Geologicheskii Vestnik

The paper presents the results of a study of the morphological features and chemical composition of gold from the Zarya gully-type placer, located within the Karasaz placer field (Southern Urals). The material was examined using morphological analysis of heavy-mineral concentrates and SEM–EDS to assess fineness and the distribution of impurities. The study shows that the gold is morphologically uniform and poorly rounded. Tabular, lobate, and platy gold grains predominate; dendritic forms are less common. By economic size classification, the gold in the Zarya placer and its eastern pay streaks falls into the coarse and medium size classes. Sieve analysis indicates that 80% of the mass is concentrated in the +0.5 and +1.0 mm fractions. The placer gold has a fairly uniform composition; silver is the main impurity, ranging from 3 to 20 wt. %. Hypergenic overgrowths on grain surfaces occur as high-fineness rims about 20 µm thick; the difference in Ag content between the core and rim reaches 4.2 wt. %, indicating a short residence time of the grains in the hypergene zone. Some grains form intergrowths with quartz and limonite; isolated grains are coated by mercury amalgam (Hg contents up to 20.74 wt. %), which is attributed to the near-ubiquitous presence of legacy mine workings. The consistent chemical composition of the metal indicates uniform lode sources and their spatial proximity. On the fineness-distribution histogram, the two main peaks for lode (Tukan deposit) and placer (Zarya placer) gold coincide, which suggests that the lode sources are quartz veins hosted mainly within outer contacts of gabbroic chonoliths and dikes of the Early Carboniferous Khudolaz and Ulugurtau complexes, widespread along the watershed of the Uluzbiik Range.

Southern Urals, Karasaz placer field, Zarya placer, gold, source, morphological description, electron microprobe analysis, fineness, trace elements

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