Rb-Sr isotopic geochronology and geochemical characteristics of S and Pb isotopes of the Lulu Pb-Zn deposit in Luquan, Yunnan Province

The Lulu Pb-Zn deposit is located on the western margin of Yangtze Block and is hosted in the dolostone of Cambrian Meishucun Formation. Ore minerals are mainly galena, sphalerite and pyrite, Gangue minerals are mainly quartz, calcite and barite. The ⁸⁷Sr/⁸⁶Sr ratios of sulfides are 0.7112~0.7115, indicating that the ore-forming materials were derived from basements. Rb-Sr isochron age of sphalerite is 223.5±2.9Ma, suggesting Late Indosinian to Early Yanshanian period. The δ³⁴S ratios of S isotope of sulfides in the deposit range from 9.72‰ to 22.44‰. The δ³⁴S values of S isotope of barite in the deposit range from 26.08‰ to 29.34‰. These data suggest that the reduced sulfur in the ore-forming fluids was the product of thermo-chemical sulfate reduction. The range of ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb are respectively from 18.259 to 18.342, from 15.608 to 15.639, and from 38.460 to 38.821. Pb isotope compositions lie in the region between the upper crust and the orogenic Pb area and fall into the field of basement rocks, which indicates that the crust source of ore-forming metals was mainly supplied by basement rocks. All the geological and geochemical information shows that the source of ore-forming metals and the fluid of the Lulu Pb-Zn deposit were the mixed products derived mainly from basement strata. The mineralization was caused by strong driving force of Indosinian movement, which prompted activation, migration, mixture and spatial emplacement of the ore-containing basement strata with ore-forming elements, thus forming industrial deposit.