Petrogenesis of ore-bearing porphyry from the Tangjiaping porphyry Mo deposit, Dabie orogen: Zircon U-Pb geochronology, geochemistry and Sr-Nd-Hf isotopic constraints

摘要

Extensive Early Cretaceous post-collisional igneous rocks, especially the large volume of granitoids developed in the Dabie orogen. Some of these granitic rocks are spatially, temporally, and genetically associated with economically important molybdenum deposits. The Tangjiaping large-scale (>0.1 million ton) porphyry Mo deposit is located in the northwest of the Northern Dabie Complex unit. The Mo mineralization is mainly hosted in molybdenite-bearing quartz veinlets and stockworks in the Tangjiaping granite porphyry, which intruded into Proterozoic biotite-plagioclase gneiss and amphibole-plagioclase gneiss. Two alteration zones from the porphyry centre outwards and downwards can be recognized: (1) IC-silicate alteration-silicification zone; (2) silicification-phyllic alteration zone. The Tangjiaping ore-bearing granite porphyry occurs as an individual stock with an outcrop of 0.4 km(2). LA-ICP-MS zircon U-Pb dating of the Tangjiaping granite porphyry yields crystallization age of 115 +/- 1 Ma, which is consistent with the molybdenite Re-Os age of the deposit given by previous studies. The Tangjiaping granitic rocks are metaluminous and belong to high-K talc-alkaline and shoshonitic series. They are relatively enriched in light rare earth elements and have moderately negative Eu anomalies. Geochemical and mineralogical characteristics indicate that the Tangjiaping granite is an A-type granite and was generated by partial melting of intermediate-felsic rocks at pressures of ca. 0.4-0.8 GPa. There are high initial Sr-87/Sr-86 ratios ranging from 0.707367 to 0.709410 and negative epsilon(Nd) (0 values varying from -15.0 to -142 for the Tangjiaping granite. In situ zircon Hf isotopic analyses show that the epsilon(Hf)(t) values of zircons from the Tangjiaping granite porphyry vary from -17.0 to -6.0. The geochemical data and Sr-Nd-Hf isotopes, coupled with the Neoproterozoic inherited zircon age (652 +/- 21 Ma), indicate that the Tangjiaping granite porphyry was most likely derived from partial melting of the Northern Dabie gneiss with some relatively enriched mantle materials involved. The Tangjiaping Mo ore-forming granite porphyry was formed in an extensional setting. The Early Cretaceous asthenospheric upwelling might have played an important role in the formation of the approximately coeval Mo-bearing magmas in the Dabie orogen. (C) 2016 Elsevier B.V. All rights reserved.