Production Scheduling

Indian iron ore and coal mines blend multiple seams or benches to meet export Fe% or ash% specs. Scheduler balances grade variance against stripping delay — high NPV schedules often have lower average grade early years.

Mine life estimate divides recoverable reserve by planned annual rate — adjust for ramp-up and recovery factor. Utilisation losses from monsoon, maintenance, and holidays appear in Indian mine budgeting (typically 75–85% utilisation).

Hartman & Mutmansky introduces Milawa scheduler concept — precedence + capacity constraints solved heuristically or with MIP.

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.

NPV = Σ CF_t/(1+r)^t — cash flows include revenue, mining cost, stripping cost, capital. Discount rate reflects cost of capital and country risk. Scheduling changes timing of CF_t — same reserves, different NPV from sequence.

Pushback: expand pit in stages — each pushback adds waste strip then ore exposure. Delaying pushback 2 preserves cash early but may lose option value if prices rise. Cut-off grade strategy: increase g_c when price low (mine high grade only).

Blend plan: linear programming or heuristic to mix benches/seams to target grade band while minimising deviation penalty. Constraints: stockpile capacity, crusher rate, contract minimums.

Utilisation = operating hours / calendar hours — distinguish from availability (up-time when needed) and mechanical availability (no breakdown). Indian monsoon season planning reduces effective utilisation in eastern coalfields.

State assumptions explicitly before using any relation for production scheduling — 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 production scheduling.
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.

Production Scheduling 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 production scheduling with earlier units — revise prerequisites before attempting mixed problems.

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

• Maximising annual ore without considering strip delay cash flow
• Mine life from total resource not recoverable reserve
• Constant cut-off over life when price varies
• Utilisation > 100% or confusing with production efficiency

Before attempting production scheduling problems, confirm you can:

1. Pushback schedule in open pit
2. Cut-off grade may vary over mine life
3. Blend plan meets mill grade targets

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