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《Geochimica》 2005-02
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Rare earth element (REE) geochemistry for scheelite from the Woxi Au-Sb-W deposit, western Hunan

PENG Jian-tang, HU Rui-zhong, ZHAO Jun-hong, FU Ya-zhou, YUAN Shun-da(Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China)  
Hunan is an important Au-, Sb-and W-producer in China. The gold, antimony, tungsten deposits are widespread in western Hunan, and the Woxi Au-Sb-W deposit is the largest in this region. The Woxi deposit was found in 1875 and began to mine in 1895. Due to the characteristic element association and a lasting mining history, the Woxi deposit is famous and attracts a lot of geologists. In spite of previous detailed researches on geological feature, ore genesis, fluid inclusion, stable isotope, ore fabric, ore-controlling tectonic and mineralogy, few attempts have made to study the widespread mineral scheelite in this deposit. The objectives of this contribution are to investigate the rare earth elements of scheelites in the Woxi Au-Sb-W deposit, and attempt to provide some constraints on the REE distribution behavior between scheelite and ore-forming fluid in this deposit. All samples were decomposed through the acid dissolution+alkaline fusion digestion, and analyzed by the ICP-AES method at the Wuhan Analysis Center of Rocks and Minerals, Hubei Province. It is revealed that scheelite samples from this deposit contain considerable concentrations of rare earth elements, with the total REE contents in the range of 40.5 to 123.6 μg/g, and there exists an obvious spatial tendency for REE concentrations in scheelite, i.e. the total REE contents decrease with an increasing elevation in the Woxi mining district, which may be ascribed to a decrease in the total REE concentrations of the ore-forming fluid during transport. All scheelite samples are characterized by MREE-and HREE-enriched, LREE-depleted pattern; the M-type tetrad effect, upward convex curve in REE pattern is observed in all samples, which reveals that fluid effect or water-rock interactions is responsible for scheelite precipitation in the mining district. There exists an obvious fractionation for rare earth elements during scheelite precipitation in the Woxi Au-Sb-W deposit, HREE, especially MREE preferentially incorporate into scheelite lattices by substitution Ca2+. Among all rare earth elements, the distribution coefficient of the element europium between scheelite and the ore-forming fluid is the largest in this deposit. These preferences in scheelite for HREE and MREE are not associated with the REE relative concentrations or REE complex stability in hydrothermal solutions, rather than with the crystallographic factors, especially the Ca-site size in scheelite crystal. The optimum ion radius of substitution site for REE in the scheelite from the Woxi deposit is about 1.046 ?, obviously smaller than the theoretical value of the ideal Ca2+ion (1.12 ?).
【Fund】: 国家自然科学基金(40472053);; 中国科学院“西部之光”人才培养计划项目;; 中国科学院知识创新工程重要方向项目(KZCX3-SW-125)~~
【CateGory Index】: P595
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