Mineral chemistry and alteration parageneses of the Chogart iron oxide-apatite occurrence, Bafq district, Central Iran

The Chogart iron oxide-apatite deposit is hosted by Early Cambrian meta-rhyolitic rocks in Central Iran. The host rocks show strong Na-Ca and Na hydrothermal alterations. The paragenetic sequence includes: (I) sodic-calcic alteration (actinolite, magnetite, early apatite, albite, chlorite, calcite and titanite), (II) sodic-ferric alteration (albite, hematite, actinolite), and (III) late carbonization or silicification (chlorite, talc, late apatite, calcite and quartz). Amphibole chemistry reveals the presence of at least two types: actinolite and magnesio-hornblende which is identified by having higher Al-IV, Cl, and Fe/(Fe+Mg) than actinolite. Plagioclase is albite and chlorites fall in the pycnochlorite and ripidolite fields. The formation temperatures of pycnochlorite and ripidolite are estimated at about 330 degrees C and 200 degrees C, respectively. Whole rock geochemistry shows that the sodic-calcic alteration zone is enriched in Na, Ca, Mg, Mn, Fe, Ti, P, Y+REEs, V and depleted in Si, Al and K. The sodic alteration zone shows depletion in K, Fe, Nb, Cr, Th, Zr, Rb as well as Ba, and enrichment in Na, Mg, Ca, Al, and Y+REEs. Geology, mineralogy and geochemistry of the iron oxide-apatite occurrence as well as mineral assemblages support mixing of magmatic and non-magmatic fluids that caused iron oxide mineralization and various hydrothermal alteration patterns in the Chogart deposit.