of 2.79 g/t Au, where most of the gold is hosted in the
syenite.
Three generations of veins have been identified based on crosscutting relationships mapped at an
underground ore crosscut: V boudinaged iron-carbonate veins, V folded quartz-pyrite veinlets and
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V planar quartz-carbonate veins. Structural characterization of the vein sets indicates that V and V
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extensional vein arrays developed during the D deformation, which generated the steeply dipping
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east-west striking penetrative S foliation that is found elsewhere along the CLLDZ. Petrographic
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analysis of mineralized syenite shows that native gold grains are most abundant in zones of intense
potassic-hematite-pyrite alteration as inclusions and along cracks in vein-related and disseminated
pyrite. Volcanic-hosted gold is mainly located in quartz-iron-carbonate veins hosted in narrow
sheared and pervasively albite-iron-carbonate-pyrite altered volcanic rocks. Whole rock
lithogeochemical analyses and mass balance calculations show that mineralized syenite is
characterized by enrichments in K, S, Na, Ba and W whereas mineralized volcanic rocks are
characterized by strong enrichments in Na, Al, Si, K, Fe, S, Ba and W. Geochemical contouring of
279 analyses of drill core along two N-S sections through the YD syenite show broad cross section
scale correlation of gold mineralization with K O, S and Ba. Sulfur is the most strongly correlated
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with gold mineralization; however, the most intense sulfidation is generally coincident with zones
containing coarse altered feldspars and a fine-grained groundmass of iron-carbonate, Na- and K-
feldspar and minor quartz.
Bulk sulfur isotopic analyses of syenite-hosted pyrite grains indicate that the dominant source of
sulfur is magmatic but there is also a component that has interacted with the reduced Archean
atmosphere. Pyrite grains in syenite and volcanic rocks contain up to 15,000 ppm Co, 4,000 ppm Ni
and 4,200 ppm As. Chemical mapping of Co, Ni and As from different vein associated pyrite grains
show: 1) Arsenic in pyrite is low, <1,000 ppm; 2) Pyrite shows Co-Ni zoning and gold in V vein
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pyrite is associated with Co-Ni rich pyrite overgrowths of earlier corroded pyrite grains; 3) gold along
fractures in V vein pyrite is also associated with Co-Ni enrichment; and 4) gold in V veins crosscuts
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Co-Ni patterns in pyrite, which suggests that the V style of mineralization has precipitated by
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different mechanisms. Pyrite mapping combined with alteration assemblages, mineralization
characteristics and mineral chemistry suggests that the syenite-hosted mineralization has formed from
interaction between multiple fluids with distinct physicochemical conditions. The proposed
formational model for the Young-Davidson deposit is of fluid mixing between magmatic and
metamorphic fluids during the deformation events that generated the extensive veining systems at
Young-Davidson.

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Acknowledgements
AuRico Gold Corporation provided logistical and financial support throughout this study. This study
has also been funded by the NSERC grant of Robert Linnen. The support from AuRico Gold
Corporation during many field seasons was vital to the completion of this thesis.
This work would not have been possible if not for my supervisor, Dr. Robert L. Linnen. Through
many technical discussions in the field, laboratory discussions, discussions about data, comments and
suggestions about methods and analytical processes, and general discussions over coffee, my
fundamental understanding of the data collected in all parts of this study has greatly improved, and I
am very thankful. Special thanks to Jian Zhang, at the University of Hong Kong, for teaching me
structural ‘thinking’ and for extensive guidance during multiple field mapping seasons. Through
many discussions on important outcrops, my understanding of how local structures tie into regional
frameworks has greatly improved. Thank you both for your guidance and patience during field work,
laboratory work and data analysis. Thanks to the geologists at AuRico Gold Corporation, J. Janzen,
C. Edmunds and C. Rockingham, for assistance, discussions and suggestions while at the study site.
Special thanks to Y. Liu, N. Heinig, C. Henderson, L. Hayden and A. Rittau for technical support and
advice during data collection. Thanks to Dr. M. Coniglio for guidance and comments regarding
laboratory testing, and to Dr. S. Lin for many insightful comments and suggestions during field
mapping. I would also like to thank Dr. R. Linnen, Dr. M. Coniglio and Dr. S. Lin for being a part of
my thesis committee, and for the comments and suggestions that have added to the quality of this
thesis.
I would like to thank my friends for supporting me over the course of this study; Ryan, Katrina, Jess,
Jon, Kaitlin, Ben, Nathan, Joel, Jen, Niloufar and many others. Your comments, suggestions and
general outlook on life have improved mine, and I am very thankful.
Finally, my loving family, Mom, Dad, Craig, Jane, Tara, Kyle, Alan and girlfriend, Lisa, have
supported me throughout the course of my thesis and I am forever grateful.

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Table of Contents
AUTHOR'S DECLARATION .............................................................................................................. iii
Abstract .................................................................................................................................................. v
Acknowledgements .............................................................................................................................. vii
Table of Contents .................................................................................................................................. ix
List of Figures ..................................................................................................................................... xiii
List of Tables ........................................................................................................................................ xv
Chapter 1 Introduction ............................................................................................................................ 1
1.1 General Introduction ..................................................................................................................... 2
1.2 Thesis Objectives ......................................................................................................................... 5
1.3 Thesis Organization ...................................................................................................................... 6
1.4 Background .................................................................................................................................. 6
1.4.1 Local Setting .......................................................................................................................... 6
1.4.2 History of Young-Davidson .................................................................................................. 7
1.4.3 Formation of the southern Abitibi greenstone belt ................................................................ 9
1.4.4 Greenstone-hosted quartz-carbonate vein mineralization ................................................... 10
1.4.5 Intrusion-associated mineralization ..................................................................................... 11
1.4.6 Structures in the Abitibi ....................................................................................................... 11
1.5 Sample and Data Collection Methodology ................................................................................. 11
1.5.1 Samples ............................................................................................................................... 12
1.5.2 Staining ................................................................................................................................ 13
1.5.3 Geochemical analyses ......................................................................................................... 14
1.5.4 Mineral-chemical analyses .................................................................................................. 15
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Chapter 2 Geology, alteration and geochemistry of the syenite-hosted Young-Davidson gold deposit,
Matachewan, Ontario ........................................................................................................................... 17
2.1 Introduction ................................................................................................................................ 18
2.2 General geology ......................................................................................................................... 20
2.3 History of Young-Davidson ....................................................................................................... 22
2.4 Local geology ............................................................................................................................. 25
2.4.1 Structure .............................................................................................................................. 25
2.4.2 Tisdale Ultramafic and Mafic Volcanic Rocks ................................................................... 26
2.4.3 Timiskaming Sedimentary Rocks ....................................................................................... 28
2.4.4 Young-Davidson Syenite .................................................................................................... 30
2.4.5 Other Intrusions .................................................................................................................. 32
2.5 Alteration, Veining and Mineralization ..................................................................................... 33
2.5.1 Alteration – Distribution and timing ................................................................................... 33
2.5.2 Veining ................................................................................................................................ 39
2.5.3 Gold Mineralization ............................................................................................................ 45
2.6 Geochemistry ............................................................................................................................. 49
2.6.1 Syenite Geochemistry ......................................................................................................... 51
2.6.2 Volcanic Geochemistry ....................................................................................................... 55
2.7 Mass Balance ............................................................................................................................. 58
2.7.1 Syenite ................................................................................................................................. 59
2.7.2 Volcanic .............................................................................................................................. 67
2.8 Discussion .................................................................................................................................. 68
2.9 Conclusions ................................................................................................................................ 72
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