Soma Gold Corp's El Bagre complex in Antioquia, Colombia, processes 1,000 tpd of gold ore through an integrated flowsheet combining gravity concentration, intensive cyanidation, flotation, regrind cyanidation, and Merrill-Crowe precipitation to produce doré bars.
Article Body
This technical report dated January 18, 2023, documents the recovery methods and processing plant operations at the El Bagre Gold Mining Complex operated by Soma Gold Corp. The plant is designed to treat ore at 1,000 tonnes per day through a process train that begins with three-stage crushing and proceeds through grinding, flash flotation, gravity concentration, intensive cyanide leaching, conventional flotation, regrind and agitated cyanidation, Merrill-Crowe precipitation, and smelting. The flowsheet integrates multiple recovery mechanisms to maximize gold and silver extraction from a complex ore body. The plant operates in a closed water circuit with thickener overflows recycled to flotation and grinding.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Nominal throughput | 1,000 | tpd | Design rate |
| Feed top size | 203 | mm | Before crushing |
| Crushed product size | 7 | mm | P80 5 mm |
| Primary ball mill | 2.44 x 2.44 | m | 298 kW (400 hp) drive |
| Secondary ball mill | 1.5 diameter x 2.44 | m | 56 kW (75 hp) drive |
| Secondary cyclone diameter | 76.2 | mm | Set of four |
| Concentrate thickener underflow solids | 60 | % | Deep cone static thickener |
| Barren solution tank | 4.27 diameter x 4.27 high | m | |
| Smelting temperature | >1,100 | °C | Gasoil-fired reverb furnace |
| Smelting frequency | 3 | per month | Approximate |
Overview
The El Bagre plant recovers gold and silver through a multi-stage process that combines gravity concentration with flotation and intensive cyanidation. The flowsheet is designed to handle ore through sequential steps: size reduction, gravity recovery, flotation concentration, regrind and cyanidation, solution purification, precipitation, and smelting. The plant recycles process water from thickener overflows to the flotation and grinding stages, operating as a closed water circuit. The reported document is a NI 43-101 technical report prepared by SLR Project No: 233.03596.R0000.
Key Process Stages
Crushing
The crushing circuit consists of three stages that reduce the mineral from a top size of 203 mm to 7 mm (P80 5 mm) at a rate of 1,000 tpd. The crushed product is stored in a fine ore silo before feeding the grinding circuit.
Grinding and Gravity Concentration
Crushed ore from the fine ore silo is fed by vibratory feeder and belt conveyor to a 2.44 m (8 ft) by 2.44 m (8 ft) ball mill with a 298 kW (400 hp) drive. The ball mill discharges into the flash flotation cell feed sump, from which slurry is pumped to a flash flotation cell. The flash flotation cell concentrate is gravity fed to a centrifugal gravity concentrator, while flash flotation tailings flow to the hydrocyclone feed sump.
Gravity concentrate is sent to an intensive cyanide leach reactor (ILR) circuit for gold recovery. The gravity concentrator tailings flow by gravity to the dewatering concentrate thickener feed sump. Flash flotation tailings are pumped from the cyclone feed sump to a cluster of cyclones for classification. Cyclone overflow flows by gravity to the flotation circuit. Cyclone underflow returns to the primary ball mill feed chute, with a portion split to a high frequency screen. The screen undersize feeds a centrifugal gravity concentrator. Gravity concentrate is processed in the ILR circuit, and gravity tailings flow by gravity to the primary ball mill feed chute.
Intensive Cyanidation
Gravity concentrate is leached with a high concentration of cyanide solution to dissolve most of the gold and silver. The package equipment comprises an intensive cyanide leach reactor (ILR100BM), a concentrate feed tank, a mixing drum, two solution tanks, pumps, and a concentrate recirculation tank. The product is a gold and silver solution, which is pumped to the gold cyanide solution tank and then to the Merrill-Crowe precipitation stage. ILR tailings are pumped to the regrind ball mill feed.
Flotation
Cyclone overflow flows by gravity to a closed conditioner tank where flotation reagents are added. The slurry is fed by gravity to a flotation circuit consisting of three rougher, two scavenger, and one cleaner tank cells. The three rougher flotation concentrates are final concentrate and are pumped to the dewatering concentrate thickener feed sump. Rougher tailings feed two scavenger tank flotation cells in series. Scavenger concentrates are recycled to the cleaner cell feed. Cleaner concentrate gravity feeds to the dewatering concentrate thickener feed sump. Cleaner tailings feed the scavenger tank flotation cells, and scavenger tailings are pumped to the tailings pond. The dewatering concentrate thickener is a deep cone type static thickener where concentrate is thickened to 60% solids. Thickened concentrate is pumped to a pre-treatment agitator, while overflow is sent by gravity to the Recycle Water Tank for redistribution to flotation and grinding.
Pretreatment
Final flotation concentrate is pumped to a pre-treatment agitator where oxygen, air, lime, lead acetate, and sodium hypochlorite are added. The agitator discharges to a high rate thickener (HR1). HR1 overflow is pumped with flotation tailings to the tailings pond; underflow is pumped to the regrind circuit.
Regrind and Cyanidation
Flotation pretreated concentrate and ILR tailings are pumped to the regrind circuit where initial cyanidation takes place. A 1.5 m (5 ft) diameter by 2.44 m (8 ft) secondary ball mill with a 56 kW (75 hp) drive operates in closed circuit with a set of four 76.2 mm (3 in) diameter cyclones. Sodium cyanide solution and lime are added at the regrind stage to start the cyanidation process. Cyclone overflow is gravity fed to the DCT #1 thickener feed sump. DCT #1 thickener overflow is gravity fed to the gold cyanide solution tank. Underflow from DCT #1 is pumped to seven agitated tanks in series where secondary cyanidation takes place. Discharge from these tanks is pumped to three thickeners in series: a high rate (HR2) thickener, DCT #2 thickener, and DCT #3 thickener. The overflow from these thickeners contains gold and silver cyanide solution and is gravity fed to the DCT #1 thickener feed sump. HR2 underflow is pumped to DCT #2 thickener, and its overflow is pumped to DCT #3 thickener. DCT #3 thickener underflow is pumped to filtration and detoxification.
Filtration and Detoxification
Cyanide tailings from DCT #3 underflow are extensively washed in a closed circuit consisting of filtration, attrition wash, and detoxification. The cyanidation tailings are sent to a filter press that separates solids from the cyanide solution. Some of the initial solution is gravity fed to the agitator (complete details not stated in the source).
Merrill-Crowe Precipitation and Smelting
In the Merrill-Crowe process, dissolved gold and silver from conventional cyanidation are recovered through addition of zinc dust to form a solid precipitate. Gold cyanide solution is pumped to two filters where suspended solids are extracted. The clarified solution is sent to a vacuum tower where dissolved oxygen is removed by means of a vacuum pump. Zinc powder and lead acetate solution are added in-line to the clarified solution, which is pumped to precipitation filters where the precipitate is removed. The precipitate is unloaded onto trays and transported to smelting.
The precipitate is dried in a drying oven to eliminate barren solution, then mixed with flux and loaded to a gasoil-fired reverb furnace. The furnace operates at high temperature, above 1,100°C, to produce molten metal and slag, which is poured into moulds to produce mixed gold and silver doré bars. Smelting of precipitates takes place approximately three times per month.
Additional Interesting Data and Summary
The depleted solution (filtrate) from the precipitation filters is pumped to a barren solution tank measuring 4.27 m (14 ft) in diameter by 4.27 m (14 ft) high. The plant's use of vacuum deaeration in the Merrill-Crowe circuit is a notable design feature.
Key Processes
- Three-stage crushing from 203 mm to 7 mm
- Primary ball mill grinding with flash flotation and centrifugal gravity concentration
- Intensive cyanide leach reactor (ILR) for gravity concentrate
- Conventional flotation with rougher, scavenger, and cleaner cells
- Pretreatment with oxygen, air, lime, lead acetate, and sodium hypochlorite
- Regrind and agitated tank cyanidation in seven tanks in series
- Merrill-Crowe precipitation with zinc dust after vacuum deaeration
- Gasoil-fired reverb furnace smelting above 1,100°C
Source: El Bagre Gold Mining Complex , 2023 Technical Report, January 18, 2023.
Project website: El Bagre Gold Mining Complex, 2023 Technical Report
