Zircon LA-ICP-MS U-Pb ages and highly oxidized features of magma associated with Luoboling porphyry Cu-Mo deposit in Zijinshan ore field, Fujian Province.

The Luoboling large porphyry Cu-Mo deposit is a recently discovered deposit in the Zijinshan Cu-Au-Mo ore field. Based on the relationship of the porphyries and the systematically petrographic study, the ore-bearing porphyries can be divided into early stage hornblende biotite granodiorite porphyry and biotite granodiorite porphyry and late stage biotite granodiorite porphyry. The early stage hornblende biotite granodiorite porphyry and biotite granodiorite porphyry has zircon LA-ICP-MS U-Pb age of 103.7 +/- 1.2Ma, with MSWD = 0.33 and of 103.0 +/- 0.9Ma with MSWD = 1.00, respectively, and the late stage biotite granodiorite porphyry has zircon LA-ICP-MS U-Pb age of 97.6 +/- 2.1Ma with MSWD = 6.00. Zircon grains from two stage ore bearing porphyries have much higher average Ce4+/Ce3+ ratios (630 similar to 770) than those (182 similar to 577) of barren granites in the ore field. Based on the zircon high Ce4+/Ce3+ ratios and the wide occurrence of anhydrite in the ore-bearing porphyries, it is concluded that the ore-bearing magma was characterized by a relatively high oxygen fugacity. According to emplaced age and high oxygen fugacity of ore forming magma, and tectonic setting of the South China in the Mesozoic, the Luoboling ore-bearing porphyries are regarded to be triggered by the westward subduction of paleo-Pacific plate during Mesozoic.