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TYPOCHEMISTRY AND MINERAL ASSOCIATIONS OF NATIVE GOLD OF WEATHERING CRUST OF YEGORIEVSKIY ORE-PLACER AREA NORTH-WESTERN SALAIR)

V. V. Kolpakov 1, P. A. Nevolko 1,2, P. A. Fominykh 1

1 V.S.Sobolev Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia, 2 Novosibirsk State University, Novosibirsk, Russia

New data were obtained on the chemical composition and mineral associations of gravitationally recoverable native gold in the residual weathering crust in areas adjacent to the Yegorievsky deposit, supplementing the available materials on the mineralogical and geochemical properties of native gold of the Yegorievsky area. According to the chemical composition, three varieties of native gold are identified in the weathering crust, the probable root sources of which are mesothermal or epithermal vein and vein-disseminated gold mineralization. Gold grains with a fineness of more than 900‰, containing up to 1–2 wt.% Hg, are most common in the weathering crust, they may also contain an admixture of Cu (0, n wt.%). Their source is vein mesothermal mineralization of the gold-quartz type. In the new area, a variety of native gold with a fineness of less than 900‰ and mercury contents from 1 to 4–5 wt.% was found, which was absent at the Yegorievsky deposit. Gold grains of this composition are generally not characteristic of the Yegorievsky area. At the same time, in the weathering crust and metasomatites of the Lapinsky site of the Yegorievsky deposit there are mercury (from 7–12 to 23 wt.% Hg) gold, often with an admixture of copper (up to 1–2 wt.%), not found in new areas. The chemical compositions of the native gold of the weathering crust and alluvial placers closely related to it are generally well comparable, but there are also differences in the prevalence of golds of a certain chemical composition in ore sources, weathering crust and placers. Hypergenic transformations of gold particles are relatively weak and more noticeable at the Yegorievsky deposit. Ore minerals found in gold in the form of microinclusions are common minerals for medium- and low-temperature hydrothermal gold mineralization.

Keywords: weathering crust, chemical composition of native gold, gold mineral associations, gold mineralization, gold placers, hypergenic transformations of gold grains.

DOI 10.20403/2078-0575-2020-2-96-109