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.

Salobo I and II
Run-of-mine ore at 2.5 m top size is hauled in 240 t trucks and crushed in one of two 60” x 89” primary gyratory crusher (600 kW motor), rated for 1,826 t/h each, to a product size distribution with 80% of the mass passing 152 mm while operated with an open-side setting (OSS) of 140 mm. The dump pocket capacity is equivalent to the volume of 2.5 trucks. Primary crushed ore is conveyed to a common crushed ore stockpile which has a live capacity of approximately 24,800 t and a total capacity of 73,400 t.

Four coarse ore stockpile reclaim feeders are used to feed onto the primary screen feed conveyor which feeds two operating double-deck vibrating screens. The screens have a 100 mm aperture top deck and 55 mm aperture bottom deck to yield and underflow product sizing of 80% passing 38 mm. Screen oversize is crushed in two MP-1000 cone crushers (746 kW motors) in a standard closed circuit. A third screen and crusher were added to the original two units with the Salobo II plant. These units are typically on standby.

Secondary-crushed product is then conveyed in a 2 km long pipe conveyor running at a speed of 2.5 m/s to the secondary crushed ore stockpile. This stockpile has a total capacity of approximately 171,000 t and a live capacity of about 75,000 t.

Two parallel lines of four operating reclaim feeders each are then used to reclaim the crushed ore and deliver it to the High Pressure Grinding Roll (HPGR) circuit via the two stockpile reclaim conveyors merging into a single line of transfer conveyors leading to the HPGR silos feed conveyor, equipped with a shuttle head. This unit delivers ore into one of four concrete silos, providing approximately 20 min of surge at nominal capacity. A reversible feed belt conveyor and feed belt feeders then feed each of the four HPGR units.

Each HPGR unit has a drum 2.0 m diameter by 1.5 m wide. The maximum feed size is 55 mm and the HPGR product is exhibiting 80% passing 17 mm while operating with a 40 mm gap and at 150 bars of hydraulic pressure applied to the floating roll. The crushed HPGR product is discharged via the product collection conveyor and is then screened at 8 mm on the bottom deck of banana screens, with the top deck aperture set at 15 mm. There are a total of eight operating screens, with half dedicated to the HPGR of either Salobo I or Salobo II. The screen undersize, at 80% passing 6 mm, discharges directly into one dedicated ball mill discharge sump. The screen oversize is recirculated back via the screen oversize collection conveyor to the HPGR silos feed conveyor for further crushing. The circulating load is typically 110% around this circuit.

Slurry in the ball mill discharge sump is pumped to a battery of ten 660 mm hydrocyclones, of which seven are typically operating. Hydrocyclone underflow is fed by gravity to an overflow ball mill of 7.9 m diameter by 12.2 m long, equipped with a 17 MW gearless motor. There are four ball mills operating in closed circuit, each with a dedicated hydrocyclone cluster.

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 ........