Nd-Sr-Pb Isotopic Geochemistry of Scheelite from the Woxi W-Sb-Au Deposit, Western Hunan:Implications for Sources and Evolution of Ore-forming Fluids
PENG Bo 1) , Robert FREI 2) , TU Xianglin 3) 1)Faculty of Resource and Environment Science, Hunan Normal University, Changsha, Hunan, 410081 2) The Geological Institute, University of Copenhagen, Oster Voldgade 10, DK-1350 Copenhagen K, Denmark 3) Guangzhou Institute of Geochemistry, Chinese Academy of Science, Guangzhou, Guangdong, 510640
This study carries out a systematic Nd-Sr-Pb isotopic analyzing on scheelites from the V4 ore vein of the Woxi W-Sb-Au ore deposit in western Hunan, China. The results show that the Sm and Nd concentrations in scheelite are a bit lower, with variable ratios of Sm/Nd (1.11 ～ 2.22) and 147 Sm / 144 Nd (0.64 ～ 1.27), and the ε_ Nd values (compared to values at 199Ma) of scheelite are also low, ranging from-27.4 to-19.9 with an average of-25.5 (n = 9). The 87 Sr / 86 Sr ratios of scheelite are high, varying from 0.7476 to 0.7504 with an average of 0.7496 (n = 11), which represents the initial 87 Sr / 86 Sr ratio of scheelite at 199 Ma. Lead-step leaching analyzing results show that the ratios of 206 Pb / 204 Pb , 207 Pb / 204 Pb , and 208 Pb / 204 Pb of scheelite are in narrow variety with averages of 18.11, 15.1, and 38.6, respectively, and these ratios of scheelites are similar to the corresponding ratios of the pyrite from the same gold-bearing quartz veins, of the alternated host rocks, and of the regional slates of the Banxi Group. The above Nd-Sr-Pb isotopic data of scheelite, complementing with previous results of Sr isotopes of sphalerite and stibnite, show that the ore-forming fluids for the mineralization might include the following possible source fluids: fluid from the ancient continental crust beneath the host rock (the Banxi Group), fluid from deep granitoid magmas, and fluid from the host rock. The ore-forming fluid is a mixture of the above source fluids. The mineralization most possibly was due to the mixing of the above fluids of different sources, and the ores might be the products of mixing the fluids from different sources. The fluid evolution might include two major stages:The early stage was probably characterized by mixing the upward fluid from the ancient continental crust underneath the host rock (the Banxi Group), with those from the host rock. This early stage of fluid mixing might have led the early stage of mineralization represented by tungsten ores. The later stage was characterized by mixing the upward granitoid fluid from the deep magmatic chamber with those from the host rock. This stage of fluid mixing might have caused the later stage of mineralization represented by antimony and gold ore for the deposit. The W-Sb-Au mineralization was mostly due to the combination of the above two stages of fluid mixing. The upward emplacement of fluids from both the ancient continental crust underneath the host rock and the deep granitoid magmas, was probably caused by the intracontinental orogenesis during the Mesozoic period, and the W-Sb-Au mineralization for the deposit was possibly due to the superposition of the above two stages of mineralization.
【Fund】： 国家自然科学基金项目(编号40002021);; 教育部留学回国科研启动基金项目(2000年)资助的成果。
【CateGory Index】： P618.67;P597
【CateGory Index】： P618.67;P597