Mining Engineering common mistakes
Mining Engineering · Understand the traps and how to avoid them.
Computing the circulating load or recovery around a closed grinding circuit by treating the classifier as if all feed reports to the overflow, instead of solving the mass balance with the actual split to underflow.
Candidates memorize the recovery formula but never practise the two-product mass balance, so they plug the circuit feed into the concentrate term without accounting for the recycle stream.
What to do instead
Before any circuit calculation, draw the flowsheet with every stream labelled and write the two balance equations (total mass and component mass) at each node. Solve the recycle stream explicitly, then compute recovery as (concentrate mass × grade)/(feed mass × grade). Work through at least three closed-circuit problems with different split ratios.
Selecting a comminution circuit (crushing vs. SAG vs. HPGR) by rule of thumb or ore hardness alone, ignoring the Bond work index, feed size distribution, and the throughput–product size relationship.
Textbook summaries present circuits as a menu of options, so candidates learn the options but not the selection criteria that tie ore properties to equipment choice.
What to do instead
Build a decision table linking Bond work index, Wi variability, top size, target P80, and capacity to the candidate circuit. For each past-style scenario, justify the choice with computed specific energy (Bond equation) rather than adjectives like 'hard' or 'abrasive'.
Using the wrong density or assuming a single specific gravity when converting between mass and volume in slurry, thickening, or tailings calculations.
Pulp density, solids specific gravity, and percent solids are conflated; candidates substitute one for another because the symbols look similar in textbook formulas.
What to do instead
Write the definitions side by side (percent solids by mass vs. by volume, pulp density = total mass/total volume) and derive the conversion once. In every problem, list knowns with units and check that the density used matches the phase (dry solids, slurry, or water).
Treating reserve and resource classification as interchangeable, or reporting a reserve figure without applying the modifying factors (mining, metallurgical, economic, marketing, legal, environmental, social, governmental).
The reporting codes are read as definitions rather than as a chain of confidence; candidates skip the step where resources become reserves.
What to do instead
Memorize the confidence ladder (inferred → indicated → measured; probable → proved) and the requirement that reserves are the economically mineable part of measured and indicated resources. For any classification question, state which modifying factor changes the category and why.
Computing cut-off grade from grade alone, omitting the recovery, smelter/refining charges, selling price, and mining and processing costs that define the break-even grade.
Cut-off grade appears in a single formula in most notes, and candidates drop the recovery and cost terms because they are not given explicitly in every prompt.
What to do instead
Derive the break-even cut-off grade from first principles (cost per tonne milled divided by value per unit recovered, adjusted for recovery and payables) and then state each assumption. Practise problems where recovery and treatment charges vary, and check whether the answer is a mill cut-off or a mine cut-off.
Sizing or selecting support (rock bolts, mesh, shotcrete, pillars) from a single RMR or Q value without checking the rating's applicability to the ground conditions or converting between classification systems.
Each classification system has its own input parameters and range of validity; candidates apply one score to every problem and skip the empirical support chart that goes with it.
What to do instead
For each system, list its inputs, its intended ground type, and the support chart it feeds. When a question gives joint orientation, stress, or water data, verify the inputs before scoring, and state the support recommendation as a range with the chart reference you used.
Designing a blast pattern by copying powder factor from a similar mine instead of computing charge per hole, burden and spacing from rock and explosive properties, and checking the resulting fragmentation and vibration limits.
Powder factor is easy to quote and hard to justify, so candidates anchor on a number and never verify the geometry or the environmental constraints.
What to do instead
Work the blast design forward: hole diameter → charge mass → burden from the explosive-to-rock ratio → spacing and stemming → powder factor as a check, not an input. Then test the design against peak particle velocity limits for nearby structures.
Mixing units or ignoring the difference between SI and imperial in ventilation, pumping, or equipment-power calculations (e.g., using m³/s in a formula written for cfm, or confusing kW with hp).
Formula sheets are memorized without their unit conventions, and exam prompts mix metric and imperial data deliberately.
What to do instead
Annotate every formula with its required units before the exam and convert all given data to one system at the start of the problem. Carry units through the arithmetic and reject any answer whose units do not match the quantity asked for.
Answering safety and regulatory questions from general good practice rather than the specific hierarchy of controls, statutory notification duties, or the defined exposure limits the question is testing.
Safety content feels intuitive, so candidates write plausible measures instead of the ordered, defined requirements that earn marks.
What to do instead
Learn the hierarchy of controls as a ranked list and the statutory trigger points (reportable incidents, exposure standards, ventilation minimums) as discrete facts. For each scenario, identify the highest-ranked control that applies and name the specific obligation rather than describing general caution.
Presenting calculations without stating assumptions, sources of data, or sensitivity, and giving a single-point answer where the question asks for an evaluation or recommendation.
Candidates treat quantitative questions as arithmetic tests; long-answer marking rewards stated assumptions and a check on how the answer changes with key inputs.
What to do instead
Adopt a fixed answer structure: state assumptions and data sources, show the calculation, give the result with units, then test one or two sensitivities (grade, recovery, cost) and state the recommendation. Practise under time so the structure becomes automatic.