Geochronology and geochemistry of the Tianmugou Mo deposit, Dabie Shan, eastern China: Implications for ore genesis and tectonic setting

The Tianmugou molybdenum (Mo) deposit is a newly discovered porphyry deposit in the Dabie Shan of eastern China. The Mo-mineralization is spatially and genetically related to the Tianmushan granite batholith, and mainly occurs as thin molybdenite-bearing pegmatite dykes and numerous hydrothermal veins, with the development of potassic alteration, silicification, serialization, propylitization, and fluoritization. The Tianmushan batholith is composed of outermost fine-grained K-feldspar granite (Phase 1), medium-grained K-feldspar granite (Phase 2), coarse-grained biotite monzogranite (Phase 3), porphyritic granite (Phase 4), and innermost fine-grained K-feldspar granite (Phase 5). Zircon crystals from the biotite monzogranite yield a weighted average Pb-206/U-238 age of 123.0 +/- 0.8 Ma, but those from the porphyritic granite do not yield a good age because of their high contents of Th, U and Pb. Seven molybdenite samples from the ores yield individual Re-Os isotopic ages of 120.5 +/- 1.7 Ma to 122.5 +/- 1.9 Ma, which are slightly younger than the U-Pb age for the biotite monzogranite. These ages constrain the ore-forming magmatic-hydrothermal activity at the Tianmugou Mo deposit that took place during the post-collisional tectonism subsequent to the collision between the Yangtze and North China continents, consistent with the 142-111-Ma regional Mo mineralization event in Dabie Shan. The biotite monzogranite and porphyritic granite have high contents of SiO2, K2O and Al2O3, and low contents of TiO2, MgO and CaO, showing a metaluminous to peraluminous high-K calc-alkaline affinity, with significant depletion in Eu, Ba, Sr, P and Ti, and enrichment in Rb, Th, U, Nb, Ta, Hf and Y. The rocks have high initial Sr-87/Sr-86 ratios of 0.73546-0.89204, and negative epsilon Nd(t) values of -11.6 to -11.0, with T-DM2(Nd) of 1.81-1.86 Ga. Their ((206)pb/(204)pb)t, ((207)pb/Pb-204)t and (Pb-208/Pb-204)t are 17.337-17.554,15.450-15.465 and 37.992-38.147, respectively. The Sr-Nd-Pb isotopic signatures indicate that the causative granitic intrusions for the Tianmugou deposit mainly originated from partial melting of the Qinling Group during Early Cretaceous post-collisional tectonic extension. The Tianmugou Mo deposit belongs to a collisional- or Dabie-type porphyry Mo system. (C) 2016 Elsevier B.V. All rights reserved.973-Projects [2006CB403508, 2012CB416602]; National Natural Science Foundation of China [40730421, 40425006]SCI(E)ARTICLE,SI484-5038