Magnetite geochemistry and iron isotope signature of disseminated and massive mineralization in the Kalatongke magmatic Cu Ni sulfide deposit, northwest China

Sulfide Copper‐Iron Isotopic Fractionation During Formation of the Kalatongke Magmatic Cu‐Ni Sulfide Deposit in the Central Asian Orogenic Belt

“…A large amount of light 54 Fe‐enriched sulfide (relative to magnetite) segregation in the immiscible sulfide melt could cause elevated δ 56 Fe values in co‐crystallized magnetite. The magnetite volume percent in disseminated ores is less than the magnetite content in massive ores, while the magnetite δ 56 Fe values are consistent in the disseminated ores (0.89–1.10‰, average = 1.01‰) with the values in massive ores (0.41–1.35‰, average = 0.94‰) (Tang et al., 2022). The main reason may be that Fe‐S coordination bond strength in sulfide minerals (Bigeleisen & Mayer, 1947; Hall & Stewart, 1973; Urey, 1947) is stronger than the Fe‐O ionic bond strength in magnetite (Fleet, 1981), resulting Fe contents and isotopic characteristics in sulfide less susceptible to magnetite crystallization.…”

“…Pyrrhotite in disseminated ores has a lighter δ 56 Fe value than pyrrhotite from massive ores (Figure 5a), but there was no difference in Fe and S components. The magnetite in disseminated and massive ores co‐crystallized with MSS and Cu‐rich ISS in the Kalatongke deposit, respectively (Tang et al., 2022). A large amount of light 54 Fe‐enriched sulfide (relative to magnetite) segregation in the immiscible sulfide melt could cause elevated δ 56 Fe values in co‐crystallized magnetite.…”

“…Kalatongke pyrrhotite crystallized from sulfide liquids with varying degrees of sulfide segregation, as evidenced by the chalcophile element content. Early crystallized sulfide is enriched in chalcophile elements (Dare et al., 2010; Mansur et al., 2021), and the chalcophile element Co concentration in pyrrhotite from Kalatongke disseminated ores varies from 85 to 639 ppm (Tang et al., 2022). Ni‐rich pentlandite formed at a higher temperature (Kitakaze et al., 2016; Kosyakov & Sinyakova, 2012; Waldner & Pelton, 2004) than Ni‐poor pentlandite.…”

“…Fe-Ni-S ternary phase diagram for stable sulfide phases, after(Naldrett, 2004), with results from EPMA analyses of pyrrhotite (squares) and pentlandite (circles) in disseminated and massive ores. EPMA data are fromTang et al (2022) andGao (2011).…”