The Qiangtang Basin（QB）, located in the central Tibetan Plateau, is a Jurassic marine basin and one of the most important prospective salt resource belts in China. In recent decades, many outcrops of gypsiferous bed...The Qiangtang Basin（QB）, located in the central Tibetan Plateau, is a Jurassic marine basin and one of the most important prospective salt resource belts in China. In recent decades, many outcrops of gypsiferous bed have been found in the Jurassic marine strata in the basin. Salt springs with abnormally high sodium（Na-＋） contents had been identified in the Late Jurassic Xiali Formation（Fm.） in the basin in the last years. However, to date, no potash or halite deposits have been identified in the QB. Gypsum outcrops and salt springs are very important signs in the investigation of halite and potash deposits. Therefore, the Xiali Fm. is a potentially valuable layer to evaluate for the possible presence of halite and potash deposits in the basin. However, few studies have explored the formation conditions of evaporites in the unit. Here, we present detailed geochemical records from the Yanshiping section related to the study of the formation conditions of evaporites in the Xiali Fm. of the QB. Climate proxies based on the obviously increased anion concentrations of SO4（2-） and Cl-- and the significant correlation coefficients of Ca2＋-SO42-（R = 0.985） and Na-＋-Cl--（R = 0.8974） reveal that the upper member of the Xiali Fm.（the upper Xiali Fm.） formed under an arid climate and evolved into the sulfate phase or early chloride phase. Provenance proxies based on the obviously increased K-＋ and Na-＋ ion concentrations and the significant correlation coefficient of Na-＋-Cl--（R = 0.8974） suggest that the upper Xiali Fm. featured optimal provenance conditions for the possible formation of halite deposits. The regression and the semi-closed tidal flat environment in the upper Xiali Fm. were favorable for the formation of potash and halite deposits. The low Mg-（2＋） /Ca-（2＋） values（mean value = 1.82） and significant Na-＋-Cl-- correlation coefficient（R = 0.8974） also suggest that the upper Xiali Fm. is the layer most likely to contain potential halite deposits. In 展开更多
The Chengchao iron deposit,the largest high-grade skarn iron deposit in southeastern Hubei Province,contains considerable amounts of magnetite and by-product anhydrite.To obtain better understanding of the ore-formati...The Chengchao iron deposit,the largest high-grade skarn iron deposit in southeastern Hubei Province,contains considerable amounts of magnetite and by-product anhydrite.To obtain better understanding of the ore-formation process,this study carried out He-Ar-S-Pb multi-isotopic analyses on the pyrites formed during two stages of mineralization.The results indicate that the δ34S values（ranging from 14.0‰ to 17.6‰） of pyrites formed from the two stages have no obvious differences,suggesting that they were not derived from a single magmatic sulfur source.The δ34S values of anhydrite mostly range from 21.9‰ to 28.4‰,similar to that of the Middle Triassic sedimentary anhydrite in the Middle-Lower Yangtze River metallogenic belt（MLYRB）.The Pb isotopic compositions of the pyrites of both stages are homogeneous,with values of 208Pb/204Pb,207Pb/204Pb,and-206Pb/204Pb being 38.006-38.257,15.523-15.556,and 17.806-18.052,respectively,indicating a mixed crust-mantle source.The He-Ar results exhibit different compositions of the two stages：the -3He/-4He（R/Ra） and 40Ar/-36Ar values for the early-stage pyrite are 0.46-0.63 and 311-322,respectively,whereas the values for late-stage pyrite are 0.23-0.34 and 305-361,respectively.Both stages of pyrites indicate the multiple sources of the ore-forming fluids,with decreasing amount of magmatic water and increasing amount of modified meteoric water（MASW） during fluid evolution.The Triassic evaporites played an important role in the mineralization process.展开更多
基金supported by the National Basic Research Program of China (Grant Nos.2011CB403003 and 2013CB956403)"Strategic Priority Research Program" of the Chinese Academy of Sciences (Grant No.XDB03020402)+1 种基金the National Natural Science Foundation of China (Grant No.41272128)the College Research Program of Gansu Province (Grant No.2016A-123)
文摘The Qiangtang Basin（QB）, located in the central Tibetan Plateau, is a Jurassic marine basin and one of the most important prospective salt resource belts in China. In recent decades, many outcrops of gypsiferous bed have been found in the Jurassic marine strata in the basin. Salt springs with abnormally high sodium（Na-＋） contents had been identified in the Late Jurassic Xiali Formation（Fm.） in the basin in the last years. However, to date, no potash or halite deposits have been identified in the QB. Gypsum outcrops and salt springs are very important signs in the investigation of halite and potash deposits. Therefore, the Xiali Fm. is a potentially valuable layer to evaluate for the possible presence of halite and potash deposits in the basin. However, few studies have explored the formation conditions of evaporites in the unit. Here, we present detailed geochemical records from the Yanshiping section related to the study of the formation conditions of evaporites in the Xiali Fm. of the QB. Climate proxies based on the obviously increased anion concentrations of SO4（2-） and Cl-- and the significant correlation coefficients of Ca2＋-SO42-（R = 0.985） and Na-＋-Cl--（R = 0.8974） reveal that the upper member of the Xiali Fm.（the upper Xiali Fm.） formed under an arid climate and evolved into the sulfate phase or early chloride phase. Provenance proxies based on the obviously increased K-＋ and Na-＋ ion concentrations and the significant correlation coefficient of Na-＋-Cl--（R = 0.8974） suggest that the upper Xiali Fm. featured optimal provenance conditions for the possible formation of halite deposits. The regression and the semi-closed tidal flat environment in the upper Xiali Fm. were favorable for the formation of potash and halite deposits. The low Mg-（2＋） /Ca-（2＋） values（mean value = 1.82） and significant Na-＋-Cl-- correlation coefficient（R = 0.8974） also suggest that the upper Xiali Fm. is the layer most likely to contain potential halite deposits. In
基金supported by the National Basic Research Program of China(973 Program:2012CB416802)the National Special Research Programs for Non-Profit Trades(Sponsored by MLR,201311136)the Basic Scientific Research Operation Cost of StateLeveled Public Welfare Scientific Research Courtyard (K1203)
文摘The Chengchao iron deposit,the largest high-grade skarn iron deposit in southeastern Hubei Province,contains considerable amounts of magnetite and by-product anhydrite.To obtain better understanding of the ore-formation process,this study carried out He-Ar-S-Pb multi-isotopic analyses on the pyrites formed during two stages of mineralization.The results indicate that the δ34S values（ranging from 14.0‰ to 17.6‰） of pyrites formed from the two stages have no obvious differences,suggesting that they were not derived from a single magmatic sulfur source.The δ34S values of anhydrite mostly range from 21.9‰ to 28.4‰,similar to that of the Middle Triassic sedimentary anhydrite in the Middle-Lower Yangtze River metallogenic belt（MLYRB）.The Pb isotopic compositions of the pyrites of both stages are homogeneous,with values of 208Pb/204Pb,207Pb/204Pb,and-206Pb/204Pb being 38.006-38.257,15.523-15.556,and 17.806-18.052,respectively,indicating a mixed crust-mantle source.The He-Ar results exhibit different compositions of the two stages：the -3He/-4He（R/Ra） and 40Ar/-36Ar values for the early-stage pyrite are 0.46-0.63 and 311-322,respectively,whereas the values for late-stage pyrite are 0.23-0.34 and 305-361,respectively.Both stages of pyrites indicate the multiple sources of the ore-forming fluids,with decreasing amount of magmatic water and increasing amount of modified meteoric water（MASW） during fluid evolution.The Triassic evaporites played an important role in the mineralization process.
