Gold distributions in black shale associations.

The distribution of gold in black-shale associations in various parts of the crust is non-uniform, but in most regions, the contents of the metal in carbonaceous shales are elevated by factors of 5-10: 6.7-65 ppb. A general estimate of average Au contents is given: 14.7 ppb for carbonaceous rocks and 2.0 ppb for clay shales. The main concentrator mineral is pyrite, which contains 27-1360 ppb. The pyrite content in sulphidized horizons in black shale ranges from 58-2000 ppm up to 2-6% by volume. The gold in the carbonaceous material often constitutes 18-60% of the total gold content of the rock. Aureoles of elevated gold content in black-shale horizons are controlled by jointing zones and are related to hydrothermal and metasomatic processes causing the redistribution and influx of heavy-metal components with plutonic solutions 032(K_a^Au = or > 10-300). Diagenesis also tends to raise Au contents in terrigenous beds. (Author's abstract)-A.W.H.Polytechnical Inst., Tomsk, USSR.