Goias, Brazil

Main commodities: Ni
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The Niquelandia lateritic nickel mineralisation, which include the Jacuba, Coriola, Angiquinho, Corrego da Fazenda, Vendinha and Ribera do Engenho deposits, are located in southern Goias, Brazil, some 200 km to the north of Brasilia.

It has been developed over sections of the 40 x 20 km Archaean to Palaeoproterozoic Niquelandia layered mafic to ultramafic igneous complex.   The ore is derived from the weathering of dunites, peridotites and pyroxenites, and is present principally as Ni-rich smectites.

The Niquelandia igneous complex consists of a lower and an upper sequence. The lower sequence is composed of a basal layered zone of gabbro, peridotite, and pyroxenite, overlain by an ultramafic zone of peridotite and pyroxenite, which are, in turn, overlain by layered gabbros. The upper sequence comprises gabbro, anorthosite and an upper amphibolite. The two sequences represent a single igneous complex, in which the lower and upper sequence are comagmatic.

The lower sequence, which is intrusive, was formed by the fractional crystallisation of a basaltic magma, and is in tectonic contact with an older Archaean basement of metamorphic gneisses, quartzites and amphibolite.

The ultramafics of the lower sequence form the 'Serra da Mantiqueira' and comprise dunites and partially serpentinised harzburgites, with some podimorph chromite bodies in the eastern part of the area, while interleaved peridotite and pyroxenite are found in the western part. Examples of the mineralisation in the area include the Jacuba and Angiquinho deposits. The Jacuba deposit is located to the west, is mostly underlain by fresh pyroxenite, and is capped by silcrete. In contrast, the Angiquinho deposit in the eastern part of the area is underlain by dunites and lenses of partially serpentinised pyroxenites, and is capped by a ferricrete crust.

The profile at Jacuba is up to 30 m thick and consists of four main layers. A 7 m thick coherent layer at the base of the profile, overlying the fresh pyroxenite, represents the earliest stages of weathering and comprises rocks varying from greenish-black to beige in color with densities that decrease from fresh rock values of 3.8 to 2.0. While the band is coherent, it is cut by a network of cracks of tectonically induced joints filled with garnierite (kerolite-pimelite series) and greenish smectite. The weathered rock between these cracks consists of enstatite and diopside that are partly altered to smectite, although the smectite is only well developed where the parent rock is strongly fractured. Some 60 to 90% of the MgO, 40 to 50% of the SiO2, O to 80% of the CaO, and ~40% of the Al203 have been depleted. Cr203 are immobile. In contrast, Ni0 grades increases to between 1080 to 5560% of the original content. Grades in the coherent layer vary from ~3.10% NiO in the weakly fractured variant to 17.43% NiO in the strongly fractured ore. The fresh bedrock contains ~0.16% NiO.

The overlying saprolitic layer is around 8 m in thickness and is browner and more friable than the underlying coherent layer. The residual joint-bounded blocks become rounder and decrease in size upward, until towards the top only a few small pieces of brownish rocks persist, scattered in a green-brown clayey matrix. Between the blocks, the greenish matrix is cut by cm- to mm-thick cracks filled with greenish smectite and garnierite, and lesser asbolane. The density of the matrix in this layer is ~1.3, but still preservesthe original rock textures. Within this layer, there is a 70% loss of SiO
2, a 60% loss of CaO, and an 80% loss of MgO. In contrast, the ~8.74% Ni0 grade is enriched by ~2100% above the content of the parent rock.

The succeeding 8 m thick clayey layer contains no residual bed-rock fragments, and is composed of green-brown smectite with reddish ferruginous pseudomorphs after 1 mm-long pyroxenes. Most cracks are filled with asbolane (Co-Mn-Ni oxides). Ca0 and MgO have been virtually completely removed; 8O% of the SiO
2 has been leached. While the ~8.81% Ni0 grade is 1420% greater than in the parent rock, it no richer than in the underlying layer.

The uppermost 4 m thick clayey ferruginous layer comprises reddish to whitish, variegated clay-sized goethite and kaolinite, and has been compacted so that the primary texture of the parent rock has been obliterated. Based on the assumption that Cr
203 has been immobile, Al203 has remained constant, while Fe203 has been introduced. The ~0.10% Ni0 grade in this layer is low, with a loss of 80% relative to the parent pyroxenite.

The 40 m thick lateritic weathering profile at Angiquinho consists of five layers and was developed over a bedrock of dunite and partially serpentinised pyroxenite. The basal 13 m-thick beige-colored coherent layer is has a bulk density of 2.01, which is less than the 2.67 of the fresh parent bedrock. It contains a dense network of one to a few cm thick, almost horizontal cracks. Where the pyroxenite is strongly serpentinised, the cracks are filled with dolomite and magnesite; while where it is unaltered or slightly serpentinised, the cracks contain garnierite. About 50% of the MgO and 20% of the SiO
2 have been depleted. In contrast, ~1.14% Ni0 grade has been enriched by 190% compared to the 0.3% NiO of the parent rock. The other elements appear to have been largely unchanged.

The overlying saprolitic layer is ~18 m thick. Where developed over dunite, blocks of the parent have been altered to a reddish clayey rock, which decrease in size and abundance upward until distinguishable fragments of weathered dunite are absent at the top of the layer. Where it contains blocks of weathered parent pyroxenite, these persist throughout the layer and preserve primary rock textures, and are progressively replaced by a green clayey saprolite which is very different from the reddish weathered products developed from dunite. Similar networks of cracks to those of the coherent layer are found in this part of the profile, although the cracks are filled with Co-Mn-Ni oxides. Relative to the parent rock, 50% of the SiO
2 and 80 to 95% of the MgO have been depleted within this layer, while the Ni0 grade has been enriched to from 1100% at the base to 570% at the top, with corresponding grades of ~7.47% and ~5.26% NiO.

The 10 m thick clayey ferruginous layer consists of reddish goethitic saprolite, which developed from the weathering of dunite, and of purple-whitish goethitic-kaolinitic saprolite formed from pyroxenite. Compaction has obliterated all primary bed-rock textures. Assuming Cr
203 has been immobile, an enrichment of Al203 and a significant loss of NiO is indicated, with an average grade of 0.75% NiO.

The overlying nodular layer is up to 4 m thick, and comprises a powdery red ferruginous material containing goethitic nodules.

The uppermost section of the profile is a 3 m thick ferricrete (Canga) crust, which consists of hard ferruginous blocks of hematitic crust with a nodular facies.

The group of deposits originally contained: 60 Mt @ 1.45% Ni

The most recent source geological information used to prepare this summary was dated: 1989.    
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.

  References & Additional Information
   Selected References:
Colin F, Nahon D, Trescases J J, Melfi A J  1990 - Lateritic weathering of pyroxenites at Niquelandia, Goias, Brazil: the supergene behavior of Nickel: in    Econ. Geol.   v85 pp 1010-1023
Garnier J, Quantin C, Martins E S and Becquer T,  2006 - Solid speciation and availability of chromium in ultramafic soils from Niquelandia, Brazil : in    J. of Geochemical Exploration   v88 pp 206-209

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 takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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