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Onca and Puma |
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Para, Brazil |
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Ni
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Super Porphyry Cu and Au
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The Onça and Puma lateritic nickel deposits are located in the separate Serra da Onça and Serra do Puma Complexes that are located within the Carajá Mineral Province, ~150 km WSW of Parauapebas in the south-east of the state of Pará, Brazil (#Location: Serra do Puma - 6° 27' 48"S, 51° 4' 42"W; Serra da Onça - 6° 34' 9"S, 51° 10' 15"W).
The Serra da Onça and Serra do Puma layered mafic-ultramafic complexes belong to the Cateté Intrusive Suite, which are anorogenic bodies, intrusive into the 2.8 Ga 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 that is several hundred kilometres in length extending 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.
For an overview of the regional setting, the stratigraphic units mentioned below and a geological map (Fig. 3) showing the location of the deposit, see the Carajás IOCG Province record. See also the record for the Vermelho deposits that have a similar setting and character, 140 km to the east.
The Serra da Onça Complex, to the south, strikes east-west, with plan dimensions of ~20 x 2 to 3 km, whilst the Serra do Puma Complex to the north, has a width that varies up to 3 km and has a strike length of near 40 km that curves from east-west in the SW, to WSW-ENE in the east. At their closest, the western section of the latter is 10 km north of the Serra da Onça Complex.
The Serra do Puma Complex (Macambira and Ferreira Filho, 2002; Rosa, 2014) is located along the McCandless fault zone, and comprises an intrusion composed of ultramafic rocks to the NW, principally dunite, peridotite and pyroxenite, and mafic rocks, specifically leucogabbro and gabbro to the SE.
The Serra da Onça Complex (Ferreira Filho et al., 2007; Rosa, 2014) is located along the Canaã fault zone, and comprises ultramafic rocks to the north, predominantly dunite and pyroxenite, and mafic rocks to the south, mainly gabbronorite and norite. Magmatic layering in both complexes has a consistently moderate southerly dip. Pristine magmatic textures and minerals are largely preserved in both, although primary magmatic structures are disrupted and igneous minerals are extensively replaced within shear zones, particularly within the western portion of the Serra do Puma Complex where the broad Canaã and McCandless fault trends/zones intersect.
The lateritic weathering profiles at Onça and Puma are differentiated on the basis of the protolith mineralogy and the accumulation of quartz. The presence of significant chlorite and/or vermiculite in the serpentine protolith at Puma distinguishes it from Onça where the dominant underlying serpentinite is largely composed of serpentine and chromite. Both have a weathering profile composed of a lower saprolitic and upper limonitic zone, except where the latter has been eroded. Non-siliceous profiles comprise serpentinite and saprolite overlain by thin layers of limonite, and rarely by some form of ferricrete. Siliceous profiles are defined as those with >15% quartz as both siliceous saprolite and siliceous limonite. The limonite zones overlying the Onca and Puma saprolites are generally thin, discontinuous, and are composed of goethite, chromite, several manganese oxide phases and sporadic quartz.
At Puma, 'laterite' nickel mineralisation has been developed along an elongate ridge for some 23 km. The ridge has a northerly slope that ranges up to 30 to 45°, whilst its southerly slopes are at an angle of 10 to 15°. An important characteristic of the deposit is an extensive silica caps to the ridge, that is regarded as likely responsible for preserving the saprolitic ores from erosion. The profile at Puma comprises, from the top to base (de Freitas Silva and Dimitrakopoulos, 2016):
• Limonite zone, which is the uppermost horizon and has been completely oxidised by chemical weathering. Primary textures are absent, with iron-rich minerals increasing towards the top, becoming pisolitic. It has an upper red and lower yellow limonite interval, separated by a highly irregular contact, and contains some nickel, low MgO and high Fe.
• Saprolite zone which is the primary host to nickel mineralisation. It grades from saprolite, through sap-rock to the underlying bedrock. Structures and textures of minerals are progressively better preserved with depth. It is rich in hydrous Mg silicates, with a low content of Fe and high MgO. Nickel occurs within serpentinite where it is associated with narrow zones of fine-grained serpentine micro-breccia and centimetre-scale subhedral patches of very fine-grained polycrystalline chlorite and vermiculite. Locally, significant amounts of chlorite and vermiculite are cut by millimetre to centimetre thick garnierite ±chalcedony veinlets controlled by structures that cross-cut the igneous-layering. Vermiculite and chlorite are strongly enriched in nickel. Because both are more insoluble than serpentine, they persist upward into the laterite profile and are also present in limonite and siliceous limonite.
• Bedrock, which is the only slightly weathered protolith, characterised by low nickel grades, high MgO and low Fe.
The principal minerals in the Onça saprolite, in decreasing order of abundance, are serpentine, limonite, quartz, chromite and vermiculite. Ni is present in solid solution, largely in serpentine, with subordinate amounts in goethite and vermiculite. Minor quantities of various green
silicates, i.e., 'garnierites', are locally evident in the Onça saprolite, intergrown with chalcedonic quartz. Grains of possible nepouite (Ni3Si2O5) containing 13 to 19 wt.% Ni have also been identified. Nickel and Cobalt also occur in manganese oxide phases but not at significant levels
within the saprolite zone. Intergrowths of a Mn-AI oxide phase have also been observed probably as lithiophorite and tamaite (K.Ba)3Mn22(Si,AI)40(0.OH)112•2(H20), with 10% contained Ni.
Proved + Probable Reserves, as quoted by Vale in 2006, were:
Saprolitic ore: 112.5 Mt @ 1.72% Ni, 18% Fe2O3, 25% MgO;
Limonitic ore: 320 Mt @ 0.75 % Ni, 33% Fe2O3, 2% MgO.
Ore Reserves at Onça and Puma as at 31 December 2020 (Vale 2013 Annual Form 20-F Report to the US Security and Exchange Commission) were:
Proved + Probable Reserves - 288.3 Mt @ 1.61 wt.% Ni.
The most recent source geological information used to prepare this decription was dated: 2021.
Record last updated: 13/12/2021
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.
Serra do Puma Serra da Onca
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Selected References:
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de Freitas Silva, M. and Dimitrakopoulos, R., 2016 - Simulation of weathered profiles coupled with multivariate block-support simulation of the Puma nickel laterite deposit, Brazil: in Engineering Geology v.215, pp. 108-121.
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Ferreira Filho, C.F., Oliveira, M.M.F., Mansur, E.T. and Rosa, W.D., 2021 - The Jaguar hydrothermal nickel sulfide deposit: Evidence for a nickel-rich member of IOCG-type deposits in the Carajas Mineral Province, Brazil: in J. of South American Earth Sciences v.111, 23p. doi.org/10.1016/j.jsames.2021.103501.
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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