Genetic primary source–placer connection as a case-study of the Gorny Priisk gold deposit, Avzyan оre placer field, Southern Urals

The study of the Avzyan ore placer field shows that native gold of the Gorny Priisk deposit is predominantly small (up to 0...n mm) and has a high fineness (955–980). The main impurity is silver 3–5 wt.%, and insignificant amounts of Bi, As, Sb, Se, Te and Ni are observed. Morphologically, gold represents spongy and dendritic forms. Microparticles of very high-fineness secondary gold 0.1–0.5 μm in size are observed on the surface of grains. Gold of the Kamenny Klyuch placer is larger and has a lumpy and irregular shape. This is a high-fineness gold (926–979) with a similar set of impurity elements. The morphology of gold grains from the Kamenny Klyuch creek deposits clearly indicates their short distance from the primary source. The alluvial gold of the Avzyan placer has the largest sizes and belongs to the medium and large size categories with good roundness. The fineness of gold is 939–971. It is characterized by hypergene neoplasms on the grain surface in the form of a high-fineness rim. Grains covered with amalgam with mercury content up to 20 wt.% are revealed, which indicates the induced contamination of the area of mining. A genesis and geology model of the bedrock–weathering crust–alluvial placer systems was built. It is shown that the valley of the Bolshoy Avzyan river is a valley of inherited development. The presence of gold of varying roundness (from poorly rounded to well-rounded grains with a high-fineness shell) is reflective of gold flow to the placer from the weathering crust (Gorny Priisk) through intermediate reservoir rocks (Kamenny Klyuch).The study was supported by the Russian Science Foundation, Grant No. 23-27-00265, https://rscf.ru/en/project/23-27-00265/.