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Pilar |
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Minas Gerais, Brazil |
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Au
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Super Porphyry Cu and Au
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The Pilar gold mine is located in the municipality of Santa Bárbara, 110 km ESE of Belo Horizonte, in the state of Minas Gerais, Brazil (#Location: 19° 59' 2"S, 4° 3' 26"W).
Pilar lies within a group of exploration and mining titles known as the Santa Bárbara Property, which were held by CVRD and then Vale who had undertaken geological mapping and other exploration, to an in-fill drilling stage at the Pilar deposit. In December 2003, Jaguar Mining Inc. acquired that property and in 2006 initiated further drilling at Pilar. In December 2008, Jaguar began trucking ore from the Pilar Mine to the Paciência Plant to supplement the ore being supplied by the latter's Santa Isabel Mine. By 2010, Jaguar had commissioned a gold plant at its new Roça Grande Mine, 55 km to the west and shipped further ore there for treatment. Between 2008 and the end of 2017, 3.12 Mt @ 3.44 g/t Au was treated with an average 88% recovery.
The Pilar deposit is hosted within the basal units of the Nova Lima Group which belongs to the Archaean Rio das Velhas Supergroup in the eastern or Santa Bárbara Domain of the Quadrilátero Ferrífero District. For details of the regional tectonic, structural and geological setting, and stratigraphic units mentioned below, see the Quadrilátero Ferrífero District Gold - Geological Setting record and the geological plan therein.
The rocks in the deposit area comprise tholeiitic basalts and komatiite flows of the Ouro Fino and Morro Vermelho Units of the Nova Lima Group, along with their intrusive equivalents. Chemical sedimentary rocks include chert and banded iron formation (BIF) up to 10 m thick and represent the only sedimentary deposition in this part of the sequence. To the west, these basal units are in fault juxtapositon with mica-quartz-, chlorite-quartz- and chlorite-sericite-schists, and chemical and clastic sedimentary rocks of the Santa Quitéria Unit. To the east, the units are in fault contact with migmatites and granitic gneisses of the Santa Bárbara Complex that also forms the basement sequence.
Within the mine area, all rock units have a NE trend, although the regional strike rotates to a southeasterly direction to the south of the mine. Regional
mapping indicates the foliation mostly dips steeply to the SE. Regional-scale thrust faulting also strikes to the NE and dips steeply to the SE at the mine. Within the deposit area, at least three different fault orientations are recognised. The earliest is a set of normal faults that strike at ~20° and dip steeply to the east. These are cross-cut and terminated by a NE-striking regional-scale thrust fault trend that forms the contact between the Santa Quitéria and the Ouro Fino and Morro Vermelho Units. The third set of faults are oriented in an east-west direction with subvertical dips. The displacement along these faults has been observed in underground exposures to be in the order of one to two metres. The host rocks of the mine have been subjected by at least one period of folding that produced fold axes that plunge at ~45°SE with an azimuth of ~135°.
The mineralisation at the Pilar deposit is hosted by a number of the host rock units, including BIFs, as well as mafic and talc-chlorite schists. Gold mineralisation is associated with sulphides, mainly arsenopyrite and pyrrhotite. Quartz veins and veinlets are also present, although the presence of quartz is not a prerequisite for higher gold grades. The sulphides mostly occur as disseminations within the host rock, although semi-massive to massive concentrations are locally developed over widths of a few tens of centimetres. Quartz veins are typically <1 m wide, with two generations having been observed. Those of the first generation are typically associated with the gold mineralisation and are folded, whilst the second generation are typically lower grade or barren and are not folded.
The deposit occurs as a composite shoot that plunges at ~50 to 60°SSW with an azimuth of ~195°. It is made up of eight separate lenses. Structural modelling has demonstrated that the envelope around the main marker mineralised iron formation unit, in which a number of these lenses occur, changes in its form, from a shape similar to a broad, open fold at surface, to a series of compact, tightly folded structural slices at depth. In the upper 800 m, these lenses are tightly constrained within the main shoot envelope. This envelope is reflected in the horizontal length and width of the of mine workings of ~500 x 100 m over this vertical interval. The horizontal length and breadth expands upwards to the surface where it appears to be folded with a closure to the north, while at depth it tapers, and below 800 m, splits into individual lenses that appear to diverge with differing plunges and more limited plan areas.
The largest lens, the SW Orebody, is hosted by BIF of the Santa Quitéria Unit, whilst most of the remaining mineralised lenses are hosted by mafic and ultramafic schists that are equivalent to the Ouro Fino and Morro Vermelho Units. All three units belong to te Nova Lima Group.
Production and Resources
The total production between 2008 and the end of 2017 was 3.12 Mt @ 3.44 g/t Au (Pressacco and Sepp, 2018).
Remaining Mineral Resources at a cut-off grade of 1.46 g/t Au, as at May 31, 2020 (Jaguar Mining Reserves and Resources Statement, 2020) were:
Total Measured + Indicated Mineral Resource - 4.017 Mt @ 4.34 g/t Au;
Total Inferred Mineral Resource - 1.254 Mt @ 4.52 g/t Au.
Ore Reserves at a cut-off grade of 2.14 g/t Au, as at May 31, 2020 (Jaguar Mining Reserves and Resources Statement, 2020) were:
Total Proved + Probable Ore Reserve - 1.867 Mt @ 4.00 g/t Au.
The information in this summary is drawn from Pressacco, R. and Sepp, J., 2018 - Technical Report on the Roça Grande and Pilar Mines, Minas
Gerais State, Brazil; An NI 43-101 Technical Report prepared by Roscoe Postle Associates Inc., Toronto for Jaguar Mining Inc., Toronto, 217p.
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.
Pilar
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Selected References:
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Silva-Alves, G.P., Correa Neto, A.V., Brando Soares, M., Neumann, R., Alves, F.E.A. and de Souza, T.P., 2022 - A multi-methodological approach for mineral exploration and predictive metallurgy: the case of the Pilar gold deposit at the Quadrilatero Ferrifero, Brazil: in Ore Geology Reviews v.149, 21p. doi.org/10.1016/j.oregeorev.2022.105113.
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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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