ABSTRACT

The Palaeozoic mafic-ultramafic complexes hosting Ni-Cu-Co mineralization occurred discontinuously and coexisted with early Palaeozoic eclogites in the East Kunlun orogenic belt (EKOB), western China. The giant Xiarihamu Cu-Ni-Co sulphide deposit in the EKOB is the largest Cu-Ni-Co sulphide deposit in an orogenic setting in the world. Early Palaeozoic eclogites are distributed as a belt for ca. 530 km in length in the Central Kunlun Zone of the EKOB. The geochronological data, geology and geochemistry of mafic-ultramafic complexes and eclogites in the EKOB are summarized for the tectonic settings of magmatic Cu-Ni-Co mineralization under the Proto- and Paleo-Tethys evolution. The mafic-ultramafic complexes show diverse lithofacies with different formation ages, indicating the multiple stages of long-lived Palaeozoic mantle-derived magmatism in the EKOB. The tectonic location, Neoproterozoic Ocean island basalt (OIB)-like mafic volcanic rocks and eclogite protolith of the EOKB imply the presence of the Neoproterozoic mantle plume magmatism as well as its contribution for enrichments of Ni-Cu-Co beneath EKOB. The ultramafic complexes show a close spatio-temporal relationship with eclogites. The basaltic protoliths of EKOB eclogite were derived from same mantle source as the mafic-ultramafic complexes. A positive correlation of geochronological data between ultramafic complexes with the eclogites in the EKOB is determined and indicated that the mafic magmatism with Cu-Ni-Co mineralization and eclogites were related to the tectonic-magmatic events in process of Proto-Tethys. The ultramafic complexes were formed under the subduction compression and post-collisional extensional settings of the Proto-Tethys and Paleao-Tethys Ocean corresponding to the peak (430–450 Ma) and retrograde (~405–410 Ma) metamorphic periods of eclogites. The Cu-Ni-Co metals were enriched extremely in the stage magma chamber by multi-stage magmatism in EKOB. Therefore, the mafic-ultramafic complexes with a large age span co-occurred with eclogites (especially retrograde eclogites) could be a favourable area for Ni-Co mineralization.