Several genetic models have been suggested for Chapada, including: (i) a deformed and metamorphosed porphyry-type copper-gold deposit (Richardson et al., 1986; Oliveira et al., 2015), (ii) a deformed and metamorphosed volcanogenic disseminated sulphide deposit (Silva and Sá, 1986; Kuyumjian, 1989), and (iii) epithermal copper-gold deposit overprinted by metamorphic remobilization (Kuyumjian, 2000).

The most accepted metallogenetic model for Chapada is a metamorphosed porphyry model associated with skarn system. The magmatic hydrothermal system was generated in island arc stage setting (approximately 884 Ma to 879 Ma) and posteriorly overprinted by remobilization of orogenic fluids during Brasiliano events (ca. 630 Ma).

The porphyry, skarn, and epithermal system can be separated into three distinct mineralization styles, based on hydrothermal alteration and metal association:
- Copper-Gold Porphyry System (Chapada Corpo Principal, Corpo Sul, and Sucupira);
- Gold (Silver-Lead-Zinc) Distal Skarn (Suruca);
- Copper-Gold Proximal Skarn (Suruca SW).

The Chapada and Suruca deposits are located in the metavolcano-sedimentary sub-unit of Mara Rosa Sequence.

UPPER METAVOLCANO-SEDIMENTARY LAYER (A LAYER). The A layer is defined by interlayering of several lithotypes, such as garnet-biotite- quartz schist (same as in the metasedimentary layer), amphibole-quartz schist, biotite-quartz schist, biotitegneiss, amphibole-biotite gneiss, and metatuff.

The A layer hosts the mineralization at Baruzinho, Chapada SW, and Suruca.

METAVOLCANIC LAYER (B LAYER).
The B layer is defined by a 50 m to 200 m thick layer of biotite-quartz schist, biotite-gneiss, and amphibole-biotite gneiss (same as described in the metavolcano-sedimentary layer).

Three intrusive facies are observed: metaquartz diorite porphyry, metadiorite porphyry, and intermediate metaplutonic rock. The metaquartz diorite porphyry represents early- to inter- mineral porphyry stocks, which are related to coppergold mineralization at most orebodies of the Chapada deposit. The metadiorite is interpreted as inter- or late-mineral porphyry stocks and occur throughout the Chapada and Suruca deposits. Only at Suruca, however, are they the host rock of both copper-gold and gold only mineralization. The intermediate metaplutonic lithotype represents late-mineral porphyry stocks that crosscut the copper-gold mineralization at the Baru, Sucupira, Corpo Sul, and Santa Cruz orebodies.

SYN-TECTONIC TO POST-TECTONIC INTRUSIONS.
The syn-tectonic and post-tectonic intrusions are represented by metadiorite, bimodal deformed dikes, and pegmatites.

The metadiorite is deformed medium grained diorite with salt-and-pepper texture, locally named as Chapada Diorite.

Bimodal syn- to post-tectonic dikes are observed throughout the Chapada and Suruca deposits with an average thickness of one metre to ten metres.

WEATHERING EVENT.
The mine area is covered by a 30 m thick lateritic profile composed of a coarse saprolite, mottled zone or argillic zone, lateritic duricrust, and pisolitic soils (products of alteration of duricrust) from bottom to top.

The Chapada deposit lithologies were grouped in “litho-structural domains” to assist mine operations. These domains are classified based on lithological relationships, intensity of hydrothermal alteration, and intensity of weathering.

MINERALIZATION.
CHAPADA.
Copper is principally present as chalcopyrite with minor amounts of bornite. Fine grained gold is closely associated with the sulphide mineralization and was likely to be contemporaneous with the copper.

The mineralization at the Chapada deposit is represented predominantly by sulphide disseminations along foliation plans (or axial surfaces of folds) and, to a lesser extent, in small massive concentrations in the hinges of folds. In general, the ore is formed predominantly by chalcopyrite, pyrite and magnetite, where chalcopyrite-magnetite (magnetite rich ore) and chalcopyrite-pyrite (pyrite rich ore) are the prevailing associations, in which pyrite is the most abundant mineral, magnetite (including hematite, ilmenite and rutile) is subordinate, and galena, bornite, sphalerite, and molybdenite are rarely reported.

The copper mineralization and grade are somewhat better in the central zone of the deposit along the anticline axis than in the surrounding anticlinal limbs, however, copper mineralization is pervasive over a broad area.

SURUCA.
The gold at Suruca is related to folded quartz veins/veinlets with sericitic and biotite alteration, rather than high sulphide concentrations. The second generation quartz veins/veinlets with sulphides (sphalerite + galena + pyrite), carbonates, and epidote also host gold which is related to zinc. The copper mineralization in the Suruca SW displays same features as Chapada, with sulphide disseminations and sulphides associated with stockwork quartz veinlets. In general, Suruca SW mineralization is formed predominantly by chalcopyrite and pyrite, with subordinate sphalerite and molybdenite.

Mineralization predominately pre-dates deformation so the gold (Suruca) and copper- gold (Suruca SW) zones are associated with skarn features, however, some structurally controlled features are also observed.

Chapada is a traditional open pit truck and excavator operation that has been in continuous operation since 2007. Production is currently entirely from Chapada, with the Chapada Main and Corpo Sul pits in operation. These pits are planned to eventually join into a single pit and extraction of the Sucupira deposit is planned as an additional series of pushbacks.

The Chapada open pit has current ultimate design dimensions of approximately 8 km along strike, up to 1.5 km wide, and 380 m deep.

Mine operations are carried out with a fleet of rigid frame haul trucks combined with a variety of diesel-powered hydraulic excavators and front-end loaders as the primary loading equipment. A fleet of large diesel-powered blast hole rigs are employed for production drilling. Blasting is required for all rock types except for unconsolidated material at surface.

The Suruca open pit mining area includes Suruca Oxide and Suruca Sulfide gold Mineral Reserves. The Suruca deposit is located approximately 7 km northeast of the Chapada open pit and final pit dimensions will be approximately 2 km along strike and approximately 1 km wide.

The Chapada LOM plan is based on the Mineral Reserves and a processing rate of up to 24.0 Mtpa with the ore stockpile to be processed intermittently throughout the mine life. The current mine life is 22 years plus an additional seven years at the end of the mine life for processing the remainder of the ore stockpile.

- subscription is required.

The Chapada concentrator is designed to treat copper sulphide ore at a nominal rate of 65,000 tpd for a total of 24.0 Mtpa. In 2018, the mill processed 22.93 Mt (62,820 tpd) of ore with average recoveries for copper and gold of 82.4% and 63.3%, respectively.

ROUGHER FLOTATION
The rougher flotation circuit consists of two lines of rougher-scavenger flotation cells. Each line has a bank of five 160 m3 Dorr-Oliver Eimco tank flotation cells that have been retrofitted with Outotec mechanisms (Outotec TankCell and FloatForce), consisting of two rougher cells, one middling cell and two scavenger cells in series.
- The concentrate from the rougher cells flows to the concentrate regrind feed pumpbox.
- The cyclone underflow feeds the vertical regrind ball mill.
- The concentrate from the middling cell can either report the concentrate regrind or to the primary cyclone feed pumpbox in the grinding circuit.
- The concentrate from the scavenger cells is pumped back to the primary cyclone feed sump in the grinding circuit.
- The scavenger tailings are pumped to the TSF.

CONCENTRATE REGRINDING
The concentrate regrind circuit consists of a Metso Vertimill, VTM-1000-WB, with a 748 kW drive in closed circuit with a bank of four 20 in. hydrocyclones (two operating).

CLEANER FLOTATION
- The cyclone overflow from the concentrate regrind circuit flows to the new SFR cleaner scalper cells.
- The concentrate from the SFR scalper cells is final concentrate grade and is pumped to the concentrate thickener.
- The cleaner scalper tailings are pumped to a bank of six 21.5 m3 conventional cleaner flotation cells.
- The cleaner tailings are pumped to a new bank of four Staged Flotation Reactor (SFR) cleaner scavenger flotation cells.
- There is an existing bank of two 160 m3 Wemco tank cells that currently operate as cleaner scavenger cells or pyrite cells in parallel with the new SFR cleaner scavengers.
- The concentrate from the cells is pumped to the feed of the cleaner flotation cells. The tailings from both banks of cells are pumped the final tailings pumpbox and then to the TSF.
- The cleaner concentrate is pumped to a final cleaner column flotation cell. The tailings from the column cell are pumped to the concentrate regrind circuit and the concentrate is pumped to the final concentrate thickener.

CONCENTRATE THICKENING, FILTRATION, AND STORAGE
The final concentrate is thickened to approximately 60% solids in a 13 m diameter x 3 m high Dorr Oliver Eimco thickener. The thickened concentrate is then pumped from the thickener underflow to an 11 m diameter x 11 m high concentrate storage tank. The concentrate is then pumped to a Larox PF60/72 M145 filter press, with a capacity of approximately 45 tph, located in the concentrate storage building above the concentrate stockpile. The pressure filter reduces the concentrate moisture to approximately 8% before discharging it onto the stockpile below. The concentrate is then loaded onto trucks and transported to the Port of Vitoria for shipping.


In 2018, a study and basic engineering report were commissioned, which combined the information gained from several studies regarding process plant upgrading, optimization and, ultimately, the expansion of the processing facilities from the current capacity to approximately 32.0 Mtpa. This expansion has not been advanced but options for mine and mill expansions are being evaluated in parallel with the significantly increased exploration efforts. These expansion options will include the need to relocate some elements of the processing plant and site infrastructure in order to mine the Sucupira mineralization. The Company completed a prefeasibility study for expansion of the Chapada operation in 2022, including the debottlenecking of the existing processing facilities to increase throughput from the current level to up to 25.2 Mtpa and the construction of a new processing line to duplicate production for a combined throughput of up to 50 Mtpa. The optimization study will advance to feasibility in 2023 seeking to achieve up to 26 Mtpa while the study for the new processing line will be put on hold pending further definition and update of the Mineral Resources and Mineral Reserves of Chapada.

For Suruca, run of mine ore, which consists of oxide and sulfide mineralization, will be processed separately; the oxide ore will be processed using conventional heap leaching technology, and the sulfide ore will be processed in the existing concentrator after some modifications.

- subscription is required.