MULTIPLES SOURCES FOR THE GENESIS OF CU-AU DEPOSITS FROM CARAJÁS MINERAL IOCG SYSTEM, BRAZIL: TRACE ELEMENT AND SM-ND ISOTOPIC EVIDENCE FROM HYPOGENE ORES

IOCG systems are traditionally linked to the cyclic aggregation and breakup of large continents throughout the geological time, however, each architectural system involves the interaction of different structural mechanisms, physicochemical conditions, and rock-buffer relationships in which metals form and evolves. As such, those characteristics are still misunderstood in Archean worldwide systems were different processes could be involved in the genesis of the largest provinces as the Carajás Mineral Province.

New Sm–Nd isotopic and REE geochemical data of magnetite and chalcopyrite concentrates from the main representative Neoarchean IOCG – Salobo, Alemão, and Sequeirinho – and Orosirian Cu-Au systems – Sossego – from the Carajás Mineral Province were compared to previous published data to constrain the metal source of Cu and Fe.

Our results demonstrate that, although both Cu-Au systems formed synchronously with anorogenic granitoid emplacement, Nd isotopes of those Cu-Au and Fe-ores coincides with derivation of the REE from more than a single source. Prolongated crustal residence times (T_DM-IOCG = 2.89–3.08 Ga; T_{DM-Granite-related Cu-Au} = 2.85–3.02 Ga) suggest that initial mineralizing fluids and metals for IOCGs probably derived from reworked ancient crust through the leaching of Mesoarchean basement rocks (e.g., greenstone belts or gneissified granitoids), but also involving the assimilation and/or contribution of Neoarchean juvenile mantle components. Oppositely, the metal source for magnetite and chalcopyrite in the Orosirian Cu-Au systems derived predominantly from remobilization processes from long-lived Meso-to late-Neoarchean crustal sources continuously reworked through restricted granitogenesis events. Therefore, although δ³⁴S from the literature suggest a magmatic source for S, the metal source for those minerals are not exclusively from magmatic elements, indicating a different behavior from Cu and Fe regarding the S.

These new findings suggest that despite world-class IOCG provinces are widely diverse, a key-factor for ore-enrichment involves significant crustal residence times previous to the main ore-depositional event, as previously stated in Paleoproterozoic IOA-IOCG deposits at Kiruna, Sweden, by Storey & Smith (2017).