The gold deposit is orogenic mesothermal, associated with the development of shear zones. The host rocks belong to the Upper Archaean Crixás Group. Gold mineralisation is associated with meta-sediments and meta-volcanics rocks from the Ribeirão das Antas and Rio Vermelho formations respectively. The Crixás Greenstone Belt is surrounded by granitic gneiss terrains from the Anta and Caiamar complexes and meta-sedimentary rocks from the Santa Terezinha Group, which is part of the Goiás magmatic arc.

The mine complex is located in the Crixás Greenstone Belt sequence, in the central portion of Brazil, and the main host rocks are the meta- sedimentary sequences with association with meta- volcanic meta-basic rocks. The mineralisation at MSG is associated with quartz veins and massive to disseminated sulphides in meta-sedimentary, meta- volcaniclastic and meta-basalt rocks, with differing degrees of hydrothermal alteration developed over orogenical stacked thrust layers (duplexes).

Two main deformation events are responsible by mineralisation style. The first event is the principal thrust event (east over west, called D1) and develops an irregular thrust ramp geometry. This event stacked and inverted the stratigraphic sequence. The second event (D2) was the Santa Terezinha sequence (Magmatic Arc) thrusting over Crixás Greenstone Belt, folding the rocks (F2) and generating the structures that control the gold mineralisation, generally parallel to the fold axis.

Geometry of the mineralised deposits is typically complex, pinch and swell, folded and boudinage shapes, dipping from 10° to 25° and with greatest continuity along north-west-plunging structures (azimuth 290°).

The mineralisation have been split into four main domains called structures – the thrust ramps themselves (named Structure II, III, IV and Palmeiras), and occurs as stacked lenses, generally concentrated in the same high deformation positions (with folds and disruptions) in the structures.

In Structure II the mineralisation is arsenopyrite associated with quartz as veinlets in carbonaceous meta-pelite.

In Structure III, the mineralisation is located in quartz veins that are hosted in carbonaceous schists, representing the highest gold grades (>8g/t, with free gold), as seen in Mina III (Inferior zone) and Ingá. This structure is also associated with massive and disseminated sulphides (mainly pyrrhotite and arsenopyrite) that occur in a sequence of hydrothermally-altered schists, commonly named superior zones.

In Structure IV, the mineralisation comprise quartz veinlets and disseminated sulphide (pyrrhotite) hosted in graphite schists as at Pequizão. The mineralised zones are hosted in sericite and chlorite schists with massive and disseminated sulphide concentrated in folded zones. The ore shoots plunge to the north-west and the dips vary between 6° and 35°.

The Palmeiras structure is associated with hydrothermal alteration of meta-basalts, with sericite, chlorite, carbonate and massive sulphides (pyrrhotite).

Serra Grande comprises three mechanised underground mines, Mina III, Mina Nova and Mina Palmeiras, and an open pit as well as a dedicated metallurgical plant.

Three mining methods are used underground: sub-level stoping (bottom-up and top-down), cut and fill, and room and pillar. The open pits use standard drill and blast, followed by truck load and haul.

Serra Grande operates a single TSF, which will support the LOM production.

The metallurgical plant has the capacity of 1.5Mtpa, combining CIL and gravimetric circuits. The ore is blended to feed the crushing circuit which has a capacity of 4,100tpd.

The leaching area of Serra Grande Operation comprises 20 tanks; such tanks are provided with mechanical stirring by means of propeller-type stirrers and stirring by compressed air injection. Leaching is divided into two stages: pre-liming and cyanidation.

The Pre-liming process takes place in tanks 1, 2 and 3 and consists in preparing the slurry for Cyanidation, which is initiated in tank 4. Lime addition, already initiated during milling is repeated in tank 1 of the leaching area. The pH is control at approximated 10:5 at 2:00 hour interval by analyses made by a pH meter and being correct according to the result of the analysis. Hydrogen Peroxide is also added in those tanks in order to increase the concentration of dissolved oxygen on the slurry, a very important reagent to the cyanidation ........