Lead isotope constraints on the genetic relationships among different ore types in the Dongshengmiao deposit, northern China

Abstract

The giant Dongshengmiao Cu-Zn-Pb-S deposit is the most representative Proterozoic sedimentary exhalative (SEDEX) deposit in China. A detailed investigation of Pb isotope compositions of sulfides from various types of ores and associated host rocks has been carried out to determine the genetic relationships among different ore types and to provide important insights on whether younger fluids have contributed mineralizing materials in the formation of the Dongshengmiao Cu-Zn-Pb ores. The substantial similarity of the Pb isotope composition between the studied stratiform Cu-Zn-Pb and S orebodies suggests that the bulk of the Dongshengmiao Cu-Zn-Pb ores belong to the same polymetallic metallogenic system with the syngenetic S ores of the Proterozoic age. Comparatively, vein-type ores show relative scattered Pb isotope signatures that fall along a well-correlated linear trend, whereas their less radiogenic end member projects towards the Pb isotope compositions of the overlying stratiform main orebody. In addition, the overall Pb isotope compositions of these vein-type ores have shown an apparent overlap and similar trend with the radiogenic disseminated pyrites in the mica schists, indicating their radiogenic Pb most likely originated from host rocks as well. The scatter of Pb isotope compositions of the Dongshengmiao Cu-Zn-Pb ores shows that lead was not homogenized regionally during subsequent metamorphism, ruling out the possibility of a deposit-scale remobilization. Furthermore, the significant difference and lack of intermediate Pb isotope values between the previously studied Hercynian feldspars and the bulk of the Dongshengmiao sulfide ores suggest that a significant introduction of metals from, or overprinting by, fluids derived from Hercynian magmatism is unlikely to have played an important role in the metal endowment. Taken together, all sulfide orebodies associated with various ore types in the Dongshengmiao deposit belong to an integrated and progressive hydrothermal ore-forming system of the Proterozoic age, and a portion of the vein-type ores and associated disseminated pyrites experienced a minor addition of evolved rock lead during subsequent greenschist face metamorphisms.