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 occurs on six meter lifts (flitches) in waste, and three meter lifts in ore. Road widths are 21 m. Berm widths normally are six meters in the oxide and transition ore, eight meters in the hanging wall fresh rock, and 12 m in the footwall fresh rock.

The processing plant was designed to process 7,000 tpd, with the potential to expand to 9,000 tpd (3.28 Mtpa) with some modifications, using three-stage crushing, ball mill grinding, CIL, sulfur dioxide-air cyanide detoxification, and a gold adsorption, desorption, and recovery (ADR) plant.

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 Metso model 125 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 th ........