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

Abstract

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 (Ad96.7, Gr1.88) and clinopyroxene (Di76.14, Hd22.65, Jo1.21), whereas apatite, magnetite, hematite, tremolite–actinolite, chlorite, talc, epidote, quartz formed during retrograde episode. Microthermometric results yield a temperature range for 222–465 ° C, with a salinity of 8 to 21 wt% NaCl for apatite that coexists with retrograde mineral assemblage. δ18O 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 °C and high ƒO2 conditions. The field, mineralogical, and geochemical evidence indicate distal calcic skarn type alteration occurred locally in the Esfordi hydrothermal system. © 2014, Saudi Society for Geosciences.