Geologia e eventos mineralizantes do depósito Cupro-Aurífero Santa Lúcia, Província Mineral de Carajás (PA), Cráton Amazônico

Abstract

The Carajás Mineral Province, located in the southeastern Amazon Craton, hosts worldclass metallic ore deposits, notably copper and gold mineralizing systems. This study integrated stratigraphic data, petrographic analyses, ore microscopy, and infrared VNIR–SWIR spectroscopy to investigate the products of hydrothermal alteration and their relationship with the mineralized zones of the Cu-Au Santa Lúcia deposit (OZ Mineral Brasil), situated near the municipality of Canaã dos Carajás, in the southern part of Pará State. Thin section and polished section descriptions were carried out to characterize the lithologies and mineral parageneses. Subsequently, 84 samples were analyzed by infrared spectroscopy, yielding 422 spectra processed using the proprietary software Spectragryph 1.2, in conjunction with the USGS mineral and mixture spectral library (version 7). This deposit, located in the southeasternmost portion of the province, occurs within a structural context controlled by shear zones and is hosted in aphyric rhyolite with a silica-feldspar matrix; mylonitic granodiorite with welldeveloped foliation and stretched quartz; zoned pegmatites with potassium feldspar crystals; and amphibolites containing well-preserved hornblende and plagioclase, and subordinately, fine-grained tourmaline associated with quartz-feldspar banding. These rocks reveal multiple mineralizing pulses, accompanied by the superposition of distinct types and styles of hydrothermal alteration. Mineralization, dominated by chalcopyrite with subordinate pyrite, bornite, and galena, occurs in a variety of styles, including veins and veinlets parallel or discordant to the rock fabric; as fracture fillings; as hydrothermal breccias cemented by sulfides; as fine disseminations in the host rock matrix; and as massive chalcopyrite mineralization at depths reaching 80 meters. The most common alteration minerals are muscovite, chlorite, epidote, calcite, microcline, as well as clay minerals such as kaolinite and montmorillonite. The distribution of these minerals corresponds with the potassic, propylitic, carbonate, and sericitic alteration domains identified in thin section. Variations in the width and position of the spectral absorption bands allowed the identification of zones with differing degrees of crystallinity, reflecting the successive influence of hydrothermal fluids under varying physicochemical conditions, including those associated with pegmatitic bodies. The integration of lithological, structural, spectral, and mineralogical data enabled the construction of a paragenetic evolutionary model, highlighting the operation of a multiphase hydrothermal system. The characteristics of the deposit—reducing environment, sulfide-dominant assemblages, low abundance of iron oxides, and association with elements such as Ni, Co, and light REEs—indicate an affinity with ISCG-type (iron sulfide copper-gold) systems. Official company data indicate that the Santa Lúcia deposit hosts measured resources of 5.8 Mt @ 2.1% Cu, 0.35 g/t Au, and 4.8 g/t Ag, with an estimated mine life of 8 years, underscoring its economic potential. Thus, the results of this research provide valuable insights into the mineralizing processes of the Santa Lúcia deposit, while also emphasizing the utility of infrared spectroscopy as an analytical tool for defining alteration zones and understanding complex hydrothermal systems. The study also evidences the role of multiple mineralizing pulses, associated with distinct stages of hydrothermal alteration and successive structural events, which contributed to the complexity and zonation of the system. The identification of affinities with ISCG-type systems is particularly relevant for the Carajás Mineral Province, where this style of mineralization is still poorly characterized in comparison to IOCG deposits, thereby expanding the range of applicable exploration models in the region.