The 2018 technical report describes a proposed whole-ore resin-in-leach processing facility at the Santa Luz Project, incorporating limited sections of a historical plant that operated from mid-2013 to September 2014.
Report context
The Santa Luz Project is covered by a NI 43-101 technical report dated January 19, 2018, prepared for Brio Gold Inc., Project #2858. The report presents a new ore-processing facility design based on whole-ore resin-in-leach (RIL) leaching, replacing the historical plant that consisted of comminution, flotation, and carbon-in-leach (CIL) of flotation concentrate with kerosene blanking of organic carbon. The historical plant operated for 14 months from mid-2013 to September 2014 and experienced both process difficulties and mechanical problems. The new facility will incorporate the crushing, crushed-ore storage, and SAG mill sections of the original plant; the rest of the plant, with the exception of the refinery, will be new. In the final year of operation, dacitic-high-sulfide ore from the A3 deposit will be processed by flotation in the existing flotation circuit, with concentrate shipped offsite for custom processing.
Processing route
Crushing
The crushing section is part of the original facility and requires no changes. It consists of a jaw crusher followed by a cone crusher, both in open circuit, with product conveyed to a conical stockpile. Run-of-mine ore is fed by front-end loader from stockpiles on a patio adjoining the crushing plant into a hopper in front of the jaw crusher. Ore is withdrawn from the hopper by a vibrating feeder-grizzly; grizzly oversize feeds the jaw crusher, and grizzly undersize drops to a conveyor that transports the grizzly undersize and jaw-crusher product to a transfer hopper and then to a second conveyor feeding a cone crusher. Crushed ore is conveyed by a third conveyor to the stockpile. Primary crush size is 80% passing 150 mm; secondary crush size is 80% passing 50 mm.
Grinding
The grinding section consists of two mills: a SAG mill and a ball mill operated in series. The SAG mill was part of the original facility; the ball mill is new. The SAG mill is unconventional in that the 10.4-m (34-ft) length is greater than the 5.8-m (19-ft) diameter, the feed (minus 50 mm) is finer than normal, and the product (minus 1 mm) is finer than normal. As originally installed, the SAG mill was the only grinding unit and was intended to grind to the final grind size. The ball mill is a conventional overflow ball mill and will grind the SAG mill product to the final grind size of 80% passing 75 µm.
Ore from the stockpile is drawn by two vibrating feeders onto a conveyor feeding the SAG mill. The SAG mill is equipped with a trommel discharge screen that screens out plus 12 mm pebbles. Pebbles are conveyed back to the SAG mill feed conveyor and are expected to constitute approximately 5% of new feed. Trommel-screen undersize is pumped to new primary-mill cyclones; cyclone underflow is recycled to the SAG mill, and cyclone overflow passes to the ball mill discharge pump box.
The pump at the ball mill discharge pump box pumps the combined SAG mill cyclone overflow and ball mill discharge to secondary-mill cyclones. Cyclone underflow constitutes the only feed to the ball mill. Dry lime is fed from a silo adjoining the ball mill pump box directly into the pump box. Cyclone overflow flows to a trash screen; trash screen oversize is recycled to the ball-mill pump box, and trash-screen undersize flows to the plant feed sampler and then to a pump box from which it is pumped to the RIL circuit. This sampler provides samples for determination of the plant head-grade assay.
Conditioning, leaching, and detoxification
Leaching is preceded by two sequential stages of conditioning using three tanks in series. Pre-aeration occurs in the first conditioning tank, and kerosene conditioning occurs in the subsequent two tanks. Oxygen is added in the pre-aeration tank. The report states that pre-aeration minimizes surface coating of the resin by a kerosene-ore film. In the kerosene-conditioning step, kerosene is added to blank organic carbon in the ore to minimize its propensity for soluble-gold adsorption, a phenomenon termed 'preg-robbing'. Total conditioning retention time is 6 hours.
Following conditioning, sodium-cyanide solution is added to the ground slurry as it flows from the kerosene-conditioning tank to the first of the RIL tanks. The RIL circuit consists of five stirred tanks in series with a leaching retention time of 20 hours. Oxygen is added to all but the last of the RIL tanks to provide oxygen for cyanide dissolution of gold while minimizing froth formation. The RIL tanks contain approximately 20 g of resin per litre of slurry. The resin is in the form of spherical beads approximately 1 mm in diameter; the ground ore particles are mostly less than one-tenth the size of the resin at approximately 90% less than 0.1 mm in diameter. Each tank is fitted with screens to retain the resin while allowing the ground ore slurry to flow from tank to tank. Each tank is fitted with pumps to intermittently pump resin-containing slurry counter-current to the normal slurry flow. Eluted resin is periodically added to the first and last RIL tanks, and loaded resin is periodically removed from the first RIL tank.
Leached slurry from the last RIL tank flows to a tailings slurry sampler for determination of plant tailings-grade assay. Discharge of the tailings sampler passes to a safety screen to recover any partially abraded resin. Safety-screen underflow flows to the detoxification circuit.
The detoxification circuit consists of two tanks in series with a retention time of 3 hours. Cyanide detoxification occurs in the first tank, and arsenic precipitation occurs in the second tank. Oxygen, sodium metabisulfite, copper sulfate, and sodium hydroxide are added to the cyanide detoxification tank to oxidize residual cyanide in the leached slurry. Ferric sulfate is added to the arsenic precipitation tank to precipitate any arsenic in the leached slurry, though the report notes that testwork indicates the amount of soluble arsenic will be so low that this addition is unlikely to be required.
Slurry from the detoxification tanks flows to the tailings pump box, and detoxified tailings are pumped to the tailings storage facility.
Resin elution, electrowinning, and refining
Loaded resin in the first RIL tank is periodically pumped to a screen to separate the resin from the ore slurry. The slurry in the screen underflow flows back to the first RIL tank. Loaded resin flows to a resin-wash tank to remove the kerosene-ore coating on the resin. The resin is washed and eluted on a batch basis. The resin-wash tank is fitted with a stirrer; wash solution containing surfactant is added to the base of the tank and flows upward to wash the coating from the resin. The wash solution containing suspended solids removed from the resin flows to the last RIL tank.
Washed resin is periodically transferred from the wash tank to one of two elution columns operated in parallel. An elution solution consisting of a mixture of sulfuric acid and thiourea heated to 60°C is pumped to the top of the elution column and flows downwards through the column to remove adsorbed gold and other adsorbed metals (primarily copper and iron) from the resin. A hot-water-heated heat exchanger is used to heat the elution solution. The elution system includes provision for a prior acid wash of the resin to partially remove adsorbed metals before elution of the gold, though the report states this appears unlikely to be needed.
Elution takes place in closed circuit with four electrowinning cells, with two electrowinning header tanks ahead of the cells and two recycle-solution tanks following the cells. Following elution, the eluted resin is washed with caustic solution to neutralize any remaining acid and is then recycled to the RIL tanks via two barren-resin screens, one over the first RIL tank and one over the last RIL tank. Barren-resin screen oversize gravitates to the RIL tanks below the screens. Underflow from the barren-resin screens passes to the resin safety screen located between the RIL and detoxification tanks and then to the detoxification tanks.
The elution solution containing gold and other metals flows to two electrowinning header tanks in parallel and then to four electrowinning cells. The cathodes of the cells are stainless-steel wool. Gold and other metals in the eluate are electrodeposited on the cathodes. Periodically the electrodeposited metals are washed from the cathodes, and the cathode sludge is collected, filtered, and dried. The dried cathode sludge is mixed with oxidizers and flux, and the mixture is smelted to produce metal and slag. The eluate is expected to contain 10 to 15 times as much copper as gold; accordingly, the metal produced consists of an alloy of copper and gold.
The copper-gold alloy will be shipped to a custom refinery. The slag will be processed to recover any coarse metal and will then be recycled to the plant feed.
Tailings storage facility
There are currently two tailings dams at the Santa Luz Project: one for flotation tailings and one for leached tails. The existing flotation TSF constructed for the prior operation will be used for storing tailings for the new operation. Because the new process plant design eliminates the flotation process and is based on whole-ore leaching, all tailings generated will have been in contact with leaching reagents and will be best stored in a lined tailings impoundment. The current flotation TSF will be modified with the installation of a geomembrane to accept leach tailings, and the prior leaching TSF will be used only for water storage.
The TSF is located in a broad, shallow valley adjoining the processing plant. A dam made of compacted borrow and waste-rock approximately 750 m long and approximately 20 m high closes the valley to impound the tailings. The upstream region of the dam wall was built of clayey material from local borrow areas. The downstream zone was constructed of waste rock. A gravel and sand chimney drain was placed between the borrow and the waste rock and linked to finger drains on the base of the dam that lead to the downstream toe.
The elevation of the dam crest is currently 260 MASL. The dam will be raised in four stages: first to a crest elevation of 266 MASL, then to 270 MASL, then to 273 MASL, and finally to 275 MASL. The dam will be raised using the downstream construction method and will include the same pattern of construction as the original dam, with clayey material on the upstream side, a gravel-sand chimney drain in the centre, and waste rock on the downstream side.
The TSF as previously operated did not include a liner. For the new operation, the TSF will be lined with 1.5-mm high-density polyethylene (HDPE) geomembrane. Additional liner will be subsequently placed in parallel with the raising of the dam.
The dam does not include an overflow system; it is designed to maintain a minimum freeboard of 2.5 m between the dam crest and water level to allow for storm events. The capacity of the TSF at the various crest elevations, including 2.5 m of freeboard, is reported as: 3.1 million m³ (4.3 Mt tailings solids) available at 260 MASL; 8.0 million m³ (11.3 Mt) at 266 MASL; 13.1 million m³ (18.4 Mt) at 270 MASL; 17.9 million m³ (25.1 Mt) at 273 MASL; and 21.7 million m³ (30.4 Mt) at 275 MASL. These capacities do not include 1.45 million m³ of tailings from the prior operation. Placement of tailings in the TSF will follow past practice, with slurry spigotted from pipes located on the perimeter of the TSF. A barge pump in the TSF will recover decant water and pump it to the plant water tank.
Dacitic-high-sulfide ore processing
Dacitic-high-sulfide ore from the A3 deposit will be processed in the last year of operation. This ore has a reported grade of approximately 1.0 g/t gold, 0.05% total organic carbon, and 2,000 ppm arsenic. The ore will be crushed and ground in the same crushing and grinding facilities as those used for regular ore. The ground ore will be floated in the flotation circuit that was constructed for the prior operation, which will be refurbished. Flotation rougher retention time is 20 minutes, and cleaning retention time is 20 minutes. The regrind mill grind size is 80% passing 45 µm. Flotation concentrate will be dewatered using a thickener (high-rate, 0.2 tonnes/hr/m²) and a pressure filter (0.2 tonnes/hr/m²). Filter cake will be stored in a new concentrate storage building with facilities for loading the concentrate into super sacks. The concentrate will be shipped offsite, either to copper smelters or to other plants offering toll processing. Reported concentrate grade is 80 g/t gold and 160,000 ppm arsenic, with 90% gold recovery and 90% arsenic recovery. Concentrate production is reported as 30,375 tpa, with gold production of 78,126 oz/yr.
Key reported parameters
| Parameter | Units | Value | Basis |
|---|---|---|---|
| Throughput rate (annual) | t/year | 2,700,000 | Proposed design |
| Throughput rate (daily) | t/day | 7,400 | Proposed design |
| Ore grade (average LOM) | g/t | 1.4 | Proposed design |
| Total organic carbon (TOC) | % | 0.6 | Proposed design |
| Arsenic | ppm | 500 | Proposed design |
| Gold recovery | % | 84 | Proposed design |
| Gold production | oz/year | 100,000 | Proposed design |
| Work index | kWh/t | 19 | Proposed design |
| Abrasion index | 0.5 | Proposed design | |
| Primary crush size (80% passing) | mm | 150 | Proposed design |
| Secondary crush size (80% passing) | mm | 50 | Proposed design |
| Primary mill grind size (80% passing) | µm | 860 | Proposed design |
| Secondary mill grind size (80% passing) | µm | 75 | Proposed design |
| Conditioning retention time | hours | 6 | Proposed design |
| Leaching retention time | hours | 20 | Proposed design |
| Detoxification retention time | hours | 3 | Proposed design |
| Power consumption | kWh/t | 42 | Proposed design |
| Fresh water (make-up) | m³/t | 0.40 | Proposed design |
| Grinding ball consumption | kg/t | 1.80 | Proposed design |
| Quick lime consumption | kg/t | 1.00 | Proposed design |
| Kerosene consumption | kg/t | 1.30 | Proposed design |
| Sodium cyanide consumption | kg/t | 0.75 | Proposed design |
| Sodium metabisulfite (SMBS) consumption | kg/t | 0.75 | Proposed design |
| Thiourea consumption | kg/t | 0.25 | Proposed design |
| Operating cost | US$/t | 14.52 | Proposed design |
| Capital cost | US$ millions | 82.2 | Proposed design |
| Projected start-up date | June 2018 | Proposed design |
Project website: https://miningdataonline.com/property/3105/Santa-Luz-Mine.aspx
Dacitic-high-sulfide ore parameters:
| Parameter | Units | Value | Basis |
|---|---|---|---|
| Throughput rate (annual) | t/year | 2,700,000 | Proposed design |
| Throughput rate (daily) | t/day | 7,400 | Proposed design |
| Gold grade | g/t | 1.0 | Proposed design |
| Total organic carbon (TOC) | % | 0.05 | Proposed design |
| Arsenic | ppm | 2,000 | Proposed design |
| Gold recovery | % | 90 | Proposed design |
| Arsenic recovery | % | 90 | Proposed design |
| Concentrate gold grade | g/t | 80 | Proposed design |
| Concentrate arsenic | ppm | 160,000 | Proposed design |
| Concentrate production | tpa | 30,375 | Proposed design |
| Gold production | oz/yr | 78,126 | Proposed design |
| Flotation rougher retention time | min | 20 | Proposed design |
| Flotation cleaning retention time | min | 20 | Proposed design |
| Regrind mill grind size (80% passing) | µm | 45 | Proposed design |
| Operating cost | US$/t | 9.59 | Proposed design |
| Capital cost | US$ millions | 3.3 | Proposed design |
| Projected start-up date | Jan 2028 | Proposed design |
Technical qualifications
The report documents that the original ore-processing plant at Santa Luz was built and placed in operation in mid-2013 and was shut down in September 2014 after 14 months of operation. The original plant consisted of a comminution circuit followed by flotation followed by CIL of the flotation concentrate with kerosene blanking of the organic carbon. The report states that the plant did not operate well as a result of both process difficulties and mechanical problems. The new ore-processing facility will incorporate only the crushing, crushed-ore storage, and SAG mill sections of the original plant; the rest of the plant, with the exception of the refinery, will be new.
For the proposed RIL process, the report indicates that testwork has shown that pre-aeration minimizes surface coating of the resin by a kerosene-ore film. The report also notes that testwork indicates the amount of soluble arsenic will be so low that ferric sulfate addition for arsenic precipitation is unlikely to be required. The elution system includes provision for a prior acid wash of the resin, though the report states it appears unlikely that this will be needed.
The existing flotation TSF constructed for the prior operation will be used for storing tailings for the new operation. The TSF as previously operated did not include a liner; for the new operation, the TSF will be lined with 1.5-mm HDPE geomembrane. The dam will be raised using the downstream construction method.
Source: Brio Gold Inc. – Santa Luz Project, Project #2858, Technical Report NI 43-101, January 19, 2018, Sections 17 (Recovery Methods).
