Native gold from the Kamenka-Barabanovsky and Kharuzovka alluvial placers (Northwest Salair Ridge, Western Siberia, Russia): Typomorphic features and possible bedrock sources

Abstract

Northwest Salair Ridge, is one of the oldest alluvial gold mining regions; it is located in the western part of the Altai-Sayan folded area. The placers localized along the Kharuzovka and Kamenka-Barabanovsky creeks (the right-branch of the Suenga River) were chosen for investigation. The only bedrock deposit in the study area is the Novolushnikovsky gold deposit located in the Suenginsky placer field of the Egoryevsky district. The source of gold supply for the Kharuzovka and Kamenka-Barabanovsky placers spatially related to the hypothetical continuation of the type II’ ore zones of the Novolushnikovsky deposit. The composition of gold grains derived from placers was determined based on a representative collection. A distinctive feature of native gold from type II’ ores is unusually high content of Hg, up to 20 wt%. The composition of gold grains from studied placers shows that the average Hg content is 1.5–5 wt%. However, there is a group of Hg-rich placers (<1% of the collection), where the mercury content is as high as 16 wt%. We suggest that possible alteration of the gold composition manifested both in the rims and in the cores is represented by significant loss of Hg, while the other analyzed components underwent relative enrichment. The first time reported demercurization processes occurring under the supergenic conditions determine this alteration. The erosion of Novolushnikovsky deposit type II’ ore zones are the source of supply of Hg-rich gold in the Kharuzovka and Kamenka-Barabanovsky placers. These placers were analyzed for the existence of mineral inclusions in gold grains. The presence of placer gold grains with mineral inclusions, that partially or fully correspond to mineral association of ores of the Novolushnikovsky deposit, as well as an unusual Hg-content of the native gold suggest several sources of gold with a similar mineralization style. The undiscovered sources of gold are might be also of intrusion related type.