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).

The Serra Grande operation comprises three underground mines, namely Mina III (including orebody IV, V and Ingá), Mina Nova (including Pequizão orebody) and Mina Palmeiras. The open pits mine the outcrop of Mina III Inferior and Structure IV zones, and Pequizão. Three mining methods are used underground: sub-level stoping (bottom-up and top-down), cut and fill, and room and pillar.

The metallurgical plant has the capacity of 1.5Mtpa, combining CIL and gravimetric circuits. The ore is blended to feed the crushing circuit with a capacity of 3,800tpd. There are two mills in operation, and 20 leaching tanks with a capacity of 4,800m3 divided between preliming and cyanidation stages. Approximately 58% of gold is captured in the parallel gravity circuit. The rest of the gold is recovered by the CIL process to form the bullion that is sent to Nova Lima for refining.