Apatite chemistry from Kiruna-type Bafq iron deposits, Central Iran: a review

The magnetite-apatite deposits in the Bafq metallogenic province in Central Iran, including the world-class Chadormalu and Choghart, as well as Se-Chahun and Esfordi, are hosted in the Late Precambrian-Cambrian volcanic-sedimentary rocks that have undergone variable sodic, calcic, potassic, silicic, chloritic, and sericitic alterations that are characteristic of iron oxide-apatite (IOA) ore systems. Apatites from various iron deposits in the Bafq district display chondrite-normalized REE patterns characteristic of Kiruna-type deposits. The REE patterns of the apatites display similarities to those of the magmatic and sedimentary country rocks. The trace-element patterns of the apatites are comparable to those of the local granitoids and mafic bodies, as well as the iron ores, and to other Kiruna-type deposits. It can be concluded, from apatite geochemistry of major magnetite-apatite deposits in the Bafq district that both magmatic and basinal fluids contributed to the formation of the iron oxide deposits. For the Chadormalu deposit, two generations of apatite are distinguished in backscattered electron images. The lower Sigma REE and Y in the earlier, and dominant, generation can be explained by local fluid aided dissolution/reprecipitation processes that led to development of monazite in close spatial association with depleted apatite. This would explain the younger monazite ages (450-250 Ma) compared with the apatite ages (533-510 Ma) obtained for Chadormalu deposit.