24-MMP-A5 Surface Mining Methods and Design · May 2016
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Paper format. National Exams, May 2016 — 09-MMP-A5, Surface Mining Methods and Design. Three hours, closed book; one hand-written, double-sided 8.5×11″ reference sheet and an approved Sharp or Casio calculator are permitted. Question 1 is compulsory (six parts, 40 marks); candidates then choose three of the five optional questions (2–6, 20 marks each) for a 100-mark paper — only the first three optional answers appearing in the answer book are graded. All six parts of Question 1 and all five optional questions are answered here, because this set is a study resource rather than an exam script.
Reference texts. The answers below are keyed to the works normally recommended for this syllabus code:
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.
2.1 — Configuration geometry. (a) Bucket-wheel excavator (BWE) system: in plan, the BWE works a long, straight bench face, its cutter wheel advancing laterally along the face while two parallel conveyor lines run behind it — one carrying ore forward to a mobile bridge conveyor that walks over the already-mined pit floor to the fixed plant conveyor and the concentrator, the other carrying waste back to the spoil area. In section, the BWE straddles the full bench height, its boom-mounted wheel cutting a continuous horizontal slice from the free face down to bench floor, with the machine itself (and, for ore, the light blast pattern ahead of it) sitting either on the ore/underlying rock or on the waste/overburden depending on which material it is cutting. (b) Dragline + re-handle BWE: in plan, the dragline sits on the overburden bench and advances along a wide face, its bucket swinging in an arc from the dig position at the ore/overburden contact to a cast position that drops the waste directly into the already-mined-out void behind it — a single-pass cast, no truck haul. Ore, left standing on the bench beside the dragline, is then re-handled by a separate BWE working at the dragline's own elevation, loading it onto conveyors that advance ahead of the dragline to the concentrator; no blasting is used anywhere in this configuration. (c) Conventional truck/shovel: in plan and section this is the now-familiar bench-by-bench drill-blast-load-haul cycle — a rope or hydraulic shovel loads blasted ore or waste into a haul truck fleet that drives a ramp network to either the crusher (ore) or a waste dump (waste), with no fixed conveyor infrastructure tying the loading tool to a single face.
2.2 — Comparison.
| Criterion | (a) BWE + conveyor | (b) Dragline + re-handle BWE | (c) Truck/shovel |
|---|---|---|---|
| Mining capital & fleet unit cost | Very high — custom-built BWE, long conveyor network, bridge/spreader infrastructure | Very high — large dragline (largest mobile land machines built) plus a second re-handle fleet | Lower per-unit capital; fleet is modular, standard catalogue equipment, and scales incrementally |
| Mining productivity | High for continuous, homogeneous material; poor at handling variability or stoppages (one jam stops the whole conveyor train) | Very high bulk waste-casting rate per machine-hour (direct cast avoids a haul leg entirely) but throughput capped by the re-handle BWE/conveyor | Lower per-machine-hour than a large continuous system, but aggregate fleet throughput scales simply by adding trucks |
| Selectivity of mining | Poor — wheel cuts a fixed-geometry slice regardless of internal ore/waste boundaries | Poor — dragline bucket geometry and cast-throw distance dictate the cut, not the ore contact | Best — shovel dig geometry and truck dispatch can follow an irregular ore contact block by block |
| Grade control | Weak — blending happens only where the conveyor stream is later blended; no block-by-block routing | Weak, same conveyor-blending limitation as BWE, compounded by the re-handle step | Strong — each truckload can be routed to ore, low-grade stockpile, or waste based on short-range block-model grade (Question 1.1) |
| Concentrator throughput & recovery | Stable, continuous feed rate is favourable, but a poorly-selective feed can dilute grade and hurt recovery | Same continuous-feed benefit; the extra re-handle step is a further dilution/contamination opportunity | Best grade control translates directly into a more consistent, less diluted mill feed, generally improving recovery |
2.3 — Why newer operations use conventional truck/shovel. Continuous BWE/conveyor and dragline systems were justified historically by their very low unit operating cost on a homogeneous, thick, shallow, low-strip-ratio deposit — exactly what early oil sands mines were. As deposits have matured, however, three factors have pushed the industry toward truck/shovel: (1) deposit variability — interburden, mudstone rip-up clasts and variable bitumen grade within the resource reward the selectivity a fixed-geometry continuous cutter cannot provide, and every tonne of avoidable dilution processed through the extraction plant is pure cost; (2) flexibility and scalability — a truck/shovel fleet can be resized incrementally, redeployed to a different pit phase, or reconfigured for a new mine plan in months, where a conveyor/BWE system is effectively fixed infrastructure for the life of the pit phase it was built to serve; and (3) capital risk — committing hundreds of millions of dollars to continuous-mining infrastructure ties the operation to a single mine plan for decades, which is a much harder commitment to justify under modern reserve-reporting and financing discipline (Question 5.1–5.3) than a modular truck fleet that can be scaled with commodity price cycles.
