24-MMP-A5 Surface Mining Methods and Design · December 2016
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Surface Mining Methods and Design (09-MMP-A5) — December 2016 National Exam. Compulsory Question 1 (six sub-questions) plus all five optional Questions 2–6 are answered in full below (candidates select only three of Questions 2–6 in the real exam; all are solved here as a complete study resource).
Reference texts: Hustrulid, Kuchta & Martin, Open Pit Mine Planning and Design (3rd ed.) — pit optimization, Lerchs–Grossmann, floating cone, dragline stripping geometry; SME Mining Engineering Handbook (3rd ed.); BC Health, Safety and Reclamation Code for Mines; Newnan, Eschenbach & Lavelle, Engineering Economic Analysis — sinking funds and future-worth factors.
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.
Grade control on a production blast pattern is normally built up hole-by-hole from the drill cuttings piled around each blast-hole collar as the rotary or DTH rig advances. The manual method has a grade-control technician walk the pattern with a shovel or scoop, taking a grab sample (or a riffled/coned-and-quartered split) from the cuttings cone at each collar once drilling is complete, bagging and tagging it against the hole number for assay. The automatic method fits the rig itself with a cyclone or rotary splitter in the cuttings discharge line that continuously diverts a fixed proportion of the cuttings stream into a sample bag as the hole is drilled, so the sample is a true increment of the whole hole depth rather than a single grab from the finished pile.
A manual grab sample is biased toward the top of the cuttings cone and toward the coarser, heavier fraction that rolls furthest from the collar — fines (which often carry a disproportionate share of sulphide/oxide mineralisation) segregate preferentially at the base of the pile and are under-represented, and wind or water can winnow fines away entirely before sampling. The pile also mixes cuttings from the FULL hole depth into one point, discarding any down-hole grade structure. An automatic in-line splitter removes the segregation bias (it samples the stream as it is generated, not after it has settled) and, if the splitter increment is logged against depth, preserves down-hole grade detail; the main improvement over manual grabbing is therefore to mechanise the split at the point of cuttings discharge and to rotary-split (not scoop) so every particle size has an equal chance of selection, consistent with Pierre Gy's sampling theory.
Grade-control blocks are normally outlined by hand or by a grade-interpolation algorithm as polygons drawn around blast-holes assayed above cut-off; the polygon boundary is placed half-way between an ore hole and the nearest waste hole, so the true ore/waste contact (which is a geological surface, not a straight bisector) is only ever approximated. Where the true contact is curved, dips steeply, or the drill pattern is coarse relative to the deposit's internal grade variability, the polygon systematically over- or under-states the true ore area/volume — concave contacts get an area shortfall, convex ones an excess — and this area error propagates directly and linearly into the tonnage (and hence the mill head-grade forecast) since tonnage = area × bench height × density for a 2-D polygon method.
