Mineralogical-geochemical characteristic and the potential ore sources of placer native gold in Kelbes-Zolotokitat Region (North Kuznetsk Alatau)

In Kelbes-Zolotokitat region widespread autochthonous and allochthonous placers of native gold. Some of them are still being worked off. At the same time, the gold ore mineralization is poorly studied, and there is no data on ore gold. The intermediate source of alluvial placers is the gold-bearing Cretaceous weathering crust, so the native gold in the placers is hypergenically transformed. However, the main features of its endogenous chemical composition are preserved. The article presents new data on the chemical composition of native gold from autochthonous and allochthonous placers in the region and, for the first time, on minerals, founded as microinclusions in native gold grains. The purpose of the study was to identify the typomorphic properties and mineral associations of native gold from placers, and to predict the primary ore sources of gold, which is important for gold placer areas. The objects of the study were 7 autochthonous alluvial placers, located near primaru ore sources and 2 allochthonous placers of near transport. For comparison, data on native gold from allochthonous deposits of distant transport (in the adjacent territory of the West Siberian lowland) and eluvial-deluvial placer closely related to the Olginsky Au-Cu-skarn Deposit are presented. Methods of optical and electron microscopy and microprobe analysis were used to study native gold. Native gold in autochthonous placers is quite large and has a fineness of mostly more than 850 %. Of the impurity elements, other than silver, it often contains a small amount of mercury. The Association of minerals-microinclusions in gold is quite simple; pyrite, arsenopyrite, chalcopyrite, and Galena, which are typical for gold mineralization, predominate. Rarely occur in inclusions of pyrrhotite, cobaltite, gersdorffite, tellurides, and sphalerite. These features are typical for the mineralization of the gold-quartz formation. In addition, chalcopyrite and pyrrhotite are common for gold-bearing skarns, Co and Ni minerals indicate a possible connection of mineralization with rocks of increased basicity, tellurides and Bi minerals are characteristic of intrusions-related mineralization. The gold particles in allochthonous placers is smaller, flattened and rounded, their fineness is also high, and the degree of hypergen-ic chemogenic transformation is higher than in autochthonous placers. Microinclusions of minerals in native gold of allochthonous placers more remote from their ore sources have not been studied. The ore sources of gold placers in the area are associated with metamorphosed in the green shale facies, broken volcanogenic and sedimentary rocks of the kamzhelinsky formation (R₃-C₁). Known gold ore sources are represented by small vein and stockwork zones. They belong to the gold-sulfide-quartz type and do not show a clear spatial relationship with intrusions, with the exception of dikes of the main composition, which rocks of the kamzhelinsky formation are saturated. In General, Intrusive magmatism in the area is weak. Gold-sulfide-quartz deposits of the Kuznetsk Alatau (Berikul Group, Zentralnoye, Komsomolskoye, etc.), on the contrary, are localized in intrusions or in significantly volcanogenic strata. Mineralization is characterized by a significantly more variegated mineral composition and lower gold fineness than in gold-quartz deposits. The predominant ore source of gold in the studied placers is most likely gold-quartz mineralization associated with the rocks of the kamzhelinsky formation. The weak occurrence of Intrusive magmatism in the area does not exclude, however, the existence of associated ore sources of gold-skarn or gold-sulfide-quartz types that participated in the feeding of placers. The obtained data contribute to the information about the gold mineralization in Kelbes-Zolotokitat region and important for its prediction.

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