Chalcophile element and S-Nd isotope geochemistry constraint on the origin of the Nanke magmatic nickel-copper sulfide deposit, Southwestern China
Year: 2024
Type: article
Abstract: • recycled oceanic sediment was involved in source of the parental magma. • PGE depletion in the parental magma before sulfide saturation. • sulfide-silicate magma interactions in the deep chamber play an important role. • significant PGE mineralization potential is expected in the staging magma chamber. The Nanke Ni-Cu sulfide deposit is situated within the Jinping-Song Da region of the Emeishan large igneous province. A sill-like body of olivine pyroxenite intruding Late Silurian strata hosts the deposit, which consists of massive, net-textured and disseminated sulfide ores. The predominant sulfide minerals are pyrrhotite, pentlandite and chalcopyrite, together they constitute over 90 % of the sulfide mineral assemblage. The Nanke deposit is notable for its significant negative Nb-Ta anomalies and enriched ε Nd (t) values (−4.4 to −6.2), like the coeval Emeishan picrite and basalt in this region. Mixing calculations indicate that these geochemical features are due to the involvement of recycled oceanic sediment in the mantle sources, rather than shallow-level crustal contamination. The ores of Nanke deposit contain relatively high contents of Ni (0.20 to 4.2 wt%) and Cu (0.06 to 1.37 wt%) but low platinum-group element (PGE) contents (1.56 to 37 ppb). They exhibit Cu/(Pd × 1,000) ratios ranging from 191 to 5897, suggesting that PGE depletion occurred within the parental magma before it reached sulfide saturation. The Ni/Cu ratios of the ores vary from 0.76 to 33, averaging 13.9 for massive ores and 3.96 for net-textured and disseminated ores, which is higher than those of the Baimazhai deposit and Ban Phuc deposit. This suggests that the PGE depletion in the Nanke deposit cannot be attributed to sulfide saturation triggered by fractional crystallization alone. The sulfide ores display a mantle-like δ 34 S range from −1.09 to + 0.03 ‰, supporting the interpretation that the parental magma underwent sulfur isotope exchange between new primitive magma and pre-existing sulfide liquid. Mass balance calculations indicate that most PGEs and some Ni were transferred from the magma to the pre-existing sulfide liquid during the reaction, resulting in a final magma with PGE content similar to the composition of PGE-depleted basalt and picrite in this area. The sulfide saturated from the magma with R-factors of 200-1000, forming the Nanke deposit. The PGE enrichment in the pre-existing sulfide liquid through reactions at greater depths suggests that exploration for PGE deposits at deeper levels is warranted.
Source: Ore Geology Reviews
Authors: Xiao Ma, Zhong-Jie Bai, Wei-Guang Zhu, Duo-Shuai Hu
Language: English
Subfield: Geophysics
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,620
OpenAlex ID: W4405394999