Preliminary economic assessment and mineral resource estimate for the Cerro de Oro Project in Zacatecas State, Mexico, dated January 5, 2023.
Report context
This NI 43-101 technical report presents a preliminary economic assessment and mineral resource estimate for the Cerro de Oro Project, located in Zacatecas State, Mexico. The report date is January 5, 2023. The processing facility design is based on preliminary test work presented in Section 13 of the report, which serves as the basis for gold recovery design criteria.
Processing route
Crushing and stockpiling
It is estimated that 30% to 35% of total mineralized production will be sent for crushing, corresponding to a crushing cut-off grade of approximately 0.40 to 0.45 g/t Au. Higher grade material above this threshold will be processed through a two-stage crushing circuit consisting of a primary jaw crusher and secondary cone crushers with vibrating screens operating in closed circuit. Feed material with a maximum lump size of 400 mm is crushed to minus 3/4 inch to 7/8 inch. Lime is added to final product transfer conveyors. The crushing circuit is designed to operate 16 hours per day at a feed rate of 6,500 to 7,000 t/d, with a surge stockpile near the jaw crusher to receive materials when the circuit is not operating.
Low-grade mineralized material below the crushing cut-off grade will be sent directly to the leach pad as run-of-mine (ROM) material via direct truck dump.
Heap leach
Mineralized material is delivered to the leach pad area by truck (ROM) and transfer conveyors (crushed) and stacked on an impermeable plastic and clay lined leach pad. The heap will be irrigated with a dilute alkaline cyanide solution that percolates through the heap to extract gold and silver. Pregnant solution reaches the liner at the bottom of the leach pad and drains into a storage pond.
The leach pads are to be constructed in phases as mining advances. Phase 1 consists of 400,000 m² of 80 mil (2 mm) thick LLDPE liner placed above a compacted clay base, with a gravel overliner protecting the membrane. Perforated solution collection pipes within the gravel overliner allow solution to flow by gravity along the sloped pad base into the pregnant solution pond.
Solution ponds
The solution storage design considers a single pond divided into multiple compartments. A berm/weir separates areas that can store pregnant solution and barren solutions respectively. Additional volume above the berm provides containment during precipitation events. Total maximum contained solution volume is approximately 180,000 m³, with approximately 100,000 m³ distributed between pregnant and barren storage areas and 80,000 m³ available for event situations.
The pond design uses impermeable plastic membranes installed above a compacted clay underliner, with a double plastic membrane (minimum 60 mil HDPE for each layer) and leak detection monitoring sumps between the two membranes.
Pregnant solution is pumped from the storage pond to the carbon columns for precious metal recovery. Barren solution exiting the carbon columns discharges by gravity into the barren storage pond and is recirculated to the leach pad. Cyanide make-up solution is injected into the barren solution stream before return to the leach pad.
Carbon column gold recovery
Four carbon column trains operating in parallel are designed to process a total of at least 800 m³/h of solution, with each train treating 200 m³/h through four columns installed in series. Solution from the pregnant solution pond is divided into four streams and fed to the first column of each train. Gold and silver cyanide complexes are adsorbed onto activated carbon in the columns, with solution overflowing by gravity between columns in series.
When carbon in a column reaches the desired gold loading capacity, solution feed to that train is stopped. Loaded carbon is removed from the column to woven polypropylene bulk bags supported on drainage frames. Carbon in downstream columns is advanced counter-current to solution flow, and new barren carbon is added to the final column. A carbon safety screen at the end of each train catches carbon fines entrained in overflow solution.
Loaded carbon bags will be temporarily stored at the mine site and transported to an offsite refinery for final metal recovery. Barren solution is discharged to the barren pond and re-used in heap leaching, with make-up cyanide added as 15% NaCN solution.
Reagents and fuel
Cyanide is delivered as solids in 1 t bulk bags and prepared as 15% NaCN solution using a two-tonne solution preparation system. Solution storage tanks provide at least four to five days of normal operating requirements, with a minimum of two weeks storage for bulk bags.
Activated carbon storage incorporates a minimum of seven weeks storage at normal production rates to cover material in transit and being processed off site.
Antiscalant is added to both barren and pregnant solutions to control scale build-up, provided in 1 m³ tote bins with metering pumps.
Above ground diesel storage tanks provide a minimum total capacity of one week of supply for power generation, with an additional tank for plant mobile equipment.
Metallurgical laboratory
A basic laboratory is included as part of this preliminary economic assessment, focused on analysis of daily production samples from the mine (blastholes) and gold recovery (solutions) operations. Due to proximity to population centers with suitable facilities, further activities such as exploration analysis and metallurgical studies are anticipated to be performed by third parties initially.
Key reported parameters
| Parameter | Unit | Design Value | Basis |
|---|---|---|---|
| Total feed to leach pads | t/a | 7,000,000 | Design |
| Crushing feed | % of feed to leach pad | 30–35 | Design estimate |
| Crushing circuit utilization | % | 65 | Design |
| Leaching and carbon loading utilization | % | 95 | Design |
| Mineralized material loose bulk density | t/m³ | 1.7–1.8 | Design |
| Carbon loading circuit solution feed rate (base case) | m³/h | 800 | Design |
| Carbon loading circuit solution feed rate (expansion) | m³/h | 1,200 | Design allowance |
| Average grade of mineralized material | g/t Au | 0.4 | Design basis |
| Gold recovery | % | 70 | Testwork basis |
| Carbon loading | g/t Au | 6,000 | Design |
| Phase 1 leach pad area | m² | 400,000 | Design |
| Total solution pond capacity | m³ | 180,000 | Design |
| Solution pond pregnant/barren storage | m³ | 100,000 | Design |
| Solution pond event storage | m³ | 80,000 | Design |
Project website: https://mineraalamos.com/our-assets/cerro-de-oro-project/
Technical qualifications
The gold recovery design criteria are based on preliminary test work presented in Section 13 of the report. The current design excludes carbon desorption and gold refining facilities, as gold-loaded carbon will be shipped off-site for final doré production. The pond design is based on site data as currently available and may be modified based on additional modelling of site precipitation information. A hydraulic breaker for the crushing circuit can be considered following more detailed fragmentation studies. It is expected that on-site laboratory capabilities would be expanded contingent on availability of suitable personnel as operations progress.
*Source: Cerro de Oro Project , NI 43-101 Technical Report, Preliminary Economic Assessment and Mineral Resource Estimate for the Cerro de Oro Project, Zacatecas State, Mexico, January 5, 2023, Sections 17 and Table 17-1.*
