Potential controls on magmatic Ni-Cu sulfide mineralization in orogenic belts: Constraints from mineral compositions of the Huangshandong and Erhongwa intrusions in eastern Tianshan, NW China

Abstract

Numerous Permian mafic-ultramafic intrusions are situated in the eastern Tianshan Orogen at the southern margin of the Central Asian Orogenic Belt. These intrusions demonstrate a diverse range of magmatic Ni-Cu sulfide mineralization. Notably, the Huangshandong intrusion hosts a large Ni-Cu sulfide deposit, whereas the Erhongwa intrusion lacks any economically significant sulfide mineralization. Both intrusions exhibit similar lithologies and mainly consist of lherzolite, gabbro, gabbronorite and diorite.To elucidate the controlling factors influencing the disparity in mineralization between two intrusions, analyses were conducted on the compositions of olivine, spinel, pyroxene and amphibole. Olivine grains from the Erhongwa lherzolite have lower Ni (361–943 ppm) contents than those from Huangshandong layered lherzolite (Ni 684–864 ppm) and Huangshandong massive lherzolite (Ni 1218 to 1878 ppm). This discrepancy may be attributed to early sulfide separation occurring at greater depths. Modeling results indicated that for the Huangshandong mantle source, 1 % slab-derived melts and 2 % slab-derived fluids were incorporated; conversely, for the Erhongwa mantle source, approximately 2.5 % slab-derived melts and 0.5 % slab-derived fluids were added.Parental magmas of the Erhongwa intrusion exhibit higher oxygen fugacity and water contents than those of the Huangshandong intrusion. Specifically, the magma of the Erhongwa intrusion undergoes magma evolution within a shallow magma chamber, whereas the magma of the Huangshandong intrusion gains sulfide saturation within a deep magma chamber. This research suggests that factors including mantle source features, suitable timing for sulfide separation, and depth of magma chamber are essential for Ni-Cu sulfide mineralization in mafic-ultramafic intrusions in convergent margin setting.