The Luanga deposit, Carajás Mineral Province, Brazil: Different styles of PGE mineralization hosted in a medium-size layered intrusion

Journal Pre-proofs The Luanga deposit, Carajás Mineral Province, Brazil: different styles of PGE mineralization hosted in a medium-size layered intrusion Eduardo T. Mansur, Cesar F. Ferreira Filho, Denisson P.L. Oliveira PII: DOI: Reference:

S0169-1368(19)30140-4 https://doi.org/10.1016/j.oregeorev.2020.103340 OREGEO 103340

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Ore Geology Reviews

Received Date: Revised Date: Accepted Date:

16 February 2019 22 August 2019 13 January 2020

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

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The Luanga deposit, Carajás Mineral Province, Brazil: different styles of PGE mineralization hosted in a medium-size layered intrusion Eduardo T. Mansur*¹,³, Cesar F. Ferreira Filho¹, Denisson P.L. Oliveira2

¹ Instituto de Geociências, Universidade de Brasília, Brasília-DF, 70910-900, Brazil. ² VALE S/A, Av. Getulio Vargas, 671/13º, 30112-020, Belo Horizonte, MG,

Brazil ³ Present affiliation: Sciences de la Terre, Université du Québec à Chicoutimi, QC G7H 2B1, Canada *Corresponding author: [email protected]

Abstract

The Luanga Complex, located in the eastern portion of the Carajás Mineral Province, is part of a cluster of PGE-mineralized layered intrusions, grouped into what is known as the Serra Leste magmatic suite. The Luanga deposit, the largest PGE deposit in South America, has two distinct styles of PGE mineralization. The first type, termed as Sulfide Zone, consists of a 10-50 m thick interval with disseminated base metal sulfides (pentlandite > pyrrhotite >>> chalcopyrite) located along the upper contact of the intrusion's Ultramafic Zone. The Sulfide Zone extends along the entire length of the intrusion (~ 3 km) and hosts the bulk of PGE resources of the Luanga Complex (i.e., 142 Mt at 1.24 ppm Pt+Pd+Au and 0.11% Ni). The second type of PGE mineralization, termed as low-S-high-Pt-Pd zones, consists of 2-10 m thick stratabound PGE mineralization within a sequence of interlayered ultramafic and mafic cumulates located above the Sulfide Zone. Host rocks of the low-S-high-Pt-Pd zones consist mainly of sulfide- and chromite-free harzburgite and orthopyroxenite. These mineralized rocks do not show any distinctive texture or change in modal composition. The Sulfide Zone and low-S-high-Pt-Pd zones have distinct PGE distribution. The Sulfide Zone has Pt/Pd ratios of 0.52 and a positive correlation between PGE and S. The low-S-high-Pt-Pd zones have Pt/Pd ratios of 1.2 and depletion in IPGE relative to primitive mantle. The platinum-group minerals (PGM) observed in the Sulfide Zone are predominantly Pt-Pd-

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bismuthtellurides, stanides and arsenides, mainly enclosed within sulfide minerals. On the contrary, the PGM found at low-S-high-Pt-Pd zones are mainly Pt-arsenides, stannides and antimonides, mostly enclosed within alteration silicates. Differences in texture, geochemistry and PGM assemblage between these mineralization styles suggest that they originated from distinct geological processes. The Sulfide Zone was formed by a major event of segregation of an immiscible sulfide liquid, whereas the low-S-high-PtPd zones formed by a sulfide liquid saturation followed by sulfur loss during postmagmatic alteration. The identification of PGE-rich layers in rocks without sulfides or chromite at the Carajás Mineral Province is important as these may have been overlooked during previous exploration programs. Keywords: PGE; nickel; layered intrusion; magmatic sulfide; Carajás

1 - Introduction Most of the global platinum-group elements (PGE) resources are hosted within a small number of layered intrusions (Cawthorn et al. 2005 and references therein). These deposits can be generally subdivided into sulfide- and chromite-related, as exemplified by the world-class PGE deposits of the Merensky reef and UG2 chromitite, from the Bushveld Complex (e.g., Barnes and Maier, 2002; Cawthorn et al. 2002 and 2005; Naldrett, 2004; Maier, 2005). The concentration of PGE global resources within just a few intrusions probably reflects the extremely efficient processes required for the formation of PGE deposits (i.e., PGE enrichment in orders of 104 to 105; Mungall and Naldrett, 2008; Maier et al. 2013). The common processes that lead to PGE concentration are the segregation of an immiscible sulfide liquid (e.g., Naldrett, 2004; Mungall and Naldrett, 2008) and crystallization of chromite crystals (e.g., Finnigan et al., 2008). However, recent studies also consider possible mechanisms for the accumulation of PGE in rocks devoid of chromite and/or base metal sulfides, and their implications for exploration (Maier, 2005; Maier et al. 2015; Barnes et al. 2016a; Canali et al. 2017; Maier et al. 2018). Understanding the mechanisms that lead to the accumulation of PGE in rocks with no sulfide minerals or chromite is critical for the mineral exploration of magmatic sulfide deposits.

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This study provides the first systematic geological and geochemical characterization of the PGE deposit of the Luanga Complex, the largest deposit of this type in South America. Our results also reveal significant PGE mineralization hosted in rocks devoid of base metal sulfides and chromite. Therefore, the Luanga Complex offers an opportunity to investigate the possible mechanisms leading to PGE accumulation in rocks lacking sulfide and chromite. Furthermore, the implications of our findings for the mineral exploration at the Carajás Mineral Province are also discussed. 2 - Regional Setting 2.1 - Carajás Mineral Province and associated mafic-ultramafic intrusions 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 (Dardenne and Schobbenhaus, 2001; Klein and Ladeira, 2002; Lobato et al. 2005; Xavier et al. 2010). The province is subdivided into two Archean tectonic domains, separated by a poorly defined Transition Subdomain (Dall'Agnol et al. 2006; 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. 2008). Several 2.75 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). The Serra da Onça and Serra do Puma Complexes in the western portion of the province (Rosa, 2014), and the Vermelho Complex (Siepierski, 2016) in the Canaan dos Carajás region host large Ni laterite deposits (Fig. 1B). The PGE-mineralized layered intrusions are constrained to the eastern portion of the province and were grouped into the Serra Leste Magmatic Suite. This suite includes the Luanga and Lago Grande Complexes (Fig. 1B; Teixeira et al. 2015; Mansur and Ferreira Filho, 2016). The Serra Leste Magmatic Suite was originally grouped based on abundant PGE anomalies of the layered intrusions, disregarding any geological, stratigraphic or petrological consideration (Ferreira Filho et al. 2007). Recent studies of the Lago Grande Complex (Teixeira et al. 2015) and Luanga Complex (Mansur and Ferreira Filho, 2016) are the first systematic stratigraphic and petrological investigations of these

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layered intrusions. The Luanga Complex, subject of this study, hosts the bulk of the PGE resources in the Serra Leste region. 2.2 - Luanga Complex The Luanga Complex is a 6 km long and up to 3.5 km wide layered intrusion (Fig. 2A). 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; Fig. 2B; Mansur and Ferreira Filho, 2016). The geological section defined by drilling indicate that the Ultramafic Zone overlies the Transition Zone, which overlies the Mafic Zone, suggesting thus that the layered sequence is tectonically overturned (Fig. 2B; Ferreira Filho et al. 2007; Mansur and Ferreira Filho, 2016). The Ultramafic Zone comprises an 800 meters-thick sequence of serpentinites (i.e., metamorphosed peridotite) with a few orthopyroxenite lenses in the upper portions. The Transition Zone consists of an up to 800 meters-thick pile of interlayered harzburgite and orthopyroxenite, with norite. The Mafic Zone consists of an up to 2000 meters-thick sequence of noritic rocks and minor interlayered orthopyroxenite with subordinate chromitite (Mansur and Ferreira Filho, 2016). The PGE mineralization occurs associated with base metal sulfides at the boundary between the Ultramafic and Transition Zones (Ferreira Filho et al. 2007) and associated with chromitite layers along the Transition Zone (Diella et al. 1995; Mansur and Ferreira Filho, 2017).

3 - Exploration Review Mafic-ultramafic rocks and chromitites of the Luanga Complex were identified in 1983 during regional exploration developed by DOCEGEO (now VALE S.A.) in the Serra Leste region. Following the discovery of up to 2-m thick chromitites, DOCEGEO carried out geological mapping, soil geochemical survey (400 m x 40 m grid) and ground magnetometric survey in the Luanga Complex. Four diamond bore holes were drilled to test the thickness and lateral continuity of outcropping chromitites. The drilling was not positive for chromite mineralization, but intersected anomalous concentrations of Pt and Pd, including 9 meters at 2.57 ppm of Pt+Pd (i.e., drill core LUFD-04). In 1997, a joint-venture DOCEGEO-Barrick Gold carried out a stream sediment campaign over the Luanga Complex area that identified Au anomalies (up to 3,061

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ppb). In 2000, Vale S.A., aiming to increase the Au resources of the Serra Leste Au Project (which included VALE’s Serra Pelada deposit), carried out a new soil geochemical survey to test the Au anomalies indicated by Barrick Gold. The sampling grid, covering the southern portion of Luanga Complex, indicated a 1 km long trend of Pt and Pd anomalies. Due to this anomalous trend with up to 1,450 ppb of Pt+Pd, in 2000 Vale S.A. carried out additional soil geochemical survey in the northern portion of the Luanga Complex (next to chromitite layers). This sampling indicated another 1 km long Pd and Pt anomalous trend with up to 804 ppb of Pt+Pd. The geochemical survey was extended to the central portion of the layered complex and indicated a 2 km extension trend of Pt and Pd anomalies with up to 1,436 ppb of Pt+Pd. In 2001, Vale S.A. started an exploration program for PGE in the Serra Leste region. Systematic geological and structural mapping using RADARSAT and TM5 integrated data, along with airborne geophysical survey, led to the discovery of several layered intrusions (e.g., Formiga, Lago Grande, Luanga Norte, Pegasus, Órion, Afrodite). From 2001 to 2007 Vale S.A performed 79,335 meters of diamond drilling and ore characterization tests in PGE-mineralized layered intrusions of the Serra Leste region. The resource drilling program in the Luanga Complex reached 45,174 meters of diamond drilling. The systematic evaluation indicated that the Luanga Complex hosts a PGE deposit with resources of 142 Mt at 1.24g/t PGE+Au and 0.11% Ni, for a given cut-off grade of 0.5 g/t PGE+Au. These resources were evaluated for a shallow (i.e., approximately 250 meter deep) open pit. 4 - Sampling and Analytical Procedures For this study, drill holes from the central and northern portions of the Luanga Complex (Fig. 2A and 2B) were systematically sampled in order to select unweathered rocks. The sampling was supported by lithogeochemical data of VALE’s exploration database (i.e., in order to select drill cores with no extensive weathering). Thin polished sections of the selected samples were studied in detail at the microscopy laboratory at University of Brasília. Two drill cores (i.e., LUFD-224 and LUFD-227; Fig. 2B) intersecting different styles of PGE mineralization were selected to investigate the whole-rock compositional variation through stratigraphy. Both cores were sampled and divided into 1 meter-long samples, disregarding any geological feature. Sample preparation and lithogeochemical

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analyses were performed at ALS Chemex (Canada). Analytical procedures include the whole-rock package plus LOI (ALS Chemex codes: ME-XRF06 and OA-GRA06), total S (ALS Chemex codes: S-IR08), PGE-nickel-sulfide collection plus Pt, Pd, Au 30g fire assay ICP-MS (ALS Chemex codes: PGM-MS23 and PGM-ICP23) and four acid ICPMS package (ALS Chemex code: ME-MS61). The ALS standards PGMS-13 and PGMS-14 were analyzed to assure the quality of the data. The obtained detection limits for PGE are below 5ppb. Analyses of both drill cores are available in the Electronic Supplementary Materials (ESM). The platinum-group minerals (PGM) and precious-metal minerals (PMM) were identified by energy-dispersive spectra (EDS) using a JEOL JSM-IT300LV Scanning Electron Microscope at the Centro Regional para o Desenvolvimento Tecnológico e Inovação (CRTI), Brazil. Furthermore, large PGM and PMM grains were analyzed by wavelength-dispersive spectra (WDS) using a JEOL JXA-8200 SuperProbe with 5 WDS spectrometers at the CRTI. Operating conditions were 15 kV accelerating voltage, with a beam current of 10 nA and probe diameters of 3 μm. Count times on peak and on background were 60s and 30s, respectively. Both synthetic and natural mineral standards were used as standards throughout the analytical work. Sulfur isotopic analyses were carried out at the Geochronology Laboratory of the University of Brasília (UnB). Approximately 2000µg of sulfide grain powders were handpicked from sulfide-bearing crushed samples. These grains were enclosed within tin capsules by the automatic sampler Thermo Scientific MAS 200R and introduced at the Thermo Scientific Flash 2000 element analyzer. The sample is heated up to 1800ºC by an automatic addition of oxygen and the combustion products are carried out by helium gas. The SO2 is separated by a chromatographic column and then sent to the ion fount of the Thermo Scientific MAT253 IRMS mass spectrometer. After the ionization and acceleration of the sample, gas species with different masses are separated and analyzed by faraday cup collectors. The spectrometer is monitored and the obtained results are treated using the software Isodat 3.0. The δ34S isotopic composition of the samples is calculated based on the reference material VCDT, using the equation δ34S=(34S32S(sample) ⁄ 34S32S ⁄ (VCDT)−1)x 1000.

5 - Geology of the Transition Zone and PGE Mineralization

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The Transition Zone of the Luanga Complex (Fig. 2) hosts several PGE mineralized intervals (Fig. 2B). The following description of the Transition Zone provides the petrographic characterization of the hosting rocks of the mineralized intervals. A complete petrographic description of various stratigraphic horizons of the Luanga Complex is provided by Mansur and Ferreira Filho (2016). The Transition Zone, about 5 km long and up to 1 km wide, represents the central part of the Luanga Complex and comprises a pile of interlayered ultramafic and mafic cumulate rocks (Fig. 2A and 2B). Interlayering of different rock types in different scales (from a few centimeters to dozens of meters) is a distinctive feature of the Transition Zone. The contact between different lithologies is normally gradational, indicated by the progressive change in cumulus and intercumulus minerals. However, sharp contacts with abrupt change in the mineralogy are locally observed (Fig. 3A). These sharp contacts may represent local flow or erosion structures (Maier et al. 2013). Cumulate rocks have variable textures, from adcumulate to orthocumulate (Fig. 3B), and variable assemblages of cumulus and intercumulus minerals, resulting in several different rocks types. Common rock types are orthopyroxenite (orthopyroxene adcumulate; Fig. 3A), harzburgite (olivine + chromite cumulate with either cumulus or intercumulus orthopyroxene; Fig. 3B), norite (orthopyroxene + plagioclase cumulate) and chromitite. The succession of rocks presented in figure 2 is simplified from a complex rock succession, and illustrates the main cumulates from the Transition Zone. Orthopyroxenite (Figs. 3A and 3C) is a medium- to coarse-grained rock with tabular crystals of orthopyroxene as cumulus mineral. The texture varies from adcumulate to meso- and orthocumulate, with plagioclase as the predominant intercumulus mineral (Fig. 3C). The crystals are in most cases partly altered, thus orthopyroxene is partly replaced by a fine intergrowth of chlorite and amphibole, whereas plagioclase is replace by chlorite and epidote (Fig. 3C). Harzburgite (Fig. 3B) is a medium- to coarse-grained olivine + chromite cumulate with meso- to orthocumululate textures. Olivine crystals are normally enclosed within large oikocrysts of orthopyroxene (Fig. 3B and 3D), whereas minor amounts of plagioclase are also found as intercumulus mineral. The fine alteration is normally restricted to fractures and grain boundaries (Fig. 3D). Norite is a medium-grained orthopyroxene and plagioclase adcumulate rock (Fig. 3E). It occurs as discontinuous layers commonly following a gradational upward fractionation from orthopyroxenite, to plagioclase orthopyroxenite

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and norite. Although the degree of weathering through the Transition Zone is variable, the textural relations are well preserved in most cases. Therefore, even in samples where the primary mineralogy has been completely replaced, magmatic textures and original minerals can still be readily assessed (Fig. 3F and 3G). Several chromitites occur near the top of the Transition Zone and into the lower part of the Mafic Zone (Diella et al. 1995; Ferreira Filho et al; 2007; Mansur and Ferreira Filho, 2017). These rocks consist of fine-grained euhedral cumulus chromite that vary from 5 to 50 centimeters-thick (Fig. 3H). The chromitite layers are normally hosted by norite, and plagioclase is the main intercumulus mineral to chromite grains. Similarly to elsewhere in the Transition Zone, the degree of weathering of the chromitite layers is variable, but original textures are mostly preserved (Mansur and Ferreira Filho, 2017). The concentration of Pt+Pd+Au in the chromitite layers reaches up to 3 ppm, with Pt/Pd ratios around 4 (VALE internal reports). A systematic description of chromitites throughout the stratigraphy of the Luanga Complex is provided by Mansur and Ferreira Filho (2017), and they are not addressed in this study. Apart from PGE mineralization hosted in chromitites (Diella et al. 1995; Ferreira Filho et al. 2007), two distinct styles of PGE mineralization occur in the Luanga Complex. These are the Sulfide Zone and the low-S-high-Pt-Pd zones (Fig. 2B). It is noteworthy that both styles of PGE mineralization belong to the class of sulfur-poor deposits (e.g., Eckstrand, 2005), following common classifications that separate typical reef-type deposits (e.g., Bushveld, Great Dyke) from sulfur-rich deposits where PGE occur associated with Ni-Cu ore (e.g., Noril'sk-Talnakh, Sudbury). 5.1 - Sulfide Zone The Sulfide Zone hosts the bulk of PGE resources of the Luanga Complex (i.e., 142 Mt at 1.24 ppm Pt+Pd+Au and 0.11% Ni; VALE internal reports). It consists of a 10–50 meters-thick stratabound interval, laterally continuous through the whole intrusion, with predominantly 1-3 vol.% interstitial sulfides hosted by orthopyroxenite and peridotite (Fig. 4A). The transition from peridotite to orthopyroxenite layers is gradational, with progressive increase in the concentration of cumulus orthopyroxene. The location of the Sulfide Zone along the contact zone is variable, such that sulfides may be hosted just by the lowermost orthopyroxenite of the Transition Zone, or

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encompasses both the orthopyroxenite and the underlying peridotite of the Ultramafic Zone (Fig. 2). The sulfide assemblage in the Sulfide Zone does not show major variation through the deposit and consists mainly of pentlandite>pyrrhotite>>>chalcopyrite (Fig. 4B). Chalcopyrite is not abundant (< 10 vol.% of the sulfides) and commonly occurs as fine-grained crystals at the borders of larger pentlandite and/or pyrrhotite crystals (Fig. 4C and 4E). Magnetite is commonly developed at the outer border or along fractures in sulfide blebs (Fig. 4C). The occurrence of silicate lamellae intergrorth with sulfide mierals is also observed (Fig. 4D). Additionally, thin lamellae of chalcopyrite occur enclosed within pentlandite crystals (Fig. 4F). Sulfides are not restricted to the Sulfide Zone in the Luanga Complex. Minor sulfide veinlets occur in thin (i.e., usually < 1 meter-thick but up to 8 meters-thick) discontinuous shear zones located along the Luanga Complex. These veins are not frequent through the complex, and crosscut the layered rocks within local shear zones, mostly surrounding the Sulfide Zone. Sulfides in these zones have texture and mineralogy different from those described in the Sulfide Zone. They are characterized by sulfide-amphibole intergrowths and higher proportions of chalcopyrite (up to 70%) with minor amounts of pyrrhotite and pentlandite. These occurrences are termed as remobilized sulfides. 5.2 - Low-S-high-Pt-Pd zones The term low-S-high-Pt-Pd zone is used to indicate PGE-mineralized rocks that do not have any visible base metal sulfides and/or chromite in hand samples. The lowS-high-Pt-Pd zones of the Luanga Complex consist of 2-10 meter-thick stratabound horizons across the Transition Zone. These zones occur stratigraphically above the Sulfide Zone and do not show extensive lateral continuity (Fig. 2B). The occurrence of low-S-high-Pt-Pd zones is normally at the contact between layers of distinct cumulate rocks in the Transition Zone (Fig. 2B and 3A), but these also occur within one rock type (e.g., norite layer intersected by drill hole LUFD-077; Fig. 2B). The hosting rocks, mainly harzburgite and orthopyroxenite, do not show any distinctive texture or change in modal composition that characterizes the PGE enrichment (Fig. 4G and 4H). Therefore, these PGE enriched intervals were not identified during core logging or petrographic studies, but only by their anomalous Pt-Pd contents. A remarkable feature

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is the occurrence of anomalously Ni-rich olivines (up to 7400 ppm Ni; Mansur and Ferreira Filho, 2016) in harzburgites within the low-S-high-Pt-Pd layers.

5.3 - Platinum-group element and precious-metal mineralogy A total of 351 platinum-group mineral (PGM) and precious-metal mineral (PMM) grains were located in six studied samples from both the Sulfide and low-Shigh-Pt-Pd zones. As the PGM and PMM are small, only few grains were analyzed (ESM_Table 1), and the remaining were identified using EDS. Most PGM and PMM consist of Pt-Pd-bismuthtellurides, arsenides, stanides and antimonides. The PGM assemblages found at both Sulfide and low-S-high-Pt-Pd zones are similar, however, no IPGE- or Rh-bearing minerals were identified in samples from the Sulfide Zone. The compositions and textural relationships of PGM and PMM are summarized in figure 5. In the Sulfide Zone, the PGM consist predominantly of Pt-Pdbismuthtellurides (5A and 6A), followed by stanides, arsenides and antimonides (6B and 6C). A few composite grains comprising different PGM, and in some cases Au alloys were also identified (Fig. 6D). Altaite grains (e.g. PbTe; ESM_Table 1) were also observed as single grains, or associated with other PGM (Fig. 6D). The PGM were found mainly enclosed within sulfide grains (Fig. 5C and 6A), or at the contact between sulfide and silicate grains (Fig. 5C and 6B). In the latter case, the sulfide minerals frequently form intergrowths with secondary minerals, suggesting a post-magmatic recrystallization (Fig. 6B). Less frequently, PGM also occur included in silicate minerals, or elongated within silicate cleavages (Fig. 5C, 6C and 6D). In the low-S-high-Pt-Pd zones (Fig. 5B), the PGM are mostly Pt-arsenides (i.e. mainly sperrylite, PtAs2; Fig. 6E), followed by Pt-Pd-stanides and antimonides, and minor bismuthtellurides (Fig. 6F). Moreover, few Rh-Pt-As-S-bearing grains were observed, which can probably be classified as holligworthite (Fig. 6G). These grains were too small for quantitative analyzes. Although some PGM occur included or in contact with sulfides (Fig. 6E), the vast majority of PGM in low-S-high-Pt-Pd zones are enclosed within silicates (Fig. 6F and 6G). It is noteworthy that even though PGM were found enclosed within primary silicates, the majority is enclosed within secondary silicate minerals (e.g. amphibole, chlorite; Fig. 6F and 6G). Less frequently, PGM also

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occur at the contact between silicates and magnetite crystals (Fig. 6H). No composite PGM grains were observed in the low-S-high-Pt-Pd zones. 6 - Litogeochemistry of PGE Mineralization Two representative drill holes (i.e., LUFD-224 and LUFD-227; Fig. 2) were investigated to characterize the geochemical features of the Sulfide Zone and low-Shigh-Pt-Pd zones. The plot of S vs PGE contents for unweathered samples with PGE contents higher than 500 ppb and/or S contents higher than 0.05 wt.% is shown in Figure 7. The correlation of these PGE-enriched (> 500 ppb) and/or sulfide-bearing (> 0.05 wt.%) samples defines three geochemically distinct groups: i. Sulfide Zone, ii. low-S-high-PtPd zones and iii. remobilized sulfides (Fig. 7). The Sulfide Zone comprises samples with high PGE and S contents (i.e., up to 7000 ppb and 1 wt.%, respectively). These samples correspond to orthopyroxenites and peridotites with interstitial base metal sulfides in the contact between the Ultramafic and Transition Zones (Fig. 4A). The lowS-high-Pt-Pd group comprises samples with high PGE (i.e., up to 2000 ppb) and very low S contents (< 0.1 wt.%). These sulfide-poor samples correspond to orthopyroxenites and harzburgites from the Transition Zone (Fig. 4G and 4H). Finally, the group referred to as remobilized sulfides corresponds to samples with high S contents (up to 0.7 wt.%) with low PGE contents (< 500 ppb). A description of these groups is provided as follows. 6.1 - Sulfide Zone and remobilized sulfides The groups referred to as Sulfide Zone and remobilized sulfides include samples with S contents higher than 0.1 wt. % (Fig. 7). The analyses presented in this section are from samples of drill core LUFD-224 (Fig. 2A; ESM_Table 2). The drill core LUFD-224 comprises the contact between the Ultramafic and Transition Zones, and consequently intersects the Sulfide Zone (Fig. 8). A sharp decrease in MgO and Al2O3 contents occurs in the transition from olivine cumulates with interstitial plagioclase below the Sulfide Zone, to overlying orthopyroxene cumulates (Fig. 8). The plots of S vs Ni, S vs Cu and Cu vs Ni (Fig. 9) have positive correlations for rocks from the Sulfide Zone, thus indicating that Ni and Cu are mainly controlled by sulfides.

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The sulfide tenors (i.e. concentrations of metals in cumulus sulfide fraction) were calculated using a regression line, extrapolated to 35% sulfur (following Barnes et al. 2011). The Ni hosted by silicates was removed from Ni tenor calculations. It is noteworthy that accumulated uncertainty may be large where the sulfide abundance is low due to extrapolated values (Barnes et al. 2011). The modal proportion of base metal sulfides in these rocks (i.e., pentlandite > pyrrhotite >>> chalcopyrite) is consistent with their high Ni tenors (15 wt.%; Fig. 9A), low Cu tenors (1.4 wt.%; Fig. 9C) and, consequently, high Ni/Cu ratios (~ 10.1; Fig. 9B). High PGE contents in drill hole LUFD-224 are restricted to samples from the Sulfide Zone (Fig. 8). These samples have strong positive correlation between Pd and S, high Pd tenors (149.4 ppm; Fig. 9E), and consistent Pt/Pd ratios (~ 0.52; Fig. 9D). Platinum values systematically lower than Pd is a characteristic feature of the Sulfide Zone. The Pt/Pd ratios below 1 are also consistence with the abundance of Pd-bearing PGM relative to Pt-beating PGM found at the Sulfide Zone (Fig. 5A). Ruthenium and S also show a positive correlation and Ru tenor is around 2.95 ppm (Fig. 9G). There is a positive correlation between Pd and Ru (Fig. 9F), and between Ru and Ir (Fig. 9H). The positive correlation between different PGE is consistent with their simultaneous collection by an immiscible sulfide liquid during magma crystallization. Mantle-normalized patterns (Fig. 10) for samples from the Sulfide Zone show high to moderate PGE enrichment (10-1000 times) and minor to moderate Ni, Cu and Co enrichment (2-10 times) relative to primitive mantle. The PGE patterns are enriched in Pt, Pd and Rh (i.e., Platinum Group PGE – PPGE) relative to Ir, Ru and Os (i.e., Iridium Group PGE – IPGE). Platinum-group element patterns indicate a progressive increase from incompatible IPGE toward compatible PPGE, as well as slightly negative anomalies of Pt and Au (Fig. 10). Two alteration zones located at the bottom of the drill hole LUFD-224 (i.e., the uppermost portion of the stratigraphic column in Fig. 8) consists of extensively sheared rocks. These altered intervals (~ 96-112 m and 145-162 m in Fig. 8) have discrete zones with lower MgO and higher Al2O3 and S contents (Fig. 8) characterized by abundant amphibole and sulfide veinlets. These alteration zones, referred as remobilized sulfides, have very low PGE contents (Fig. 7 and 8) and are not a subject to be addressed in the present study.

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6.2 - Low-S-high-Pt-Pd zones The group referred to as low-S-high-Pt-Pd includes samples with PGE contents higher than 500 ppb and very low S contents (i.e., below 0.1 wt.%; Fig. 7). The analyses from this section are from samples of drill core LUFD-227 (Fig. 2A; ESM_Table 3). The drill hole LUFD-227 intersects the upper portion of the Transition Zone, comprising mainly orthopyroxenite with minor interlayered harzburgite at the top (Fig. 11). Once the sequence of rocks is overturned the drill hole goes upward in the stratigraphic section of the complex. The high PGE and S values observed at the top of the drill hole (i.e., the lower portion of the stratigraphic column in Fig. 11), consist of samples of the Sulfide Zone at the northern portion of the Luanga Complex (Fig. 2A). Samples from the Sulfide Zone in drill hole LUFD-227 are variably weathered and were not considered in the following discussion, aimed to investigate a representative interval of low-S-high-Pt-Pd mineralization. No significant variation is observed in MgO and Al2O3 contents throughout the monotonous sequence of orthopyroxene adcumulates in drill core LUFD-227 (Fig. 11). High Ni values (i.e., around 750-1000 ppm) through the stratigraphy are consistent with Ni contents of 800-1200 ppm in orthopyroxene in the lowermost portion of the Transition Zone reported by Mansur and Ferreira Filho (2016). The reported values for Ni in orthopyroxene of the Transition Zone, together with very low S contents in orthopyroxenite in drill core LUFD-227 (i.e., lower than 0.1 wt.%), indicate that bulk rock Ni is mainly controlled by silicates. The distribution of Ni also indicates a consistent upward decrease from ~ 1000 ppm above the weathering profile down to ~ 750 ppm at the base of the PGE-mineralized zone (Fig. 11). Following an abrupt increase to ~ 1000 ppm at the base of the PGE-mineralized zone, Ni contents remain at values of ~ 1000 ppm in the upper portions of drill core LUFD-227. High Pt and Pd contents in the low-S-high-Pt-Pd zone are not correlated with S contents (Fig. 7). In fact, the PGE-mineralized interval (up to 9 meters at 1.2 ppm of Pt+Pd; Fig. 2B) has little or no sulfides and very low S contents (< 0.1 wt.%). Different from the Sulfide Zone, Pt values are systematically higher than Pd in the low-S-high-PtPd zone (Fig. 11), with Pt/Pd ratios consistently at 1.2-1.3 (Fig. 12A). This is also consistent with the PGM mineralogy identified in the low-S-high-Pt-Pd zones, which is dominated by Pt-bearing minerals (Fig. 5B). Mantle-normalized patterns (Fig. 12B) for

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samples from the low-S-high-Pt-Pd zone show none to moderate PGE enrichment relative to primitive mantle (1-100 times), and depleted Ni, Cu and Co contents. The PGE patterns are enriched in PPGE relative to IPGE, with Ir and Os contents below their detection limits of 2 ppb. These patterns indicate a progressive increase from incompatible IPGE toward compatible PPGE, as well as a distinct negative anomaly for Au (Fig. 12B). The lower contents of base metals are compatible with the absence of base metal sulfides in these rocks. 7 - Sulfur isotopes Three sulfide-bearing samples from the Sulfide Zone and one sample from remobilized sulfide zone (i.e., sample LUFD-224-102) were analyzed (Table 1). The δ34S values for sulfides of these samples are bracketed between -1.69‰ and 0.35‰. The analyzed samples, collected from different stratigraphic positions of the Sulfide Zone, show no systematic variation in δ34S values across the stratigraphy. Additionally, no significant difference in δ34S values is observed between samples from Sulfide Zone and remobilized sulfides. 8 - Discussion 8.1 - Crustal assimilation and sulfur source The role of crustal assimilation in the formation of magmatic Ni-Cu-PGE sulfide deposits is widely discussed (e.g., Barnes and Lightfoot, 2005; Mungall and Naldrett, 2008; Naldrett, 2010). To form magmatic Ni-Cu-PGE deposits it is necessary that a given silicate magma attain sufide liquid saturation, and thus segregate an immiscible liquid (Barnes and Lightfoot, 2005; Li and Ripley, 2009). Sulfur isotopes are commonly used to evaluate the importance of the assimilation of crustal rocks during ascent and emplacement of mafic-ultramafic intrusions (Ripley and Li, 2003 and 2007; Barnes and Ripley, 2016). The δ34S values of the mantle are traditionally considered to be 0±2‰, but some studies suggest a larger range around 0‰ (Seal, 2006). The δ34S values of the analyzed samples from the Sulfide Zone of the Luanga Complex fall in the range of 0 ± 2‰, which suggests that the sulfur of these rocks is mantle-derived (Fig. 13). However, the country rocks of the Luanga Complex were not investigated, and sulfur isotope results do not provide unequivocal evidence for mantle-derived sulfur. The Archean country rocks of the Luanga Complex (Docegeo, 1988; Vasquez et al. 2008) may also have an

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isotopic composition with δ34S values close to the mantle-derived interval. This may happen because the lack of fractionation and decoupling between heavy and light S isotopes via bacterial activity in sediments from the Archean (Ripley and Li, 2003; Queffurus and Barnes, 2015). Nevertheless, δ34S value obtained from a sample of hydrothermal sulfide (i.e., 0.35 ‰) is similar to the values obtained for the Sulfide Zone. Therefore, hydrothermal sulfides may represent local remobilizations of the Sulfide Zone, as both have the same δ34S signature. The evaluation of crustal assimilation during the formation of the Luanga Complex cannot rely exclusively on S isotope results. Previous studies using alterationresistant trace elements evaluated the process of crustal contamination in two intrusions of the Serra Leste Suite (Teixeira et al. 2015; Mansur and Ferreira Filho, 2016). Alteration-resistant trace elements of mafic cumulates from the Lago Grande and Luanga Complex are characterized by significant negative Nb and Ta anomalies and LREE enrichment. These features were interpreted as the product of primitive magmas partially contaminated with older continental crust (Teixeira et al. 2015; Mansur and Ferreira Filho, 2016). This is consistent with the emplacement of 2.76 Ga layered intrusions of the Serra Leste Suite within gneisses and migmatites of the Xingu Complex (ca. 3.0 Ga). The assimilation of crustal rocks is commonly considered as a key factor for the formation of magmatic sulfide Ni-Cu-PGE deposits in mafic-ultramafic intrusions (e.g., Ripley and Li, 2003; Barnes and Lightfoot, 2005). However, recent studies have also suggested that magmatic sulfide deposits originated solely from mantle-derived sulfur. Some examples are the Nebo-Babel Ni–Cu–PGE deposit (Fig. 11; Seat et al. 2009) and the Santa Rita deposit (Lazarin, 2011). Our results do not rule out the possibility of sulfur addition due to contamination of Archean country rocks, especially considering that crustal contamination is suggested by trace elements results. An additional consideration is that high-R factors may be responsible for diluting crustal S signatures, thus overprinting the effect of the external addition of S (Lesher and Burnham, 2001; Penniston-Dorland et al. 2008). Therefore, additional investigations still have to be carried out to better constrain the source of sulfur for the PGE mineralized Sulfide Zone of the Luanga Complex.

8.2 - Genetic model for the different styles of PGE mineralization

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Our results indicate that two different styles of PGE mineralization occur in the Luanga Complex. These are termed as Sulfide Zone and low-S-high-Pt-Pd zones (Fig. 2). Our results indicate that any genetic model for the PGE mineralization of the Luanga Complex needs to consider: 1) the petrographic and geochemical differences of both mineralization styles, 2) the magmatic evolution of the Transition Zone, which is the stratigraphic interval that host both styles of PGE mineralization, 3) the variable degree of alteration of cumulate rocks that host the PGE mineralization, and 4) the different PGM assemblages observed at both PGE-rich zones. Therefore, in the light of our results, a genetic model and its implications are presented for the PGE deposit of the Luanga Complex. The Sulfide Zone consists of PGE associated with interstitial base metal sulfides and resembles typical deposits originated from sulfide liquids segregated from maficultramafic magmas (e.g., Campbell et al. 1983; Naldrett, 2004; Barnes and Lightfoot, 2005). The low-S-high-Pt-Pd zones occur in rocks with no base metal sulfides and, consequently, are different from typical deposits. The Sulfide Zone and low-S-high-PtPd zones have distinct mantle-normalized PGE profiles (Fig. 10 and 12A) and Pt/Pd ratios, typically 0.5 and 1.2, respectively. Moreover, the PGM observed in the Sulfide Zone are predominantly Pt-Pd-bismuthtellurides and stanides, mainly enclosed within sulfide minerals (Fig. 5A and 5C). On the contrary, the PGM found at low-S-high-Pt-Pd zones are mainly Pt-arsenides, stannides and antimonides, mostly enclosed within alteration silicates (Fig. 5B and 5D). The differences between both mineralization styles, together with its different stratigraphic positions, suggest that a sequence of different processes took place during their formation. The crystallization of olivine cumulates in the Ultramafic Zone without the crystallization of sulfide minerals progressively upgrades the S content of the residual magma (stage 1; Fig. 14). The Transition Zone marks an abrupt change in the dynamics of the magmatic chamber, caused by several magma inputs and characterized by cyclic units (Mansur and Ferreira Filho, 2016). Hence, these periodic inputs of primitive magma may be associated with the sulfide liquid segregation in specific stratigraphic horizons of the Transition Zone. It would be also possible that the enhanced layering observed in the Transition Zone may reflect local sorting of the cumulates triggered by magma replenishment events (Maier et al. 2013). However, cryptic variation of silicates (Mansur and Ferreira Filho, 2016) support that the layers were not extensively modified and layering is mainly controlled by new magma influxes.

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The timing and the mechanism of S saturation of the magma, and consequently the segregation and concentration of the sulfide liquid, are controversial issues in many deposits (Barnes et al. 2016b). Sulfides may be the result of in-situ segregation and concentration from the silicate magma, the result of sulfide droplets transported by silicate magma, or a combination of both mechanisms (Naldrett et al. 2009; Barnes et al. 2016b). The vertical distribution of sulfides may also suggest the downward percolation of the sulfide liquid in the cumulus rocks (Godel et al. 2006). Regardless of the mechanism, the Sulfide Zone is the result of PGE and base metals collected by sulfide liquids (stage 2; Fig. 14). Low-S-high-Pt-Pd zones occur stratigraphically above the Sulfide Zone (Fig. 2B). Such PGE-rich rocks devoid of base metal sulfides and chromite have been described in several studies (Pentek et al. 2008; Knight et al. 2011 and 2017; Sluzhenikin et al. 2014; Tuba et al. 2014; Maier et al. 2015; Tanner et al. 2018). Two different possibilities for the formation of low-S-high-Pt-Pd zones have been proposed. These are interpreted as the result of direct crystallization of platinum-group minerals from silicate magmas, or by segregation of PGE-rich immiscible sulfide liquids which further underwent S-loss. The crystallization of PGM from magmas has been proposed in some studies (e.g., Hiemstra, 1979; Brenan and Andrews, 2001). However, recent experimental studies show that extensive external addition of semi-metals (e.g. As, Sb, Te, Sn, Bi) would be necessary prior to the crystallization of PGM from silicate liquids (Canali et al. 2017). Considering that in low-S-high-Pt-Pd zones, Pt and Pd occur as discrete PGM which contains these semi-metals, the direct crystallization from a silicate liquid is unlikely. On the contrary, the low-S-high-Pt-Pd zones could have originally formed in response to the segregation of a base metal sulfide liquid (stage 3; Fig. 14), similarly to the Sulfide Zone. Further, these rocks may have undergone sulfur loss due to late- or post-magmatic alteration processes. Similar processes of sulfur loss have already been considered important during the formation of PGE and Ni-Cu-PGE deposits (Li et al. 2004; Polovina et al. 2004; Godel and Barnes, 2008; Knight et al. 2011; Kawohl and Frimmel, 2016; Maier et al. 2018). This model is also compatible with some textural observations in low-S-high-Pt-Pd zones of the Luanga Complex, such as magnetite rims around sulfide droplets (Fig. 4C). Moreover, the textural relationships of the PGM assemblage found in the low-S-high-Pt-Pd zones, mostly associate with alteration silicates, support this model. The PGM comprise Pd-, Rh-, and IPGE-bearing PGM,

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which unlike crystallized from a silicate liquid. The PGM most likely formed during post-magmatic alteration of the rocks, thus S was removed and PGE combined with other semi-metals (As; Sb; Te; Sn; Bi) and formed PGM. The alteration may also be responsible for preferable remobilization of Pd relative to Pt, leading to higher Pt/Pd ratios relative to the Sulfide Zone (Holwell et al. 2017; Kerkhof et al. 2018; Oberthür et al. 2018). In summary, the Sulfide Zone marks an event of sulfide liquid saturation, whereas the low-S-high-Pt-Pd zones may represent a sulfide liquid saturation followed by sulfur loss. It is noteworthy that rocks from the Sulfide Zone were probably also affected during post-magmatic alteration, however, to a lesser extent relative to rocks from the low-S-high-Pt-Pd zones. Both types of PGE mineralization are associated with periodic influxes of primitive magma in the Transition Zone (Fig. 14). The formation of PGE-bearing rocks within stratigraphic horizons that marks dynamic periods in the evolution of a given magmatic chamber is commonly documented in PGE-mineralized intrusions (e.g., Naldrett, 2004 and references therein).

8.3 - Classification and comparison with other PGE deposits Magmatic PGE deposits are broadly grouped into two types based on the amount of base metal sulfide minerals present (e.g., Eckstrand, 2005): i. sulfide-poor deposits and ii. sulfide-rich deposits. The first group, sulfide-poor deposits, includes the deposits primarily mined for their PGE contents (e.g., Bushveld, Great Dyke, Stillwater), whereas the second group, sulfide-rich deposits, includes Ni-Cu sulfide deposits that contain PGE as a by-product (e.g., Sudbury, Noril'sk-Talnakh). The different types of PGE mineralization of the Luanga Complex, including the Sulfide Zone and the low-Shigh-Pt-Pd zones, belong to the sulfide-poor group of PGE deposits. Further classification of sulfide-poor PGE deposits is based on their location in the intrusion. In general, these deposits may be separated into those located in the interior of the complex and those located in the margins. Mineralization located in the interior of the intrusion encompass most of the economic PGE deposits (e.g., Naldrett, 2004; Green and Peck, 2005), including the typical reef-type deposits (e.g., Merenky Reef and UG-2 in the Bushveld Complex; Main Sulfide Zone in the Great Dyke; J-M Reef in the Stillwater Complex). The Platreef deposit, located along the footwall of the

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Northern Limb of the Bushveld Complex (e.g, Naldrett, 2004), is the economically most significant example of PGE mineralization located in the margin of a layered intrusion. Different types of PGE deposits that form relatively thin stratabound mineralized zones within mafic/ultramafic layered intrusions, broadly known as reef-type deposits, are classified in three different types based on the composition of the host rocks (Eckstrand, 2005): i. sulfide-Reef, ii. chromitite-Reef and iii. magnetite-Reef. The Sulfide Zone of the Luanga Complex, consisting of a relatively thin stratabound zone of sparsely disseminated sulfides in silicate layers, may be classified as a Sulfide-Reef deposit (Table 2). It is noteworthy that the Sulfide Zone has a greater average thickness (~ 10-50 m), and lower PGE contents (~ 1.2 Pt+Pd) compared with economic SulfideReef deposits (e.g., Merensky Reef, Main Sulfide Zone, J-M Reef; Table 2). Several studies point out that economic reef-type PGE deposits (e.g., Bushveld, Great Dyke, Stillwater) are hosted in very large layered intrusions (e.g., Naldrett, 2004; Mungall and Naldrett, 2008; Maier et al. 2013). This suggests that reef characteristics (i.e., thickness, PGE content, resources) somehow correlate with the size of the hosting intrusion. Although the origin of Sulfide-Reef deposits is controversial (see Naldrett et al. 2011 for a review of different models), this correlation has been explained by a model where reefs form through cumulate sorting during subsidence of the intrusion. This process favors larger intrusions due to slower cooling rates, and a greater degree of slumping and sorting (Maier et al. 2013). Based on compositional variations across mineralized zones Eckstrand (2005) identified two subtypes of sulfide reefs. One subtype, designated "unzoned sulfide reef", is characterized by strong positive correlation between PGE contents and the sulfide content of the rock (e.g., Mungall and Naldrett, 2008). The Merensky Reef in the Bushveld Complex and the J-M Reef in the Stillwater Complex, are examples of this subtype. The second subtype, designated "zoned sulfide reef", is characterized by vertical zoning in metal distribution across the reef and poor correlation between PGE contents and sulfide contents. The Main Sulfide Zone of the Great Dyke (e.g., Naldrett and Wilson, 1990), the sulfide zone of the Munni-Munni Complex (e.g., Hoatson and Keays, 1989, Barnes, 1993), and the Platinova Reef of the Skaegaard intrusion (Andersen et al. 1998; Nielsen et al. 2005) belong to the "zoned sulfide reef" subtype.

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The distributions of metals across the Sulfide Zone of the Luanga Complex (Fig. 6), and the positive correlation between PGE contents and modal sulfide concentrations (Fig. 7), indicate that the Sulfide Zone is an "unzoned sulfide reef". Similar to typical "unzoned sulfide reefs" (i.e., Meresnky Reef and J-M Reef), the Sulfide Zone is located immediately above the Ultramafic Zone of the intrusion (Fig. 6). Therefore, the Sulfide Zone is closely associated with cyclic units interpreted to result from new magma inputs (e.g., Naldrett, 2004). The low-S-high-Pt-Pd zones differ from many aforementioned PGE deposits due to the relative low content of sulfide minerals. A close analogue to these zones is the Ptrich layer of the Monts de Cristal Complex (Maier et al. 2015; Barnes et al. 2016a). At both cases, the PGE-rich rocks are mainly hosted by orthopyroxenites, and lack of sulfide minerals. The main difference is that at the Monts de Cristal Complex, the main hosts for PGE are Pt-arsenides, whereas at low-S-high-Pt-Pd zones, a more variable assemblage of PGM was identified (Fig. 5 and 6). Another possible analogue to these zones are the PGE reefs of the Penikat intrusion, which are mostly metamorphosed, and loss S, and also some Pd (Maier et al. 2018). Therefore, the low-S-high-Pt-Pd zones of the Luanga Complex can be classified as similar to the PGE reefs of the Penikat intrusion. The characteristics of the Sulfide Zone of the Luanga Complex indicate a mineralization compared with Sulfide-Reef deposit (Table 2). On one hand, the features described for the low-S-high-Pt-Pd zones do not fit into current classifications (e.g., Ekstrand, 2005) or deposit models (e.g., Naldrett, 2004; Mungall and Naldrett, 2008). However, two comparable analogues for the low-S-high-Pt-Pd zones of the Luanga Complex are the PGE reefs of the Penikat intrusion (Maier et al. 2018), and the Pt-rich layer of the Monts de Cristal Complex (Maier et al. 2015; Barnes et al. 2016a). Although PGE resources of these horizons were not evaluated, the 2-10 meters thick stratabound zones of orthopyroxenite or harzburgite (up to 9 meters at 1.2 ppm of Pt+Pd) resemble those observed in other typical reef-type deposits.

8.4 - Constrains for Ni and PGE exploration in the Carajás Mineral Province The identification of anomalously high-Ni magmatism (Mansur and Ferreira Filho, 2016), and the different styles of PGE mineralization in the Luanga Complex,

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provides additional constrains for mineral exploration in the Carajás Mineral Province. Following the model developed by Kerr and Leitch (2005), Mansur and Ferreira Filho (2016) interpreted these features as the result from the "cannibalization" of previously formed Ni-PGE sulfides. This model implies that the new inputs of Ni-rich fresh magma of the Transition Zone have partially dissolved early formed magmatic sulfides. Exploration for magmatic Ni-Cu-PGE deposits in the Carajás Mineral Province indicated several PGE-mineralized layered intrusions, but typical massive Ni-Cu-PGE deposits were not described in the region. 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 maficultramafic intrusions (Barnes et al. 2016b), as exemplified by Nebo-Babel (Seat et al. 2009) and Limoeiro (Mota-e-Silva et al. 2013) deposits. Fingerprints of conduit-type Ni-Cu sulfide deposits are usually very small, representing thus a challenge to exploration. Another important feature to be considered during further exploration programs in the Carajás Mineral Province is the occurrence of low-S-high-Pt-Pd zones in the Luanga Complex. Platinum-group element mineralization not related to sulfide- and/or chromite-bearing rocks do not provide the usual geochemical anomalies (e.g., Cu and Cr) expected in PGE deposits. In the Carajás Mineral Province, low-S-high-Pt-Pd mineralizations were also reported in the Serra da Onça Complex (Macambira and Ferreira Filho, 2005; Ferreira Filho et al. 2007) (Fig. 1B). These stratabound PGE mineralizations in the Carajás Mineral Province are also not indicated by any characteristic textural or mineralogical feature that may be recognized during drill core logging. This suggests that they may have been overlooked during previous exploration focused on traditional PGE deposits associated with base metal sulfides or chromitites. Mafic-ultramafic intrusions in the Carajás Mineral Province have characteristics suggesting a favorable potential to host magmatic Ni-Cu-PGE deposits. The most significant ones are: i.

The Carajás Mineral Province hosts several mafic-ultramafic intrusions within an Archean cratonic terrain;

ii.

Many layered intrusions have primitive parental magmas emplaced in dynamic magmatic system (e.g., Vermelho Complex; Luanga Complex);

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iii.

The cluster of PGE-mineralized intrusions in the Serra Leste region suggests the existence of a PGE-fertile suite in the eastern portion of the Carajás Mineral Province;

iv.

The Ni-rich parental magma of the Luanga Complex may result from the "cannibalization" of previously formed Ni-PGE sulfides, suggesting the existence of hidden magmatic sulfide deposits.

9 - Conclusions The main conclusions derived from the present study are listed below. 

Apart from PGE associated with chromitites, two distinct styles of PGE mineralization occur in the Luanga Complex. These are referred to as Sulfide Zone and low-S-high-Pt-Pd zones.



The Sulfide Zone is a 10-50 m thick stratabound zone of disseminated base metal sulfides (~ 1-3 vol.%) located along the contact of the Ultramafic and Transition Zones. This mineralized interval extends along the entire length of the intrusions (~ 3 km) and hosts the bulk of PGE resources of the Luanga Complex (142 Mt at 1.24g/t PGE+Au and 0.11% Ni).



The Sulfide Zone has high Ni tenors (16-18 wt.%) and Ni/Cu ratios (10-12), Pt/Pd ratios lower than 1 (0.5-0.6) and PPGE-enriched mantle-normalized patterns.



The low-S-high-Pt-Pd zones consists of 2-10 meters thick stratabound horizons, located stratigraphically above the Sulfide Zone. These PGE-rich horizons consist of cumulates (orthopyroxenite and harzburgite) with no distinctive textural and mineralogical features compared to equivalent (i.e., orthopyroxenite and harzburgite) barren cumulates.



Low-S-high-Pt-Pd zones are characterized by Pt/Pd ratios higher than 1 (1.21.3), PPGE-enriched mantle-normalized patterns, and very low contents of Ir and Os.



The PGM observed in the Sulfide Zone are predominantly Pt-Pdbismuthtellurides, stanides and arsenides, mainly enclosed within sulfide minerals. On the contrary, the PGM found at low-S-high-Pt-Pd zones are mainly Pt-arsenides, stannides and antimonides, mostly enclosed within alteration silicates.

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

Sulfur isotopes show a narrow range of variation for δ34S values (i.e., between 1.69‰ and 0.35‰), which may suggest that S is derived from a mantle source. However, considering that the country rocks of the Luanga Complex are Archean, the possibility of external addition of S cannot be ruled out.



Textural and geochemical differences between Sulfide Zone and low-S-high-PtPd zones support that different geological processes took place during their formation. The Sulfide Zone results of segregation of immiscible sulfide liquids, whereas the low-S-high-Pt-Pd zones formed by sulfide saturation followed by sulfur loss.

Acknowledgements This study was supported by CNPq (Conselho Nacional de Desenvolvimento Científico e Teconológico) and VALE S.A. (Projeto 550398/2010-4). Analytical facilities of the Instituto de Geociências of the University of Brasília (UnB) provided additional support for this research. The authors acknowledge VALE's Exploration Managers for Brazil and Carajás (Mr. Fernando Greco and Mr. Fernando Matos, respectively) for field support and access to exploration data. Cesar F. Ferreira Filho is a Research Fellow of CNPq and acknowledges the continuous support through research grants and scholarships for the "Metalogenênese de Depósitos Associados ao Magmatismo MáficoUltramáfico" Research Group. Eduardo T. Mansur received a scholarship from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) and this study is part of his M.Sc. thesis developed at the Instituto de Geociências (Universidade de Brasília). The authors thank the reviewers Dr. Steve Barnes and Dr. Wolfgang Maier, and guest editor Dr. Steffen Hagemann for carefully handling the manuscript. References Andersen, J.C.Ø., Rasmussen, H., Nielsen, T.F.D., and Ronsbo, J.G., 1998, The Triple Group and the Platinova gold and palladium reefs in the Skaergaard intrusion: Stratigraphic and petrographic relations: Economic Geology, v. 93, p. 488-509. Barnes, S.J., Fisher, L.A., Godel, B., Maier, W.D., Paterson, D., Howard, D.L., Ran, C.G., Laird, J.S., and Pearce, M.A., 2016a, Primary cumulus platinum minerals in the

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Monts de Cristal Complex, Gabon: magmatic microenvironments inferred from highresolution X-ray fluorescence microscopy: Contributions to Mineralogy and Petrology, v. 171, p. 23. Barnes, S.J., Cruden, A.R., Arndt, N., and Saumur, B.R., 2016b, The mineral system approach applied to magmatic Ni–Cu–PGE sulphide deposits: Ore Geology Reviews, v. 76, p. 296–316. Barnes, S.J., Osborne, G.A., Cook, D., Barnes, L., Maier, W.D., and Godel, B., 2011, The Santa Rita nickel sulfide deposit in the Fazenda Mirabela intrusion, Bahia, Brazil: Geology, sulfide geochemistry, and genesis: Economic Geology, v. 106(7), p. 10831110. Barnes, S.J., 1993, Partitioning of the platinum group elements and gold between silicate and sulphide magmas in the Munni Munni Complex, Western Australia: Geochimica et Cosmochimica Acta, v. 57, p. 1277-1290. Barnes, S-.J., and Lightfoot, P.C., 2005, Formation of magmatic nickel sulfide deposits and processes affecting their copper and platinum group element contents: Economic Geology 100th Anniversary Volume, p. 179-214. Barnes, S-J., and Maier, W.D., 2002, Platinum-group element distributions in the Rustenberg Layered Suite of the Bushveld Complex, South Africa, in, Cabri, L.J., ed., The Geology, Geochemistry, Mineralogy and Mineral Beneficiation of Platinum-Group Elements, Canadian Institute of Mining, Metallurgy and Petroleum, Special Volume 54: p. 431-458. Barnes, S.-J., and Ripley, E.M., 2016, Highly siderophile and strongly chalcophile elements in magmatic ore deposits: Reviews in Mineralogy and Geochemistry, v. 81, p. 725–774. Brenan, J.M., and Andrews, D.R.A., 2001, High-temperature stability of laurite and RuOs-Ir alloy and their role in PGE fractionation in mafic magmas: Canadian Mineralogist, v. 39, p. 341-360. Campbell, I.H., Naldrett, A.J., and Barnes, S.J., 1983, A model for the origin of the platinum-rich horizons in the Bushveld and Stillwater Complexes: Journal of Petrology, v. 24, p. 133-165.

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Canali, A.C., Brenan, J.M., and Sullivan, N.A., 2017, Solubility of platinum-arsenide melt and sperrylite in synthetic basalt at 0.1 MPa and 1200ºC with implications for arsenic speciation and platinum sequestration in mafic igneous systems: Geochimica et Cosmochimica Acta, in press. Cawthorn, R.G., Merkle, R.K.W., and Viljoen, M.J., 2002, Platinum-group element deposits in the Bushveld Complex, South Africa, in, Cabri, L.J., ed., The Geology, Geochemistry, Mineralogy and Mineral Beneficiation of Platinum-Group Elements, Canadian Institute of Mining, Metallurgy and Petroleum, Special Volume 54: p.389430. Cawthorn, R.G., Barnes, S.J., Ballhaus, C., and Malich, K.N., 2005, Platinum group element, chromium and vanadium deposits in mafic and ultramafic rocks: Economic Geology 100th Anniversary Volume, p. 215-249. Crocket, J.H., 2002, Platinum-group element geochemistry of mafic and ultramafic rocks; in The Geology, Geochemistry, Mineralogy and Mineral Beneficiation of Platinum-Group Elements, in, L.J. Cabri, ed., Canadian Institute of Mining and Metallurgy, Special Volume 54: p. 177–210. Dall'Agnol, R., Oliveira, M.A., Almeida, J.A.C., Althoff, F.J., Leite, A.A.S., Oliveira, D.C., and Barros, C.E.M., 2006, Archean and Paleoproterozoic granitoids of the Carajás metallogenetic province, eastern Amazonian craton, in, Dall'Agnol, R., Rosa-Costa, L.T., Klein, E.L., ed., Symposium on Magmatism, Crustal Evolution, and Metallogenesis of the Amazonian Craton, Abstracts Volume and Field Trips Guide: p. 150. Dardenne, M.A., and Schobbenhaus, C.S., 2001, Metalogênese do Brasil: Brasília, UnB-CNPq, 392 p. Diella, V., Ferrario, A., and Girardi, V.A.V., 1995, PGE and PGM in the Luanga maficultramafic intrusion in Serra dos Carajás (Pará State, Brazil): Ore Geology Reviews, v. 9, p. 445-453. Docegeo - Rio Doce Geologia e Mineração, 1988, Revisão Litoestratigráfica da Província Mineral de Carajás, in, SBG-NNO, ed., 35º Congresso Brasileiro Geologia, Belém, Anais: p. 11-59. Eckstrand, O.R., 2005, Ni–Cu–Cr–PGE mineralization types: Distribution and classification. in, Mungall, J. E., ed, Exploration for Platinum Group Element Deposits Mungall JE, Mineral Assoc Canada, Short Course Notes vol 35, p 487–490.

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Feio, G.R.L., Dall’Agnol, R., Dantas, E.L., Macambira, M.J.B., Santos, J.O.S., Althoff, F.J., and Soares, J.E.B., 2013, Archean granitoid magmatism in the Canaã dos Carajás area: Implications for crustal evolution of the Carajás province, Amazonian craton, Brazil: Precambrian Research, v. 227, p. 157-185. 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, volume 5: p. 01-14. Finnigan, C.S., Brenan, J.M., Mungall, J.E., and McDonough, W.F., 2008, Experiments and models bearing on the role of chromite as a collector of platinum group minerals by local reduction: Journal of Petrology, v. 49, p. 1647-1665. Godel, B., and Barnes, S-J., 2008, Platinum-group elements in sulfide minerals and the whole rock of the J-M Reef (Stillwater complex): Implication for the formation of the reef: Chemical Geology, v. 248, p. 272–294. Godel, B., Barnes, S-J., and Maier, W. D., 2006, 3-D distribution of sulphide minerals in the Merensky Reef (Bushveld Complex, South Africa) and the JM Reef (Stillwater Complex, USA) and their relationship to microstructures using X-ray computed tomography: Journal of Petrology, 47(9), p. 1853-1872. Green, T., and Peck, D., 2005, Platinum Group Elements exploration: Economic Considerations and Geological Criteria. in, Mungall, J. E., ed, Exploration for Platinum Group Element Deposits Mungall JE, Mineral Assoc Canada, Short Course Notes vol 35, p 247–274. Hiemstra, S. A., 1979, The role of collectors in the formation of the platinum deposits in the Bushveld Complex: Canadian Mineralogist, v. 17, p. 469-482. Holwell, D.A., Adeyemi, Z., Ward, L.A., Smith, D.J., Graham, S.D., McDonald, I. and Smith, J.W., 2017, Low temperature alteration of magmatic Ni-Cu-PGE sulfides as a source for hydrothermal Ni and PGE ores: Ore Geology Reviews, v. 91, p. 718–740. Holwell D. A., and Keays, R. R., 2014, The formation of low-volume, high-tenor magmatic PGE-Au sulfide mineralization in closed systems: evidence from precious and base metal geochemistry of the Platinova Reef, Skaergaard Intrusion, East Greenland: Economic Geology, v. 109, p. 387-06.

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Li, C., Ripley, E.M., Merino, E., and Maier, W.D., 2004, Replacement of base metal sulfides by actinolite, epidote, calcite, and magnetite in the UG2 and Merensky Reef of the Bushveld Complex, South Africa: Economic Geology, v. 99, p. 173−184. Lobato, L.M., Figueiredo e Silva, R.C., Rosière, C.A., Zucchetti, M., Baars, F.J., Seoane, J.C.S., Rios, F.J., and Monteiro, A.M., 2005, Hydrothermal origin for the iron mineralisation, Carajás Province, Pará State, Brazil, in, Proceedings Iron Ore 2005, The Australian Institute of Mining and Metallurgy, Publication Series, vol 8, p. 99-110. Macambira, E.M.B., and Ferreira Filho, C.F., 2005, Exploration and origin of stratiform PGE mineralization in the Serra da Onça layered complex, Carajás Mineral Province, Brazil [ext. abs.]: International Platinum Symposium, 10th, Oulu, Finland, 2005, Extended Abstracts, p. 178-181. Maier, W.D., Halkoaho, T., Huhma, H., Hanski, E., and Barnes, S.J., 2018, The Penikat Intrusion, Finland: Geochemistry, Geochronology, and Origin of Platinum–Palladium Reefs: Journal of Petrology, v. 59(5), p. 967-1006. Maier, W.D., 2005, Platinum-group element (PGE) deposits and occurrences: Mineralization styles, genetic concepts, and exploration criteria: Journal of African Earth Sciences, v. 41, p. 165-191. Maier, W.D., Rasmussen, B., Fletcher, I., Godel, B., Barnes, S.J., Fisher, L., Yang, S.H., Huhma, H., and Lahaye, Y., 2015, Petrogenesis of the ~2.77 Ga Monts de Cristal Complex, Gabon: evidence for direct precipitation of Pt-arsenides from basaltic magma: Journal of Petrology, v. 56, p. 1285-1308. Maier, W.D., Barnes, S.J., and Groves, D.I., 2013, The Bushveld Complex, South Africa: formation of platinum–palladium, chrome-and vanadium-rich layers via hydrodynamic sorting of a mobilized cumulate slurry in a large, relatively slowly cooling, subsiding magma chamber: Mineralium Deposita, v. 48(1), p. 1-56. Mansur, E.T., and 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, v. 266-267, p. 28-43.

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Mansur, E.T., and Ferreira Filho, C.F., 2017, Chromitites from the Luanga Complex, Carajás, Brazil: Stratigraphic distribution and clues to processes leading to postmagmatic alteration: Ore Geology Reviews, v. 90, p. 110-130. Mota-e-Silva, J., Ferreira Filho, C.F., and Della Giustina, M.E.S., 2013, The Limoeiro deposit: Ni–Cu–PGE sulfidemineralization hostedwithin an ultramafic tubular magma conduit inthe Borborema Province, Northeast Brazil: Economic Geology 108, 1753– 1771. Mungall, J.E., and Naldrett, A.J., 2008, Ore deposits of the platinum-group elements: Elements, v. 4, p. 253-258. Naldrett, A.J., 2004, Magmatic sulphide deposits: Geology, geochemistry and exploration: Berlin, Springer-Verlag, 728 p. Naldrett, A.J., 2010, Secular variation of magmatic sulfide deposits and their source magmas: Economic Geology, v. 105, p. 669-688. Naldrett, A.J., Wilson, A., Kinnaird, J., and Chunnett, G., 2009, PGE Tenor and metal ratios within and below the Merensky Reef, Bushveld Complex: implications for its genesis: Journal of Petrology, v. 50, p. 625–659. Naldrett, A.J., and Wilson, A.H., 1990, Horizontal and vertical variations in noble-metal distribution in the Great Dyke of Zimbabwe: A model for the origin of the PGE mineralization by fractional segregation of sulfide: Chemical Geology, v. 88, p. 279-300 Nielsen, T.F.D., Andersen, J.C.Ø., and Brooks, C.K., 2005, The Platinova Reef of the Skaergaard intrusion: Mineralogical Association of Canada, Short Course Series, v. 35, p. 431−456. Oberthür, T., Melcher, F., Fusswinkel, T., van den Kerkhof, A. M., and Sosa, G.M., 2018, The hydrothermal Waterberg platinum deposit, Mookgophong (Naboomspruit), South Africa. Part 1: Geochemistry and ore mineralogy: Mineralogical Magazine, v. 82(3), p. 725-749. Penniston-Dorland, S.C., Wing, B.A., Nex, P.A.M., Kinnaird, J.A., Farquhar, J., Brown, M., and Sharman, E.R., 2008, Multiple sulfur isotopes reveal a primary magmatic origin for the Platreef PGE deposit, Bushveld Complex, South Africa: Geology, v. 36, p. 979982.

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Péntek, A., Molnár, F., Watkinson, D.H., and Jones, P.C., 2008, Footwall-type Cu–Ni– PGE mineralization in the Broken Hammer area, Wisner Township, North Range, Sudbury Structure: Economic Geology, v. 103, p. 1005–1028. Polovina, J. S., Hudson, D. M., and Jones, R. E., 2004, Petrographic and geochemical characteristics of postmagmatic hydrothermal alteration and mineralization in the J-M Reef, Stillwater Complex, Montana: Canadian Mineralogists, v. 42, p. 261-278. Queffurus, M., and Barnes, S-J., 2015, Processes affecting the sulfur to selenium ratio in magmatic nickel–copper and platinum-group element deposits: Ore Geology Reviews, v. 69, p. 301–324. Ripley, E.M., and Li, C., 2003, S isotope exchange and metal enrichment in the formation of magmatic Cu-Ni-(PGE) deposits: Economic Geology, v. 98, p. 635-641. Ripley, E.M., and Li, C., 2007, Applications of Stable and Radiogenic Isotopes to Magmatic Cu-Ni-PGE Deposits: Examples and Cautions: Earth Science Frontiers, v. 14(5), p. 124–132. Rosa, W.D., 2014, Complexos acamadados da Serra da Onça e Serra do Puma: Geologia e petrologia de duas intrusões Máfico-Ultramáficas com sequência de cristalização distinta na Província Arqueana de Carajás, Brasil: Unpublished M.Sc. thesis, Brasília, Brazil, Universidade de Brasília, 65 p. Seal, R.R., 2006, Sulfur isotope geochemistry of sulfide minerals: Reviews in Mineralogy and Geochemistry, v. 61, p. 633-677. Seat, Z., Beresford, S.W., Grguric, B.A., Gee, M.A.M., and Grassineau, N.V., 2009, Reevaluation of the role of external sulfur addition in the genesis of Ni-Cu-PGE deposits: evidence from the Nebo-Babel Ni–Cu–PGE Deposit, West Musgrave, Western Australia: Economic Geology, v. 104, p. 521-538. Siepierski, L., 2016, Geologia, petrologia e potencial para mineralizações magmáticas dos corpos máfico-ultramáficos da região de Canaã dos Carajás, Província Mineral de Carajás, Brasil, Unpublished Ph.D. thesis, Brasília, Brazil, Universidade de Brasília, 156 p. Sluzhenikin, S,F., Krivolutskaya, N.A., Rad’ko, V.A., Malitch, K.N., Distler, V.A., and Fedorenko, V.A., 2014, Ultramafic–mafic intrusions, volcanic rocks and PGE–Cu–Ni

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sulfide deposits of the Noril’sk Province, Polar Siberia. Field trip guidebook. 12th International Platinum Symposium IGG UB RAS, Yekaterinburg. Sun, S.-S., McDonough, W.F., 1989, Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes, in, Saunders, A.D., Norry, M.J., ed., Magmatism in the Ocean Basins, Geological Society Special Publication, volume 42: pp. 313–345. Tanner, D., McDonald, I., Harmer, R.E. J., Muir, D.D., and Hughes, H.S.R., 2018, A Record Of Assimilation Preserved By Exotic Minerals In The Lowermost PlatinumGroup Element Deposit Of The Bushveld Complex: The Volspruit Sulphide Zone: Lithos, in press. Teixeira, A.S., Ferreira Filho, C.F., Giustina, M.E.S.D., Araujo, S.M., and 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, v. 64, p. 116-138. Tuba, G., Molnár, F., Ames, D.E., Péntek, A., Watkinson, D.H., and Jones, P.C., 2014, Multi-stage hydrothermal processes involved in “low-sulfide” Cu (-Ni)-PGE mineralization in the footwall of the Sudbury Igneous Complex (Canada): Amy Lake PGE zone, East Range: Mineralium Deposita, v. 49, p. 7–47. van den Kerkhof, A.M., Sosa, G.M., Oberthür, T., Melcher, F., Fusswinkel, T., Kronz, A., and Dunkl, I., 2018, The hydrothermal Waterberg platinum deposit, Mookgophong (Naboomspruit), South Africa. Part II: Quartz chemistry, fluid inclusions and geochronology: Mineralogical Magazine, v. 82(3), p. 751-778. Vasquez, M.L., Carvalho, J.M.A., Sousa, C.S., Ricci, P.S.F., Macambira, E.M.B., and Costa, L.T.R., 2008. Geological map of the Pará state in GIS, Geological Survey of Brazil-CPRM. Xavier, R., Monteiro, L.V.S., Souza Filho, C.R., Torresi, I., Carvalho, E.R., Dreher, A.M., Wiedenbeck, M., Trumbull, R.B., Pestilho, A.L.S., and Moreto, C. P. N., 2010, The iron oxide copper-gold deposits of the Carajás Mineral Province, Brazil: an updated and critical review, in, Porter, T.M., Org., Hydrothermal Iron Oxide Copper-Gold & Related Deposits: A Global Perspective, vol. 3, Advances in the Understanding of IOCG Deposits, Adelaide, PGC Publishing, volume 3: p. 285-306.

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Figure captions Fig. 1. Geological setting of the Carajás Mineral Province. A) Location of the Carajás Mineral Province. AM - Amazonic Craton; B – Borborema Province; M – Mantiqueira Province; SF – São Francisco Craton; T – Tocantins Province. B) Geological map of the Carajás Mineral Province (modified from Vasquez et al. 2008). The dashed rectangle indicates the location of the Serra Leste magmatic suite. Fig. 2. Local geology of the Luanga Complex. A) Geological map of the Luanga Complex (partially modified from unpublished report of VALE). Note the location of drill holes referred to in this study. B) Geological section on the central portion of the Luanga Complex. Different PGE mineralizations are indicated (partially modified from Mansur and Ferreira Filho, 2016). Abbreviations: PGE= ΣPt;Pd;Rh:Ru;Ir;Os. Fig. 3. General aspects of rocks from the Transitional Zone of the Luanga Complex. A) Core sample showing a sharp contact of orthopyroxenite and harzburgite. Orthopyroxenite consists of cumulus orthopyroxene with minor intercumulus plagioclase, whereas harzburgite consists of cumulus olivine with intercumulus orthopyroxene. B) Core sample of harzburgite with olivine enclosed within orthopyroxene oikocrysts. Note interstitial plagioclase. C) Photomicrograph of orthopyroxenite with interstitial plagioclase. Note the partial alteration of orthopyroxene and plagioclase. D) Photomicrograpf of harzburgite with olivine inclusion in orthopyroxene oikocryst. E) Core sample of norite with cumulus plagioclase and orthopyroxene. F) Core sample of altered harzburgite with preserved cumulus texture. G) Photomicrograph of harzburgite with primary mineralogy completely replaced by secondary silicate minerals. Note that olivine is replaced by serpentine and magnetite, whereas orthopyroxene is replaced by amphibole and chlorite. H) Chromitite layers hosted by adcumulate norite. Ol: olivine; Opx: orthopyroxene; Plg: Plagioclase. Fig. 4. General aspects of the PGE-bearing rocks of the Luanga Complex. A) Core sample of orthopyroxenite from the Sulfide Zone with cumulus orthopyroxene and interstitial base metal sulfides. B) Photomicrograph of typical sulfide assemblage of the Sulfide Zone with pentlandite > pyrrhotite >>> chalcopyrite. C) Photomicrograph of typical interstitial base metal sulfides of the Sulfide Zone. Note that sulfides are partially replaced by magnetite with minor remobilization along fractures to host

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silicates D) Photomicrograph of pyrrhotite and pentlandite, with minor secondary pyrite. Note the sulfide intergrowth with silicate lamellae. E) Photomicrograph of chalcopyrite crystals at the contact between pyrrhotite and pentlandite. F) Photomicrograph of intergrowth between thin chalcopyrite lamellae and pentlandite. . G) Typical core sample of harzburgite from the Transition Zone. The harzburgite consists of cumulus olivine and intercumulus orthopyroxene and plagioclase. This rock has high PGE contents (around 2 ppm ΣPGE) and no visible sulfides. H) Photomicrograph of orthopyroxenite with interstitial plagioclase. Note that the minerals are partly replaced, but the magmatic texture is well preserved. Cpy: Chalcopyrite; Mt: Magnetite; Ol: olivine; Opx: orthopyroxene; Pn: Pentlandite; Plg: Plagioclase; Py: Pyrite; Po: Pyrrhotite. Fig. 5. Pie charts summarizing the proportion of each PGM and PMM within the (A) Sulfide Zone and (B) low-S-high-Pt-Pd zones; and textural association of these minerals within the (C) Sulfide Zone and (D) low-S-high-Pt-Pd zones of the Luanga Complex. Fig. 6. Backscattered images of PGM in rocks from the Sulfide Zone (A-D), and low-Shigh-Pt-Pd zones (E-H) of the Luanga Complex. A) Grain of kotulskite [Pd(Te,Bi)] included in pentlandite. B) Grain of palarstanide [Pd5(Sn,As)2] at the contant between pentlandite and amphibole. Note the intergrowth between pentlandite and amphibole. C) Grains of sperrylite (PtAs2), paolovite (Pd2Sn) and composite PGM included in orthopyroxene. D) Detail of composite PGM grain indicated in (C), comprising arsenopalladinite [Pd8(As,Sb)8], altaite (PbTe) and native gold grains. E) Grain of sperrylite (PtAs2) at the contact between pentlandite and amphibole. F) Elongated grain of arsenopalladinite [Pd8(As,Sb)8] within amphibole cleavage. G) Grains of hollingworthite [(Rh,Pt,Pd)AsS] included in amphibole. H) Grains of sperrylite (PtAs2) at the contact between magnetite and chlorite. Amph: amphibole; Chl: chlorite; Mt: Magnetite; Opx: orthopyroxene; Pn: Pentlandite. Fig. 7. Plot of PGE versus S contents for samples with S and PGE values higher than 500 ppb and 0.01 wt.%, respectively. The samples split into three groups: i. Sulfide Zone, ii. low-S-high-Pt-Pd Zone and iii. remobilized sulfides. Fig. 8. LUFD-224 drill core log and its MgO, Al2O3, Ni, Pt, Pd and S assay results and Cu/Pd ratios. The thin dashed black line indicates the lower limit of the weathering profile, while the dashed gray line indicates the contact between the Transition and

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Mafic Zones. The shadow gray rectangles indicate the Sulfide Zone and remobilized sulfides. See Figure 2 for the color code of the stratigraphic column. Fig. 9. Plots of Ni (A), Cu (C), Pd (E) and Ru (G) vs S, Ni vs Cu (B), Pt vs Pd (D), Pd vs Ru (F) and Ru vs Ir (H) for sulfide-bearing samples from the drill core LUFD-224. Trend lines correspond to the linear correlation for samples of the Sulfide Zone. The equation and r² values for the linear correlations are indicated for reference. The metal tenors indicated in each plot are estimated by linear extrapolation of metal data (Ni, Cu, Pt, Pd, Ru) against sulfur. The extrapolation assumed that 100 vol.% of sulfides would produce a rock with 35 wt.% S, which is approximately the expected grade for a rock containing 100 vol.% of magmatic sulfides (Barnes et al. 2011). Fig. 10. Primitive mantle-normalized chalcophile element profiles for representative samples from the Sulfide Zone. Average komatiite and MORB values are from Crocket (2002). Primitive mantle normalization values are from Sun and McDonough (1989). Fig. 11. LUFD-227 drill core log and its MgO, Al2O3, Ni, Pt, Pd and S assay results. Note that once the sequence of rocks is overturned the drill hole goes upward in the stratigraphic section of the complex. The high PGE and S values observed at the top of the drill hole (i.e., the lower portion of the stratigraphic column), consist of samples of the Sulfide Zone at the northern portion of the Luanga Complex. Fig. 12. Geochemical analyses of samples from a low-S-high-Pt-Pd zone. A) Plot of Pt vs Pd. B) Primitive mantle-normalized chalcophile element profiles and average Komatiite and MORB values from Crocket (2002). Primitive mantle normalization values are from Sun and McDonough (1989). Fig. 13. Relation of the δ34S data for magmatic Ni-Cu-PGE deposits worldwide. The two black dashed lines indicate the mantle-derivered sulfur interval. References Noril’sk, Duluth, Voisey’s Bay, Jinchuan and Nebo-Babel: Seat et al. (2009) and references therein; Santa Rita: Lazarin (2011). Fig. 14. Schematic model illustrating the formation of different styles of PGE mineralization throughout the Luanga Complex. See text for explanation. UZ: Ultramafic Zone; TZ: Transition Zone; MZ: Mafic Zone.

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Table captions Table 1. Sulfur isotopic data of samples from Sulfide Zone and remobilized sulfides of the Luanga Complex. Cpy: Chalcopyrite; Pn: Pentlandite; Po: Pyrrhotite. Table 2. Characteristics of selected sulfide-reef PGE deposits.

Electronic Supplementary Materials (ESM) Table 1 - Composition of platinum-group minerals found in the Sulfide and Low-S high-Pt-Pd zones at the Luanga Complex. Table 2 - Complete dataset for drill hole LUFD-224. Table 3 - Complete dataset for drill hole LUFD-227. TABLE 2. CHARACTERISTICS OF SELECTED SULFIDE-REEF PGE DEPOSITS. Stratabound Zone Merensky Reef JM - Reef Main Sulfide Zone

Host Intrusion Bushveld Complex RSA Stillwater Complex USA Great Dyke Zimbabwe

Intrusion Thickness (km)

Intrusion Dimension (km)

7.0

350-250

5.5

42-10

3.5

550-11

Reef Type Unzoned Sulfide-Reef Unzoned Sulfide-Reef Zoned SulfideReef

Reef Thickness (m)

Resources (Mt)

1-3

4988

1-2

154

1-5

2574

Munni Munni

Munni Munni Complex Australia

4.9

25-10

Zoned SulfideReef

5-15

24

Platinova

Skaergaard Intrusion Greenland

3.5

11-8

Zoned SulfideReef

~ 60 (10 zones)

23

Sulfide Zone

Luanga Complex Brazil

3.5

6-3.5

Unzoned Sulfide-Reef

10-50

142

References: 1 - Green and Peck (2005), 2 - Eckstrand (2005), 3 - Naldrett (2004), 4 - Hoatson and Keays (1989), 5 - Holwell and Keays (2014).

Highlights 

The Luanga deposit hosts the largest PGE deposit in South America (142 Mt at 1.24 ppm Pt+Pd+Au and 0.11% Ni).



The Luanga Deposit is part of a cluster of PGE-bearing mafic-ultramafic intrusions located at the eastern portion of the Carajás Mineral Province.

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

Two distinct styles of PGE mineralization occur in the Luanga Complex, referred to as Sulfide Zone and low-S-high-Pt-Pd zones.



Textural, mineralogical and geochemical differences between Sulfide Zone and low-S-high-Pt-Pd zones support that different geological processes took place during their formation.

B

550000

500000

650000

600000

N Fau

Tap i

eF

aul

t

Cu-Au Salobo

Au-Cu Breves

Au-Pd - Serra Pelada

2

PGE Luanga

Cu-Au - Igarapé Bahia/Alemão

Fe - Serra Norte

Parauapebas

Mn Azul

Car

ajas

9300000

1

Fau

lt

9300000

9350000

rap

9350000

lt

rdo

a Ric

3 Ni Puma

Fe - Serra Sul

7

Cu-Au Sossego

Ni Onça

Cu-Au Cristalino

4

Ni Vermelho

Canaan dos Carajas

Se

5

Tucumã

rin

ga

9250000

9250000

6

Água Azul do Norte

Fa

ul

t

Sapucaia

Xinguara 0 550000

500000

Legend

Archean

N

60ºW 80ºW

AM SL

40ºW 0º

Águas Claras Formation: sedimentary rocks Mafic-Ultramafic Layered Intrusions

Carajás Domain

30 km

20 650000

600000

A Araguaia Belt (Neoproterozoic) Anorogenic Granites (Paleoproterozoic)

10

AM

Grão Para Group: BIFs

B T

Itacaiúnas Supergroup (e.g. Grão Pará Group)

SF M

Syn-Orogenic Granites

20ºS

Piun Granulite Complex Xingu Complex

Rio Maria Domain

Undifferentiated TTG and Granitic Rocks Andorinhas Supergroup

City/Town

Mafic - Ultramafic Intrusions 5 - Búzios 1 - Luanga 2 - Lago Grande 6 - Onça 3 - Santa Inês 7 - Puma 4 - Vermelho

Lineament

Cratons 40ºS 60ºW

Sedimentary cover Andean chain Proterozoic Fold Belts

A

656000

658000

662000 9344000

9344000

660000

70°

80°

9342000

9342000

LUFD-227

75° 75°

LUFD-105 LUFD-079 LUFD-078 LUFD-077 LUFD-071 LUFD-069 LUFD-224

9340000

1000

500

0

meters

Legend PGE mineralization

Dolerite

Drill hole

Granitic rocks

Strike and dip

Luanga Layered Intrusion

Norite

Grão Pará Group

Harzburgite

Xingu Complex

9338000

Orthopyroxenite Peridotite 656000

B

658000

Ultramafic 1 07 Zone 69 0 D-

Transition Zone

Mafic Zone

9 -07

5

-10

D UF

L

FD

LU

8 -07

FD

LU

7 -07

FD

LU

[email protected] PGE [email protected] PGE

Legend Norite Harzburgite Orthopyroxenite Perido te Sulfide-related PGE Silicate-related PGE Drill hole

[email protected] PGE

FD

LU

[email protected] PGE

[email protected] PGE [email protected] PGE

-

F

LU

[email protected] PGE

[email protected] PGE

? ?

0

? 250 meters

9340000

N

B

A Orthopyroxenite

Harzburgite

Plg

Opx

Plg

Ol

Opx Ol

Opx

C

D

Opx Plg Ol

Opx

150 µm

E

500 µm

F

Ol

Plg Opx

Opx

G

H Altered orthopyroxene

Altered olivine

Adcumulate norite

300 µm

Chromitite layers

A

B Po

Sulfide

Opx

Pn

Cpy 50 µm

C

D

Pn

Mt

Cpy Py

Po Pn

Po

50 µm

E

50 µm

F

Cpy

Po Pn

Pn

Cpy

Po 50 µm

50 µm

H

G

Plg

Ol Plg Opx

Opx

300 µm

A) Mineralogy - Sulfide Zone Pd-Sn (4%)

B) Mineralogy - Low-S high-Pt-Pd Zone

Alloy (5%)

Rh-Pt-As-S (3%)

Alloy (5%)

Pd-As (5%)

Pd-As-Sb (4%)

Pb-Te (14%)

Pd-Pt-Te-Bi (53%)

Pd-As-Sb (17%)

Pd-Pt-Te-Bi (8%)

Pt-As (46%)

Pd-As-Sn (13%) Pd-As-Sn (16%)

Pt-As (7%)

C) Textural association- Sulfide Zone Silicate cleveage (7%)

Included in silicate (15%) Contact sulfide-silicate (23%)

Contact magnetite-silicate (3%)

D) Textural association- Low-S high-Pt-Pd Zone Contact magnetite-silicate (10%)

Silicate cleveage (22%)

Included in sulfide (3%)

Contact sulfide-silicate (14%)

Included in sulfide (52%) Included in silicate (51%)

A

B

Amph Pd-As-Sn

Pt-Pd-Bi-Te Opx Pn

Pn

D

C

Pb-Te Pt-Pd-Sn

Pt-As Opx

Pd-As-Sb

D

Au

Pn

F

E

Pn Amph

Pn Pt-Pd-As-Sb

Pt-As Amph

H

G

Chl

Pt-As

Amph Rh-Pt-As-S Mt Amph 10μm

25μm

8000

Total PGE (ppb)

7000 6000 Silicate-related PGE

5000 4000

Sulfide-related PGE

3000 2000 1000

Remobilized sulfides

0 0

0.2

0.4

0.6

S (wt. %)

0.8

1

1.2

LUFD-224

Al2O3 (wt. %)

MgO (wt. %)

Pt (ppm) Pd (ppm)

Ni (ppm)

S (wt. %)

162

Cu/Pd ratio

150

Remobilized sulfides

100

Transition Zone Sulfide Zone 50

Ultramafic Zone Weathering profile

10000

100

1

6

4

2

0

7500

5000

2500

0

1,5

1

0,5

0

35

25

15

15

10

5

0

0 (m)

A.

B.

7000

Ni tenor: 15% y=4286.7x r²=0.9535

6000 5000

7000 5000

Ni 4000 (ppm) 3000

Ni 4000 (ppm) 3000

2000

2000

1000

1000 0

0 0

C.

0.2

0.4

0.6 0.8 S (Wt. %)

1

0

1.2

D.

500 Cu tenor: 1.4% y=401.02x r²=0.9443

400 Cu (ppm)

400

500

4

5

400

500

Pt/Pd ratio: 0.52 r²=0.9885

Pt 1.5 (ppm) 1

100

0.5 0

0 0 5

0.2

0.4

0.6 0.8 S (Wt. %)

1

0

1.2

1

2

3 Pd (ppm)

F.

Pd tenor: 149.4ppm y=4.269x r²=0.8429

4

5000 4000

3

Pd (ppb)

2 1

3000 2000 1000

0

0

0

G.

200 300 Cu (ppm)

2

200

Pd (ppm)

100

3 2.5

300

E.

Ni/Cu ratio: 10.1 r²=0.8978

6000

120

0.2

0.4

0.6 S (Wt. %)

0.8

1

1.2

H.

Ru tenor: 2.95ppm y=84.255x r²=0.6867

100

0

100

200 300 Ru (ppb)

125 100

80

Ru (ppb)

Ru 60 (ppb) 40

75 50 25

20

0

0 0

0.2

0.4

0.6 S (Wt. %)

0.8

1

1.2

PGE-bearing sulfides

0

10

20

Hydrotermal sulfides

30 Ir (ppb)

40

50

60

Sulfide Zone

LUFD-227

Al2O3 (wt. %)

MgO (wt. %)

S (wt. %)

Pt (ppm) Pd (ppm)

Ni (ppm)

173

Silicate-related PGE

150

100

50

3

4

2

1

0

2000

1500 1000

500 0

1 0.75

0.5

0.25 0

35

25

15

8 6 4 2 0

40 (m)

A Pt/Pd ratio: 1.2 r²= 0.8426

B

Luanga

Santa Rita

Nebo-Babel

Jinchuan

Voisey’s Bay

Duluth Mantle-derived interval

Noril’sk -10 -8

-6

-4

-2

0

2 34

∂ S

4

6

8

10 12 14

Stage 1

Stage 2

Stage 3

Stage 4

-- -- -- -- -- -- -- --

-- -- -- -- -- -- -- --

-- -- -- -- -- -- -- --

-- -- -- -- -- -- -- --

-- -- -- -- -- -- -- -MZ

Low-S-highPt-Pd

Low-S-highPt-Pd Sulfide-related PGE (SZ)

Sulfide-related PGE (SZ)

Sulfur loss?

TZ

~ ~ ~ ~ ~~ ~ ~

Hydrothermal sulfides

UZ

-- -- -- -- -- -- -- --

-- -- -- -- -- -- -- --

-- -- -- -- -- -- -- --

Periodic magma influxes, and sulfide liquid saturation at higher statigraphic layers?

Post magmatic remobilization of previously formed sulfides, and local shear zones

-- -- -- -- -- -- -- --

Periodic magma Periodic magma influxes and sulfur influxes and sulfide liquid saturation followed by accumulation PGE accumulation

Ol cumulate

Opx cumulate

Residual magma

Ol + Opx cumulate

Opx + Plg cumulate Sulfide-related PGE

-- -- -- -- -- -- -- -Luanga Complex

~~~

---

Shear zones Host rocks

Silicate-related PGE

Stage 1

Stage 2

Stage 3

Stage 4

-- -- -- -- -- -- -- --

-- -- -- -- -- -- -- --

-- -- -- -- -- -- -- --

-- -- -- -- -- -- -- --

Low-S-highPt-Pd

Low-S-highPt-Pd Sulfide-related PGE (SZ)

Sulfide-related PGE (SZ)

-- -- -- -- -- -- -- --

~ ~ ~ ~ ~~ ~ ~

Hydrothermal sulfides

-- -- -- -- -- -- -- --

-- -- -- -- -- -- -- --

Periodic magma influxes, and sulfide liquid saturation at higher statigraphic layers?

Post magmatic remobilization of previously formed sulfides, and local shear zones

-- -- -- -- -- -- -- --

Periodic magma Periodic magma influxes and sulfur influxes and sulfide liquid saturation followed by accumulation PGE accumulation

Sulfur loss?

Ol cumulate

Opx cumulate

Residual magma

Ol + Opx cumulate

Opx + Plg cumulate Sulfide-related PGE

~~~

---

Shear zones Host rocks

Silicate-related PGE