Mineralogical and technological features of gold from placers of the southern slope of Belaya Gora (Khabarovsk Krai) and stages of its formation

The gold-placer deposit of Pokrovsky-Verny streams is formed on the southern slope of Belaya Gora (Khabarovsk Krai), where streams drain gold formations of the same-name deposit. The gold content in the waste dumps of past years often reaches commercial concentrations, which allows to be re-processed them and some of the gold goes back into the dumps. The field formed by ore and alluvial formations is a complex volcanic structure with a concentric-zone structure underlined by faults. At the initial stage of research, the goal was to determine the content of the precious metal in gravity concentrate samples from the placers, the study of the mineralogical and technological characteristics of gold going into dumps. 135 gold grains ranging in size from 10–15 µm to 3 mm were studied using an electron scanning microscope. Six main species were distinguished by composition and morphology: high-grade in the form of isometric crystals; aggregates of gold crystals with 0–29% silver admixture; dendrites with up to 41% silver admixture; grayish gold and silver amalgams; loose weishanite (Au,Ag)3Hg2 formations of gray color; aggregates of ore-bearing and nonmetalliferous minerals with gold, in which the precious metal is less than half the grain. All gold grains have a flattened shape, variably contain inclusions of clay minerals, quartz, hematite, ilmenite, magnetite, limonite. Grains of native metals and intermetallic compounds are isolated in mineral association with gold. The revealed features of gold show that the formation of the precious metal is associated with hypogenic and epithermal processes, as well as with fluid emanations coming through late deep faults. Effective gold recovery requires several stages mineral processing.