Brazil

Ernesto Mine

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Categories

Overview

Mine TypeOpen Pit
Commodities
  • Gold
Mining Method
  • Truck & Shovel / Loader
Production Start2019
Mine Life2023
ShapshotThe Ernesto Project was revisited during 2018 and after careful evaluation, the company decided to start its mining operation using an open pit method instead of underground, which further de-risks the project.

Due to the depletion of ounces from the Elephant zone (higher grade) in Ernesto Mine, the Company is currently exploring multiple near-mine targets including Nosde (deeper schist zone), Pombinhas, with the goal of increasing the life of the mine and, potentially, increasing production volumes into 2024.
Related AssetApoena (EPP) Complex

Owners

SourceSource
CompanyInterestOwnership
Aura Minerals Inc. 100 % Indirect
Mineracao Apoena Limitada (operator) 100 % Direct
The EPP Project is 100% beneficially owned by Aura. Mineração Apoena S.A (“Apoena”), a company wholly owned by Aura.

Name of Mine Operator: Mineração Apoena.

Deposit type

  • Vein / narrow vein

Summary:

Ernesto/Pau-a-Pique mine complex (“EPP”) is comprised of multiple operating open pits (Lavrinha, Ernesto and Japones), an open pit mine under development (Nosde), and one underground mine (Pau-Pique).

Ernesto-Lavrinha is described as a detachment-style gold deposit that typically has the following characteristics:
-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;
-Mineralization is commonly characterised by quartz-rich vein and veinlet zones (in the ±25% range) with magnetite or hematite, coarse euhedral pyrite (in the ±1% range), sericite, some clay mineral, some late stage calcite and gold. The gold is commonly associated with only very small amounts of silver;
-Mineralization is typically located along a 3 m to 8 m thick rubble zone or mylonite of a detachment (or thrust) fault that intersects high angle structures, either faults or folds. The detachment is commonly within a deformed zone 10 m to 30 m thick;
-The continuity of the mineralization within the detachment zone is normally quite good, extending over 100 m;
-Detachment–style gold mineralization is in altered rock parallel to anticline axes and faults;
-Multiple styles of mineralization are common with local stacked mineralized zones;
-Fluid inclusion studies indicate temperatures of formation about 200°C to 250°C.

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 sulfidic 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 Intermediate and Upper traps are in either permeable conglomeratic horizons or dilatent zones in the meta-arenite stratigraphy. Mineralization in the Upper and Intermediate traps is much less continuous than in the Lower Trap. The Intermediate Trap, which is about 80 m above the Lower Trap, is restricted to a conglomeratic horizon, where it intersects dilation structures developed by folding and faulting.

Mineralization in the Lower Trap is from 130 m to 210 m wide, with an average thickness of 5 m and is more-or-less continuous for at least 1,000 m along its northern plunge direction. The change in plunge angle appears to affect both the thickness and grade of the gold mineralization, with the thickest and highest-grade mineralization occurring where the plunge is less steep.

These zones have been defined by mapping and drill hole logging and sampling. The Lower Trap is within the detachment fault and includes the Ernesto resource referred to in this Report. The Lower Trap mineralized zone in Ernesto is widely developed within a mylonitic zone. The mylontic zone is a deformed version of meta-arenite which was altered and intruded by quartz veining. The mylonitic zone often resembles that of a healed fault zone that developed along detachment structures. The presence of extensional faulting in time of mineralization caused alteration footwall of tonalitic unit. The tonalite is extensively altered and represent of a weak rock which historically logged and called saprolite. However the mineralogical composition of this altered footwall unit is completely different from saprolite on surface. The footwall saprolites are mainly composed from clay minerals produced by alteration of feldspar and mica from tonalite groundmass. The dominant clay mineral is kaolinite.

The footwall saprolite is poor rock in terms of geotechnical characteristics. The alteration is gradational and kaolointic saprolite gradually changes to weakly altered tonalite. The altered tonalite has usually whitish color but groundmass of tonalite is recognizable in cores. However feldspar and micas are replaced by clay. The footwall saprolite is usually entirely replaced by clay minerals (kaolinite). Although in most cases fresh tonalite is located below footwall saprolite, in some local areas in Ernesto gradational changes from tonalite to saprolite both in upper contact with mylonite and lower contact with fresh tonalite are observed in core. This is another indicator of later movements along these detachment faults that accommodate weathering of protolith along weak contact with the mylonitic zone.

The footwall saprolite is weakly mineralized but there is no mineralization within fresh tonalite at Ernesto. This is an indicator that faulting and mineralization events are concordant.

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. In addition, there is saussuritization forming fine-grained sericite, chlorite, and carbonate. 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 Upper Trap seems to be eroded in the Ernesto Deposit area.

Coarse gold is probably a factor in the Ernesto- Lavrinha Deposits, as indicated by the gravimetric recoveries used by the garimpeiros. Screen fire assays for gold in the seven samples collected from mineralized faces in the artisanal underground workings developed in the Lower Trap returned one sample with probable coarse gold.

The Ernesto mine would be developed to exploit the mineralized Lower Trap zone generally bounded by mine sections 8,303,792 NW and 8,304,172 NW and the 255 m and 365 m mine elevations.

The Ernesto Lower Trap zone is a gentle but variable dip and variable thickness deposit that strikes northwest and typically dips 15° to approaching 50° to the northeast.

The Lower Trap mineralization occurs within a mylonite-magnetite-sericite schist zone which is located between hanging wall metasediments and the footwall tonalite. The mylonite rock zone is 6 to 28 m thick and averages about 6 m thick. Saprolite (altered tonalite) is often present between the footwall tonalite and the lower contact of the Lower Trap zone. The saprolite is typically 10 m to 15 m thick in the centre of the proposed mining area and is thinner along the northwest, southwest and southeast margins of the proposed mining area. In addition, rafts of unaltered tonalite are at times present between the saprolite and Lower Trap zone.

Reserves

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Mining Methods

  • Truck & Shovel / Loader

Summary:

Ernesto/Pau-a-Pique mine complex (“EPP”) is comprised of the following gold deposits: the Lavrinha open-pit mine (“Lavrinha”), the Ernesto open pit mine (“Ernesto”), the Pau-aPique underground mine (“Pau-a-Pique” or “PPQ”), the Japonês open pit mine, the Nosde open pit mine, and the near mine open pit prospects of Bananal North and Bananal South.

The Ernesto Project was revisited during 2018 and after careful evaluation, the company decided to start its mining operation using an open pit method instead of underground, which further de-risks the project.

In December 2019, the company started mining operations at the high-grade Ernesto mine. In November 12, 2020, the Ernesto open pit mine, part of the Ernesto/Pau-a-Pique mine complex (“EPP”) declared commercial production effective October 1, 2020.

Comminution

Crushers and Mills

Milling equipment has not been reported.

Summary:

Primary crushing:
The first step to obtain gold is crushing. The crusher used in the plant is a jaw crusher, which is fed through a vibrator feeder (220-FE-001) with the support of a wheel loader.

The vibratory feeder (220-FE-001), with opening in the 100 mm grille, removes the ore with solids mass flow with a rate of 280 t/h. The ore retained in the grille of this feeder is discharged into the jaw crusher (220-CR-001). Both the passing material in the vibrating feeder grid and the material in the crusher discharge are collected and transported to the crushed ore’s silo through the conveyor belts (220-CV-001/002), which are equipped with a metal detector (220-MD-001) and a metal extractor (220-EX-001).

Related to environmental compliance in the crushing stage, it has a dust reduction system, in all transfer. In the crushing stage only, physical processes are performed and so sodium cyanide is not used.

Grinding/ Milling and Gravimetric concentration:
The grinding/ milling circuit is intended to receive the crushed ore, with a top size of 101.6 mm and generate a product granulometrically compatible for the CIL step, with size 80% passerby in a mesh of 0.106 mm. To carry out the comminution process in the SAG mill, 5" steel balls are used.

The replacement of the SAG mill’s balls is done directly in the mill feed, through the hopper (330-BN-003). The balls are discharged, with the support of electric hoist (330-CN-003) in box (330-XM-001) and later in the hopper.

The resumption of crushed ore for grinding, in the solids mass flow with a rate of 205 t/h, is carried out by the feeders (260-FE-002/003/005) and by the conveyor belt (260-CV-003) equipped with a scale (260-SL-004).

The crushed ore (new feed) feeds the SAG mill (330-ML-001), which has dimensions of 19' x 19' (5.7 x 5.7 meters) and installed power of 2.5Mw (Megawatts). The trommel (opening 10 x 20 mm) removes the pebbles from the discharge, which return to the SAG mill through the conveyor belts, 330-CV-004 and 260-CV-003, equipped with a scale (330-SL-002), constituting the part of the circulating load. The passerby in the trommel is collected in the box (330-PB-001) where process water is added to adjust the percentage of solids in the pulp (up to 52% solids) to feed 5 hydro cyclones with 500 mm in diameter, this feeding is performed by pumps (330-PP001/001R). Hydro cyclones classify the pulp through centrifugal force into overflow and underflow.

The underflow of hydro cyclones is collected in the distribution box (330-DI-001), where half of the flow feeds by gravity the scalping sieve (360-SC-002), with opening in the 2 mm screen and the other half returns to the SAG mill, constituting another part of the circulating load. In the scalping sieve the retained material returns to the SAG mill, constituting one more part of the circulating load, while the passerby feeds the centrifugal concentration (360-CG-001). The centrifugal concentration aims at the recovery of free and relatively coarse gold, and it is predicted that 0.16 t/h (dry base) of heavy concentrate (approximately 0.14% of the feed’s plant) are transferred to the intensive leaching area. The light fraction of the centrifugal concentration returns to the SAG system, constituting another part of the circulating load. In short, the circulating load consists of the following flows: retained in the trommel, 50% of the underflow of the cyclones, retained in the scalping sieve and tailings of the centrifugal concentration.

The overflow of hydro cyclones feeds the thickening step.

The drainage of the area is carried out by the pumps (330-PS-002/003).

In the grinding stage, only physical processes are performed with a reduction from 101.6 mm to 0.106 mm and sodium cyanide is not used.

Processing

  • Gravity separation
  • Carbon re-activation kiln
  • ACACIA reactor
  • Hydrochloric acid (reagent)
  • Smelting
  • Centrifugal concentrator
  • Intensive Cyanidation Reactor (ICR)
  • Agitated tank (VAT) leaching
  • Carbon in leach (CIL)
  • Carbon adsorption-desorption-recovery (ADR)
  • AARL elution
  • Dewatering
  • Solvent Extraction & Electrowinning
  • Cyanide (reagent)

Summary:

The technology adopted for the processing of ore begins in primary crushing, followed by single stage milling (cyanide solution is not added at the milling circuit, so the milling circuit is not a cyanide facility), in which a SAG (Semi-Autogenous Grinding) mill system operating in closed circuit with hydro cyclones is used. The hydro cyclones act by separating the pulp coming from the mill through centrifugal force, the less dense part is concentrated in the center of the cyclone coming out of the upper part of the cyclone, which is called overflow and the denser part is concentrated on the sides of the cyclone coming out from the bottom, being called underflow.

The part of the underflow’s classification mass feeds the concentration centrifugal circuit which after classification passes through intensive leaching (Acacia process) for the recovery of free gold. The overflow of the cyclone classification is thickened and pumped to CIL (Carbon in Leaching). In the CIL’s process the gold goes through the process of solubilization by cyanide and adsorption in carbon.

The gold is adsorbed in carbon and goes to the next step, called elution, in this process a solution of cyanide percolated by carbon, thus removing the adsorbed gold. Once the elution process is completed, the solution now enriched with gold proceeds to the electrolytic extraction process, in which process the gold is deposited in the cathode. The final step is due to the melting of the product of the cathode that is deposited in molds that after solidified, form the metallic bullions.

Thickening:
The cyclones’ overflow (330-CY-001) of the SAG circuit are collected in the box (330- PB-002) and feeds the protection sieve (330-SC-001), DSM screen type (sieve bend screen), with opening on the screen of 0.8 mm. The material retained in the sieve is collected in a box to be discarded while the passerby pulp, containing 32% solids, feeds the thickener (380-TH-001), E-CAT type (Compact Automatic Thickener), with 11 meters in diameter. The thickener’s overflow, consisting of water practically free of solids, feeds the process water tank (550-TK045) for recirculation. The underflow composed of thickened pulp containing 52% solids is pumped (380-PP-004/004R) to the CIL area.

Intensive Leaching (Acacia Process):
Intensive leaching consists of the processing of gravimetric concentrate (0.16 t/h, dry base), obtained in continuous regime. Intensive leaching is conducted on a two batches per day, with the proportion of: 50 kg of cyanide and 3.0 kg of caustic soda per ton of concentrate on a dry basis, in addition an agent for activating gold solubilization at the ratio of 80 g/t of concentrate. In this phase, leachaid (a chemical product to improve the leaching dynamic) is added in the proportion of 0.003 kg/t in relation to the ground ore, this reagent accelerates the leaching kinetics. The auriferous liquor resulting from the stage is considered electrolyte, being pumped into the rich solution tank of the elution/electrolysis circuit, while the poor solution of this step returns to the cyanide solution distribution tank.

Leaching / CIL (Carbon in Leaching):
The thickening underflow, pulp containing 52.0% solids (205 t/h) dry base, feeds the distribution box (430-PB-005) being normally discharged into the conditioning tank and preleaching (430-TK-003), mechanically agitated (430-AG-002), with a useful volume of 567 m3 and can alternatively feed the first CIL tank. Leaching is conducted at pH between 10.5 and 10.8 obtained by adding hydrated lime at the ratio of 1.0 kg/t of ore and sodium cyanide at the ratio of 0.35 kg/t of ore. The CIL (leaching circuit) contains 7 tanks (430-TK-003/009) arranged in series, mechanically agitated (430-AG-003/009), with a nominal capacity of 567m3 each. The total residence time considered for pre-leaching and CIL is 24 hours, resulting in the solubilization of 88% of the gold values contained in the solids. Each CIL tank, in addition to the continuous cascading pulp, contains (4.0 to 8.0) tons of active carbon. Knowing that each CIL tank has interstage sieves (430-SC-005/010), with an opening on the 0.8 mm screen, with the function of retaining carbon. New or regenerated carbon after dewatering through a sieve (430-SC-004) preferably feeds the last CIL tank (430-TK-009) or, alternatively, the tank 430-TK-008.

Carbon operates on a countercurrent regime, in other words, new/regenerated carbon fed in the last tank, which feeds the penultimate tank 430-TK-008 and then, until it reaches the first CIL tank (430-TK-003). The carbon cycle in the CIL stage consists of its batch transfer for 5 hours a day through the pumps (430-PS-010/015).

The pulp containing carbon loaded from the first CIL tank (430-TK-003) feeds the vibratory sieve (430-SC-003) with opening 0.8 mm for retention of carbon that is transferred to the washing acid area. The passing pulp without carbon returns to the same leaching tank. In the last tank (430-TK-009), CIL effluent, feeds the DETOX process area.

Acid Wash:
Acid washing begins when the acid washing column (461-TK-010), with 12 m³ volume, is complete with charged carbon (4 ton.). Hydrochloric acid solution (3% HC1), preheated (461-HE-003), is added to the column to eliminate alkaline ground ions (nobly calcium carbonate) in carbon pores that impair the adsorption/elution capacity of gold. Hydrochloric acid consumption is 0.15 kg/ton of ground ore. After acid washing the carbon is washed with water and caustic solution and transferred by ejector (461-ED-001) for the elution step. The washing stage as well as the entire elution area operates in cycles, being considered 01 (one) complete cycle per day.

Elution:
The configuration adopted for elution is the AARL (The Anglo-American Research Laboratories) method. Elution occurs in the column (460-TK-011) by circulating a solution containing 3.0% NaOH and 3.0% NaCN by weight through charged carbon at 120°C and pressure from 3 to 3.5 atm. The solution, previously heated by the heat exchangers (460-HE-001/001R/002/002R), comes from the tank (460-TK-012) and is fed into the columns through the pumps (460-PP022/022R). The elution consists of the physical-chemical displacement of gold adsorbed in carbon to the poor electrolyte until its exhaustion, generating 57.5 m³ of electrolyte. The electrolyte, after being cooled from 130°C to 60°C by heat exchangers (460-HE001/001R), feeds the electrolytic extraction of gold and the elude carbon is removed from the column and transferred by the ejector (460-ED-002) for dewatering in the inclined vibratory sieve (461-SC-012) with 0.8 mm screen. The eluded carbon retained in the sieve feeds the regeneration step.

Carbon Regeneration:
The carbon retained in the sieve is sent to the carbon tank (461-TK-015) and transferred by the vibratory feeder (461-FE-005) to the rotary oven (461-BO-004), at a temperature of 700 °C, with an approximate residence time of 1 (one) hour, at the feeding of 0.22 t/h. Regenerated carbon feeds the quench tank (461-TK-016) and is transferred by the ejector (461-ED-003) to the CIL area.

Production

Combined production numbers are reported under Apoena (EPP) Complex

Production Costs

Commodity production costs have not been reported.

Heavy Mobile Equipment

Fleet data has not been reported.

Personnel

Mine Management

Source Source
Job TitleNameProfileRef. Date
Director of Operations Frederico Silva LinkedIn Jun 28, 2023
Processing Manager Junior Cesar Santos Souza LinkedIn Jun 28, 2023

Aerial view:

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