Geochemical signatures of the Neoarchean and Paleoproterozoic copper systems in the Carajás Mineral Province, NW Brazil: Implications for metal endowment

The main copper deposits of the Carajás Mineral Province are grouped into: i) iron oxide-copper-gold (IOCG), and ii) granite-related Cu-Au. They were formed during multiple mineralizing events in the Neoarchean (ca. 2.7; ca. 2.5 Ga) and Paleoproterozoic (ca. 2.1; ca. 1.8 Ga). A combination of non-composition and composition data analysis, molar element ratio, and principal component analysis using a lithogeochemical dataset (n = 1040) has been applied to recognize geochemical associations in these deposits. The Neoarchean IOCG deposits in the Northern and Southern Copper Belts of the Carajás Domain are controlled by ductile structures and comprise high-temperature hydrothermal associations within sodic (albite-scapolite), sodic-calcic (albite-actinolite-scapolite±hastingsite), calcic-iron (magnetite-actinolite-apatite), potassic (biotite-tourmaline±scapolite), potassic-iron (biotite-magnetite; almandine-grunerite-biotite) and iron-rich alteration zones. These zones envelop chalcopyrite-magnetite-actinolite-apatite (e.g., Sequeirinho orebody), magnetite-chalcopyrite-siderite (i.e., Igarapé Bahia deposit) breccias, or massive magnetite bodies with bornite-chalcocite (i.e., Salobo). The Fe-Cu-Au-P-REE association is common to all Neoarchean IOCG deposits of the province. Nevertheless, the IOCG deposits from the northern sector (ca. 2.5 Ga) are also enriched in Ba-Pb-Zn-Ag-Mo-REE ± Sn ± W ± Bi±U ± Nb ± Ta ± Y. Conversely, the chemical signature of Neoarchean (ca. 2.7 Ga) IOCG deposits from the southern sector display enrichment in V-Ni-Co-Cr. Part of these chemical variations may be due to differences in the nature of 7host rocks, including greenstone belt sequences in the south and metasedimentary exhalative rocks in north. Both in the northern and southern sectors, the sodic alteration is marked by Na, Ga, Ti, Sr, Th and Mo. The sodic-calcic displays Na, Ca, Mo, Mn, Mg, Pb, Zn and Sn enrichment. The iron-rich alteration zones (grunerite-almandine-magnetite) from the northern sector display a Fe, Mg, Ba, V, Ni, Co, Cr, Cu association. The calcic-iron alteration within the southern sector is marked by enrichment in Ca, Fe, V, Ni, Co, Cr, Mn, Mg, Th, P, HREE and Cu. The Fe-V-Ni-Co signature typical of the iron-rich and calcic-iron alteration stages is thus a lithogeochemical footprint of early Neoarchean IOCG mineralization, providing a useful proxy for exploration. Significant amounts of K, Rb, Ba, Al, Si, Nb, Ta, Th, U, Zr, Pb, Zn and Cu are common in potassic-iron alteration zones from Neoarchean deposits in both northern and southern sectors. The Paleoproterozoic IOCG and granite-related deposits are controlled by brittle structures and represent oxidized (muscovite-potassium feldspar-pyrite-hematite-chlorite), low temperature, sulfur-rich (pyrite-rich) and iron-deficient hydrothermal systems. The Paleoproterozoic IOCG deposits display potassic or potassic-iron alteration (potassium feldspar-biotite±magnetite), generally overprinted by chlorite alteration with late chalcopyrite-rich vein/breccia containing calcite-quartz-albite-chlorite-epidote-sericite. The Paleoproterozoic IOCG mineralized zones display enrichment in granitophile elements, defined by Sn-Mo-REE ± W ± Be±Bi±Nb ± Y. The granite-related deposits are marked by chlorite-rich or greisen alteration types characterized by enrichment in K, Sn, W, Mo, and Bi. The ore zones within these deposits are related to the Cu-Au-Mo-W-Sn-Bi-Be-Nb-U-Y signature. The recurrence and superposition of multiple hydrothermal events at a deposit-scale is evidenced by hybrid geochemical signatures, marked by an intermediate composition between the Neoarchean (Fe-V-Ni-Co-Ba-Pb-Zn) and Paleoproterozoic (Sn-W-Mo-Bi) signatures. The results obtained provide insights on the chemical evolution of the Carajás copper systems and demonstrate the influence of the multiple hydrothermal episodes on the geochemical signature of these deposits.