Re-Os and U-Pb Geochronology of the Erlihe Pb-Zn Deposit, Qinling Orogenic Belt, Central China, and Constraints on Its Deposit Genesis

The Erlihe Pb-Zn deposit is an important mine of the Pb-Zn metallogenic zone in the South Qinling Orogen. It has been considered a sedimentary exhalative deposit in previous investigations because the ore body occurs concordantly at the transitional location of an upright fold. Re and Os isotopic analyses for paragenetic pyrites with sphalerite and galena from the ore body have been used to determine the timing of mineralization and to trace the source of metallogenic materials. The R isotopic data of four pyrite samples construct an isochron, yielding a weighted average age of 226 +/- 117 Ma (mean square weighted deviation=1.7), which is considered the main mineralization age. A dioritic porphyrite vein sample, showing weaker mineralization, was also dated using the SHRIMP zircon U Pb isotopic method to constrain the youngest metallogenic age of the ore deposit, because it distributes along a group of tensional joints cutting not only the upright fold in the deposit field, but also the main ore bodies. The dioritic porphyrite sample yields a weighted mean Pb-206/U-238 age of 221 +/- 3 Ma, which is slightly younger than the Re-Os isotopic isochron age of the pyrites, considered as the upper age limit of the mineralization, namely the ending age of the mineralization. The Os isotopic compositions of sulfide minerals distribute within a range between Os isotopic compositions of the crust and the mantle, indicating that the ore deposit can be derived from magma-related fluid, and the metallogenic materials are most likely derived from the mixing source of the crust and the mantle. The Erlihe Pb-Zn deposit and associated dioritic porphyrite vein, important records of Qinling tectonic-magmatism-mineralization activities, were formed during the Triassic collisional orogeny processes.