The Pau-a-Pique and Ernesto-Lavrinha Deposits are situated in the Middle Proterozoic (ca. 1.0 Ga) Aguapeí belt, a foreland fold and thrust belt that overlies the Early Proterozoic and Middle Proterozoic terrains (Geraldes et al. 2001). The Aguapeí group in the Pau-aPique and Ernesto – Lavrinha areas is structurally marked by reverse faults, isoclinal folds and strong penetrative axial planar cleavage, often crenulated.

The Aguapeí Group is composed of conglomerate, sandstone (arenite) and siltstone that are unconformably deposited on the underlying basement in a braided fluvial to marine depositional environment. The metasediments occur within a fold and thrust belt that is deformed under brittle- ductile conditions and are commonly in tectonic contact with the basement. Strong hydrothermal alteration and associated gold mineralization occurs in association with the lower contact of the Aguapeí Group with the underlying basement.

In the Ernesto Deposit, the contact zone between the Aguapeí sediments and the underlying basement tonalite consists of a 5 m to 25 m thick magnetite-sericite schist unit, containing lenses and elongated bodies of quartz generally concordant with the foliation, and a 1 m to 3 m thick basal layer of intensely altered, crushed and decomposed rock. The magnetite-sericite schist apparently represents strongly altered and deformed sediment, probably a hydrothermally altered and sheared metapelite (mylonite).

The Lavrinha Deposit which is closely linked to the Ernesto Deposit has been interpreted as gold- rich quartz veins and veinlets with coarse grained pyrite occurring along shallow-dipping structure. The main difference with Ernesto is the position of the mineralization in the metasedimentary sequence. Gold mineralization is located along quartz boudins in highly sericitized rock and plunges to the north.

The Pau-a-Pique Deposit occurs in close association with the contact of the meta-tonalite basement and the overlying Aguapeí Group metasediments. The tonalite is metamorphosed with a foliated structure but preserving the original igneous texture. The rocks are metamorphosed and deformed under lower green-schist facies conditions. Muscovite schist is developed in the contact between the metatonalites and metasediments and is an important host of mineralization. The muscovite schist has S-C structures and abundant shear bounded sigmoidal veins. The schist has a strong stretching lineation oriented at N20–50W that controls the form of the deposit and sub-surface mineralization.

The Ernesto-Lavrinha Deposits consists of gold-rich quartz veins and veinlets occurring along a relatively thick, shallow-dipping structure at the base of the metasedimentary sequence and within altered sulphidic horizons in overlying meta-arenite units. The basal structure is interpreted to be a low-angle detachment fault that has been folded and faulted together with the overlying stratigraphy. Gold mineralization is located along asymmetrical anticlines and synclines that plunge gently to the north and are cut by NW and NE-trending narrow faults. The gold mineralization occurs in three zones: Lower Trap, Middle Trap and Upper Trap.

The Lower Trap mineralized zone in Ernesto is widely developed within a mylonitic zone. The mylonitic zone is a deformed version of meta-arenite which was altered and intruded by quartz veining. The mylonitic zone often resembles a healed fault zone that developed along detachment structures. Mineralization in the Lower Trap is 130 m to 210 m wide, with an average thickness of 5 m and is moreor-less continuous for at least 1,000 m along its northern plunge direction. Alteration associated with gold mineralization within the mylonitic unit includes abundant quartz veins and veinlets with coarse-grained euhedral pyrite and medium grained bipyramidal crystalline magnetite. This alteration and mineralization occurs in mylonitic zones near the base of the detachment fault.

The Upper Trap, which is widely developed in the Lavrinha Deposit, occurs in metapelitic rocks (hematite sericite schist) in dilation zones of the intensely deformed synclinal troughs. The Upper and Intermediate traps share similar alteration and mineralization suites.

The Ernesto-Lavrinha Deposits are described as detachment-style gold deposits, where typically gold mineralization is associated with low-angle to flat detachment faults, generally with a normal (extensional) sense of movement which consistently places younger units over older units.

The Pau-a-Pique gold mineralization is associated with intense hydrothermal alteration, and correlates with the occurrence of pyrite, sulphide alteration, quartz veins and sericitization. The envelope of the mineralized zone is approximately 550 m long, maximum of 15 m thick and 400 m deep in the largest extension. In the deeper levels the most common hydrothermal alteration with gold enrichment is strong albite-anorthosic quartz veining associated with chloritization and pyrite. In the shallow levels the most pervasive alteration is silicification, represented by a strong injection of quartz veins and weaker gold enrichment. The albitic alteration probably represents deeper and hot sources of the hydrothermal feeder. The Pau-a-Pique Deposit is developed within brecciated-sheared host rocks which are strongly foliated and moderately metamorphosed and can be described as structurally controlled orogenic gold lode deposit.

In December 2019, the company started mining operations at the high-grade Ernesto mine. Since this mine is still in Prestripping phase, it is expected that Ernesto will generate positive cash flows in the second semester of 2020.
[2019, Management Discussion & Analysis, P.14]

Ernesto Underground
Due to its nature of gentle and variable shallow dip and thickness, the Ernesto Deposit will be extracted by the Drift and Fill mining method, using a combination of drifting in ore and transverse primary and secondary small stopes in a 32%:36%:32% drift/primary/secondary tonnage ratio. The deposit is relatively close to surface at a maximum depth of approximately 170 m and will be accessed by one main ramp portal, with a second portal for definition drilling access and ventilation.

Backfill material will be waste rock for secondary stopes and ore drifts and cemented rock fill (“CRF”) for all primary stopes. Waste rock to fulfill the required backfill quantities will be obtained from two sources; the primary source will be from mine waste development and the second source will from the existing Ernesto open pit waste rock storage facility.

A six month pre-production period will be followed by approximately 3.5 years of production to mine an estimated 0.87 Mt of ore at an average grade of 5.03 g/t Au. Ore production will average 800 tpd.

The majority of underground mining activities at Ernesto will use Aura’s own employees, with external contractors or suppliers to undertake the supply of explosives, piping and services, ground support consumables, cement supply for the CRF plant, and other specialised tasks. Aura will have 100% ownership of all major fixed plant components used at Ernesto. Activities such as diamond drilling and other specialized activities or Project work will be contracted.

Lavrinha Open Pit
Approximately 1.11 Mt of ore at an average grade of 1.69 g/t Au and 14.0 Mt of waste rock will be mined from the Lavrinha open pit over a 2.5 year period. The overall strip ratio for Lavrinha is 12.6:1 with mining conducted 365 days per year by a contractor. The contract is full service and includes providing all mining equipment, drilling, blasting, loading, hauling and maintenance. Total material movement rates for the LOM range from 15,000 to 25,000 tpd.

Conventional truck and hydraulic shovels will be utilized. Four excavators, supported by three front-end loaders, will load a fleet of ten 38-tonne trucks and five 25-tonne trucks. Ore will be transported to the primary crusher and run-of-mine (“ROM”) pad, and waste material will be hauled to a nearby waste rock storage facility.

Pau-a-Pique Underground
Mining at Pau-a-Pique will be conducted by a modified Avoca choke blast stoping method with ore transported to the ROM pad on surface by 30 tonne haulage trucks operating through the main ramp. Ore will be subsequently hauled on a 47 km surface road to the Ernesto processing plant. Primary access to the underground mine is via a single portal located next to the main mining office.

Approximately 0.32 Mt of ore at an average grade of 3.24 g/t Au will be mined over a 17 month period at an average of 850 tpd when the Project achieves full production. Once the deposit has been depleted most of the equipment and operators will be transferred to the Ernesto operation.

The stoping method applied to the Area 7 and Area 8, NW, and P3 and P4 ore bodies will be via Hanging Wall (“HW”) access ore drives with levels spaced at 15 m and 21 m vertical intervals, for the upper and lower areas of the deposit, respectively. The upper and lower areas will be separated by a sill pillar. Unconsolidated waste rock will be used to backfill the stopes.

The majority of underground mining activities will utilize Aura’s employees, with external contractors or suppliers to undertake the supply of explosives, piping and services, ground support consumables, truck haulage underground and on surface and other specialized tasks (i.e. site security, doré bar transportation, etc.). Aura has 100% ownership of all major fixed plant components utilized at the mine.

CRUSHING
Haul trucks deliver run-of-mine feed to the ROM pad. A front-end loader is used to feed the crusher feed bin, which is fitted with static grizzly bars with an aperture of 600 mm. The primary crusher grizzly feeder, which has an aperture of 150 mm, withdraws feed from the crusher feed bin at an average rate of 130 tph and discharges oversize material to the 1,045 mm x 840 mm primary jaw crusher, which operates at a final product size of 80–100 mm.

Grizzly feeder undersize and primary crusher product are combined on the primary crusher product conveyor, which discharges to the feed hopper. The feed hopper can also receive feed from a loader. A belt magnet removes tramp steel from the primary crusher product conveyor.

GRINDING
Crushed feed, pebbles, cyclone underflow, and gravity concentrator tailings are directed to the SAG mill feed chute. The SAG mill dimension is 5.8 m in diameter, 5.8 m long and has an installed motor power of 2.65 MW.

The recirculating load is 4.5 times the mass of the newly crushed feed. The SAG trommel screen (15 mm aperture) removes oversize (‘pebbles’) from the mill discharge at an estimated rate of 33 tph. The pebbles are directed to the pebble recycle conveyor, which includes a belt magnet to remove tramp steel and a metal detector located after the magnet.

SAG trommel screen undersize slurry flows to the cyclone feed hopper, where water is added to adjust the solids content to cyclone requirement. The primary cyclone feed pump feeds the cyclone cluster. Cyclone overflow flows to the trash screen bypass box. Cyclone underflow reports to the cyclone discharge distributor box, which directs half of the underflow to the concentrator scalping screen (2 mm aperture) and the remainder of the underflow to the SAG mill feed chute. Concentrator scalping screen oversize (estimated to be half the scalping screen feed) returns to the SAG mill feed chute, while the undersize feeds the gravity concentrator.

Gravity concentrate is discharged intermittently to an intensive cyanidation reactor (“ICR”) package unit. The ICR unit intermittently discharges leached concentrate to the cyclone feed hopper and discharges pregnant solution to the gold room.

Process water is added at the following points in the grinding area:
· SAG mill feed chute dilution
· SAG trommel screen spray · Cyclone feed hopper dilution
· Concentrator scalping screen spray
· Gravity concentrator fluidization (flush).

Two sump pumps in the grinding area discharge intermittently to the cyclone feed hopper to return spillage to the feed system.

The Project’s gold processing plant, located next to the Ernesto Deposit, was commissioned in 2012 and treated ores from Paua-Pique and the Ernesto open pit until its closure in December 2014. It is centrally located to these deposits and has a capacity of 3,000 tonnes per day (“tpd”) through a conventional carbon-in-leach process and is designed to treat up to 1 Mtpy feed. The process includes crushing, grinding, gold extraction/recovery and cyanide detoxification stages followed by final deposition in a tailings storage facility.

The process plant flowsheet is based on a low-risk proven technological configuration for processing gold bearing feed. A primary jaw crusher is located at the front-end of the process plant. ROM feed will be blended and fed through the plant’s primary screen. The screen oversize is crushed and the combined crushed feed is ground in a single-stage, closed-circuit SAG mill.

Approximately 25% of the mill cyclone underflow feeds a gravit ........