On the role of salty coals in kaolinite transformation into paragonite-type hydromica within the Donbass tonsteins

Abstract

The character of kaolinite hydromicatization within the Donetsk Basin tonsteins in the course of metamorphism depends on the types of enclosing coals: either normal or salty ones. Alongside with terrigenous minerals within the coal-bearing masses and the fossil sea waters, indicator authigenous minerals fromsaltycoals – halite and glauberite –should bespecified as thesources ofsodium and potassium for kaolinite hydromicatization. The conditions, most favorable for formation of the most stable phase of paragonite-type hydromica in kaolinite interlayers, arise within paralic formations over the areas of alkaline caustobioliths formation in the course of metamorphism. In the case when halite and glauberite from salty coals make the principal source of sodium, brammalite generation begins in matatonsteins during anthracite formation. The process goes on until feldspars and micas begin active supply of potassium into chloride Cl-Ca-Na brine. From this moment on, brammalite in clay interlayers is being rapidly replaced with illite. Eventually, association of paragonite and muscovite-type hydromicas arises within the clay interlayers. If the principal source of the alkaline elements responsible for kaolinite hydromicatization consists of terrigenous minerals from normal (nonsaline) coal-bearing masses (potassium feldspars, micas, plagioclases), exclusively illite develops within metatonsteins.