Petrogeochemical Features and Conditions of Accumulation of Carbonaceous Deposits of the Bredy Formation (Southern Urals, Russia)

The petrogeochemical characteristics of the black shales of the Bredy Formation are given. It is proved that they fall into the fields of terrigenous-carbonaceous and siliceous-carbonaceous formations. Carbonaceous matter is represented by two types: weakly metamorphosed sapropel sedimentary-diagenetic and metamorphic graphite. The terrigenous high-alumina sedimentary material underwent minimal transport and was formed mainly due to the destruction of mafic rocks, as well as the products of erosion of felsic volcanic rocks at the base of the section of the Bredy Formation. Sediments have experienced a high degree of weathering, characteristic of a humid humid climate with oxidizing and partially sub-oxidizing conditions. The material was deposited in a transitional geodynamic setting from riftogenic to collisional. Black shale deposits of the Kumak ore field according to the parameter Na2O/K2O = 0.62 belong to normal-potassium formation type, typical for deposits mainly with gold-sulfide mineralization.