SHEN Nengping1*, ZHANG Zhengwei1, YOU Fuhua1, 2, PENG Jiantang1, ZHU Xiaoqing1, and XIAO Jiafei1
1 State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China
2 Graduate University of Chinese Academy of Sciences, Beijing 100049, China
Abstract The polymetallic (Pb, Zn, Cu, etc) ore belt on the southwestern margin of Tarim is one of the major regions with the greatest prospecting potential in Xinjiang. Reported in this paper are the lead isotope data for 66 sulfide samples (including 50 galena samples, 15 chalcopyrite samples and 1 pyrite sample) collected from such representative deposits as Tamu, Tiekelike, Kalangu, Abalieke, etc. in this ore belt. The Pb isotopic ratios of 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb in the galena samples range from 17.931 to 18.176, 15.609 to 15.818 and 38.197 to 38.944, with the average values of 18.017, 15.684 and 38.462, respectively. Those in the chalcopyrite samples range from 17.926 to 18.144, 15.598 to 15.628 and 38.171 to 38.583, with the average values of 18.020, 15.606 and 38.262, respectively. The pyrite sample has the Pb isotopic ratios of 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb to be 17.980, 15.604 and 38.145, respectively. In combination with the previous Pb isotope data for sulfides, it is found that there is only a slight variation in the Pb isotopic composition of galena, chalcopyrite, sphalerite and pyrite in the ore belt. However, there is some difference in Pb isotopic characteristics between galena and chalcopyrite, especially the Pb isotopic composition of galena shows an obvious linear correlation with some other relevant parameters (e.g. Dβ and Dγ). The comprehensive analysis suggested that lead in galena (maybe including sphalerite and pyrite) was derived principally from wall rocks and underlying basement, and that in chalcopyrite only originated from the basement. The single-stage model ages of these sulfides couldn’t indicate the time limit of metallogenesis (Pb, Zn, Cu, etc.), and the positive linear correlations for the Pb isotopic composition of galena are of no single-stage and two-stage Pb-Pb isochron significance. Furthermore, there are significant differences in Pb isotopic composition characteristics between the genetic type of deposits in this polymetallic ore belt and the Mississippi Valley type (MVT). In addition, the authors also pointed out that there is a phenomenon of differentiation (not paragenesis) for lead and copper elements during the process of metallogenesis in this ore belt.
Key words lead isotope; lead source; Pb-Zn-Cu deposit; southwestern margin of Tarim
* Corresponding author, E-mail:shennengping@vip.gyig.ac.cn
CHINESE JOURNAL OF GEOCHEMISTRY Vol. 31, No. 4, 2012, page 362-375
© Science Press and Institute of Geochemistry, CAS and Springer-Verlag Berlin Heidelberg 2012
