Constraints of C-O-S-Pb isotope compositions and Rb-Sr isotopic age on the origin of the Tianqiao carbonate-hosted Pb-Zn deposit, SW China

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• 作者：Jiaxi Zhou^a ; ^b ; Zhilong Huang^a ; ^{huangzhilong@vip.gyig.ac.cn} ; Meifu Zhou^b ; Xiaobiao Li^a ; Zhongguo Jin^a
• 关键词：C&ndash ; O&ndash ; S&ndash ; Pb isotopes ; Sulfide Rb&ndash ; Sr isotopic age ; Tianqiao carbonate-hosted Pb&ndash ; Zn deposit ; SW China
• 刊名：Ore Geology Reviews
• 出版年：2013
• 出版时间：September, 2013
• 年：2013
• 卷：53
• 期：Complete
• 页码：77-92
• 全文大小：2819 K

文摘

The Tianqiao Pb-Zn deposit in the western Yangtze Block, southwest China, is part of the Sichuan-Yunnan-Guizhou (SYG) Pb-Zn metallogenic province. Ore bodies are hosted in Devonian and Carboniferous carbonate rocks, structurally controlled by a thrust fault and anticline, and carried about 0.38 million tons Pb and Zn metals grading > 15 % Pb + Zn. Both massive and disseminated Pb-Zn ores occur either as veinlets or disseminations in dolomitic rocks. They are composed of ore minerals, pyrite, sphalerite and galena, and gangue minerals, calcite and dolomite. ¦Ä³⁴S values of sulfide minerals range from + 8.4 to + 14.4¡ë and display a decreasing trend from pyrite, sphalerite to galena (¦Ä³⁴S_pyrite > ¦Ä³⁴S_sphalerite > ¦Ä³⁴S_galena). We interpret that reduced sulfur derived from sedimentary sulfate (gypsum and barite) of the host Devonian to Carboniferous carbonate rocks by thermal-chemical sulfate reduction (TSR). ¦Ä¹³C_PDB and ¦Ä¹⁸O_SMOW values of hydrothermal calcite range from -5.3 to -3.4¡ë and + 14.9 to + 19.6¡ë, respectively, and fall in the field between mantle and marine carbonate rocks. They display a negative correlation, suggesting that CO₂ in the hydrothermal fluid was a mixture origin of mantle, marine carbonate rocks and sedimentary organic matter. Sulfide minerals have homogeneous and low radiogenic Pb isotope compositions (²⁰⁶Pb/²⁰⁴Pb = 18.378 to 18.601, ²⁰⁷Pb/²⁰⁴Pb = 15.519 to 15.811 and ²⁰⁸Pb/²⁰⁴Pb = 38.666 to 39.571) that are plotted in the upper crust Pb evolution curve and overlap with that of Devonian to Carboniferous carbonate rocks and Proterozoic basement rocks in the SYG province. Pb isotope compositions suggest derivation of Pb metal from mixed sources. Sulfide minerals have ⁸⁷Sr/⁸⁶Sr ratios ranging from 0.7125 to 0.7167, higher than Sinian to Permian sedimentary rocks and Permian Emeishan flood basalts, but lower than basement rocks. Again, Sr isotope compositions are supportive of a mixture origin of Sr. They have an Rb-Sr isotopic age of 191.9 ¡À 6.9Ma, possibly reflecting the timing of Pb-Zn mineralization. C-O-S-Pb-Sr isotope compositions of the Tianqiao Pb-Zn deposit indicate a mixed origin of ore-forming fluids, which have Pb-Sr isotope homogenized before the mineralization. The Permian flood basalts acted as an impermeable layer for the Pb-Zn mineralization hosted in the Devonian-Carboniferous carbonate rocks.