| Isotope geochemistry of ore fluids for the Dongsheng sandstone-type uranium deposit, China |
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| 作者姓名： | 李荣西 王兴理 |
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| 作者单位： | Chang'an University，Institute of Geochemistry Chinese Academy of Sciences，Xi'an 710054 China，Guiyang 550002 China |
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| 摘 要： | The Dongsheng sandstone-type uranium deposit is one of the large-sized sandstone-type uranium deposits discovered in the northern part of the Ordos Basin of China in recent years. Geochemical characteristics of the Dongsheng uranium deposit are significantly different from those of the typical interlayered oxidized sandstone-type uranium ore deposits in the region of Middle Asia. Fluid inclusion studies of the uranium deposit showed that the uranium ore-forming temperatures are within the range of 150–160℃. Their 3He/4He ratios are within the range of 0.02–1.00 R/Ra, about 5–40 times those of the crust. Their 40Ar/36Ar ratios vary from 584 to 1243, much higher than the values of atmospheric argon. The δ18OH2O and δD values of fluid inclusions from the uranium deposit are -3.0‰– -8.75‰ and -55.8‰– -71.3‰, respectively, reflecting the characteristics of mixed fluid of meteoric water and magmatic water. The δ18OH2O and δD values of kaolinite layer at the bottom of the uranium ore deposit are 6.1‰ and -77‰, respectively, showing the characteristics of magmatic water. The δ13CV-PDB and δ18OH2O values of calcite veins in uranium ores are -8.0‰ and 5.76‰, respectively, showing the characteristics of mantle source. Geochemical characteristics of fluid inclusions indicated that the ore-formation fluid for the Dongsheng uranium deposit was a mixed fluid of meteoric water and deep-source fluid from the crust. It was proposed that the Jurassic-Cretaceous U-rich metamorphic rocks and granites widespread in the northern uplift area of the Ordos Basin had been weathered and denudated and the ore-forming elements, mainly uranium, were transported by meteoric waters to the Dongsheng region, where uranium ores were formed. Tectonothermal events and magmatic activities in the Ordos Basin during the Mesozoic made fluids in the deep interior and oil/gas at shallow levels upwarp along the fault zone and activated fractures, filling into U-bearing clastic sandstones, thus providing necessary energy for the formation of uranium ores.
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| 关 键 词： | 中国 东胜铀矿 沙岩型铀矿 成矿流体 同位素 地球化学 |
| 收稿时间： | 2006-04-10 |
| 修稿时间： | 2006-06-11 |
Isotope geochemistry of ore fluids for the Dongsheng sandstone-type uranium deposit, China |
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| Rongxi Li,Xingli Wang.Isotope geochemistry of ore fluids for the Dongsheng sandstone-type uranium deposit, China[J].Chinese Journal of Geochemistry,2007,26(2):114-122. |
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| Authors: | Rongxi Li Xingli Wang |
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| Institution: | (1) Chang’an University, Xi’an, 710054, China;(2) Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550002, China |
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| Abstract: | The Dongsheng sandstone-type uranium deposit is one of the large-sized sandstone-type uranium deposits discovered in the northern
part of the Ordos Basin of China in recent years. Geochemical characteristics of the Dongsheng uranium deposit are significantly
different from those of the typical interlayered oxidized sandstone-type uranium ore deposits in the region of Middle Asia.
Fluid inclusion studies of the uranium deposit showed that the uranium ore-forming temperatures are within the range of 150–160°C.
Their 3He/4He ratios are within the range of 0.02–1.00 R/Ra, about 5–40 times those of the crust. Their 40Ar/36Ar ratios vary from 584 to 1243, much higher than the values of atmospheric argon. The δ18OH2O and δD values of fluid inclusions from the uranium deposit are −3.0‰–−8.75‰ and −55.8‰–−71.3‰, respectively, reflecting the
characteristics of of meteoric water and magmatic water. The δ18OH2O and δD values of kaolinite layer at the bottom of the uranium ore deposit are 6.1‰ and −77‰, respectively, showing the characteristics
of magmatic water. The δ13CV-PDB and δ18OH2O values of calcite veins in uranium ores are −8.0‰ and 5.76‰, respectively, showing the characteristics of mantle source.
Geochemical characteristics of fluid inclusions indicated that the ore-formation fluid for the Dongsheng uranium deposit was
a mixed fluid of meteoric water and deep-source fluid from the crust. It was proposed that the Jurassic-Cretaceous U-rich
metamorphic rocks and granites widespread in the northern uplift area of the Ordos Basin had been weathered and denudated
and the ore-forming elements, mainly uranium, were transported by meteoric waters to the Dongsheng region, where uranium ores
were formed. Tectonothermal events and magmatic activities in the Ordos Basin during the Mesozoic made fluids in the deep
interior and oil/gas at shallow levels upwarp along the fault zone and activated fractures, filling into U-bearing clastic
sandstones, thus providing necessary energy for the formation of uranium ores. |
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| Keywords: | He-Ar isotopes fluid inclusion uranium ore |
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