The deposition of gold in the iron formation occurred when sulfur-rich auriferous hydrothermal solutions, ascending through favorable pathways in the shear zone and fault structures, reached the iron-rich minerals and reacted with them, collected iron from the magnetite and iron silicates and dumped iron and sulfur as sulfides, in the process also precipitating silica, carbonates and the gold.

The pattern and intensity of mineralization varies from place to place, from disseminations to massive ore shoots, with combined thickness of up to 25 meters.

The orebodies are composed of concentrations, bands, veins, veinlets and disseminations of fine-grained silica, carbonates and sulfides, which fill open spaces and totally or partially replace the host rocks. The initial data indicated a dominance of pyrrhotite at north and pyrite at south, followed by variable quantities of arsenopyrite, chalcopyrite and galena. Gold occurs in free form or included in the sulfides.

Open pit mining is currently being undertaken by new mine contractor Unienge & Modulo (U&M), the largest mining and locally experienced contractor in Brazil. The mining operations are based on the use of hydraulic excavators and a haul truck fleet engaged in conventional open pit mining techniques.

Excavated material is loaded to trucks and hauled to either the ROM, long term low grade or marginal stockpiles, the iron ore stockpile, or the waste dump. Ore excavation and haulage is monitored by quality control personnel employed by the Geology department and details of material movement are recorded by a radio dispatch system “Tecmine”. Oxide material is free dig with transitional material lightly blasted to loosen it for digging. Fresh rock is typically blasted on 4 m benches however 8 m benches are also fired. For wide sulphide ore lodes, the ore can sometimes be blasted separately if the shot is sufficiently large to minimize dilution. Normally ore and waste are fired together requiring the use of 8 m long poly pipes or Blast Vector Indicators (BVI) at each node of the ore polygon to determine post- blast movement. Ore sent to the ROM is stockpiled on fingers of oxide or sulphide within various grade cut-off categories to facilitate blending to achieve the desired oxide / sulphide proportions and grade.

The existing Tucano Mill consists of a jaw crusher feeding a single-stage, semi-autogenous grinding mill (SSAG), with the ore then being treated in a CIL plant. GPR is currently planning on mining and treating approximately 3.6 Mtpa of ore through the process plant, elution, and electrowinning facility to produce around 140,000 to 150,000 ounces of gold per year. The plant treats an ore blend of 80% oxide and 20% sulphide.

Ore is delivered to a run-of-mine (ROM) pad where ore of oxide and sulphide are stockpiled separately on fingers of specified grade ranges. Ore is fed to the crusher hopper by means of a front-end loader to achieve the planned sulphide / oxide blend and grade for the day. A vibrating grizzly allows the finer, sticky oxide ore to bypass the crusher. Crushing is achieved using a 1,220 mm x 1,070 mm single toggle jaw crusher with a closed side setting (CSS) of 125 mm. In addition to the jaw crusher, a separate Spent Ore Feeder is located in the emergency stockpile area to facilitate the feeding of Spent Ore direct to the SAG mill. A surge bin with 30 min residence time and a diversion chute to an emergency stockpile feeder is located halfway between the crusher and the SAG mill.

Grinding is achieved with a SSAG mill with a 7 MW single-pinion drive, a diameter of 7.32 m and an effective grinding length (EGL) of 7.95 m. Cyclones operate in closed circuit with the mill to produce a product size which is currently coarser than 80% < 105 µm. After construction of the 6 MW ball mill, the grinding circuit will achieve a finer grind of 80% < 75 µm.

Cyclone overflow from the grinding circuit is screened in the trash screen and is then pumped to the CIL circuit. The CIL circuit consists of six 2,650 m3 (live volume) carbon contactors, located south of the reagent storage area on the area formerly occupied by the rich solution pond from the heap leach operation. A seventh tank will be installed as part of the current mill expansion. It will not be fitted with a screen and will operate as leach tank only, ahead of the existing CIL.

The six existing CIL tanks operate in series. Launders connect the tanks to allow slurry to flow by gravity through the tank train. All tanks are fitted with bypass launders to allow any tank to be removed from service for agitator or screen maintenance.

Each tank is fitted with a 110 kW mechanical agitator to ensure uniform mixing. Air is currently sparged into each leach tank to provide adequate oxygen for gold dissolution. An oxygen plant will be constructed during the expansion to provide increased recoveries at the higher proportion of sulphide material in the ore blend.

Each CIL tank is fitted with a single 12 m2 mechanically-swept, wedge-wire inter-tank screen to retain carbon. The style of inter-tank screen selected is known as a “pump screen”, which allows each of the CIL tanks to be installed at the same elevation, in contrast to the stepped arrangement used for conventional cascade carbon-in-pulp (CIP) plants. This simplified the civil engineering requirements of the CIL area. Barren carbon enters the adsorption circuit at the last tank, CIL Tank 6, and is advanced counter-currently to the slurry flow by moving slurry and carbon from CIL Tank 6 to CIL Tank 5 using recessed impeller carbon-transfer pumps. The inter-stage screen in CIL Tank 5 retains the carbon and the slurry flows by gravity back to CIL Tank 6. This counter-current process is repeated until the carbon reaches CIL Tank 1. A single recessed-impeller pump is used to transfer slurry to a loaded-carbon recovery screen. The carbon reporting as screen oversize flows to the carbon transfer column and the screen undersize returns to CIL Tank 1.

The loaded carbon is washed with process water in the carbon transfer column to remove slimes prior to the elution circuit. An eductor, using raw water, is used to transfer the washed carbon to the existing desorption circuit. Barren carbon returning to the adsorption circuit from the carbon regeneration kiln is screened over a vibrating screen to remove fine carbon which is then collected and stockpiled for processing off site. The sized and regenerated carbon reports directly to CIL Tank 6.

Sodium cyanide (NaCN) solution is metered into Leach Tank No. 1 and CIL Tanks 1 and 2 via a ring main system. Final pH adjustments are made by the addition of lime to the CIL feed box from a lime slurry ring main system. Tailings slurry from the last CIL tank flows to the vibrating carbon safety screen to recover any carbon that may be present due to damage, wear, or incorrect installation of the final stage inter-stage screen. Carbon recovered on the screen is delivered to a bulk bag for re-use. Tailings discharging from the carbon safety screen underflow are transferred via gravity to the cyanide detoxification circuit. The leach and adsorption area is provided with three spillage pumps, which deliver any spillage in the area back to the process. Maintenance of the CIL tanks and agitators is achieved using an overhead crane.

The new leach tank and the six CIL tanks, give the combined CIL tanks a total residence time of just over 24 hrs at the expected slurry density.

The existing Pressure Zadra elution circuit and gold room were already in place when BDR acquired the plant from the previous heap leach operation and the CIL plant was configured to use these facilities. The elution columns are primed with a solution of 0.1% cyanide and 1% caustic soda that is prepared in the electrowinning solution tank. This solution is recirculated through the elution columns at 135°C to promote the elution of gold ions that are adsorbed in the micro pores of the loaded carbon. The heating of the recirculating solution is provided by a 720 kW electrical elution heater. The current elution circuit is sized to treat 4.8 tonne of carbon per day.

Once the acid wash cycle is complete, the carbon is educted to the kiln feed hopper, where the carbon is screw-fed to the kiln dewatering screen, to dewater the carbon to 50% w/w solids. The undersize of the kiln dewatering screen is brought to grade, to be collected by the acid wash area sump pump. The kiln dewatering screen oversize reports to the kiln feed hopper. Carbon is withdrawn from the kiln feed hopper by a screw feeder and fed to the carbon regeneration kiln. Carbon regeneration is achieved at a temperature of 700°C. After regeneration, the barren carbon is discharged into the carbon quench tank to reduce the temperature of the carbon to room temperature. The barren carbon is then transferred back to the CIL circuit. The carbon regeneration kiln acquired from the previous heap leach operation has been extensively refurbished by BDR.

The rich solution leaving the elution columns passes through two heat exchangers, arranged in series, to reduce the solution temperature, then through a cyclone separator to the electrowinning feed tank. The solution flows from the electrowinning feed tank through a bank of two electrowinning cells, where the gold in the solution is deposited on the cathodes within the cells. The weak solution leaves the electrowinning cells and returns to the electrowinning solution tank. This solution is then pumped back through the elution heater to the elution columns. The solution is recirculated through this closed circuit for 12 hrs, until the disposition of gold onto the cathodes is complete. At the end of the elution cycle, the carbon is transferred to the acid wash column. The barren eluate solution is pumped from the electrowinning solution tank back to the CIL circuit.

The acid wash cycle consists of a six-hour acid wash, in which 15% hydrochloric acid (HCl) is recirculated through the column, followed by a two-hour water wash. The HCl is delivered to the acid wash column by a dedicated acid wash HCl tank and pump set, located in the desorption area. The 15% solution is prepared by the addition of 33% HCl from t