First Finds of Rare-Earth-Noble Metal Mineralization in the Upper Devonian Bedded Ichthyodetrital Phosphorites of KMA (Central Russia)

摘要

The data on gold and platinum content in phosphorites of the central part of the East European Platform (EEP) are related to their nodular type, which is extremely widespread in the composition of Meso-Cenozoic, predominantly Cenomanian sandy sediments. The deposits of ichthyodetrital phosphorites, characteristic of argillaceous-terrigenous sequences of the Devonian, occur very restrictedly, and data on their potential productivity for noble and other metals are absent. Layers of ichthyodetrital phosphorites (thickness 0.4-1.0 m) with higher concentrations of noble metals, uranium, and rare earths were first discovered by the authors in wells and outcrops of the Mikhailovka iron ore quarry (Fig. 1). Among the fragments of a mass burial place of fish fauna, a predominance of the detritus of placoderms of the anti-archs class of the family Asterolepis ornate Eichwald was established. This fact made it possible to refer ore bedded ichthyodetrital phosphorites to the Sargaev Formation (D_3sr) of the basement of the middle sub-stage of the Upper Frasnian stage of the Devonian. The phosphorite layers have an ungraded stratified structure, combining the rounded and angular fragments of placoderm detritus (from less than a centimeter to 5-7 cm or more), carbonaceous-argillaceous, and carbonaceous cement with the smallest bone fragments. In the cement and in the broken web tissue of fish bones, sulfide extractions are macroscopically observed (up to 1-5%).