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.

The mining methods used at Fazenda include conventional truck and shovel for the open pit mining and mechanized sublevel stoping method for the underground mining.

Open Pit Mine
Currently, several small open pits are in operation and being mined by contractors. These small pits are 25 to 80 m deep and are being developed using air-track drills for grade control drilling, backhoe excavators for mining, and highway-type trucks for haulage to the mill. Pit depths are dependent on the economics of stripping overlying waste. Mineralization exceeding pit depths is considered for underground mining.

Underground Mining
Underground mining employs blasthole stoping from sublevels developed in the mineralization footwall. The stoping areas are accessed initially from 5 m wide by 5.5 m high main haulage ramps developed at a 15% road grade in the footwall, which leads to primary development crosscuts with the same dimensions of the main ramps, and secondary development drifts and crosscuts of 4.5 m wide by 4.9 m high. Sublevels are spaced at 20 m vertical intervals. In general, mined-out stopes are not backfilled.

From the sublevels, access drifts are developed into the stoping areas, and fan drilling of blastholes into the mineralization is used to further define the boundaries of the mineralization and design the ultimate blast patterns. After blasting, remote-controlled, 10 tonne-capacity load-haul dump (LHD) machines are used to load and haul the ore from the stoping areas, and 30 tonne-capacity haulage trucks are used at loading points in the sublevels.

The plunge of the orebody is approximately 45° dip and the maximum stopes 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. To date, most of the waste rock has been hauled to surface.

Mining Design:
• Minimum distance between lenses: 5 m;
• Development with a 15% maximum inclination;
• Main ramp in the footwall at a minimum distance of 15 m from deposit;
• Cut-off grade: 1.32 g/t;
• Most stopes designed with 6.25 m (X) by 2 m (Y) by 20 m (Z);
• Minimum stope width: 2 m;
• Overall average planned stope dilution: 20%–30%;
• Mining recovery for sublevel stoping method: 90%.

The main access to the underground operation is through a series of declines. To date, eight main declines have been developed along the strike of the mineralization—B, C, D, E, F, G, EW, and EDEEP.

The B, C, D, E, and G declines have surface portals, and the F decline was developed from an underground split from the G decline. The EW and EDEEP declines were developed from an underground split from the E decline. A 470 m deep main central shaft 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 used only as a part of the escapeway and ventilation circuit.

- subscription is required.

Currently, the two leaching circuits operate with pre-aeration and CIL. With improvements made over time, the plant is capable of processing 175 t/h, and approximately 1.35 Mt/a (3,300 t/d).

The overall process flowsheet consists of:
• Three-stage crushing;
• Ball mill grinding consisting of two mills in parallel, closed with hydrocyclones;
• Gravity concentration using centrifugal concentrators; treating the underflow of one hydrocyclone in each of the grinding hydrocyclone 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 Concentration
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