Zinc and lead isotope signatures of the Zhaxikang PbZn deposit,South Tibet: Implications for the source of the ore-forming metals |
| |
| Institution: | 1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China;2. MLR Key Laboratory of Metallogeny and Mineral Resource Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China;1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China;2. Centre for Exploration Targeting and Australian Research Council Centre of Excellence for Core to Crust Fluid Systems (CCFS), University of Western Australia, Perth, Western Australia 6009, Australia;3. Institute of Mineral Resources, Chinese Academy of Geological Science, Beijing 100037, China;4. Centre for Microscopy, Characterisation and Analysis, University of Western Australia, Perth, WA 6009, Australia |
| |
| Abstract: | Stable Zn isotopes may be applied to trace the source of ore-forming metals in various types of Pb Zn deposits. To test this application, Zn and Pb isotope systematics for sulfides and associated basement rocks as well as FeMn carbonates (gangue) from the Zhaxikang PbZn deposit in South Tibet have been analyzed. The basement in this region includes metamorphosed mafic to felsic rocks (dolerite, quartz diorite, rhyolite porphyry, pyroclastics and porphyritic monzogranite). These rocks have similar δ66Zn values of 0.33 to 0.37‰, with an average value of 0.36 ± 0.03‰ (2σ), except for the more evolved porphyritic monzogranite that has a heavier value of 0.49‰. FeMn carbonates are present as hydrothermal veins and were probably precipitated from magmatic fluids. They have an average δ66Zn value of 0.27 ± 0.05‰, which is slightly lighter than the basement rocks, possibly representing δ66Zn isotopic compositions of the hydrothermal fluids. Sphalerite and galena have similar Zn isotopic compositions with δ66Zn ranging from 0.03 to 0.26‰ and 0.21 to 0.28‰, respectively. Considering the Zn isotope fractionation factor between sphalerite and fluids of − 0.2‰ at ~ 300 °C as reported in literature, hydrothermal fluids from which these sulfides precipitated will have δ66Zn values of ca. 0.39 ± 0.10‰, which are consistent with the values of basement rocks and the FeMn carbonates. This similarity supports a magmatic-hydrothermal origin of the Zhaxikang PbZn deposit. Both Pb and S isotopes in these sphalerite and galena show large variations and are consistent with being derived from a mixture of basement and sedimentary rocks in various proportions. Zn isotopic compositions of the sulfides significantly extend the range of regional basement rocks, suggesting that sedimentary rocks (e.g., shales) are also a significant source of Zn. However, the Zn isotopic compositions of sphalerite and galena differ from those of marine carbonates and those of typical SEDEX-type deposits (e.g. Kelley et al., 2009), confirming a magmatic-hydrothermal model. Combined with regional geological observations and the age constraints of ~ 20 Ma (Zheng et al., 2012, 2014), the results of our investigation indicate that the Zhaxikang PbZn deposit is most likely a magmatic-hydrothermal deposit. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
