24-MMP-A5 Surface Mining Methods and Design · December 2013
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
3.1 – Sketch plan/section of each method.
3.2 – Comparison.
| Criterion | (a) Dragline + BWE re-handle | (b) BWE direct-load conveyors | (c) Truck/shovel |
|---|---|---|---|
| 3.2.1 Productivity | High, continuous, but capped by dragline cycle and re-handle step | Highest continuous throughput – no re-handle, no discrete cycle | Lower – limited by discrete truck cycle time, queuing and haul distance |
| 3.2.2 Unit cost | Low $/t at design capacity (no diesel haul), high capital | Lowest $/t at design capacity – single continuous system | Highest $/t at high volume (fuel, tires, labour scale with tonnage and distance); lowest capital and $/t at low volume |
| 3.2.3 Selectivity | Poor – dragline works a fixed wide-face cut, cannot dodge small pods | Poor – BWE cuts a continuous face at a fixed geometry | Excellent – shovel/truck can follow an irregular contact tonne by tonne |
| 3.2.4 Grade control | Coarse – blending only at the re-handle/conveyor transfer point | Coarse – blending only where conveyors merge | Fine – each truckload can be graded/routed independently |
| 3.2.5 Concentrator throughput/recovery | Very steady, continuous feed – good for process control and recovery | Very steady, continuous feed – best process stability | More variable feed (batch arrivals) – needs surge/blending capacity ahead of the plant to hold recovery steady |
3.3 – Why newer conventional oil-sand (and similar) deposits use truck/shovel. Continuous systems (dragline/BWE-conveyor) are only economic where the deposit is large, uniform, shallow and geometrically regular enough to justify their very high capital cost and low flexibility over a long mine life; modern oil-sand (and comparable) deposits increasingly present variable overburden thickness, more complex/irregular ore geometry, seasonal ground-condition changes (freeze/thaw, muskeg), and a need to blend variable-grade material for consistent bitumen content – conditions that favour truck/shovel’s selectivity and flexibility. Truck/shovel fleets can also be scaled incrementally (add one truck at a time) to match a phased development plan, whereas a continuous system is a large discrete capital commitment sized for the whole deposit up front; the combination of blending needs, geometric variability and staged-capital preference is why newer conventional operations default to truck/shovel even though a continuous system is cheaper per tonne at full, uniform-face production.
