Geologicheskii Vestnik

In the section of the Biryan subformation in the Inzer synclinorium on the western slope of the Zilmerdak ridge, Cr, Ni, Si, Zn, Pb and elevated concentrations of As, typical for sandstones of this stratigraphic interval, were found, which are on average 2–13 times higher than clark. It was found that the main minerals concentrators of As are arsenopyrite and goethite. Goethite mainly replaces leached arsenopyrite and / or arsenical pyrite, and also develops along the boundaries of quartz grains, occurs in the form of fringes around quartz pebbles and is observed along the cleavage cracks of potassium feldspar. The zonal distribution of As with the highest concentrations up to 207 g / t in one of the layers of the section was established. This is explained by the lithological control and the fact that As is confined to competent rocks (gravelites with interlayers of arkose quartzite-like sandstones), which are underlain by less competent ones (siltstones). It is assumed that siltstones acted as a fluid barrier during the layered movement of metasomatic fluids. It is shown that the rocks of the section have lithological, geochemical and mineralogical search signs for gold mineralization. The area in the eastern continuation of the section, in which deposits of the Biryan subformation are intruded by numerous dikes of the Inzer gabbrodolerite complex, is assumed to be promising. The enrichment of the rocks of the studied section in As may have been due to the circulation of postmagmatic fluids associated with the dikes of this complex.

Bashkir meganticlinorium, Zilmerdak formation, Biryan subformation, arsenic, goethite, gravelites, sandstones

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