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Article

Geology and Hydrothermal Evolution of the Antas North Iron Sulfide–Copper–Gold (ISCG) Deposit in the Carajás Mineral Province

by
Sérgio Roberto Bacelar Hühn
1,*,
Rafael Nascimento Paula
2,
Francisco José Ferreira Fonseca
3 and
Isac Brito Barreira
1
1
Department of Geology, Federal University of Ceará (UFC), Fortaleza 60440-554, Brazil
2
Ero Copper, Ero Brazil Caraíba, Fazenda Caraíba, Jaguarari 49967-000, Brazil
3
Laboratório de Geofísica Aplicada, Universidade Federal do Paraná, Curitiba 81531-980, Brazil
*
Author to whom correspondence should be addressed.
Minerals 2025, 15(10), 1081; https://doi.org/10.3390/min15101081
Submission received: 30 July 2025 / Revised: 11 October 2025 / Accepted: 14 October 2025 / Published: 17 October 2025
(This article belongs to the Special Issue Novel Methods and Applications for Mineral Exploration, Volume III)
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Abstract

The Antas North mine, located in the southeastern Amazonian Craton within the Carajás Mineral Province, is hosted by mafic and felsic metavolcanic rocks that have undergone extensive hydrothermal alteration. Field and petrographic data reveal a hydrothermal sequence comprising sodic (albite), potassic (biotite + scapolite), calcic (amphibole + apatite), silicification (quartz), and propylitic (chlorite + epidote + calcite) assemblages. Copper–gold mineralization, spatially associated with calcic alteration, occurs as massive sulfide lenses, breccia zones, and vein networks dominated by chalcopyrite, pyrrhotite, and pyrite. The absence of magnetite/hematite and the dominance of sulfides and ilmenite classify Antas North as an Iron Sulfide–Copper–Gold (ISCG) system, representing a reduced endmember within the broader IOCG spectrum. New U–Pb titanite geochronology yields two concordant age populations at ca. 2476.6 ± 15.9 Ma Ga and 2162.9 ± 28.1 Ma Ga, recording a late Archean mineralizing stage and subsequent Paleoproterozoic reactivation during the Transamazonian orogeny. These ages parallel the multistage evolution recognized in other Carajás IOCG deposits, where copper–gold-related mineralization was repeatedly overprinted by later tectono-hydrothermal events. The reduced character of Antas North, marked by ilmenite and sulfide dominance with scarce magnetite, demonstrates that reduced IOCG styles were already established in the Neoarchean–Paleoproterozoic transition and underscores the diversity of mineralizing processes within the Carajás IOCG–IOA spectrum.

1. Introduction

The Carajás Mineral Province (CMP), located in the southeastern Amazonian Craton, is Brazil’s most significant mineral province and one of the most important globally. It is renowned for its high-grade iron, manganese, platinum group elements (PGEs), nickel and, notably, its Iron Oxide–Copper–Gold (IOCG) deposits [1,2,3,4,5,6,7,8]. Since the discovery of the Salobo, Igarapé Bahia, Furnas, Cristalino and Sossego deposits, Carajás has been a key area for understanding IOCG systems and their diverse geological expressions.
Despite considerable advances, many aspects regarding the diversity of mineralization types within the province remain poorly understood. In particular, the Iron Sulfide–Copper–Gold (ISCG) subtype has been little explored. ISCG deposits are a subset of the broader IOCG family in which chalcopyrite, pyrrhotite and pyrite dominate over magnetite and hematite and in which titanium is hosted by ilmenite rather than magnetite [9,10]. These deposits form under reduced redox conditions at deeper crustal levels and are distinguished by the presence of calcic alteration assemblages (hornblende + actinolite + apatite) and the relative absence of iron oxides. The Antas North deposit presents a rare opportunity to study this reduced mineralization style and evaluate its relationship to the better documented oxidized IOCG systems [8,11,12].
The present study integrates fieldwork, petrographic analyses, structural interpretation and geological modelling to characterize the Antas North deposit. By delineating hydrothermal alteration patterns, mineralization styles and structural controls, the study aims to better understand the processes controlling mineralization in reduced environments within the Carajás Province. In the following sections we provide a brief overview of IOCG and ISCG deposits worldwide, describe the regional geological setting, document the host rocks and alteration assemblages, and discuss the geochronological and structural constraints on ore formation.

2. Geological Background

The CMP is part of the southeastern Amazonian Craton and comprises Archean basement rocks, Neoarchean supracrustal sequences, and Paleoproterozoic intrusions. The province is subdivided into two major domains—the Rio Maria and Carajás domains—separated by an east–west trending shear zone [1,13,14,15,16].
The Carajás Domain hosts the Xingu and Pium Complexes, the Rio Novo Group, and the Itacaiúnas Supergroup, as well as granitoid magmatism events spanning from 2.76 Ga to 1.88 Ga [17,18,19,20,21]. These geological units present a complex evolutionary history, marked by extensive hydrothermal activity and multiple mineralization events (Figure 1).

3. IOCG Deposits in the Carajás Province

The IOCG deposit class emerged as a major exploration target following the discovery of the Olympic Dam deposit in Australia [23,24,25,26]. IOCG systems typically exhibit significant copper reserves and grades, along with enrichment in elements such as Au, Ag, U, REE, Co, and Ni. However, there are no universally accepted genetic models, given the broad diversity of host rocks, structural settings, alteration styles, and fluid sources [8,24,25,26].
In the Carajás Province, IOCG deposits show a wide range of hydrothermal alterations and ore mineral assemblages, reflecting diverse crustal levels of formation and fluid evolutions.
Key characteristics of Carajás IOCG deposits include [2,3,4,5,6,7,8,24,25,26,27,28,29,30,31,32,33,34,35,36].
  • Metavolcano-sedimentary host rocks from the Itacaiúnas Supergroup;
  • Strong structural control, often associated with shear zones;
  • Proximity to diverse intrusive suites (granite, diorite, gabbro);
  • Abundant hydrothermal breccias;
  • Intense sodic, potassic, and magnetite alterations;
  • Polymetallic enrichment (REE, P, U, Ni, W, Sn, Co, Pd);
  • Wide variation in formation temperatures (100–570 °C) and salinities (0–69 wt.% NaCl eq.).
Both northern (e.g., Salobo, Furnas and Igarapé Bahia) and southern (e.g., Sossego, Cristalino and Corta Goela) deposits record high-temperature Archean hydrothermal alteration (sodic–calcic to potassic) typical of oxidized IOCG systems. However, the Paleoproterozoic (~1.8 Ga) Cu–Au systems described by [2,3,4,5,6,7,8] represent a distinct, later hydrothermal event: reduced, quartz- and sulfur-rich, lacking major iron oxides, and genetically linked to A-type B-Li-F granites and greisenized cupolas. Thus, these younger deposits are not upward or lateral continuations of Archean IOCG systems, but separate Paleoproterozoic reduced mineralizing events [2,3,4,5,6,7,8,29,30,31,32,33,34,35,36].

4. Materials and Methods

4.1. Fieldwork, Petrography, and Structural Geology

Field investigations at the Antas North mine included the description of 10 drill cores and 9 outcrops. Observations focused on deposit geometry, lithology, hydrothermal alteration, and mineralization styles.
Petrographic analyses of 34 samples were conducted at the Federal University of Ceará (UFC) to characterize hydrothermal alteration assemblages and ore mineral associations. Additionally, scanning electron microscopy combined with energy-dispersive Xray spectroscopy (SEM–EDS) was used to determine the chemical composition of accessory and ore minerals. SEM–EDS analyses were performed on carbon-coated polished thin sections using a 20 kV accelerating voltage and 1 nA beam current with a 30 s live time. Data were corrected with a ZAF algorithm calibrated on natural and synthetic mineral standards to obtain semiquantitative elemental abundances. Integration of geological mapping was performed using Leapfrog Geo 2023 [37].
U–Pb analyses were performed by LA–ICP–MS using a 193 nm excimer laser (30 µm spot) coupled to a quadrupole ICP–MS at the University of Campinas. Data reduction used the GEMOC titanite (2.089 Ga) and NIST 610 glass as primary and secondary standards, respectively, processed with Iolite. Concordant analyses (<5% discordance) were used for age calculations following the methods of [38].

4.2. U–Pb Titanite Geochronology

U–Pb dating of titanite was conducted by laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) at the Geochronology Laboratory of the University of Campinas (UNICAMP). A 193 nm excimer laser (30 µm spot size, 6 Hz repetition rate) was coupled to a quadrupole ICP–MS. Ablation products were transported in a He carrier gas to the plasma. Analytical standards included the GEMOC titanite (2.089 Ga) and NIST 610 glass, and data reduction was performed using the Iolite v4 software. Concordant analyses were filtered with a discordance threshold of <5%, following the procedures of [38].
A total of 49 analytical spots were obtained from 24 titanite grains collected in calcic and potassic alteration zones from three representative samples (Table 1). The data define two concordant age populations: an older group (n = 24 spots) yielding a weighted mean of 2476.6 ± 15.9 Ma (2σ; MSWD = 3.77), and a younger group based on five concordant spots, giving a weighted mean of 2162.9 ± 28.1 Ma (2σ; MSWD = 0.86).

5. Local Geology

5.1. Host Rocks

The Antas North deposit is located near the Estrela Granite Complex and is hosted by mafic and felsic metavolcanic rocks belonging to the Grão Pará Group, part of the Itacaiúnas Supergroup (Figure 2). Gabbro dikes crosscut the host sequence and the mineralized zones. Regional structures have WNW-ESE trend, linked to the Carajás Fault, whereas the ore body is aligned along a NE–SW secondary shear zone [38].
Mafic volcanic rocks (Figure 3) exhibit fine to medium grain size and dark gray to greenish color. These rocks present shearing degrees and hydrothermal alteration, which have obliterated up to 90% of their original mineralogy. In the distal parts of the deposit, penetrative mylonitic foliation (Figure 3A) is observed, while brecciation (Figure 3B) is common in proximal zones. Despite the extensive alteration, the presence of relic minerals, such as clinopyroxene (Figure 3F), k-feldspar (Figure 3E), and titanite (or ilmenite) (Figure 3D), provides clues about their original composition. Hydrothermal minerals, including amphiboles (hornblende and actinolite) (Figure 3) and biotite (Figure 3F), replaced most primary minerals. Other alteration minerals include apatite (Figure 3B,E), scapolite (Figure 3F), chlorite (Figure 3D), ilmenite (Figure 3B,D), and epidote (Figure 3E). Albite (Figure 3A,C), quartz (Figure 3A,C), and chalcopyrite (Figure 3B) are also present, especially near felsic volcanic rocks and mineralization zones [39,40].
Minerals 15 01081 g002
Figure 2. Geological map of the Antas North mine area (Modified from [41] internal map).
Figure 2. Geological map of the Antas North mine area (Modified from [41] internal map).
Minerals 15 01081 g002
Primary minerals, such as clinopyroxene, K-feldspar, and titanite (or ilmenite), are preserved as relics within a matrix dominated by hydrothermal minerals, including hornblende, actinolite, biotite, scapolite, chlorite, and apatite. Albite and quartz are present, especially near felsic volcanic rocks and mineralized zones.

5.2. Felsic Volcanic Rocks

Felsic volcanic rocks are fine-grained, presenting light gray to reddish coloration, moderately brecciated, and intensely altered. Phenocrysts of feldspar and quartz occur in a fine-grained albite-quartz matrix, suggesting dacitic composition. Sodic alteration is dominant, characterized by pervasive albite replacement. Hornblende and calcite are common near mafic-felsic contacts.
Felsic volcanic rocks (Figure 4A,C,E) are fine-grained with light gray to reddish coloration. Brecciation is moderate, and hydrothermal alteration is prominent, with feldspar (Figure 4E) and quartz phenocrysts (Figure 4C,E) set in a fine-grained albite (Figure 4E) and quartz matrix, indicating dacitic composition. Sodium alteration is dominant, forming albite as the main hydrothermal product. Amphiboles (Figure 4A,C) and calcite (Figure 4C,E,F) are present near contacts with mafic rocks [39,40].

5.3. Gabbro Dikes

Gabbro dikes are subparallel to the mineralized shear zone and show medium- to fine-grained phaneritic texture (Figure 4F). Less altered gabbros exhibit ophitic to subophitic textures composed of plagioclase and pyroxene. Increased alteration results in mineral assemblage dominated by amphiboles, albite, and chlorite.

6. Hydrothermal Alterations

The alteration sequence recognised at Antas North comprises, in order of decreasing temperature and salinity [39,40]:
  • Sodic alteration—dominated by pervasive albite replacement of feldspar and mafic minerals; quartz and ilmenite may accompany albite. This stage occurs mainly in felsic metavolcanic rocks away from the ore zone.
  • Potassic alteration—characterised by the growth of brown biotite and turbid scapolite replacing amphiboles and feldspars. Scapolite occurs as cloudy porphyroblasts and may be difficult to identify in thin section. Potassic alteration is centred around mineralized zones and overprints sodic assemblages.
  • Calcic alteration—marked by the development of green amphibole (magnesiohornblende to actinolite) and apatite, often with minor allanite. Actinolite forms fibrous rims around hornblende cores, reflecting decreasing temperature. This stage is closely associated with copper mineralization and often obliterates earlier fabrics.
  • Silicification—pervasive quartz veining and replacement that can occur throughout the hydrothermal system. Silicification overprints sodic, potassic and calcic assemblages and is especially common along brittle fractures.
  • Propylitic alteration—characterised by chlorite, epidote and calcite, typically developed in the distal portions of the system and along the margins of mineralized breccias. Propylitic alteration is a late overprint reflecting cooler, more oxidizing fluid conditions and may be subtle in thin section due to overprinting by surface weathering (9).
The progressive evolution from sodic through potassic and calcic to propylitic assemblages suggests cooling and decreasing salinity of hydrothermal fluids during the mineralization process. The transition from magnesio-hornblende to actinolite within the calcic assemblage implies a drop in temperature during ore formation (9).
Distal zones primarily exhibit sodic and potassic alterations. Sodic alteration forms albite (Figure 5A), with minor quartz and ilmenite (Figure 5A). Potassic alteration forms biotite (Figure 5B) and scapolite (Figure 5B). Proximal zones are dominated by calcic alteration, marked by amphiboles (Figure 5C) and apatite (Figure 5C). Mineralized breccia bodies (Figure 5E,F) contain altered rock clasts surrounded by a sulfide matrix, predominantly chalcopyrite (Figure 5D).
Figure 6 shows hydrothermal alterations in the Antas North Area [39,40], focusing on sodic and potassic alterations (Figure 6A–I).
The spatial and textural relationships suggest that sodic, potassic and calcic alterations were developed under ductile to ductile–brittle regimes, closely associated with progressive deformation within the shear zone. These assemblages are commonly penetrative, fabric-parallel, and syn-kinematic, indicating that they formed during active shearing and fluid flux at elevated temperatures. In contrast, silicification and propylitic alteration are more irregular, veining- to fracture-controlled, and overprint earlier assemblages. Their geometry and crosscutting relations indicate an association with late brittle reactivation events, when cooler, more oxidizing meteoric-dominated fluids infiltrated the system. This duality reinforces the interpretation that hydrothermal evolution at Antas North was strongly coupled to the tectonic evolution of the shear zone, with early ductile deformation channeling high-temperature fluids, and later brittle reactivation allowing widespread influx of cooler external fluids [2,3,4,5,6,7,8,29,30,31,32,33,34,35,36].

7. Mineralization

Copper mineralization at Antas North is confined to the mafic and felsic metavolcanic rocks of the Grão Pará Group and is spatially associated with calcic hydrothermal alteration (hornblende + actinolite + apatite ± allanite ± titanite). The mineralized body dips steeply southeast and trends NE–SW, parallel to the controlling shear zone. Three principal mineralization styles are recognized. Massive sulfide bodies dominate the core of the orebody and consist mainly of chalcopyrite with subordinate pyrrhotite and pyrite (Figure 7); relic cores of earlier hydrothermal minerals such as hornblende, actinolite and apatite are locally preserved within the sulfide mass. Brecciated sulfide zones form along the margins of massive ore, where hydrothermally altered clasts are cemented by chalcopyrite, pyrrhotite and pyrite; angular to rounded fragments of hornblende, actinolite, quartz and apatite occur within the breccia matrix. Veins and veinlets of chalcopyrite ± pyrrhotite ± ilmenite cut across both calcic and sodic alteration zones but contribute little to the total ore volume. Gabbro dikes intersecting the ore zone contain only trace sulfides, suggesting late intrusion or limited fluid interaction [39,40].
The mineralization is associated with a ductile–brittle regime, where the central zones remain relatively undeformed, while brecciation affects the edges. The presence of gold is inferred from chemical analyses, as it was not identified in petrographic slides.
In massive sulfide portions, chalcopyrite dominates (Figure 7A,E), with inclusions of pyrrhotite (Figure 7E), pyrite (Figure 7D), and sphalerite (Figure 7E). These zones envelop areas of prior alteration, where hornblende, actinolite, and apatite cores are preserved (Figure 7F).
Breccias show mineral association of chalcopyrite + pyrrhotite + pyrite ± ilmenite + sphalerite ± pentlandite + hornblende + actinolite ± quartz + apatite ± chlorite ± epidote ± albite. Chalcopyrite dominates the breccia matrix (Figure 7G–K), with accessory phases including pyrrhotite (Figure 7K), pyrite, ilmenite (Figure 7J), sphalerite, pentlandite and chalcopyrite (7L). Hydrothermal minerals such as hornblende (Figure 7H,I), actinolite (Figure 7H,I), quartz (Figure 7I), and apatite form angular to rounded clasts. Chlorite (Figure 7H) and epidote (Figure 7H) appear in areas of propylitic alteration, while albite (Figure 7I) occurs at contacts between calcic and sodic alteration zones [39,40].

8. Geochronology

Data reduction was carried out with the Iolite package using the Titanite GEMOC standard (2.089 Ga) as a primary standard and NIST 610 glass as a secondary reference material. Individual spot ages were screened for discordance and common Pb; only concordant spots (<5% discordance) were considered in the age interpretation.
Two concordant age populations were identified. The older population yields a 206Pb/238U weighted-mean age of 2476.6 ± 15.9 Ma (2σ; n = 24; MSWD = 3.77), whereas the younger population gives 2162.9 ± 28.1 Ma (2σ; n = 5; MSWD = 0.86). Reported uncertainties are 2σ and include overdispersion scaling by √MSWD where MSWD > 1. Reported uncertainties are 2σ and include overdispersion where MSWD > 1 (uncertainty scaled by √MSWD). The older population was interpreted as recording a late Archean hydrothermal event associated with early stages of crustal thickening and magma emplacement in the Carajás Province. The younger population corresponds to Paleoproterozoic tectono-thermal reactivation linked to the Transamazonian orogeny (Figure 8).
Comparable Paleoproterozoic ages (~2.2 Ga) have also been documented in other deposits of the province, including Corta Goela (biotite 40Ar/39Ar age of 2193 ± 4 Ma; [4,5,8]), Sossego (amphibole U–Pb and 40Ar/39Ar ages [4,5]), Cristalino (U–Pb titanite and 40Ar/39Ar ages; [3]), and Igarapé Bahia (U–Pb and 40Ar/39Ar ages; [3]), where multiple isotopic systems consistently record rejuvenation of earlier Archean IOCG mineralization during the Transamazonian orogeny. These correlations confirm that the Antas North titanite ages are part of the broader metallogenic framework of multistage IOCG systems in Carajás [2,3,4,5,6,7,8].

9. Structural Framework and Distribution of Hydrothermal Alteration

The Carajás Mineral Province has undergone multiple tectonic events from the Archean to the Paleoproterozoic, resulting in a complex network of ductile to brittle structures. Regional tectonics are dominated by the Carajás Transcurrent System, characterized by NW–SE trending shear zones that exert strong control over ore localization [8,9,10,11,12,13,14,15]
Fieldwork and structural analyses in the Antas Norte deposit reveal that tectonics are controlled by broad NW–SE regional structural lineaments belonging to the Carajás Transcurrent System. Deformation in the host rocks is heterogeneous, with the development of ductile to brittle fabrics. Outcrop and drill-core descriptions document mylonitic foliations and brecciation associated with a NE–SW shear zone, which is a secondary structure to the main regional trend and spatially related to the control of mineralization. Fault zones with distinct orientations also reflect the influence of these regional lineaments.
The deformational history promoted the development of shear zones that facilitated fluid circulation, establishing a hydrothermal system that partially or completely obliterated primary lithological features and their relationships with protoliths. Structural descriptions indicate a relatively simple framework at deposit scale, with two main deformational phases ranging from ductile to ductile–brittle. These are interpreted as part of the same regional shearing system that affected the CMP.
A pre-existing foliation (Sn), preserved locally despite intense hydrothermal alteration, is defined by amphiboles, plagioclase, and biotite, trending NNE–SSW and dipping ESE. The subsequent shear zone development produced a penetrative, anastomosing to parallel mylonitic foliation (Sn + 1), marked by the preferred orientation of amphiboles and biotite around quartz and feldspar porphyroclasts, with common comminution and recrystallization textures. This Sn + 1 foliation is associated with hydrothermal mineral assemblages, oriented ENE–WSW with SSE dip. Brecciation zones with rounded fragments in amphibole–sulfide-rich matrices are also present, representing successive hydrothermal and tectonic reactivation that reworked pre-existing mylonitic zones and increased the thickness of mineralized bodies. The main ore body is structurally hosted within these shear-related domains, where fluid percolation was concentrated in dilatational sites. Stretching lineations plunge 54/225° (Az), indicating that subsurface kinematics strongly influenced ore body geometry and continuity.
At Antas North, the mineralized body is hosted within a secondary NE–SW-oriented shear zone, distinct from the major WNW–ESE Carajás Fault. This shear zone developed under a dextral transpressional regime, with deformation patterns transitioning from ductile to brittle conditions [39,40].
Structural analysis reveals two generations of foliations:
  • Sn foliation: a pervasive mylonitic fabric defined by the preferred orientation of amphiboles, plagioclase, and biotite, trending NNE–SSW and dipping ESE.
  • Sn + 1 foliation: a younger foliation formed during shearing and hydrothermal overprint, marked by oriented amphiboles and biotite around quartz and feldspar porphyroclasts, trending ENE–WSW and dipping SSE.
The orebody is localized along sigmoidal SC (shear–C) structures, where dilatational zones between Sn and Sn + 1 foliations concentrate copper–gold mineralization. Stretching lineations plunge 54° towards 225° (SW), consistent with the orientation of high-grade ore shoots (Figure 9).
Hydrothermal alteration patterns are strongly controlled by this structural framework. Distal zones are dominated by sodic (albite, quartz and ilmenite) and potassic alteration, whereas proximal zones adjacent to the orebody are characterized by calcic alteration assemblages (amphibole ± apatite). Both alteration domains are overprinted by strong mylonitic foliations, reflecting the tight interplay between deformation and fluid flow.
Late brittle structures are represented by faults, fractures, and veins that truncate earlier deformational domains. The main set of NE–SW-trending faults, locally filled with gabbro, crosscuts the ore zone and runs parallel to the mineralized shear corridor. Another set, trending NNW–SSE, produced local left-lateral displacements of ore-bearing domains. Slickensides on fault planes confirm relative block movements. Veins and small fractures filled with quartz, chlorite, amphibole, calcite, or epidote ± sulfides occur in multiple orientations.
Hydrothermal fluids exploited these deformation zones, resulting in intense alteration and mineral precipitation along the structural conduits.

10. Discussion

10.1. Structural Framework and Ore Controls

The Antas North deposit is structurally controlled by a secondary NE–SW shear zone, overprinted by NNW–SSE brittle faults that segment the orebody. This geometry differs from the broader transpressional corridors that host the Salobo and Sossego deposits, where multiple parallel shear bands accommodate mineralization [2,3,4,5,6,7,8,29,33,35,36]. At Antas North, copper–gold mineralization is concentrated within a single tabular body, with the plunge of ore shoots (54° towards 225°) consistent with stretching lineations measured in the field. This correspondence confirms that shear-related dilation was the dominant control on fluid pathways. Comparable structural settings are described in Candelaria (Chile) and Olympic Dam (Australia) [12,23,24,25,26], although these systems show wider alteration halos dominated by magnetite and hematite. The absence of such extensive iron oxides at Antas North suggests lower oxygen fugacity and possibly greater crustal depth during ore formation.

10.2. Hydrothermal Evolution and Alteration Zonation

Antas North records a systematic hydrothermal evolution from sodic (albite ± quartz ± ilmenite) to potassic (biotite ± scapolite) and calcic (amphibole + apatite ± allanite) alteration. This sequence mirrors the progression described at Salobo and Sossego [2,3,4,5,6,7,8,29,33,35,36], yet the calcic assemblage at Antas North is spatially closer to the ore, marking it as the most diagnostic indicator of Cu–Au mineralization. In contrast, deposits such as Igarapé Bahia [3,8,31,34], Candelaria, and Olympic Dam display extensive magnetite–hematite halos, typical of oxidized IOCG systems [12,23,24,25,26]. The persistence of ilmenite and scarcity of magnetite in Antas North indicate reduced redox conditions (low fO2) and align with a deeper crustal environment. These features support the interpretation of Antas North as part of a reduced Iron Sulfide–Copper–Gold (ISCG) subtype within the IOCG–IOA continuum [9,10,11,12,42].

10.3. Redox State and Mineralogical Implications

The coexistence of ilmenite and Fe-sulfides (pyrrhotite + pyrite), combined with the absence of magnetite, defines the reduced nature of the Antas North system. This mineralogical association implies that magnetite stability was suppressed under low oxygen fugacity, promoting ilmenite formation. The progressive evolution from magnesio-hornblende to actinolite reflects fluid cooling and re-equilibration during late hydrothermal stages. Globally, similar trends occur in reduced iron-oxide systems such as the Kiruna-type IOA deposits and ilmenite-bearing IOCG systems of Sweden, Chile, and Australia [9,42,43,44,45,46,47]. Thus, Antas North represents a deeper, more reduced endmember of the IOCG–ISCG–IOA spectrum, linking Cu–Au mineralization to redox-controlled mineral equilibria and temperature gradients in the crust.

10.4. Geochronological Constraints and Metallogenic Significance

Two concordant U–Pb titanite age populations constrain the evolution of Antas North:
  • 2476.6 ± 15.9 Ma (2σ, n = 24, MSWD = 3.77)—a late Archean hydrothermal stage synchronous with Cu–Au mineralization.
  • 2162.9 ± 28.1 Ma (2σ, n = 5, MSWD = 0.86)—Paleoproterozoic reactivation during the Transamazonian orogeny.
The older event correlates with Cu–Au mineralization in Salobo and Sossego (2.70–2.50 Ga), whereas the younger reflects regional tectono-hydrothermal rejuvenation also recorded in Igarapé Bahia, Corta Goela, GT-34 and Cristalino (2.50–2.2 Ga) [2,3,4,5,6,7,8,29,30,31,32,33,34,35,36]. Together, these ages confirm a multistage evolution characteristic of the Carajás Province, though Antas North formed under more reduced and deeper crustal conditions.

10.5. Broader Implications for IOCG–ISCG–IOA Systems

Antas North expands the genetic spectrum of Cu–Au systems in Carajás by documenting a reduced, ilmenite- and sulfide-dominated endmember that bridges classic magnetite-rich IOCG deposits and ilmenite-bearing IOA systems [2,3,4,5,6,7,8,9,29,31,33,34,35,36,42,43,44,45,46,47]. Its evolution demonstrates that structural reactivation, fluid evolution, and redox state collectively govern ore type and mineral assemblage.
These insights refine exploration models: reduced systems like Antas North may lack strong magnetic responses, requiring integration of structural and redox indicators.
The younger (~1.8 Ga) Cu–Au deposits described by [2,3,4,5,6,7,8] represent a separate, post-orogenic metallogenic event unrelated to the Transamazonian reactivation. Those granite-related systems are quartz- and sulfur-rich, iron-oxide poor, and associated with A-type. Antas North, by contrast, records the earliest reduced Cu–Au mineralization in the Carajás tectonic framework, preceding these younger granite-linked events.

11. Conclusions

The Antas North deposit represents a reduced Cu–Au system within the Carajás Mineral Province, where ilmenite and iron sulfides dominate over magnetite. This mineralogical signature reflects ore formation under low-fO2 conditions, marking Antas North as a deeper and more reduced endmember of the IOCG–ISCG–IOA spectrum. Structural reactivation along NE–SW shear zones focused hydrothermal fluids and controlled ore deposition, while U–Pb titanite ages of 2476.6 ± 15.9 Ma and 2162.9 ± 28.1 Ma record Archean mineralization and Paleoproterozoic reactivation, respectively. Together, these features confirm that Antas North belongs to the multistage metallogenic framework of Carajás and extend its diversity beyond classic magnetite-rich IOCG deposits. Recognizing such reduced systems emphasizes the need for exploration strategies that integrate redox, structural, and geochronological indicators to identify similar concealed deposits in Carajás and worldwide.

Author Contributions

Conceptualization, S.R.B.H. and R.N.P.; methodology, F.J.F.F. and I.B.B.; investigation, R.N.P. and I.B.B.; writing—original draft, S.R.B.H.; writing—review and editing, all authors. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

Data are contained within the article.

Acknowledgments

The authors gratefully acknowledge OZ Minerals for providing access to the Antas North mine and for logistical support during fieldwork. We also thank the Universidade Federal do Ceará (UFC) for institutional support. Constructive comments from the reviewers and the handling editor significantly improved the quality of this manuscript.

Conflicts of Interest

The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

References

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Figure 1. (A) Location of the Carajás Province (black) within the Amazonian Craton (light gray). (B) Compartmentalization of the Carajás Province into the Rio Maria Domain (RMD, south) and the Carajás Domain (CD, central–northern portion). (C) Simplified geological map of the Carajás Domain showing the location of major copper deposits and main structural features (modified from [22]). The Bacajá Domain (BD) is located to the NNW of the area.
Figure 1. (A) Location of the Carajás Province (black) within the Amazonian Craton (light gray). (B) Compartmentalization of the Carajás Province into the Rio Maria Domain (RMD, south) and the Carajás Domain (CD, central–northern portion). (C) Simplified geological map of the Carajás Domain showing the location of major copper deposits and main structural features (modified from [22]). The Bacajá Domain (BD) is located to the NNW of the area.
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Figure 3. Mafic lithotypes from the Antas North mine area. (A) Mafic volcanic rock from the distal mineralization zone, showing mylonitization with hornblende, actinolite, albite, and quartz bands. (B) Brecciated mafic volcanic rock from the proximal mineralization zone, with hornblende, apatite, ilmenite, and chalcopyrite. (C) Photomicrograph (PPL) showing mylonitic banding, with mafic portions (Hbl + Act) and felsic portions (Ab + Qz). (D) Photomicrograph (PPL) of hydrothermally altered rock, showing albite, quartz, hornblende, chlorite, and ilmenite; titanite relics suggest protolithic origin. (E) Photomicrograph (XPL) of the proximal mineralization, showing significant alteration with apatite, hornblende, actinolite, epidote, and partially consumed K-feldspar. (F) Photomicrograph (XPL) showing intense alteration, with scapolite, biotite, and hornblende, alongside relict clinopyroxene. Scale bars: (A,B) = 1 cm; (C,E,F) = 500 µm; (D) = 10 µm.
Figure 3. Mafic lithotypes from the Antas North mine area. (A) Mafic volcanic rock from the distal mineralization zone, showing mylonitization with hornblende, actinolite, albite, and quartz bands. (B) Brecciated mafic volcanic rock from the proximal mineralization zone, with hornblende, apatite, ilmenite, and chalcopyrite. (C) Photomicrograph (PPL) showing mylonitic banding, with mafic portions (Hbl + Act) and felsic portions (Ab + Qz). (D) Photomicrograph (PPL) of hydrothermally altered rock, showing albite, quartz, hornblende, chlorite, and ilmenite; titanite relics suggest protolithic origin. (E) Photomicrograph (XPL) of the proximal mineralization, showing significant alteration with apatite, hornblende, actinolite, epidote, and partially consumed K-feldspar. (F) Photomicrograph (XPL) showing intense alteration, with scapolite, biotite, and hornblende, alongside relict clinopyroxene. Scale bars: (A,B) = 1 cm; (C,E,F) = 500 µm; (D) = 10 µm.
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Figure 4. Felsic lithotypes and gabbros from the Antas North mine area. (A) Felsic volcanic rock showing brecciation with albite (white/pink) and hornblende veins. (B) Gabbro with a hornblende and augite matrix, and plagioclase crystals. (C) Photomicrograph (XPL) of altered felsic rock with albite, quartz, hornblende, and calcite. (D) Photomicrograph (XPL) of gabbro, highlighting plagioclase crystals with hornblende, actinolite, and chlorite. (E) Photomicrograph (XPL) of felsic rock showing feldspar and quartz phenocrysts in an albite and quartz matrix with calcite. (F) Photomicrograph (XPL) of gabbro showing corroded augite alongside hornblende, chlorite, and albite. Scale bars: (A,B) = 1 cm; (C–F) = 500 µm.
Figure 4. Felsic lithotypes and gabbros from the Antas North mine area. (A) Felsic volcanic rock showing brecciation with albite (white/pink) and hornblende veins. (B) Gabbro with a hornblende and augite matrix, and plagioclase crystals. (C) Photomicrograph (XPL) of altered felsic rock with albite, quartz, hornblende, and calcite. (D) Photomicrograph (XPL) of gabbro, highlighting plagioclase crystals with hornblende, actinolite, and chlorite. (E) Photomicrograph (XPL) of felsic rock showing feldspar and quartz phenocrysts in an albite and quartz matrix with calcite. (F) Photomicrograph (XPL) of gabbro showing corroded augite alongside hornblende, chlorite, and albite. Scale bars: (A,B) = 1 cm; (C–F) = 500 µm.
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Figure 5. Representative field photographs and photomicrographs illustrating the range of hydrothermal alterations at Antas North. (A,B) Distal mafic metavolcanic rocks showing pervasive sodic alteration (albite ± quartz) and incipient potassic alteration marked by biotite and scapolite; chlorite highlights the onset of propylitic alteration. (C,D) Proximal rocks affected by calcic alteration with hornblende, actinolite and apatite replacing earlier albite and feldspar. (E,F) Mineralized breccias and veins where chalcopyrite and pyrrhotite form the matrix around altered clasts. Silicification is pervasive in all subfigures, while propylitic alteration (chlorite + epidote + calcite) overprints earlier assemblages at the edges. Scapolite is present as cloudy porphyroblasts but may be difficult to distinguish due to its turbidity. Reddish stains visible on some outcrop surfaces represent surficial hematite formed during weathering and are not part of the primary hydrothermal assemblage. Pen (~14 cm long) shown for scale in (E,F). Abbreviations: Ab = albite; Act = actinolite; Ap = apatite; Bt = biotite; Cc = calcite; Chl = chlorite; Ccp = chalcopyrite; Ep = epidote; Hbl = hornblende; Il = ilmenite; Qz = quartz; Scp = scapolite.
Figure 5. Representative field photographs and photomicrographs illustrating the range of hydrothermal alterations at Antas North. (A,B) Distal mafic metavolcanic rocks showing pervasive sodic alteration (albite ± quartz) and incipient potassic alteration marked by biotite and scapolite; chlorite highlights the onset of propylitic alteration. (C,D) Proximal rocks affected by calcic alteration with hornblende, actinolite and apatite replacing earlier albite and feldspar. (E,F) Mineralized breccias and veins where chalcopyrite and pyrrhotite form the matrix around altered clasts. Silicification is pervasive in all subfigures, while propylitic alteration (chlorite + epidote + calcite) overprints earlier assemblages at the edges. Scapolite is present as cloudy porphyroblasts but may be difficult to distinguish due to its turbidity. Reddish stains visible on some outcrop surfaces represent surficial hematite formed during weathering and are not part of the primary hydrothermal assemblage. Pen (~14 cm long) shown for scale in (E,F). Abbreviations: Ab = albite; Act = actinolite; Ap = apatite; Bt = biotite; Cc = calcite; Chl = chlorite; Ccp = chalcopyrite; Ep = epidote; Hbl = hornblende; Il = ilmenite; Qz = quartz; Scp = scapolite.
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Figure 6. Hydrothermal alterations in the Antas North area, focusing on sodic and potassic assemblages. (A) Photomicrograph (XPL) of sodic alteration with albite and quartz. (B) Photomicrograph (XPL) of sodic alteration with albite, quartz, and calcite vein with apatite. (C) Photomicrograph (XPL) showing K-feldspar with albite and quartz. (D) Photomicrograph (XPL) of sodic–calcic interaction near mineralization, with albite, hornblende, apatite, and chalcopyrite. (E) Photomicrograph (PPL) of ilmenite bordered by albite and quartz. (F) Photomicrograph (PPL) of biotite (potassic alteration) with quartz. (G) Photomicrograph (PPL) of scapolite porphyroblast with biotite and chlorite (incipient potassic alteration). (H) Photomicrograph (XPL) of potassic–calcic interaction with scapolite, biotite, hornblende, actinolite, and chalcopyrite. (I) Photomicrograph (reflected light—PPL) showing biotite with chalcopyrite. Scale bars: (A) = 5000 µm; (B–F,H) = 500 µm; (G) = 2 mm; (I) = 0.1 mm.
Figure 6. Hydrothermal alterations in the Antas North area, focusing on sodic and potassic assemblages. (A) Photomicrograph (XPL) of sodic alteration with albite and quartz. (B) Photomicrograph (XPL) of sodic alteration with albite, quartz, and calcite vein with apatite. (C) Photomicrograph (XPL) showing K-feldspar with albite and quartz. (D) Photomicrograph (XPL) of sodic–calcic interaction near mineralization, with albite, hornblende, apatite, and chalcopyrite. (E) Photomicrograph (PPL) of ilmenite bordered by albite and quartz. (F) Photomicrograph (PPL) of biotite (potassic alteration) with quartz. (G) Photomicrograph (PPL) of scapolite porphyroblast with biotite and chlorite (incipient potassic alteration). (H) Photomicrograph (XPL) of potassic–calcic interaction with scapolite, biotite, hornblende, actinolite, and chalcopyrite. (I) Photomicrograph (reflected light—PPL) showing biotite with chalcopyrite. Scale bars: (A) = 5000 µm; (B–F,H) = 500 µm; (G) = 2 mm; (I) = 0.1 mm.
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Figure 7. Photographs and photomicrographs illustrating the three mineralization styles at Antas North. (A) Field view of massive sulfide ore dominated by chalcopyrite with subordinate pyrrhotite and pyrite. (B) Brecciated ore along the orebody margin with altered host-rock clasts cemented by chalcopyrite–pyrrhotite–pyrite. (C) Sulfide veinlet cutting albite-rich host rock with chalcopyrite, pyrrhotite, and ilmenite. (D–H) Reflected and transmitted light photomicrographs showing intergrowths of chalcopyrite, pyrrhotite, pyrite, and sphalerite, with relics of hornblende, actinolite, and apatite preserved in massive and brecciated ores. (I–L) Chalcopyrite dominates the breccia matrix, with accessory phases including pyrrhotite (K), pyrite, ilmenite (J), sphalerite, pentlandite and chalcopyrite (L). Scale bars: (A,B) = field photographs (no scale bar); (C–H) = 500 µm.
Figure 7. Photographs and photomicrographs illustrating the three mineralization styles at Antas North. (A) Field view of massive sulfide ore dominated by chalcopyrite with subordinate pyrrhotite and pyrite. (B) Brecciated ore along the orebody margin with altered host-rock clasts cemented by chalcopyrite–pyrrhotite–pyrite. (C) Sulfide veinlet cutting albite-rich host rock with chalcopyrite, pyrrhotite, and ilmenite. (D–H) Reflected and transmitted light photomicrographs showing intergrowths of chalcopyrite, pyrrhotite, pyrite, and sphalerite, with relics of hornblende, actinolite, and apatite preserved in massive and brecciated ores. (I–L) Chalcopyrite dominates the breccia matrix, with accessory phases including pyrrhotite (K), pyrite, ilmenite (J), sphalerite, pentlandite and chalcopyrite (L). Scale bars: (A,B) = field photographs (no scale bar); (C–H) = 500 µm.
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Figure 8. Concordia diagram of U-Pb isotopic data for hydrothermal titanite from the Antas North deposit. Two distinct concordant age populations are observed at approximately 2476.6 ± 15.9 Ma and 2162.9 ± 28.1 Ma, indicating multiple hydrothermal events related to Archean and Paleoproterozoic tectono-thermal episodes.
Figure 8. Concordia diagram of U-Pb isotopic data for hydrothermal titanite from the Antas North deposit. Two distinct concordant age populations are observed at approximately 2476.6 ± 15.9 Ma and 2162.9 ± 28.1 Ma, indicating multiple hydrothermal events related to Archean and Paleoproterozoic tectono-thermal episodes.
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Minerals 15 01081 g009
Figure 9. Hydrothermal alteration map and structural interpretation of the Antas North mine (modified from [41] internal files). The map highlights the NE–SWtrending shear zone (black arrows) that hosts the mineralized body and shows the distribution of sodic, potassic and calcic alteration zones. A north arrow (N) indicates geographic north for the cross section. Sn foliation defined by the preferred orientation of amphiboles, plagioclase and biotite, trending NNE–SSW and dipping ESE. Sn+1 foliation associated with hydrothermal minerals, marked by oriented mafic minerals surrounding quartz and feldspar porphyroclasts; this foliation trends ENE–WSW and dips SSE (Modified from [41] internal map).
Figure 9. Hydrothermal alteration map and structural interpretation of the Antas North mine (modified from [41] internal files). The map highlights the NE–SWtrending shear zone (black arrows) that hosts the mineralized body and shows the distribution of sodic, potassic and calcic alteration zones. A north arrow (N) indicates geographic north for the cross section. Sn foliation defined by the preferred orientation of amphiboles, plagioclase and biotite, trending NNE–SSW and dipping ESE. Sn+1 foliation associated with hydrothermal minerals, marked by oriented mafic minerals surrounding quartz and feldspar porphyroclasts; this foliation trends ENE–WSW and dips SSE (Modified from [41] internal map).
Minerals 15 01081 g009
Table 1. LA–ICP–MS U–Pb analytical results for hydrothermal titanite from the Antas North deposit, Carajás Mineral Province (n = 49 analytical spots from 24 titanite grains).
Table 1. LA–ICP–MS U–Pb analytical results for hydrothermal titanite from the Antas North deposit, Carajás Mineral Province (n = 49 analytical spots from 24 titanite grains).
Ages (Ma)
Spot207Pb/206Pb207Pb/235U206Pb/238U207Pb/206Pb±2σ206Pb/238U±2σ207Pb/235U±2σ
AAND070 (SAMPLE)
Spot 720.164410.3830.4591247843242945246722
Spot 730.162510.4480.4643246927245532247014
Spot 740.14747.7090.3930220979211970217335
Spot 750.159110.1560.4651244128246232244914
Spot 760.161410.2240.4675245228246634244916
Spot 770.162310.3370.4640246135244638245818
Spot 780.158310.5580.4792242528251233248015
Spot 790.162110.5030.4668246032246835247217
Spot 800.159010.5550.4753244424250533248013
Spot 810.161910.3590.4653246041245141245720
Spot 820.170410.4990.4509252250239650246723
Spot 830.168310.6530.4677250153246854248925
Spot 840.160310.4760.4765244036250337247317
Spot 850.159710.4160.4768243139252141247518
Spot 860.167210.6790.4624251936244438249119
Spot 870.160510.1290.4637243837246040244418
Spot 880.168611.2440.4799253536252843254018
Spot 890.163911.0030.4833247539253244251521
Spot 900.15419.2290.4468231696235678233541
Spot 910.14507.7590.4027218582215566220332
Spot 920.14837.8940.4097228274220665221835
Spot 930.13617.3410.40052077104216677213741
Spot 940.13217.2570.4023206455216448213025
Spot 950.158610.7550.4831243543254544249622
Spot 960.163810.7570.4759248345250650250223
Spot 980.161210.7880.4755246326250232250214
Spot 990.162510.6500.4726247653248656249325
Spot 1000.159710.4510.4677245031246839247018
Spot 1010.15369.2660.4505231258238257235128
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Hühn, S.R.B.; Paula, R.N.; Ferreira Fonseca, F.J.; Barreira, I.B. Geology and Hydrothermal Evolution of the Antas North Iron Sulfide–Copper–Gold (ISCG) Deposit in the Carajás Mineral Province. Minerals 2025, 15, 1081. https://doi.org/10.3390/min15101081

AMA Style

Hühn SRB, Paula RN, Ferreira Fonseca FJ, Barreira IB. Geology and Hydrothermal Evolution of the Antas North Iron Sulfide–Copper–Gold (ISCG) Deposit in the Carajás Mineral Province. Minerals. 2025; 15(10):1081. https://doi.org/10.3390/min15101081

Chicago/Turabian Style

Hühn, Sérgio Roberto Bacelar, Rafael Nascimento Paula, Francisco José Ferreira Fonseca, and Isac Brito Barreira. 2025. "Geology and Hydrothermal Evolution of the Antas North Iron Sulfide–Copper–Gold (ISCG) Deposit in the Carajás Mineral Province" Minerals 15, no. 10: 1081. https://doi.org/10.3390/min15101081

APA Style

Hühn, S. R. B., Paula, R. N., Ferreira Fonseca, F. J., & Barreira, I. B. (2025). Geology and Hydrothermal Evolution of the Antas North Iron Sulfide–Copper–Gold (ISCG) Deposit in the Carajás Mineral Province. Minerals, 15(10), 1081. https://doi.org/10.3390/min15101081

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