New Data on the Age of the Ozernoe Polymetallic Deposit (Western Transbaikalia)

The article presents results of the biostratigraphic and U–Pb geochronological (detrital zircon) studies of the volcanoterrigenous lacustrine member of the upper subformation (Lower Paleozoic Oldynda Formation), which contains polymetallic massive sulfide ores of the Ozernoe deposit (Kurba–Eravna ore district, western Transbaikalia). The first, second, and “crystalline tuff” horizons of the first ore-bearing level of the Ozernaya member were studied. It is represented by an alternation of tuffs, calcareous, siliceous, carbonaceous tuffites, pelitomorphic limestones, calcareous gravelstones with interlayers and lenses of mineralized tuffaceous conglobreccia and layers of banded siderite pyrite ores. For the first time, bryozoans, algae, and palynoflora were recorded in calcareous tuffaceous siltstones and limestones of the second and “crystalline tuff” productive horizons. These data indicate the Early Carboniferous (Tournaisian) time of sediment accumulation. Results of the U–Pb geochronological studies of detrital zircons from the mineralized tuffaceous conglobreccia of the third productive horizon suggest that the lower boundary of rock formation is not older than Late Cambrian.