Internal Structures of Placer Gold Grains As Prospecting Indicators of Primary Gold Sources in the Northeast of the Siberian Platform

Typomorphic features of placer gold are carriers of important information necessary for reconstruction of the formation history of gold placers and can be used as mineralogical criteria to search primary sources. The internal structure of grains of native gold is one of the most informative features. Internal structures of gold grains from modern placers and Early Permian conglomerates in the northeast of the Siberian Platform are studied. Structural etching of native gold was performed using the reagent (HCl + HNO 3 + FeCl 3 ⋅6H 2 O + CrO 3 + thiurea + water). It was found that the well-rounded high-grade gold grains from modern placers experienced repeated redeposition through intermediate reservoirs. The discovery of slightly rounded gold grains, the internal structure of which bear no signs of exogenous transformation indicates that they were supplied to the modern alluvium from a nearby primary source. Apo-carbonate hydrothermal–metasomatic formations with the disseminated gold-sulfide mineralization were identified in the course of gold-ore exploration.