Re-Os and U-Pb Geochronology of the Dawan Mo-Zn-Fe Deposit in Northern Taihang Mountains, China

The Dawan Mo-Zn-Fe deposit located in the Northern Taihang Mountains in the middle of the North China Craton (NCC) contains large Mo-dominant deposits. The mineralization of the Dawan Mo-Zn-Fe deposit is associated with the Mesozoic Wanganzhen granitoid complex and is mainly hosted within Archean metamorphic rocks and Proterozoic-Paleozoic dolomites. Rhyolite porphyry and quartz monzonite both occur in the ore field and potassic alteration, strong silicic-phyllic alteration, and propylitic alteration occur from the center of the rhyolite porphyry outward. The Mo mineralization is spacially related to silicic and potassic alteration. The Fe orebody is mainly found in serpentinized skarn in the external contact zone between the quartz monzonite and dolomite. Six samples of molybdenite were collected for Re-Os dating. Results show that the Re-Os model ages range from 136.2 Ma to 138.1 Ma with an isochron age of 138 +/- 2 Ma (MSWD = 1.2). U-Pb zircon ages determined by laser ablation inductively coupled plasma mass spectrometry yield crystallization ages of 141.2 +/- 0.7 (MSWD = 0.38) and 130.7 +/- 0.6 Ma (MSWD = 0.73) for the rhyolite porphyry and quartz monzonite, respectively. The ore-bearing rhyolite porphyry shows higher K2O/Na2O ratios, ranging from 58.0 to 68.7 (wt%), than those of quartz monzonite. All of the rock samples are classified in the shoshonitic series and characterized by enrichment in large ion lithophile elements; depletion in Mg, Fe, Ta, Ni, P, and Y; enrichment in light rare earth elements with high (La/Yb)(n) ratios. Geochronology results indicate that skarn-type Fe mineralization associated with quartz monzonite (130.7 +/- 0.6 Ma) formed eight million years later than Mo and Zn mineralization (138 +/- 2 Ma) in the Dawan deposit. From Re concentrations in molybdenite and previously presented Pb and S isotope data, we conclude that the ore-forming material of the deposit was derived from a crust-mantle mixed source. The porphyry-skarn type Cu-Mo-Zn mineralization around the Wanganzhen complex is related to the primary magmatic activity, and the skarn-type Fe mineralization is formed at the late period magmatism. The Dawan Mo-Zn-Fe porphyry-skarn ores are related to the magmatism that was associated with lithospheric thinning in the NCC.