Typomorphism, Composition, and Probable Sources of Alluvial Gold in the Southern Part of the Ochparma Upland (Southern Timan)

A comprehensive study of the morphological features and chemical composition of alluvial gold discovered in the Ochparma Upland (the Southern Timan, the Vol River) has been conducted for the first time. It has been established that gold grains are predominantly plate-like, scaly and flat-cake-shaped with a shagreen and tuberculate surface; their size varies within 0.1–0.25 mm. The internal structure of the particles is heterogeneous. The main impurity in gold is silver (Ag 0.1–31.39 wt %), and individual grains contain copper (Cu 0.78–1.25 wt %). Riphean schists of the Pokyuk formation, characterized by sulphide mineralization, are considered as a probable primary source of gold in the Southern Timan. Authigenic gold associated with pyrite has been discovered in these rocks for the first time. Pyrite contains inclusions of galena and scotlandite, indicating hydrothermal-metamorphic transformations of the rock. The fineness of alluvial gold (650–850‰) and the presence of Co (up to 5.85 wt %) and As (up to 4.08 wt %) impurities in pyrite suggest its connection with the gold-quartz type of the primary source. The similarity of typomorphic features of alluvial gold in the Southern and Middle Timan indicates the possible existence of a single gold ore zone within the Timan ridge.