Uranium-lead ages of apatite from iron oxide ores of the Bafq District, East-Central Iran

Iron oxide-apatite (IOA) deposits, often referred to as Kiruna-type iron ore deposits, are known to have formed from the Proterozoic to the Tertiary. They are commonly associated with calc-alkaline volcanic rocks and regional- to deposit-scale metasomatic alteration. In the Bafq District in east Central Iran, economic iron oxide-apatite deposits occur within felsic volcanic tuffs and volcanosedimentary sequences of Early Cambrian age. In order to constrain the age of formation of these ores and their relationship with the Early Cambrian magmatic event, we have determined the U-Pb apatite age for five occurrences in the Bafq District. In a Pb-206/U-238 vs. Pb-207/U-235 diagram, apatite free of or poor in inclusions of other minerals plots along the Concordia between 539 and 527 Ma with four out of five samples from one deposit clustering at the upper end of this range. For this deposit, we interpret this cluster to represent the age of apatite formation, whereas the spread towards younger ages may reflect either minor Pb loss or several events of IOA formation. Apatite with inclusions of monazite (+/- xenotime) yields disturbed systems with inclusions having developed after formation of the iron ore-apatite deposits, possibly as late as 130-140 Ma ago. Obtained apatite ages confirms that (IOA) and the apatite-rich rocks (apatites) of the Bafq district formed coevally with the Early Cambrian magmatic (-metasomatic) events.