Geochemical data for ultramafic rocks and sulfide minerals from the disrupted lower stratigraphy of the Stillwater Complex, USA

The layered mafic and ultramafic Stillwater Complex in southwest Montana is known for its platinum-group element (PGE) production from reef-style mineralization (J-M Reef) in the Lower Banded series. Rocks near the base of the complex—the Basal series and Ultramafic series, Peridotite zone—also host elevated concentrations of Ni, Cu, Co, Cr, and PGE. These rocks of the complex’s lower stratigraphy were studied in the area just east of the Chrome Mountain summit where magmatic layering is disrupted by the presence of magmatic breccias, heavily serpentinized discordant dunites, pyroxenite pegmatoids, and disaggregated chromitite seams or chromitite schlieren.

The geochemistry and mineralogy of these PGE-enriched zones, with variable total sulfide content, were examined to determine the distribution of noble and base metals and processes affecting ore tenors. This release includes three geochemical datasets: 1) drill core assays, 2) high precision PGE and Te, As, Bi, Sb, Se (TABS) bulk rock analytical results, and 3) trace element concentrations of sulfide minerals by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS).

Whole rock PGE concentrations were determined by nickel sulfide fire assay (NiS-FA) tellurium co-precipitation followed by inductively coupled plasma mass spectrometry (ICP-MS) (Savard and others, 2010). Concentrations of TABS for sulfur-poor samples (