Constraints on timing and origin of the Dayinjian intrusion and associated molybdenum mineralization, western Dabie orogen, central China

Abstract

The Early Cretaceous geology of the western Dabie Mountains is characterized by widespread granitoid pluton emplacement and associated Mo mineralization. We report LA-ICP-MS zircon U-Pb and molybdenite Re-Os dating, whole-rock chemical and Sr-Nd-Pb isotopic compositions, as well as in situ zircon Hf isotopic geochemistry, for the Dayinjian granite in the region to better constrain its petrogenesis. U-Pb zircon dating yielded a weighted average age of 124.9 ± 1.3 Ma (mean square weighted deviation (MSWD)=0.51, 2σ). Re-Os isotopic dating of molybdenite from the Dayinjian ore deposit yielded an isochron age of 125.07 ± 0.87 Ma (MSWD=0.015), and a weighted average age of 124.54 ± 0.67 Ma (MSWD=0.34). The petrogenesis and metallogenesis of the Dayinjian complex are related to the onset of widespread post-orogenic magmatism and local mineralization in the western Dabie orogen. Whole-rock geochemistry indicates that the Dayinjian granite is a highly fractionated calc-alkaline granite possessing relatively high ( 87Sr/ 86Sr)i ratios (0.706379-0.707173), low Nd(T) values (-15.62 to-15.17), high Nd model ages (=2.15-2.18 Ga), and low radiogenic Pb isotopes (( 206Pb/ 204Pb) i =16.793-16.979, ( 207Pb/ 204Pb) i =15.379-15.487, and ( 208Pb/ 204Pb) i =37.559-37.976). Its magmatic zircons also exhibit very low Hf(T) values (-24.80 to-17.80) and old Hf model ages (=2.31-2.75 Ga). These isotopic compositions suggest that the Dayinjian granite is probably of anatectic origin and was derived from the lower crust at a depth <35 km, similar to the western Dabie gneiss. Ore-bearing fluids were produced during late-stage magmatic hydrothermal activity and were thereafter influenced by the circulation of meteoric water that concentrated molybdenite in open-space areas.