Skarn mineral assemblages in the Esfordi iron oxide-apatite deposit, Bafq district, Central Iran

The Esfordi iron oxide-apatite deposit is located in the Bafq district, Central Iran. The ore body is hosted by the Lower Cambrian succession of rhyolite, rhyolitic tuff, cherty dolomite, and limestone. Calc-silicate assemblages occur locally in altered host rocks as stratigraphically controlled patches. The main hydrothermal minerals include apatite, magnetite-hematite, actinolite, garnet, clinopyroxene, talc, calcite, and quartz. The prograde calc-silicate mineral paragenesis manifests as garnet (Ad(96.7), Gr(1.88)) and clinopyroxene (Di(76.14), Hd(22.65), Jo(1.21)), whereas apatite, magnetite, hematite, tremolite-actinolite, chlorite, talc, epidote, quartz formed during retrograde episode. Microthermometric results yield a temperature range for 222-465 degrees C, with a salinity of 8 to 21 wt% NaCl for apatite that coexists with retrograde mineral assemblage. delta O-18 isotopic variations of apatite (1.23-14.9%), magnetite (6.8-8.3%), and quartz (13.8-15.8%) suggests that mixing of magmatic and meteoric fluids occurred during mineralization. Calc-silicates prograde stage is believed to have formed at T<550 degrees C and high fO(2) conditions. The field, mineralogical, and geochemical evidence indicate distal calcic skarn type alteration occurred locally in the Esfordi hydrothermal system.