Uranium scavenging during mineral replacement reactions

作者：Li Kan^*; Pring Allan; Etschmann Barbara; Macmillan Edeltraud; Ngothai Yung; O'Neill Brian; Hooker Anthony; Mosselmans Fred; Brugger Joel

来源：American Mineralogist, 2015, 100(8-9): 1728-1735.

DOI：10.2138/am-2015-5125

• Uranium
• scavenging
• IOCG deposits
• experiment
• sulfidation reaction
• interface coupled dissolution-reprecipitation reactions

Interface coupled dissolution-reprecipitation reactions (ICDR) are a common feature of fluid-rock interaction during crustal fluid flow. We tested the hypothesis that ICDR reactions can play a key role in scavenging minor elements by exploring the fate of U during the experimental sulfidation of hematite to chalcopyrite under hydrothermal conditions (220-300 degrees C). The experiments where U was added, either as solid UO2+X(s) or as a soluble uranyl complex, differed from the U-free experiments in that pyrite precipitated initially, before the onset of chalcopyrite precipitation. In addition, in UO2+X(s)-bearing experiments, enhanced hematite dissolution led to increased porosity and precipitation of pyrite+magnetite within the hematite core, whereas in uranyl nitrate-bearing experiments, abundant pyrite formed initially, before being replaced by chalcopyrite. Uranium scavenging was mainly associated with the early reaction stage (pyrite precipitation), resulting in a thin U-rich line marking the original hematite grain surface. This "line" consists of nanocrystals of UO2+X(s), based on chemical mapping and XANES spectroscopy. This study shows that the presence of minor components can affect the pathway of ICDR reactions. Reactions between U- and Cu-bearing fluids and hematite can explain the Cu-U association prominent in some iron oxide-copper-gold (IOCG) deposits.

• 出版日期2015-9