A revised oxygen barometry in sulfide-saturated magmas and application to the Permian magmatic Ni–Cu deposits in the southern Central Asian Orogenic Belt

摘要: Oxygen fugacity is a key parameter in controlling the petrogenesis of mafic-ultramafic rocks and their associated sulfide mineralization, especially convergent settings. This study uses new previously published experimental data on olivine-sulfide pairs to reparameterize an expression for oxygen barometry using distribution coefficient K D FeNi Fe-Ni exchange between olivine sulfide. We derive expression, ΔQFM = (9.775 + 0.416 ∙ C Ni − K FeNi)/4.308, where ΔQFM denotes divergence from fayalite–magnetite–quartz buffer. The revised has been applied Permian magmatic Ni–Cu deposits Central Asian Orogenic Belt, NW China. East Tianshan—North Tianshan, Beishan—are considered as single mineral system, whereas spatially separated Junggar are separate system. deposit Tianshan group exhibits large range (QFM − 2 ~QFM + 1) Ni tenor (metal concentration pure sulfide, ~ 5 16 wt%). Poyi Huangshannan contain high-Ni sulfides, varying 12 16 wt%. relatively high Fo values (> 85 mol%) contents (> 2000 ppm) these indicate that sulfides were segregated less differentiated magmas also had (~QFM + 1). remaining Tianshan—the Huangshandong, Huangshanxi, Hulu, Tulaergen, Tudun, Xiangshanzhong deposits—have intermediate tenors (5–8 wt%). These correspond (80–84 mol%) (700–1400 ppm) coexisting olivine, illustrating they with lower thought be result amount (15–20%) fractionation at depth. more reduced (− 2 < ΔQFM < + 0.3) than evolved It shown value calculated decreases decreasing value, indicating host became gradually during evolution, which can explained by primarily oxidizing magma progressively assimilating crustal material containing reducing agents, such carbon. Kalatongke belt, lowest (3–5 wt%) low (< 78 mol%), was derived experienced significant plus clinopyroxene plagioclase propose variation Belt gradual contamination variable degree fractional crystallization.