Controls on the metal compositions of magmatic sulfide deposits in the Emeishan large igneous province, SW China

Abstract

Magmatic sulfide deposits in the Emeishan large igneous province, SW China, have variable chalcophile and siderophile metal contents and can be divided into PGE, Ni–Cu–PGE and Ni–Cu deposits. PGE sulfide deposits include the Jinbaoshan and Zhubu deposits and have ores with very low sulfide contents (~ 1 to 2 vol.%) and very high Pt and Pd (0.3 to 10 ppm) and Ir (0.02 to 0.5 ppm). Typical Ni–Cu–PGE sulfide deposits include the Yangliuping and Qingkuangshan deposits, which contain sulfide ores with more than 10 vol.% sulfides (0.1–6.2 wt.% Ni, 0.03–11 wt.% Cu) and have moderate PGE contents (0.1–5 ppm Pt, 0.01–1.8 ppm Pd, < 0.5 ppm Ir). The Ni–Cu sulfide deposits, such as the Limahe and Baimazhai deposits, have sulfide-rich ores with more than 10 vol.% sulfides (0.1–4 wt.% Ni, 0.02–6.5 wt.% Cu) and are extremely poor in PGE (< 0.2 ppm Pt and < 0.3 ppm Pd, < 0.007 ppm Ir). Silicate rocks from the hosting intrusions of these three types of deposits have distinctive PGE concentrations. On the 100% sulfide basis, Pt and Pd correlate positively with Ir in the ores from the PGE deposits, whereas they correlate negatively in the Ni–Cu–PGE and Ni–Cu deposits. PGE geochemistry and model calculations indicate that the PGE-rich sulfides were separated from primary basaltic magmas, whereas the Ni–Cu–PGE sulfides were produced from magmas that had experienced minor sulfide removal (about 0.01%), and the Ni–Cu sulfides were separated from magmas that experienced about 0.025% sulfide segregation. Fractionation of monosulfide solid solution resulted in differentiation between IPGE and PPGE in the Ni–Cu–PGE and Ni–Cu deposits.