Geology, geochemistry, and geochronology of the Wangjiazhuang porphyry-breccia Cu(-Mo) deposit in the Zouping volcanic basin, eastern North China Block

摘要

The Wangjiazhuang porphyry-breccia Cu(-Mo) deposit is located in the Zouping volcanic basin, western Shandong Province. Seven molybdenite samples yield a Re-Os weighted mean age of 127.8 +/- 0.7 Ma (2 sigma), which is identical within error to the zircon weighted mean Pb-206/U-238 age of 1283 +/- 1.3 Ma (2 sigma) determined for quartz monzonite samples. The host rock is characterized by high concentrations of K2O (4.26-4.53 wt.%), Na2O (4.97-5.76 wt.%), LILEs and LREEs, and high Mg#(>40), and low concentrations of HFSEs and HREEs, with K2O/Na2O ratios of 0.76-0.88. The quartz monzonite also has high Sr/Y (69.9-112.5) and (La/Yb)(N) (22.0-30.0) ratios, similar to adakitic rocks worldwide. Relatively low initial Sr-87/Sr-86 ratios (0.70549-0.70556), high epsilon(Nd)(t) values (2.58-3.06), high radiogenic Pb [(Pb-206/Pb-204)i = 18.3424-18.4606, (Pb-207/Pb-204)(i) = 15.5692-15.5985, (Pb-208/Pb-204)(i) = 38.1714-38.2734] and high zircon epsilon(Hf)(t) values (-2.1 to +4.3) indicate that the magma was likely derived from the partial melting of subducted oceanic crust which then reacted with the peridotitic mantle wedge. Both the breccia and porphyry ores have a narrow range of delta S-34 (-4.8 to +2.1 parts per thousand) and Pb isotopic compositions (Pb-206/Pb-204 = 18.295-18.402,Pb-207/Pb-204 = 15.551-15.573, and Pb-208/Pb-204 = 38.215-38.331), suggesting that the ore metals were extracted primarily from the quartz monzonite or similar source. Subduction of the Paleo-Pacific slab during the Early Cretaceous resulted in the formation of the Wangjiazhuang quartz monzonite and associated Cu(-Mo) deposit in western Shandong Province. (c) 2014 Elsevier B.V. All rights reserved.