Kurtmaly Gold Placer: Geology, Geochemical Features of the Metal, Relationship with Indigenous Sources (Southern Urals, Russia)

The article briefly outlines the geological structure of the Aktash ore field (East and West Aktash bedrock occurrences and the Kurtmaly placer). It is shown that the East Aktash ore occurrence belongs to the gold-quartz-sulfide formation. The richest mineralization is localized either along the contacts of the gabbro-diorite dike or in it itself. In terms of chemical composition, gold is of medium fineness (821–859) and is most often found in the composition of quartz-sulfide or quartz-carbonate mineral associations. The content reaches tens and even hundreds of grams per ton. Ore bodies of the West Aktash ore occurrence are represented by quartz metasomatites with sulfides and stockwork-type quartz veinlets. Abnormally high gold contents were found in zones of silicification development. The gold is high-fineness (880–998), its typomorphic feature is a consistently high bismuth content (0.1–0.3%), which is characteristic of quartz veins of the gold-quartz formation of the Southern Urals. The Kurtmaly placer, located in the valley of the Aktash creek, contains gold particles of both medium roundness and completely unrounded. Their chemical composition is noticeably different from the gold from nearby ore occurrences; it is low-grade (550–600) gold. The primary sources for the placer could be zones of quartz-sulfide mineralization, brown iron ores of the Kurtmaly deposit, as well as carbonaceous shales of the Avzyan and Zigazin-Komarovo Formations. In conclusion, the article substantiates the high prospects of the Aktash ore field for both primary and placer gold.