The Xiasai vein-type Ag-Pb-Zn deposit in the Yidun Terrane, SW China: source and timing of magmatism and mineralization

The Xiasai-Lianlong metallogenic belt in the central Yidun Terrane hosts numerous Sn-Ag and (Sn-) Ag-Pb-Zn deposits, which are spatially associated with Cretaceous granites. The Xiasai Ag-Pb-Zn deposit (0.27 Mt Pb+Zn, 1028 t Ag, and 20000 t Sn), is the largest deposit in the belt and is related to a monzogranite intrusion. The deposit consists of (quartz-) sulfides in veins, resulting from three successive mineralization stages (I-III). Rb-Sr isochron dating of sphalerite samples yielded an age of 99 +/- 3 Ma and zircon U-Pb LA-ICP-MS dating of the monzogranite gave ages between 102 +/- 1 and 101 +/- 1 Ma. The delta S-34 values of eleven sphalerite separates range from -9.7 to -3.1 parts per thousand and those from nineteen galena samples from -10.5 to -4.9 parts per thousand. The estimated delta S-34 value of the ore forming fluid is -8.5 parts per thousand, using the sulfur isotopic fractionation of sphalerite-galena pairs that are assumed to be in equilibrium. Eighteen sulfides from sub-stages II-2 and II-3 have relatively homogeneous Pb isotopic compositions, which are similar with the ones of K-feldspars from the Xiasai monzogranite. Geochronological and isotope data support a magmatic-hydrothermal origin for the Xiasai Ag-Pb-Zn deposit.