The Riacho dos Machados gold deposit is considered to be a classic mesothermal orogenic gold deposit in a sheared and deformed Archean to Proterozoic age greenstone belt sequence. It is comprised of metamorphosed volcanic-sedimentary rock units intruded by slightly younger post-tectonic igneous bodies.

The principal host for the gold mineralization is the quartz-muscovite schist of the RMG. The mineralization occurs in a belt of hydrothermally altered rock developed along a district-scale shear zone that extends almost 30 km along a N20°E strike direction and dips 40° to 45° east. The mineralization has a typical amphibolite facies mineral association which is progressively altered to greenschist facies assemblage. The gold mineralization occurs as “stacked” tabular horizons that are mostly concordant with the principal rock foliation (shear zone). These tabular zones typically consist of a main zone which may be sided by a thinner footwall or hanging wall zones, separated by three meters to ten meters of unmineralized rock. Continuity along strike and at depth is good with gold mineralization occurring continuously over a 2,000 m strike length and up to 1,000 m down dip.

Mineralization occurs in the hydrothermal/shear zone and gold grades are closely related to the sulfide content, especially arsenopyrite. Gold occurs as microscopic native-gold grains - typically, finer than 400 mesh (37 microns) - at contacts between recrystallized quartz grains, muscovite grains and as inclusions in arsenopyrite, and less commonly in pyrrhotite, quartzveinlets, tourmaline, and pyrite.

The following minerals and features, listed from high to low importance, are noted as indicators of gold mineralization:

-Arsenopyrite (both anhedral and euhedral needles) -Pyrrhotite
-Abundant quartz veinlets (sheared into foliation plane)
-Pyrite
-Crenulation folding
-Tourmaline veins (fine-grained massive intergrown).

The arsenic content of the mineralization is quite high with an average of approximately 3,935 ppm As for samples greater than 1.0 g/t Au. Silver content is very low with the average Ag/Au ratio equal to 0.5 for samples with a gold concentration of greater than 1.0 g/t Au. Antimony, copper, lead, and zinc are mostly non-anomalous.

The gold mineralization is closely related to the structural fabric. The main mineralizing fluid upward flow was possibly along the thrust movement direction with lateral escape along interconnecting sub-horizontal structural fabric. Brittle deformation at the Riacho dos Machados gold deposit is limited to poorly defined cross-faults which may have anomalous geochemistry but do not host gold mineralization.

Conventional open pit mining methods are employed at the MRDM open pit including drilling, blasting, loading, and hauling.

The bench height is 12 m, however, mining will occur on 12 m cuts in waste and three metre lifts in ore. Inter-ramp slopes are designed at 34° in the hanging wall for oxide, 43° in the hanging wall for transition, and 52° in the hanging wall for fresh rock. Footwall inter-ramp slopes are 28° for oxide and transition, and 43° for fresh rock.

The final design is approximately 1,620 m long and 700 m wide, with elevations that range from a high of 900 MASL to a low of 600 MASL. Final pit exits for the south and north ramps are at approximately 865 MASL and 800 MASL, respectively. The crusher dump pocket is less than 500 m horizontal distance from the pit exit. MRDM has left adequate buffers around the open pit for possible future expansions, e.g., if the price of gold increases. Some condemnation holes have been drilled in the infrastructure and waste dump areas.

The strip ratio of the design pit is relatively high at approximately 7.5:1 (waste:ore). The mined tonnage is proposed to be at a constant rate throughout the LOM.

The crushing circuit includes a three-stage crushing plant with an availability based on 80% for the crushing circuit. ROM ore is dumped into a feed hopper. A variable speed apron feeder reclaims ore from the feed hopper onto a vibrating grizzly with openings set at 152 mm (6 in.). Oversize from the grizzly discharges into the primary jaw crusher. Undersize from the grizzly combines with the discharge from the jaw crusher onto a conveyor belt. The conveyor belt feeds the primary double deck vibrating screen. Undersize from the screen is conveyed to a fine ore bin via a conveyor belt. Oversize from the screen is fed to the secondary Metso HP-500 cone crusher. Product from the secondary cone crusher is transferred to the vibrating single deck secondary screen. Undersize from the screen is conveyed to the fine ore bin. Oversize from the screen feeds the tertiary crushers. Discharge from the tertiary crushers is returned to the feed of the secondary screen, thus operating the tertiary crusher in closed circuit.

Ore is reclaimed from the fine ore bin by four apron feeders and designed to be fed to the ball mill at the rate of 310 tonnes per hour (tph).

Ore is transferred from the fine ore storage bin to the ball mill feed conveyor. Water mixes with the ore in the feed chute to the ball mill. The mill is 6.7 m diameter by 11.1 m long with twin 4,500 kW motors.

The processing plant was designed to process 7,000 tpd (2.55 Mtpa). The plant can potentially be expanded to 9,000 tpd (3.28 Mtpa) with completion of the power line, addition of another tertiary crusher, installation of a larger mill discharge pump, and installation of larger conveyor belts.

The processing plant includes three-stage crushing, ball mill grinding, CIL, sulphur dioxide-air cyanide detoxification, and a gold adsorption, desorption, and recovery (ADR) plant.

Slurry discharges from the ball mill into the cyclone feed box where the slurry is pumped to the cyclones. Underflow from the cyclones returns to the ball mill feed. The cyclone overflow is the product from the comminution circuit and flows by gravity to a linear trash screen. The underflow from the trash screen flows by gravity into a thickener feed box. Thickened slurry is pumped to slurry holding tanks that feed the CIL circuit. The thickener overflow solution is returned to the process water ta ........