The proposed Imperial Gold Project processing route is based on conventional open pit mining with run-of-mine heap leaching and an adsorption-desorption-recovery (ADR) plant.
Report context
This technical report for the Imperial Gold Project (Kore Mining Ltd) is dated June 7, 2021. The processing description presents a conceptual design for a heap leach operation on a 365-day per year, 24-hour per day basis. The report includes both proposed design parameters and, where noted, typical industry ranges or historical testwork observations.
Processing route
Mine-to-Heap Delivery
The Imperial project would employ open pit mining with a conventional heap leach system. The heap leach would utilize run-of-mine (ROM) material delivered directly from the open pit via mine haul trucks. Trucks would pass under a silo that deposits a measured amount of lime on the load for pH control.
Heap Leach Pad and Stacking
The heap leach would consist of a suitable area lined with a containment system, typically a linear low-density polyethylene (LLDPE) liner with an over liner of sized material to facilitate drainage. Drainage pipes within the over liner conduct leach solution to centralized collection ponds.
ROM material would be stacked in lifts on the lined pad by truck dumping. Lifts are targeted at 32 feet (10 meters) in height, with a total heap height of 328 feet (100 meters). Once a suitable area has been stacked (a cell), the cell would be irrigated with dilute cyanide solution. Stacking would continue to advance, and each area would be irrigated for a set period (primary leach cycle). The heap leach is typically designed to have multiple lifts installed, often utilizing 10 or more lifts to reach an ultimate height of 328 feet to 492 feet (100 to 150 meters). The configuration is heavily dependent on material permeability, available terrain, and geotechnical site aspects.
Irrigation would be provided by an emitter-type system designed to deliver 0.005 gallons per minute per square foot (12 liters per hour per square meter). The heap would be placed under primary irrigation for approximately 90 days. No rinse phase is included because of the multiple lift system; rinsing would only occur before closure or once the heap reaches its ultimate height.
Solution Collection
High-concentration gold leach solutions (pregnant leach solution, PLS) flow from the pad to a PLS sump by gravity. Solution is pumped from the sump to the ADR circuit, with excess diverted to the PLS pond. Solution is collected from each heap cell by drain pipes under the heap that transport solution to perimeter piping. Storm water collected during heavy precipitation events can be diverted to a storm water pond and used as fresh make-up water.
Adsorption-Desorption-Recovery (ADR) Plant
During normal operations, PLS solution is pumped to carbon-in-column (CIC) tanks. The CIC circuit consists of two trains of five vessels, each containing six tons of carbon. Carbon is advanced counter-current to the PLS flow as the first tank reaches its loading limit. The target carbon loading is 3,000 grams per tonne of gold.
Loaded carbon from the first tank is pumped across a loaded carbon screen to an acid wash column. Barren solution exiting the last CIC vessel is returned to the heap leach barren solution tank/pond after passing through a carbon safety screen. Fine carbon from screen underflow is stockpiled for off-site recovery.
Loaded carbon is acid washed with dilute nitric acid to remove calcium and adsorbed metals. After acid washing, carbon is passed to an elution column using the modified ZADRA system. A solution of caustic and cyanide is passed through the elution column to remove adsorbed gold. The rich electrolyte is pumped to electrowinning cells where gold and silver are recovered on cathodes. The cathodes are washed, and the recovered sludge is refined in a conventional induction furnace after drying. The circuit is designed to conduct two strip cycles per day. The doré produced is assayed and stored in a vault before off-site refining.
Barren carbon from the elution column is returned to the CIC circuit after passing across a carbon sizing screen. Approximately 50% of the barren carbon reports to an indirect-fired kiln for thermal regeneration.
Crushing Circuit Option
The report notes an option to utilize a crushing circuit to treat higher-grade mineralized material and develop a combination ROM and crushed material heap leach facility. The report states that crushed material showed significantly higher gold extraction during testing. However, the study only presents the lowest capital cost option represented by the ROM heap leach facility.
Heap Leach Pad Design and Phasing
The heap leach facility (HLF) consists of the pad, liner system, leachate collection system, storm pond, stormwater management system, and freshwater supply. To minimize capital expenditure, the pad has been designed in phases, with each phase requiring advanced expansion. The HLF would be constructed in three phases: an initial three-year period and two additional two-year periods.
The leach pad has an approximate final footprint area of 10,763,910 square feet (1,000,000 square meters) and is designed to operate as a fully drained system with no leachate storage within the pad.
Liner System
A double liner system is planned using two layers of synthetic material. The system consists of:
- 1.6-foot-thick (0.5-meter) over liner using ore (1.5-inch minus with less than 10% fines content)
- 80-mil (2-mm) LLDPE geomembrane
- 1-foot-thick (0.3-meter) compacted low permeability soil liner
- Leak Detection and Recovery System (LDRS)
- 60-mil (1.5-mm) LLDPE geomembrane
LLDPE was proposed for the geomembrane because of higher interface friction values, ease of installation in cold climates, good performance under high confining stresses, and higher allowable strain for moderate settlement.
Solution Storage
The Storm Pond is designed to provide storage for excess leachate and runoff from rainfall events, with capacity to contain the 1-in-100-year, 24-hour storm event without discharge and overflow designed for the 1-in-200-year, 24-hour storm event. Total pond storage capacity is 3,335,860 cubic feet (94,500 cubic meters).
The PLS Pond is designed to contain up to 24 hours of solution at a maximum irrigation rate of 15 lph/m², with a capacity of approximately 2,349,880 cubic feet (66,550 cubic meters). The Barren tank is designed to hold 15 minutes of solution at a capacity of 24,717 cubic feet (700 cubic meters).
Pond liner systems use a double liner design with HDPE geomembrane rather than LLDPE, due to higher ultraviolet resistance for exposed surfaces.
Key reported parameters
| Parameter | Value | Unit | Basis |
|---|---|---|---|
| Annual operation | 365 days, 24 hours/day | , | Proposed design |
| Heap lift height | 32 (10) | ft (m) | Proposed design |
| Total heap height | 328 (100) | ft (m) | Proposed design |
| Maximum heap height (typical) | 328–492 (100–150) | ft (m) | Typical industry range |
| Irrigation rate | 0.005 (12) | gpm/ft² (lph/m²) | Proposed design |
| Primary leach cycle | 90 | days | Proposed design |
| CIC vessels per train | 5 | vessels | Proposed design |
| Carbon loading per vessel | 6 | tons | Proposed design |
| Target carbon loading | 3,000 | g/t Au | Proposed design |
| Strip cycles per day | 2 | cycles | Proposed design |
| Final pad footprint | 10,763,910 (1,000,000) | ft² (m²) | Proposed design |
| Minimum pad grade | 1–2 | % | Proposed design |
| Over liner thickness | 1.6 (0.5) | ft (m) | Proposed design |
| Liner: primary geomembrane | 80-mil (2-mm) LLDPE | , | Proposed design |
| Liner: secondary geomembrane | 60-mil (1.5-mm) LLDPE | , | Proposed design |
| Liner: soil liner thickness | 1 (0.3) | ft (m) | Proposed design |
| Lateral pipe spacing | 16 (5) | ft (m) | Proposed design |
| Storm pond capacity | 3,335,860 (94,500) | ft³ (m³) | Proposed design (100-yr storm + 10% safety factor) |
| PLS pond capacity | 2,349,880 (66,550) | ft³ (m³) | Proposed design (24-hour capacity at max irrigation) |
| Barren tank capacity | 24,717 (700) | ft³ (m³) | Proposed design (15-minute capacity) |
| Crushed material gold extraction | Significantly higher (qualitative) | , | Testwork observation |
Project website: https://koremining.com/projects/imperial/overview/
Project website: https://digbee.com/organisation/adr-capital-corp/overview
Technical qualifications
The processing description in this report is conceptual. The heap leach flowsheet is described as conceptual, and Figure 17-1 shows the complete conceptual flowsheet. The crushing circuit is presented only as an option, with the study based on the ROM heap leach facility representing the lowest capital cost option. Design details for pile height, lift numbers, and leach configuration are noted as heavily dependent on permeability, terrain, and geotechnical conditions. The liner material recommendation for ponds (HDPE) differs from the pad (LLDPE) based on exposure conditions. No historical operating data for this specific project is included in the recovery methods section; all parameters are proposed design values unless identified as testwork observations or typical industry ranges.
Source: Imperial Gold Project PEA NI 43-101 Technical Report, Kore Mining Ltd, June 7, 2021, Section 17.0 Recovery Methods.
