By Jean-Michel Rendu
An advent to Cut-off Grade Estimation examines probably the most vital calculations within the mining undefined. Cut-off grades are necessary to settling on the industrial feasibility and mine lifetime of a undertaking. elevated cut-off grades can lessen political dangers by way of making sure greater monetary returns over a shorter time period. Conversely, reduce cut-off grades could elevate undertaking existence with longer fiscal advantages to shareowners, staff, and native groups. Cut-off grades additionally effect pronounced reserves, that are heavily monitored by means of inventory exchanges and regulatory companies.
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Additional info for An Introduction to Cut-off Grade Estimation
Electronic edition published 2009. 32 Tonnage and Metal Content Above Cut-off 200 Cut-off Grade, %Cu FIGURE 5-1 year Graphical representation of grade–tonnage relationship for coming pounds of copper. 24 = $108 million Because of an unexpected increase in copper price, the mining company is investigating whether short-term changes could be made to mill feed and throughput, which would result in increased utility. 00 that was used for planning. The mine plan cannot be changed for at least one year and only changes in operating conditions can be made to the processing plant.
The utility of wasting material of grade x can be calculated as follows: U waste ( x ) = – ( M w + P w + O w ) To calculate the utility of stockpiling, one must take into consideration stockpiling costs and the cost of retrieving material from stockpile and processing it at a later date. In addition, metallurgical recoveries of stockpiled © 2008 by the Society for Mining, Metallurgy, and Exploration. All rights reserved. Electronic edition published 2009. MINIMUM CUT-OFF GRADES 29 material may differ from those of freshly mined material, and the price of the product sold may be different from that prevailing when the decision to stockpile is made: U stp ( x ) = – ( M stp + P stp + O stp ) – NPV (future costs of stockpile maintenance) – NPV (future rehandling and processing costs) + NPV (future revenues from sales) Mstp = current mining costs per metric ton delivered to the low-grade stockpile Pstp = current costs of stockpiling material that will be processed later, including the cost per metric ton of extending the stockpile area if required Ostp = current overhead costs associated with mining and stockpiling NPV (future costs of stockpile maintenance) = net present value of yearly costs that will be incurred to maintain stockpiled material in an environmentally safe fashion until it is processed NPV (future rehandling and processing costs) = net present value of the one-time costs that will be incurred when the material is retrieved from the stockpile and processed NPV (future revenues from sales) = net present value of revenues expected from sales when processed material is sold.
For such material, blasting and haulage costs must be incurred whether the material is treated as ore or waste. Only incremental costs need be considered. The minimum cut-off grade is estimated using the formula presented previously for material in the middle of an open pit mine: xc = [ ( Mo – Mw ) + ( Po – Pw ) + ( Oo – Ow ) ] ⁄ [ r ⋅ ( V – R ) ] If ore and waste mining costs are the same (Mo = Mw) and waste processing and overhead costs are negligible (Pw = 0 and Ow = 0), this formula can be written xc = [ Po + Oo ] ⁄ [ r ⋅ ( V – R ) ] The mill cut-off grade is recognized here.