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ABSTRACT: Platinum-Group Elements and Gold in Pacific Ferromanganese Deposits

James R. Hein, Herbert Kirschenbaum, Renee L. Olson, Marjorie S. Schulz

About 150 analyses for each of Pt, Rh, and Pd (PGE) and 70 analyses for Au were completed on four ferromanganese deposit types from the Pacific: (1) hydrogeneric ferromanganese-oxyhydroxide crusts from intraplate seamounts and ridges; (2) hydrothermal stratabound manganese-oxyhydroxide deposits from active volcanic arcs; (3) hydrothermal ferromanganese-oxyhydroxide cemented volcaniclastic sandstones from active volcanic arcs; (4) mixed hydrothermal-hydrogenetic ferromanganese-oxyhydroxide crusts from spreading centers and from active volcanic arcs. Pt, Pd, Rh, and Au were determined by fire assay preconcentration on large samples (>10 g) and analyzed by graphite furnace atomic absorption spectrometry. Pt, Pd, and Rh range up to 0.940, 0.062, and 0.100 ppm, respectively which are 200, 6, and 100 times enriched over the lithospheric average, respectively. Two sets of Au analyses yielded only concentrations below the detection limits of 0.040 and 0.020 ppm. For nearly all samples, Pd and probably Au are at or below the lithospheric average, whereas Pt and Rh are much greater than the average. Central Pacific hydrogenetic crusts have the highest mean Pt values (0.223 ppm) followed by hydrogenetic continental margin crusts (0.078 ppm), genetically mixed crusts (0.046 ppm), stratabound deposits (0.004 ppm), and manganiferous sandstones (0.003 ppm). PGE are not strongly correlated with any other elements in hydrogenetic crusts, but Pt and manganophile elements are moderately correlated in continental margin hydrogenetic crusts. In all other deposits, PGE are negatively correlated with Si and Al; PGE are positively correlated with Mn and Ni in spreading center mixed crusts, with Fe, Mo, Co, and Ni in volcanic arc mixed crusts, and with Ni, Co, and P in stratabound and sandstone deposits. Pt, Co, and Ni concentrations and ratios indicate that platinum is of hydrothermal origin in volcanic arcs and of hydrogenetic origin in seamount crusts.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990