July 2020 LIP of the Month

An overview of the ultramafic-mafic magmatism in the Carajás Mineral Province, Brazil: constraints for the presence of magmatic sulfide deposits, and potential LIP context

Eduardo Mansur¹*; Cesar Ferreira Filho²; Richard Ernst^3,4

¹Sciences de la Terre, Université du Québec à Chicoutimi, Québec G7H 2B1, Canada

²Instituto de Geociências, Universidade de Brasília, Brasília-DF, 70910-900, Brazil

³Department of Earth Sciences, Carleton University, Ottawa, K1S 5B6, Canada

⁴Faculty of Geology and Geography, Tomsk State University, Tomsk, 634050, Russia

* etmansur@gmail.com

This LIP of the month is based on the following:

Siepiersk, L.,  Ferreira Filho, C. F. (2020). Magmatic Structure and Petrology of the Vermelho Complex, Carajás Mineral Province, Brazil: Evidence for Magmatic Processes at the Lower Portion of a Mafic-Ultramafic Intrusion. Journal of South American Earth Sciences, doi.org/10.1016/j.jsames.2020.102700.

Mansur, E.T., Ferreira Filho, C.F., & Oliveira, D.P.L. (2020). The Luanga deposit, Carajás Mineral Province, Brazil: Different styles of PGE mineralization hosted in a medium-size layered intrusion. Ore Geology Reviews, 118, doi.org/10.1016/j.oregeorev.2020.103340.

Mansur, E. T., & Ferreira Filho, C. F. (2016). Magmatic structure and geochemistry of the Luanga Mafic–Ultramafic Complex: Further constraints for the PGE-mineralized magmatism in Carajás, Brazil. Lithos, 266, 28-43.

Teixeira, A. S., Ferreira Filho, C. F., Della Giustina, M. E. S., Araújo, S. M., & da Silva, H. H. A. B. (2015). Geology, petrology and geochronology of the Lago Grande layered complex: evidence for a PGE-mineralized magmatic suite in the Carajás Mineral Province, Brazil. Journal of South American Earth Sciences, 64, 116-138.

Silva, K. S. (2015). Geologia, petrologia, geocronologia e mineralizações sulfetadas do complexo ézio, província mineral de carajás, Brasil. M.Sc. Thesis, University of Brasília.

Rosa, W. D. (2014). Complexos acamados da Serra da Onça e Serra do Puma: geologia e petrologia de duas intrusões máfico-ultramáficas com sequencia de cristalização distinta na Província Arqueana de Carajás, Brasil. M.Sc. Thesis, University of Brasília.

Ferreira Filho, C.F., Cançado, F., Correa, C., Macambira, E.M.B., Siepierski, L., and Brod, T.C.J. (2007). Mineralizações estratiformes de EGP-Ni associadas a complexos acamadados em Carajás: os exemplos de Luanga e Serra da Onça, in, Contribuições à Geologia da Amazônia, ed., Publitec Gráfica & Editora, v. 5, p. 1–14.

Introduction

The Carajás Mineral Province contains the largest concentration of mafic–ultramafic layered intrusions in the Amazonian Craton. These intrusions are best known for hosting world-class Ni-laterite deposits, and PGE deposits and occurrences. The U-Pb zircon ages obtained for few layered intrusions of the Carajás Mineral Province (2763 ± 6 Ma) overlap with ages of bimodal volcanism in the province (2759±2 Ma), leading to the interpretation that mafic volcanics and mafic–ultramafic layered intrusions resulted from a coeval major magmatic event in the Carajás region region (Machado et al., 1991; Ferreira Filho et al., 2007). The spatial association of PGE-mineralized layered intrusions easternmost portion of the Carajás Mineral Province (Serra Leste Suite) suggests that they originated from a PGE-fertile parental magma (Ferreira Filho et al., 2007). How magmas with distinctive geochemical characteristics that enhance the origin of Ni–Cu–PGE deposits are formed and whether such compositions are systematically associated with Ni–Cu–PGE deposits are a debated issue (e.g., Fiorentini et al., 2010; Griffin et al., 2013; Zhang et al., 2008). Some studies have proposed that a Large Igneous Province (LIP) containing Ni–Cu–PGE deposits have magmas with distinctive geochemical compositions, usually attributed to specific characteristics of the subcontinental lithosphere (e.g., Griffin et al., 2013; Maier and Groves, 2011). However, other studies indicate that a systematic association of unusual magmas and magmatic deposits is not supported by current data (e.g., Barnes et al., 2015; Fiorentini et al., 2010). In this contribution we provide an overview of the ultramafic-mafic magmatism in the Carajás Mineral Province. We also consider the geodynamic setting and consider a LIP context for this event which comprises the Carajás intrusions and also metavolcanics (mainly mafic) of the Parauapebas formation.

The Carajás Mineral Province

The Carajás Mineral Province is located in the southeastern portion of the Amazonian Craton (Fig. 1A). It has become widely known due to several important mineral deposits, including iron oxide cooper-gold, Ni deposits, and the largest iron resources of the world (Lobato et al., 2005; Xavier et al., 2010; Monteiro et al., 2014; Moreto et al., 2015; Melo et al., 2019; Motta et al., 2019). It is limited to the east and south by the Neoproterozoic Araguaia Fold Belt and, to the west, by Proterozoic sequences of the Uatumã Supergroup (DOCEGEO, 1988; Araújo and Maia, 1991). To the north, it is limited by the Bacajá Domain, which includes reworked Archean terrains and juvenile Paleoproterozoic units (Vasquez et al., 2008a). The province is subdivided into two Archean tectonic domains, separated by a poorly defined Transition Subdomain (Dall'Agnol et al., 2006, 2013; Feio et al., 2013). These domains are defined as the Rio Maria Domain to the south and the Carajás Domain to the north (Fig. 1B; Vasquez et al., 2008b).

The Rio Maria Domain consists of greenstone belt sequences, tonalitic trondhjemitic assemblages (TTG), high-Mg and potassic granites, and metasedimentary rocks of the 2.97 to 2.90 Ga Andorinhas Supergroup (DOCEGEO, 1988; Macambira and Lancelot, 1996; Souza et al., 2001).  This domain was formed in a complex system of collisions of greenstone and granite domains with ages ranging from  3050 Ma to2820 Ma (Dall’Agnol et al., 2006; Almeida et al., 2011, 2013; Althoff et al., 2000; Oliveira et al., 2011). Also, a number of recent contributions support the collision of the Rio Maria Domain with the Carajás Domain to the north, which originated the deformed Transition Subdomain in between both zones (Martins et al., 2017; Tavares et al., 2018; Marangoanha et al., 2019). The collisional event is considered coeval with the acid magmatism found at the Canaã dos Carajás region (Fig. 1B; Feio et al., 2013; Tavares, 2015).

The Carajás Domain basement units consist of gneisses and migmatites of the Xingu Complex and mafic to felsic ortho-granulites of the Pium Complex (Fig. 1B; DOCEGEO, 1988; Machado et al., 1991). Crystallization ages of ~3.0 Ga are reported for basement rocks (Moreto et al., 2015). Greenstone belt sequences with spinifex-textured komatiites (Selva Greenstone Belt; Siepierski and Ferreira Filho, 2016) are interpreted as part of basement units of the Carajás Domain. Overlying the basement units is the Neoarchean Carajás Basin, which comprises the 2.73 to 2.76 Ga metavolcanic-sedimentary units of the Itacaiúnas Supergroup (DOCEGEO, 1988; Machado et al., 1991; Vasquez et al., 2008a). This supergroup is formed dominantly by a bimodal volcanism and associated banded iron formations, metamorphosed in sub-greenschist or greenschist facies conditions. The Grão Pará Group, the dominant volcanic-sedimentary unit in the Carajás Basin, contains the giant iron deposits of the Carajás Mineral Province (Fig. 1B; DOCEGEO, 1988; Vasquez et al., 2008a). The Itacaiúnas Supergroup is overlain by an extensive succession of low-grade meta-sedimentary units known as the Águas Claras Formation, or the Rio Fresco Group (DOCEGEO, 1988).

Granitic magmatism in the Carajás Mineral Province comprises magmas of distinct ages and compositions (e.g., Feio et al, 2013; Teixeira et al., 2019). They are correlated to three episodes: (1) Neoarchean intrusions (ca. 2.75 - 2.70 Ga) are widespread through the Carajás Domain and include synorogenic alkaline granites; (2) Younger Neoarchean intrusions (ca. 2.5 Ga) are restricted to the north part of the Carajás Domain and include peralkaline to meta-aluminous granites, coeval with the Carajás and Cinzento transcurrent fault systems; (3) Paleoproterozoic intrusions (ca. 1.88 Ga) are widespread in the Carajás Mineral Province and include A-type alkaline granites.

The Grão-Pará Group is the main volcano-sedimentary sequence of the Carajás Basin, located in its northern portion. This Neoarchean (~2.76 Ga) volcano-sedimentary pile covers an area of approximately 18,000 km², comprising a bimodal volcanism, but predominantly mafic, namely the Parauapebas Formation (Olszewski et al., 1989; Machado et al., 1991; Trendall et al., 1998; Martins et al., 2017). The Parauapebas Formation contains mainly basalts and basaltic andesites, with minor basic to intermediate pyroclastic rocks and rhyolites (Zuchetti, 2007; Martins et al., 2017). The age of volcanism of the Grão Pará Group was determined at ∼2.75 Ga by several authors (Olszewski et al., 1989; Machado et al., 1991; Trendall et al., 1998; Martins et al., 2017). The tectonic setting of the Carajás Basin is still a matter of debate. Interpretation of geologic, geochemical, and isotopic data for the mafic rocks of the Itacaiúnas Supergroup has resulted in two distinct models for its tectonic setting. These include an intraplate rifting of older continental crust (DOCEGEO, 1988; Tavares, 2015; Martins et al., 2017), and a compressional orogenic setting (Lobato et al., 2005; Meirelles and Dardenne, 1991; Zuchetti, 2007).

Layered intrusions in the Carajás Mineral Province

Several Neoarchean (2.76 Ga) mafic–ultramafic layered complexes intrude rocks of the Xingu Complex and Archean volcano-sedimentary sequences, in the Carajás Domain (Fig. 1B; Docegeo, 1988; Ferreira Filho et al., 2007). Based on the geographic distribution across the region, the intrusions can be separated into three main groups, referred as i. the Tucumã-Ourilândia Region (Fig. 2), ii. the Canaã dos Carajás Region (Fig. 3), and iii. the Serra Leste Region (Fig. 4). A brief description of these groups is provided as follows.

The Tucumã-Ourilândia Region

            Layered intrusions hosting word-class nickel laterite deposits in the Tucumã region include the Serra da Onça and Serra do Puma Complexes (Ferreira Filho et al., 2007; Rosa, 2014), and other smaller intrusions consisting mainly of ultramafic rocks (e.g., Carapanã, Fafá) and those consisting mainly of gabbroic rocks (e.g., Guepardo). The location of the layered complexes is controlled by major regional lineaments associated with dip crustal discontinuities. Mafic-ultramafic intrusions are emplaced into banded gneiss-migmatite of the Xingu Complex and/or slightly foliated granitic intrusions (Fig. 2).

            The Serra da Onça Complex is a 24 km long and up to 3.5 km wide EW trending intrusion, with magmatic layering dip of 40-45° to the south. The stratigraphy of the Serra da Onça Complex consists of a Lower Border Group at the base, an Ultramafic Zone (up to 1.1 km thick), and an upper Mafic Zone (up to 1.5 km thick). Primary igneous minerals and textures are largely preserved, except for the serpentinization of olivine-rich rocks. The Lower Border Group forms a thin (< 150 m thick) discontinuous zone of medium- to fine-grained gabbronorite (Opx + Cpx + Pl cumulate) located at the base of the intrusion. The Ultramafic Zone forms an elongated hill and consists mainly of dunite (Ol + Chr cumulate) with interlayered orthopyroxenite (Opx + Chr cumulate) in the upper portions. The Mafic Zone consists mainly of medium-grained gabbronorite. Repeated sequence of cumulates within the Ultramafic and Mafic Zones suggests multiple injections of parental magma during the magmatic fractionation of the magma chamber. The crystallization sequence of the Serra da Onça Complex consists of Ol+Chr; Ol+Opx+Chr; Opx+Chr; Opx; Opx+Pl; Opx+Pl+Cpx; Pigeonite+Pl+Cpx and Pigeonite+Pl+Cpx+Mag+Ilm. The composition of olivine crystals in dunite and olivine orthopyroxenite samples from the Ultramafic Zone ranges from Fo92.4 to Fo86.2, indicating very primitive compositions for the parental magma.

            The Serra do Puma Complex is a 25 km long and up to 3 km wide SW-NE trending layered intrusion, with magmatic layering consistent dip of 30-40° to the southeast. The stratigraphy of the intrusion consists of a discontinuous Lower Border Group at the base, an Ultramafic Zone (up to ~1.0 km thick), and an upper Layered Zone (up to ~1.1 km thick). The Lower Border Group forms a thin and poorly outcropping (< 100 m thick) zone of fine- to medium-grained gabbro (Cpx + Pl cumulate) located in the northern border of the intrusion. The Ultramafic Zone forms an elongated hill and consists mainly of dunite (Ol + Chr cumulate) with minor interlayered peridotite (mainly wehrlite) and clinopyroxenite. The Layered Zone consists mainly of gabbro (Cpx + Pl cumulate) with abundant interlayered peridotite (mainly Ol + Cpx + Chr cumulate) and minor clinopyroxenite (Cpx cumulate). Common interlayering of gabbro and peridotite in the Layered Zone also suggests the existence of multiple injections of parental magma during the magmatic fractionation, leading to the interpretation that this zone originated in a dynamic magma chamber with successive influxes of parental magma. Analyses of olivine in peridotites from the upper portion of the Ultramafic Zone and throughout the Layered Zone range from Fo85.0 to Fo76.2, indicating moderately primitive compositions for the parental magma of the half upper portion of the Serra do Puma intrusion.

Canaã dos Carajás Region

            The mafic-ultramafic intrusions from the Canaã dos Carajás region (Fig. 3) have variable size, magmatic structure, rock types and metamorphic/hydrothermal alteration. Recent systematic studies of the Vermelho and Touro Complexes (Siepierski, 2016; Siepierski and Ferreira Filho, 2020), as well as the Ezio Complex (Silva, 2015) located at the eastern edge of Carajás Mineral Province, point out very distinctive features for each intrusion. The additional intrusions indicated in Figure 3 are likely to be part of this cluster of mafic-ultramafic intrusions.

            The Vermelho Complex is a remarkably well-preserved mafic-ultramafic layered intrusion in the Carajás Mineral Province, best known for hosting a world-class nickel laterite deposit. Mafic-ultramafic rocks form a 9.5 km long and 1.5 km wide NE-SW trending intrusion hosted by banded gneiss and massive granitic country rocks (Fig. 3). The complex consists of a sub-horizontally layered sequence of ultramafic cumulates (Ultramafic Zone) overlying a complex but broadly concordant sequence of mafic-ultramafic cumulates (Lower Zone). The Lower Zone consists of dunite and harzburgite in the base (where the most primitive olivine composition is Fo90.5), followed by interlayered orthopyroxenite, melanorite and norite, and quartz-bearing gabbronorite in the upper portions (where the most fractionated Opx composition is En57.5). The overlying Ultramafic Zone consists of two major sub-horizontal layers. The lower layer consists of ~50 meters thick orthopyroxenite with minor associated chromitite seams. The upper layer consists of ~100 meters thick pile of extensively weathered dunite and harzburgite. The composition of orthopyroxene from few samples of orthopyroxenite of the lower layer ranges from En85.7 to En83.0. The magmatic structure of the Vermelho Complex is interpreted as the result of two major magmatic events.

            The Touro Complex form a 4.8 km long and 1.2 km wide ENE-WSW trending intrusion hosted by granitoid rocks (Fig. 3). The Touro Complex consists of two zones, an Ultramafic Zone in the lower SE portion and a Mafic Zone in upper NW portion of the intrusion. The intrusion shows a progressive transition from dunite and wehrlite in the base, to olivine clinopyroxenite and clinopyroxenite in the upper portions of the Ultramafic Zone, to gabbro and leucogabbro in the upper Mafic Zone. The compositional range of cumulus olivine in the Touro Complex (Fo67.9-76.3) indicates relatively fractionated parental magmas.

            The Ézio Complex is located along the Serra do Rabo Fault Zone, a major tectonic feature linked to IOCG-type mineralization of the Cristalino Cu-Au deposit (Craveiro et al., 2019). The rocks outcropping in an area of ~7 km², consist mainly of gabbroic rocks and minor dunite, peridotite and pyroxenite. The primary magmatic structure is poorly constrained due to common shearing and poor outcropping of the igneous rocks. Gabbroic rocks consist of extensively to moderately saussuritized plagioclase crystals and clinopyroxene crystals largely replaced by fine-grained aggregates of hornblende, actinolite, quartz, chlorite and epidote group minerals. Peridotite, serpentinite and amphibole-bearing serpentinite occur as up to few hundred meter-thick layers of highly transformed olivine-chromite cumulate rocks. Rare relicts of olivine (Fo67-69) and orthopyroxene (En73-74) indicate moderately primitive compositions for the parental magmas.

The Serra Leste Region

            A cluster of small- to medium-size mafic-ultramafic intrusions occurs in the eastern portion of Carajás, namely the Serra Leste region (Fig. 4). Mafic-ultramafic intrusions of the Serra Leste region were grouped based on abundant PGE anomalies, disregarding any geological, stratigraphic or petrological consideration, in the Serra Leste Magmatic Suite (Ferreira Filho et al., 2007; Mansur and Ferreira Filho, 2016). Several poorly exposed mafic-ultramafic intrusions are located to the south of the Serra Leste region, as well as a few to the north, such that Figure 4 just covers the larger intrusions of the region. Recent studies of the Lago Grande Complex (Teixeira et al., 2015) and Luanga Complex (Mansur and Ferreira Filho, 2016; Mansur et al., 2020) are the first systematic stratigraphic and petrological investigations of layered intrusions ascribed to the Serra Leste Suite.

            The Luanga Complex is a 6 km long and up to 3.5 km wide layered intrusion (Mansur and Ferreira Filho, 2016; Mansur et al., 2020). From base to top the intrusion consists of ultramafic cumulates (Ultramafic Zone), an intercalation of ultramafic and mafic cumulates (Transition Zone) and mafic cumulates (Mafic Zone). The Ultramafic Zone comprises an up to 800 meters-thick sequence of serpentinites (i.e., metamorphosed peridotite) with few orthopyroxenite lenses at the upper portions. The Transition Zone consists of an up to 800 meters-thick sequence of interlayered ultramafic (i.e., harzburgite and orthopyroxene) and mafic (i.e., norite) cumulate rocks, with minor interlayered chromitites (Mansur and Ferreira Filho, 2017). The Mafic Zone consists of an up to 2000 meters-thick homogeneous sequence of noritic rocks and minor interlayered orthopyroxenite with subordinated chromitite. The PGE mineralization occurs associated with base metal sulfides at the boundary between the Ultramafic and Transition Zones (Ferreira Filho et al., 2007; Mansur et al., 2020) and associated with chromitite layers along the Transition Zone (Mansur and Ferreira Filho, 2017).

            The Lago Grande Complex is a 12 km long and average 1.7 km wide NE-trending layered intrusion consisting mainly of mafic cumulate rocks (Mafic Zone) and minor ultramafic cumulates (Ultramafic Zone). The Ultramafic Zone, about 4 km long and 500 m wide, comprises an up to 250 meters-thick sequence of interlayered harzburgite and orthopyroxenite at the base and orthopyroxenite at the top. The Mafic Zone consists of a monotonous sequence of gabbroic rocks (mainly norite) with an estimated thickness of up to 1000 m in the central portion of the intrusion.

            The architecture of the intrusion and the crystallization sequence described in the Luanga and Lago Grande Complexes indicate an overturned layered sequence. Even though the tectonic processes leading to the overturned sequence of layered rocks in both complexes have so far not been studied in detail, regional structural studies in the Serra Leste region indicate significant tectonic transport that may lead to major overturned blocks (Holdsworth and Pinheiro, 2000; Tavares, 2015). Metamorphic assemblages commonly replace primary igneous minerals of the Luanga and Lago Grande Complexes. This metamorphic alteration is heterogeneous and characterized by an extensive hydration that largely preserves primary textures, bulk rock compositions and the compositional domains of igneous minerals. The crystallization sequence of the Luanga and Lago Grande Complexes consists of Ol + Chr, Opx + Chr, Opx and Opx + Pl. The compositional range of cumulus olivine within the Ultramafic and Transition Zones of the Luanga Complex (Fo78.9–86.4) and the Ultramafic Zone of the Lago Grande Complex (Fo80.0–84.7) are similar and indicate moderate primitive parental magmas for these intrusions.

Remarks on the occurrence of magmatic sulfide deposits in the Carajás Mineral Province

Mafic-ultramafic intrusions in LIPs are a primary host for magmatic mineralization (e.g., Ernst and Jowitt, 2013; Barnes et al., 2016). Most review papers (e.g., Naldrett, 2004; Barnes and Lightfoot, 2005; Ripley and Li, 2013; Barnes et al., 2016) concur that major mining camps of magmatic sufide deposits share common features that may be used as guidelines for regional exploration. These features commonly include: (1) presence of large volumes of mafic-ultramafic rocks; (2) existence of crustal scale structures associated with mafic and ultramafic intrusions; (3) dynamic magmatic systems involving multiple events of magma injection; and (4) available sulfur-bearing country rocks for assimilation by mafic and ultramafic magmas. Except for sulfur-bearing country rocks, all these features are contemplated in several investigated mafic-ultramafic intrusions in Carajás. However, apart from the chromite and PGE-Ni-Cu deposit of the Luanga Complex (Ferreira Filho et al., 1997, Mansur and Ferreira Filho, 2020), this promising event for the formation of magmatic deposits didn't result yet in the discovery of major deposits. Considering the overall geological knowledge and exploration maturity for magmatic deposits in Carajás Mineral Province, the potential for future discoveries of this hard exploration targets should not be disregarded.

The ages of the layered intrusions of the Carajás Mineral Province (2763 ± 6 Ma Luanga Complex: Machado et al., 1991) overlap with ages of bimodal volcanism in the Grão Pará Group (Machado et al., 1991; Trendall et al., 1998; Martins et al., 2017), supporting the interpretation that mafic volcanics and mafic–ultramafic layered intrusions resulted from coeval major magmatic events in the Carajás region (Machado et al., 1991; Ferreira Filho et al., 2007). The location of the layered complexes in the Carajás Domain is controlled by major E-W or NE-SW regional lineaments, interpreted to be associated with deep crustal discontinuities (Fig. 1B; Vasquez et al., 2008a). In this scenario, each individual layered complex likely represents a small portion of a complex regional network of mafic-ultramafic intrusions. As suggested by Mansur and Ferreira Filho (2016), this magmatic event reaches the scale attributed to a LIP (Ernst et al., 2005).

The extensive basaltic volcanism, and also the coeval layered intrusions, are considered to result either from intra-plate rifting of older continental crust (e.g., Olszewski et al., 1989; Martins et al., 2017) or from subduction-related settings (Dardenne et al., 1988; Zuchetti, 2007). The distribution of the layered complexes along major structures suggests that parental melts were transported from the mantle to the crust through a regional deep structure, possibly by upward crack propagation. Ascent of large volumes of high-MgO magma by crack propagation requires a long-lived continuous supply of magma (e.g., Lister and Kerr, 1991). Regardless of the specific geodynamic setting, the abundance of large- to medium-sized layered intrusions in the Carajás Domain indicates a significant flux of magma originated in the mantle into the crust.

The composition of the parental magmas of the layered intrusions from the Carajás Mineral Province cannot be constrained by common approaches used to define their composition in well-exposed and unaltered intrusions (e.g., chilled margin, bulk composition, extrusive equivalents, related dykes, and melt inclusions). The most-magnesium olivine compositions of several layered intrusions in the province (Fig. 5; Mansur and Ferreira Filho, 2016) indicate primitive parental magmas, as illustrated by Fo contents of the Jacaré (up to 92.7 mol%), Serra da Onça (up to 92.4 mol%), Vermelho (up to 90.5 mol%), Serra do Puma (up to 87.7 mol%), Luanga (up to 86.4 mol%) and Lago Grande (up to 84.7 mol%) complexes. Apart from unusually high Ni contents in some intrusions in Carajás (Fig. 5), a subject discussed by Mansur and Ferreira Filho (2016), olivine compositions are consistent with primitive parental magmas derived from a peridotitic mantle source (Sobolev et al., 2007).

Field relations indicate that several of the layered complexes such as the Luanga, Lago Grande and Vermelho, have intruded into older granite-gneissic terrains of the Xingu Complex (ca. 3.0 Ga; Teixeira et al., 2015; Mansur and Ferreira Filho, 2016; Siepierski and Ferreira Filho, 2020). Contamination of mafic magmas by crustal components is expected during emplacement of large volume of high temperature primitive magmas into sialic crust (e.g., Sparks, 1986). Layered intrusions with mafic-ultramafic rocks dominated by orthopyroxene (e.g., Bushveld, Vermelho, Luanga, Lago Grande) crystallize from silica-saturated melts, a feature commonly interpreted as the result of crustal contamination of primitive high-Mg magmas (e.g., Campbell, 1985; Barnes, 1989). Assimilation of older gneiss and migmatites of the Xingú Complex during emplacement and/or ascent of parental magmas in Carajás is also supported by similar Sm-Nd isotopic data for the Vermelho and Lago Grande complexes (Teixeira et al., 2015; Siepierski and Ferreira Filho, 2020). Neodymium isotopic data obtained for mafic-ultramafic cumulates of these complexes render Nd model ages (from 2.90 to 3.30 and 2.94 to 3.56 for the Vermelho and Lago Grande complexes, respectively) and εNd (T) values (from -7.3 to +0.1 and - 4.25 to -0.32 for the Vermelho and Lago Grande complexes, respectively) consistent with a primitive mantle melt variably contaminated with older continental crust.

Exploration for magmatic Ni-Cu-PGE deposits in the Carajás Mineral Province indicated several PGE-occurrences in layered intrusions (mostly in the Serra Leste Region), but typical massive Ni-Cu-PGE deposits were not described. The indirect evidence that such deposits may have formed in the Carajás Mineral Province is very positive for mineral exploration. Massive Ni-Cu-PGE deposits are commonly hosted in small conduit-type mafic–ultramafic intrusions, as exemplified by Nebo- Babel (Seat et al., 2007) and Limoeiro (Mota-e-Silva et al., 2013) deposits. Fingerprints of conduit-type Ni-Cu sulfide deposits are usually very small, thus representing a challenge to exploration. Overall, the mafic-ultramafic intrusions in the Carajás Mineral Province have characteristics suggesting a favourable potential to host magmatic sulfide deposits.

            LIPs are really extensive (up to millions of square km) (Ernst 2014) and so, if the 2.76 Ga Carajás intrusions (along with the Parauapebas formation metavolcanics) belong to a LIP then continuation of this LIP (and potentially metallogeny) should be sought on other crustal blocks. Archean LIP units (greenstone belts and intrusions) of similar age are present in the Abitibi belt of the Superior craton, Eastern Goldfields region of Yilgarn craton, Pilbara craton    (Ernst 2014; Ernst et al. 2020).  However, evaluation of LIP linkages between these regions will require more robust late Archean paleocontinental reconstructions than are presently available. Such reconstructions may allow verifying if the Neoarchean (2.76 Ga) mafic-ultramafic magmatism found at the Carajás mineral province represent a discrete event or were part of wider LIP with similar ages (e.g. Bleeker, 2003; Kumar et al., 2017; Gumsley et al., 2020).