THE BAMSK GOLD DEPOSIT, STANOVOI RANGE, RUSSIA

Abstract

The recently discovered Bamsk gold deposit is of a large scale. It is situated in the Amur oblast in Russia. The deposit is confined to a central type volcanoplutonic uplift of that formed during the early Cretaceous megastage of the Precambrian Stanovoi fold belt. The deposit is a set of auriferous quartz and carbonate-quartz vein and veinlet zones, which are located over the early Cretaceous Nevachansk subvolcanic syenite-porphyry intrusion. The ore mineralization is controlled by a system of en echelon fissures developed in the hanging wall of the Bamsk ore-screening fault. Quartz, carbonates, and sericite prevail. Pyrite, chalcopyrite, galena, scheelite, and native gold are the prevalent minerals, the total amount of which does not exceed 1 to 5 vol %. Tennantite-tetrahedrite minerals, gold and silver tellurides, sulfobismuthides, acantite, sphalerite, and cinnabar are less widespread. Four stages of mineralization were recognized. The gold-sulfide-sulfosalt stage with gold and silver tellurides is the most commercially important for gold extraction. The deposition of major amount of native gold, sulfosalts, and tellurides is assumed to have occurred from relatively low-temperature (250 to 180°C) hydrothermal solutions under nearly neutral to weakly alkaline conditions and in a weakly oxidized environment. A set of elements (including Au, Ag, Cu, Bi, Mo, Pb, and Sb), which is characteristic for ores, was revealed. The lateral and vertical geochemical zonality of mineralization was established. The vertical zoning trend is as follows (from bottom to top) of (W1, Pb1, Mo)-Cu-(Ag, Bi, Sb, Mn, W2, Pb2). Host rocks were subjected to processes of listvenitization-beresitization. Gumbeitization and argillization occur more rarely. The K-Ar and Rb-Sr ages of gold mineralization were determined at 109 to 129 Ma and 130.6 Ma, respectively.