Chemical Signatures of Apatite in the AQW2 Deposit: Petrogenetic Insights on a Wide Archean–Paleoproterozoic Iron Oxide–Copper–Gold Mineral System in the Carajás Mineral Province

Iron oxide–copper–gold (IOCG) deposits are widespread throughout the Carajás Province, Brazil, reflecting multiple Precambrian hydrothermal events. The Aquiri region is a relatively unexplored geological frontier in the northwestern Carajás Province. The AQW2 IOCG deposit is hosted by a Neoarchean mafic intrusive suite within metavolcano–sedimentary rocks. The pre-mineralization (Na and Na-K) and mineralization (Fe-Ca and Fe-P) hydrothermal stages appear as replacement fronts and as cement within ductile-deformed breccias. Late-mineralization (Fe-K, chlorite, and calcic-rich) assemblages occur in multidirectional veins controlled by brittle structures. Early- and main-mineralization apatite (Ap I-III) is enriched in F, Mn, and Sr, depleted in Y, shows unusually high Fe and Si (Ap III), and exhibits a pronounced positive Eu anomaly (Ap II). These characteristics indicate an alkaline fluid composition, substantial fluid–rock interaction, and episodic CO2 degassing with the release of overpressured fluids, resulting in multiple brecciation events. A rapid decrease in temperature due to boiling is interpreted as a principal mechanism for copper precipitation. Late-mineralization apatite (Ap V–VI) is characterized by relatively higher Cl, Y, and LREE contents, lower Sr and Mn, and negative Eu-anomaly ratios, suggesting control by shallower paleostructures and more oxidizing conditions associated with the influx of basinal brines. These results highlight the evolution of the AQW2 deposit within a broader IOCG system and provide new insights into the metallogenic processes responsible for copper resources essential to the clean energy transition.