Mafic-ultramafic magma activity and copper-nickel sulfide metallogeny during Paleozoic in the Eastern Kunlun Orogenic Belt, Qinghai Province, China

Abstract

ABSTRACT The Eastern Kunlun Orogenic Belt (EKOB) has a complex geological structure and diverse magmatic activities, which are closely related to the Qaidam Basin and the Tethys tectonic evolution. There are at least 3 stages mafic-ultramafic rocks occurred in the Early Paleozoic in EKOB. The first stage is the Later-Silurian to Early Devonian, represented by the giant Xiarihamu super large magmatic Cu-Ni deposit, containing about 1.18 million metric tons (Mt) of nickel with average grades of 0.65% Ni, and its age of ore-forming pyroxene peridotite is 411 Ma; The second stage is the Early Carboniferous, represented by the large Shitoukengde magmatic Cu-Ni sulfide deposit, and its ore-forming age of the olivine websterite is 334 Ma; The third stage of mafic-ultramafic rocks occurred mainly during the Middle-Late Triassic, represented by Xiaojianshan, Lalinggaoli, and Kaimuqi complexes, and no economical ore bodies have been found in this period. The authors summarized the difference between the ore-bearing and the nonmineralized mafic-ultramafic rocks in the EKOB. The olivine of the ore-bearing complexes contains higher MgO and SiO2 content but lower FeO and CaO contents, and the clinopyroxene of ore-bearing complexes contains lower FeO and CaO contents. Crustal sulfur contamination is key to the formation of the giant Xiarihamu Ni deposit, and crustal sulfur contamination degree of the giant magmatic Ni deposit is higher than that of large Ni deposit. The above indicators could guide the exploration and evaluation of similar deposits in the EKOB.