PEC EPE Mining common mistakes
PEC EPE Mining · Understand the traps and how to avoid them.
Answering calculation questions on reserves, tonnage, or grade with a memorised formula before checking which variables the question actually supplies (e.g., using a simple volume × density tonnage formula when the stem gives in-situ density, moisture content, and a dilution factor).
Candidates drill standard formulas during revision and pattern-match on keywords like 'tonnage' or 'grade', then substitute numbers without auditing units and given modifiers. Mining problems deliberately embed moisture, swell factor, or dilution to test whether the formula is being selected, not recalled.
What to do instead
Before computing, write a one-line inventory of every given quantity with its unit and a one-line list of what is asked. Explicitly decide whether each modifier (moisture, dilution, recovery, swell) belongs in the calculation or is a distractor, and state the chosen formula in words before substituting numbers.
Treating rock-mass classification schemes (RMR, Q, GSI, RQD) as interchangeable and quoting a single number without stating the scheme, its version, or the rating inputs used.
All these indices produce a dimensionless score, so a value like 'RMR 55' looks self-explanatory. Candidates memorise thresholds for support selection but forget that RMR and Q are not convertible without an explicit correlation, and that RQD alone is not a classification.
What to do instead
Always name the scheme and version alongside the value, list the input parameters used, and when a question asks for a conversion, use only the correlation stated in the stem. Practise writing answers as 'RMR89 = 55 (UCS rating x, RQD y, spacing z, ...)' so the reasoning is visible.
Choosing a stoping or mining method by name association (e.g., 'narrow vein = shrinkage stoping') without testing the method against the stated ground conditions, dip, thickness, and required productivity.
Method-selection questions read like vocabulary tests, and candidates answer from a memorised one-to-one mapping. Real selection depends on a matrix of geometry, geotechnical, and economic factors, and the stem usually includes one factor that rules out the textbook default.
What to do instead
For every method-selection question, tabulate the candidate methods against the four or five controlling factors named in the stem, and eliminate explicitly. If a factor is not given, say so rather than assuming it. Learn each method's limiting conditions (minimum dip, maximum hangingwall span, ore hardness, subsidence tolerance) as constraints, not labels.
Confusing the sequence and purpose of drilling, blasting, loading, and hauling calculations, such as applying powder factor to total rock moved instead of the blasted volume, or mixing bucket payload with truck payload when computing cycle match.
These unit operations share vocabulary (tonnes, cubic metres, cycles per hour) and candidates carry a number from one sub-calculation into the next without re-checking what it represents. The exam tests the boundary between the steps, not each step in isolation.
What to do instead
Annotate every intermediate result with its physical meaning and unit (e.g., 'bank cubic metres broken per hole', 'payload tonnes per truck cycle'). When matching equipment, compute the loader and truck productivities separately in the same unit (tonnes per operating hour) before comparing, and check that the number of passes per truck is a whole number.
Ignoring the difference between bank, loose, and compacted volumes, and between in-situ, run-of-mine, and saleable tonnes, when reporting a final answer.
Swell and moisture factors are often given as percentages in a separate sentence, and candidates apply them in the wrong direction (dividing where they should multiply) or skip them because the arithmetic already 'works out'.
What to do instead
Draw a small flow diagram from in-situ to broken to delivered material, writing the factor applied at each arrow and its direction. Sanity-check: broken volume must exceed in-situ volume for a swell factor above one, and saleable tonnes must not exceed mined tonnes minus losses.
Answering ventilation and mine-environment questions with a single airflow figure while omitting the basis (per person, per diesel kW, per unit of explosive, or to dilute a specified gas) and the leakage or recirculation allowance.
Regulatory and design airflow requirements are quoted as simple numbers in study notes, so candidates reproduce the number without the multiplying basis. Questions frequently ask for the controlling requirement among several, which requires computing each and taking the maximum.
What to do instead
Compute each airflow requirement separately and label it, then select the largest as the design value, adding any leakage allowance stated in the stem. Memorise the bases (airflow per person, per kW of diesel equipment, per kilogram of explosive) as multipliers rather than as final figures.
Misreading ground-control and support questions by specifying support type alone (e.g., 'rock bolts') without spacing, length, pattern, or the failure mechanism being addressed.
Candidates equate naming a support element with designing support. Support questions usually hinge on whether the mechanism is blocky, bedded, or squeezing, and the answer must match the mechanism as well as the geometry.
What to do instead
Structure support answers as mechanism, then element, then geometry (length relative to the unstable zone, spacing, pattern), then verification. Where a classification scheme is given, derive the support recommendation from that scheme's chart or table rather than from general experience.
Handling economic and feasibility questions by comparing undiscounted cash flows or ignoring the stated discount rate, royalty, recovery, or smelter terms.
Cut-off grade and net present value problems look like simple arithmetic, and candidates compute a total revenue or total cost instead of a margin per tonne or a discounted series. The stem often supplies a discount rate that must be applied year by year.
What to do instead
Write the cut-off grade as (operating cost per tonne) / (metal price × recovery × payable factor) with units carried through, and for NPV build a year-by-year table applying the discount factor explicitly. Check whether the question asks for a break-even, a maximum, or a constrained optimum before choosing the formula.
Treating health, safety, and statutory questions as general good practice and selecting the 'safest-sounding' option rather than the specific control required by the hierarchy of controls or by the stated regulation.
Options are written so that several are defensible in practice. The exam tests whether the candidate can rank controls (elimination, substitution, engineering, administrative, PPE) and identify the required notification, inspection, or record-keeping step.
What to do instead
For each safety scenario, classify the hazard, then rank the proposed controls by the hierarchy and choose the highest-level control that is feasible. Separately memorise the statutory triggers (reportable incidents, statutory inspections, emergency response requirements) as a checklist rather than relying on intuition.
Leaving calculation answers without units, significant figures, or a stated assumption, and presenting a bare number as the response to a multi-part question.
Under time pressure candidates treat the number as the answer and skip the audit trail. Marking schemes for professional practice exams award method and assumption marks, and a bare number cannot earn them even when the arithmetic is right.
What to do instead
Adopt a fixed answer template: given data, assumption, formula, substitution, result with unit and appropriate significant figures, and a one-sentence interpretation. Rehearse it on timed past-style problems so the template survives time pressure.