Typomorphism of Native Gold of the Klyuchevsky Ore-Placer District (Eastern Transbaikalia)

The article presents the results of studies of morphology, grain-size distribution, chemical composition, and characteristic mineral parageneses of native gold from the Klyuchevsky deposit, as well as their comparison with gold from placer sources in the Davenda–Klyuchevsky district. The research clearly demonstrates that native gold from the Davenda–Klyuchevsky ore-placer cluster corresponds to gold from a bedrock source in terms of fineness, grain size distribution, and mineral assemblages. Based on the relationship of minerals, two varieties of native gold have been identified, which differ in fineness. The crystallization of native gold with a lower purity level is associated with the earliest formation processes at the Klyuchevsky deposit; the deposition of gold with a relatively high purity level is associated with the influence of later hydrothermal fluids, which is supported by the synchronous formation of massive sulfide association minerals. The bimodal nature of the gold distribution is typical for all gold–sulfide–quartz objects in the region. The results presented in this study suggest the influence of intrusions of the Amanan and Amudjikan–Sretensk complexes on the formation of the multistage mineralization at the Klyuchevsky deposit. Inherent characteristics of the chemical composition of native gold and its association with certain sulfides support the hypothesis of two stages in the formation of gold mineralization. This is also consistent with the close association of native gold with tourmaline and later formation of large metasomatic pyrite crystals, similar in time to the aggregates of late mineral assemblages including fahlore, galena, sphalerite, and arsenopyrite. Comparative analysis of gold from hardrock gold deposits and placers makes it possible not only to identify the sources of the latter, but also to obtain additional data to improve understanding of the genesis of gold–quartz–sulfide objects in Eastern Transbaikalia.