TY - JOUR

T1 - Response of Fe-Ni-Cu isotope systematics to sulfide liquid oxygen content

T2 - Implications for magmatic sulfide Co enrichment in orogenic settings

AU - Tang, Dongmei

AU - Lazarov, Marina

AU - Wang, Dachuan

AU - J. Evans, Noreen

AU - Qin, Kezhang

AU - Xue, Shengchao

AU - Horn, Ingo

AU - Weyer, Stefan

N1 - Publisher Copyright: © 2024 Elsevier Ltd

PY - 2024/12/18

Y1 - 2024/12/18

N2 - The initial silicate melt related to magmatic Ni-Cu deposits located in orogenic settings in China (e.g., East Tianshan orogenic belt, East Kunlun orogenic belt) had a high fO2 that progressively decreased with continued magmatic evolution. It is still unknown if the sulfide melt that separated from the silicate melt inherited this high fO2, or even whether oxygen fugacity in sulfide plays an important role in the mineralization processes. In this work we undertook new in situ Fe, Cu, and Ni isotopic analyses of base metal sulfides from the Xiarihamu magmatic sulfide deposit (East Kunlun orogenic belt), and combined this new data with previously published Fe and Cu isotopic results from orogenic and cratonic magmatic sulfide deposits to assess changes in fO2 in sulfide during sulfide melt evolution, and the role of these processes in metal enrichment. In the Xiarihamu deposit, pentlandite has a Fe/Ni ratio similar to high-temperature pentlandite (Fe4.95Ni4.08S7.96) found in the upper disseminated ores which host high-temperature maucherite inclusions. These findings indicate a high formation temperature for the sulfide in the upper disseminated ores. Atomic % Fe in pyrrhotite suggests that fO2 increased during the transition from disseminated mineralized ultramafic rocks (47.2–50.7), through net-textured + massive mineralized ultramafic rocks (47.1–48.1), to disseminated mineralized gabbros (46.9–47.3). Early crystallized, high temperature sulfides in disseminated ores do not display high oxygen fugacity characteristics (high Fe3+/ΣFe), whereas in the silicate melt, fO2 continued to decrease with progressed evolution. Orogenic magmatic sulfide deposits show consistent, uniquely lighter δ56Fe and δ65Cu in disseminated ores relative to the same sulfides from massive ores. This cannot be explained by crustal contamination and sulfide melt fractionation based on Fe and Cu isotopes. Uncoupled δ62Ni (insensitive to fO2 variations) and δ56Fe, as well as heavy δ56Fe and Co enrichment in late crystallized pentlandite (low temperature and high Fe3+/ΣFe) from the Xiarihamu and Kalatongke deposits (located in different orogenic belts), suggests that an increase in oxygen fugacity and related Fe3+/ΣFe ratios exert control on Co mineralization. Iron, Cu and Ni isotopes in sulfide can be used as indicators of Fe3+/ΣFe ratios in magmatic sulfide deposits in an orogenic environment, and changes in the Fe3+/ΣFe ratio play a critical role in Co enrichment.

AB - The initial silicate melt related to magmatic Ni-Cu deposits located in orogenic settings in China (e.g., East Tianshan orogenic belt, East Kunlun orogenic belt) had a high fO2 that progressively decreased with continued magmatic evolution. It is still unknown if the sulfide melt that separated from the silicate melt inherited this high fO2, or even whether oxygen fugacity in sulfide plays an important role in the mineralization processes. In this work we undertook new in situ Fe, Cu, and Ni isotopic analyses of base metal sulfides from the Xiarihamu magmatic sulfide deposit (East Kunlun orogenic belt), and combined this new data with previously published Fe and Cu isotopic results from orogenic and cratonic magmatic sulfide deposits to assess changes in fO2 in sulfide during sulfide melt evolution, and the role of these processes in metal enrichment. In the Xiarihamu deposit, pentlandite has a Fe/Ni ratio similar to high-temperature pentlandite (Fe4.95Ni4.08S7.96) found in the upper disseminated ores which host high-temperature maucherite inclusions. These findings indicate a high formation temperature for the sulfide in the upper disseminated ores. Atomic % Fe in pyrrhotite suggests that fO2 increased during the transition from disseminated mineralized ultramafic rocks (47.2–50.7), through net-textured + massive mineralized ultramafic rocks (47.1–48.1), to disseminated mineralized gabbros (46.9–47.3). Early crystallized, high temperature sulfides in disseminated ores do not display high oxygen fugacity characteristics (high Fe3+/ΣFe), whereas in the silicate melt, fO2 continued to decrease with progressed evolution. Orogenic magmatic sulfide deposits show consistent, uniquely lighter δ56Fe and δ65Cu in disseminated ores relative to the same sulfides from massive ores. This cannot be explained by crustal contamination and sulfide melt fractionation based on Fe and Cu isotopes. Uncoupled δ62Ni (insensitive to fO2 variations) and δ56Fe, as well as heavy δ56Fe and Co enrichment in late crystallized pentlandite (low temperature and high Fe3+/ΣFe) from the Xiarihamu and Kalatongke deposits (located in different orogenic belts), suggests that an increase in oxygen fugacity and related Fe3+/ΣFe ratios exert control on Co mineralization. Iron, Cu and Ni isotopes in sulfide can be used as indicators of Fe3+/ΣFe ratios in magmatic sulfide deposits in an orogenic environment, and changes in the Fe3+/ΣFe ratio play a critical role in Co enrichment.

KW - Base metal sulfide

KW - Co enrichment

KW - Fe/ΣFe

KW - In-situ Fe-Cu-Ni isotopes

KW - Magmatic sulfide deposit in orogeny

UR - http://www.scopus.com/inward/record.url?scp=85212650603&partnerID=8YFLogxK

U2 - 10.1016/j.gca.2024.12.018

DO - 10.1016/j.gca.2024.12.018

M3 - Article

AN - SCOPUS:85212650603

VL - 390

SP - 1

EP - 23

JO - Geochimica et cosmochimica acta

JF - Geochimica et cosmochimica acta

SN - 0016-7037

ER -