There appear to be two classes of copper–gold deposits in the Carajás region. The first roup includes Cu–Au–(W–Bi–Sn) deposits which contain quartz veins, and may or may not have associated iron oxides and are genetically related to the cooling of Palaeoproterozoic (ca. 1.88 Ga) granites. The second group includes iron oxide Cu–Au (±U–rare earth elements) deposits (e.g., Salobo, Sossego, Cristalino, 118 and Igarapé Bahia) that may be related to more alkaline rocks, including the ca. 2.57 Ga alkaline complexes of the Carajás belt (e.g., Estrela Complex, Old Salobo Granite) and the base metal mineralization-associated 1.88 Ga intrusives. The second group of deposits are commonly referred to as iron oxide copper gold deposits (IOCG). Global examples of IOCG deposits include Olympic Dam in Australia, Candelaria–Punta del Cobre in Chile, and Sossego in Brazil.

Mineralization at the Salobo deposit is hosted by upper greenschist to lower amphibolite metamorphosed rocks of the Igarapé Salobo Group. The group thickness varies from 300–600 m in the Project area, and may be weathered to depths of 30–100 m. The rocks strike approximately N70°W and have a subvertical dip.

The major host units are biotite (BDX) and magnetite schists (XMT). Granitic intrusions (GR) occur adjacent to the north and southern sides of the BDX and XMT, and a series of much younger diorite dykes (DB) cross-cut the mineralization forming barren zones.

The Salobo deposit extends over an area of approximately 4 km along strike (west– northwest), is 100–600 m wide, and has been recognized to depths of 750 m below the surface.

The sulphide mineralization typically consists of assemblages of magnetite–chalcopyrite– bornite and magnetite–bornite–chalcocite. Accessory minerals include hematite, molybdenite, ilmenite, uraninite, graphite, digenite, covellite, and sulphosalts.

The mineral assemblages can be found in a number of styles: forming disseminations, stringers, stockworks, massive accumulations, filling fractures, or in veins associated with local concentrations of magnetite and/or garnet filling the cleavages of amphiboles and platy minerals, and remobilized in shear zones.

There is a positive relationship between copper minerals and magnetite. Copper content is typically >0.8% in XMT and BIF, whereas in gneisses and schists it is <0.8%. A positive correlation between copper content and uranium contents has also been established.

Chalcopyrite, bornite, and chalcocite occur interstitially to silicate minerals. These sulphide minerals are commonly found filling cleavage planes of biotite and grunerite. Hematite is rare, but in places it can reach as much as 4% by volume. It exhibits tabular textures (specularite), with infilling bornite, and partial replacement by magnetite.

Native gold occurs as grains smaller than 10 µm in cobaltite, safflorite, magnetite and copper sulphides, or interstitial to magnetite and chalcopyrite grains. Native gold grains contain up to 10 wt% Cu, with subordinate silver, arsenic, and iron.

Salobo mine utilizes standard open pit methods, developed in 15 m benches, with trucks and shovels. After drilling and blasting the material, cable shovels, large front-end loaders and hydraulic excavators are used to load this material. A fleet of 240 t and 360 t trucks are used to haul the waste material to waste dumps proximal to the pit or ore material to the primary crusher. Lower grade ore is stockpiled for later processing.

The mine planning objective is to mine the ore sequentially in mining phases, considering the largest possible vertical spacing between phases. The plan is to provide an approximately steady annual production of 36.0 million tonnes to the mill. Initial production from the expansion is expected in January 2022.

The Salobo bulk mining operations primarily utilize large electric (rope) shovels for ore and waste production. Hydraulic shovels are used for the oxide saprolite and transition material where a lower ground pressure is required. Wheel loaders are used for miscellaneous clean up jobs and for backup of the shovels when needed.

- subscription is required.

The run-of-mine is processed by means of standard primary and secondary crushing, conveying, roller press grinding, ball milling copper concentrate flotation, tailings disposal, concentrate thickening, filtration and load out.

Ball mill discharge feeds into the discharge sump for recirculation to the hydrocyclones. The design grinding circuit product is set at 80% passing 106 µm. Hydrocyclone overflow advances to the Rougher 1 flotation circuit at 45% solids by weight. The ball mills were designed to operate at a 30–35% ball charge using 76 mm diameter steel balls and with a circulating load of approximately 300%. These conditions were adjusted by the operations, now showing use of a 30% ball charge. Under these conditions, 15 MW are drawn from the mill motors. A higher ball charge would reportedly require the addition of a retainer ring at the mill discharge. The circulating load is about 200%.

The flotation circuit is of conventional design but the cleaning c ........