The Iron Cap zone of the KSM project is a large area of well-exposed, gossanous weathered, intensely and pervasive quartz-sericite-pyrite altered intrusive and volcanic. It covers a roughly 500 by 1500 meter, northeast trending area between the Iron Cap glacier and Mitchell glacier. Alteration is controlled by northeast trending, near vertical structures and associated stockwork fracture and veins. Quartz-pyrite veins up to several meters thick occupy some of the structures.
The KSM project consists of 4 main deposits: the Kerr (104B 191), Sulphurets (104B 182), Mitchell (104B 103) and Iron Cap (104B 173).
The Iron Cap zone is located above the north side of Mitchell Glacier just west of the northern extension of the north trending Brucejack fault system. Mineralization occurs in an altered sequence of volcanic, volcaniclastic and clastic sediments of the Lower Jurassic Unuk River Formation, Hazelton Group. Feldspar and hornblende porphyry intrusives of Jurassic age are reported in the area. Alteration consists of pervasive silicification, pyritization and lesser sericitization and chloritization. The host rocks are commonly reported as quartz sericite schist or chlorite schist. The rocks typically contain from 3 to 5 per cent pyrite.
The zone is a separate but related mineralized system within the KSM district, and occurs structurally above the Mitchell deposit, in the panel of rocks between the Mitchell and Sulphurets thrust faults. It differs from the Mitchell deposit primarily in that much of the host rock is hydrothermally altered intrusive (porphyritic monzonite to diorite) rather than volcanics and sediments. The volcanics are mostly andesitic porphyry, generally similar to the main host of the Mitchell deposit. There is a high degree of silicification which overprints earlier potassic and chloritic alteration. Intense phyllic alteration and high density stockwork veining, which are pervasive at Mitchell are less pervasive at Iron Cap. Copper bearing zones at Iron Cap demonstrate higher grades than Mitchell, which is reported to be consistent with the intrusive setting and potassic alteration that indicates a deeper and hotter environment.
Associated with the silicification are wide zones of hydrothermal brecciation, scattered meter-scale quartz-pyrite-chalcopyrite veins and centimeter-scale quartz-pyrite-chalcopyrite-sphalerite-galena-tetrahedrite veins that are interpreted to be superimposed on earlier stockwork and disseminated mineralization associated with the intrusion. Microscopic examinations of polished thin sections confirm that Iron Cap was also subjected to a post-mineral deformational event evidenced by widespread mylonitic textures. “Mylonite” and “Ultramylonite” are terms used as rock names in petrographic descriptions of several Iron Cap mineralized samples.
Generally intense silicification at the higher, eastern portions gives way to chloritization with some preserved k-spar alteration at depth and towards the west which correlates with increasing proportion of intrusive rock. Relative to Mitchell, stockwork veining is much weaker. There is a distinct overprint of structurally controlled, centimeter scale quartz-carbonate veins with chalcopyrite, galena, sphalerite, and tetrahedrite. High silver values are generally associated with presence of galena and sphalerite.
Three major parallel sets of quartz-pyrite veins and stockwork were originally observed over a total length of 700 metres and a vertical extent of 400 metres. These vein zones range in width from 0.5 to 6 metres. The Iron Cap West vein is the westernmost of the veins. It is exposed for 300 metres horizontally along length and 140 metres vertically. The vein strikes from 10 to 25 degrees and dips vertically to steeply east. The lower half of the vein averages 5 metres in width; the upper half averages 3 metres. The vein is controlled by a prominent fault set; the south end terminates abruptly, and the north end may split into two or three veins and is offset by numerous cross- faults. The veins consist of massive quartz and from 5 to 10 per cent pyrite. Minor amounts of tetrahedrite and trace amounts of molybdenite, chalcopyrite, sphalerite, galena, hematite and magnetite also occur. Assays of 19 samples across the vein indicate a rough average grade of 3.43 grams per tonne gold and 34.29 grams per tonne silver (Bridge et al, 1983).
Forty partially leached rock chip samples collected by Noranda over an area of 1200 by 300 metres from the Iron Cap West and adjacent Iron Cap zone averaged 1.0 gram per tonne gold and 0.32 per cent copper (Press Release, Seabridge Gold Inc., July 25, 2005).
In 1980, Esso Minerals completed a program of blast trenching and three diamond drill holes on the Iron Cap zone. Drilling yielded intercepts of up to 0.35 per cent copper and 0.53 gram per tonne gold over 93 metres in hole S80-15 and 0.51 gram per tonne gold over 229 metres in hole S80-11 (Lechner, M.J. (2007-04-06): Mitchell Creek Technical Report).
In June 2000, Seabridge Gold Inc. entered into a Letter of Intent with Placer Dome to acquire a 100 per cent interest in Kerr-Sulphurets. In the fall of 2002, Seabridge granted Noranda (since folded into Falconbridge) rights to earn a 50 per cent interest in the Kerr-Sulphurets project by spending $6 million on exploration over six years.
During 2003 and 2004 Noranda Exploration Inc. conducted field programs designed to explore outside the known Kerr and Sulphurets deposits to expand the known resources. The programs consisted of mapping, rock and soil sampling and IP surveys. In 2004, Noranda’s geological mapping IP survey focused on the North Mitchell (104B 180) and Iron Cap (104B 173) areas. The size of mineralized zones at Iron Cap, Mitchell and Main Copper were expanded into areas or recent glacier retreat which were not accessible by Placer Dome. Two chip samples, collected 30 metres apart from a recently exposed area of outcrop due to melting of the Mitchell Glacier located approximately 700 metres to the southeast of the main Iron Cap zone, averaged 2.5 per cent copper and 2.2 grams per tonne gold (Lechner, M.J. (2007-04-06): Mitchell Creek Technical Report).
The 2004 Noranda/Falconbridge work on the Iron Cap consisted of five holes spaced 200 to 300 metres apart and 250 metres deep. These penetrated quartz-sericite-pyrite altered monzonite and andesite. Very fine-grained chalcopyrite occurs throughout four of the holes; over their entire assay lengths of 243 to 249 metres, the four holes returned an average grade of 0.20 per cent to 0.22 per cent copper with 0.27 to 0.52 gram per tonne gold (Exploration and Mining in BC 2005, page 32). For 2005, Noranda is planning to conduct a 1-million-dollar helicopter supported drill program targeting untested mineralized zones and geophysical anomalies.
In 2005, Falconbridge Limited completed 4092 metres of drilling in 16 holes, distributed over six zones: Iron Cap (104B 173); West Mitchell zone (104B 176); Icefield zone (104B 203); Main Copper (104B 182; 3 holes); North Mitchell (MINFILE 104B 180; 3 holes) and MacQuillan (104B 285; 1 hole). Five drill holes, totalling 1246.6 metres, were completed on the Iron Cap zone yielding intercepts including 0.20 and 0.21 per cent copper with 0.52 and 0.50 gram per tonne gold over 246 and 249 metres, respectively, in holes IC-05-01 and IC-05-02 (Lechner, M.J. (2007-04-06): Mitchell Creek Technical Report).
In 2006, Seabridge Gold purchased Falconbridge's option and conducts drilling programs on Mitchell and Sulphurets deposits (9,098.8 metres in 29 holes, operated by Falconbridge).
In 2007, Seabridge Gold puchased Arbee prospect from D. Ross. Drilling at the KSM (Kerr-Sulphurets-Mitchell) project was undertaken within and peripheral to the Mitchell zone. A total of 15,294 metres of core drilling in 37 holes were completed.
In March 2011, a mineral resource of 361.700 million tonnes indicated grading 0.44 gram per tonne gold, 0.21 per cent copper, 5.4 grams per tonne silver and 0.005 per cent molybdenum with an additional 297.300 million tonnes inferred grading 0.36 gram per tonne gold, 0.20 per cent copper, 3.9 grams per tonne silver and 0.006 per cent molybdenum was reported, using a 0.50 gram per tonne gold equivalent cut-off grade, for the Iron Cap deposit (Lechner, M.J. (2011-03-29): March 2011 Updated KSM Mineral Resources).
In 2011, a total of 20,718 metres of NQ core was drilled by Seabridge Gold on the KSM project in 2011. Of the sixty-three holes drilled, nine were drilled at the Kerr Zone, forty-one at the Sulphurets Zone, six at the Mitchell Zone, and seven at areas outside of the mineralized zones.
A July 24, 2012, resource estimate update for the Iron Cap deposit at 0.50 gram per tonne gold equivalent cut-off grade as follows: Measured plus Indicated - 361,000,000 tonnes grading 0.44 gram per tonne gold, 0.21 per cent copper, 5.4 grams per tonne silver and 0.0047 per cent molybdenum; Inferred - 297,300,000 grading 0.36 gram per tonne gold, 0.20 per cent copper, 3.9 grams per tonne silver and 0.0060 per cent molybdenum (http://www.seabridgegold.net).
The 2013 program primarily focused on intersecting deep mineralization at the Kerr deposit (29 holes) and the Iron Cap deposit with 6 core holes totaling about 5,800 metres. Additional drilling was completed at the Camp and McQuillan targets. No holes were drilled into the Sulphurets deposit in 2013. Evidence from the 2013 drilling program strongly suggested that the Iron Cap deposit sits above and is displaced to the south-southeast of a near magmatic high-grade core zone. Evidence from the 2013 drilling program strongly suggested that the Iron Cap deposit sits above and is displaced to the south-southeast of a near magmatic high-grade core zone.
The 2014 program focused on exploring the down-dip extension of mineralization below the Kerr Zone (16 holes) and Iron Cap Zone (10 holes). Additional drilling was completed at the Sulphurets Zone (9 holes) and McQuillan Zone (2 holes). In 2014, ten core holes totaling about 10,429 metres were completed at Iron Cap in order to test the continuity and extent of a potential northwest plunging core zone located below the Iron Cap deposit (the Iron Cap Lower Zone). Based on drill hole results after the 2014 drilling program, the Iron Cap Lower Zone is interpreted as a northwest plunging, northeast-southwest striking tabular body located immediately below the existing reserves. Drill holes testing the down plunge extent of the deposit intercepted higher copper and gold grades, which is consistent with a core zone.
In 2015, Seabridge drilled nine core holes totaling nearly 14,000 metres. The majority of that meterage was designed to extend the known limits of mineralization beneath the Kerr deposit (6 holes). Three holes (about 5,000 m) were drilled to test the down-dip projection of mineralization at the Mitchell deposit. No holes were drilled into the Sulphurets or Iron Cap zones in 2015.
In 2016, Seabridge reported that the Iron Cap Underground contained 224 million tonnes of ore in the Proven and Probable Reserves category, grading 0.49 grams per tonne gold, 0.20 per cent copper, 3.6 grams per tonne silver and 0.0013 per cent molybdenum (Ghaffari, H. (2016-10-06): 2016 KSM (Kerr-Sulphurets-Mitchell) Prefeasibility Study Update and Preliminary Economic Assessment).
In 2017, Seabridge completed 10,383 metres of drilling in 11 holes at the Iron Cap deposit. All 11 holes returned wide zones of significant grade. Highlights include 858 metres of 0.86 grams per tonne gold and 0.51 per cent copper including 113 metres of 2.98 grams per tonne gold and 1.56 per cent copper (Exploration in BC 2017, page 125).
In 2018, Seabridge continued to drill the Iron Cap deposit. Results extended its high-grade core down-plunge. Highlight drill results include 548 metres grading of 0.63 grams per tonne gold and 0.44 per cent copper (Exploration and MIning in BC 2018, page 120). Thirteen exploration drill holes at Iron Cap have been completed and the final five are in progress, totalling about 16,700 metres of drilling.
In 2018, Seabridge Gold released an updated resource estimate for the Iron Cap deposit, dated Feb. 9, 2018, at 16-dollar NSR Cut-off. The Iron Cap has an Indicated mineral resource of 370,000,000 tonnes grading 0.43 gram per tonne gold, 0.23 per cent copper, 4.2 grams per tonne silver and 0.0048 per cent molybdenum; and an inferred resource estimate of 1,297,000,000 grading grading 0.48 gram per tonne gold, 0.30 per cent copper, 2.9 grams per tonne silver and 0.0034 per cent molybdenum (Seabridge Gold Inc., News Release, February 13, 2019). The estimate incorporates all previous drilling plus 10,383 metres of diamond core drilling completed in 11 holes drilled in 2017.
In September, 2018, 5 holes were cited to confirm mineral reserves in those areas where production would likely begin. Drill holes in the Mitchell, Sulphurets and Kerr deposits confirmed block grades comparable with model predictions (Results in Seabridge Gold Inc., News Release, Sept.24, 2018). A total of eight drill holes oriented into the margins of the Mitchell and Sulphurets deposits have been completed and an additional four holes are planned for a total of 4,919 metres. These holes were designed to test an updated block model of waste types on the margins of the deposits. Eight exploration drill holes at Iron Cap have been completed and the final five are in progress, totalling about 16,700 metres of drilling. The exploration drill program was designed to continue testing the core zone of the Iron Cap deposit down-plunge to the west. Initial indications are that the deposit approaches near vertical continuity to depth of at least 1,800 metres. Nine geotechnical drill holes have been completed during the current season, totalling 3,609 metres of drilling. The work focused on evaluating the material properties of fractures and faults on the planned pit high-walls. Results will be used to plan additional work for the Mitchell and Sulphurets deposits.
In March 2019, Seabridge Gold Inc. reported that the Iron Cap deposit had an Indicated mineral resource estimate at of 423,000,000 tonnes grading 0.41 gram per tonne gold, 0.22 per cent copper, 4.6 grams per tonne silver and 0.0041 per cent molybdenum (16 dollars NSR Cut-off); and an inferred resource estimate of 1,899,000,000 grading grading 0.45 gram per tonne gold, 0.30 per cent copper, 2.6 grams per tonne silver and 0.0030 per cent molybdenum (16 dollars NSR Cut-off) (Seabridge Gold Inc., News Release, March 12, 2019). Seabridge reports that this updated resource estimate, dated as of March 7, 2019, incorporates all previous drilling plus 20,341 metres of diamond core drilling completed in 18 holes during the 2018 program.
See Kerr (104B 191) for details of a 2016 Combined Mineral Resource (Measured and Indicated) of 2.9 billion tonnes and an additional Inferred Resource of 2.7 billion tonnes for the KSM project which includes resources from 4 zones; Kerr (104B 191), Sulphurets (104B 182), Mitchell (104B 103) and Iron Cap zones (104B 173).
In 2019, Seabridge Gold Inc. completed an airborne magnetic and electromagnetic survey on the KSM project. Also at this time, 26 diamond drillholes, totalling 6121 metres, were completed on the Sulphurets (MINFILE 104B 182) deposit.
In December 2019, Seabridge Gold Inc. released an updated mineral resource for the KSM project (Kerr [MINFILE 104B 191], Sulphurets [MINFILE 104B 182], Mitchell [MINFILE 104B 103] and Iron Cap [MINFILE 104B 173]) totalling 3 038 000 000 tonnes measured and indicated grading 0.52 gram per tonne gold, 2.8 grams per tonne silver, 0.21 per cent copper and 0.0048 per cent molybdenum plus an additional 4 599 000 000 tonnes inferred grading 0.38 gram per tonne gold, 2.2 grams per tonne silver, 0.32 per cent copper and 0.0029 per cent molybdenum (Threlkeld, W.E., Ghaffari, H. [2020-04-30]: KSM (Kerr-Sulphurets-Mitchell) Prefeasibility Study and Preliminary Economic Assessment Update, NI 43-101 Technical Report). For a complete summary of each deposit refer to the above cited report.
Refer to Mitchell (104B 180) and Kerr (104B 191) for a more detailed work history and to the Snowfield (104B 179) for related area details.