The genesis of iron oxide-apatite (IOA) deposits: evidence from the geochemistry of apatite in Bafq-Saghand district, Central Iran

The Origin of Iron Oxide-Apatite deposits (IOA) with low Ti or Kiruna type deposits has long been a matter of debate. In this case, several provenances have been proposed for these deposits which include: magmatic, magmatic-hydrothermal, hydrothermal, banded iron formations, and sedimentary-exhalative. Bafq-Saghand metallogenic zone is located in central Iran and hosts several large IOA type deposits including Chadormalu, Choghart, Se-Chahun, and Esfordi with nearly ~1500 mt ore with an average grade of 55%. Mineralization of REE-rich apatite is very common in these deposits, an issue that could be utilized for the study of their genesis. Fifteen apatite samples from the deposits of Chadormalu, Choghart, Se-Chahun, and Esfordi were taken and analyzed using LA ICP-MS. According to the geochemical analysis, the apatite of the abovemnetioned deposits show high enrichment of Y, Na, and Si, while very low content of Cl. Total REE content varies from 0.36-2.25% in which the LREE show an enrichment indicating strongly fractionation from HREE. Strong negative Eu anomaly (0.69-0.256) is observed. Sr and Y contents in apatites are 165-365 and 743-1410 ppm, respectively. The Fe-OH-Cl diagram shows that apatites is situated in the Hydroxil-fluoroapatite domain. The results show that these deposits are similar to those of IOA type deposits (e.g. Kiruna, El Laco, Abagong, Avnik, etc.). Apatite mineralization is unlikely related to carbonatitic magmatism, but situated in the Kiruna type and mafic rocks domain. The main mineralization event was likely related to tonalite-trondhjemite-granodiorite (TTG) and diorite-granite of arc magmatism (525-532 Ma) which were intruded into the Cambrian volcano sedimentary units (as country rock). Then the hydrothermal processes following alkaline intrusion (syenite and monzosyenite) led to mineralization. In general, the iron oxide-apatite (IOA) mineralization with low Ti has occurred through the magmatic-hydrothermal processes in the Bafgh-Saghand zone.