Mineralogy and Primary Sources of Gold in the Davenda-Klyuchevskiy Ore-Placer Cluster (Eastern Transbaikalia)

The Davenda-Klyuchevskiy ore cluster contains a significant number of gold placers and ore occurrences, as well as deposits of gold-sulfide–quartz and gold-bearing porphyry Mo formations of both stockwork and vein types. The morphology of the gold suggests that most of the placers are spatially related to the ore sources. However, data on the chemical composition of the placer and ore gold are very limited in the literature. This study provides a detailed mineralogical and geochemical analysis of the placer gold, offering crucial genetic information that can be used for predicting and prospecting gold mineralization. The study finds that the fineness of the placer gold closely matches that of the ore gold. In the autochthonous placers forming a distant halo around the Klyuchevskiy deposit, gold with a fineness of 900–950‰ predominates. This gold often contains inclusions of ore minerals and forms intergrowths with them. These minerals primarily include pyrite, galena, and Bi minerals (tetradymite, Bi tellurides, Bi-bearing sulfosalts, native Bi, bismuthinite) and, less frequently, arsenopyrite, chalcopyrite, and fahlore. In the autochthonous placers around the Davenda deposit, gold with a fineness of over 950‰ predominates, and inclusions of ore minerals (pyrite, galena, tetradymite, PbBiCuS mineral, arsenopyrite) in this gold are rare. The third type of gold (850–900‰) is less common in the aforementioned placers but predominates in the autochthonous placers of the Malyi and Levyi Amudzhikan rivers. In the predominantly allochthonous placers on the periphery of the Davenda-Klyuchevskiy ore cluster and the Chernyi Uryum River, lower-fineness gold is also widespread. In this group of placers, the mineral association of Au changes slightly. Galena and Bi minerals are rarely found together in the gold particles. Hessite, acanthite, and petzite, which are associated with Bi minerals or pyrite, appear. Cinnabar is present in the heavy-mineral concentrates. The fineness of the placer gold and its associations with ore and nonore minerals indicate telescoping mineralization in the ore sources. This suggests that productive placer-forming mineralization resulted from the reworking of gold during the later stages.