The mechanism of Cu enrichment is closely linked to the differentiation of mantle-derived magma and subsequent magmatic-hydrothermal processes. Experimental determination of Cu speciation and partitioning coefficients among minerals, melts, and fluids (including vapor) is critical for understanding the mobility and enrichment of Cu during magma differentiation, crystallization along cooling, fluid exsolution, the precipitation of Cu-bearing minerals, and water-rock interactions under subsolidus conditions. The summarization of experimental data demonstrates that Cu predominantly exists as cuprous ions (Cu+) in both ore fluids and melts at temperatures above 100°C. The speciation of Cu species is affected by the system’s components and temperature. In Cl- and S-poor silicate melts, Cu primarily exists as CuO0.5. In hydrothermal fluids with intermediate to low salinities at temperatures above 300°C, the dominant species are [CuCl]0, [CuCl2]− and CuHS0. At lower temperatures (<300°C), in alkaline and intermediate to low salinity fluids, Cu(HS)<Stack> 2 − </Stack> and CuHS0 become more prevalent. Cu2+ and Cu+ readily form higher coordination complexes with Cl in hypersaline brines. Experimental data of Cu partition coefficients yield the following sequence: DCusilicate mineral/melt (0.007±0.002–0.82±0.08)<DCuFe-Ti oxide/melt (0.19±0.02–1.72±0.68)<DCufluid/melt (2–2698)<DCubrine/vapor (2–7066)<DCusulfide/melt (180–42000). Numerical modeling of Cu distribution during magma differentiation, with a potential link to the formation of porphyry Cu deposits, suggests that (i) low-degree partial melting (10%–25%) of S-bearing and S-absent mantle peridotite leads to Cu enrichment in mantle-derived basaltic arc magmas; (ii) sulfur saturation and fluid exsolution during crustal magmatic and hydrothermal processes can cause significant Cu depletion in the melt, while sulfide dissolution tends to enrich Cu in fluids. The combination of natural samples and experimental results indicates that ore-forming fluids with Cu concentrations exceeding 1000 to >10000 ppm can effectively precipitate Cu-bearing minerals such as chalcopyrite.

Cu speciation and partitioning among minerals, melts and fluids: Experimental advances and implications for ore formation

期刊论文
发表日期：

2025年2月21日

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Dongmei Qi,
Nuo Li,
Xiaoyan Li,
Chao Zhang

摘要

The mechanism of Cu enrichment is closely linked to the differentiation of mantle-derived magma and subsequent magmatic-hydrothermal processes. Experimental determination of Cu speciation and partitioning coefficients among minerals, melts, and fluids (including vapor) is critical for understanding the mobility and enrichment of Cu during magma differentiation, crystallization along cooling, fluid exsolution, the precipitation of Cu-bearing minerals, and water-rock interactions under subsolidus conditions. The summarization of experimental data demonstrates that Cu predominantly exists as cuprous ions (Cu⁺) in both ore fluids and melts at temperatures above 100°C. The speciation of Cu species is affected by the system’s components and temperature. In Cl- and S-poor silicate melts, Cu primarily exists as CuO_0.5. In hydrothermal fluids with intermediate to low salinities at temperatures above 300°C, the dominant species are [CuCl]⁰, [CuCl₂]⁻ and CuHS⁰. At lower temperatures (<300°C), in alkaline and intermediate to low salinity fluids, Cu(HS) ₂ ⁻ and CuHS⁰ become more prevalent. Cu²⁺ and Cu⁺ readily form higher coordination complexes with Cl in hypersaline brines. Experimental data of Cu partition coefficients yield the following sequence: D_Cu^{silicate mineral/melt} (0.007±0.002–0.82±0.08)<D_Cu^{Fe-Ti oxide/melt} (0.19±0.02–1.72±0.68)<D_Cu^fluid/melt (2–2698)<D_Cu^brine/vapor (2–7066)<D_Cu^sulfide/melt (180–42000). Numerical modeling of Cu distribution during magma differentiation, with a potential link to the formation of porphyry Cu deposits, suggests that (i) low-degree partial melting (10%–25%) of S-bearing and S-absent mantle peridotite leads to Cu enrichment in mantle-derived basaltic arc magmas; (ii) sulfur saturation and fluid exsolution during crustal magmatic and hydrothermal processes can cause significant Cu depletion in the melt, while sulfide dissolution tends to enrich Cu in fluids. The combination of natural samples and experimental results indicates that ore-forming fluids with Cu concentrations exceeding 1000 to >10000 ppm can effectively precipitate Cu-bearing minerals such as chalcopyrite.