Source and Bedrock Distribution of Gold and Platinum-group Metals in the Slate Creek Area, Northern Christochina Mining District, East- central Alaska.
Placer gold and platinum-group metals (PGM) in the Slate Creek Area, northern Chistochina Mining District, are derived from silicified and carbonate-altered, Cretaceous-Tertiary dikes and related Mafic and Ultramafic rocks. Gold in the placer deposits is also derived from Tertiary conglomerate and altered Jurassic-Cretaceous argillite. The argillite and igneous bedrock sources show a unique ag-au-cu-hg-PGM association that is attributed to a combination of magmatic, hydrothermal, and supergene processes. The bedrock and placer deposits contain a variety of gold-silver-lead-copper and PGM alloys. The observed geochemical, mineralogic, and alteration features are consistent with current geological models for turbidite- hosted gold deposits. No economic gold or PGM lodes were identified, but several areas warranting more detailed investigation were identified. Conventional geochemical sampling and analysis of small sample splits weighing between 10 and 30 g were shown to be unreliable as a consistent means of identifying gold- and PGM- bearing bedrock. Pan concentration of pulverized rock samples was shown to be a more effective, but still imperfect, means of identifying gold and PGM source rocks. Geochemical data and mineralogic examination indicate that gold and PGM in potential load sources are very finely and erratically disseminated, are chemically combined with other elements, and may not be entirely free-milling or amenable to simple gravity concentration.