24-MMP-A2 Underground Mining Methods and Design · December 2016
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Mining and Mineral Processing Engineering, 09-MMP-A2 Underground Mining Methods and Design, 2016-Dec. 3 hours duration, closed book; only a Casio or Sharp approved calculator permitted. Question 1 is compulsory (40 marks, all six parts 1.1–1.6); a candidate then selects TWO of Questions 2–4 (Section B) and ONE of Questions 5–6 (Section C), each worth 20 marks.
Reference texts: Hartman & Mutmansky (eds.), SME Mining Engineering Handbook, 3rd ed. (underground mining methods, backfill systems, mine hoisting design, mine ventilation, mine cost estimation — the primary reference throughout this paper); Hustrulid & Bullock, Underground Mining Methods: Engineering Fundamentals and International Case Studies (room-and-pillar, VCR, cut-and-fill, longhole, shrinkage and sub-level caving practice); ASHRAE, ASHRAE Handbook — Fundamentals (psychrometric relations, humidity ratio and enthalpy of moist air); BC Ministry of Energy, Mines and Low Carbon Innovation, Health, Safety and Reclamation Code for Mines in British Columbia (Canadian regulatory context for hoisting-rope safety factors); Camm, T.W. (1989), Simplified Cost Models for Prefeasibility Mineral Evaluations, U.S. Bureau of Mines IC 9298 (Question 4 parametric cost models); O'Hara, T.A. (1980), "Quick Guides to the Evaluation of Orebodies," CIM Bulletin, February 1980 (Question 1.4.3).
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.
Cut & fill is a selective, horizontal-slice method in which ore is mined in successive lifts, each lift backfilled (rock, hydraulic or paste fill) before the next is taken, so the exposed working face and back are always close to the fill surface; longhole (sub-level open stoping) mines a large, unsupported open stope in one campaign by drilling and blasting long, near-vertical or steeply inclined blastholes from sub-level drill drifts, drawing broken ore from the bottom without backfilling until the stope is complete. The two methods sit at opposite ends of the selectivity/bulk-mining spectrum, and the comparison below follows the twelve criteria the question specifies.
| Criterion | Cut & fill | Longhole (sub-level open stoping) |
|---|---|---|
| Geology, orebody shape/size/orientation | Irregular, narrow to moderate width, variable dip; tolerates erratic grade/geometry since mining is selective lift-by-lift | Regular, tabular to massive, moderate-to-wide, steeply dipping; needs a fairly consistent geometry to keep long blastholes on-ore |
| Host and ore rock properties | Works in weaker, less competent ground — fill provides continuous wall/back support | Requires strong, self-supporting host and ore rock, since the open stope stands unsupported through the full blast-and-draw cycle |
| Development size/amount/cost/time to start | Access via ramp/raise plus a sill drift per lift; less up-front development but development recurs every lift, spreading cost over the mine life | Heavier up-front development: top and bottom sub-level drifts, undercut, slot raise; higher initial capital/time but development is largely front-loaded once per stope |
| Ground support | Rock bolts/mesh/shotcrete on exposed back and ribs of each lift; the previous lift's fill is itself the "floor support" | Minimal support inside the stope (none once blasting starts); support concentrated in the sub-level drifts and any crown/sill pillars |
| Mining sequence and mill feed rate | Sequential lift-by-lift (mine–fill–mine); steady but comparatively low, batch-like mill feed rate limited by the fill-curing cycle | Continuous drill–blast–draw within one large stope; high, sustained mill feed rate once blasting begins |
| Personnel (number/skills) | More personnel per tonne; skilled miners for selective drilling/blasting/bolting and fill placement each lift | Fewer personnel per tonne; specialised long-hole drillers and blast crews, less continuous face labour |
| Mechanized equipment | Smaller-scale jumbo drills, LHDs, shotcrete/bolting rigs, fill-delivery pipework — equipment sized to a narrow working lift | Large-diameter long-hole drill rigs, bulk LHDs/trucks at drawpoints, minimal fill equipment |
| Cost of mining | High unit cost (USD/t) — selectivity, support and fill placement all add cost per tonne | Low unit cost (USD/t) — bulk, largely unsupported extraction spreads cost over a large blasted tonnage |
| Mine life | Can extend mine life on marginal/irregular deposits that only a selective method can mine economically | Shorter, higher-intensity extraction of a given reserve given the much higher mining rate |
| Mining rate | Low to moderate (limited by lift cycle and fill curing time) | High (limited mainly by drilling/blasting/mucking capacity, not a fill cycle) |
| Dilution and recovery | Low dilution (selective mining follows ore contacts closely); high recovery, including narrow/irregular ore | Higher dilution (blast overbreak, wall slough over the unsupported stope life); recovery high in the primary stope but constrained by any pillars left |
| Pillar recovery method/cost | Rib/sill pillars are comparatively small and can often be mined as a later lift with fill already in place on one side, at moderate incremental cost | Crown/sill pillars between stopes are large and structurally critical; recovery (if attempted at all) needs a dedicated, higher-risk secondary mining campaign, often left unmined |
| Post-mining stabilization | Mined-out volume is already filled as part of normal cycle — minimal separate stabilization needed | Large open voids typically require deliberate backfilling or controlled caving/closure after extraction to manage long-term ground stability |
