GOLD-SILVER MINERALIZATION IN THE VERKHNEKRUCHININSKOYE FLUORITE DEPOSIT IN TRANSBAIKALIA

Abstract

The relevance lies in the establishment of mineral forms of gold and silver in a new mineral type of gold-silver deposits, where the leading minerals are fluorite and quartz. Hence, the aim of the study was to study the mineral composition of the sulfide-quartz association, on which the fluorite-quartz mineralization of the Verkhnekruchininskоyе fluorite deposit is superimposed. The object of the study is the vein material of the Verkhnekruchininskоyе fluorite deposit, and the subject is the mineral composition of mineral aggregates for the detection of thin inclusions of silver and gold minerals, their chemical composition and paragenesis. The methodology included the manufacture of polished sections, thin sections and their study, using optical and electron microscopic methods, as well as traditional methods for studying the chemical composition of a mineral substance. A preliminary study of polished sections was carried out using a polarizing microscope. An electron microscopic study was carried out by the author – candidate of technical sciences, S. V. Kanakin, the head of the laboratory of the Geological Institute of the SB RAS. Results. The study of the mineral and chemical composition of the fluorite-quartz vein samples containing pyrite was carried out. Sulfides are found mainly in fragments of ferromuscovite-kaolinite-carbonate-quartz composition, which are in fluorite-quartz material. It also contains apatite, represented mainly by fluorine-apatite. For the first time, the features of the chemical composition of pyrite have been identified and the associated acanthite (AgS), which is allocated along its periphery, has been identified. Some pyrite crystals are characterized by their arsenicity (up to 0,63 %), sometimes accompanied by the presence of cobalt (up to 0,59 %) and nickel (up to 0,34 %). The same elements are also present in iron hydroxides developing along pyrite in the oxidation zone. The content (wt %) of iron in pyrite varies from 47,31 to 48,74, and sulfur from 51,26 to 52,84. Formula coefficients, respectively, vary from 1,02 to 1,06 for iron and from 1,94 to 1,98 for sulfur. A significant part of the pyrite crystals is oxidized and surrounded by thin rims of iron hydroxides. Pyrite contains petcite (Ag3 AuTe2) and acanthite (Ag2S). Petzite is found in pyrite in the form of inclusions of the smallest crystals, while acanthite is found in the outer zone of pyrite crystals. It forms a fine dissemination of 1...2,5 microns in size. Its chemical composition is usual. It contains (wt%) 87.82 - 87.88 Ag and 12,12...12,18 S. According to its formula Ag2.05 S0.95, the mineral is characterized by an excess of silver and a lack of sulfur. The combination of petcite and acanthite in the early clastic material with pyrite cemented by a quartz-fluorite aggregate unambiguously indicates the possibility of sulfide-fluorite-quartz shallow gold-silver mineralization