Magmatic evolution and chromite mineralization in the Gayahe ultramafic Complex, East Kunlun orogenic Belt, western China

• Massive chromitite is newly identified in the Gayahe ultramafic complex. • Massive chromitite formed during Early Silurian (∼430 Ma) magmatism. • Massive chromitite shows high-Cr, low-Ti signatures of boninitic melts. • Chromitite formation is linked to subduction-related boninitic arc magmatism. Integrating chromite–silicate geochemistry with apatite U–Pb geochronology, this study deciphers the magmatic evolution and chromite mineralization of the Gayahe ultramafic complex in the East Kunlun Orogenic Belt. Newly identified massive chromitites occur within serpentinite, dunite, olivine pyroxenite, and pyroxenite. Apatite U–Pb dating yields an age of 430 ± 17 Ma, placing their formation in the Early Silurian during a major pulse of mantle-derived magmatism. Chromite from massive chromitite is characterized by high Cr# (70.2–80.6), low TiO 2 , and trace-element patterns marked by relative Zn–Co–Mn enrichment and pronounced Sc depletion, indicating crystallization from a low-Ti parental melt consistent with forearc boninitic magmatism. Systematic contrasts among chromite types show that re-equilibration chiefly overprinted low-modal-abundance chromite in serpentinite and other ultramafic host rocks, whereas the multivalent-element chemistry of chromite from massive chromitite samples preserves near-primary melt signatures. Coexisting olivine shows high Mg# and Ni contents, consistent with crystallization from a depleted mantle-derived melt. Field, petrographic, and geochemical evidence collectively indicates that the Gayahe chromitite formed in an Early Silurian subduction-related arc setting, where chromite–silicate crystal-mush accumulation followed by gravitational settling generated the massive chromitite layers. These findings refine the petrogenesis of the Gayahe ultramafic complex and establish a geochemical framework for identifying high-Cr chromitite associated with boninite-series magmatism in comparable orogenic belts.