Geochronology and geochemistry of the Taipingchuan copper-molybdenum deposit in Inner Mongolia, and its geological significances

Abstract

Recently discovered Taipingchuan porphyry Cu-Mo deposit is located in the north of Derbugan metallogenic belt,Ergun city of Inner Mongolia.Concentric rings of hydrothermal alteration and Cu-Mo mineralization occurred surrounding the granodiorite porphyry.Two hydrothermal alteration zones from the host porphyry to wall rocks have been recognized in Taipingchuan mine:A silicified-sericite zone and an argillic alteration zone.The Cu-Mo mineralization is clearly controlled by the silicified-sericite alteration.By using the zircon U-Pb dating methods a precise age data of the host porphyry is obtained.The dating data show that the age of host porphyry is 202 ± 5.7Ma.The inherited zircon(784Ma) has also been found in the host porphyry,which indicates that a Proterozoic block was probably located in the study area.Geochemically,the host porphyry of Wunugetushan possesses some geochemical characteristics of adakite(i.e.,high SiO2,Al2O3,Na2O and Sr contents,as well as La/Yb ratios,low MgO,Y and HREE contents).Some geochemical characteristics of the host porphyry,including relatively high SiO2,Yb contents and Th/Nb,Ce/Nb ratios and relatively low Al2O3,TiO2,MgO,Sr,Th contents and Th/Ce ratio indicate that the porphyry derived from partial melting of the subducted slab.The Sr-Nd isotopic composition of the porphyry displays an initial(87 Sr/86 Sr) i ratio of 0.70943 to 0.71019,a negative eNd(t) values of -3.4 to -3.9.The Sr-Nd isotopic data indicates that Proterozoic block had some contribution to the magma sources of the host porphyry.Combining the regional geology,we infer that the subduction of Mongol-Okhotsk ocean slab under the Ergun block led to the host porphyry forming,and Taipingchuan Cu-Mo deposit was related to a continental arc environment.