Acta Petrologica et Mineralogica

Magmatic sulfide and oxide deposits rarely commonly appear due to their different genetic mechanism, and the studies about their co-existence mechanism are important for understanding the mineralization of mantle-derived magmas. Chengde, Hebei Province is an important magmatic mineral resource rich area in China. Sulfides coexisting with magnetite appear in Habaqin iron deposit, and the magnetite has been studied, but few studies on sulfide are involved. We carried out the major and trace elements, and in situ S isotopes of sulfides as well as in situ Sr isotopes of amphibole and apatite on the basis of petrography of host hornblendite, to reveal the genesis of sulfides. The hornblendite shows cumulate texture and consists of amphibole (80%~85% by volume), magnetite (10%~15%), apatite (3%~5%), and minor sulfides (<5%). The magnetite appears as granular aggregates and sulfides as sparse disseminations (<5%). The sulfides are mainly pyrite with inclusions of magnetite and apatite, suggesting that sulfides crystallized at late stage. The contents of S and Fe in pyrites range from 52.0% to 53.0% and 45.4% to 46.5%, respectively, with higher concentration of Co (up to 1.68%), suggesting its formation is controlled by magmatic segregation, accompanied by slight magmatic hydrothermal process. The initial ⁸⁷Sr/⁸⁶Sr ratios of amphibole and apatite range from 0.705 82 to 0.708 30 and 0.706 16~0.708 09, respectively, and the δ³⁴S values of pyrites range from -2.8‰ to +1.3‰, suggesting that the hornblendite and its sulfur mainly originate from an enriched lithospheric mantle; sulfur saturation is primarily controlled by the fractional crystallization of the parental magma. The crystallization of magnetite leads to delayed sulfide saturation, and weak assimilation and contamination of crustal material results in weak sulfides separation compared to oxides.

sulfide; hornblendite; magnetite; S isotope; Sr isotope; North China