Hydrothermal Footprint of the Salobo Profundo Cu-Au Orebody, Carajás Mineral Province, Brazil

Located in the northern sector of the Carajás mineral province, the Salobo Cu-Au deposit is the largest copper deposit in Brazil. “Salobo Profundo” (Deep Salobo) refers to the portion of the orebody beneath the final proposed pit, where deep exploration drill holes have investigated a panel approximately 700 m deep and 1,800 m long. The alteration footprint of this portion of the deposit has been documented through the integration of petrographic, hyperspectral, and geochemical data from three boreholes, totaling approximately 3,000 m. Hydrothermal zoning is characterized by albitization (Na (I)) and silicification in the distal halo, transitioning to calcic-potassic iron zones proximal to mineralization. Intense Fe metasomatism, along with potassic iron and iron alteration is most closely associated with copper and gold mineralization. Late-stage alteration is characterized by Na-Ca (II) alteration and a later type of a more intense albitic alteration (Na (II)). Hyperspectral scanning, encompassing visible-near infrared (VNIR, 380–1,000 nm), short-wave infrared (SWIR, 1,000–2,500 nm), and long-wave infrared (LWIR, 7,700–12,300 nm) wavelength ranges, has mapped the main minerals involved in the alteration processes at a centimeter-scale resolution. Minerals such as amphiboles, biotite, garnet, chlorite, quartz, and albite were identified, with garnet abundance showing a close association with copper-rich zones. The geochemical data are consistent with the characteristics of many iron oxide copper-gold (IOCG) systems, exhibiting the classic association of Fe, Cu, ± Au, along with enrichment in Ag, Bi, Co, Cs, F, Mo, Ce, La, and U. These results indicate that hyperspectral core scanning, combined with geochemical data analysis, is an effective approach for defining alteration zonation around IOCG deposits. This method enhances the characterization and refined modeling of hydrothermal zoning, providing a powerful tool for exploring for similar deposits, not only in Carajás but also in other metallogenic provinces worldwide.