| China’s First Independent Cobalt Deposit and its Metallogenic Mechanism: Evidence from Fluid Inclusions and Isotopic Geochemistry |
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| 作者姓名： | FENG Chengyou QI Feng ZHANG Dequan LI Daxin and SHE Hongquan |
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| 作者单位： | 1 School of Earth and Space Sciences, Peking University, Beijing 100871, Chinal;2 Key Laboratory of Metallogeny and Mineral Resource Assessment, Ministry of Land and Resources; Institute of Mineral Resources, CAGS, Beijing 100037, China |
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| 基金项目： | This study was financially supported by grant no. K0901 from the Scientific Research Fund of the China Central Non-Commercial Institute; the Program of Excellent Young Scientists from the Ministry of Land and Resources (200809); grant No. 40302019 from the National Natural Science Foundation of China, and by Geological Survey Program Grant 1212011085528 from the China Geological Survey. We are indebted to Prof. Li Yanhe for assistance with He and Ar isotopic analyses. |
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| 摘 要： | The Tuolugou cobalt deposit is the first independent large-scale Co- and Au-bearing deposit discovered in northwestern China. It is located in the eastern Kunlun orogenic belt in Qinghai Province, and occurs conformably in low-grade metamorphic volcano-sedimentary rock series with well-developed Na-rich hydrothermal sedimentary rocks and typical hydrothermal sedimentary ore fabrics. Fluid inclusions and isotopic geochemistry studies suggest that cobalt mineralizing fluid is dominated by NaCl-H2O system, accompanied by NaCl-CO2-H2O-N2 system responsible for gold mineralization. Massive, banded and disseminated pyrite ores have similar compositions of He and Ar isotopes from the mineralizing fluid, with 3He/4He range between 0.10 to 0.31Ra (averaging 0.21Ra), and 40Ar/36Ar between 302 and 569 (averaging 373), which reflects that Co mineralizing fluids derived dominantly from meteoric water deeply circulating. δ34S values of pyrite approaches to zero (δ34S ranging from ?4.5‰ to +1.5‰, centering around ?1.8‰ to ?0.2‰), reflecting its deep source. Ore lead is characterized by distinctly high radiogenesis, with 206Pb/204Pb>19.279, 207Pb/204Pb>15.691 and 208Pb/204Pb>39.627, and its values show an increase trend from country rocks, regional Paleozoic volcanic rocks to ores. This may have suggested that high radiogentic ore Pb derived mainly from country rocks by leaching meteoric water-dominated hydrothermal fluid during its circulation at depth. Cobalt occurs mainly in sulfide phase (such as pyrite), but cobalt enrichment, and presence and increasing contents of Co-bearing minerals have a positive correlation with metamorphic degree. The Tuolugou deposit and other typical strata-bound Co-Cu-Au deposits have striking similarities in the geological features and metallogenic pattern of primary cobalt. All of them are syngenetic hydrothermal exhalative sedimentation in origin.
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| 关 键 词： | cobalt deposit fluid inclusion isotopic geochemistry SEDEX metallogenic mechanism Tuolugou in Qinghai Province eastern Kunlun orogenic belt |
| 收稿时间： | 2010/12/1 0:00:00 |
| 修稿时间： | 7/8/2011 12:00:00 AM |
China's First Independent Cobalt Deposit and its Metallogenic Mechanism: Evidence from Fluid Inclusions and Isotopic Geochemistry |
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| Authors: | FENG Chengyou QI Feng ZHANG Dequan LI Daxin SHE Hongquan |
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| Institution: | 1. School of Earth and Space Sciences, Peking University, Beijing 100871, China;2. Key Laboratory of Metallogeny and Mineral Resource Assessment, Ministry of Land and Resources;3. Institute of Mineral Resources, CAGS, Beijing 100037, China |
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| Abstract: | The Tuolugou cobalt deposit is the first independent large‐scale Co‐ and Au‐bearing deposit discovered in northwestern China. It is located in the eastern Kunlun orogenic belt in Qinghai Province, and occurs conformably in low‐grade metamorphic volcano‐sedimentary rock series with well‐developed Na‐rich hydrothermal sedimentary rocks and typical hydrothermal sedimentary ore fabrics. Fluid inclusions and isotopic geochemistry studies suggest that cobalt mineralizing fluid is dominated by NaCl‐H2O system, accompanied by NaCl‐CO2‐H2O‐N2 system responsible for gold mineralization. Massive, banded and disseminated pyrite ores have similar compositions of He and Ar isotopes from the mineralizing fluid, with 3He/4He range between 0.10 to 0.31Ra (averaging 0.21Ra), and 40Ar/36Ar between 302 and 569 (averaging 373), which reflects that Co mineralizing fluids derived dominantly from meteoric water deeply circulating. δ34S values of pyrite approaches to zero (δ34S ranging from –4.5‰ to +1.5‰, centering around ‐1.8‰ to ‐0.2‰), reflecting its deep source. Ore lead is characterized by distinctly high radiogenesis, with 206Pb/204Pb>19.279, 207Pb/204Pb>15.691 and 208Pb/204Pb>39.627, and its values show an increase trend from country rocks, regional Paleozoic volcanic rocks to ores. This may have suggested that high radiogentic ore Pb derived mainly from country rocks by leaching meteoric water‐dominated hydrothermal fluid during its circulation at depth. Cobalt occurs mainly in sulfide phase (such as pyrite), but cobalt enrichment, and presence and increasing contents of Co‐bearing minerals have a positive correlation with metamorphic degree. The Tuolugou deposit and other typical strata‐bound Co‐Cu‐Au deposits have striking similarities in the geological features and metallogenic pattern of primary cobalt All of them are syngenetic hydrothermal exhalative sedimentation in origin. |
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| Keywords: | cobalt deposit fluid inclusion isotopic geochemistry SEDEX metallogenic mechanism Tuolugou in Qinghai Province eastern Kunlun orogenic belt |
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