This technical report describes the processing facilities at the Morelos Property, covering both the currently operating ELG Process Plant and the proposed Media Luna flowsheet, supported by historical operating data and testwork.
Report context
This technical report, dated 31 March 2022, documents the recovery methods for the Morelos Property. The report covers two distinct processing operations: the existing ELG Process Plant, which has been in commercial operation since March 2016, and the proposed Media Luna (ML) Process Plant, for which a mineral beneficiation process has been designed.
Processing route
ELG Process Plant
The ELG Process Plant process design description follows these steps: Primary Crushing and Grinding, Cyanide leach, CIP, Tails filtration, SART, ADR, Electrowinning, and Onsite smelting to doré bars. The recovery methods described are all currently in operation.
The basic process flow is crushing, grinding, agitation leaching, carbon adsorption, carbon acid wash, carbon desorption (stripping), carbon regeneration, gold electrowinning, gold smelting, tailing detoxification, tailing filtration and disposal. In late 2016, the SART plant was added to the process to deal with elevated copper identified in the ELG ore during ramp up.
Tailings generated from the process in the Filtration Plant are stored in the Filtered Tailings Storage Facility (FTSF). Process water is reclaimed and recycled, minimizing water consumed by process.
Crushing and Grinding: Two identical crushing systems are installed to process ROM ore from the El Limón and Guajes pits. A RopeCon conveyor system delivers ore from the El Limón crusher to the processing plant over approximately 1 km horizontal and 385 m vertical distance. At each crusher location, a 200-tonne capacity feed hopper is fed from rear dump haul trucks of 100 tonne capacity. The 1.067 m by 1.651 m primary gyratory crushers produce a 150-mm product. A coarse ore stockpile has a live capacity of 14,000 tonnes. Ore is ground to a final product size averaging 80% passing 85-95 µm in a SAG and ball mill grinding circuit. The SAG mill is 9.15 m diameter by 4.15 m EGL with a 7,000 kW motor. The ball mill is 7.3 m diameter by 12.65 m EGL with two 7,000 kW motors.
Leaching and CIP: A 32 m diameter high-rate thickener thickens grinding cyclone overflow to 50% solids. Precious metals are leached in five to eight of eleven installed 15.55 m diameter by 21.34 m high agitated tanks, each providing a working volume of 3,815 m³ at 20.1 m slurry level. Six to seven leach tanks typically provide retention time of approximately 18 to 26 hours. Oxygen is sparged into the first two leach tanks. Cyanide solution is added to tanks as required. The pH is maintained over 10.5. Leached gold and silver are adsorbed onto activated carbon in the CIP circuit, which consists of six 250 m³ AAC Pump Cell tanks in carousel configuration, nominally containing 48 g/L of 6 by 12 mesh granular activated carbon.
SART Plant: The SART plant removes ~90-95% of copper from the feed and produces a saleable high grade (~40-50% Cu) copper precipitate. Sulfuric acid reduces solution pH to 4.5, with sodium hydrosulphide added for precipitation of copper sulphide. The design production rate of copper filter cake is approximately 31.8 t/d (wet basis at 50% moisture content) with a copper content of about 42.6% Cu (dry basis). The copper thickener overflow is neutralized using slaked lime to above pH 10.5.
Tailing Detoxification, Dewatering and Disposal: WAD cyanide is oxidized by the SO₂/Air process using MT-2000 (ammonium bisulfite) with oxygen injection. The filter plant consists of seven Diemme high pressure filters (HPF) and two Delkor horizontal belt filters (HBF). The HPFs throughput is approximately 100 tonnes per hour each, producing filter cake at 17% moisture. The HBFs throughput is 160 tonnes per hour each, producing cake at 18% moisture. Each HBF has a filtering area of 162 m².
Carbon Stripping and Regeneration: Carbon stripping uses a pressure Zadra process circulating 140°C caustic cyanide solutions upward through a partially fluidized bed of carbon in 12-tonne batches. For reactivation, carbon is heated to 700-750°C in a horizontal rotary carbon reactivation kiln.
Refining: Gold is recovered from pregnant strip solution by electrowinning, with four 3.5 m³ electrowinning cells in parallel at a flow rate of 45 m³/h. Sludge is retorted at up to 600-700°C prior to smelting to doré bars.
Media Luna Process Plant (Proposed)
The proposed ML process will make extensive use of the existing ELG Process Plant and facilities. The envisioned process would produce three salable products: a copper/gold/silver concentrate, doré containing gold and silver, and a copper precipitate.
The ML process will use the existing ELG comminution plant followed by sequential flotation to produce a copper/gold/silver concentrate, followed by further flotation of the copper rougher tailing to produce Fe-S concentrate and tails streams. The flowsheet is based on the results of metallurgical testing conducted by Base Metallurgical Laboratories Ltd. in Kamloops, British Columbia.
The design basis for the ML ore processing facility is 10,600 dry t/d, nominally operating at a 92% availability. The footprint of the ML process plant fits within the current ELG Mine Complex area.
Process Description:
A new conveyor will transport material from the Guajes Tunnel directly to the ELG plant area. ML material will be stockpiled separately from ELG ores. After grinding, the ML ore will pass through copper sulphide rougher and Fe-S rougher flotation circuits.
The copper rougher flotation circuit consists of seven cells of 100 m³ each. The copper rougher concentrate will be reground (target P80 30 µm) and cleaned through three cleaning stages to generate a saleable copper-gold-silver concentrate. The copper cleaner circuit is envisioned to have six 20 m³ cells for first stage, four 20 m³ cleaner scavenger cells, six 16 m³ cells for second cleaner, and four 16 m³ cells for third cleaner.
The Fe-S rougher flotation circuit envisions five 100 m³ cells. The Fe-S rougher concentrate will be combined with copper cleaner tailing and, after regrind to 80% passing 30 µm, will be subject to leaching for gold and silver utilizing part of the existing ELG leach circuit.
The Fe-S flotation tailing will be subjected to Cyanide Leach/CIP through the existing ELG plant. Cyanide will be recovered from the CIP tails stream via the existing cyanide recovery thickener and a new water treatment plant. Reverse osmosis will be used to maximize recovery of cyanide and gold to the SART and CIC circuits.
Tailings Systems: Two tails streams will be generated and pumped to a new tailings handling facility at the Guajes portal area. Tailings will be placed as either backfill in the ML mine or thickened via a new 30 m diameter Guajes thickener and stored in the Guajes Pit Tails Storage Facility (GTSF). The priority will be to place the higher Fe-S content tails as backfill material.
Water Systems: Two distinct water circuits will be used. The water treatment plant has two main components: high cyanide content streams passed through reverse osmosis to concentrate cyanide species for the SART plant, and low cyanide content streams sent to a solution DETOX circuit to generate cyanide free solution for reuse in the grinding and flotation circuit.
Early Fe-S Process Plant: The installation of the Fe-S flotation circuit, regrind and separate leaching is planned to be accelerated by several months to enable recovery and reagent saving benefits when processing high cyanide consuming ELG ores. This early Fe-S circuit does not add any additional major equipment compared to the full ML design, though the future copper rougher flotation cells are to be installed to accommodate the higher mill production rate for the period prior to the reduction in throughput for ML ores.
Key reported parameters
| Parameter | Units | ELG (2021 Actual) | ML Design (min-avg-max) |
|---|---|---|---|
| Mill Feed | t/d | 12,362 | 10,600 |
| Plant Availability | % | 88.6 | 92.0 |
| Feed Grades | |||
| Gold | g/t Au | 3.65 | 1.45 – 2.57 – 4.07 |
| Silver | g/t Ag | 3.91 | 2.89 – 21.8 – 39.9 |
| Copper | % Cu | 0.15 | 0.20 – 0.73 – 1.18 |
| Overall Recovery | |||
| Gold | % | 88.3 | 90.0 |
| Silver | % | 30.6 | 86.0 |
| Copper | % | – | 93.0 |
| Copper Concentrate Recovery | |||
| Mass | t/d | – | 120 – 280 – 460 |
| Copper | % of feed | – | 82 – 90 – 92 |
| Gold | % of feed | – | 52 – 58 – 65 |
| Copper Concentrate Grade | |||
| Copper | % Cu | – | 22.0 – 24.5 – 29.0 |
| Gold | g/t Au | – | 26.0 – 60 – 160 |
| Silver | g/t Ag | – | 240 – 660 – 910 |
| ML Reagent Usage | |||
| Sodium Cyanide (leaching) | kg/t mill feed | – | 3.01 |
| Lime (leaching) | kg/t mill feed | – | 2.00 |
| Calcium Hydroxide (flotation) | kg/t mill feed | – | 3.00 |
Project website: https://www.properstar.ca/mexico/morelos/buy/house
Technical qualifications
The report states that the SART plant was added to address operational issues caused by the presence of soluble copper in the ore. The current bottleneck in the ELG Process Plant is the grinding circuit, which is currently being optimized to balance the workload between the SAG Mill, Ball Mill and Pebble Crusher.
The ML reagent usage estimates are supported by test work completed to date and may be revised as a result of new information. Separate leaching of the high metal sulphide concentrate results in a reduction in overall cyanide consumption of 20-30% as compared to bulk leaching. Metallurgical testing indicates that minor blending of ELG open pit ores with ML and ELG underground ores does not negatively affect the copper flotation process.
The longer than designed retention times required for reactivation does not allow thermal regeneration of carbon after every strip cycle. The deportment of gold in the mineralized ores is highly variable, and at times the Fe-S flotation tails may contain insufficient soluble gold to cover operational costs for processing that stream.
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Source: Morelos Property , Form 43-101F1 Technical Report, M3-PN200103, 31 March 2022, Revision 0. Relevant sections: 17 Recovery Methods; 17.1 ELG Process Plant; 17.2 Media Luna Process Plant; 17.3 Media Luna Early Fe-S Process Plant.
