科研之友
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摘要
Over 400 carbonate-hosted Pb-Zn deposits in the western Yangtze block constitute the giant Sichuan-YunnanGuizhou (SYG) Pb-Zn metallogenic province. The majority of Pb-Zn deposits hosted in Devonian carbonates are characterized by low delta S-34 values, causing debates on their ore genesis. To address this issue, the Yunluheba Pb-Zn deposit is chosen as a case study. Ore bodies of this deposit are hosted in middle Devonian carbonates. Ore minerals are sphalerite, galena and pyrite. Sphalerite Rb-Sr dating yields an isochron age of 206.2 +/- 4.9 Ma, consistent with ages of most Pb-Zn deposits in the SYG province, arguing for a regional intensive Pb-Zn mineralization event during the late Indosinian orogeny. Sulfides have Pb isotopic compositions that form a linear trend above the average crustal Pb growth curve in the Pb-207/Pb-204 vs.Pb-206/(204)Fb plot. Moreover, Pb isotopic ratios are consistent with the Devonian to Permian carbonates' age-corrected Pb isotopic ratios, suggesting mixed crustal Pb sources with the majority of Pb derived from country rocks. Combined with initial Sr-87/Sr-86 ratios of sphalerite, approximately equal to Sr-87/(88)Srzoolvto ratios of the D-P carbonates, ore-forming metals are considered to have been derived mainly from ore-hosting rocks. Sulfides' delta S-34(CDT) values range mainly from - 2.0 parts per thousand to 2.9 parts per thousand, interpreted to be a result of mixing by syn-sedimentary pyrite originated biogenic S and thermochemically reduced S. We conclude that the Yunluheba deposit and other Pb-Zn deposits in the SYG province should belong to Mississippi Valley-type deposits.
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单位中国科学院; 云南大学
