The source of metals in the Qilinchang Zn-Pb deposit, northeastern Yunnan,China: Pb-Sr isotope constraints

Qilinchang a Mississippi Valley-type Zn-Pb deposit, has essentially homogen eous lead isotope compositions as follows: Pb-206/Pb-204 = 18.432 to 18.487 (i.e., 18.360 +/-0.15%), Pb-207/Pb-204 = 15.664 to15.720 (i.e., 15.697 +/- 0.18%), and Pb-208/Pb-204 = 38.729 to 38.874 (i.e., 38.833 +/-0.19%). Stron tium isotope compositions at the time of mineralization were relatively het erogeneous: (87)Sd/Sr-86 = 0.7170 for pyrite, 0.7138 to 0.7180 for sphaleri te, 0.7109 to 0.7143 for galena, and about 0.7158 to 0.7168 for calcite. The mineralizing metals of the Qilinchang ore deposit, Pb and Zn, have only one source rock. The Pb isotope compositions of sulfides of the deposit ar e essentially the same as those of tile Upper Proterozoic (i.e., lower Sini an) igneous rock suite, if the preferential migration of Pb isotopes during the leaching and the in situ radiogenic Pb back correction are taken into account. The Pb-207/Pb-206 ratios of sulfides in the deposit are notably hi gh (0.850-0.851), which suggests that this ore deposit contains material wi th vert; old signatures. On the basis of kinetic and thermodynamic calculations of water/rock intera ction, we obtain a value of about 0.745 of source rock Sr-87/Sr-86 for the mineralizing metals. This value is similar to that of tile lower Sinian ign eous rock suite at the time of mineralization. That the lower Sinian igneous rock suite served as the source is also favor ed by its characteristic of leachability and its content of metals in this and other geologic bodies.