The Fazenda Brasileiro gold deposit is an epigenetic, structurally controlled and hydrothermally altered Precambrian quartz vein hosted lode gold deposit that has been subjected to greenschist facies metamorphism. There is some suggestion of a partial syngenetic origin for the gold because of the anomalous gold content (0.05 g/t Au to 0.10 g/t Au) throughout visibly unmineralized CLX.

Gold mineralization is related to multi-phase quartz veining events. The gold occurs in at least three textural settings at MFB: as particles attached to sulphide grains, as particles within fractures in sulphide grains, and as particles within fractures in quartz/albite gangue. Gold grains typically contain less than 5% silver.

The bulk of the mineralization is hosted by quartz-albite-sulphide veins within the chlorite schist (CLX) unit. Individual veins vary from one to four centimetres thick, have irregular margins, and are typically oriented sub-parallel to the predominant east-west trend of the felsic and mafic schists. The veins occur in multiple vein sets which vary in true width from 1.5 m to 40 m and in horizontal mining width from a minimum 3 m to 40 m. The veins are generally arcuate in an east-west trend and south dipping at 40° to 70°, with a shallow to moderate east plunge. The plunge, however, is quite variable, with some zones plunging westerly.

Mineralization is also found stratigraphically below the CLX unit in the CLX2 and Canto horizons. Economic mineralization occurs in horizontal to sub-horizontal shoots, the locations of which are influenced by a combination of folding and shearing. Shoots range from tens of metres to hundreds of metres in length and tens of metres in height.

OPEN PIT
Many of the identified mineralized lenses outcrop to surface. Over the course of the operation’s history, several shallow open pits have been excavated to extract these near surface deposits. Currently, several small open pits are in operation, and mining is being completed using contractors. Typically, these small pits are 30 m to 50 m deep and employ air-track drills and backhoe excavators for mining, and highway-type trucks for haulage to the mill.

UNDERGROUND
The main access to the underground operation is through a series of declines. Over the life of the operations, eight main declines - the B, C, D, E, F, G, EW, and EDEEP - have been developed along the strike of the mineralization. A main central shaft (470 m deep) exists, however, it is no longer used for hoisting as the portion of the deposit located within economic distance of the shaft has been mined out. The shaft is now utilized only as a part of the escapeway and ventilation circuit.

Underground mining employs blast hole stoping from sub-levels developed along the trend of the mineralization. The stoping areas are accessed initially from 5 m wide by 5.5 m high main haulage ramps developed at 12% road grade in the footwall, which leads to primary development crosscuts of 4.5 m wide by 5.1 m high, and secondary development drifts and crosscuts of 4.5 m wide by 4.7 m high. Sub levels are spaced at 25 m vertical intervals. Mined out stopes are not backfilled.

Sub-levels are developed into the stoping areas and fan drilling of blast holes into the mineralization is used to further define the boundaries of the mineralization and design the ultimate blast patterns. Remote-controlled 12 t Load-Haul-Dump (LHD) machines are used to load and haul the ore from the stoping areas to 25 t and 35 t articulated haulage trucks at loading points in the sub-levels.

The sub-horizontal plunge and approximate 45° dip of the orebody, combined with a thickness up to 40 m, provides for low development and operating costs. Maximum stope heights are 20 m. Future operations in the deeper areas of E Ramp will have higher haulage costs that will be partially offset by the shorter underground haulage in the F and G Ramps.

All bodies have a planned dilution of 14%, except for the F Body, which has a dilution of 20%. Planned mining recovery was estimated to be 91%, except for F Body, which is 89%. In a small number of areas, where weaker ground is anticipated, planned mining recovery was estimated between 83% and 85%.

PRIMARY CRUSHING
The ore flows from the feed hopper to a twin shaft Blake type 1,200 mm by 900 mm primary jaw crusher with a closed side setting of 89 mm. The discharge from the primary crusher is conveyed to a crushed ore stockpile with a nominal capacity of 19,000 t.

SECONDARY/TERTIARY CRUSHING
The crushed ore is drawn from the stockpile by two vibrating feeders, installed in a tunnel under the stockpile, and conveyed to the secondary/tertiary crusher area. The ore is conveyed to the primary double deck, vibrating screen. The upper deck has 30 mm openings and the bottom deck has 12 mm openings. The oversized material from both decks feeds a Metso HP300 secondary cone crusher with a closed side setting of 19 mm. The secondary crusher product is conveyed to the secondary screen feed bin and then to two secondary double deck vibrating screens operating in parallel. The upper and lower decks of the secondary screens have 12 mm screen openings. The oversized material from the secondary screens feeds two tertiary Metso HP200 cone crushers operating in parallel, with closed side settings of 10 mm. The tertiary crushers operate in closed circuit with the secondary screens, therefore, the discharge of the tertiary crushers is conveyed to the secondary screen feed bin and to the secondary vibrating screen closing the circuit.

The -12 mm undersized material from the primary screen joins the undersize material from the secondary screen and is conveyed through a flow divider to the grinding mill feed silos, where a reversible conveyor distributes the ore between the two silos. There are separate feed bins for each of the two parallel mills. The flow divider allows for bypassing material from secondary/tertiary crushing to an emergency stockpile with a capacity of 6,000 t. The emergency stockpile provides feed for the mills during interruptions in crusher operation, typically for maintenance.

GRINDING
The crushed ore is drawn from the mill feed bins by belt feeders into the two overflow ball mills operating in parallel. One ball mill is 3.8 m diameter by 7.3 m long with a 1,500 kW drive and a capacity of 116 tph. The second mill is a 3.0 m diameter by 5.2 m long with a 635 kW drive and a capacity of 45 tph. The discharges of the ball mills are fitted with trommel screens to remove ball chips.

The ball mills operate at a slurry density of approximately 75% solids. The slurry discharges into separate cyclone feed sumps. Each mill operates with a separate set of cyclones for classification. The cyclone clusters include two dedicated cyclones that feed a portion of the cyclone underflow slurry to the gravity concentration circuit. The cyclone feed slurry density is controlled at approximately 50% solids resulting in a cyclone overflow density of 30% solids and a particle size distribution of 80% passing 74 µm. The cyclone underflow slurry will have a density of approximately 75% solids.

The ball mill work indexes of the underground and open pit ores are 16 kWh/t and 10.5 kWh/t respectively and the ball consumption is in the range of 720 g/t.

The cyclone underflow from each set of cyclones flows to the ball mill feed chute, closing the circuit. The overflow slurry from all of the cyclones will flow to the leach feed thickener.

The overall process flow sheet consists of:
• Three stage crushing.
• Ball mill grinding consisting of two mills in parallel, closed with cyclones.
• Gravity concentration using centrifugal concentrators; treating the underflow of one cyclone in each of the grinding cyclone clusters.
• Thickening to produce a leach feed of 50% solids.
• Cyanide leaching in two parallel circuits, Circuits 1 and 2.
• CIL in two parallel circuits, Circuits 1 and 2.
• Zadra pressure stripping of the carbon.
• Intensive cyanidation of the centrifugal concentrator concentrates.
• Electrowinning of the carbon eluent and gravity concentrate leach solution.
• Casting of gold bars in an induction furnace.

GRAVITY SEPARATION
The smaller, 3.0 m diameter ball mill feeds a bank of four cyclones, with two cyclones operating and two in reserve. The cyclone overflow flows to the leach feed thickener. A portion of the cyclone underflow is diluted to 40% s ........