The Occurrence State of Metal Sulfides and Its Relationship with Uranium Mineralization in Diantou-Shuanglong Area,Ordos Basin
In the exploration of sandstone-hosted uranium deposits,besides pyrite,other types of metal sulfides have been identified.Nevertheless,there is currently a lack of systematic investigation and research into the metal sulfides about their complex mineral types,microstructure,occurrence characteristics,and relationship with uranium minerals.Therefore,this paper takes the ore-bearing rock strata of the Middle Jurassic Zhiluo Formation in the Diantou-Shuanglong area as the research object.By utilizing optical microscopes,scanning electron microscopes,energy spectrometer,and synchrotron X-ray fluorescence,a large number of metal sulfides were identified,mainly including pyrite,sphalerite,chalcopyrite,and galena.Furthermore,in the transition zone of ore-bearing sandstone,the four principal metal sulfides manifest residual oxidation traces and are replaced by uranium minerals.Through the statistical analysis of the content of metal sulfides,the distribution of various metal sulfides in different zones of the ancient interlayer oxidation zone is as follows,ranked from highest to lowest content:ore-bearing sandstone in the transition zone＞gray ore-free sandstone in the reduction zone＞green sandstone in the secondary reduction zone≥oxidized red sandstone.The order of different types of metal sulfides content from high to low is pyrite＞sphalerite＞chalcopyrite ≥ galena.Comprehensive analysis indicates that the acidic or weakly acidic groundwater and the presence of Fe3+in the oxidation zone can provide favorable conditions for the oxidation of metal sulfides.Uranyl ions accompanied by ion complexes formed by oxidation of metal sulfides migrate in the uranium reservoir with the oxidizing fluid.As reducing media dominates,the migrated metal ions are re-enriched and precipitated in the transition zone to form mineralization stage metal sulfides.Meanwhile,SO42-formed by oxidation of metal sulfides in the transition zone can be reduced to H2S,which has a strong reducing ability for uranyl ions.Therefore,metal sulfides are closely associated with uranium minerals,indicating that beyond the well-known pyrite,other metal sulfides can also serve as reducing agents,actively participating in the enrichment and precipitation of uranium.This discovery offers valuable insights for the study of inorganic reducing media in other sandstone-hosted uranium deposits.
metal sulfidesuranium mineralizationZhiluo Formationmetallogenic modelDiantou-Shuanglong areaOrdos Basin
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