ABSTRACT: Platinum and Palladium in Mafic-Ultramafic Igneous Rocks, Northwestern Alaska

Thomas C. Mowatt, June C. Mowatt

Extensive bodies of mafic-ultramafic igneous rocks outcrop in northwestern Alaska, in the Noatak River region. Principal occurrences are at Avan River, Misheguk Mountain, Agashashok River, and Siniktanneyak Mountain. Investigations of these localities, as well as peripheral surficial materials, demonstrate relatively high concentrations of platinum (Pt, 412-1826 ppb) and palladium (Pd, 343-1426 ppb), associated with zones of sulfide minerals. Samples analyzed were from selected sulfide-bearing zones, including appreciable proportions of silicate minerals.

Within limits of resolution of optical microscopy, discrete phases consisting of Pt-Pd in major proportions were not recognized. Pt-Pd are anticipated to occur intimately associated with sulfide phases, and chemical and mineralogic data support such a mode of occurrence here (chalcopyrite). Comparison of analyses of northwestern Alaska samples with Pt and Pd values in recent literature indicate that the former reflect concentrations of possible mineral resource significance. These concentrations are comparable to or exceed many reported concentrations associated with deposits of Pt-Pd-bearing mineralization elsewhere. Given the relatively low modal amounts of sulfides in the Alaska samples (2-8%), the high Pt and Pd values reported essentially represent concentrations in silicate rock , containing minor sulfides and oxides. This is corroborated by the copper concentrations (1000-4200 ppm). There is a direct relationship between concentrations of copper and Pt-Pd, in individual samples, suggesting genetic affiliation.

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