Fe-Ti Oxide Mineralization in the XV Intrusion, Bafq Mining District, Central Iran: Insights from Mineralogy, Mineral Chemistry and S Isotopic Data.

The mafic-ultramafic intrusion in the XV anomaly area, contains magmatic Fe-Ti ox-ides±(p) ore, is located in the Bafq mining district in the Central Iran. It consists of cumulate and layered Fe-Ti-bearing gabbros and pyroxenites. The mineral assemblages include clinopyroxene, Fe-Ti oxides, plagioclase, amphibole, apatite and sulfides (pyrite and chalcopyrite). The Fe-Ti oxides mainly consist of magnetite-titanomagnetite and ilmenite, which occurred as disseminated, intergrowth, lamellae (trellis and sandwich textures) and inclusions. Magnetite in the gabbroic rocks is from the near end-member of Fe3O4 (<1 wt.% TiO2) to titanomagnetite containing up to 8 wt.% TiO2 (about 3.73 wt.% to 26.84 wt.% Ulvospinel (XUsp)). Magnetite in pyroxenite rocks is characterized with TiO2 range from 0.46 wt.% to 3.14 wt.% (XUsp varied from 1.76 wt.% to 10.46 wt.%). The abundances of V2O3 range from 0.03 wt.% to 1.29 wt.% and 0.24 wt.% to 1.00 wt.% for gabbro and pyroxenite, respectively. XUsp contents of magnetite show insignificant correlations with Al2O3 and MgO. The average XIlm in the ilmenite of gabbro is 92%, whereas it is 90.37% in the pyroxenite rocks. The MgO and V2O3 contents show a slightly positive correlation with TiO2 in ilmenite. The composition of clinopy-roxenes in gabbro and pyroxenite rocks fall in the diopside to augite field with Mg# ranging from 67 to 98 and 74 to 96, respectively. In both rock types, amphiboles are mainly pargasite and rarely actin-olite. Plagioclase in pyroxenite rocks is clustered in the labradorite to andesine fields with a compositional ranges of An46–69 and in gabboic rocks fall in two fields with compositional ranges of albite with An0.65–5.95 and labradorite with An50–63. The δ 34S isotopic values cover a limited range from +3.15‰ to +4.10‰ V-CDT consistent with magmatic origin. Fe-Ti mineralization is formed in two stages, minor inclusions of Fe-Ti oxide minerals in the pyroxene and plagioclase crystallized in the early magmatic stage, whereas interstitial oxides formed by fractional crystallization processes that accumulated by gravitational settling in the later stage as intercumulus phase. Gravitational settling process is supported by the observation of decreasing the amount of Fe-Ti oxides from Fe-Ti oxide-rich pyroxenite to weak mineralized gabbro (base to top). The high contents of H2O, phosphorate and high initial Ti-Fe in parental magma are the crucial factors controlling the Fe-Ti oxides enrichment and mineralization. [ABSTRACT FROM AUTHOR]