|
Caboclo dos Mangueiros, Angico dos Dias |
|
|
Bahia, Brazil |
| Main commodities:
Ni Cu P V Ti Fe
|
|
 |
|
|
 |
Super Porphyry Cu and Au
|
IOCG Deposits - 70 papers
|
All papers now Open Access.
Available as Full Text for direct download or on request. |
|
|
The low grade Caboclo dos Mangueiros nickel sulphide deposit and associated carbonatite phosphate and layered Ti-V-Fe deposit are located near the village of Caboclo dos Mangueiros on the northwestern margin of the São Francisco craton, close to the contact with the Rio Preto Neoproterozoic fold belt. It is 45 km WSW of the town of Campo Alegre de Lourdes and ~630 km NW of Salvador in northern Bahia state, Brazil. The Angico dos Dias Complex carbonatite is part of the same cluster of mafic-utramafic and carbonatite intrusions scattered within a 20 km radius, and is ~30 km north of the Caboclo dos Mangueiros deposit. It is mined for phosphate.
Pyroxenite was mapped in the area by Companhia Baiana de Pesquisa Mineral (CBPM - Bahia State Geological Survey) during a regional mapping program in 1987. In 2005 to 2006, several aeromagnetic anomalies were identified in a regional airborne survey conducted by CBPM and CPRM (Brazilian Geological Survey). Follow-up exploration of the aeromagnetic anomalies by CBPM in 2009, including geological mapping and lithogeochemical analyses, identified Ni-Cu anomalies associated with ultramafic rocks in the Caboclo dos Mangueiros target. Ground mapping, geophysics and geochemistry, followed by drilling was completed in 2015 by CBPM, culminating in an intersection of 213 m of disseminated sulphides @ 0.22 wt.% Ni, 0.13 wt.% Cu, 0.015% Co (Matos and Ferreira Filho, 2018; CBPM 2017).
The deposit is located on the northwestern edge of the São Francisco craton (Almeida, 1977), near the contact with the Rio Preto fold belt (Uhlein et al., 2011). The craton is composed of four major crustal segments assembled during the ~2.0 Ga Palaeoproterozoic cycle (Barbosa and Sabaté, 2004; Peucat et al., 2011), designated as the Gaviáo, Jequié and Serrinha blocks, and the Itabuna-Salvador-Curacá belt, bounded by adjacent Neoproterozoic fold belt rocks (Uhlein et al., 2011). These crustal blocks are mainly composed of amphibolite to granulite facies orthogneiss and migmatites, metamorphosed during the ~2.0 Ga Trans-Amazonian orogeny, from protoliths interpreted to be Archaean tonalite-trondhjemite-granodiorite (TTG) terranes and greenstone belts, partially to extensively reworked by the Palaeoproterozoic event.
The Caboclo dos Mangueiros deposit lies within the the Archaean to Palaeoproterozoic Gaviáo block. The principal units within this block include:
• Archaean Sobradinho-Remanso Complex, which is interpreted to be a TTG terrain metamorphosed by the Palaeoproterozoic orogeny. It consists of a complex of orthogneiss and migmatite, which has yielded dates of 2564±11 and 3537±8 Ma (U-Pb zircon; Dantas et al., 2010).
• Serra da Boa Esperança Sequence, comprising carbonate schist with lenses of marble as well as minor mica schist and mica-quartz schist (Leite, 1997; Barbosa et al., 2012). This originally carbonaceous-pelitic sedimentary sequence has been metamorphosed to greenschist facies, and has been correlated with a Palaeo or Mesoproterozoic sedimentary cover sequence overlying the São Francisco craton (Barbosa et al., 2012), although recent geochronological data suggest Neoproterozoic (Tonian) sources for similar metasedimentay units located in the northern portion of the São Francisco craton (Alcantara et al., 2017).
A cluster of mafic-utramafic and carbonatite intrusions scattered within a 20 km radius occur within the Sobradinho-Remanso Complex and Serra da Boa Esperança Sequence immediately to the west of the town of Campo Alegre de Lourdes. These intrusions are usually strongly weathered and lateritised and/or largely covered by Cenozoic sedimentary sequences. Apart from a U-Pb zircon and baddeleyite 2010±6 Ma age from the granulite facies Angico dos Dias carbonatite complex (Silva et al., 1987), no reliable age dating is available for these intrusions. The principal mafic-ultramafic complexes in the district are:
• Angico dos Dias Complex composed of pyroxenite, alkali diorite, albitite, pyroxenite, syenite, carbonatite and lamprophyre, all of which have been metamorphosed to granulite facies (Silva et al., 1988, 1997; Antonini et al., 2003). The complex has been classified as a calcium carbonatite, and is predominantly composed of calcite and apatite with subordinate dolomite, olivine, phlogopite and magnetite. It is ~5 km long, north-south elongated and is ~30 km north of the Caboclo dos Mangueiros Ni-Cu-Co deposit. The phosphate deposit developed in the weathered profile of an apatite-rich carbonatite, which was being mined in 2018 by Mineração Galvani S.A. It has undergone significant supergene alteration that has depleted much of the overall carbonate content and hosts minerals from the apatite family that were formed in both primary (sovite) and secondary (supergene alteration) regimes (Luciano and Godoy, 2017; Matos and Ferreira Filho, 2018).
• Campo Alegre de Lourdes mafic-ultramafic complex, which is a gabbro-anorthositic intrusion hosting a large Fe-Ti-V deposit (Sampaio et al., 1986). It is ~37 km ENE of the Caboclo dos Mangueiros deposit, and is a north-south elongated, 11 km long intrusion composed of interlayered pyroxenite, gabbro, anorthosite and ilmenite-magnetitite metamorphosed under greenschist to amphibolite facies. Fe-Ti-V mineralisation occurs as several individual bodies of massive to banded ilmenite-magnetitite (Sampaio et al., 1986).
• Peixe mafic-ultramafic complex which is ~10 km long, elongated NE-SW, ~20 km NNE of the Caboclo dos Mangueiros deposit, and also contains Fe-Ti-V mineralisation. It is largely masked by Cenozoic eluvial/colluvial sediments. Its margins are interpreted from aeromagnetic date (Leite et al., 1993; Leite, 1997) and geological knowledge is limited to exploratory drilling carried out by CBPM in 1988. Drill intersections reveal a sequence of interlayered metagabbro, metapyroxenite and massive ilmenite-magnetitite.
• Caboclo dos Mangueiros Intrusion, the main host to nickel-copper mineralisation, outcrops as rare partially weathered wehrlite and pyroxenite blocks within a flat region covered by eluvial/colluvial sediments. Additional occurrences of these rock types were mapped by Leite (1997) who suggest they belong to a cluster of small ultramafic bodies. The main tested mineralised intrusion comprises a ~2000 x 500 m, WNW-ESE trending ultramafic body. Due to regional Cenozoic sedimentary cover and ferruginous lateritic crusts, geologic knowledge of the deposit and host ultramafic intrusion is based on drill logs and geophysical data alone. The lateritic crust to the intrusion outcrops as ferruginous silexites that form gentle, ~20 m high hills, that protrude through the surrounding flat terrane composed of unconsolidated sediment.
Below the weathering profile, fresh ultramafic rocks comprise olivine and clinopyroxene cumulates with disseminated sulphides. The intrusion is characterised by the absence of well defined layering, which together with abrupt changes in textures, suggest a magmatic structure broadly similar to those described as 'channelised sills' (e.g., Williams et al.,1998; Lesher, 2007). Except for minor discrete sheared zones and the thin, <4 m thick, fine-grained border zone described below, the ultramafic intrusion consists of massive cumulates with magmatic textures. It comprises dunite in the channelised facies, with more fractionated wehrlite and clinopyroxenite toward the margins. The bulk rock composition and range of Mg# of cumulus clinopyroxene from 0.78 to 0.94 are interpreted to support a moderate to primitive mafic composition for the parental magma (Matos and Ferreira Filho, 2018).
The cumulus assemblage is partially to extensively altered to hydrous minerals, occurring as pseudomorphic replacement of olivine by serpentine and magnetite, and clinopyroxene by tremolite-actinolite, although, igneous textures are preserved throughout the intrusion. Penetrative fabric is restricted to narrow sheared domains of up to few metres in thickness, whilst igneous minerals and/or pseudomorphs are identified in adjacent non-deformed zones. These rocks have been described by Matos and Ferreira Filho (2018) using igneous terminology as the original igneous textures are largely preserved in the ultramafic rocks, allowing the original cumulate minerals can be identified.
The section of the Caboclo dos Mangueiros intrusion that has been drilled forms an elongated body, thicker in the centre, progressively tapering toward its extremities. This elongated intrusion is partially coincident with a 5 km long discrete magnetic anomaly which extends NW beyond the delineated ultramafic intrusion indicating the body has concealed extensions.
Dunite and wehrlite predominate in the northern portion of the longitudinal core of the intrusion, while clinopyroxenite predominates to the south, indicating a progressive fractionation from olivine cumulates to clinopyroxene cumulates from north to south.
Dunite occurs as a massive dark-green olivine cumulate with up to 5 vol.% interstitial sulphides. Medium grained adcumulate to mesocumulate textures predominate with minor medium- to coarse-grained orthocumulate textures. The latter is made up of large (up to several cm) clinopyroxene oikocrysts enclosing euhedral olivine pseudomorphs.
Wehrlite is a massive medium- to coarse-grained greyish-green cumulate with up to 5 vol.% interstitial sulphides. Lenses of dunite or clinopyroxenite are commonly interlayered in wehrlite. Mainly gradational contacts, characterised by intermediate compositions, i.e., olivine clinopyroxenite and clinopyroxene-bearing dunite separate wehrlite from both dunite and clinopyroxenite. Cumulus olivine and clinopyroxene adcumulate textures predominate in wehrlite. Meso- to orthocumulate textures, characterised by abundant clinopyroxene oikocrysts enclosing cumulus olivine are found in wehrlite, closely associated with dunite in the northern part of the intrusion.
Clinopyroxenite occurs as a massive, light greenish-grey, medium- to coarse-grained clinopyroxene adcumulate containing interstitial sulphides. It commonly contains preserved cores rimmed by variable replacements of tremolite-actinolite. Clinopyroxene is usually twinned and eventually has tiny acicular exsolutions of ilmenite.
Fine-grained chlorite-actinolitite or chlorite-actinolite schist are fine-grained greenish rocks located along the contact of the ultramafic intrusion with the country rocks, occurring as up to 4 m thick zones of variable composition, common containing >70% modal actinolite, although rocks with mild foliation and/or abundant (up to 10 vol.%) biotite also occur. The contacts with the country rocks are usually sharp and characterised by abrupt changes in texture, mineral composition, and grain size. The 1 to 5 vol.% disseminated sulphides throughout the ultramafic intrusion sharply disappear in this marginal chlorite-actinolite schist unit.
• Serra do Meio alkaline suite is hosted by mica-quartz schists of the Serra da Boa Esperança Sequence, and is composed of alkali granite with subordinated syenite. This felsic suite is correlated with Neoproterozoic to Cambrian anorogenic plutons in the district (Plá Cid, 1994).
• Parnaíba basin Palaeozoic sedimentary rocks overlie the older rocks 20 km to the NW of the Caboclo dos Mangueiros intrusion, discordantly covering the Proterozoic and Archaean suites of the São Francisco craton and adjacent Neoproterozoic Brasiliano belts in the region.
Country rocks to the intrusion are folded, fine- to medium-grained graphite-bearing quartz-biotite schist with prominent foliation, crosscut by rare veins or granitic dykes that are up to 2 m thick. The tectonic foliation parallels a lamination composed of alternating darker graphite-rich and lighter quartz-plagioclase rich irregular laminae. The quartz-biotite schist is mainly composed of variable proportions (30 to 35 vol.%) quartz, 20 to 25 vol.% biotite, 20 to 25 vol.% albite, up to 20 vol.% muscovite and up to 10 vol.% graphite, with accessory epidote, chlorite, ilmenite, pyrite and garnet. Chlorite is a common alteration mineral replacing biotite. The metamorphic paragenesis is typical of metasediments that underwent regional upper greenschist facies metamorphism (Bucher and Grapes, 2011).
Disseminated sulphides are homogeneously distributed in different cumulates throughout the entire ultramafic intrusion. Positive correlations between S and Ni (0.81) and S and Cu (0.87) in the sulphide mineralisation indicate that both metals are mainly contained in sulphides. Similarly, positive correlations between Pd and Pt suggest these metals are also contained within the sulphides. The form of the deposit, supported by Cu, Ni, Pt, and Pd tenors suggests the metal contents of the parental magma resulted from previous sulphide segregation of the primitive magma during residence in a lower staging chamber from which it was expelled.
The bulk, ~99 vol.%, of the sulphide mineralisation typically occurs as disseminated magmatic sulphides associated with ultramafic cumulate rocks, and consists of 1 to 5 vol.% sulphide blebs hosted by dunite, wehrlite or clinopyroxenite. Disseminated sulphides occur throughout the entire drilled portion of the ultramafic intrusion, suggesting a low-grade orebody coincident with the elongate boat-shaped intrusion. Preliminary estimates by CBPM indicate a 1700 x 400 m body in plan, that is 200 m thick of mineralisation with a consistent low Ni and Cu content. Remobilised sulphides, representing ~1 vol.% of the sulphide resource, are limited to a few discrete shear zones which are commonly <0.5 m thick, occurring as irregular strings. These zones with abundant remobilised sulphides have the highest Ni and Cu grades reported in the deposit (up to 4 m at 1.0 wt.% Ni). However, these zones are discontinuous, and no high-grade ore zones have been so far indicated.
The Ni-Cu deposit within the Caboclo dos Mangueiros intrusion contains an estimated 200 Mt @ 0.20 wt.% Ni, 0.13 wt.% Cu, 0.016 wt.% Co (Matos and Ferreira Filho, 2018).
The Fe-Ti-V deposit within the Campo Alegre de Lourdes mafic-ultramafic complex contains 100 Mt @ 45 wt.% Fe, 21 wt.% TiO2, and 0.71 wt.% V2O5 (Sampaio et al., 1986).
The apatite-rich carbonatite within the Angico dos Dias Complex contains a total resource of 15 Mt @ 15.4 wt % P2O5 (Matos and Ferreira Filho, 2018).
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.
|
|
|
|
Luciano, R.L. and Godoy 2017 - Geology of the Angico dos Dias meta-carbonatite complex, Bahia/Piaui border, Brazil: in Geociencias v.36, pp. 301-314.
|
Matos, V.B.M. and Ferreira Filho, C.F., 2018 - The Caboclo dos Mangueiros Deposit: Ni-Cu Sulfide Mineralization Hosted by an Ultramafic Intrusion in the Northern Edge of the Sao Francisco Craton, Brazil: in Econ. Geol. v.113, pp. 1525-1552.
|
|
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.
|
Top | Search Again | PGC Home | Terms & Conditions
|
|
