Study on ore-forming material source and metallogenic epoch of the Taiping Pb-Zn deposit, Yunnan Province, China

摘要

In the Cu-Au-Pb-Zn-Ag polymetallic mineralization belt of the conjuncture of Sichuan, Yunnan, and Guizhou, occurs the Taiping Pb-Zn deposit in Proterozoic metamorphic rock strata accompanied by late Proterozoic volcanic rocks. Previous studies on this type of Pb-Zn deposits are limited. The main purpose of this work is to investigate its metallogenic characteristic and genesis. Rb-Sr dating of sphalerite yields 714 +/- 11 Ma for the Taiping Pb-Zn deposit, which is a new mineralization age of Pb-Zn deposits in the Sichuan-Yunnan-Guizhou Pb-Zn metallogenic belt, reflecting that the Pb-Zn deposits in the Proterozoic basement strata formed in the Neoproterozoic. In addition, the characteristics of its minerals, including pyrite, sphalerite, chalcopyrite, gersdorffite, and galena, imply that the deposit formed in moderately low temperature and moderately shallow-seated environments. Sulphur (delta S-34 of 10.4-12.3 parts per thousand) was dominantly derived from the reduction of marine sulphate in the strata. Lead isotope data showed normal Pb characteristic, indicating that Pb came from the basement strata and it was affected by metamorphism.Sr-87/Sr-86 values of trachyandesite are 0.77-0.87, reflecting that Sr was derived from crustal sources. For sphalerite, (Sr-87/Sr-86)(i)(t= 714 Ma) = 0.72064-0.72135, indicating that metallogenic materials (metal) came mainly from the basement strata. The enrichment of Zn was associated with ankerite alteration. Ore-forming fluid is characterized by moderately low temperature (112.6-188.7 degrees C), moderate salinity (10.61-19.68% NaCl), and moderately low pressure. Compositions of H and O isotopes show that the ore-forming fluid was derived mainly from formation water, and that tensile spaces in the carbonate rocks likely provided conduits for fluid transport and space for metal precipitation, forming layered zinc ore bodies. In conclusion, the Chengjiang period in this study area was an important stage for zinc mineralization, and the Taiping Pb-Zn deposit is a MVT type deposit in the Proterozoic basement.