Abstract
Kemess South is the only Cu–Au–Mo mine in the Toodoggone district and a major Cu and Au producer in British Columbia. Porphyry-style Cu–Au–Mo mineralization is mainly hosted by the tabular, SW-plunging, 199.6 ± 0.6-Ma Maple Leaf granodiorite, which intrudes tightly folded, SW-dipping, Permian Asitka Group siltstone and limestone and homogeneous Triassic Takla Group basalt. Southwest-dipping 194.0 ± 0.4-Ma Toodoggone Formation conglomerate, volcaniclastic, and epiclastic rocks overlie the granodiorite and Asitka Group rocks. Minor Cu–Au–Mo mineralization is hosted by the immediate Takla Group basalt country rock, whereas low-tonnage high-grade Cu zones occur beneath a 30-m-thick leached capping in supergene-altered granodiorite and in exotic positions in overlying Toodoggone Formation conglomerate. Granodiorite has an intrusive contact with mineralized and altered Takla Group basalt but displays a sheared contact with unmineralized and less altered Asitka Group siltstone. The North Block fault is a deposit-scale, E-striking, steeply S-dipping normal fault that juxtaposes the granodiorite/basalt ore body against unmineralized Asitka Group rocks. Younger NW- and NE-striking normal–dextral faults cut all rock types, orebodies, and the North Block fault with displacements of up to 100 m and result in the graben-and-horst-style block faulting of the stratigraphy and ore body. Both basalt and granodiorite host comparable vein sequence and alteration histories, with minor variations in hydrothermal mineral assemblages caused by differing protolith chemistry. Early potassic alteration (and associated early-stage Cu ± Au ± Mo mineralization) is partly replaced by phyllic and intermediate argillic alteration associated with main-stage Cu–Au–Mo mineralization. Two main-stage veins have Re–Os molybdenite ages of 201.3 ± 1.2 and 201.1 ± 1.2 Ma. These mineralization ages overlap the 199.6 ± 0.6-Ma U–Pb zircon crystallization age for the Maple Leaf granodiorite. Late-stage pyrite-rich stringer veins and related phyllic alteration assemblages are cut by anhydrite-rich, carbonate-rich, and chlorite veins. Fluids and metals associated with early-, main-, and late-stage veins were probably derived principally from the same deep magma chamber as the Maple Leaf granodiorite. These magmatic-derived fluids interacted with Asitka and Takla Group country rocks and possibly with meteoric and metamorphic fluids prior to mineralization.
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Acknowledgments
The Kemess South study is part of a larger NSERC-CRD grant research project between the University of British Columbia, Northgate Minerals Ltd., and Stealth Minerals Ltd. The latter two companies are thanked for providing generous financial and logistical support for fieldwork in the Toodoggone district. Carl Edmunds, Brian Kay, Ron Konst, Brian O’Connor, Gary Parrup, and Chris Rockingham from Northgate Minerals Ltd. are thanked for providing logistical support and access to the Kemess South pit and drill core. Field assistants, Andy Orr and Colin Smith, contributed greatly with their enthusiasm and dedication during fieldwork and subsequent laboratory work. Greg Dipple is thanked for his advice regarding the interpretation of C and O isotope data. Greg Arehart, Thomas Bissig, Alan H. Clark, Jean Cline, Steve Garwin, Steve Kesler, David Love, W.J. McMillan, and Larry Meinert are thanked for their careful reviews of the manuscript and helpful comments. The first author acknowledges financial support from the second stage of the Brain Korea 21 project at Pukyong National University. The Radiogenic Isotope Facility at the University of Alberta is supported, in part, by an NSERC Major Resources Support Grant.
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Duuring, P., Rowins, S.M., McKinley, B.S.M. et al. Magmatic and structural controls on porphyry-style Cu–Au–Mo mineralization at Kemess South, Toodoggone District of British Columbia, Canada. Miner Deposita 44, 435–462 (2009). https://doi.org/10.1007/s00126-008-0227-x
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DOI: https://doi.org/10.1007/s00126-008-0227-x