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Araguaia Nickel South, Araguaia Nickel North |
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Para, Brazil |
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Ni Co
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Araguaia Nickel South and Araguaia Nickel North lateritic nickel deposits are located 25 and 80 km north of Conceição do Araguaia respectively in southeastern Pará State, near the eastern border with the state of Tocantins in Brazil. Araguaia Nickel North is ~ 110 km SSE of Parauapebas in the Carajás Mineral Province, but is east of that province in the adjoining Araguaia Belt. The two centres each represent the amalgamation of a number of separate projects in four non-contiguous blocks, into one operation.
(#Location: Araguaia Nickel South - 7 ° 58' 49"S, 49° 25' 11"W).
Araguaia Nickel South comprises seven deposits: Pequizeiro, Baiao, Pequizeiro West, Jacutinga, Vila Oito East, Vila Oito West and Vila Oito, while Araguaia Nickel North hosts the Vale do Sonhos deposit. Discovery of these deposits and their eventual amalgamation into a single project were the culmination of exploration undertaken in the Araguaia Nickel North from as early as 2003 by Falconbridge Brazil Ltda (later to become part of Xstrata and then Glencore), with Vale do Sonhos being discovered in 2004. At Araguaia Nickel South, exploration was initially by a company known as Lara to 2006, who were in joint venture with Teck until November 2008. During this period nickel laterite mineralisation was discovered at Vila Oito and Floresta, and at other locations. Horizonte Minerals, who had been undertaking exploration in the area, entered into an agreement to acquire Teck Cominco Brasil S.A. which owned 100% of Teck's Araguaia project. In July 2011, in an agreement with Lara Exploration Ltd, Horizonte Minerals acquired 100% of the licences containing the Vila Oito West and Floresta discoveries. In September 2015, Horizonte Minerals concluded an agreement with Glencore over the licence area, containing the Vale do Sonhos deposit, and has been the sole project operator since 2015.
Regional Setting
The Araguaia Fold Belt represents the northern extension of the Brasilia Belt. It is developed along the eastern margin of the Amazonian Craton and lies to the west of the western edge of the Parnaíba cratonic block and the São Francisco Craton. It trends north-south, is >1000 km long and is related to the collision, and other complex interactions, between the Amazonia and the then amalgamated São Francisco, Congo and West African Continents (see Fig 1 in the Carajás IOCG Province record). It is exposed over a width of <150 km, bounded to the east by sedimentary cover rocks of the Palaeozoic Parnaíba Basin. The north-south trending Brasilia and Araguaia fold belts are laterally separated by the ~800 km long Goiás Massif, which also partially separates those same belts from the Paraguaia Fold Belt to the west that follows the southern margin of the Amazonian Craton. Those three folds belts together form the Tocantins Province, centred on the Goiás Massif/Magmatic Arc. That massif is a complex 800 x 350 to 400 km block developed between the Amazonia and São Francisco cratons that is well endowed with a range of copper, gold and nickel deposits. For more detail see the Araguaia Fold Belt, Tocantins Province and Goiás Massif links and geological images at the top of the Atlantic Shield - Tectonics, Geology, Metallogeny record.
Within the project area, the country rocks principally belong to the Tocantins Group, intruded by mafic and ultramafic bodies. The mafic-ultramafic bodies and numerous NW-SE to north-south trending lineaments are evident in magnetic data and outcrop. These mafic-ultramafic bodies are often bounded by a siliceous breccia. Masses of pillow lava and other volcanic material have also been detected, and the area is cut by numerous mafic dykes.
Araguaia Nickel South
The Araguaia Nickel South Project area embraces metasedimentary sequences of the Tocantins Group that cover the vast majority of the surrounding area, intruded by elongated mafic and ultramafic complexes. It is characterised by extensive plateaux that vary from a few hundred square metres to several square kilometres in area, and are generally capped by a hard iron-rich duricrust that is occasionally silicified and frequently developed over mafic and ultramafic bodies. These bodies and numerous NW-SE to north-south trending lineaments are evident in both magnetic data and outcrop, and are frequently bounded by a siliceous breccia. Pillow lava and other volcanic material are also evident, and the area is cut by numerous mafic dykes.
A distinctive lateritic profile is developed over ultramafic and mafic rocks at each of the mineralised sites, although the thickness and extent of each facies varies from location to location. The profile can be split into the following main facies, as well as numerous sub-facies.
• Soil horizon - a thin, 1.0 to 1.6 m thick, dark brown layer that is rich in humus and comprises the uppermost layer that is absent in many places. It includes occasional ironstones as well as organic material was derived from the breakdown of plants and a networks of fine plant roots. It is characterised by low nickel and magnesium oxide contents.
• Ferricrete horizon, that is present in virtually all locations, and varies from being absent, to up to ~15 m, but normally 2 to 3 m in thickness. It is hard, cohesive, and red to yellow-brown, with high hematite/goethite contents and often contains magnetite and occasional chromite. It occurs as both an unconsolidated horizon with ubiquitous haematitic pisolites, and as a cemented goethite rich horizon containing distinctive worm burrows.
• Limonite horizon, which thicknesses that range from 7.5 to 11.6 m up to maxima that vary from 23.9 to 45 m. It is found immediately below the soil or ferricrete layer, and comprises deeply weathered material. An upper and lower part have been recognised, which can both be well developed; although in places only one may be present or occasionally neither. These are as follows:
- the upper part, sometimes referred to as 'red limonite', is a red-brown or more frequently, chocolate-brown clayey material with little internal structure other than layering. It consists entirely of fine-grained silt to clay fractions, predominantly composed of hydrated iron oxides;
- the lower part, sometimes called 'yellow limonite', is yellow-brown to orange, and is generally more compact than the red limonite. It rarely contains coarse fragments of weathered material.
The limonite facies laterite typically contains 0.78% Ni, 0.11% Co, 2.4% Cr2O3, <2% MgO, 36.5% Fe and 19.7% SiO2.
• Transitional horizon, which has three sub-facies:
- Upper transition facies - a dark red to brown-red, cohesive, soft, plastic and fictile material, with fine granulation. It can contain up to 15% disseminated green serpentine, which results in an increases the nickel content of the horizon. The presence of manganese oxide also corresponds to a considerable increases the cobalt and nickel content;
- Green transition facies, which predominately contains ~85 to 90% nontronite/kaolinite, and ~5% manganese minerals, and is characterised by the association of green and brown clayish material. Chlorite, vermiculite, asbolane (manganese oxide), and talc may also occur as >1% disseminations, whilst free silica can be found in the form of millimetre-sized veins or pockets;
- Brown transition facies, which is the most common transition facies, and is composed of ~40% nontronite/kaolinite, 30% manganese minerals and ~20% limonite/goethite, the latter being responsible for the brownish, clayey fraction.
The transition facies is thinner than the enclosing limonite and saprolite horizons above and below, and generally less continuous laterally. It typically contains 1.20% Ni, 0.05% Co, 11.7% MgO, 18.3% Fe and 44.3% SiO2.
• Saprolite horizon, which has similar average thicknesses to the Limonite facies, although the total thicknesses are highly variable. It also has three sub-facies, as follows:
- Earthy saprolite, which is pervasively altered and composed of hydrated iron oxides, serpentine and clays, with minor quartz, olivine and chromite;
- Rocky saprolite, a hard, competent, dark green to greyish saprolite, composed of weathered peridotite with moderate saprolite alteration, mostly occurring along fractures;
- Silicified saprolite, characterised by a high silica content.
The earthy and rocky saprolite typically contains 1.29% to 0.92% Ni, 0.04% to 0.03% Co, 18.3% to 27.0% MgO, 14.8% to 9.7% Fe, and 41.8% to 42.2% SiO2.
• Bedrock, which is generally dark green to dark brown, and comprises massive to fractured, variously serpentinised, peridotite, whose interface with the weathered profile can be very irregular and undulating. Bedrock is usually only exposed along rivers beds and creeks and in major landslides.
Mineralogical studies (July 2011, SGS Mineral Services, Lakefield, Ontario, Canada) indicated mineralogical distribution and the percentage of the contained nickel in those minerals for the principal facies is as follows:
• Limonite horizon - limonite/goethite (74%), nontronite/kaolinite (2%) and Mn minerals (23%);
• Saprolite horizon - Serpentine (66%), limonite/goethite (11%), nontronite/kaolinite (8%), chlorite (4%) and Mn minerals (11%);
• Green transition facies - nontronite/kaolinite (89%), chlorite (4%) and Mn minerals (7%);
• Brown transition facies - nontronite/kaolinite (42%), limonite/goethite layer (23%), chlorite (4%) and Mn minerals (29%).
The individual deposit clusters within the Araguaia Nickel South group may be summarised as follows:
Jacutinga, Vila Oito West, Vila Oito and Vila Oito East
This cluster is distributed over an area of 10 km2. Only Jacutinga and Vila Oito West are exposed, whilst the other two are located in flat areas with no discernible outcrop, and their connection is unconfirmed. The geology of the mapped deposits show NW-SE, NE-SW and north-south and east-west trending silica filled fault zones separating ultramafic and sedimentary bedrock rock, with exposures of massive silica and silicified sedimentary rocks. Duricrust covers both sediment and ultramafic rocks ove a large part of this area.
Pequizeiro and Pequizeiro West
The Pequizeiro group comprises the small, ~1 km long, NW-SE trending Pequizeiro East to the NE, and three semi-contiguous, NW-SE trending mineralised bodies, Pequizeiro Northwest, Pequizeiro West and Pequizeiro covering an area of ~3 km2 and length of ~10 km. The latter three are enclosed by steeply dipping fault zones along their north-eastern and south-western margins. These three bodies comprise the same style of mineralisation and characteristics and are interpreted as one body of mineralisation that has been partitioned by the major NW-SE trending fault system and later stage NE trending cross-faults. The sedimentary rocks are intensely folded and silicified at the ultramafic contact where massive silica is absent.
Baião
Three separate ultramafic bodies have been mapped in the Baião are, the largest of which is Baião. A steeply dipping, silica filled fault zone up to 250 m wide is located along a NNW-SSE trending ridge in the northeastern part of Baião. A 200 m wide outcrop of fresh ultramafic lies within this structure, bounded by two steep NE-SW trending cross-faults. The western margin of the Baião intrusive is marked by a zone of massive silica and silicified sedimentary rock that is almost 1 km wide. Steeply dipping structures trend NNE-SSW and NE-SW, and are dislocated by cross-faults.
Araguaia Nickel North
Within the Araguaia Nickel North area of various metasediments that cover the bulk of the surrounding area, enclosing extensive mafic and ultramafic plateaux, varying in size from a few hundred square metres to several square kilometres. The latter have been identified in both magnetic data and outcrop observation, and are generally capped with a hard iron rich duricrust that is occasionally silicified and are often bounded by a siliceous breccia. Pillow lava and other volcanic material has also been encountered, and the area is cut by numerous mafic dykes. Magnetic data has also revealed numerous NW-SE to north-south trending lineaments, interpreted as either thrust fronts with a west vergence, and/or later sub-vertical faults.
The ultramafic rocks are largely serpentinised peridotites, with common mylonitic serpentinites, tourmalinites and cherts. Silexite crusts are common, protecting the underlying ultramafic bodies from erosion. Dolerite and gabbro dykes are also frequent. Vale dos Sonhos, the principal deposit at Araguaia Nickel North, was discovered by the recognition of limonite crusts at surface, which were identified by Xstrata geologists as being related to lateritisation of ultramafic rocks. The deposit is a NNW-SSE elongated body that is nearly 4 km long, with average width of 800 m, located in a relatively flat area, although altitudes range from 50 m below to 160 m above the mean elevation.
A very similar lateritic profile has been developed at Araguaia Nickel North to that at Araguaia Nickel South, as follows, from the surface down to bedrock.
• Soil horizon, which averages ~0.2 m in thickness, and is composed of organic and disaggregated material that is usually magnetic. It is characterised by high iron and low nickel and magnesium oxide contents.
• Ferricrete horizon, which lies immediately below the soil horizon and is dark brown to red. It is composed of aggregated iron oxy-hydroxide pisolites that are often very hard and porous.
• Limonite horizon, which underlies the soil and ferricrete horizons, and is composed of five distinct sub-facies:
- Dark brown to red pisolite sub-facies, comprising up to 70% loose pisolites, plus ferricrete fragments and up to 30% fine iron clay.
- Red limonite sub-facies, which is dark red-brown with a plastic texture, composed mainly of iron oxides and iron clays. White and black wisps and crusts of magnesium-manganese-cobalt hydroxides can also been found. This subfacies may be underlain by a 'yellow limonite', as described in the Araguaia Nickel South deposits above.
- Red tapa sub-facies, which is red-brown, also with a plastic texture, containing <30% smectitic clays or serpentine in a matrix of iron oxides. It occurs as centimetre scale bands and laminations.
- Orange tapa sub-facies, which is orange-brown due to the dominance of goethite over hematite. It contains <30% smectitic clays or serpentine, has a weakly plastic texture, and is frequently lightly banded.
• Upper saprolite horizon, composed of four sub-facies:
- Green tapa 1 sub-facies, which is hard and composed of up to 90% smectitic clays, and in which the original rock texture is absent. It is green to dark green with minor brown clay bands containing goethite and manganese oxy-hydroxides, and silica veinlets.
- Green tapa 2 sub-facies, which is green to brown, and is soft and plastic with 30 to 85% smectitic clay, 6 to 60% iron oxy-hydroxides and up to 2% disseminated manganese oxy-hydroxides. It is laminated but has no preserved protolith textures and contains.
- Transitional 1 sub-facies, which is orange to brown, soft, and composed of millimetre to centimetre sized granules of up to 30% green serpentine set in an iron oxy-hydroxide matrix, with traces of magnesium oxide and talc. Goethite dominates over hematite.
- Transitional 2 sub-facies, which is soft, weakly plastic and green to brown, composed of up to 30% millimetre to centimetre granules of green serpentine in a matrix of iron oxide.
• Lower saprolite horizon, composed of two facies:
- Green tapa 3 sub-facies, which is a light green and weakly plastic, containing up to 70% of serpentine granules with 5 to 10% talc, and traces of chlorite and manganese oxide.
- Saprock, predominantly composed of serpentine, but also has minor smectitic clay and talc. It is light green and friable with original rock textures preserved, with abundant amorphous silica and iron oxy-hydroxides.
• Silicified saprolite and fault zone, composed of:
- Talc, which is white to purple, soapy, soft but not plastic and is foliated in fault zones. This zone is very talc rich, with <5% serpentine and brown clay, and is free of silica and manganese oxy-hydroxides.
- Silicified saprolite and silcrete - that silicified saprolite sub-facies is pink to grey-green and hard, and is spatially associated with silcrete or silexite. Silification is associated with an increase in hardness and change in colour to pink.
• Bedrock, the following bedrock lithologies are recognised:
- Weathered harzburgite, composed of grey-green friable weathered rock with blocks of unweathered hard rock, orange filled fractures and manganese oxy-hydroxides;
- Harzburgite, a hard, grey-green and composed of millimetre to centimetre pseudomorphic crystals of bastite resulting from orthopyroxene weathering in a dark green to grey-green mass of serpentine. It is usually accompanied by veinlets and fractures filled by light green serpentine, talc and minor carbonate;
- Silexite, a competent purple, brown or red silica rich breccia of green magnetic material commonly with silica veinlets;
- Gabbronorite, which is brown with an ophitic texture, and weathers to be yellow and friable with distinct white plagioclase;
- Metasediments, light yellow to grey, soft with weak foliation and are frequently absent from the column.
Another facies that is present locally is mafic saprolite, which is yellow-brown and friable with poor plasticity with relict white plagioclase and an ophitic texture.
Mineralogical studies (SGS Lakefield, Canada, 2006) show that the mineralogy of composite mineralised samples is dominated by serpentines, with ~15% clays associated with the alteration of serpentine, iron-montmorillonites, chlorites, iron oxides and minor amounts of asbolane, quartz and talc. Higher oxide content in Vale dos Sonhos composite suggests that weathered limonitic and transitional facies dominate. With the exception of quartz and trace gibbsite, all other species identified in this study carry nickel. Sixteen nickel-bearing minerals were quantified, the richest of which are nickel-serpentine and two varieties of asbolane (manganese oxide), namely low manganese asbolane and low nickel-cobalt asbolane. These three species carry an average of 4.8, 12.0 and 3.5% nickel, although asbolane is only relatively minor. The bulk of nickel within Vale dos Sonhos is hosted by nickel-serpentine, chlorite, iron-montmorillonite, antigorite and oxide species. Nickel grade are slightly reduces in very coarse size fractions due to an increase in antigorite, and a corresponding decrease in other species such as chlorite and iron-montmorillonite. Antigorite carries an average of 0.95% Ni, whereas the chlorites and iron-montmorillonites have nickel grades between 1.4% Ni and 1.74% Ni.
The Vale dos Sonhos deposit is orientated NNW-SSE and is approximately 4 km long, with an average width of 800 m. It is bounded on the west by faults that dip between 30 and 60°E, while on its eastern margin it is enclosed by meta-sediments.
Mineral Resources and Ore Reserves
Snowden Consultants (2018) estimated the following Mineral Resources as of February 2017, for the combined Araguaia Nickel South and North deposit cluster that had been tested using a cut-off of 0.9% Ni:
Measured Resource
Limonite type - 1.232 Mt @ 1.20% Ni, 0.15% Co, 37.43% Fe, 2.00% MgO, 17.15% SiO2, 11.07% Al2O3, 2.98% Cr2O3;
Transition type - 6.645 Mt @ 1.75% Ni, 0.07% Co, 18.89% Fe, 10.20% MgO, 42.06% SiO2, 6.59% Al2O3, 1.29% Cr2O3;
Saprolite type - 10.291 Mt @ 1.27% Ni, 0.03% Co, 12.03% Fe, 24.08% MgO, 41.24% SiO2, 3.95% Al2O3, 0.87% Cr2O3;
Total Measured - 18.168 Mt @ 1.44% Ni, 0.05% Co, 16.26% Fe, 17.51% MgO, 39.91% SiO2, 5.40% Al2O3, 1.17% Cr2O3;
Indicated Resource
Limonite type - 19.244 Mt @ 1.12% Ni, 0.12% Co, 36.22% Fe, 2.40% MgO, 20.46% SiO2, 9.61% Al2O3, 2.65% Cr2O3;
Transition type - 30.917 Mt @ 1.42% Ni, 0.07% Co, 21.38% Fe, 11.26% MgO, 38.95% SiO2, 5.37% Al2O3, 1.51% Cr2O3;
Saprolite type - 51.008 Mt @ 1.18% Ni, 0.03% Co, 11.83% Fe, 25.79% MgO, 40.59% SiO2, 3.16% Al2O3, 0.85% Cr2O3;
Total Indicated - 101.169 Mt @ 1.25% Ni, 0.06% Co, 19.39% Fe, 16.90% MgO, 36.26% SiO2, 5.06% Al2O3, 1.39% Cr2O3;
TOTAL Measured + Indicated - 119.337 Mt @ 1.27% Ni, 0.06% Co, 18.91% Fe, 16.99% MgO, 36.81% SiO2, 5.11% Al2O3, 1.36% Cr2O3;
Inferred Resource
Limonite type - 2.751 Mt @ 1.08% Ni, 0.10% Co, 34.92% Fe, 3.04% MgO, 22.84% SiO2, 9.23% Al2O3, 2.50% Cr2O3;
Transition type - 4.771 Mt @ 1.30% Ni, 0.07% Co, 21.23% Fe, 11.04% MgO, 39.09% SiO2, 5.62% Al2O3, 1.40% Cr2O3;
Saprolite type - 5.398 Mt @ 1.15% Ni, 0.03% Co, 11.80% Fe, 24.36% MgO, 41.81% SiO2, 3.69% Al2O3, 0.82% Cr2O3;
Total Inferred - 12.920 Mt @ 1.19% Ni, 0.06% Co, 20.21% Fe, 14.90% MgO, 36.77% SiO2, 5.58% Al2O3, 1.39 Cr2O3;
NOTE: Bulk densities were Limonite - 1.37 to 1.39; Transition - 1.20 to 1.26; Saprolite - 1.31 to 1.40; Measured + Indicated and Inferred both 1.30 tonnes / cubic metre.
Proved + Probable Ore Reserves as of October 2018 (Horizonte Mineral website, viewed April 2023) at an average 1.03% Ni cut-off - depending on trucking distance to central treatment facility.
27.29 Mt @ 1.69% Ni, 17.15% Fe, 4.94% Al2O3, SiO2:MgO ratio - 2.52.
This summary is largely drawn from Blanchfield, F., Ross, A., Palmieri, M., Barcza, N.A., Haughton, D. and Kalanchey, R., 2018 - Horizonte Minerals Plc, Amended NI 43-101 Technical Report, Feasibility Study for the Araguaia Nickel Project, Federative Republic of Brazil; an NI 43-101 Technical Report prepared by Snowden Mining Industry Consultants for Horizonte Minerals Plc., 342p.
The most recent source geological information used to prepare this decription was dated: 2018.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
Araguaia Nickel South
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