The Oldest Copper Deposits in the Carajás Mineral Province, Brazil: Evidence for a Mesoarchean (2.89–2.84 Ga) Cu-Au-Fe Mineralization

The Hades and Hades Nordeste copper deposits lie along a west branch of the WNW to ESE Canaã shear zone in the southwestern Carajás mineral province. Their host rocks include Paleoarchean (3.38–3.23 Ga) orthogneiss and amphibolite, the oldest rocks in the Amazonian craton. These host rocks underwent high-grade metamorphism between 2.96 and 2.90 Ga, during the accretionary phase of the Carajás-Rio Maria orogeny. Early hydrothermal sodic (albite) and potassic (orthoclase + microcline) alterations were followed by a Ca-Fe(-K) assemblage (actinolite ± K-feldspar ± albite ± epidote ± calcite ± magnetite) associated with chalcopyrite ± pyrite-molybdenite-pentlandite-hessite-bismuthinite (mineralization I). Widespread chlorite-rich alteration linked to a mylonitic foliation is related to the main ore stage (mineralization II), represented by chalcopyritequartz ± pyrite-molybdenite breccias. Apatite and titanite U-Pb (laser ablation-inductively coupled plasma-mass spectrometry) combined with molybdenite Re-Os data indicate a Mesoarchean ore-forming event between 2.89 and 2.84 Ga, coeval with regional deformation related to the collisional phase of the Carajás-Rio Maria orogeny. Hydrothermal alteration patterns, deformation-related structures, geochemistry, and ore style suggest similarities with Cu-Au-Fe mineral systems, with possible affinities with the iron sulfide copper-gold (ISCG) subclass. Neoarchean apatite U-Pb ages (ca. 2.67 Ga) at Hades suggest overprinting by a nonmineralizing event, likely related to Canaã shear zone reactivation. A second superposed event is characterized by Paleoproterozoic (1.95–1.88 Ga) granitic and volcanic rocks related to a younger magmatic-hydrothermal system, associated with potassic, propylitic, and sericite alterations. These findings highlight the potential for Mesoarchean Cu-Au-Fe mineral systems and encourage further evaluation of the iron oxide-copper-gold and ISCG linkages, as well as Paleoproterozoic magmatic-hydrothermal mineralization in the western Carajás mineral province.