Reserve Estimation

Indian mines report reserves under UNFC code — G1/G2/G3 categories map to measured/indicated/inferred. Block models in Micromine or Surpac populate grade into 10×10×5 m blocks; kriging variance indicates estimation uncertainty.

Cut-off grade optimisation uses Lane's formula or iterative NPV — B.Tech exams often use simpler break-even: g_c = processing cost / (metal price × recovery). Dilution and mining recovery reduce in-situ grade to delivered mill grade.

Hartman & Mutmansky distinguishes resource (in situ) from reserve (economic, legal to extract).

Relation 1 —

Write this relation with symbols exactly as in Hustrulid Open Pit Mine Planning — Standard reference before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.

Relation 2 —

Write this relation with symbols exactly as in Hustrulid Open Pit Mine Planning — Standard reference before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.

Relation 3 —

Write this relation with symbols exactly as in Hustrulid Open Pit Mine Planning — Standard reference before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.

Tonnage T = volume × bulk density — volume from wireframe or block model sum; density from lab tests zoned by lithology. Metal content = Σ (block tonnes × block grade) for each element.

Cut-off grade: block is ore if grade ≥ g_c where g_c makes net smelter return positive after mining, processing, G&A. Raising g_c increases grade but loses tonnes — optimum maximises NPV not grade.

Kriging (geostatistics) weights nearby drill composites by spatial correlation (variogram model). Search ellipse orientation follows ore continuity direction. Do not krige without declustering biased drill data.

Dilution: waste mixed into ore during mining — add to denominator. Mining recovery: fraction of in-situ ore actually extracted — multiply tonnage. Combined: plant feed grade = in-situ grade × recovery / (1 + dilution) approx.

State assumptions explicitly before using any relation for reserve estimation — steady state, uniform properties, linear elastic material, ideal gas, incompressible flow, etc., as applicable.

Wrong assumptions invalidate the entire solution even when the formula is correct. In Mine Planning viva and GATE descriptive questions, listing valid assumptions often earns separate marks.

1. Read the question and list given data with SI units (common in Mine Planning papers).
2. Draw a neat labelled diagram where applicable — examiners in Indian universities award diagram marks even when arithmetic slips.
3. Identify which relation from this topic applies to reserve estimation.
4. Use equation 1: .
5. Use equation 2: .
6. Substitute values, compute, and verify units and sign (direction).
7. State conclusion in one line — e.g. safe/unsafe, stable/unstable, feasible/infeasible.

Reserve Estimation appears in life-of-mine studies. In Indian mining curricula this topic is tested because it connects theory to reserves, layout, and scheduling.

GATE and semester exams often combine reserve estimation with earlier units — revise prerequisites before attempting mixed problems.

Industry interview panels sometimes ask: "Where did you use reserve estimation?" — answer with a lab, mini-project, or plant visit example if possible.

• Reporting resource tonnage as reserve without economic cut-off
• Using dry density on wet in-situ volume
• Kriging block grade without compositing to equal support
• Ignoring dilution and recovery in mineable reserve statement

Before attempting reserve estimation problems, confirm you can:

1. Measured, indicated, inferred resource classes
2. Krigeing geostatistical grade estimation
3. Dilution and recovery factors in reserve

Revise the solved examples in Hustrulid Open Pit Mine Planning — Standard reference and one previous-year GATE or university paper for this unit.