Gold from alluvial sediments of the Middle Kyvvozh (Vol’sk-Vym’ ridge, Timan)

The study results of gold from the Middle Kyvvozh alluvial placer (Middle Timan, Russia) are presented. Gold is present at a wide range of grainsize classes - from fine to the nuggets. The morphology of gold is irregular, with the dominance of flattened and cloddy particles of average roundness. Flaky secondary deformed particles of pseudo-ore angular form are found. The overwhelming majority of gold grains are heterogeneous in structure, expressed by discontinuous or continuous very high-grade rims (thickness of the first tens of micro- meters), that indicates the transformation of gold in exogenous conditions, maybe, in the crusts of chemical weathering. In general, the internal parts of gold grains are homogenous and correspond to the gold of high fineness and moderately high-grade gold. The maximal silver content in gold is of up to several tens wt.%. Monotonous silveriness of this gold makes it similar to the gold of gold-quartz-sulphide hydrothermal formations. In the distribution of gold on the silver content (fineness) the polymodal structure is observed, apparently being the reflection of the existence of several types of gold sources or their inhomogeneity. The rare and sometimes coarsegrain (nuggets) gold grains were found, which have a specific mosaic structure of recrystallization, accompanied by epi- gene vein-interstitial (cementing) allocation of electrum (silver content up to 55 wt.%). Inside the discovered gold grains the micro- and submicro-size inclusions of sulfides (chalcopyrite, galena) and also quartz, Mg-Fe-bearing carbonates, silicates etc. were found. The combination of mineralogical data indicates the existence of bedrock sources of gold located directly in the Kyvvozh region.