Chalcophile element geochemistry and petrogenesis of high-Ti and low-Ti magmas in the Permian Emeishan large igneous province, SW China

Abstract

Sulfide-poor mafic layered intrusions, sills/dykes and lava flows in the Funing region, SW China, are part of the ~260 Ma Emeishan large igneous province. They belong to either a high-Ti group (TiO2 = 1.6–4.4 wt%) with elevated Ti/Y ratios (351–1,018), or a low-Ti group (TiO2 1, low (Y/Pd)PM ratios (0.2–7.1) and nearly constant (Cu/Pd)PM ratios (1.5–3.8). The even and parallel chalcophile element patterns of the high-PGE low-Ti subgroup rocks are likely a result of olivine-dominated fractionation under S-undersaturated condition. The low-PGE low-Ti group rocks have low MgO (4.5–8.9 wt%) and very poor PGE (Pt + Pd 0.5–1.6 ppb, Ir 0.004–0.02 ppb) with low Cu/Zr ratios (0.1–0.5), high (Y/Pd)PM (26–70) and variable (Cu/Pd)PM ratios (2.8–14). The trough-like chalcophile element patterns of the low-PGE low-Ti subgroup rocks indicate that the magmas were sulfide saturation and sulfide melts were extracted from the magmas. The extracted sulfide melts might be potential Ni–Cu sulfide ores at depth in the Funing region.