Placer Gold Deposits of the Shagan-Oba River (Eastern Kazakhstan)

Abstract

The aim of this study is to identify the patterns of gold distribution and the mineral composition of placers in the Shagan-Oba River (Eastern Kazakhstan) area in order to clarify their genesis and assess the prospects for further exploration. The study employed methods of panning sampling, mineralogical analysis, and electron microprobe investigation of heavy minerals. The results show that the distribution of gold is closely related to the morphology of alluvial terraces and the composition of heavy mineral assemblages. Elevated gold contents were recorded in certain grain-size fractions (0.25 mm and 0.5–1.0 mm); the concentrates are dominated by quartz, magnetite, ilmenite, and titanite. The morphology of gold grains and their association with accessory minerals indicate a mixed origin, caused both by the re-deposition of ancient placers and by the influx of gold from nearby primary sources. The ancient placers, identified on terrace-like ledges of bedrock and on the valley slopes of the Shagan-Oba River, represent remnants of eroded alluvium resting on a bedrock floor.