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Platinum-group Elements in the Tonsina Ultramafic Complex, Southern Alaska.

Foley-JY; Mardock-CL; Dahlin-DC

Proc Symp Process Mineral Metall Soc Ann Mtg 1987 Feb; :165-195

10006997

According to this U.S. Bureau of Mines study, platinum-group elements (pge) are preferentially associated with chromian spinels, including high-iron chromite, magnesian-chromian hercynite, and chromian magnetite in clinopyroxene-rich upper stratigraphic portions of the tonsina Ultramafic complex in southern Alaska. Ratios of pt:pt+pd are proportional to chromium content in the associated chromian spinels. The maximum pge content of geochemical rock samples from Dust Mountain is greater than 20,000 ppb (>0.6 Oz/ton) with minor gold values. The maximum pge content of tabled chromite concentrates is 3,430 ppb (0.1 Oz/ton) at Dust Mountain, 1,029 ppb (0.03 Oz/ton) at Sheep Hill, and 1,749 ppb (0.051 Oz/ton) at Bernard Mountain. High-iron chromite at Dust Mountain yields tabled chromite concentrates with cr:fe ratios between 0.5 and 1.2. Lower pge contents are found in more chromium-rich chromitites from Sheep Hill and Bernard Mountain that yield concentrates wth cr:fe ratios between 1.0 and 2.8. Platinum-group minerals include amalgams, arsenides, pge alloys, and sulfides. These minerals are between 3 and 40 um in size and are concentrated along grain boundaries and fractures of metasomatically and hydrothermally altered chromian spinel grains.

19870201

OP;

1987

OP 85-89

AFOC;

Proc. Symp. Process Mineral., Metall. Soc. Ann. Mtg, Feb, 1987; Metall. Soc., 1988, PP. 165-195

AK;