The Vazante deposit is one of the major known nonsulfide zinc deposit in the world (Hitzman et al., 2003), and includes ore types characterized by predominance of hemimorphite or willemite. The hemimorphite-rich ore is associated with karstrelated collapse breccias developed in pelitic–dolomitic units of the Neoproterozoic Vazante Group (Dardenne, 2000) and controlled by NE-oriented brittle faults and fractures. The willemitic ore (18.8 Mt at 23.7% Zn; T.F. Oliveira, 2006; personal communication) is structurally controlled and occurs imbricated with small sulfide-rich ore, hydrothermally altered dolostones, slates, and metabasites.

The Vazante deposit is one of the major known nonsulfide zinc deposit in the world (Hitzman et al., 2003), and includes ore types characterized by predominance of hemimorphite or willemite. The hemimorphite-rich ore is associated with karstrelated collapse breccias developed in pelitic–dolomitic units of the Neoproterozoic Vazante Group (Dardenne, 2000) and controlled by NE-oriented brittle faults and fractures. The willemitic ore (18.8 Mt at 23.7% Zn; T.F. Oliveira, 2006; personal communication) is structurally controlled and occurs imbricated with small sulfide-rich ore, hydrothermally altered dolostones, slates, and metabasites.

The nonsulfide zinc mineralization is epigenetic, linked to the development of the Vazante Shear Zone (Fig. 3A), which is approximately 12 km long, strikes N50E, dips 60NW, and has been interpreted as a transpressional transcurrent fault later reactivated as a normal fault (Pinho, 1990).

The zinc ore is hosted by gray- to pink-colored dolostone with cyanobacteria mats and bird's-eyes, slate and phyllite of the Lower Pamplona Member, close to the contact with dark gray dolostone and pyrite-bearing carbonaceous slate and marl of the Upper Morro do Pinheiro Member.

Metamorphosed basic dikes occur tectonically imbricated with hydraulic breccias, hydrothermally altered dolostones and slates, and with the nonsulfide zinc ore within the Vazante Shear Zone (Monteiro, 1997; Monteiro et al., 1999; Babinski et al., 2005).

The nonsulfide zinc ore bodies are tectonically controlled mainly by antithetic faults subsidiary to the main shear zone and display pod morphology. Small sulfide-rich ore bodies are essentially composed of sphalerite and galena. Sphalerite is dark brown and remarkably homogeneous under transmitted light and has strong yellow cathodoluminescence (CL), which could be related to its high Cd (average of 8410 ppm) and low Fe (average of 0.09%) contents (Monteiro et al., 2006). Willemite is also present in the sulfide-rich ore bodies and is commonly associated with pervasive silicification along the mylonitic foliation, as part of two distinct associations: willemite + sphalerite+ franklinite ± zincite (without quartz) and willemite+ quartz + dolomite + franklinite ± barite ± smithsonite (without sphalerite). These assemblages suggest the formation of willemite from sphalerite and quartz by the reaction: 2ZnS+ 2SiO2+ 2O2= 2ZnSiO4+ S2, which indicates that f S2 and fO2 may have played an important role in the stability of this mineral assemblage (Monteiro et al., 1999, 2006).

The massive nonsulfide zinc ore, which represents the bulk of the Vazante ore, is composed mainly of coarse-grained colloform or fibrous-radiated willemite partly replaced by finegrained willemite, both with strong green CL. Commonly, quartz, dolomite, zincite, barite, and apatite occur associated with willemite, but sulfide relicts are absent. The predominance of this ore type could also suggest hydrothermal formation of willemite from the mineralizing fluids at high f O2/f S2. These conditions are consistent with those experimentally predicted by Brugger et al. (2003), leading to the formation of willemite instead of sphalerite, especially at temperatures higher than 150 °C.

In the brittle–ductile or brittle structures, hematite and Zn– chlorite are also present. In general, these minerals cut the previous willemite generations and form hematite rich nonsulfide zinc ore bodies, which are ubiquitous in the Vazante deposit. Later siderite and sphalerite veinlets cut the nonsulfide zinc ore, and are considered as related to fluctuations in the f O2/fS2 conditions (Monteiro, 1997; Monteiro et al., 1999).

The Vazante mine is an underground and open pit mine located about seven kilometers from the municipality of Vazante, in the state of Minas Gerais, Brazil.

The Vazante underground mine has been in operation since 1983, and is a fully mechanized mine using rubber tired diesel equipment for development and production activities. Access is through two portals for Vazante and one portal for Extremo Norte. As development progresses at Extremo Norte, a connecting drift will be established from Vazante to Extremo Norte.

The mine has a current depth of 350 m below surface and currently is producing from six levels. Future expansion is planned below the current Level 326 horizon to expose additional mineralization for extraction.

Two primary mining methods are employed at Vazante for extraction:
- SLOS; used where there is no continuity of the mineralization between levels

- VRM; used where the mineralization is continuous between levels.

Backfill is used in conjunction with VRM; with SLOS, the stopes are left open after mining.

Waste from lateral and ramp development is used as backfill in the VRM stopes. Waste rock is dumped into the stopes from the overcut drifts to provide support to the hanging wall and reduce dilution of subsequent mining lifts. Between stopes, a 10 m rib pillar is left to prevent backfill dilution of adjacent stopes, and sill pillars are left every 60 m of mining height to prevent backfill dilution from mining blocks extracted from higher mine levels.

Ore is hauled to surface with 28 t haul trucks via ramps, and is stored in surface stockpiles at the portals for later re-handle. Ore is delivered to the concentrator with a surface haul truck fleet.

Vazante is a trackless operation utilizing a diesel-powered mobile equipment fleet. The selected equipment is sized to meet the mine production targets for material movement with the calculated cycles and productivities. The current mine haulage fleet, and stope mucking and development waste mucking equipment are split between the Vazante and Extremo Norte Mines. The fleets are not restricted to the currently- assigned mines and can be moved between sites as operational requirements dictate.

Vazante is the largest zinc mine in Brazil, processing about 1.5 Mt of ore annually grading an average of about 11.3 wt% Zn to produce about 135 kt of zinc metal contained in willemite and bulk sulphide concentrates. Concentrates are sent to Votorantim’s Tres Marias zinc smelter, located about 250 km from the operations.

Processing is conducted in two adjacent plants (C and W) based on crushing, grinding and flotation with some interconnected concentrate handling systems. The main differences between the flowsheets for the plants is that Plant W incorporates a sulphide flotation stage for recovery of a lead–silver concentrate. Both plant flowsheets include crushing, grinding and willemite flotation. Willemite concentrate is filtered for transport to the smelter, and combined Plant W and Plant C tailings are thickened prior to disposal in the tailings storage facility (TSF).

Plant W is a modern plant and processes about 80% of the total tonnage of highergrade ........