SHRIMP zircon U-Pb and molybdenite Re-Os age of the copper polymetallic deposit in Zouping volcanic basin, Shandong Province

Zouping volcanic basin is one of the important copper, molybdenum and polymetallic mineral areas in Shandong Province. There is a series of multicycle multi-stage volcano-intrusive complexes in this area. The already-discovered copper deposits and mineralization spots have close relations with intrusive complex rocks and volcanic structures of late Yanshanian period. In order to identify diagenesis-mineralization age of the mine, the authors employed SHRIMP isotope measurement techniques to conduct zircon U-Pb dating of intrusive rocks related to copper, molybdenum polymetallic mineralization in this area. The results show that the emplacement age of quartz monzonite diorite which is the ore-hosting country rock of the Wangjiazhuang porphyry type copper (molybdenum) deposit is (128.8±0.8)Ma, while the emplacement age of cyclic monzonite dykes which serve as the country rock of the hydrothermal quartz vein type copper deposit is (122.9±0.5)Ma. Rhenium-osmium isotopes of five molybdenite samples collected from the Wangjiazhuang copper deposit were analyzed, and the results gave an isochron age of (127±4)Ma and a weighted average of (128.2±0.8)Ma for the model ages. The Re-Os age represents the age of molybdenite precipitation in the ore-forming fluid. The obtained ages can give the time limits of late magmatism and mineralization, so the emplacement of Wangjiazhuang igneous complex was earlier than that of the cyclic monzonite wall, the polymetallic mineralization took place close to the time of the crystallization, and the rock mass was closely related to the mineralization. The formation of the hydrothermal quartz vein type copper deposit was later than that of the ringed monzonite wall with clear structure-controlled mineralization characteristics. The results obtained by the authors have important significance for studying regional ore-forming regularity and further guiding the ore prospecting work.