Mineralogy and primary sources of gold in Davenda-Klyuchevsky ore-placer cluster (Eastern Transbaikalia)

The Davenda-Klyuchevsky ore cluster contains a large number of gold placers and ore occurrences, deposits of gold-sulfide-quartz and gold-bearing Mo-porphyry formations of stockwork and vein types. Judging by the morphology of gold, most placers are closely spatially related to ore sources, but data on the chemical composition of gold from placers and ores are very limited in the literature. A detailed mineralogical and geochemical study of placer gold, which is the subject of this work, provides important genetic information that can be used to predict and search for gold mineralization. It has been established that the fineness of placer gold is well comparable to the fineness of ore gold. In the autochthonous placers, that formed a distant aureole around the Klyuchevskoye deposit, are dominated by gold with a fineness of 900–950‰. Gold often contains inclusions of ore minerals and forms intergrowths with them. First of all, these are pyrite, galena and Bi minerals (tetradymite, Bi tellurides, Bi-containing sulfosalts, native Bi, bismuthine), less often – arsenopyrite, chalcopyrite, fahlores. In the autochthonous placers, located around the Davenda deposit, gold with a fineness of more than 950‰ predominates; inclusions of ore minerals (pyrite, galena, tetradymite, PbBiCuS mineral, arsenopyrite) in the gold of these placers are rare. The third type of gold (850–900‰) is less common in the above-mentioned placers, but predominates in the autochthonous placers of the Maly and Levy Amundzhikan rivers. In essentially allochthonous placers on the periphery of the Davenda-Klyuchevsky ore cluster and the Cherny Uryum River, lower grade gold is also common. In this group of placers, the mineral association of Au changes somewhat. Galena and Bi minerals are almost never found together in gold grains; hessite, acanthite, and petzite appear, associated with Bi minerals or pyrite. The heavy concentrates contain cinnabar. The fineness of placer gold and its associations with ore and nonmetallic minerals indicate telescoping mineralization in ore sources and the superimposed nature of placer-forming gold mineralization.