The Vazante Group hosts the largest Zn–Pb district in South America. Morro Agudo and Vazante mines, and several other minor deposits like Ambrósia and Fagundes are hosted in dolomitic rocks of the Vazante Group.

The lead–zinc deposits of the Vazante Group have been compared to Mississippi Valley-type (MVT) (Amaral, 1968; Rigobello et al., 1988; Iyer et al., 1992), sedimentary-exhalative (SEDEX) (Misi et al., 1996; Freitas-Silva and Dardenne, 1997) and IRISH-type (Hitzman, 1997a; Cunha et al., 2000; Misi et al., 2000; Dardenne, 2000; Monteiro, 2002).

The sulphide mineralization at Morro Agudo mine is composed of sphalerite, galena and minor pyrite. They are accompanied by calcite, microquartz (length slow), megaquartz and barite. Massive and disseminated mineralization is distributed along a fault zone striking N10–20W and dipping 75° to S. The main fault is a normal fault and mineralization was restricted to hanging wall. It is subdivided into four main types (Romagna and Costa, 1988) (Fig. 3):

M orebody: composed of coarse-grained galena and sphalerite forming irregular bodies in dolarenites at the top of the Morro do Calcário Formation.

N orebody: composed of fine-grained, stratiform mineralization in dolarenitic beds. The alternating lamina of chert, galena, sphalerite and pyrite and the presence of millimetric beds of ultra-fine sphalerite suggest a syngenetic to syndiagenetic mineralization for this ore body, as demonstrated by Cunha (1999) and Misi et al.
(2005). Nodular sulphide mineralization is associated with microcrystalline, fibrous and length-slow quartz, suggesting that a previous evaporític facies controlled the mineralization (Folk and Pittman, 1971). The N orebody is confined to the argilodolomitic sequence (SAD) on the top of the Morro do Calcário Formation.

JKL orebody: consists of massive fine-to coarse-grained sulfides (mainly sphalerite), cementing peloidal dolarenitic beds. Peloidal and oncolitic grains are neomorphosed and dolomitized and partially preserved from late silicification.

GHI orebody: consists of coarse-grained sphalerite and galena cementing brecciated structures. Breccias contain angular clasts and blocks of dolostones, including clasts of the N orebody. The clasts characteristics suggest that at least part of the breccia bodies were formed by dissolution and collapsing of the upper strata.

The primary extraction method at the Morro Agudo Mine is inclined room-and-pillar. The mineralized zones are accessed via a ramp system that is developed in the hanging wall of the deposit. Cross-cuts are then developed into the deposit to access the mineralized material. The ore drives are developed along the strike of the deposit, and stubs are developed to establish pillars and extract the mill feed material. Backfill is in limited use at the Morro Agudo Mine and is specified on an operational basis depending upon the deposit geometry.

The Morro Agudo Mine is a mature operation, and staff have a well-developed understanding of the hydrogeology, geology, and mining methods required to safely extract the mineralization. Development and access profiles take advantage of the known hanging wall structural characteristics to minimise ground support requirements. Water inflows into the Morro Agudo Mine are not a major source of water volume to the mine.

The Morro Agudo Mine ventilation infrastructure is essentially at the full extent of development and is not currently planned to have significant expansion going forward.

The primary mine access for material and personnel is a ramp via the portal. A shaft is used primarily for hoisting mill feed and waste material and can be used as an emergency egress if necessary. Electrical power supply is in place underground.

Grade control is accomplished using the block model, stope grades developed by the short-range planners, face calls, and production sampling.

Assumptions presented the Ambrosia Sul and Bonsucesso deposits are based on direct analogues with, and factoring from, the Morro Agudo Mine, or Votorantim’s Vazante Operations.

The proposed mine plan envisages a bulk mining operation with two mining methods: vertical retreat mining (VRM), and sub-level open stoping (SLOS). Uncemented waste rock backfill will be employed to fill the VRM stopes to provide hanging wall support to reduce mining dilution. The backfill will also provide a mucking floor for the SLOS stopes during mining. By analogy with the Morro Agudo Mine, there is assumed to be negligible water inflows.

The proposed Ambrosia Norte/Bonsucesso underground mines will be accessed through a portal and ramp developed from surface. Mine levels will be developed at nominal 30 m intervals to support the stoping extraction.

Underground distribution of the fresh air will be through a series of raises from surface and exhaust air will be returned to surface through the haulage ramp system.

It is assumed that the current 13.8 kV power supply to the Ambrosia Sul operations will be extended to support development at Ambrosia Norte and Bonsucesso. Bonsucesso will require an extension of the distribution network and an electrical substation.

The Ambrosia Sul open pit is approximately 35 km north of the Morro Agudo plant site. Production and waste rock from the Ambrosia Sul open pit is mined using contract mining equipment operated by Votorantim employees. Truck haulage to the Morro Agudo Mine is undertaken using contract haulage.

The pit is planned to be developed in two phases. Phase 1 is the main longitudinal development and at completion, will be 673 m long, approx. 100 m wide and 75 m deep. Phase 2 will be a smaller sub- pit that is developed on the east side of the Phase 1 pit and will be 166 m long, 65 m wide and 90 m deep.

Electrical power is provided to the Ambrosia Sul Mine by CEMIG, a regional energy provider in Minas Gerais. CEMIG has a contract to supply the mine through an existing 13.8kV distribution network.

Grade control is accomplished through an integration of the block model, the bench grades developed by the short-range planners, in field calls on the muck pile grade, and production sampling.

The Morro Agudo mill uses a conventional crushing, grinding and flotation circuit to produce separate lead and zinc sulphide concentrates.

Mineralization is delivered by skip from the mine haulage shaft and stored in a silo ahead of the primary crusher. Mineralized material is withdrawn using a vibratory feeder to the single-axis Nordberg jaw crusher that operates in open circuit. The primary crusher capacity is 1.5 Mt/a but this is not fully utilized due to upstream and downstream constraints. The primary crusher discharge is conveyed to an intermediate stockpile and weighed using a continuous weighing scale. A fixed electromagnet removes metallic material to avoid equipment damage.

Primary crushed material is then processed in open circuit through the Nordberg HP 1352 hydro-cone secondary crusher. The secondary crusher discharge is classified on a double-deck vibrating screen (8 mm and 20 mm). The screen undersize is sent to a homogenizing stockpile, whereas the oversize is directed to the closed crushing circuit in the Metso/Nordberg HP400 hydro-cone tertiary crusher.

The undersize feeds a conveyor belt, which has a continuous weighing scale and automatic sampler. Crusher plant product is analyzed for particle size and zinc, lead and iron assays. The product size is 80% passing 7.2 mm and 100% passing 9.6 mm. Material is discharged to the tripper, which directs flow to the appropriate storage location according to sample content, for blending in the homogenization stack. This helps minimize feed variation to the process plant. The homogenization stockpile capacity is 14,000 t. Five belt feeders under the stockpile reclaim material into two silos ahead of the grinding circuit.

Crushed and blended mineralized material is fed to two parallel grinding circuits, each consisting of one overflow ball mill in closed circuit with hydrocyclones for classification:

- Ball mill 1 is 13.6 ft diameter x 20 ft effective grinding length, has a 1,500 kW motor, is steel lined, and operates at 73% critical speed

- Ball mill 2 is 12 ft diameter x 18.3 ft effective grinding length, has a 900 kW motor, is steel and rubber lined, and operates at 72% critical speed.

Each ball mill is filled to approximately 38% charge with 63.5 mm (2½ ") diameter steel balls.

The Mill 1 circuit includes a battery of 12 Krebs model D10LB 10” cyclones, of which normally nine operate. The circulation rate is approximately 700% of the fresh feed of the mill. The Mill 2 circuit includes a battery of eight Krebs model 8xD10Gmax3061 10” cyclones, of which normally four operate. The circulation rate is approximately 400% of the fresh feed of the mill. Water is added to dilute each cyclone feed, and the resulting cyclone overflow is 40–42% solids. The resulting combined grinding circuit product produces a flotation feed with 65% passing 44 µm (325 mesh) or 80% passing 74 µm. Mill 1 has a capacity of approximately 750,000 t/a and Mill 2 approximately 400,000 t/a of mineralized material.

The lead flotation circuit follows grinding. The pulp is conditioned with sodium amyl xanthate collector to render galena hydrophobic. Most of the galena in feed is recovered in a rougher flotation column cell. The rougher column tails are sent to the scavenger stage, which uses six conventional mechanical flotation cells. The scavenger concentrate is returned to the rougher column feed. Rougher concentrate is treated in a two-stage cleaner circuit. The first cleaner stage is a single flotation column, with first cleaner concentrate reporting to a second cleaner (recleaner) column, that was installed in 2017. Both the first and second cleaner tailings report back to rougher concentrate feed. Previously in 2016, an Eriez stack cell had been installed into the second cleaner duty. The stack cell is currently being tested for alternative duties.

Overall, the lead flotation circuit recovers approximately 80% of the lead in mill feed, at a final lead concentrate grade of approximately 50%. A key objective of the lead flotation circuit is to limit how much lead reports to the zinc concentrate while minimizing zinc losses into the lead concentrate.

Lead scavenger tails are directed to the zinc flotation circuit, where they are mixed in a conditioning tank with copper sulphate (activator) and sodium amyl xanthate (collector). Sphalerite is then recovered in the zinc rougher column cell, with rougher column tails reporting to a bank of eight conventional zinc rougher scavenger cells together with additional copper sulphate and xanthate. Zinc rougher scavenger concentrate is returned to the zinc rougher feed. Zinc rougher concentrate is pumped to the zinc first cleaner column. First cleaner concentrate is directed to a zinc second cleaner, consisting of three conventional flotation cells, which produces the final zinc concentrate. Second cleaner tailings are returned to the zinc first cleaner feed. First cleaner tailings are directed to the zinc cleaner scavenger feed, which consists of two conventional cell banks with a total of four cells. Zinc cleaner scavenger concentrate reports to the zinc first cleaner, while the tailings are sent to the zinc rougher scavenger. The zinc rougher scavenger tailings form the final tailings from the plant. Final zinc concentrate grade is 38–40% zinc with a zinc recovery of approximately 90%.

The final lead and zinc concentrates are sent to respective vertically mounted plate and frame pressure filters to target moisture contents of 8.5% and 11% respectively. Concentrates are separately held in the concentrate storage yard, then are loaded onto truck by wheel loaders. Zinc concentrate is transported to Votorantim’s Tres Marias zinc smelter.

Lead concentrate is packaged in bulk bags and exported to international customers via the Port of Itaguai.

Tailings from the zinc flotation circuit are placed in the tailings storage facility (TSF) and are decanted, dewatered, and reclaimed for sale as a limestone soil amelioration product to local farmers.