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Kerr Sulphurets Mitchell, or KSM Project of the Iskut River District - Mitchell, East Mitchell or Snowfields, Sulphurets, Kerr, Iron Cap |
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British Columbia, Canada |
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Cu Au Ag
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Kerr-Sulphurets-Mitchell, or KSM Project alkalic porphyry copper-gold and precious metal vein deposits lie within the Iskut River District of north-western British Columbia, Canada, some 65 km northwest of the town of Stewart. The principal deposits of the project include Mitchell, East Mitchell, Sulphurets, Kerr and Iron Cap. Other deposits within the district include Eskay Creek, Brucejack and Red Bluff.
Note this record includes resource figures from both MacDonald, et al. (1996) and Ghaffari, et al. (2022), from different times and cut-offs and states of knowledge.
The Project lies within the rugged coastal mountains of northwestern British Columbia, with elevations ranging from 520 masl in Sulphurets Creek Valley, to over 2300 masl at the highest peaks. Modern exploration began in the 1960s, with brief programs undertaken by Newmont Mining Corp., Granduc, Phelps Dodge and the Meridian Syndicate. All were focused on gold exploration. Various explorers were attracted to the area by the numerous large, prominent pyritic gossans that are exposed in alpine areas. Evidence exists indicating prospectors were active in the area prior to 1935. Several shallow reconnaissance drilling programs were undertaken between 1969 and 1991. The Sulphurets Zone was first drilled by Esso Minerals in 1969, Kerr was first drilled by Brinco Ltd. In 1985, Mitchell Creek by Newhawk in 1991, and Iron Cap by Esso Minerals in 1980. In 1989, Placer Dome acquired a 100% interest in the Kerr deposit from Western Canadian Mines, and in the following year, they purchased the adjacent Sulphurets Property from Newhawk. The Sulphurets Property also hosts the Mitchell Creek deposit and other mineral occurrences. In 2000, Seabridge acquired a 100% interest from Placer Dome in both the Kerr and Sulphurets properties, subject to capped royalties. In 2020, Seabridge acquired the Snowfield deposit from Pretium Resources and renamed it to East Mitchell as it is geologically the sheared off top of the Mitchell deposit that was displaced eastward (Ghaffari, et al., 2022).
The Project lies within 'Stikinia', a long-lived volcanic island-arc terrane that extends over much of the Canadian Cordillera. It was accreted onto the Paleozoic basement of the North American continental margin in the Middle Jurassic. Early Jurassic sub-volcanic intrusive complexes in the Stikinia terrane host several large Cu-Au porphyry deposits including the KSM deposits (Ghaffari, et al., 2022).
The deposit is said to feature many characteristics regarded as typical of gold-enriched, diorite hosted calc-alkaline porphyry copper deposits, with gold, molybdenum, and silver at low concentrations, occurring as fine disseminations in quartz veinlet stockworks with accompanying pyrite, pervasively dispersed over hundreds of metres. All of the deposits are at least partially exposed at the surface, are largely unoxidized, and have had significant portions eroded away by glacial processes (Ghaffari, et al., 2022).
The Kerr deposit is centered on a north-south trending, steep westerly dipping tabular intrusive complex with a strike extent of 2400 m, width of 800 m, and vertical extent of 2200 m. It is interpreted to be a deformed porphyry copper-gold deposit hosted by probable upper Triassic to lower Jurassic tuffaceous and sedimentary rocks which are intruded by dykes and stocks comprising pre-mineralisation (plagioclase-augite porphyritic diorite), syn-mineralisation (plagioclase hornblende porphyritic monzonite; syenodiorite; augite porphyry; hornblende porphyry; K feldspar hornblende and plagioclase porphyry) and post-mineralisation (albite, plagioclase, hornblende porphyries and diorites).
The Kerr intrusive complex comprises a suite of northerly-striking and steeply west dipping dykes and intrusions emplaced into a sequence of rhythmically bedded siltstones, sandstones, conglomerates, and debris flows of the Lower Jurassic Hazelton Group. Wall rocks adjacent to the intrusions have been hornfelsed and hydrothermally altered but generally contain marginal metal grades. The complex is comprises an east and west limb separated by a thin wedge of intensely altered sedimentary wall rock. The mineralisation at Kerr is associated with numerous sequentially emplaced synmineral, plagioclase-hornblende-(biotite-K feldspar-apatite)-phyric diorite to monzodiorite dykes, which display a porphyritic texture with 30 to 40 vol.% phenocrysts up to 5 mm in length. Dykes are typically several metres to several tens of metres wide, with three distinct phases of emplacement being recognised. Differentiation of these phases is based upon typical metal content, quartz vein abundance, degree of hydrothermal alteration, and presence of xenoliths of earlier phases. The initial syn-mineral phase, P1, is characterised by strong Au and Cu mineralisation and a high, 50 to 90 vol.% abundance quartz veins. The second syn-mineral intrusive diorite phase intrusions, P2, comprises the bulk of the Kerr intrusive complex and features variable mineralisation and quartz vein abundance. P2 envelops and truncates portions of P1, and is observed to contain occasional P1 xenoliths. Finally, late syn-mineral to post-mineral dykes, P3, with weak to no mineralisation, cut the earlier phases. Volumetrically minor post-mineral dykes, with true thicknesses typically <1 m are also observed at the Kerr deposit. These include a set of un-mineralised, K feldspar megacrystic, plagioclase-hornblendephyric porphyritic dykes, aphanitic diabase dykes, and amygdaloidal lamprophyre dykes. Geochronological data for the Kerr deposit includes a U-Pb zircon ages of 197 ±3 Ma for a syn-mineral 'syenodiorite' intrusion, as well as a slightly younger U-Pb zircon age of 195 1.5 Ma for a late syn-mineral K feldspar megacrystic porphyry dyke (Bridge, 1993). Small volumes of syn-mineral hydrothermal breccias are also found at Kerr, with subangular to angular clasts of local intrusions or wall rock and rock flour matrices. Hydrothermal breccias with abundant anhydrite and quartz vein fragments (QABX) are also evident, and are commonly overprinted with strong sericitic alteration and a high-sulphidation bornite – pyrite ±enargite mineral assemblage, with local strong copper mineralisation. Mineralisation persists for several tens of metres into the host sedimentary rocks (Ghaffari, et al., 2022).
Pervasive foliation and vein deformation resulting from mid-Cretaceous deformation is evident throughout the Kerr deposit. However, as at the Mitchell and East Mitchell Zones (e.g., Febbo et al., 2015), foliation is most intense in rocks characterised by alteration assemblages with low rock strengths, such as zones with strong sericitic alteration (Ghaffari, et al., 2022).
Chalcopyrite the dominant copper mineral, typically occurring as isolated grains of ~0.2 to 2 mm across, disseminated and clustered in quartz veins, fractures, and surrounding haloes. Bornite is found almost exclusively in the north half of the east leg, within a QABX zone containing >50% crackled quartz veins, and is accompanied by coarse grained chalcopyrite and minor tennantite. Tetrahedrite-tennantite is rare, but widely distributed in late quartz-carbonate veins, mostly in wall rocks, along with minor sphalerite, rare galena, and arsenopyrite. Dark, arseniferous pyrite is associated with these minerals. Molybdenite is only a very minor constituent, while Kerr contains significantly lower overall Mo grades than the other deposits in the district. Visible gold has not been observed except under the microscope, where it occurs as <100 µm inclusions within sulphides, mainly chalcopyrite, and along sulphide grain boundaries. High grade mineralization at Kerr is primarily associated with early potassic alteration and A- B-type quartz veins (as per Gustafson and Hunt, 1975). At shallower levels in the system, both copper and gold grades are highly correlatable with the density of A- and B-type veining. At depth, however, mineralization does not correlate as strongly with quartz vein density, and is of a more disseminated style.
Reserves, as known in 1996 were quoted at: 135 Mt @ 0.76% Cu, 0.34 g/t Au (MacDonald, et al., 1996). The current resources and reserves are a quoted below (Ghaffari, et al., 2022).
Sulphurets, which contains several mineralised zones, is 3 km north of Kerr, while the Mitchell Zones are a further 3km NNE and include Mitchell with 200 Mt @ 0.2% Cu, 0.86 g/t Au, and 2 km to the SE Snowfields gold deposit (also known as East Mitchell) with 7 Mt @ 2.8 g/t Au. Both are associated with extensive K feldspar, sericite, tourmaline, chlorite, carbonate, pyrite and pyrophyllite alteration systems. The Snowfields or East Mitchell disseminated gold occurrence is interpretted to represent an epithermal overprint on a porphyry system. The Brucejack precious metal vein deposit in the same vicinity contained 0.75 Mt @ 15.4 g/t Au, 648 g/t Ag (MacDonald, et al., 1996).
The Sulphurets deposit comprises stacked thrust fault panels of Triassic and Jurassic volcano-sedimentary strata intruded by a number of dykes and stocks. It occurs as a lens dipping 30° NW, extending over a distance of 2200 m horizontally, 550 m down dip, and thickness of up to 330 m. The Mitchell Zone is underlain by intrusive, volcanic and clastic rocks that are exposed in an erosional window below the shallow dipping Mitchell Thrust Fault. Mineralisation is genetically and spatially related to the Early Jurassic Mitchell intrusive complex of diorite, monzodiorite and granodiorite stocks and dykes. Mineralisation also extends into surrounding sedimentary and volcanic rocks, with a total extent of 1000 m east-west and 850 m north-south, and a vertical extent of 1100 m. The Mitchell complex comprises three successive intrusive phases accompanied by the development of different hydrothermal assemblages, veining and mineralisation. The East Mitchell deposit is the upper portion of the Mitchell deposit, displaced some 1.5 km to the southeast by the Mitchell Thrust Fault during Cretaceous age compressive deformation that produced the regional Skeena Fold and Thrust belt (Ghaffari, et al., 2022).
The Iron Cap deposit is also structurally above the Mitchell Thrust Fault and is 2.5 km NNE of Mitchell. It is a tabular body striking north-south and dipping 60°W, extends for 1500 m along strike, 1,500 m down dip, and is 800 m in thickness (Ghaffari, et al., 2022).
Red Bluff with 102 Mt @ 0.15% Cu, 0.72 g/t Au is associated with a tonalitic to granodioritic porphyry that intrudes Triassic clastic sediments and has an early K feldspar with quartz, biotite and magnetite alteration phase overprinted by a sericite-quartz-pyrite-albite phase (MacDonald, et al., 1996).
The Snip precious metal vein deposit which is associated with a Jurassic intrusion, with reserves of 0.96 Mt @ 28.5 g/t Au is 50 km NW of Kerr. The similar, nearby Johnny Mountain Mine (Stonehouse deposit) contained 0.207 Mt @ 14.1 g/t Au (MacDonald, et al., 1996).
The Eskay Creek deposits are also in the Iskut River District (see the separate record on this deposit) (MacDonald, et al., 1996).
See the Brucejack and Eskay Creek records for more detail of the geology and setting of the district (MacDonald, et al., 1996).
Mineral Resources, as Mitchell and East Mitchell in March 31, 2022; Kerr, Sulphurets and Iron Cap is December 31, 2019 were (Ghaffari, et al., 2022):
• Measured Mineral Resources
Mitchell - 691.700 Mt @ 0.68 g/t Au, 0.19% Cu, 3.3 g/t Ag, 52 ppm Mo;
East Mitchell - 1012.800 Mt @ 0.65 g/t Au, 0.11% Cu, 1.8 g/t Ag, 89 ppm Mo;
KSM Total - 1074.500 Mt @ 0.66 g/t Au, 0.14% Cu, 2.4 g/t Ag, 74 ppm Mo.
• Indicated Mineral Resources
Mitchell - 1667.00 Mt @ 0.48 g/t Au, 0.14% Cu, 2.8 g/t Ag, 66 ppm Mo;
East Mitchell - 746.200 Mt @ 0.42 g/t Au, 0.08% Cu, 1.7 g/t Ag, 79 ppm Mo;
Sulphurets - 446.000 Mt @ 0.55 g/t Au, 0.21% Cu, 1.0 g/t Ag, 53 ppm Mo;
Kerr - 374.000 Mt @ 0.22 g/t Au, 0.41% Cu, 1.1 g/t Ag, 5 ppm Mo;
Iron Cap - 423.000 Mt @ 0.41 g/t Au, 0.22% Cu, 4.6 g/t Ag, 41 ppm Mo;
KSM Total - 3 656.200 Mt @ 0.44 g/t Au, 0.17% Cu, 2.4 g/t Ag, 58 ppm Mo.
• Inferred Mineral Resources
Mitchell - 1282.600 Mt @ 0.29 g/t Au, 0.14% Cu, 2.5 g/t Ag, 47 ppm Mo;
East Mitchell - 281.100 Mt @ 0.37 g/t Au, 0.07% Cu, 2.3 g/t Ag, 61 ppm Mo;
Sulphurets - 223.000 Mt @ 0.44 g/t Au, 0.13% Cu, 1.3 g/t Ag, 30 ppm Mo;
Kerr - 1999.000 Mt @ 0.31 g/t Au, 0.40% Cu, 1.8 g/t Ag, 23 ppm Mo;
Iron Cap - 1899.000 Mt @ 0.45 g/t Au, 0.38% Cu, 2.6 g/t Ag, 30 ppm Mo;
KSM Total - 5 684.700 Mt @ 0.36 g/t Au, 0.28% Cu, 2.2 g/t Ag, 33 ppm Mo.
• Proved + Probable Ore Reserves
Mitchell - 935 Mt @ 0.67 g/t Au, 0.18% Cu, 2.9 g/t Ag, 61 ppm Mo;
East Mitchell - 1206 Mt @ 0.62 g/t Au, 0.11% Cu, 1.8 g/t Ag, 89 ppm Mo;
Sulphurets - 151 Mt @ 0.68 g/t Au, 0.26% Cu, 1.0 g/t Ag, 70 ppm Mo;
KSM Total - 2292 Mt @ 0.64 g/t Au, 0.14% Cu, 2.2 g/t Ag, 76 ppm Mo.
The information in sections of this summary are drawn from: Ghaffari, H., Kim, H., Huang, J., Gray, J.H., Kinakin, D., Willms, D., Brazier, H., Schmidt, R. and Hammett, R., Seabridge Gold Inc., KSM (Kerr-Sulphurets-Mitchell) Prefeasibility Study and Preliminary Economic Assessment, NI 43-101 Technical Report.
For detail consult the reference(s) listed below.
The most recent source geological information used to prepare this description was dated: 2022.
Record last updated: 03/07/2025
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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MacDonald A J, Lewis P D, Thompson J F H, Nadaraju G, Bartsch R D, Bridge D J, Rhys D A, Roth T, Kaip A, Godwin C I, Sinclair A J 1996 - Metallogeny of an early to middle Jurassic arc, Iskut River area, northwestern British Columbia: in Econ. Geol. v91 pp 1098-1114
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