Sphalerites from the giant Wuzhishan Pb-Zn deposit in Guizhou: Rb-Sr dating and its geological implications

The Wuzhishan Pb-Zn deposit explored in recent year is a giant carbonate-hosted strata bound Pb-Zn deposit in western Guizhou. However,it is much debatable about the mineralization age,genetic type and orecontrolling factor of the Pb-Zn deposit. The Rb-Sr dating of sphalerites in the disseminated and network sulfide ores from the Nayongzhi ore block in the Wuzhishan Pb-Zn deposit gives an isochron age of 458.2±2.9 Ma (MSWD=1.07,n=5),with an initial ⁸⁷Sr/⁸⁶Sr ratio of 0.713823±0.000010. The mineralization ages may be traced back to the late Middle Ordovician to early Late Ordovician,obviously later than the depositional periods of the host rocks,representing a typical epigenetic deposit. Geologically and geochemically,the Wuzhishan Pb-Zn deposit should be classified into a representative Mississippi Valley-type (MVT) Pb-Zn deposit. Tectonically,the Wuzhishan Pb-Zn deposit is genetically closely associated with the Caledonian orogeny in correspondence with the uplifting of central Guizhou. The basement fault structures and fracture zones are interpreted as the internally controlling facors of mineralization,whereas the collision and mountain building of the Cathysia and Yangtze continental masses during the Caledonian,corresponding to the Duyun and Guangxi movements,are believed to be the externally controlling factors of metallogenesis for the giant Wuzhishan Pb-Zn deposit.