| 其他摘要 | The Sichuan-Yunnan-Guizhou carbonate-hosted Pb-Zn metallogenic province, located in the SW margin of the Yangtze block, is one of the important Pb-Zn-Ag producers in China. Up to now, there are more than 400 ore deposits (points) have been found over the past several hundred years, distributed in the field, where was limited by three faults (the Xiaojiang fault, the Shizong-Mile fault and the Ziyun-Yadu fault. Based on the detail studies on the regional geological setting, the genesis of deposits in the NW Guizhou carbonate-hosted Pb-Zn metallogenic district has been studied by application of new method of cadmium and germanium isotopic systems. Combined with elemental and isotopic geochemistry, the relationships between stratum, tectonic, Permian Emeishan flood basalts magmatic activity and mineralization, the sources of the ore-forming metals, origin and evolution of the ore-forming fluids and the fractionation mechanisms of cadmium and germanium isotope have been discussed. Finally, a possible fractionation model of Cd isotope is proposed. This thesis's main results are as follows:① The high precise cadmium isotopic compositions of Pb-Zn deposits in China have been analyzed by MC-ICP-MS: the representative deposits are the Huize deposit (Yunnan Province), the Fule deposit (Yunnan Province), the Tianbaoshan Pb-Zn deposit (Yunnan Province), the Gacun Pb-Zn deposit (Sichuan Province), the Dadongla Pb-Zn deposit (Guizhou Province), the Shagou Pb-Zn deposit (Henan Province), the Langshan Pb-Zn deposit (Inner Mongolia Autonomous Region), the Baiyinnuoer Pb-Zn deposit (Inner Mongolia Autonomous Region), and the Cd isotope fractionation characters in the Fule deposit have been studied in details. The results showed that obvious Cd isotope fractionation has been found between different colors of sphalerite and different minerals, in which light color sphalerite was rich in heavy isotopes of Cd, and dark color sphalerite was rich in light isotopes of Cd; early stage sphalerite was rich in light isotopes of Cd, and late stage sphalerite was rich in heavy isotopes of Cd. These results indicated that the cadmium isotope fractionation belongs to a Rayleigh fractionation model, and fractionation factor αsphalerite-fluid is between 0.99943 to 0.99967, this factor is similar to the experiment that calcite was precipitated from artificial sea water (Horner et al., 2011). Meanwhile, the Cd isotope compositions in precipitated smithsonite showed that early stage smithsonite was rich in light isotopes of Cd, while late stage smithsonite was rich in heavy isotopes of Cd, similar to that of sphalerite, indicating that Rayleigh fractionation model is suitable to explain the Cd isotope fractionation in sphalerite in the Fule deposit. What’s more, the cadmium isotopic compositions in sphalerite were changed regularly from the bottom to the top from the Fule deposit, indicating the cadmium isotopic compositions in sphalerite will be a deep ore-hunting indicator.② The process of oxidation can result in Cd isotope fractionation: Previous studies showed that there is no or few Cd isotope fractionation during the process of oxidation. However, our studies showed that the Cd isotopic fractionation has been observed during the oxidation process, which can result in about 0.33‰（δ114/110Cd）Cd isotopic fractionation, and this process belongs to close-system equilibrium during the sphalerite oxidized(αsphalerite-oxidation fluid=0.999674). This result can be used to explain why the published δ114/110Cd values in the river waters are rich in heavy isotopes of Cd. Leaching experiments and exchangeable Cd experiments for different typical samples from lead-zinc mine show that the leached liquid always favors heavier Cd isotopes than the corresponding residuals. The obvious Cd isotopic fractionation between leached liquid and residuals could be up to about 0.50‰, which was observed in the sulfide samples. Meanwhile, a negative correlation between the Cd concentrati |
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