矿床地球化学国家重点实验室知识库

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 δ34S values, causing debates on their ore genesis. To address this issue, the Yunluheba PbZn 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 207Pb/204Pb vs. 206Pb/204Pb 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 87Sr/86Sr ratios of sphalerite, approximately equal to 87Sr/86Sr200Ma ratios of the D-P carbonates, ore-forming metals are considered to have been derived mainly from ore-hosting rocks. Sulfides’ δ34SCDT values range mainly from −2.0‰ to 2.9‰, 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.