Geochemical features of metalliferous black shale of North Caucasus

Abstract

The objects of the study are terrigenous rocks that are part of the Tokhan complex (Tokhan cover), located within the Advanced ridge of the North Caucasus and traced for more than 200 kilometers. The Tokhan complex is composed of pelitomorphic carbonaceous sediments (black shales) with subordinate manifestations of volcanogenic, clay-siliceous, clay-carbonate and psammitic rocks, has experienced greenstone metamorphism. The aim of the work was to analyze the geochemical features of the carbonaceous black shale Hercynian strata of the North Caucasus. Specific for black shale is a complex of elements typomorphic to ultramafic rocks: chromium, cobalt, nickel, titanium, manganese, vanadium, phosphorus. Chalcophilic elements of hydrothermalites in black shales, such as copper, zinc, lead, are usually contained in small quantities, but locally, in fluid-active zones of tectonic disturbances, their content increases sharply. A group of elements, typomorphic satellites of gold – arsenic, bismuth, antimony, in unmodified shales is weakly manifested, concentrating in the areas of superimposed hydrothermal development. A significant perturbing role of magnesium in shale has been established. All this indicates the originality of black shale deposits and the significant influence of ultrabasic material on their petrochemical characteristics. Petrochemical modules indicate the established low manifestation of mechanical differentiation processes, a low degree of contribution of chemical weathering processes and a low level of maturity of the material in the drift area during the formation of the bulk of the deposits. Areal and point testing of black shale for noble metals showed the ubiquitous presence of gold, platinum and palladium in abnormal amounts in the sum of three metals-not less than 1 g / t.The presented material for the first time clearly indicates ultrabasites as a single primary source of precious metals in the black shale complex. It is shown that noble metals (Au, Pt, Pd) are syngenetic to the host sedimentary terrigenous strata and are deposited during sedimentogenesis. Analysis of the ore-bearing black shales of the Caucasus and the establishment of the oldest source of precious metals became the starting point for the creation of the authors metallogenically geologicalgenetic models of noble metals in the North Caucasus spanning the entire Phanerozoic stage of its development. The black shale zone of the North Caucasus can be considered as a new promising province of precious metals - Au, Pt, Pd.