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The Ouvidor/Catalão phosphate and Catalão niobium mines exploit mineralisation distributed within two separate alkaline-carbonatite complexes, Catalão I and II that are 10 km apart, located in the state of Goiás in Brazil, ~220 km SE of the capital Goiânia and ~260 km SW of Brasilia, #Location: 18° 10'S, 47°56' 30"W.
The Catalão niobium mine (Mineração Catalão) exploits niobium-rich ore developed in the weathered zone over the alkaline-carbonatite complexes, while the Ouvidor (Copebrás) operation exploits phosphate-rich ore, also from the oxide zone of the same complexes. The tailings produced by the Ouvidor treatment facility, following the extraction of phosphate minerals, is supplied to the treatment plant associated with the Catalão niobium mine where the contained by-product niobium is extracted and treated with the Catalão mine ore for the production of ferroniobium (Anglo American and Copebrás websites, viewed 2012). A separate Catalão (Fosfértil) phosphate mine is also in operation within the complex (Vale website, 2012).
These complexes lie within the 1500 km long NNW-SSE trending Meso- to Neoproterozoic Brasilia fold belt, to the SW of the Archaean to Palaeoproteozoic São Francisco craton, and immediately adjacent to the northeastern margin of the Palaeozoic-Mesozoic Paraná Basin. The Catalão I and II complexes have been dated at 82.9±4.2 Ma (K/Ar whole rock) and 85.0±0.9 Ma (syenites), i.e., Late Cretaceous. Catalão I is a sub-circular, 6 km diameter intrusion, while Catalão II, 10 km to the NW, comprises two upwardly flaring pipes that have coalesced to cover a 5 x 2.7 km, NE-SW elongated shape at the surface with re-entrants on the NW and SE sides.
The igneous complex is intruded into metasediments of the Brasilia fold belt to the west of the São Francisco craton. The intruded basement comprises a sequence of quartzites and schists of the Mesoproterozoic Araxá Group that rest on basic and ultrabasic magmatic rocks, and is a member of the Espinhaço Supergroup that was deposited within an aulacogen (rift basin) to the west of, and laps onto, the São Francisco craton. These sediments were most likely metomorphosed when they were thrust eastward onto the São Francisco craton during both the ~1100 Ma Uruaçu and 600 Ma Brasiliano orogenies. The Paraná Basin to the SW includes the thick, extensive Cretacous Paraná Flood Basalts that temporally overlap the extensive NW-SE-trending, 300 x 100 km, Alto Paranaíba Igneous Province that includes the Catalão carbonatite complexes, and is related to deep seated faults within the Brasilia Fold Belt.
Intrusion of the Catalão I ultramafic-alkaline complex has updomed the Araxá Group country rocks, forming a 6 km diameter subcircular plateau that rises around 100 m above the regional ground surface. This landform reflects the greater resistance to weathering of the fenitised quartzite ring surrounding the complex, and protects the thick (>100 m) blanket of weathered lateritic material overlying the complex in the core of the dome. The weathered mantle contains abundant residual apatite, pyrochlore, monazite, Ti-bearing minerals (perovskite, ilmenite, and anatase) and vermiculite.
The Catalão I intrusion is composed of dunite with subordinate pyroxenite, accompanied by phoscorite, phlogopitite and carbonatite, as well as volcaniclastic rocks. The dunite and pyroxenite were intensely altered to phlogopitic rocks by the intense potassic metasomatism that accompanied the multiple intrusions of carbonatitic phases that followed, leaving only remnant relicts patches of recognisable ultramafic rocks among the dominant carbonatites and phlogopitites. Subsequent to the development of the phlogopite alteration stage, nelsonitic and carbonatitic intrusions occurred in successive events. Nelsonite is a rock of the foscorite group containing pyrochlore, essentially composed of magnetite, phlogopite, calcite and/or dolomite, with accessory to abundant pyrochlore, apatite and sulphides minerals. Pyrrhotite and calcite are the dominant sulphide and carbonate respectively. Pyrochlore is dominantly a Na- or Ca- varieties, with a Pb- phase also occurring. Sections of the carbonatite carbonatite are enriched in either Nb and Ba or Mg and the rare-earth elements (REE), while zones of hydrothermally altered volcaniclastic rocks are characterised by monazite mineralisation.
Three deposits of niobium have been developed over carbonatites intruded in the central portion of the complex, and occur within the weathered portions of the intrusives. The mineralised thickness averages ~80 m, reaching a maximum of 120 m. The weathered materials are made up of lateritic cover and underlying saprolite.
The lateritic zone constitutes the overburden to the mineralisation and is made of a ferruginous and intensely weathered material, with no recognisable relict structure. Its
thickness is variable, in general not exceeding 25 m. The dominant crandallite-group mineral gorceixite (BaAl3(PO4)(PO3OH)(OH)6) is responsible for the ochre colour of this zone. Goethite predominates at a depth of 17 to 20 m. Quartz occurs a spherical or fractured nodules. Pyrochlore, though always present, is generally fine-grained and, in most cases, stained with a film of iron hydroxides.
The saprolite zone contains the economic niobium mineralisation. It is composed of weathered rocks in which relicts of the primary structures are still recognisable, grading into the underlying fresh rocks at the base of the saprolite. This transition is characterised by a vermiculite horizon which is always above the fresh rocks. The saprolite is rich in apatite and anatase, although not evenly distributed. The distribution and grade of niobium mineralisation is variable, both horizontally and vertically, reflecting the distribution of pyrochlore, which occurs within dykes and fracture-filling veins in the unweathered rock. Large blocks and masses of supergene silexite are abundant in the saprolites resulting in a large mineralogical variation, with magnetite, barite, apatite and secondary phosphates being always visible.
Of the main concentrations of apatite, pyrochlore, monazite, anatase and vermiculite recognised within the complex, only apatite and pyrochlore (Nb) are being exploited.
The Catalão II intrusion consists of a primary ultramafic phase, composed essentially of pyroxenites, foscorites and syenites. In contrast to the dominance of carbonatites at Catalão I, which resulted in the almost complete destruction of the primary ultramafic rocks, the carbonatitic intrusions at Catalão II occupy a relatively smaller volume, with the preservation of much of the ultramafic rocks. Never-the-less the introduction of nelsonites and carbonatites resulted in intense phlogopite aureoles, with the nelsonitic and carbonatitic intrusions being responsible for both Nb and phosphate mineralisation. The different intrusive and alteration phases may be summarised as follows:
Pyroxenite Series - includes pyroxenites, and specific magnetite- and biotite-pyroxenite phasess, often associated with rocks referred to as apatitites and other metasomatic altered zones.
Syenite Series - generally a homogenous alkali feldspar syenite, but localised occurring as a quartz syenite where in contact with country-rock quartzites.
Foscorites - which represent the last silicate phase that preceded the introduction of the carbonatite phase, and is composed of homogeneous and massive mafic rocks that, with the preceding rocks, are extensively cut by veins and dykes of carbonatite. Nelsonite is the most important rock among the foscorites, usually containing calcite and trace amounts of chalcopyrite and bornite.
Carbonatite Series - an intrusive phase, composed essentially of carbonate minerals, and occurring as dykes and veins cutting the ultramafic rocks described above. Four successive stages have been recognised, with a clear differentiation between each, from the initial phase, which is rich in silicates, oxides, sulphides and phosphates, to the final pulse which is predominantly composed of carbonate minerals.
Lamprophyre Series - a group of undifferentiated melanocratic and ultramelanocratic rocks, present as narrow dykes that penetrate into cracks and faults within the complex.
Metasomatic aureoles fringe the dykes of carbonatite within the pyroxenites, to produce an assemblage of Na-amphibole, Na-pyroxene, K-feldspar and carbonate, which is in general rich in phlogopite, the last mineral to be formed and the most stable of the metasomatic alteration paragenesis. The intense metasomatism also gave rise to other rock types, which
have high contents of Na amphiboles and phlogopite. In addition to this metasomatism, the Araxá Group country rocks are altered to quartzites at the outer contact of the complex, passing outward into fenitised schists.
Weathering of these lithologic types produced a continuous blanket of weathered material, characterised by abundant ferruginous minerals, particularly hydroxides. This blanket also contains large quantities of mica group minerals, including muscovite, biotite and phlogopite which have been partially or totally altered to clay minerals and vermiculite. Silexites are found throughout the weathered zone.
The exploited ores of Catalão II are the result of supergene modification of the entire package of rocks, recrystallisation and leaching of the most soluble components, particularly carbonates, and the residual concentration of the most resistant minerals, including pyrochlore. The ore is predominantly composed of magnetite, either fresh or weathered into martite, and by ferric hydroxides such as goethite and limonite, followed by ilmenite, micas, quartz and rare-earth minerals. Pyrochlore, which is almost always associated with magnetite, is easily observable near preserved nelsonite veins. The ore also contains clay minerals derived mostly from phlogopites and serpentine.
The principal phosphate minerals comprising >85% of the phosphate ore with >10% P2O5 are fluorapatite and dahllite, accompanied by secondary phosphate minerals generally also containing Fe, Al, Mn and REE. Clay, quartz, magnetite, ilmenite, hematite, anatase, barite, vermiculite are also present in variable quantities in the phosphate orebody which occurs in both the weathered blanket and in the foscorites of the fresh bedrock.
The Niobium reserves and resources at 31 Dec., 2010 at the Catalão mines (0.5% Nb2O5 cut-off; Anglo American Fact Book, 2010) were:
Proved + probable reserves, Oxide ore - 5.1 Mt @ 1.07% Nb2O5,
Measured + indicated resource, Oxide ore - 2.8 Mt @ 1.22% Nb2O5,
Inferred resource, Oxide ore - 1.2 Mt @ 1.18% Nb2O5,
Measured + indicated resource, Fresh ore - 33.2 Mt @ 1.24% Nb2O5,
Inferred resource, Fresh ore - 18.1 Mt @ 1.37% Nb2O5
The phosphate reserves and resources at 31 Dec., 2010 at the Ouvidor/Copebrás mines (7% P2O5 cut-off; Anglo American Fact Book, 2010) were:
Proved + probable reserves, Oxide ore - 243.9 Mt @ 13.4% P2O5,
Measured + indicated resource, Oxide ore - 64.2 Mt @ 11.9% P2O5,
Inferred resource, Oxide ore - 58.9 Mt @ 11.1% P2O5
The phosphate reserves and resources at 31 Dec., 2010 at the Coqueiros project/Catalão II complex, (7% P2O5 cut-off; Anglo American Fact Book, 2010) were:
Measured + indicated resource, Oxide ore - 18.3 Mt @ 12.6% P2O5,
Inferred resource, Oxide ore - 26.2 Mt @ 11.2% P2O5,
Measured + indicated resource, Fresh ore - 35.2 Mt @ 8.5% P2O5,
Inferred resource, Fresh ore - 16.2 Mt @ 7.6% P2O5.
The phosphate reserves in 2006 at the Fosfértil Catalão mine, (DNPM 2006 Mineral Annuary) were:
Reserves - 223.6 Mt @ 8.96% P2O5, concentrated to grades of 34 to 36% P2O5.
This summary was largely drawn from Guimarães and Ricardo A. Weiss, 2011 ? and Northolt et al., 1989.
The most recent source geological information used to prepare this summary was dated: 2011.
This description is a summary from published sources, the chief of which are listed below.
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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 takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.
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