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Sm-Nd and Sr Isotope Geochemistry of Hydrothermal Scheelite from the Zhazixi W-Sb Deposit,Western Hunan

PENG Jiantang1), ZHANG Dongliang1,2), HU Ruizhong1), WU Mengjun3), LIN Yuanxian4)1)State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550002; 2) Graduate School, Chinese Academy of Sciences, Beijing, 100049; 3) Zhaizixi Antimony Mine, Anhua County, Hunan Province, 413500; 4) Tianjin Institute of Geology and Mineral Resources, Tianjin, 300170  
The Zhazixi W-Sb deposit, located in the middle part of Xuefengshan arc tectonic zone, is one of typical vein-filled hydrothermal deposits in China. Sm-Nd and Sr isotope systematics of scheelite from the Zhazixi W-Sb deposit have been investigated in this paper. It shows that there exists a relatively wide variation in Sm/Nd ratios for the scheelite samples collected from this deposit (0.36~0.63), and its 143Nd/144Nd values fall in the range of 0.51211~0.51288. Scheelite samples are scattered in the diagram of 147Sm/144Nd-143Nd/144Nd, which has no geochronological implications for W-Sb mineralization in the studied deposit. and it is impossible to define exact metallogenic time for the deposit. Nd isotope initial compositions of the samples can be classified into two groups, -10.2~-14.7 and -3.79~+0.01. The ore-forming fluid are mainly derived from two sources: one probably originating from the Prototerozoic sequence or underlying terrigenous basement clastic rocks and the other probably related to the basic/ultrabasic rocks of the Lengjiaxi Group. Contrary to the Nd isotope, Sr isotope compositions of the mineralized fluids in the Zhazixi W-Sb deposit are relatively homogenized, and the 87Sr/86Sr values of scheelite vary from 0.7304 to 0.7329. This kind of high radiogenic Sr excludes the possibility that the ore-forming fluid of the Zhazixi deposit is predominately derived from seawater and that host strata are sole sourebed for the ore-forming materials of the studied deposit. Comparison with the adjacent Woxi Au-Sb-W deposit reveals both deposits display distinct differences in sources of ore-forming materials; the sourcebed of the Woxi deposit should be an older, more mature and more radiogenic Sr-rich underlying basement.
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