This report describes the processing facilities at the Pilar mine, which were commissioned in 2013 and reached commercial production in October 2014, as documented in the March 2020 technical report.
Report context
The processing facilities at the Pilar mine were started up in June 2013, with the first gold pour in July 2013. Commercial production was officially reached in October 2014. The report documents the plant as designed to process 3,500 tpd from the underground mines at Pilar, Caiamar, and Maria Lázara. Target production from the Pilar and Maria Lázara mines is approximately 3,000 tpd for a total of up to 1,450,000 tpa, with the Caiamar mine closed in 2015.
Processing route
Ore delivery
Ore is delivered from the Pilar mine using 14 t haul trucks. The Maria Lázara mine is 15 km from the Pilar process plant, and the Caiamar mine is 38 km from the plant. Ore from the Caiamar mine was delivered in over-the-road haul trucks until the mine was put on care and maintenance in 2015. The Maria Lázara mine is being mined by a contractor who is responsible for delivery of the ore to the Pilar coarse ore stockpile. The ore is stockpiled and then loaded into the primary crusher feed hopper using a front end loader. The feed hopper is equipped with a static grizzly with 800 mm openings. A mobile hydraulic rock hammer is used to break oversized rocks.
Primary crushing
Ore is drawn from the feed hopper using a vibrating grizzly feeder and fed to the primary crusher. Grizzly feeder undersize material bypasses the crusher and falls directly onto the crushed ore conveyor. The primary crusher is a 1,000 mm by 760 mm single toggle jaw crusher with a 110 kW drive. The crusher is sized for a nominal feed rate of 206 tph with a closed side setting of 75 mm. The primary crusher discharge combines with the grizzly feeder undersize and is conveyed to the crusher ore storage silo. The silo has a live storage capacity of 1,000 tonnes allowing for eight hours of mill operation at the design mill production rate of 127 tph.
Primary grinding
Ore is drawn from the storage silo by two vibrating feeders, which feed the fixed speed SAG mill feed conveyor. The SAG mill is 5.8 m diameter by 5.8 m long with a 3,000 kW drive and a capacity of 165 tph. The typical mill operating power draw is reported to range between 2,200 kW and 2,600 kW. The discharge of the mill is fitted with a trommel screen with 10 mm by 10 mm openings to remove oversized pebble and ball chips. The mill operates with a 30% ball charge made up with 125 mm balls. The circulating load is estimated to be 400%. The trommel oversized material is conveyed to a cone crusher, with a 132 kW drive, positioned above the SAG mill feed conveyer. The pebble size material is reduced to –8 mm and discharged directly onto the SAG mill feed conveyor and recycled to the mill. The cone crusher capacity is 90 tph and is currently operating at approximately 20 tph.
The SAG mill operates with a slurry density of approximately 75% solids and discharges into the cyclone feed sump where it is diluted and pumped to a cluster of eight 380 mm cyclones for classification. The cyclone feed slurry density is controlled to approximately 53% solids to obtain a cyclone overflow density of 34% solids and a target particle size distribution of 80% passing 125 µm. The cyclone underflow slurry is typically 76% solids and flows by gravity to the feed of the SAG mill.
Gravity separation
A portion of the cyclone underflow is diverted to two centrifugal concentrators for gravity gold recovery. The tailings from the centrifugal concentrators recombine with the cyclone underflow and return to the mill feed chute, closing the circuit. The concentrate from the centrifugal concentrators is treated in an Acacia intensive cyanide leach reactor, located in a locked section directly beneath the concentrators. The Acacia reactor is an automated system providing security for the processing of gravity gold concentrates. The concentrate is leached at 54°C in a 2.5% sodium cyanide and 1.5% sodium hydroxide solution to recover the gold. The pregnant Acacia leach solution is then pumped to a storage tank in the carbon stripping area in preparation for electrowinning. The tailings from the Acacia leach reactor is pumped to the cyclone feed sump for re-processing.
Thickening
The cyclone overflow flows through a horizontal vibrating trash screen to remove oversize material, plastic and other debris, before reporting to the pre-leach thickener. The screen underflow flows by gravity to a 12 m diameter high rate leach feed thickener where it is diluted to 15% solids and directed into the thickener feed well. The thickener underflow density is controlled between 55% and 60% solids using density measurement and variable speed underflow pumps. The underflow slurry is pumped to the cyanide leach tanks. There is a significant elevation drop between the thickeners, located at the mill, and the leach circuit, which is located on a lower bench. The underflow pumps and control valves are used to control the slurry flow between the two levels. The thickener overflow solution is very low in solids and is pumped to the grinding circuit process water tank for use as dilution water.
Leaching and carbon in pulp
The thickener underflow slurry is adjusted to 55% solids and pumped to the leaching and CIP circuit. The leaching circuit consists of six 700 m³ tanks in series for a total retention time that is not further specified in the report excerpt.
Cyanide detoxification, stripping, electrowinning, and casting
The overall flowsheet includes cyanide detoxification using sodium metabisulphite in five tanks in series, Anglo American Research Laboratory (AARL) stripping of the carbon, electrowinning of the carbon eluent and gravity concentrate leach solution, and casting of gold bars in an induction furnace.
Plant layout
The plant was designed to take advantage of gravity flow. The ore stockpiles and primary crushing are at the highest level, the crushed ore storage bin and grinding circuit are located on the next lower elevation, and the ground slurry from grinding flows by gravity to the leaching circuit on the next lower bench.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Design plant throughput | 3,500 tpd (up to 1,450,000 tpa) | Design |
| Target production (Pilar and Maria Lázara) | Approximately 3,000 tpd | Design |
| Design mill production rate | 127 tph | Design |
| Primary crusher nominal feed rate | 206 tph at 75 mm CSS | Design |
| Primary crusher drive | 110 kW | Design |
| SAG mill dimensions | 5.8 m diameter x 5.8 m long | Design |
| SAG mill drive | 3,000 kW | Design |
| SAG mill capacity | 165 tph | Design |
| SAG mill typical operating power draw | 2,200 kW to 2,600 kW | Historical operating data |
| SAG mill ball charge | 30% (125 mm balls) | Design |
| SAG mill slurry density | Approximately 75% solids | Historical operating data |
| Circulating load | Estimated 400% | Design estimate |
| Pebble crusher capacity | 90 tph | Design |
| Pebble crusher operating rate | Approximately 20 tph | Historical operating data |
| Cone crusher drive | 132 kW | Design |
| Cyclone feed slurry density | Approximately 53% solids | Design |
| Cyclone overflow density | 34% solids | Design |
| Target particle size (cyclone overflow) | 80% passing 125 µm | Design |
| Cyclone underflow slurry density | Typically 76% solids | Historical operating data |
| Silo live storage capacity | 1,000 tonnes | Design |
| Pre-leach thickener diameter | 12 m | Design |
| Thickener underflow density control range | 55% to 60% solids | Design |
| Leach feed solids | 55% solids | Design |
| Leach tanks | Six tanks, 700 m³ each | Design |
| CIP tanks | Eight tanks in series | Design |
| Cyanide detoxification tanks | Five tanks in series | Design |
| Acacia leach temperature | 54°C | Testwork / design |
| Acacia leach solution | 2.5% sodium cyanide, 1.5% sodium hydroxide | Testwork / design |
Project website: https://www.equinoxgold.com/news/equinox-gold-sells-pilar-gold-mine/
Project website: https://miningrecord.com/brio-gold-reports-on-production-of-three-brazilian-mines/
Technical qualifications
The information presented in this report is based on a review of the processing facilities at the Pilar mine as conducted by RPA, as documented in the NI 43-101 Technical Report for Equinox Gold Corp. dated March 26, 2020. The flowsheet description and parameters show the design basis of the plant, supplemented by historical operating data where indicated. Specific testwork conditions are noted for the Acacia reactor leach parameters. No verification of current operating performance or economic analysis is provided in the report excerpt.
Source: Equinox Gold Corp. – Pilar Operations, Technical Report NI 43-101 – March 26, 2020, Section 17 Recovery Methods.
