Abstract
The Hongchuan Cu-Ni sulphide deposit within the North Qilian orogenic belt is an important discovery in recent years. In order to find out the age of intrusion, petrogenesis and nature of the source area of this deposit, petrology, geochemistry, zircon U-Pb isotope chronology and Hf isotope geochemistry studies have been carried out. The mineralized intrusions of Hongchuan Cu-Ni deposit mainly consists of peridotite and hornblende phases, and the peridotite phase is distributed in the lower part of the intrusion, which is the main mineralized rock phase. The geochemical characterization of the rocks shows that the major elements of the Hongchuan intrusion have low SiO2 (39.13-46.35%), high MgO (13.69-27.47%), high Mg# (68.28-79.91), and belong to the subalkaline series and the island arc zebra basalt series. The spider diagram of trace rare earth elements shows flat-type characteristics, enriched in Rb,Ba,Pb and K,and deficient in Nb,Ta,P and Ti.LA-ICP-MS zircon U-Pb isotope dating of plagioclase-bearing peridotite in the intrusion No. Ⅳ was carried out, and the weighted average age of zircon 206Pb/238U was obtained to be 486.9±5.9 Ma, the zircon εHf(t) values ranged between -0.19 and 7.12. Combined with the comparative analysis of the rock geochemical data and the regional geologic background, it is concluded that the intrusion was formed in an island arc environment, the source area of the magma is a lossy mantle that underwent subducted slab fluid accounting, and the magma intrusion process underwent weak mixing of lower crustal materials.
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