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 (<3% S) were determined by hydride-generator atomic-fluorescence spectrometry (HG-AFS) (Mansur and others, 2019). Both procedures were performed at LabMaTer, Université du Québec à Chicoutimi (UQAC). Partial drill core assays for one Iron Mountain drill hole and four Chrome Mountain drill holes are included in this release. We report the downhole concentrations of Au, Pt, Pd, S, Se, Te, Cu, Ni, and Cr. Trace element concentrations in pyrrhotite, pyrite, chalcopyrite, cubanite, pentlandite, and pentlandite partially altered to violarite were determined by LA-ICP-MS at LabMaTer. Globular and disseminated sulfides associated with chromitite schlieren at Chrome Mountain and both massive and disseminated sulfides at Iron Mountain were analyzed. References Mansur, E.T., Barnes, S-J., Savard, D., and Webb, P.C., 2019. Determination of Te, As, Bi, Sb and Se (TABS) in Geological Reference Materials and GeoPT Proficiency Test Materials by Hydride Generation‐Atomic Fluorescence Spectrometry (HG‐AFS). Geostandards and Geoanalytical Research, v. 44, p. 147–167, https://doi.org/10.1111/ggr.12289. Savard, D., Barnes, S-J., and Meisel, T., 2010. Comparison between nickel‐sulfur fire assay Te co‐precipitation and isotope dilution with high‐pressure asher acid digestion for the determination of platinum‐group elements, rhenium and gold. Geostandards and Geoanalytical Research, v. 34(3), p. 281–291, https://doi.org/10.1111/j.1751-908X.2010.00090.x.

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  "geospatial"
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