Late Triassic Magmatism and Controls on Cobalt Mineralization in the Galinge Deposit, East Kunlun, China: Evidence from Geochronology, Zircon Lu–Hf Isotopes, and Geochemistry

The Galinge deposit in East Kunlun, China is a large Fe-polymetallic skarn system with a significant by-product, Co, but the respective roles of magmatism, skarn evolution, and wall rock interaction in Co enrichment remain incompletely understood. We integrate zircon and garnet U–Pb geochronology, zircon Lu–Hf isotopes and trace elements, whole-rock geochemistry, and SEM-EDS and EPMA mineral chemistry. Granodiorite and diorite porphyry yield zircon U–Pb ages of 230.09 ± 0.91 Ma and 229.4 ± 1.3 Ma, respectively, whereas skarn garnet yields 224.4 ± 9.3 Ma, placing intrusion and skarn formation within a Late Triassic magmatic–hydrothermal system. Both suites are metaluminous, LREE-enriched, and Nb–Ta–Ti-depleted; zircon εHf(t) values of −9.4 to −1.8 indicate the predominant reworking of older crustal material with variable input from a more radiogenic component. Strictly screened Ti-in-zircon temperatures and lattice strain Ce anomalies yield median apparent ΔFMQ values of +3.36 for granodiorite and +3.04 for diorite porphyry, indicating comparably oxidized magmatic conditions. The analyzed intrusions contain 2.12–13.4 ppm Co, whereas cobaltite and Co-bearing arsenopyrite contain 32.83–34.14 wt% and 0.38–4.53 wt% Co, respectively. Spatial and paragenetic relations place Co enrichment after magnetite deposition, during an early sulfide-stage hydrothermal sulfarsenide event within the skarn system. We infer that Late Triassic intrusions supplied heat, fluids, and ligands, whereas structural focusing and cooling, coupled with carbonate wall rock reactions and a reduction in carbonaceous or Fe2+-bearing domains, promoted As–S-rich Co precipitation; the leaching of intermediate–mafic wall rocks may have supplemented the Co inventory.