Stillwater West PGE-Ni-Cu (Montana)

The Stillwater West PGE-Ni-Cu project, consists of 44 square kilometres adjacent to, and contiguous with, Sibanye-Stillwater’s high-grade Platinum PGE mining operations, which include the Stillwater, East Boulder and Blitz mines in Montana, USA.  Group Ten’s acquisition of the highly-prospective Stillwater West project positions the Company as the second-largest land holder in the Stillwater ultramafic complex. Prior work on the project generated significant geological and exploration data which will be instrumental in Group Ten’s advancement of the project and is currently under review by the Company’s technical team.

The Sibanye-Stillwater mines occur along the J-M Reef within the Stillwater Complex; one of the largest and richest PGE deposits in the world. These mines have produced over 12 million ounces of palladium and platinum to date1, and host a Measured and Indicated resource of 31.3 million ounces at a grade of 17.0 grams/tonne (g/t) Pt+Pd and an additional 49.4 million ounces at 16.6 g/t Pt+Pd in Inferred resources2. Group Ten’s Stillwater West project covers approximately 40 square kilometres in two claim groups with each parcel including over 17 kilometers of strike length parallel to the J-M Reef within the Stillwater layered ultramafic complex.

The Stillwater Complex is recognized as one of the top regions in the world for PGE-nickel-copper mineralization, alongside the Bushveld Complex and Great Dyke in southern Africa, which are similar layered intrusions. The J-M Reef, and other PGE-enriched sulphide horizons in the Stillwater Complex, share many similarities with the highly prolific Merensky and UG2 Reefs in the Bushveld Complex, while the lower part of the Stillwater Complex also shows the potential for much larger scale disseminated and high-sulphide PGE-nickel-copper type deposits, possibly similar to Platreef in the Bushveld Complex3. Work at Group Ten’s Stillwater West property has identified three broad deposit target types including “Reef Type” high-grade PGE-Ni-Cu deposits, disseminated PGE-Cr-Ni-Cu deposits, and magmatic sulphide-related “Contact Type” PGE-Ni-Cu deposits.

Group Ten’s Picket Pin deposit in the upper portion of the Stillwater Complex is a Reef Type deposit similar to Sibanye-Stillwater’s J-M Reef deposit, with high-grade PGE mineralization associated with nickel and copper sulphides. These Reef Type deposits are similar in style to the Merensky Reef in the Bushveld Complex in South Africa, which hosts some of the world’s largest and highest-grade PGE deposits.

Group Ten’s claims covering the lower Stillwater Complex stratigraphy include the Chrome Mountain and Iron Mountain target areas, which show potential for much larger-scale disseminated and high-sulphide PGE-nickel-copper type deposits, potentially similar to the lower Bushveld Complex.
At the Chrome Mountain target area, a newly-recognized style of PGE mineralization is associated with disseminated chromite over broad stratigraphic intervals tens or hundreds of meters in thickness. Host rocks are complexly textured Ultramafic Series lithologies that are locally pegmatoidal and have features suggesting the presence of magmatic breccias. This type of mineralization has not been previously recognized in the Stillwater Complex and is spatially-associated with the highest PGE-Ni-Cu-Cr values in soils at Chrome Mountain.

At the Iron Mountain target area, mineralization is thought to be Contact Type, being magmatic sulphide-hosted PGE-Ni-Cu hosted by lower Stillwater Ultramafic and Basal Series rocks and immediate footwall lithologies. Primary targets are accumulations of PGE enriched Ni-Cu sulphides occurring close to the base of the intrusion that are laterally extensive and up to several hundreds of meters thick. Mineralization is often associated with xenoliths and rafts of country rock, suggesting their interaction could have provided a trigger for sulphide deposition. Comparable deposits may include the Platreef, Waterberg and Mogalakwena mines in the Bushveld Complex3. The Iron Mountain target and much of the lower Ultramafic and Basal Series along strike have significant potential for deposits of this type and appear to be associated with the elevated PGE-Ni-Cu values in soils over this part of the stratigraphy.

The first discoveries in the Stillwater district were high-grade nickel and copper sulphides, and later chromite, within the lower part of the Stillwater Complex in the 1880s.  Exploration and mining of these metals continued intermittently from the lower sequence up to the 1970s. The PGE potential of the Stillwater Complex was first recognized in the 1930s and ultimately led to the discovery of the high-grade J-M Reef deposit in the 1970s within the lower-middle part of the Stillwater Complex, along with at least six other PGE-enriched sulphide horizons (including the Picket Pin PGE horizon situated above the J-M Reef, now owned by Group Ten), and additional high-sulphide PGE-rich occurrences in the lower part of the Stillwater Complex, now within the expanded Group Ten holdings4.Past work on the Stillwater West project includes broad soil and rock geochemical sampling, geologic mapping and some initial drilling. Results of these programs demonstrate the occurrence of multi-kilometric scale areas of highly anomalous palladium, platinum, gold, copper and nickel values in soil and rock samples and resulted in the identification of multiple targets with a primary focus on high-grade PGE and gold deposits.

In January 2018, the Group Ten announces the identification of an extensive area of highly elevated platinum group elements (PGE), nickel, copper and chromium in soils at its Stillwater West project, in south-central Montana. The highly anomalous soil values, which cover the Chrome Mountain and Iron Mountain target areas and measure approximately 10km and 8km long respectively, are up to 2km in width with grades exceeding 100 ppb palladium, platinum and gold, 1,250 ppm nickel and copper, and 4,000 ppm chromium. The soil anomalies, shown in Figure 1 below, cover approximately 18 kilometers (11.2 miles) of strike length over the lower Stillwater Ultramafic and Basal Series stratigraphy and include more than 13,500 soil assays. Importantly, the correlations of these soil values with mineralization in the Basal and Ultramafic zones of the lower Stillwater Complex, as shown in Figure 2, demonstrate that soils are a highly effective tool for targeting PGE and Ni-Cu deposits in the district.

The Company looks forward to issuing additional geo-technical releases in Q1 which will further highlight the potential at our Stillwater West project.


  1. Public production records from 1992 to present.
  2. Report on Montana Platinum Group Metal Mineral Assets of Sibanye-Stillwater, November 2017, Measured and Indicated Resources of 57.2 million tonnes grading 17.0 g/t Pt+Pd containing 31.3 million ounces and 92.5 million tonnes grading 16.6 g/t containing 49.4 million ounces.
  3. Magmatic Ore Deposits in Layered Intrusions—Descriptive Model for Reef-Type PGE and Contact-Type Cu-Ni-PGE Deposits, Michael Zientek, USGS Open-File Report 2012–1010.
  4. A Geologic and Mineral Exploration Spatial Database for the Stillwater Complex, Montana, Michael Zientek and Heather Parks, USGS Scientific Investigations Report 2014–5183.

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