Rock-forming and ore-forming ages of the Nantai Mo polymetallic deposit in North Qinling Mountains and its zircon Hf isotope composition

Abstract：The Nantai Mo polymetallic deposit is a typical porphyry-skarn deposit in North Qinling Mountains，the magmatic rocks in this deposit include granite-porphyry, quartz porphyry veins and explosion breccia, and there occur porphyry-type and skarn-type Mo polymetallic mineralizations within and around the granite-porphyry body. The granite-porphyry from the Nantai Mo polymetallic deposit is dated at (151±1)Ma（N=12，NSWD=0.32）by using zircon U-Pb LA-ICPMS. Six molybdenites samples from the deposit yield Re-Os isotope model ages ranging from (146±2)Ma to (151±2)Ma，with an weighted average of (148.8±1.7)Ma (N=12，NSWD=0.84). The granite age and the metallogenic age are consistent with each other within the error limits, suggesting that the Nantai Mo polymetallic deposit was formed in the late Jurassic period, consistent with the formation epoch of the main porphyry-skarn type molybdenum deposits on the southern margin of North China Block. The zircon Hf isotope composition of the granite-porphyry has a large variation, with initial ratios of 176Hf/177Hf ranging from 0.281 864 to 0.282 454, εHf(t) from -28.8 to -7.9, and two-stage model ages from 2654Ma to 1506Ma. These data suggest that granite-porphyry was probably derived form several sources dominated by curstal materials with the addition of small amouts of mantle materials, and the old crust was dominated by the contribution of juvenile components. Therefore, the source of the metallogenic material for the Nantai Mo polymetallic deposit was probably the same as that of the granite.