BISMUTH MINERALIZATION IN NEOGENE VOLCANITES OF UKRAINIAN CARPATHIANS AND SLOVAKIA

Abstract

The paper discusses distributional features of bismuth mineralization in the Neogene volcanites covering Ukraine and Slovakia. Bismuth is a typical element of many gold, polymetallic, and copper-porphyry Neogene deposits of the Ukrainian trans-Carpathians and Slovakia. Due to its intrinsic minerability, bismuth produces sundry minerals that are sensitive to certain physical and chemical environment. Therefore, studying bismuth features reveals principles of ore formation. Despite the fact that bismuth minerals mostly form submicroscopic aggregates, they can be indicators of the physical and chemical environment essential to form ore systems, for their composition is highly sensitive to minor variations in such parameters as temperature, Eh-pH, fTe2, fS2, fSe2, fO2, and others. Both within the trans-Carpathian region of Ukraine and on the territory of Slovakia there are distinctly traced two stages of bismuth mineralization, both being synchronous with volcanic eruptions of the Miocene and Pliocene ages, accordingly. Each stage of volcanic ejection reveals a certain typo-morph of bismuth minerals and a different degree of bismuth mineralization manifestation. It has been established that bismuth sulphosalts are the products of the Miocene volcanites and the associated epithermal deposits, while manifestations of bismuth-tellurium mineralization are widespread in the metasomatically altered volcanites of the Pliocene age. Miocene epithermal deposits are characterized by native gold-Bi-sulphosalts-bismutite-chalcopyrite-quartz paragenesis formed from neutral solutions persisting adularia due to the replacement of the earlier formed sulphides, mostly galenite. This stage shows the reduction of Ag/Cu ratio in time. Minerals going through a number of phases during mineralization is put down to the fact that most of them form metastable and intermediate links during metasomatic replacements caused by spatial and time variations in hydrothermal solutions. Bismuth-tellurium-selenic mineralization is distributed in the metasomatically altered Pliocene volcanites of the Vyhorlat-Ghuta ridge. Bismuth-tellurium ore manifestations are associated with high-temperature pneumatolytic-hydrothermal systems, with acid solutions being predominant, which is proved by a wide distribution of kaolinite-hydromica metasomatites. Broad distribution of Bi-Te-Se mineralization in the Pliocene volcanites of the Vyhorlat-Ghuta ridge provides evidence to considering this structure a unique metallogenic province on the European continent.