New mineral uramarsite, a hydrous ammonium ura-nylarsenate, was found in the supergene zone of the Bota-Burum molybdenite-pitchblende deposit (southern Kazakhstan), which is made up of carbonatized fel-site porphyry and tuff breccia. In the supergene zone, the uranium mineralization is represented by arsenate uranite; the molybdenum mineralization, by U-bearing powellite and less abundant wulfenite. According to Kopchenova and Skvortsova , the close association of pitchblende with fine-grained molybdenite, arse-nopyrite, and pyrite in primary ores defined the specifics of supergene mineralization. At the initial stage of supergene zone formation, arsenates of Al and Fe (mansfieldite and pharmacosiderite) were formed under acid conditions in the arsenopyrite-rich zones. Uranites (uranospinite, sodium uranospinite, metaze-unerite, chistyakovaite, and uramarsite) were formed at the last stage. Researchers of the process of mineralization at the Bota-Burum deposit noted that the oxidation of pitchblende-sulfide mineralization is confined to the highly fractured zones in the hydrothermally altered felsic rocks. The formation of ammonium uranite (uramarsite) is just related to these processes. The name of the new mineral reflects its chemical composition.
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