This article summarizes the processing design and recovery approach for the Skouries copper/gold project as presented in the July 2011 NI 43-101 technical report, outlining the proposed conventional concentrator flowsheet and design cases.
Report context
The technical report, dated July 2011, details the Skouries Cu/Au Project process plant and infrastructure engineering, which was advanced from the 2007 Cost and Definition study. The design work was conducted by Outotec of Finland for basic engineering and ENOIA of Athens for basic and detailed engineering, under the direction of the project owner. The report covers plant design for open pit and underground ore feed schedules, defined design cases, and the process description.
Processing route
Plant scope and design basis
The process plant engineering scope includes surface ore reception facilities, primary crusher, coarse ore stockpile, grinding, gold gravity circuit, flotation, filtration, and paste thickening. Infrastructure includes administration, workshops, fuel station, welfare facilities, and power, water, and other services.
The project involves open pit mining for the first six years. Feed rate is 8 Mtpa for Years 1 to 5, with the remaining 7.0 Mt of open pit ore processed in Year 6. From Year 7, the plant will be supplied from underground operations at 6.4 Mt, then between 3.1 Mtpa and 4.8 Mtpa for at least the next 20 years. The plant design assumes a nominal throughput for harder underground material of approximately 881 tph. During Years 1–6, softer open pit ore is treated, and the selected mills accommodate the required tonnage.
The process plant design is based on a conventional flowsheet for porphyry copper ores, using proven equipment. Design margins and simple ore metallurgy are cited as providing a robust, low-risk processing solution. The Alumbrera mine in Argentina is referenced as a recent similar copper/gold operation.
Ore feed and products
Initially, for the first year, plant feed will be oxidised ore from the open pit. As near-surface oxidised ore is depleted, there is a transition to sulphide ore for the next five years from the pit. Thereafter, underground sulphide ore is extracted. Primary products are a high-quality gold-copper concentrate and gold doré ingots, estimated to contain approximately 30% of the gold in the ore feed.
Process description
The Skouries concentrator flowsheet comprises gyratory primary crushing, a coarse ore stockpile and reclaim system, single-stream SAG/Ball Mill grinding with cyclone classification, free gold recovery by gravity separation and doré production, flotation, tailings thickening and disposal, and copper/gold concentrate thickening and filtration. The design includes a pebble crushing circuit, coarse and fine free gold recovery circuits, and a doré production facility.
The coarse ore stockpile has a live capacity of 21,000 t, about 33% of total volume, and is covered and conical in form.
Evaluated design cases
Two design cases were evaluated by Outotec:
- Nominal design case: Processing underground sulphide ore.
- Second case: shows higher tailings and concentrate production scenario.
Both cases use the same feed grades and recovery assumptions, with the difference being the SAG pebble circulating load (0–25% for nominal, 50% for the second case).
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Cu in feed (%) | 0.54 | Life of mine average, both design cases |
| Au in feed (g/t) | 0.83 | Life of mine average, both design cases |
| % Cu in rougher concentrate | 5 | Design case |
| % Cu overall recovery | 91.1 | Design case |
| % Cu in final concentrate | 26 | Design case |
| % Au recovered by gravity | 30 | Design case |
| % Au overall recovery | 84.0 | Design case |
| SAG pebble circulating load (%) | 0–25 (nominal); 50 (high case) | Design case |
| Nominal throughput hard underground ore | ~881 tph | Design assumption |
| Open pit feed rate Years 1–5 | 8 Mtpa | Design schedule |
| Underground feed rate from Year 7 | 6.4 Mt, then 3.1–4.8 Mtpa | Design schedule |
| Coarse ore stockpile live capacity | 21,000 t (about 33% of total volume) | Design |
Project website: https://www.eldoradogold.com/investors/news-releases/eldorado-gold-announces-results-skouries-project-feasibility-study-after
Technical qualifications
The report provides several limitations and basis notes:
- The process plant design was advanced from the 2007 Cost and Definition study; the current design incorporates improvements reducing cut and fill requirements and capital cost.
- The plant design exceeds underground mining output, so operations will be based on campaign treatment to operate at optimum efficiency, allowing higher throughput if alternative or additional ore streams are identified.
- The design assumes nominal throughput for harder underground material at approximately 881 tph; softer open pit ore is treated during Years 1–6 with selected mills accommodating required tonnage.
- Design cases assume life of mine average feed grades of 0.54% Cu and 0.83 g/t Au, and both cases apply the same overall copper and gold recovery figures.
- The SAG pebble circulating load differs between design cases (0–25% versus 50%), affecting the tailings and concentrate production scenario.
Source: Skouries Cu/Au Project , NI 43-101 Technical Report, July 2011, Sections 17.1, 17.2, and 17.3 (Recovery Methods, Process Plant Engineering Overview, Process Description, Coarse Ore Stockpile).
