The ATO Project comprises two distinct phases: a completed oxide heap leach operation and a concentrator for fresh and transition ores currently in design.
Report context
This NI 43-101 technical report, dated November 2021, covers the Altan Tsagaan Ovoo (ATO) Phase 2 Expansion Project. Phase 1 of the Project has been operational since 2020 and remains operational as of the Effective Date of this Technical Report. The current mandate of the report is to provide the design for Phase 2 work only, which is described in Section 17.3 of the report.
Processing route
Phase 1 – Heap Leach (Oxide Ore) – Completed
The oxide portion of the ATO Project employs a conventional oxide heap leach flowsheet including crushing, heap leaching, and gold recovery facilities. The existing oxide ore processing facilities include the following unit operations:
Crushing and Ore Handling: The primary crusher consists of a vibrating grizzly screen and jaw crusher in open circuit producing a product P₈₀ of approximately 190 mm. Secondary and tertiary crushers comprise a vibrating screen and cone crushers operating in closed circuit producing a final product P₈₀ of 25 mm. Crushed ore is stacked to a 3,000 t capacity stockpile.
A new three-stage crushing plant was purchased in Q3 2020 which will increase crushing rates above design capacity. The crushing circuit will consist of primary, secondary, and tertiary stages and will feed the Heap Leach Facility at a rate of 1,000 tph with a product size (P₁₀₀) of approximately 10 mm.
Heap Leach Pad: The existing heap leach facility includes ore heap leaching and barren solution delivery and pregnant solution recovery piping systems.
ADR Plant: The ADR process plant is located near and down-gradient from the heap leach facility and operates 365 days per year. The plant processes 5 t of carbon per strip using the ADR process: carbon-in-column (CIC) adsorption of solution gold onto carbon particles; desorption comprising acid wash of carbon to remove inorganic foulants, elution of carbon to produce a gold-rich solution, and thermal regeneration of carbon to remove organic foulants; and recovery and refining including gold electrowinning (sludge production), filtration, drying, mercury retorting, and smelting to produce gold doré.
The crushing plant operates 275 days per year. A single crushing circuit is utilised for preparation of the heap leach feed. The circuit consists of a primary jaw crusher, a secondary crusher and an optional tertiary cone crusher operating in closed circuit with a final product screen. Lime is added to the stockpile feed conveyor from the 200 t lime silo by screw conveyor for pH control.
Phase 2 – Concentrator (Fresh and Transition Ores) – Design in Progress
The Phase 2 Concentrator will consist of collecting the crushed ore beneath the ore storage building, conveying to the concentrator, milling, flotation, and dewatering unit operations to produce saleable concentrates of lead, zinc, and pyrite. Tailings will be disposed of in the new Tailings Storage Facility.
The Phase 2 Concentrator facilities will include the crushed ore feeders located under the ore storage facility and conveyors to the concentrator, grinding and classification; sequential flotation circuits for concentrates of lead, zinc and pyrite; dewatering of concentrates of lead, zinc, and pyrite; and tailings thickening, handling, and disposal.
Key reported parameters
| Description | Unit | Value | Basis |
|---|---|---|---|
| Phase 1 Design Plant Throughput (Dry) | Mtpa | 1.2 | Design |
| Phase 1 ATO Oxide Gold Grade | g/t | 1.13 | Design |
| Phase 1 Gold Recovery (average) | % | 70 | Design |
| Phase 1 Silver Grade (average) | g/t | 9.25 | Design |
| Phase 1 Silver Recovery (average) | % | 40 | Design |
| Phase 1 Crushing Plant Design Throughput | tpd | 5,860 | Design |
| Phase 1 Crushing Plant Operating Days | days/year | 275 | Design |
| Phase 1 Crushing Plant Utilisation | % | 75 | Design |
| Phase 1 Crushing Feed Top Size (F100) | mm | 800 | Design |
| Phase 1 Crushing Feed Product Size (P80) | mm | 25 | Design |
| Phase 1 New Crushing Plant Feed Rate | tph | 1,000 | Design |
| Phase 1 New Crushing Plant Product Size (P100) | mm | 10 | Design |
| Phase 1 ADR Pregnant Solution Nominal Rate | m³/h | 200 | Design |
| Phase 1 ADR Pregnant Solution Design Flowrate | m³/h | 250 | Design |
| Phase 1 Leach Cycle Time | days | 60 | Design |
| Phase 1 Gold Under Irrigation (to Dec 31, 2020) | – | – | Actual |
| – Ore Crushed and Stacked | t | 1,068,462 | Actual |
| – Gold Grade Stacked | g/t | 2.03 | Actual |
| – Gold Stacked | oz | 69,734 | Actual |
| – Gold Produced | oz | 33,154 | Actual |
| – Gold Recovery (reconciled as of Dec 31, 2020) | % | 47.5 | Actual |
| Phase 1 Gold Recovery (reconciled Q1 2021) | % | 40.8 | Actual |
| Phase 1 Expected Ultimate Gold Recovery | % | >70 | Testwork expectation |
Project website: https://steppegold.com/operations/producing-mines/altan-tsagaan-ovoo/
Technical qualifications
The Phase 2 Concentrator design is described as “design in progress” and the report states that the current mandate is to provide the design for Phase 2 work only. The Phase 1 description draws information from the report entitled “Altan Tsagaan Ovoo Project (ATO), 2021 Mineral Resources, Technical Report (Amended NI 43-101)” prepared by GeoRes with an effective date March 30, 2021, issued on March 30, 2021 and amended on June 9, 2021. Ultimate gold recoveries above 70% are stated as expected upon completion of irrigation, representing an expectation rather than demonstrated performance.
Source: Altan Tsagaan Ovoo (ATO) , 2021 Technical Report, NI 43-101 Technical Report, November 2021, Section 17 Recovery Methods.
