The Weathering Of Placer Gold And The Quaternary Geology Of Valdez Creek, Clearwater Mountains, Alaska

Thesis (M.S.) University of Alaska Fairbanks, 1995Placer gold grains collected from six paleochannels in the Valdez Creek drainage, south-central Alaska, were deposited during successive interglacial/interstadial intervals since the mid-Early Pleistocene. Statistical analysis of grain size, shape, grain surface characteristics, and the gold content of the interior and exterior of the gold grains determined by electron microprobe analysis demonstrates that the grains were affected by both mechanical and chemical weathering, and that the weathering increased with time. Etch pits, observed under a scanning electron microscope, are a ubiquitous feature of the grain surfaces. Grain surfaces average 26.7% richer in gold than the interior of the grains. The gold content of the surface of the grains increases with age. No high gold fineness rims were observed in cross section on the grains. This evidence indicates that the gold grains experienced corrosion.