Petrogenesis and metallogenic potential of the early devonian Yugusayi mafic-ultramafic complex in Qimantagh, East Kunlun orogeic belt

The Yugusayi mafic-ultramafic complex, located in the Qimantagh area, East Kunlun orogenic belt, consists of harzburgite, olivine orthopyroxenite, hornblende pyroxenite, and hornblende gabbro, which were once considered to be a part of the Early Palaeozoic ophiolite suite. However, the Yugusayi mafic-ultramafic rocks are characterized by thermal emplacement, accompanied by Cu-Ni sulphide mineralization, which is different from typical ophiolite suite. The LA-ICP-MS zircon U-Pb dating yields a 405 ± 2.8 Ma age for the hornblende gabbro, which belongs to the Early Devonian. All rocks are enriched in LREE but depleted in HREE, with a characteristic of ferrous mafic-ultramafic rocks. The εHf(t) values of the zircons from hornblende gabbro are 5.6–14.8, the εNd(t) values of whole rocks are from −4.27 to 0.08, and the δ34S values of sulphide are 1.36–8.72‰, indicating that the magma originated from the depleted mantle and contaminated by continental crust material during the ascending process. Based on the regional geological background, it is reasonable that the rocks formed in the post-collision extension stage after the closure of the Proto-Tethys Ocean and the continental collision, which represents an important metallogenic period for Cu-Ni sulphide deposits in the East Kunlun oregenic belt. Early Devonian magmatic mafic-ultramafic intrusions are developed in the early Palaeozoic ophiolitic tectonic melange belt of Qimantagh area. Combined with good metallogenic conditions and remarkable mineralization characteristics, it is believed that the Qimantagh area is a potential area for the prospecting of magmatic Cu-Ni sulphide deposits.