Abstract—

This article provides a comparative analysis of data on the petrology of ore-bearing felsic volcanics and low-temperature near-ore metasomatites of the Streltsovka volcanic structure in Eastern Transbaikalia, the Xiangshan structure in Southern China, and the McDermitt structure in the Western United States. The ore-bearing structures are represented by relatively large resurgent (revived) calderas (Streltsovka and McDermitt) and the Xiangshan volcanic dome with several small calderas in its apical part. The leading geodynamic mechanism of the development and functioning of the magmatic ore systems of these volcanic structures is a crustal extension setting expressed by rifting, which took place during the Late Jurassic–Early Cretaceous in Eastern Transbaikalia; the Late Cretaceous and Early Paleocene in Southern China; and the Miocene, in the McDermitt caldera within the Yellowstone hotspot. Magmatic activity produced bimodal volcanic series of basites–felsic volcanics–basites, and the host rocks of uranium mineralization, as a rule, consist of metaluminous or moderately peraluminous high-K effusive and/or subvolcanic rock types corresponding to A2-type “anorogenic granites.” Rhyolites, rhyodacites, trachyrhyolites, extrusive syenites, quartz syenites, rhyolite dikes and domes of all three volcanic structures are enriched in fluorine and display a fairly high degree of fractionation. The leading types of near-ore metasomatic alteration are preore illitization and argillization, which are succeeded by synore albitization, carbonatization, chloritization, and fluoritization, followed by postore argillization. Ore field structures are defined by the presence of delimiting (ring) faults and the proportions of intracaldera fluid conduits; and ore deposit and orebody structure, by the combination of intrastratal steeply dipping and gently dipping fault. It is demonstrated that, despite different time frames and evolutionary profiles of the structure-forming processes, these volcanic structures display numerous similarities in the evolution of magmatic and hydrothermal processes, and this accounts for their definition as “typical” ore-bearing structures in the current IAEA classification of volcanic-related uranium deposits.