Question 6 of 27

Question 1.6 (5 marks)

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.

1.6.1 — block model development. The deposit volume is discretized into a regular 3-D grid of blocks (typically 10–30 m cubes, sized to bench height and drill spacing); each block’s grade is estimated from surrounding drill-hole assay data by an interpolation/estimation method (inverse-distance weighting, ordinary kriging, or indicator methods for skewed distributions), honouring geological domain boundaries (rock type, alteration, structure) so grade is only interpolated within its own geological domain. The single most important piece of information attached to every block is its net (economic) block value — the dollar value of that block if mined and processed, netting revenue (grade × recovery × metal price) against mining, processing, and G&A cost, converted from raw grade via the geological/grade model plus a cut-off economic model. Every downstream pit-optimization step (moving cone, Lerchs–Grossmann, floating cone) operates on this economic block value, not on grade directly.

1.6.2 — the two inclusion rules. (1) Slope/precedence rule — a block can only be included if every block required to expose it (the overlying cone or column of blocks, set by the stable pit-slope angle for that sector) is also included; a positive-value block cannot stand alone if it cannot be physically reached within slope constraints. (2) Positive cumulative value rule — a block (or precedence-linked group) is included only if its OWN value plus the net value of everything that must be removed to expose it is ≥ 0; a block that is individually positive but whose required overburden/waste cone makes the group net negative is excluded, exactly the moving-cone test formalised in Question 1.8.