Torex Gold Resources Inc. is advancing the Los Reyes gold-silver project in Sinaloa and Durango, Mexico, with a processing plant designed around whole-ore cyanide leaching and Merrill-Crowe recovery.
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The Los Reyes Project is an advanced development project located in the Sierra Madre Occidental mountain range in Sinaloa and Durango, Mexico, approximately 110 km by air from Mazatlán and 27 km southeast of the town of Cosalá. The target commodities are gold and silver, hosted in a low-sulphidation epithermal system. Torex Gold Resources Inc. acquired the project in October 2025 through its purchase of Prime Mining Corp., giving it indirect ownership of 100% of the property, which consists of 37 contiguous mining concessions covering 6,273 hectares. The project is at the preliminary economic assessment (PEA) stage, with a technical report effective date of April 25, 2026. The PEA describes a combined underground and open-pit mining operation feeding a single 5,000 t/d processing plant. The technical report does not state expected construction timing.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Plant capacity | 5,000 | t/d | Design value |
| Life of mine | 15 | years | Design value |
| Gold head grade, LOM average | 1.68 | g/t | Design value from PEA mining inventory |
| Silver head grade, LOM average | 63.4 | g/t | Design value from PEA mining inventory |
| Gold head grade, design | 2.27 | g/t | Design value |
| Silver head grade, design | 90.1 | g/t | Design value |
| Sulphur, design | 1.4 | % | Design value |
| Crushing availability | 65 | % | Assumed design value |
| Grinding availability | 92 | % | Assumed design value |
| Filtering availability | 85 | % | Assumed design value |
| Paste plant availability | 65 | % | Assumed design value |
| JK Axb, design | 37.2 | Not applicable | Design value |
| Bond ball work index, design | 18.5 | kWh/t | Design value |
| Bond abrasion index, average | 0.396 | Not applicable | Average value |
| Specific gravity | 2.57 | Not applicable | Design value |
| ROM feed size, F100 | 600 | mm | Design value |
| ROM feed size, F80 | 317 | mm | Design value |
| Ball mill recirculating load | 400 | % | Design value |
| Grinding product size, P80 | 75 | µm | Design value |
| Primary cyclone overflow density | 35 | % solids (w/w) | Design value |
| Leach residence time | 72 | h | Design value |
| Pre-leach thickener settling rate | 0.7 | t/h/m² | Design value |
| Pre-leach thickener underflow density | 50 | % solids w/w | Design value |
| CCD suspended solids in last thickener overflow | <500 | ppm | Design value |
| CCD settling rate | 0.7 | t/h/m² | Design value |
| CCD underflow density | 55 | % solids w/w | Design value |
| CCD wash ratio | 3.5 | m³ water:m³ water in feed slurry | Design value |
| Clarification filter suspended solids in product | <10 | mg/L | Design value |
| Clarifier rise rate | 1.0 | m/h | Design value |
| Clarification filter specific capacity | 2.2 | m³/m²/h | Design value |
| Tailings thickening, solids flux loading rate | 0.7 | t/m²/h | Design value |
| Tailings thickener underflow density | 60 | % solids w/w | Design value |
| Tailings filter stock tank residence time | 4 | h | Design value |
| Cyanide detoxification residence time | 90 | min | Design value |
| Detox circuit pulp density, nominal | 43 | % w/w | Design value |
| Specific tailings filtration rate | 126-150 | kg/h/m² | Design range |
| Paste plant capacity, design | 0.71 | Mm³/a | Design value |
| Paste plant capacity, design | 1.21 | Mt/a | Design value |
| Total installed power | 13.0 | MW | Estimated value |
| Raw water requirement, normal operation | 27 | m³/h | Approximate nominal value |
| Raw water requirement, with paste plant | 62 | m³/h | Approximate estimated value |
| LOM gold recovery | 95.8 | % | Test-based model result |
| LOM silver recovery | 82.1 | % | Test-based model result |
| Plant design recovery deduction | 1 | % | Applied for solution losses |
| Gold recovery, open pit plant resource assumption | 94.8 | % | Resource estimate assumption |
| Silver recovery, open pit plant resource assumption | 81.1 | % | Resource estimate assumption |
| Heap leach gold recovery assumption | 73 | % | Resource estimate assumption |
| Heap leach silver recovery assumption | 25 | % | Resource estimate assumption |
Overview
The process flowsheet at Los Reyes is based on preliminary metallurgical testwork completed on the deposit, Ausenco's database of reference projects, and in-house process modelling. The plant is designed to process 5,000 t/d of mineralised material to produce gold and silver doré. The processing design consists of crushing, grinding, cyanide leaching, counter-current decantation (CCD), and precious metal recovery through the Merrill-Crowe process. Tailings are detoxified using the SO₂/O₂ cyanide detoxification process, thickened, and filtered before being dry-stacked on a filtered tailings storage facility. When cemented paste is required for backfilling underground workings, detoxified tailings are diverted to a paste plant located near the underground mine portal.
The plant operates on a schedule of two 12-hour shifts per day, 365 days per year. The design assumes availability of 65% for the crushing stage, 85% for tailings filtering, 92% for grinding, and 65% for the paste plant.
Metallurgical testwork has been extensive. Five programs have been conducted, with the most recent evaluating gravity concentration, froth flotation, and bottle roll cyanide leaching, along with some comminution testing. The testwork included 25 composites and 47 variability samples obtained from six of the main deposits. Gold occurs as native gold or electrum with grains described as sub-20µm, while silver is primarily present as argentite with grains ranging from 2µm to 250µm.
The materials responded well to cyanide bottle roll leach tests, with gold extraction levels of approximately 95% consistently achieved across all deposits within 48 hours at a grind size of 75µm P80. Silver kinetics were slower, requiring generally 72 hours of residence time and higher sodium cyanide dosages. High silver extractions in the range of 90-95% were measured on samples from the Guadalupe and Noche Buena deposits, whereas lower extractions in the 60-80% range were measured on San Miguel and Tahonitas deposits. Zapote samples consistently returned silver extractions in the 40% range despite longer leaching times or increased sodium cyanide tenors.
Extraction models as a function of feed grades were developed from the metallurgical data for each deposit. Life of mine grades for each deposit were applied to the models and weighted by contained ounces to obtain a project-wide LOM recovery estimate of 95.8% for gold and 82.1% for silver. Plant design includes a 1% deduction on these recoveries to account for solution losses.
Key Process Stages
The crushing circuit uses a three-stage closed circuit to reduce run of mine material from an 80% passing feed size of 317 mm to an 80% passing product size of 10 mm. ROM material is dumped into a hopper that feeds a vibrating grizzly screen. Grizzly oversize reports to a jaw crusher, with the crushed product recombined with grizzly undersize and conveyed to a double-deck vibrating screen. Upper-deck oversize goes to the secondary crusher and lower-deck oversize to the tertiary crusher. Discharge from the secondary and tertiary crushers returns to the secondary screen feed conveyor. Screen undersize conveys to the crushed material stockpile.
Fresh feed is reclaimed from the stockpile and conveyed to the grinding circuit. The ball mill operates in closed circuit with a classifying cyclone cluster. Mill discharge passes through a trommel to remove scats. Trommel undersize reports to the cyclone feed pump box, is diluted, and pumped to primary cyclones. Cyclone underflow returns to the ball mill for further grinding. Cyclone overflow gravitates to a trash screen to remove debris and ensure clean slurry feed to the pre-leach thickener.
The grinding product, at 80% passing 75µm, advances from the trash screen to a pre-leach thickener where flocculant is added to facilitate solids settling. Thickener overflow transfers to the process water tank while underflow pumps to the leaching tanks. Leaching occurs in a series of five mechanically agitated tanks providing a total of 72 hours of residence time. Hydrated lime, sodium cyanide, and lead nitrate are added to the first two tanks for pH control, cyanide maintenance, and catalysis respectively. Barren solution from the Merrill-Crowe circuit recycles to the first two leaching tanks. Oxygen is sparged into all tanks to facilitate leaching of gold and silver.
Leached solids pass through a series of five counter-current decantation thickeners where pregnant solution is washed from the solids. In each thickener, solids are washed through the addition of overflow from the subsequent stage, with settling facilitated by flocculant addition. Thickener overflow advances to the preceding stage, and the first thickener in series advances to the pregnant solution clarifier. Clarifier overflow goes to a pregnant solution tank for feeding to the Merrill-Crowe circuit. Underflow from the clarifier pumps back to the start of the bulk leaching circuit as required. The target for gold concentration in the tailings discharge from the last thickener is 0.02 ppm, with a target silver concentration of less than 0.76 ppm. Barren solution is added to the last thickener to achieve the target wash ratio of 3.5 m³ water per m³ water in feed slurry.
In the Merrill-Crowe circuit, solution is pumped from the pregnant solution tank through clarifier filters and a deaeration tower to reduce dissolved oxygen content. Deaerated solution then pumps to precipitation filters to recover the precious metal rich precipitate. Zinc powder is added to the precipitation filter feed to provide the necessary levels of zinc for precipitation. Solids from the precipitate filters are manually moved to the smelting furnace for doré production, while filtrate advances to the barren solution tank. Barren solution distributes to the CCD circuit as wash water, flocculant dosing streams, and the detoxification circuit for dilution as necessary. Antiscalant is added to pregnant and barren solution tanks to inhibit scale formation, and diatomaceous earth is added to both clarifying and precipitation filters to improve filter performance.
The refinery receives zinc precipitate from the precipitation filters for retorting and smelting into silver-gold doré bars. Retorting and smelting operates in batch mode in a secure, enclosed area with restricted access. The refinery is a vendor package that includes two precipitation filters, a smelting furnace, flux dosing and mixing system, mercury retort, doré scale and storage vault, slag handling equipment, and dust collection system.
Underflow from the final CCD thickener pumps to cyanide detoxification tanks where weak-acid-dissociable cyanide (CNWAD) is detoxified using the SO₂/air process, reducing CNWAD concentration to below 5 mg/L over a 90-minute residence time. Sodium metabisulphite is the main reactant, copper sulphate acts as a catalyst, and hydrated lime maintains the required reaction pH. Oxygen is sparged into the tanks. Discharge slurry flows by gravity to the tailings thickener where flocculant is added. Underflow reports to tailings filter storage tanks, and filter cake discharges to a stockpile. An excavator reclaims material from the stockpile and trucks deliver it to the dry stack facility. Filtrate from the filters returns to the tailings thickener feed.
The paste plant operates as required for underground backfill, sized to accommodate the highest year of paste demand, equivalent to approximately 50% of tailings material from the process plant. Material exiting the cyanide detoxification circuit bypasses the tailings thickener and pumps to the paste plant on an as-required basis. At the paste plant, tailings are thickened and filtered then added to a paste mixer unit with cement binder. Paste is then pumped to the underground reticulation distribution system using two positive displacement paste pumps.
Additional Interesting Data and Summary
The testwork program included a limited amount of comminution testing. Drop weight SMC tests on four samples returned Axb values averaging 38, indicating moderate competence with respect to impact breakage in a SAG mill. Bond ball mill work index tests on eight samples averaged 17.7 kWh/t and ranged from 15.8 to 19.2 kWh/t. The design values for the plant are 37.2 for JK Axb and 18.5 kWh/t for Bond ball mill work index.
The material showed a modest response to gravity concentration, averaging 23% gold and 10% silver recovery on Knelson plus Gemini table upgrading tests conducted on samples ground to 80% passing 150µm. Froth flotation response was varied, with tests on Guadalupe East samples returning gold and silver recoveries to rougher concentrates as high as 90-95% while Tahonitas and Zapote tests recovered only 85% and 70% or lower of the feed gold and silver respectively. A limited amount of column leach testing indicated that the materials are amenable to heap leaching for gold, although silver extractions were quite low. Seven samples tested at a crush size of 12.5mm averaged 67% gold and 17% silver extractions from average feed grades of 1.5 g/t Au and 23 g/t Ag.
Process water for the plant consists of pre-leach thickener overflow and tailings thickener overflow, with raw water provided as required for makeup. Raw water is obtained from collection ponds on site and mine dewatering, or alternatively from groundwater wells in the region of Potrerillo de los Torres. The raw water tank provides 12-hour live storage capacity. During normal operation, when the paste plant is not in use and plant throughput is maintained at 5,000 t/d, the nominal fresh water requirement is approximately 27 m³/h. When the paste plant is in operation, the estimated water requirement increases to approximately 62 m³/h. Potable water is produced by an on-site treatment plant and stored in a dedicated tank with 48-hour live capacity. Fire water is stored in a dedicated volume within the raw water tank.
Reagents are received and handled with unloading and storage facilities, mixing and storage tanks, and feeding equipment for each required reagent. Each set of compatible reagents is located in a dedicated containment area to prevent environmental contamination and mixing of incompatible reagents. Quicklime is received as powder in bulk shipments, stored in a silo, slaked with raw water in a vertical mill, and distributed via ring main to the leaching and detoxification circuits. Sodium cyanide is received in bulk bags, dissolved, and transferred to a storage tank before distribution to cyanide leaching circuits. The nominal annual consumption of sodium cyanide is 3,947 t/a, with quicklime consumption of 777 t/a for leaching and 4,130 t/a for detoxification.
Oxygen gas for cyanide leaching and detoxification circuits is generated at an on-site plant employing vacuum swing adsorption technology, producing an oxygen stream of 93% purity at 100 psig. Compressed air is produced by compressors to meet plant requirements of 750 kPa for high-pressure and 250 kPa for low-pressure applications.
The gold-silver ore at Los Reyes is quartz hosted with low sulphur content. The process design criteria specify a sulphur content of 1.4%. The total installed power requirement for the process plant is estimated at 13.0 MW.
Key Processes
- Three-stage closed-circuit crushing from 317 mm F80 to 10 mm P80
- Ball milling in closed circuit with classifying cyclones to 75 µm P80
- Whole-ore cyanide leaching in five mechanically agitated tanks with 72 hours residence time
- Counter-current decantation through five thickeners with a 3.5:1 wash ratio
- Precious metal recovery via Merrill-Crowe zinc precipitation, deaeration, and clarification
- Retorting and smelting to produce silver-gold doré bars
- Cyanide detoxification using SO₂/air process with sodium metabisulphite
- Tailings thickening and filtration for dry-stack disposal
- Paste backfill plant for underground void filling
Source: Los Reyes Project NI 43-101 Technical Report and Preliminary Economic Assessment, July 7, 2026. Project website: Los Reyes Project
