Equinox Gold's 2021 pre-feasibility study for the Aurizona expansion in Maranhão, Brazil, needs no major plant changes for the Piaba underground, apart from a pebble crusher planned for 2022 as more fresh rock is mined.
The Technical Report on the Aurizona Gold Mine Expansion Pre-Feasibility Study, Maranhão, Brazil, was prepared by AGP Mining Consultants for Equinox Gold Corp. with an effective date of September 20, 2021 and a report date of November 4, 2021. The Aurizona plant treats ore by conventional cyanidation: primary crushing, SAG and ball milling, a gravity circuit, carbon-in-leach (CIL), and gold recovery and carbon handling to produce doré, with cyanide destruction ahead of the tailings storage facility (TSF). The plant was upgraded in 2018 and 2019 to 8,000 t/d (2.9 Mt/a) and restarted in May 2019. Its leach/CIP circuit was converted to CIL in 2020.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Report effective date | September 20, 2021 | Not applicable | AGP Mining Consultants for Equinox Gold Corp. |
| Design capacity | 8,000 | t/d | 2.9 Mt/a; up to 10,000 t/d with less than 50% fresh rock |
| Average recovery, 2019 to mid-2021 | About 90.5 | % | Feed grades of 1 to 2 g/t, mainly saprolite and transition ore |
| Throughput, 2020 | 8,841 | t/d | 89.7% recovery, 130,933 oz |
| SAG mill | 8.5 m x 4.0 m EGL, 5,300 kW VFD | Not applicable | Open circuit, 10 mm trommel |
| Ball mill | 5.5 m x 7.4 m EGL, 3,800 kW | Not applicable | Closed with cyclones, about 250% circulating load |
| Grind | P80 75 | µm | Cyclone overflow about 32% solids |
| Gravity | KC-XS-40 concentrator, Acacia CS2000 | Not applicable | About 25% of cyclone underflow treated |
| CIL | 11 tanks, 36 h | Not applicable | Three 4,100 m³ and eight 1,500 m³ tanks |
| Elution | Pressurized AARL, 6 t | Not applicable | 5% HCl acid wash |
| Carbon kiln | 500 | kg/h | Electric, 650 to 700°C |
Overview
The plant was upgraded to treat a blend of laterite and saprolite, transition and fresh rock. From 2019 to mid-2021 it treated mainly saprolite and transition ore at 1 to 2 g/t and recovered about 90.5% of the gold. In 2020 it averaged 8,841 t/d at 1.41 g/t and 89.7% recovery, producing 130,933 oz. The report says the plant needs no major changes for the mine expansion, including the Piaba underground. The one exception is a pebble crusher, deferred from the 2019 upgrade and planned for 2022, to handle a rising share of fresh rock.
Key Process Stages
Primary crushing. Run-of-mine ore is tipped into the crusher feed bin or reclaimed by front-end loader to a 120 m³ ROM bin. An apron feeder and vibrating grizzly feed a Metso C120 jaw crusher (160 kW), which crushes to a P80 of less than about 120 mm.
Mill feed. A 45 m³ surge bin, nine minutes of live capacity, feeds the SAG mill conveyor. Excess crusher output goes to an emergency stockpile with 30 hours of storage, reclaimed by loader during outages.
Grinding. The SAG mill runs in open circuit with a small pebble recycle and an integrated 10 mm trommel. The ball mill runs in closed circuit with cyclones at about 250% circulating load. Cyclone overflow at P80 75 µm goes to pre-leach thickening. Total installed grinding power is 9.1 MW. Lime added at the SAG mill holds the pH at 10.5 or above.
Gravity and intensive leaching. About 25% of the cyclone underflow passes two screens to a KC-XS-40 centrifugal concentrator. The concentrate is leached in an Acacia CS2000 reactor for 12 hours at 54°C in 2.5% sodium cyanide and 1.5% sodium hydroxide at pH 14, and the pregnant solution goes to electrowinning.
Pre-leach thickening and CIL. After a trash screen, a 50 m thickener raises the slurry to 50% solids. Eleven CIL tanks give 36 hours of retention at 8,000 t/d: three newer 4,100 m³ tanks and eight refurbished 1,500 m³ tanks, aerated with compressed air. Cyanide is added to tanks 2 and 3 at pH about 10.2. Carbon is added to tanks 7 and 8 and advanced upstream, with 10 to 20 g/L of carbon in the slurry.
Elution and reactivation. Loaded carbon is washed in a 6 t FRP vessel with 5% hydrochloric acid and stripped in a 6 t pressurized AARL elution vessel. An electric kiln reactivates it at 500 kg/h and 650 to 700°C in an inert atmosphere.
Electrowinning and smelting. Three 0.9 m³ cells, two operating and one standby, deposit gold onto stainless steel wool cathodes. The sludge is filter pressed, dried, fluxed and melted at about 1,200°C in a 170 kW induction furnace to doré.
Cyanide destruction and tailings. Two reactors use the SO2/air process with sodium metabisulphite, copper sulphate and lime to lower WAD cyanide before the tailings go to the TSF.
Additional Interesting Data and Summary
When the feed is less than 50% fresh rock, the grinding circuit can treat up to 10,000 t/d or more without coarsening the grind. The 2021 study therefore leaves the restarted plant largely unchanged and plans only the pebble crusher for the harder ore to come.
In summary, Aurizona is a recently upgraded SAG-ball, gravity and CIL gold plant running at about 8,000 to 9,000 t/d and 90.5% recovery, with capacity in hand for the expansion study's ore.
Key Processes
- Jaw crushing with surge bin and emergency stockpile
- SAG milling in open circuit and ball milling with cyclones to P80 75 µm
- Gravity concentration with Acacia intensive leaching
- Pre-leach thickening and 11-tank CIL
- Acid wash, pressurized AARL elution and electric kiln reactivation
- Electrowinning and induction smelting to doré
- SO2/air cyanide destruction and tailings storage
Source: Technical Report on the Aurizona Gold Mine Expansion Pre-Feasibility Study, Maranhão, Brazil, prepared by AGP Mining Consultants for Equinox Gold Corp., effective date September 20, 2021.
Earlier report summaries
Earlier versions of this profile, based on older technical reports, are retained below for source traceability. Dates and figures reflect each report’s own effective date and are superseded by the current information above.
Aurizona Mine Update — 2015 Technical Report
This technical report provides an update on Aurizona processing operations, historical metallurgical testwork, and proposed plant modifications following suspension of mining activities.
Report context
The effective date of this report is March 27, 2015. The report presents an update on Aurizona mining operations, including updated Mineral Resources and withdrawal of all Mineral Reserves. Mining activities were suspended in February 2015, and the plant is processing a mineralized stockpile through approximately July 2015, after which the mine will be temporarily placed in care and maintenance pending additional exploration and a prefeasibility study incorporating a hardrock crush and grind circuit.
Processing route
Current plant configuration
The processing plant utilizes conventional processing technologies for the production of gold doré bars, which are shipped to offsite gold refineries. The processing plant is comprised of the following circuits for the processing of oxide ore: ore receiving; grinding; pre-leach thickener; carbon in leach gold recovery; gold elution; carbon acid washing; gold electro winning; induction fusion furnace; tailings thickening; and neutralization of the tailings pulp. Prior to the pre-leaching thickener, a portion of the coarser material gets classified by two Knelson concentrators for gravity gold recovery. The material is then smelted and shipped together with the rest of the product.
The current process plant has been operational since June 2010 with processing through the gravity concentration and CIL circuits. In 2012 process plant recovery enhancement initiatives were directed at improvements in CIL pulp carbon concentration, carbon inventory level and pre-leach circuit pulp feed density optimization.
Phase 1 expansion
A Phase 1 plant expansion focused on increasing the throughput of mineralized saprolite to a nominal rate of 10,000 tpd was undertaken in 2013 and 2014 and partially completed, including much of the procurement program. However, the previous geological model did not properly characterize the existence of a harder saprolite unit that could not be processed efficiently in the current processing plant. As a result, the nominal throughput production targets could not be met and rendered the existing plant as well as the Phase 1 expansion uneconomical to run. In retrospect, the installation of a more powerful crushing and grinding circuit rather than an expansion to the leaching and thickening would have been more appropriate given the upcoming hardrock phase of operations.
Historical metallurgical testwork
A series of historical metallurgical test programs were carried out on the saprolite, laterite and unweathered ("Fresh") mineralized material from Aurizona between 1994 and 2008. The results of these test programs were the basis for the feasibility study prepared for Aurizona's Piaba project. Additional metallurgical studies, including cyanidation testwork, comminution studies and solid/liquid separation studies have since been conducted and reported by Metcon Research.
Proposed hardrock circuit
The report recommends completing prefeasibility and/or feasibility studies for a crush and grind circuit so that hardrock can be processed and the resources and reserves updated to show the updated exploration program, as well as the upgraded process capacity. This will allow a mine plan to be developed based on a variety of blends consisting of both soft saprolite and hardrock.
Plant improvements
The Phase 1 expansion was partially completed along with a significant portion of the procurement process. Much equipment is on site awaiting installation. The report recommends completing the installation of the waste treatment plant, carbon kiln, pressure elution column and the high intensity leach circuit in order to improve processing capacity and efficiencies for the restart.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Plant throughput design (Phase 1 expansion) | 10,000 tpd | Proposed design for saprolite |
| 2014 total ore processed | 2,155,555 tonnes | Actual operating data |
| 2014 average process grade | 1.31 g/t Au | Actual operating data |
| 2014 average plant productivity | 281 t/hr | Actual operating data |
| 2014 average plant availability | 91% | Actual operating data |
| 2014 average metallurgical recovery | 88.1% | Actual operating data |
| 2014 gold production | 74,622 ounces | Actual operating data |
| Cumulative production through December 31, 2014 | 285,817 ounces | Actual operating data |
| Historical testwork period | 1994–2008 | Testwork on saprolite, laterite, fresh material |
| Additional metallurgical studies | Cyanidation, comminution, solid/liquid separation | Testwork by Metcon Research |
| Estimated tailings dam raise capacity | 2 additional years at current production | Proposed design |
Project website: https://en.cmoc.com/html/2025/News_1215/82.html
Technical qualifications
The report was prepared as a National Instrument NI 43-101 Technical Report. The qualified persons responsible for specific sections include Marc Leduc, P. Eng. (Sections 1, 7-12, 14-16, 20-28 and reviewer of all sections), Richard Pearce, P.E. (Sections 2–6, 18 and 19), and Deepak Malhotra, Ph.D. (Sections 13 and 17).
The report contains forward-looking information with respect to expected costs, capital expenditures, mine life, mineral resource estimates, expected grades, planned exploration activities, operating parameters, and plans to advance the project. Forward-looking statements are based on assumptions that may prove to be incorrect, and actual results may differ materially.
Mineral Resources are classified in accordance with the Canadian Institute of Mining, Metallurgy and Petroleum Standards on Mineral Resources and Reserves: Definitions and Guidelines. The report withdraws all Mineral Reserve estimates. An Inferred Mineral Resource has a great amount of uncertainty as to its existence and as to its economic and legal feasibility. It cannot be assumed that all or any part of an Inferred Mineral Resource will ever be upgraded to a higher category. Under Canadian rules, estimates of Inferred Mineral Resources may not form the basis of feasibility or pre-feasibility studies.
The report contains certain non-GAAP measures such as expected cash costs, which have non-standardized meaning under International Financial Reporting Standards and may not be comparable to similar measures used by other issuers.
Source: NI 43-101 Technical Report – Aurizona Mine Update, Brazil, March 27, 2015. Relevant sections include 1.11 Mineral Processing and Metallurgical Testing, 1.12 Process Plant, 1.14 Capital and Operating Cost Estimates, 1.15 Conclusions, and 1.16 Recommendations.
