Formation environment and metallogenic mechanism of Weng'an phosphorite in the Early Sinian,Central Guizhou Province |
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| Authors: | Yang Hai-Ying Xiao Jia-Fei Hu Rui-Zhong Xia Yong He Hong-Xi |
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| Institution: | 1.State Key Laboratory of Ore Deposit Geochemistry,Institute of Geochemistry,Chinese Academy of Sciences,Guiyang 550081,China;2.University of Chinese Academy of Sciences,Beijing 100049,China |
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| Abstract: | Weng'an phosphorites are located at the east of Central Guizhou oldland and are important constituent of Hubei-Hunan-Guizhou phosphorite belt. Among them,the Datang ore block developed intact Early Ediacaran stratigraphic sequence,and the phosphorite occurred in the Doushantuo Formation which are divided into the lower layer of dolomite, layer A, the upper layer of dolomite, and layer B. Geochemistry showed that the P2O5 concentration of phosphorites in the layer A was higher than that of layer B,while the Sr and Mg/Ca were opposite. These characteristics indicate the degree of aridity and torridity increased from layer A to layer B. δ13C,δ18O,and Z value in layer A are -4.30‰-2.03‰, -11.30‰-7.53‰, and 112119,respectively,and those of layer B are -1.16‰1.49‰, -8.41‰-2.26‰, and 123129,respectively,indicating that the salinity increased from layer A to layer B. Ceanom of the layer A are greater than -0.1, whereas those of the layer B are less than -0.1, suggesting the redox conditions changing from anoxic to oxic. The NASC-normalized REE distribution patterns of the layer A show “left-inclining”,indicating the input of hydrothermal fluids. Furthermore,the Si,Al,and Ti content in the phosphorite and the periodical change of δ13C indicate the input of terrigenous weathering and deep seawater. The “left-inclining”REE plots,high psephicity,and intraclast and blocky textures of phosphate from the layer A collectively suggest the phosphorite formed via mechanical power of seawater. The “hat-shaped”REE plots and microbial debris of phosphate from the layer B indicate the phosphorite formed via microbially mediated accretionary growth. |
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| Keywords: | geochemistry formation environment ore-forming material metallogenic mechanism Central Guizhou |
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