GATE 2021 MN – Question 63
Ultimate-pit cumulative million tonnes below Cu grades 0.1%, 0.4%, 0.5%, 0.6%, 0.7%, 0.9%+ are 0, 15, 17, 18, 19, 23. Mill cutoff is 0.5% Cu. Mining capacity(ore+waste) is 4.5 Mt/year and milling capacity 1 Mt/year; at least one facility runs at full capacity. Find planned mine life in years, to one decimal.
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Correct answer: 6.0 to 6.0
Explanation
Total material is 23 Mt. Material below cutoff is 17 Mt, leaving 6 Mt to mill. Mining all material needs 23/4.5≈5.11 years, while milling ore needs 6/1=6 years. Both requirements must be met, so the controlling duration is 6.0 years; the mill remains at full capacity in that plan.