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Salitre |
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Minas Gerais, Brazil |
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P Nb Ti
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Super Porphyry Cu and Au
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The Salitre phosphate, titanium and niobium deposits, that are hosted by the composite Salitre-Serra Negra carbonatite-alkaline igneous complex, are located ~10 km to the east of Patrocinio in Minas Gerais, Brazil, 360 km SSW of Brasilia and 320 km WNW of Belo Horizonte, #Location: 19° 00'S, 46° 45'W.
The Salitre-Serra Negra complex is located ~75 km north of the similar Barreiro complex (Araxá), and also lies within the 1500 km long NNW-SSE trending Meso- to Neoproterozoic Brasilia fold belt, immediately adjacent to the southwestern margin of the Archaean to Palaeoproteozoic São Francisco craton, and adjacent to the northeastern edge of the Palaeozoic-Mesozoic Paraná Basin.
The Brasilia fold belt delineates the southwestern margin of the São Francisco craton. The São Francisco craton is composed of an Archaean to Palaeoproterozoic crystalline basement core exposed around Belo Horizonte, overlain by the flat-lying Mesoproterozoic Espinhaço Supergroup which is only exposed over limited areas where the upper units of sandstones and siltstones outcrop, and then by the ~2000 m thick transgressive Neoproterozoic São Francisco Supergroup. The São Francisco Supergroup comprises the basal lenticular Jequitaí Group, composed of tillites lying on glacial striated surfaces, followed by the Bambuí Group which commences with a local lenticular conglomeratic unit, the Carrancas Formation, overlain by four formations characterised by alternating finely detrital sediments and stromatolitic carbonate beds. This suite is overlain by the partially continental upper unit, the Três Marias Formation.
Both the Espinhaço and São Francisco Supergroup are found in the Brasília fold belt. To the west the Araxá Group composed of basic and ultrabasic magmatic rocks which are succeeded by gneisses, mica-schists, schists and quartzite that are equivalents of the Espinhaço Supergroup. Eastward they pass into the Canastra Group, a sequence of quartzites and schists. The Araxá and Canastra groups were deposited in a rift basin (aulacogen) to the west of the São Francisco craton. The Canastra Group passes upwards into the Paranoã Group which can be correlated with the upper part of the Espinhaço Supergroup on the craton to the east. The Araxá, Canastra and Paranoã groups were most likely metamorphosed during the Uruaçu orogeny at ~1100 Ma, the intensity of which diminishes rapidly to the east. The overlying Unai Formation found in the Brasilia fold belt, with its basal tilloid Ibia Formation can be correlated with the similar Jequitaí Group tillites and overlying Bambuí Group of the São Francisco Supergroup on the craton. At around 600 Ma all the metasedimentary rocks and basement were refolded by the Brasiliano orogeny obliterating earlier structural textures and thrusting the Araxá, Canastra and Paranoã group rocks eastward onto the São Francisco craton, with increasing deformation and metamorphism westward.
The Palaeozoic-Mesozoic 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 Salitre-Serra Negra carbonatite-alkaline igneous complex, and is related to deep seated faults within the Brasilia Fold Belt.
The Salitre and Serra Negra complexes has been dated (K/Ar whole rock) at 79.0±1.2 to 86.3±5.7 Ma and 83.0±3.0 to 83.7±4.5 Ma respectively, i.e., Late Cretaceous. They have been intruded into metasediments of the Brasilia fold belt on the southwestern margin of the São Francisco craton. The intruded basement comprises metasediments of the Bambuí Group, its basal Ibia Formation tilloid, as well as the Paranoã group that is updomed around the margins of the intrusive complex. Several kms to the west, the Canastra Group of Mesoproterozoic Espinhaço Supergroup becomes the dominant outcropping unit.
The Salitre-Serra Negra complex is represented by two interconnected oval-shaped bodies, separated by NE-SW-trending faulting. Together, the larger Serra Negra intrusive to the north, and the smaller Salitre mass to the south, have a 'figure of eight' shape, separated by a gap of <2 km, aligned NNW-SSE over an interval of 21 km, varying in width from 5 to 12 km. The main lateritic crust developed over the complexes and rare exposed weathered ultramafic and carbonatite rocks cover a NE-SW elongated ovoid area of ~12 x 9.5 km at Serra Negra, and a NNW-SSE elongated ovoid that is sone 6 x 11 km at Salitre. Both have a comparable composition, although only the smaller Salitre intrusive has been shown to host economic grade mineralisation, with testing of the mineralogically similar Serra Negra complex having been hampered by environmental considerations and thicker cover.
The Salitre complex is mainly composed of syenites showing clear evidence of fenitisation, ultramafic rocks (clinopyroxenites, mica-bearing clinopyroxenites, locally referred to as bebedourites, dunites, glimmerites and perovskitites), radial dykes of trachytes/tinguaites, and carbonatites. The carbonatites occur as small veins and elongated plugs of up to ~500 sq. m in area. In a few cases the carbonatitic rocks grade into phoscorites because of an increase in magnetite content.
Texturally, the ultramafic rocks are described as adcumulates, although meso- and orthocumulate rocks are also evident. No distinctive layering is evident in the rocks at the drill hole scale. Clinopyroxene, olivine, phlogopite, perovskite and apatite represent the main cumulus phases, sphene being less common. Intercumulus material consists of the same minerals in addition to melanite. Fresh rocks are rarely present at the surface. The crystallisation sequence of the main rock-forming minerals of the ultramafic rocks progresses from early perovskite and opaques (Cr-spinel), followed by olivine, clinopyroxene, and finally phlogopite, which is clearly a two-generation phase, the latest being related genetically to the fenitisation processes. Geological, petrographic and mineralogical evidence from the Salitre rocks indicates a highly complex origin involving multistage crystallisation processes from an initial ultrapotassic magma source. Carbonatitic rocks are interpreted as resulting from an unmixing process that developed during the evolution of the parental magma. The distribution patterns of REE display LREE enrichment and strong LREE/HREE fractionation typical of alkaline suites; higher REE concentrations are related to the perovskitic rocks.
The bulk of the mineralisation at Salitre is developed within the thick sheet of oxidised, laterite/saprolite developed over the complex, similar to that described at Catalão (see the separate record which describes this mineralisation in more detail).
Phosphate resource in 2006 (DNPM 2006 Mineral Annuary) - 852.0 Mt @ 10.74% P2O5
Niobium resource in 1996 (Melo et al. 1997) - 196.0 Mt @ 0.48% Nb2O5
Titanium resource in 1966 (Melo et al. 1997) - 694.3 Mt @ 17.5% TiO2.
The most recent source geological information used to prepare this decription was dated: 2010.
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.
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Selected References:
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Carvalho, L.M.M., Pires, A.C.B. and Vidotti, R.M., 2015 - Phosphate prospection in the alkaline province of Alto Do Paranaiba, Brazil, based on airborne geophysical data: in Revista Brasileira de Geofisica (Brazilian Journal of Geophysics), v.33, pp. 237-249.
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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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