The Cuiaba Complex is owned and operated by AngloGold Ashanti Córrego do Sítio Mineração S.A. (AGA Mineração), a company registered in Brazil. AGA Mineração through AngloGold Ashanti Holdings plc., is wholly owned by AngloGold Ashanti plc.
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Summary:
Cuiabá mine
The Cuiabá mine is located in the Iron Quadrangle, which is a geotectonic unit on the southern edge of the São Francisco Craton, comprising Archaean and Proterozoic terrains, and bordered by Neoproterozoic mobile belts. From a regional viewpoint, the Cuiabá mine is located in the eastern extension of the Serra do Curral inverted homocline, located on the northeastern edge of the Iron Quadrangle. The mine lithostratigraphy consists of an intermediate metavolcanic sedimentary sequence of the greenstone belt type and is hosted in the Nova Lima Group at the bottom of the Rio das Velhas Supergroup.
Deposit type
Cuiabá is an Archaean BIF-hosted gold deposit that produces sulphuric acid as a processing by-product. It is characterised by hydrothermal alteration of the rocks, with the mineralisation occurring mainly in BIF layers, subordinate quartz veins or in schists. The host to the gold mineralisation in the volcanosedimentary Nova Lima Group that occurs at the base of the Rio das Velhas Supergroup. The upper sequence of the Rio das Velhas Supergroup is the metasedimentary Maquiné Group. The gold mineralisation at Cuiabá has features and characteristics that match the epigenetic orogenic gold deposit model typical of Archaean lode gold deposits.
Mineralisation style
Cuiabá mine’s gold mineralisation is associated with sulphides and quartz veins in BIF and volcanic sequences. Structural control and fluid flow are the most important factors for gold mineralisation with a common association between largescale shear zones and their associated structures. Where BIF is mineralised, the ore appears strongly stratiform due to the selective sulphidation of the iron-rich layers. Steeply plunging shear zones tend to control the ore shoots, which commonly plunge parallel to intersections between the shears and other structures. Mineralisation is hosted in the limbs of a fold system.
Mineralisation characteristics
The main orebodies at Cuiabá are as follows:
• Normal limb: Fonte Grande Sul and Serrotinho;
• Overturned limb: Balancão, Galinheiro and Canta Galo.
Secondary orebodies occur in hydrothermally altered schists in the footwall of Galinheiro (Galinheiro footwall (GFW) orebody), hydrothermally altered schists/quartz veins near the footwall of Fonte Grande Sul and Serrotinho (Quartz vein orebody), and close to the hangingwall of Serrotinho (Viana orebody).
Lamego mine
The Lamego mine is located in the Iron Quadrangle, which is a geotectonic unit on the southern edge of the São Francisco Craton, comprising Archaean and Proterozoic terrains, and bordered by Neoproterozoic mobile belts. From a regional viewpoint, the Lamego mine is located in the eastern extension of the Serra do Curral inverted homocline, located on the northern edge of the Iron Quadrangle
The mine lithostratigraphy consists of an intermediate metamafic sequence of the greenstone belt type and is hosted in the Nova Lima Group, which is part of the Rio das Velhas Supergroup. This sequence is characterised by lower metabasaltic rocks at the base, overlain by Algoma-type BIF metasediments, a quartz layer (known locally as metachert), carbonaceous schist, graphite schist and a further sequence of sediments consisting of alternating metapelites and metapsammitic rocks with a volcanoclastic contribution. The upper sequence of the Rio das Velhas Supergroup is the metasedimentary Maquiné Group.
Deposit type
The gold mineralisation at Lamego has features and characteristics that match the epigenetic orogenic gold deposit model presented for Archaean gold-lode deposits.
Mineralisation style
The gold mineralisation at Lamego is characterised by orebodies associated with two horizons of chemical sedimentary rocks: BIF and metachert, with shear zones containing abundant quartz veinlets. The proportions of these lithotypes vary substantially from one deposit to another. In the BIF, sulphide mineralisation is associated with gold, while in the metachert it is associated with quartz veins. The gold occurs either as native gold or in sulphides. Lamego has a similar rock assemblage to Cuiabá, but with higher structural complexity. The mineralised BIF is more structurally deformed and contains more silica when compared to Cuiabá, which reacted less with the hydrothermal fluid.
Mineralisation characteristics
The mineralisation is characterised by sulphidation in the form of disseminated sulphide bands or as fracture fill and, more rarely, as massive sulphide hosted in BIF or metachert although sulphide bands are rare in the latter. The metachert (or quartz vein) is concentrated in the hinges of the Lamego structure and has free gold as the main mineralisation with a lesser amount associated with sulphides. The plunge of the mineralised zones coincides with both fold axes of the first two structural events and the stretching fabric.