Apatite chemistry from the XV IOA deposit, the Bafq–Saqand Metallogenic Province (BSMP), Central Iran: constrains on the genesis of IOA deposits

In this study, we present petrographical and microanalytical (EPMA, LA–ICP–MS) results of apatites associated with Fe–Ti±P mineralization in the XV deposit in the BSMP. Apatite is predominantly observed as subhedral to euhedral, homogeneous grains, with no zoning or inclusions. Geochemically, apatite is fluorapatite of magmatic origin, with Cl/OH and Cl/F ratios of <0.05 and 0.01 to 0.07, respectively. Apatites from XV and other IOA deposits in the BSMP display a high F/Cl ratio, which is likely the main characteristic of IOA–type deposits such as the Kiruna-type deposit. Apatites from both rock types (gabbro and pyroxenite) exhibit similar rare earth elements (REEs) and multitrace element patterns, indicative of a shared origin. The highly light rare earth elements (LREEs)–enriched pattern in chondrite–normalized fractionation trends, along with positive Eu and slight negative Ce anomalies, as well the high (La/Sm)N and (La/Yb)N ratios of XV apatite, further corroborates the magmatic genesis of fluorapatite. The Eu/Eu* and Ce/Ce* ratios in XV rocks imply a high oxidation condition, as well as other IOA deposits in BSMP. The sulfur content is less than 1 wt% and shows a positive correlation with SiO2, implying coupled dissolution–reprecipitation of primary fluorapatite. Considering the geological setting of XV and other IOA deposits in the BSMP, the parental magma(s) appear to have originated from oxidizing Fe-Ti±P-rich magma(s), likely formed within an extensional postcollisional setting, influenced by the Proto–Tethys and Central Iranian Microcontinent (CIMC) convergence events.