MINERALOGY AND FORMATION CONDITIONS OF URANIUM-VANADIUM DEPOSITS IN THE ONEGA BASIN (RUSSIA)

Uranium-vanadium deposits of the Onega basin are confined to fold-faul t structures and are located at a distance from the basement at the tr ansition from red-colored to black shale. The rock deposits are contro lled by a system of faults situated in the cores of the zones of fold- fault deformations (FFD). The deposits were formed during a period of tectonic-magmatic activization (1800-1700 Ma). Mineralization is repre sented by albitites, vanadium-mica rocks, and veins and veinlets with sulfides of molybdenum, copper, iron, uranium minerals, selenides of z inc, bismuth, silver, copper, palladium, and native gold and silver. A bout 1000 Ma ago, hydrothermal mineralization was influenced by superg ene processes, which caused the origin of oxidation zones and secondar y enrichment by sulfides. The hydrothermal mineralization was formed b y concentrated carbonate-chloride solutions at initial pressures highe r than 1 kbar and at a subsequent temperature drop from more than 300 degrees C for albitization to approximately 100 degrees C for selenide veinlets. The basement of the basin is assumed to be the source of or e mineralization.