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The Vermelho lateritic nickel-cobalt deposits are located 3 km WNW to NNW of the town of Canaã dos Carajás and 45 km south of Parauapebas in the southern part of the Carajás Mineral Province of Para State in northern Brazil, ~70 km south of the Serra Norte iron ore mines and 15 to 20 km SE of the Sossego Copper deposit (#Location: V2 - 6° 29' 20"S, 49° 53' 38"W).
For an overview of the Carajás Mineral Province see the Carajás IOCG Province record. Figure 3 in that record illustrates the geology and structure of the province, with Vermelho being located in the ultramafic-gabbroic intrusion shown to the SE of Sossego.
The mafic-ultramafic intrusive bodies that underlie and are the source of the lateritic mineralisation mainly intrude the 2.8 Ga Xingu Complex gneisses and migmatites, as well as the less extensive east-west trending orthogranulites of the 3.0 Ga Pium Complex and the 2.75 Ga Plaque Suite of the Rio Maria granitoids.
All of these rocks are part of the southern half of the Archaean Amazon craton, South of the Amazon Basin. The Xingu Complex is interpreted to represent highly metamorphosed and reactivated rocks of the Rio Maria granite-greenstone terrane. Two main tectonic blocks are recognised in the southern Amazon Craton. The 'southern block' is occupied by the Rio Maria terrane, composed of the Andorinhas Supergroup greenstones and the Rio Maria, Mogno and Parazonia granitoids which grade north into the undifferentiated Xingu Complex metamorphics. The WNW trending 'northern block' (or Itacaiunas Belt) is composed of the 2.75 Ga volcano-sedimentary rocks of the Itacaiunas Supergroup (of the Carajás Basin) and the overlying platformal sandstones and siltstones of the 2.0 to 1.9 Ga Rio Fresco Group, both of which are intruded by anorogenic granites. The Itacaiunas Supergroup unconformably overlies undifferentiated metamorphic rocks equated with the Xingu Complex. Successive Archaean to Paleoproterozoic mafic magmatic events are represented in the region, including the Vermelho ultramafic suite which parallel a major NE-SW set of faults cutting the Xingu Complex.
The source intrusions of the lateritic nickel cap belong to the Vermelho layered intrusion, which in turn, belongs to the Cateté Intrusive Suite, which are anorogenic bodies, intrusive into the Xingu Complex migmatites and granite-gneisses, and have been variously dated at 2766 ±6 Ma (Lafon et al., 2000) to 2.4 Ga (Vale internal report, quoted by Finch et al., 2019). This intrusive suite forms a generally east-west belt developed along the southern margin of the Carajás Mineral Province. They have not been deformed or metamorphosed and their intrusion is related to distensional Neoarchaean to Palaeoproterozoic events that formed other intrusive bodies, including those at Serra da OnÇa and Serra do Puma, 140 km to the west.
The Vermelho ultramafic suite is composed of a string of serpentinised dunites, bronzites, peridotites, pyroxenites, norites and gabbros, two of which, Vermelho 1 and 2 (V1 and V2) that are composed of serpentinised dunite and peridotite, and underlie the corresponding Vermelho nickel laterite deposit. The intruded lithologies surrounding V1 and V2 comprise granite gneiss, quartz-diorite and amphibolites. In more detail, the ultramafic bodies are erosional relicts of the upper sheet of a three-layer intrusion represented, from bottom to top, by
• a mafic zone - composed of very heterogeneous silica-rich lithotypes, mainly gabbros, gabbro-norites and norites and occurs in the northern, southern and central massifs. The gabbros are of intermediate composition with interstitial quartz and zircon. Lenticular pyroxenite intercalations are common within the serpentinised sections of the zone. Generally, the mafic rocks correspond to zones of low relief;
• a pyroxenitic zone which is ~50 m thick, and comprises orthopyroxenites and layers of cumulate chromitite. Locally, the primary mineralogy is well preserved, with localised transformations to talc, serpentine, magnetite and carbonate. Massive cumulate chromite exhibits adcumulated texture. Chromitites are 1 to 10 cm thick and occur as massive layers of magnetic Fe-chromite, with preserved primary textures, but with no Precious Group Metals; and
• a peridotitic zone , comprising ~150 m of serpentinites after dunites and harzburgites, in which the primary rock textures are well preserved. Dunites have adcumulate textures with cumulate olivine, whilst harzburgites have mesocumulate textures with olivine cumulate and orthopyroxene intercumulus. The fine to medium granulated serpentinite of this zone is a product of hypogene alteration of the dunites and peridotites, and forms a dark green to black rock. The contact between the pyroxenitic and overlying peridotitic zones has a consistent east-west strike, dipping gently to the north.
Dolerite dykes cut through the whole sequence, especially at V1.
The superposition of the Vermelho layered zones, where the primitive ultramafic cumulates, namely the dunites and harzburgites, are sequentially situated below the orthopyroxenites and mafic cumulates, indicating the rocks have become progressively more primitive from bottom to top. This may be explained by either: i). the tectonic inversion of the stratigraphy, which is unlikely given the apparent lack of tectonic deformation, or ii). that the complex represent progressive injection from different levels in another, larger, progressively differentiating magma chamber.
The complex has undergone hydration as the magmatic chamber aged, with dunites and peridotites being strongly serpentinised, whilst pyroxenites are amphibolitised. Silicification, which is the starting point of the weathering processes, supports and preserves the topographic relief.
The V1 and V2 deposits occur on flat lying, mesa-like topographical highs, with V1 reaching altitudes of around 500 m, standing out from the adjacent flat terrain of the Xingu Complex at an elevation of 175 m, whilst the V2 body reaches a height of 450 m above sea level. V1 and V2 are both of the order of 3 km in length and 1200 to 1500 m in width and elongated east-west within the NE-SW trending composite intrusive that is ~10 km long by 2 km wide. Approximately 40% of the ultramafic bodies have been serpentinised forming zones that are 450 to 500 m wide in the cores of each of V1 and V2. A third ultramafic body Vermelho 3 (V3) is located southwest of V2 in the same trend.
Both the igneous and the tectonic foliation are parallel to sub-parallel, and are horizontal to sub-horizontal, representing only mildly undulating planes. This supports the conclusion that the deposit have not been subjected to intense deformation. Joints and fractures are the most significant structures in V1 and V2. Two main groups of joints and fractures have been identified, and are interpreted as possible conjugate pairs, with orthogonal NE/NW and north-south/east-west directions. These structural features are interpreted to have controlled the evolution of weathering and development of supergene mineralisation. The horizontal to sub-horizontal foliation planes in association with the vertical joints and fractures acted as conduits for water migration during weathering and assisted the leaching processes, as well as the precipitation of silica and other elements responsible for the formation of the boxwork texture of the silicified saprolite ore.
CVRD/Vale subdivided the lateritic profile as follows, from the top to base:
i). Lateritic soil, which is a few cm thick, composed of clays and lateritic fragments, ferruginous pisolites, magnetite, weathered bedrock, etc.;
ii). Laterite, which is 0.3 to 0.5 m thick of clay and red-brown ferruginous material;
iii). Saprolite, which is around 2.5 m thick, composed of reddish brown to dark yellow clays retaining the texture of the original ultramafic protolith, divided into an upper half described as ferruginous saprolite and the lower or main saprolite;
iv). Saprolitised serpentinite, which is around 0.5 m thick and made up of partially saprolitised blocks of serpentinite separated by fracture controlled saprolitisation;
iv). Serpentinite, fresh bedrock from a depth of around 3.5 to 4 m.
v). Silicate Zones, which cut the saprolite occurring as irregular veins exhibiting boxwork textures.
Horizonte Minerals have since re-evaluated the profile with different sub-divisions. They recognised that the deposit had been influenced by a two stage weathering evolution, which resulted in the truncation of lateritic evolution and the resumption of the process following a climate change event. The formation of an initial lateritic soil was followed by significant silicification, generating a thick layer of chalcedony, erosion of the primary lateritic package and generation of a new lateritic profile beneath the silicified level. Thus, the profile represents interdigitation of lateritic units with significant thickness variations. These weathering products are described as follow, from top to bottom:
• Soil to ferricrete, which is the overburden, and comprises a fine ferruginous soil with organic residues, and ferruginous concretions. It is up to a metre thick and is relatively enriched in Fe2O3 and Al2O3. This ferruginous carapace is generally underlain by 2 to 3 m of ferruginous limonite which lacks ferruginous concretions.
• Silica horizon, composed of a thick, averaging 30 m, very resistant massive silica/chalcedony crust, with SiO2 contents commonly >65%, sometimes reaching 90%. This represents intense leaching, although not as intense as that of the 'soil and ferricrete' layer.
• Silicified limonite layer, which averages 20 m in thickness and underlies the 'Silica horizon'. It contains varying proportions of oxides and hydroxides of iron and silica, with SiO2 ranging from 35 to 65%, and boxwork structures that are usually packed with Fe oxides and hydroxides. In V1, thick and continuous bands of sub-horizontal ferruginous limonite occur within the siliceous limonite, with grades that range from 0.6 to 1.5% Ni.
• The underlying ferruginous limonite layer is composed of fine grained and porous Fe oxides and hydroxides, including goethite, limonite and hematite, and occurs as discontinuous and irregular lenses that average 15 m in thickness within siliceous limonite below the massive silica units. As such there may be more than one layer of silicified limonite and ferruginised limonite within the profile. The Fe2O3 content of the ferruginous limonite is commonly >80%, while SiO2 is <35%. Nickel grades range from 0.6 to 1.5%.
• The saprolite layer, which averages 15 m in thickness and marks the transition from weathering to fresh bedrock. In general, its upper margin with siliceous limonite is transitional and strongly silicified over an interval of 2 to 3 m, whilst the contact between ferruginous limonite and saprolite can be either abrupt or transitional. It is characterised by the predominance of serpentinite and relict structures, with MgO >10%. The nickel grades are usually >1.5%, sometimes reaching 10% Ni.
Contacts between zones are commonly transitional, while other lithologies may be present within the profile in varying degrees, including weathered and semi-weathered serpentinites, fresh serpentinites, pyroxenitic and gabbroic saprolites, and fresh gabbros and pyroxenites.
Two types of nickeliferous laterite are recognised,
i). Garnieritic or silicate ore found in the lower or main sparolite zone and saprolitised serpentinite at the base of the weathering profile. This style has a high Ni content averaging 1.8% NiO, reaching as much as 2% Ni, but a low Fe and high MgO content. In 1988, half the delineated reserve was of this type, averaging 1.80% Ni, 20.51% MgO, 22.48% Fe2O3, 1.10 Fe:MgO ratio and 80 ppm Cu. This zone is largely composed of serpentine, chlorite and spinels, with only minor quartz and goethite. Serpentine and chlorite are the main nickel-bearing minerals, with nickel being about equally distributed between the two phases (2% to 3% NiO).
ii). Limonitic or oxidised ore which is found towards the top of the weathering profile. It has a lower Ni content of around 1.1% (averaging 1.2% NiO), high Fe and low MgO content. In 1988, the other half of the delineated reserve was of this type, averaging 1.21% Ni, 2.71% MgO, 48.93% Fe2O3, 18.06 Fe:MgO ratio and 211 ppm Cu. The oxidised ore is predominantly composed of goethite, but also contains chlorite, spinels and silica. Nickel is highly concentrated in chlorite (average 12% NiO), whereas in goethite NiO content range from 0.9 to 1.7%. Consequently, the presence of chlorite, even in minor quantities, is important in elevating the grade of the oxide ore. Locally, higher grades of mineralisation can also be a result of the presence of nickeliferous smectites.
There is no significant development of an enriched transition mineralisation type between the oxide and silicate horizons. There is a transitional saprolitic zone at the base of the mineralised profile, where nickel grades usually range from 0.25 to 0.5%. Serpentinite blocks, strongly silicified bands, mafic or pyroxenitic dykes, and ferruginous concretions that are common at the top of the section, are all responsible for barren zones within the profile.
Beneficiation through the removal of quartz is comparatively more efficient when treating the siliceous limonite ore. This is due to the difference in grain size between the abundant <50 µm quartz/chalcedony and the nickel bearing minerals. However, the separation of quartz and Mg silicates in saprolite ores appears more complex as both mineral species are found in the same two particle size fractions, causing loss of Ni to the tailings and increase of silica in the leach feed. This may be related to textural aspects, such as high particle size, quartz inclusion and low porosity, due to the lower degree of weathering of saprolite. In addition, Ni appears more dispersed, as it occurs at lower levels in Mg silicates of this unit.
Following discovery, CVRD which became Vale in 2007, undertook exploratory and delineation drilling between 1974 and 2004, followed by a Feasibility Study, including drilling and pitting programs totalling 152 000 m, batch and full-scale pilot testwork, in addition to detailed engineering studies, with a positive development decision in 2005. However, the Project was subsequently placed on hold following Vale's purchase of Canadian nickel miner INCO in late 2005. The deposit was acquired from Vale, by Horizonte Minerals plc in late 2017.
Reserves quoted in 1988 (Bernardelli and Alves) were: 43.97 Mt @ 1.50% Ni, 11.49% MgO, 35.88% Fe2O3, 3.12 Fe:MgO ratio and 146 ppm Cu.
Proven + probable reserves quoted in 2007 (CVRD/Vale website) were: 290 Mt @ 0.8% Ni.
The scheduled annual production rate of CVRD/Vale was estimated to be 47 000 t of contained metallic nickel and 280 t of metallic cobalt.
In 2018, Horizonte Minerals released NI 43-101 compliant Mineral Resource estimates as follows at a 0.70% Ni equiv. cut-off grade (Horizonte Minerals release to the AIM and TSX):
Measured + Indicated Resource - 145.7 Mt @ 1.05% Ni, 0.05% Co, 30.9% Fe2O3, 41.3% SiO2, 11.2% MgO.
Inferred Resource - 3.1 Mt @ 0.96% Ni, 0.05% Co, 24.0% Fe2O3, 42.2% SiO2, 15.5% MgO.
Open Pit Ore Reserves (October, 2018) at an ~0.5% Ni cut-off - 141.3 Mt @ 0.91% Ni, 0.052% Co, 23.1% Fe, 0.79% Al2, 3.81% Mg.
At full production capacity, Horizonte Minerals expects (in 2021) the Vermalho Project to produce an average of 25 000 tonnes of nickel and 1250 t of cobalt per annum, utilising the High-Pressure Acid Leach process, with a 38 year initial projected mine life .
The information in this summary is largely drawn from: Finch, A., Ross, A.F. and Walsh, S., 2019 - Vermelho Project, Pará State, Brazil; An NI 43-101 Technical Report prepared for Horizonte Minerals Plc by Snowden Mining Industry Consultants, 260p.
The most recent source geological information used to prepare this summary was dated: 2019.
Record last updated: 13/12/2021
This description is a summary from published sources, the chief of which are listed below.
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