Rb-Sr dating of sphalerite and S-Pb isotopic studies of the Xinxing crypto-explosive breccia Pb Zn (Ag) deposit in the southeastern segment of the Lesser Xing'an Zhangguangcai metallogenic belt, NE China

摘要

The Xinxing Pb-Zn-(Ag) deposit is located in the southeastern segment of the Lesser Xing'an-Zhangguangcai metallogenic belt, NE China. It is a small-scale deposit (Pb + Zn 50,000 tonnes) that occurs in a cryptoexplosive breccia pipe. Ore bodies are hosted in Permian granodiorite, structurally controlled by three sets of faults. This paper reports results of Rb-Sr isotopic dating of sphalerite, which yields an isochron age of 182.8 +/- 3.1 Ma (MSWD = 1.02). The concentrations of Rb and Sr in sphalerite range from 0.0839 x 10(-6) to 0.7124 x 10(-6) and 0.4775 x 10(-6) to 7.4810 x 10(-6), respectively. The initial 87Sr/86Sr ratio of sphalerite is 0.710954 0.000061, indicating that the ore-forming components were derived from a mixed crust-mantle source. Sulfur isotopic values of the sulfides vary in a narrow range from-4.4% to- 2.0% (ay. of- 3.28%), indicating a magmatic source for the sulfur. Lead isotopic compositions of the sulfide minerals ((206)pb/(204)pb = 18.277-18.323, (207)pb/(204)pb = 15.514-15.571, Pb-208/Pb-204 = 38.016-38.199) are relatively consistent and cluster together between the mantle and orogenic belt lines, but are closer to the latter, reflecting the mixing of mantle-derived and minor crust-derived materials. These results, combined with the region geology, indicate that the Xinxing Pb-Zn-(Ag) deposit resulted from regional tectono-magmatic metallogenic processes that were related to the westward subduction of the Pacific plate underneath Eurasia in the Early Jurassic.