The KSM Property is in the Stikinia Terrane, a long-lived volcanic island-arc terrane that joined with the Paleozoic basement of the North American continental margin in Middle Jurassic time. Early Jurassic sub-volcanic intrusive complexes are common in the Stikinia terrane, and several host well-known precious- and base-metal-rich hydrothermal systems. These include gold-copper porphyry zones such as Bronson Slope, Galore Creek, Red Chris, Kemess, Mt. Milligan, and KSM. At KSM, there are four identified mineral systems that contribute to resources and form the KSM mining camp.
The Kerr deposit, the southern-most porphyry gold-copper deposit, is a north-south trending, steep westerly-dipping tabular intrusive complex. Deep drilling since 2012 has identified two sub-parallel zones that coalesce near the topographic surface. The deposit has an overall strike of 2,400 m and extends vertically at least 2,200 m. The west limb is up to 500 m thick and the east limb up to 300 m thick. Each limb is represented by a series of mineralized intrusions emplaced into sedimentary rocks that are locally mineralized. Kerr has a form that seems to follow fault trends in a sedimentary basin.
At Kerr, mineralization is centered on the elongate north-south trending diorite dyke-like bodies. There are multiple diorite eruptive events, showing little compositional variation, that concentrate ore grades. Post-mineral intrusions follow a similar trend to the mineralizing diorite intrusions. Disseminated and stockwork veining concentrate the sulfide ores, with high quartz vein density proportional to copper grades. Kerr has the highest copper/gold ratio in the KSM camp, owing to the high proportion of chalcopyrite over pyrite in the system. Other copper bearing minerals include bornite, tennantite, tetrahedite and enargite while molybdenite is a minor component. Potassic alteration of the diorite intrusions is the most common alteration-style, characterized by abundant biotite, mostly metamorphosed to chlorite, patchy orthoclase, anhydrite, and magnetite.
References: Rosset, S, 2017, Evolution of Hydrothermal Alteration and Mineralization at the deformed Kerr and Deep Kerr Cu-Au Porphyry Deposits, Northwestern British Columbia, Canada. MSc Thesis Univ. of British Columbia, 919 pages.
Campbell, M…..in press, Ditson, G., Wells, R and Bridge, D., 1995, Kerr: The geology and evolution of a deformed porphyry copper-gold deposit, Northwestern British Columbia, Canadian Institute of Mining, Metallurgy and Petroleum Special Volume 46, T. Schroter editor, pp 509-52.
Sulphurets is an amalgamation of structurally complex deposits distinctly different from the other KSM deposits with most of the resource contained in the thermally metamorphosed sedimentary wall rock. Stacked thrust fault panels are a defining feature of the deposit containing slices of Upper Triassic Stuhini Group fine grained clastic rocks and Lower Jurassic Hazelton Group volcano-sedimentary strata. These units are intruded by several narrow dykes, sills and stocks related to the diorite intrusion associated with the other KSM deposits. The main body of the Sulphurets deposit has a lens-shaped geometry, dipping about 30 degrees to the northwest and extending horizontally for 2,200m, down dip for 550m, and up to 330m thick.
The majority of Sulphurets ore is below the lower most splay to the Sulphurets Thrust Fault (STF), but ore zones are found between this structure and the main STF as well as above the STF. Historically, the main part of the deposit is divided into discrete zones running from southwest to northeast that include:
- The Canyon zone: a broad area of thermally metamorphosed sedimentary rock with abundant quartz-filled fractures.
- Breccia Gold zone: a discrete pipe-like breccia and the surrounding shatter zone. The breccia is characterized by sedimentary and intrusive rock clasts in a matrix of sulfide minerals.
- Raewyn Copper-Gold zone: a series of narrow dykes or sills with intense thermal metamorphism of surrounding sedimentary rocks and intense potassic alteration of both the intrusive rocks and the wall rocks.
Mitchell is a composite intrusive complex emplaced in the Upper Triassic and Lower Jurassic sedimentary basin. The deposit is exposed in an erosional window below the shallow north dipping Mitchell Thrust Fault (MTF). The proximity of the MTF and alteration mineralogy has conspired to create extensively foliated rocks at Mitchell. This deposit crops out in the Mitchell Creek Valley in a roughly elliptical pattern covering 1,000m east-west and 850m north-south, with a vertical extent of 1,100m.
The Mitchell complex has been subdivided into three major intrusive phases. Successive intrusive phases are accompanied by the development of overlapping hydrothermal assemblages, stockwork veining and gold-copper deposition. Mitchell shows a well-developed concentric zoning pattern of alteration and metal distribution centered on the intrusive complex and extending into the country rocks. The inner zone potassic alteration is focused on the early intrusions and contains the highest gold and copper grades. Outboard of this central core is a broad zone of sericite-rich alteration with continuous gold and copper grades. Beyond the sericite alteration is chlorite-clay alterations containing gold-molybdenum and depleted in copper. This outer alteration zone continues into the Snowfield deposit that represents the upper part of the mineral system off-set on the MTF.
The Iron Cap deposit is the northern-most porphyry gold-copper-molybdenum deposit in the KSM district. It is structurally above the Mitchell deposit in a fault panel between the MTF and STF. Iron Cap is a tabular body striking roughly north-south and dipping approximately 60 degrees to the west. The deposit is about 1,500m along strike, at least 1,500m down dip, and up to 800m in thickness
An Early Jurassic series of closely related intrusions is represented in this intrusive complex that is roughly contemporaneous with intrusions at the Mitchell and Kerr zones. The complex is composed of multiple intrusion and breccia phases, with the diorite in the northwestern portion of Iron Cap associated with some of the highest gold and copper grades. Mineralized breccias are significantly more abundant and voluminous at Iron Cap than at Mitchell, Sulphurets, and Kerr. Parts of this system have experienced intensive, texturally destructive silicic alteration making it difficult to recognize the original lithology. Away from this texturally destructive alteration style, systematically-zoned porphyry-style alteration is preserved. Locally sedimentary wall rock on the margins of intrusions or breccias is intensively altered, producing good gold and copper grades.