Native gold from placers of the Evotinskii region (Aldano-Stanovoy Shield): mineralogical and geochemical features, and possible primary sources

The Evotinskii Ore and Placer Region (EOR) is located in the central part of the Aldano-Stanovoy Shield and is characterized by a significant presence of gold-bearing placers, many of which have undergone extensive mining activities. Despite geological investigations that have been conducted since the 1930s, the main sources of numerous placers remain largely unidentified. This study employed traditional mineralogical and geochemical methods, along with LA-ICP-MS analysis, to investigate placer gold within the Evotinskii Ore and Placer Region. The findings indicate that native gold within the placers of the EOR is predominantly represented by particles measuring between 0.1 and 1.2 mm, which primarily exhibit forms of cementation, fracture, and interstitial characteristics. The degree of roundness varies, and high-fineness shells and intergranular high-fineness veins are not uncommon. Structural etching revealed a multi-phase, granular, concentric, and vaguely zonal internal structure of the native gold. Furthermore, granulation and twinning structures were also identified. The LA-ICP-MS analysis of the native gold from the placers indicated a diverse array of trace element impurities within the particles. These extensive investigations suggest that the primary sources of placer gold are likely to be ore occurrences similar to the P. Pinigin deposit, as well as sulfide and epithermal occurrences associated with alkaline Mesozoic magmatism, which are prevalent in the Central-Aldan ore region. The possibility of a certain amount of gold originating from mineralizations associated with porphyry systems and iron ore deposits cannot be excluded. The discovery of ore-like particles may signify the proximity of bedrock sources and enhances the potential of the region for the discovery of previously unidentified ore occurrences.