24-MMP-A2 Underground Mining Methods and Design · May 2013
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, 2013-May. 3 hours duration, closed book; only a Casio or Sharp approved calculator permitted. Question 1 is compulsory (40 marks, all seven parts 1.1–1.7); a candidate then selects FOUR of Questions 2–7 (each worth 15 marks).
Reference texts: Hartman & Mutmansky (eds.), SME Mining Engineering Handbook, 3rd ed. (underground mining methods, mine ventilation, shaft hoisting systems, backfill practice — the primary reference throughout this paper); BC Ministry of Energy, Mines and Low Carbon Innovation, Health, Safety and Reclamation Code for Mines in British Columbia (Canadian regulatory context for mine ventilation and hoisting-plant safety); Wills & Finch, Wills' Mineral Processing Technology, 8th ed. (tailings thickening/filtration and paste preparation for backfill).
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-and-fill and longhole (sublevel open stoping) sit at opposite ends of the selectivity-versus-bulk-tonnage spectrum, and nearly every difference below traces back to one root cause: cut-and-fill fills the void as it goes (so it can follow an irregular, narrow orebody safely), while longhole leaves a large open void until the panel is finished (so it needs a wide, regular, self-supporting orebody to be safe at all).
| Criterion | Cut and fill | Longhole (sublevel open stoping) |
|---|---|---|
| Geology, orebody shape/size/orientation | Narrow to moderate width, irregular boundaries, any dip — the method follows the ore | Wide, regular, steeply dipping tabular or massive orebodies with well-defined, planar contacts |
| Host and ore rock properties | Tolerates weak to moderate host/ore rock (fill provides wall support) | Needs competent, self-supporting host and ore rock able to stand an open span unsupported for the panel's life |
| Development size/amount/time to extraction | Extensive access development per tonne (sill drifts on every lift); slower to first ore | Concentrated top/bottom sill and ring-drill drift development; less development per tonne, faster to first ore once developed |
| Ground support | Heavy, recurring support (bolts/mesh/shotcrete) in every newly exposed lift back | Support concentrated in permanent access/drill drifts only; stope walls are largely unsupported |
| Mining sequence & mill feed rate | Sequential lift-by-lift; feed rate limited by the fill cure/strip cycle — lower, steadier rate | Panel-by-panel drill-blast-muck; feed rate can be high and lumpy (large blasts) but paused for the panel outside blasting/mucking |
| Personnel numbers & skills | More crews, more varied skills (drilling, bolting, fill placement) per tonne produced | Fewer personnel per tonne; specialised longhole drillers and LHD operators |
| Mechanized equipment types/numbers | Small-profile jumbo drills, bolters, fill-placement equipment, small LHDs | Large-diameter production drills (fewer units), large LHDs, minimal fill equipment |
| Cost of mining | High unit cost ($/t) — fill cycle, support, low mechanization scale | Low unit cost ($/t) — bulk mechanized drill/blast/muck cycle |
| Mine life | Can extend mine life by economically extracting narrow/marginal ore bulk methods would leave | Extracts a defined panel quickly; overall mine life set by total reserve and panel sequencing |
| Mining rate | Low (tens to low hundreds of t/day per stope) | High (hundreds to thousands of t/day per stope) |
| Dilution & recovery | Low dilution, high recovery — selective, boundary-following mining | Higher dilution from wall sloughing/blast overbreak into the open void; recovery slightly lower unless well controlled |
| Pillar recovery methods/cost | Pillars are largely avoided by design (fill supports the walls continuously) | Rib/sill pillars often left between panels; recovered later by secondary longhole blasts, at extra cost and higher risk (unsupported void) |
| Post-mining stabilization | Stope is left filled and self-supporting; minimal further stabilization needed | Void is backfilled (if at all) or left open/allowed to relax; larger, unfilled voids may need monitoring or eventual controlled collapse |
In short, cut-and-fill trades cost and rate for selectivity and safety in poor ground, while longhole trades selectivity for the low unit cost and high rate that only a self-supporting, regular orebody can safely deliver.
