| Carbonatites in China: A review for genesis and mineralization |
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| 作者姓名： | Cheng Xu Linjun Wang Wenlei Song Min Wu |
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| 作者单位： | Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China; Graduate School, Chinese Academy of Sciences, Beijing 100039, China,Laboratory of Orogenic Belts and Crustal Evolution, Peking University, Beijing 100871, China,Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China; Graduate School, Chinese Academy of Sciences, Beijing 100039, China |
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| 摘 要： | <正>Carbonatites are commonly related to the accumulation of economically valuable substances such as REE.Cu,and P.The debate over the origin of carbonatites and their relationship to associated silicate rocks has been ongoing for about 45 years.Worldwide,the rocks characteristically display more geochemical enrichments in Ba,Sr and REE than sedimentary carbonate rocks.However,carbonatite's geochemical features are disputed because of secondary mineral effects.Rock-forming carbonates from carbonatites at Qinling.Panxi region,and Bayan Obo in China show REE distribution patterns ranging from LREE enrichment to flat patterns.They are characterized by a Sr content more than 10 times higher than that of secondary carbonates.The coarse- and fine-grained dolomites from Bayan Obo H8 dolomite marbles also show similar high Sr abundance,indicating that they are of igneous origin.Some carbonates in Chinese carbonatites show REE(especially HREE) contents and distribution patterns similar to those of the whole rocks.These intrusive carbonatites display lower platinum group elements and stronger fractionation between Pt and Ir relative to high-Si extrusive carbonatite.This indicates that most intrusive carbonatites may be carbonate cumulates.Maoniuping and Daluxiang in Panxi region are large REE deposits.Hydrothermal fluorite ore veins occur outside of the carbonatite bodies and are emplaced in wallrock syenite.The fiuorite in Maoniuping has Sr and Nd isotopes similar to carbonatite.The Daluxiang fiuorite shows Sr and REE compositions different from those in Maoniuping.The difference is reflected by both the carbonatites and rock-forming carbonates,indicating that REE mineralization is related to carbonatites.The cumulate processes of carbonate minerals make fractionated fluids rich in volatiles and LREE as a result of low partition coefficients for REE between carbonate and carbonatite melt and an increase from LREE to HREE.The carbonatite-derived fluid has interacted with wallrock to form REE ore veins.The amount of carbonatite dykes occurring near the Bayan Obo orebodies may support the same mineralization model,i.e.that fluids evolved from the carbonatite dykes reacted with H8 dolomite marble,and thus the different REE and isotope compositions of coarse- and fine-grained dolomite may be related to reaction processes.
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| 关 键 词： | 碳酸岩 岩浆成因 成矿模式 中国 地球化学特征 稀土元素 碳酸盐岩 稀土碳酸盐 |
| 收稿时间： | 6/7/2010 12:00:00 AM |
http://www.sciencedirect.com/science/article/pii/S1674987110000125 |
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| Cheng Xu,Linjun Wang,Wenlei Song,Min Wu.Carbonatites in China: A review for genesis and mineralization[J].Geoscience Frontiers,2010,1(1):105-114. |
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| Authors: | Cheng Xu Linjun Wang Wenlei Song Min Wu |
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| Institution: | 1. Laboratory of Orogenic Belts and Crustal Evolution, Peking University, Beijing 100871, China
2. Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China;Graduate School, Chinese Academy of Sciences, Beijing 100039, China |
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| Abstract: | Carbonatites are commonly related to the accumulation of economically valuable substances such as REE, Cu, and P. The debate over the origin of carbonatites and their relationship to associated silicate rocks has been ongoing for about 45 years. Worldwide, the rocks characteristically display more geochemical enrichments in Ba, Sr and REE than sedimentary carbonate rocks. However, carbonatite's geochemical features are disputed because of secondary mineral effects. Rock-forming carbonates from carbonatites at Qinling, Panxi region, and Bayan Obo in China show REE distribution patterns ranging from LREE enrichment to flat patterns. They are characterized by a Sr content more than 10 times higher than that of secondary carbonates. The coarse- and fine-grained dolomites from Bayan Obo H8 dolomite marbles also show similar high Sr abundance, indicating that they are of igneous origin. Some carbonates in Chinese carbonatites show REE (especially HREE) contents and distribution patterns similar to those of the whole rocks. These intrusive carbonatites display lower platinum group elements and stronger frac-tionation between Pt and Ir relative to high-Si extrusive carbonatite. This indicates that most intrusive carbonatites may be carbonate cumulates. Maoniuping and Daluxiang in Panxi region are large REE deposits. Hydrothermal fluorite ore veins occur outside of the carbonatite bodies and are emplaced in wallrock syenite. The fluorite in Maoniuping has Sr and Nd isotopes similar to carbonatite. The Daluxiang fluorite shows Sr and REE compositions different from those in Maoniuping. The difference is reflected by both the carbonatites and rock-forming carbonates, indicating that REE mineralization isrelated to carbonatites. The cumulate processes of carbonate minerals make fractionated fluids rich in volatiles and LREE as a result of low partition coefficients for REE between carbonate and carbonatite melt and an increase from LREE to HREE. The carbonatite-derived fluid has interacted with wallrock to form REE ore veins. The amount of carbonatite dykes occurring near the Bayan Obo orebodies may support the same mineralization model, i.e. that fluids evolved from the carbonatite dykes reacted with H8 dolomite marble, and thus the different REE and isotope compositions of coarse- and fine-grained dolomite may be related to reaction processes. |
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| Keywords: | Carbonatite Carbonatite parental magmas Carbonate cumulates Carbonatite-expelled fluid REE mineralization |
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