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TIMA-X Bright Phase Analysis of Platinum-Group Minerals in Selected Samples from the Chrome and Iron Mountain areas of the Stillwater Complex, Montana

June 20, 2019

Sulfide- and chromite-bearing samples of the Basal and Ultramafic series of the Stillwater Complex are known to contain elevated concentrations of platinum-group elements (PGE). Thin sections were prepared from drill core and surface samples from the Chrome and Iron Mountain areas. Core samples are from exploration drilling programs by AMAX in the 1960s and 1970s and Beartooth Platinum in 2004-2007. The degree to which PGE occur in the rocks as discrete platinum-group minerals was investigated using a TESCAN Integrated Mineral Analyser (TIMA-X) based on a TESCAN MIRA 3 field-emission scanning electron microscope coupled with an EDAX energy-dispersive spectrometer. TIMA-X combines backscattered electron (BSE) imaging and energy-dispersive spectroscopy (EDS) to identify minerals. Thin sections were first analyzed using Bright Phase Search mode which performs a rapid search for the specific particles of interest (platinum-group minerals). Due to their high average atomic number, platinum-group, gold, and silver minerals appear very bright in BSE mode. Once the minerals were located on thin sections, the spots associated with the bright phases were reoccupied so that energy-dispersive spectra could be acquired for the platinum-group minerals and the other minerals surrounding them. Each Portable Document Format (PDF) file in this data release (EDAX Chrome-Iron Mountain EDS pdf reports.zip) consists of an annotated BSE image of an identified area of interest and energy-dispersive spectra of the platinum-group minerals and surrounding minerals (usually sulfides and/or chromite). Separate high-resolution BSE images of each identified area of interest are provided in Tagged Image File Format (TIF) format in a separate zip folder (TESCAN MIRA 3 Chrome-Iron Mountain BSE images.zip). An accompanying comma-separated values (CSV) file is provided that lists the samples that were analyzed, drill hole identification number and depth (if applicable), and latitude/longitude location information. The sample names can be correlated to the pdf and tif file names. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.