The geology of the Vazante Operation area consists of a sequence of pelitic carbonate rocks belonging to the Serra de Garrote and Serra do Poço Verde formations of the Vazante Group. The currently known mineralization has been traced along a strike length of approximately 10.5 km, extending from the southern end of the Vazante Mine to the northern limits of the Extremo Norte Mine.

The zinc-lead-silver mineralization at the Vazante Operation is hosted by the Vazante Shear Zone which has been traced by drilling and sampling along a strike length of approximately 12 km. The Vazante Shear Zone has a general strike of azimuth 50° and dips approximately 60° to the northwest at surface. The hanging wall lithologies of the Vazante Shear Zone are comprised of dolostone and sericitic phyllite, slates and marl units of the Serra do Poço Verde Formation while the footwall lithologies to the Vazante Shear Zone are dominated by dark grey dolostones of the Upper Morro do Pinheiro Member. Drilling information indicates that the dip of the zinc mineralized zone gradually decreases with depth in the southern portions of the structure.

The zinc mineralization at the Vazante and Extremo Norte mines is composed largely of hypogene zones that are composed mainly of willemite (Zn2SiO4) veins, veinlets, and stockworks that are hosted by sphalerite-rich carbonate. The mineralization typically contains willemite (50% to 70%), dolomite (10% to 30%), siderite (10% to 20%), quartz (10% to 15%), hematite (5% to 10%), zinc-rich chlorite (5% to 10%), barite (<5%), franklinite (<5%), and zincite (<5%), with subordinate concentrations of magnetite and apatite (Monteiro et. al., 2006). Lead and silver are also recovered from the hypogene mineralization is produced from the Vazante Operation. While no detailed studies regarding the specific lead and silver bearing minerals have been carried out on samples of the hypogene mineralization, several detailed mineralogical studies have been conducted using concentrate samples. RPA notes that the majority of the lead mineralization in the concentrates has been found to be related to galena (PbS), with lesser amounts of lead being contained in cerussite (Pb(CO3)). Mineralogical studies have indicated that the silver values are contained in the minerals acanthite (Ag2S) and jalpaite (Ag2CuS2).

Supergene zones of zinc-rich mineralization have been developed in the near-surface portions of the hypogene mineralized zones. These supergene zones are referred to as the calamine zones at the Vazante Operation. The calamine mineralization is composed principally of smithsonite (ZnCO3) that includes subordinate amounts of hemimorphite (Zn4(Si2O7)(OH)2.H2O) and quartz. The calamine mineralized zones were derived from weathering of the primary willemite mineralization.

DEPOSIT TYPES
The zinc deposit found at the Vazante Operation is the largest known non-sulphide zinc deposits in the world and is the type example for this class of mineral deposit. The Vazante Operation mineralization is composed primarily of hypogene zinc silicate minerals dominate in abundance by willemite. The primary hypogene willemite mineralization has been subjected to supergene weathering processes to produce secondary zinc mineralization, referred to as the calamine mineralization, which is composed of smithsonite (ZnCO3) and hemimorphite (Zn4Si2O7(OH)2).

Non-sulphide hypogene zinc deposits are known to occur either as stratiform deposits, or structurally controlled deposits. The mineralization at the Vazante Operation is an example of a structurally controlled deposit.

The hypogene mineralization has two strong controls, lithostratigraphic and structural. The Vazante Operation deposit is clearly confined to a clay-dolomite interval near the contact between the Lower Pamplona Member and the Lower Morro do Pinheiro Member. Mineralization is restricted to the brecciated area in the fault zone that has had a long history of reactivation (Monteiro, 2002). This hypogene mineralization is interpreted to result from deposition of metals from hydrothermal fluids that have moved through the Vazante Shear Zone.

The morphology of the Vazante Operation deposit consists of veins and anastomosing podiform bodies that are fault bounded. The geochemical controls on the deposition of the mineralization are not well understood and the source of the metals is not known. The deposit genesis is thus in debate, as it may have originally represented a sulphide deposit that was subsequently silicified, or it may have consisted of primary zinc silicate mineralization that was later re-concentrated into the Vazante Shear Zone.

Work by Monteiro et. al, (1999, 2006, and 2007) suggest that the willemite can form by reacting sphalerite and quartz through the reaction: 2ZnS + 2SiO2 + 2O2 = 2ZnSiO4 + S2 . This reaction would presumably occur during a low-grade metamorphic event.

Brugger et. al. (2003) investigated the origin of these deposits and suggested that the willemite could form by direct precipitation from hydrothermal fluids under high pH and high oxygen fugacity conditions.

Furthermore, Hitzman et. al. (2003) concluded that the fluids responsible for transporting zinc to the Vazante Operation type zinc deposits appear to be geochemically similar to solutions produced in many continental sedimentary basis. As non-sulphide zinc deposits appear to form from the mixing of highly oxidized, sulphur poor solutions with zinc bearing solutions, they could be found in the same districts as sphalerite-rich Mississippi Valley type or Irish type deposits formed by fluid mixing. Such appears to be the case in the Bambuí Group in Brazil.

The Vazante Operation consists of two mechanized underground mines, the Vazante Mine and Extremo Norte Mine, currently operating at a rate of approximately 1.5 Mtpa. The mineralized zones dip between 45° and 70° and the mine extends over a strike length of five kilometres. With the addition of the North Extension, this will increase to approximately 10 km. The Vazante Mine currently extends over a vertical depth of 300 m from surface to the 326 level. The Vazante Mine is being deepened by 186 m to the planned 140 level. There are former open pits along portions of the strike of the Vazante deposit.

There are two access ramps to the Vazante Mine and one to the Extremo Norte Mine. Mine headings range from 5.0 m high by 4.5 m wide ore drives to 6.0 m high by 5.0 m wide main ramps.

The Vazante Operation is designed based upon mechanized longitudinal longhole stoping for areas with a dip greater than 45°. Longhole stopes are developed with footwall access drives parallel to the orebody. Crosscuts are driven from the footwall drive and then the ore is developed along strike. Sublevels are typically 30 m apart though the distance varies depending on the orebody. Long holes are often a combination of downholes or vertical retreat mining (VRM) and uppers or sublevel longhole open stopes (SLOS). Both longhole methods employ a retreat sequence along strike. The SLOS stopes are not backfilled whereas the VRM stopes are backfilled.

Backfilling at the Vazante Operation consists of loose waste rock fill at the current planned rate of approximately 10,000 t per month.

Ore is mucked with 5 m³ (12.5 t) LHDs working manually when possible (brow full of muck) and on remote control for mucking in the stope (non-man entry conditions). Ore is loaded into 30 t articulated haul trucks at the stope and hauled to surface stockpiles located at the portal. Oversize material is placed aside in a separate stockpile and secondary breaking is carried out with mechanical rockbreakers.

LONGHOLE STOPING
Longhole mining methods are employed for the major portion of the total Mineral Reserves at the Vazante Operation for stopes with a dip in excess of 45°. Levels and haulage drifts are designed to run parallel to, and in the footwall of, the mining blocks. Levels to access longhole stopes are spaced at a vertical interval of approximately 30 m. Crosscuts from the footwall access are generally 70 m along strike.

Both up hole and downhole drilling is carried out. Sill pillars are left as required above an area drilled with up holes. These pillars can be recovered using downholes from the level above.

Sill pillars are left after every second level and are designed to be ten metres in height. There are plans for the recovery of part of these pillars.

Rib pillars ten metres wide are included along strike between every 60 m long stope section. These rib pillars are partially recovered at the completion of the stoping, with a planned recovery of six metres of the rib pillar. The rib pillars serve only to retain the rock fill in adjacent stopes.

Longhole drilling is carried out using Simba longhole drills on up holes and downholes. Drill holes are up to 10 cm in diameter, drilled on rings spaced 2.4 m apart, and with holes spaced two metres apart on each section. The Vazante Operation has four Simba production drills in the drilling fleet with productivities averaging 20 m/h. The fleet includes one in-the-hole (ITH) drill and three top hammer type longhole drills providing the stope drilling requirements.

PLANT C
Run of mine (ROM) ore is crushed in a three-stage crushing circuit in closed circuit with screens to 98% passing 9.5 mm. ROM ore is dumped into a silo and fed to the primary jaw crusher, which discharges onto a primary double deck vibrating screen. The top deck has a 38 mm aperture screen, and the bottom deck is a 16 mm x 14 mm aperture screen. Material retained on the top deck reports to two secondary jaw crushers, while material retained on the bottom deck feeds the tertiary cone crusher. The product of both secondary jaw crushers is returned to the primary vibrating screen. The primary vibrating screen bottom deck undersize is combined with the tertiary crusher discharge, which then forms the overall product from the Plant C crushing plant. This crushed ore is stored in a covered conical pile of up to 4,000 t capacity.

Crushed ore is reclaimed by FEL and fed to the Plant C grinding circuit, which consists of a 2.4 m diameter x 11 m effective length ball mill in closed circuit with three hydrocyclones. The target grind size is approximately 88% passing 150 µm. Grinding circuit product is pumped to Plant W for sulphide flotation.

PLANT W
ROM ore is crushed in a four-stage crushing circuit in closed circuit with screens to 98% passing 9.5 mm. Crushed ore is homogenized on a stockpile with a capacity of approximately 6,000 t by a stacker-reclaimer before being fed to the Plant W grinding circuit, which consists of a ball mill in closed circuit with a high frequency vibrating screen. The screen undersize is approximately 88% passing 150 µm (P80 of approximately 125 µm) and is directed to two conditioning tanks in series prior to feeding the Plant W sulphide flotation circuit.

The Vazante Operation processing facilities have a nominal design processing capacity of approximately 4,400 tpd or 1.6 Mtpa at 96% utilization and produce approximately 350,000 tonnes per annum (tpa) to 370,000 tpa of zinc concentrate and approximately 4,000 tpa to 5,000 tpa of lead concentrate that contains small amounts of silver. They consist of two adjacent plants, Plant C and Plant W, that are interconnected at various points. Zinc concentrate produced at the Vazante Operation is sent to Nexa’s Três Marias zinc smelter approximately 250 km from Vazante.

Processing at the Vazante Operation comprises conventional crushing, grinding, flotation, concentrate dewatering, and tailings disposal. The main differences between the two plants is that Plant W incorporates a sulphide flotation stage for the recovery of a lead–silver concentrate. Both plants include crushing, grinding, and zinc flotation. Combined Plant W and Plant C tailings are thickened and filtered prior to dis ........