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Barro Alto |
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Goias, Brazil |
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Ni
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Super Porphyry Cu and Au
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The Barro Alto lateritic nickel deposit is located in the State of Goias, Brazil, approximately 170 km north-west of Brasilia and 240 km north of Goiania (#location: 14° 37'34"S, 48° 42'28'W).
The deposit is located over the northern section of the Barro Alto igneous-metamorphic complex which is found within a Mesoproterozoic eugeosynclinal sequence overlying a metamorphosed Palaeoproterozoic basement.
The Barro Alto Complex comprises an: i). Eastern Metagabbroic; ii). Ultrabasic; iii). Anorthositic; and iv). Western Metagabbroic Zone. Overall it is a layered intrusive composed of gabbronorite with minor dunite, peridotite, norite, gabbro, anorthosite and banded clinopyroxene-garnet amphibolite (Moraes and Fuck, 2000)
The tectonic evolution of the complex includes: i). an initial granulite facies, represented by pyroxene gneisses and ortho-amphilbolites enclosed within the basal complex; ii). a retrograde phase characterised by qreenschist and high amphibolite facies affecting both the complex and the enclosing metasediments, and iii). greenschist facies, observed in fault zones.
The lateritic nickel mineralisation is developed from serpentinised meta-peridotites of the Ultrabasic Zone and occurs as three main laterite/saprolite ore types occurring as a chain of six discrete areas developed along a broad fault zone. The initially mined deposit covered an area of 4.3 square km, over a strike length of 4.2 km and width of 1.25 km. It is part of a larger chain of resources that extends in an arc from SW to NE over a length of ~35 km. The lateritic profile is generally <25 m thick, averaging 18 m. The laterites were developed from the Cretaceous to early Tertiary.
The typical profile comprises:
2.5 m or more of barren ferruginous lateritic overburden
ferruginous saprolite;
argillaceous saprolite with 2.2 to 2.7% Ni oxide (the main ore zone);
coarse saprolite cut by garnierite veins
saprock and bedrock.
The principal nickeliferous minerals include, garnierite, gibbsite, goethite, hematite, limonite, maghemite and serpentine, with a gangue of chalcedony and quartz.
Before production commmenced, the deposit was reported to have contained a resource of 116.2 Mt @ 1.54% nickel, of which 62.4 Mt @ 1.66% nickel will be mined by conventional open pit methods and treated over a 26 year period. Mine production began in 2004, with ore transported to the Codemin plant at Niquelandia until a processing plant was commissioned at Barro Alto in 2011.
At December 31st 2009 resources and reserves were (Anglo American Annual Report - resources are additional to reserves):
Proved + probable reserves - 40.7 Mt @ 1.73% Ni
Measured + indicated resources - 21.1 Mt @ 1.28% Ni
Inferred resources - 60.5 Mt @ 1.45% Ni
Total reserve + resource - 122.3 Mt @ 1.5% Ni.
Remaining JORC compliant Ore Reserves and Mineral Resources at 31 December, 2020 were (Anglo American plc Ore Reserves and Mineral Resources Report, 2020 - Resources are additional to Reserves):
Barro Alto Saprolite
Proved + Probable Reserves - 54.7 Mt @ 1.28% Ni;
Measured + Indicated Resources - 9.4 Mt @ 1.19% Ni;
Inferred Resources - 7.9 Mt @ 1.25% Ni.
Niquelandia Ferruginous Laterite
Inferred Resources - 4.2 Mt @ 1.18% Ni.
The most recent source geological information used to prepare this decription was dated: 2006.
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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Giovanardi, T., Girardi, V.A.V., Correia, C.T., Tassinari, C.C.G., Sato, K., Cipriani, A. and Mazzucchelli, M., 2017 - New U-Pb SHRIMP-II zircon intrusion ages of the Cana Brava and Barro Alto layered complexes, central Brazil: constraints on the genesis and evolution of the Tonian Goias Stratiform Complex: in Lithos v.282-283, pp. 339-357.
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Silveira, C.S., Lagoeiro, L., Cavalcante, C., Taufner, R., Barbosa, P.F., de Freitas Suita, M.T. and Conte, T., 2021 - Deformation mechanisms and seismic anisotropy in lower crustal rocks from the Barro Alto Complex, Central Brazil: in Tectonophysics v.819, 20p. doi.org/10.1016/j.tecto.2021.229087.
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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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