Institute of Geology, Ufa Federal Research Center, Russian Academy of Sciences, Ufa, Russia:

A. V. Snachev, Head of Laboratory, Candidate of Geologo-Mineralogical Sciences, SAVant@rambler.ru
V. I. Snachev, Professor, Doctor of Geologo-Mineralogical Sciences

Institute of Mineralogy, South Urals Federal Research Center for Mineralogy and Geoecology, Ural Branch, Russian Academy of Sciences, Miass, Russia:

M. A. Rassomakhin, Junior Researcher

Orenburg State University, Orenburg, Russia:

A. V. Kolomoets, Lecturer

The article briefly discusses the geological structure of the Kamensk block located on the eastern slope of the Southern Urals in the Alapaevsk–Chelyabinsk deep fault zone. The territory is a keyboard structure of alternating grabens and horsts composed of volcanic–sedimentary rocks of the Devonian and Carboniferous ages. A particular attention is paid to the description of the carbonaceous shales of the Birgilda Series widely developed here. It is shown that they contain up to 2.7% Corg and are of the low-carbon type. In standard petrochemical diagrams, the considered rocks fall into the fields of silicon–carbonaceous and carbonate–carbonaceous formations. These data, together with the presence of carbonates in the section, indicate their formation in the shallow and coastal-shallow areas of the sedimentary basin. Terrigenous material in the process of sedimentation underwent minimal transport, and its source was mainly of mafic and average igneous rock. In the black shale formations of the Kamensk block, industrial gold and silver contents have been established, confined to intensely dislocated, silicified and sulfidized rocks. The testing of core samples from wells showed gold contents of up to 4.6 g/t and silver up to 11 g/t. During washing of the Neo-Pleistocene weathering crust, consisting mainly of yellowish-brown loams and clays with fragments of vein quartz and carbon shales, several gold grains up to 1×1.5 mm in size were obtained. Microprobe analysis showed their heterogeneous composition. An insignificant part of the gold is represented by small, high-finely leafy flakes indicating their connection with quartz veins (gold-quartz type). Large gold is heterogeneous, has a high-quality skin of the hypergenic stage and contains noddles of copper and silver, as well as inclusions of native silver. This allows us to attribute it to the gold-sulfide type associated with carbonaceous-clay shales of the Birgilda Series. The conducted studies give the right to highly evaluate the prospects of the Kamensk block for the identification of a new gold ore object here.
The geologic work was fulfilled against the state contract, Topic No. 0246-2019-0078. The analytical studies were supported by the Regional Grant for Science, Research and Technology in 2019, Agreement No. 23 as of August 14, 2019. Microprobe tests were carried out within the framework of state-budgeted Topic No. AAAA-A19-119072390050-9.
The authors express their deep gratitude to the members of Chelyabinskgeosemka E. P. Shchulkin and B. A. Puzhakov for the offering an opportunity to participate in geological survey, as well as to the analysts from the Institute of Geology, South Urals Federal Research Center for Mineralogy and Geoecology, Russian Academy of Sciences, T. I. Chernikov, S. A. Yagudin and N. G. Khristoforov for the implemented research work.

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