Conditions of Recrystallization of Ores of the Ozernoe Polymetallic Deposit (Western Transbaikalia, Russia)

Abstract

The Ozernoe lead–zinc deposit is the largest in Russia in terms of zinc reserves. It has been established that primary layered–banded, massive and brecciated sulfide ores were subject to intensive post-ore deformation and recrystallization, which accompanied dynamic and contact metamorphism. The transformations are expressed in the increase in the size of mineral aggregates and formation of carbonate–quartz–sulfide veins and veinlets with different ratios of constituent minerals. Ore minerals in veins and veinlets are represented by sphalerite, galena, and pyrite in different proportions; chalcopyrite, pyrrhotite, arsenopyrite, and marcasite occur in smaller quantities; and Ag sulfides and sulfosols are rare. The vein minerals are quartz, siderite, and manganese siderite (oligonite); Ba-bearing muscovite (ellacherite) and chlorite are also present. It was established that recrystallization of ores occurred at elevated PT-parameters—up to 535°C and up to 2 kbar—in the presence of relatively highly concentrated fluid phase (salinity up to 21.5 wt % eq. NaCl). Ore transformations are mainly caused by processes of dynamometamorphism. There is still uncertainty both with the age of ore mineralization of the Ozernoe deposit and with the development time of metamorphic processes. This does not allow linking these processes with the stages of geodynamic evolution in the region.