Filizchay pyrite-polymetallic deposit (the southern slope of the Greater Caucasus) – as a typical representative of the SEDEX type pyrite deposits

Abstract

The article has been devoted to one of the largest deposits of the southern slope of the Greater Caucasus – the Filizchay pyrite-polymetallic deposit. It has been found that the main morphology peculiarity of the pyrite-polymetallic deposit of the Filizchay deposit is that it is a single, compact sheet-like body composed mainly (at 90-95%) by the aggregates of the sulfide ores which are based on pyrite, sphalerite, galena and to a far lesser extent chalcopyrite and pyrrhotite. The carbonate minerals played a subordinate role in the deposit composition and quartz, sericite and chlorite – even less. The pyrite –polymetalic ores of the deposit are characterized by the following main mineralogical-textural varieties of ores: layered-bedded pyrite-polymetallic, massive sulfur-pyrite, massive pyrite-polymetallic, spotted-disseminated pyrite-polymetallic and vein-disseminated pyrite-polymetallic. The vein-disseminated ores are adjacent to the deposit on the footwall and are considered as independent bodies. Two industrial-techno- logical types of ores, oxidized and pyrite-polymetallic, have been distinguished at the deposit. The latter is in turn divided into two grades: mixed and primary ores. These three varieties of ores differ in the content of the oxidized lead forms. The ores with a content of the oxidized lead speciation above 60% have been classed as oxidized ores, those from 20% to 60% as mixed and those below 20% as primary. The Filizchay deposit consists of thin-bedded massive sulfides with shales, siltstones or sandstones interbeds («ore flysch») which have been formed exclusively or mainly as a result of the exhalative processes on the seabed and differ from massive sulfide deposits in volcanic rocks. On the basis of this and also according to the geological structure, the reserves of the valuable Zn + Pb components of the deposit belong to the SEDEX type that is the most important source of lead, zinc and silver. The deposit had been developing for a long time starting from the period of sedimentation and up to the ore’s formation of the copper-pyrrhotite stage. The lower age limit of the mineralization is determined by the presence of the hydrothermal-sedimentary ores of the Upper Pliensbachian. The upper age limit is established by the presence of the pebbles of the hydrothermally altered rocks and by their sulfide ores in the conglomerates underlying the deposits of the lower parts of the Upper Jurassic.