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A OPEN PIT MINING AÇIK OCAK MADENCİLİĞİ

A OPEN PIT MINING AÇIK OCAK MADENCİLİĞİ

A OPEN PIT MINING AÇIK OCAK MADENCİLİĞİ

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limestone and some other industrial minerals,<br />

this formula cannot be applied to evaluate<br />

the economic value of blocks. The reasons is<br />

that, the aim of mining the latter group of<br />

minerals (i.e. iron ore, coal, limestone), is to<br />

achieve a predetermined quality, and the<br />

price obtained for blended ore is constant<br />

and it does not depend on the quality of each<br />

individual block. In fact, there are various<br />

blocks with different qualities and ore-types<br />

which must be blended to produce a<br />

marketable product with regard to<br />

consumer’s targets. Ore-types are assigned<br />

on the basis of ore grade and contaminants.<br />

The solution to the problem of how to<br />

generate an optimal pit which contains an<br />

optimal mix of ores blocks is a combined<br />

operation of pit and blend optimizing. The<br />

aim of combined pit and blend optimizing is<br />

to produce a pit which yields different oretypes<br />

in such quantities that the sum of the<br />

profits of mining and blending operation is<br />

maximized.<br />

Mol and Gillies (1984) take the<br />

advantages of grade-tonnage curve to<br />

determine a cut-off grade in iron ore<br />

deposits, in accordance with the blend<br />

requirements. The main drawback of the<br />

approach is that it does not optimize the pit<br />

design. This technique may also lead to<br />

abandoning of some low grade blocks with<br />

low impurities, which might be included in<br />

the blended product.<br />

Srinivasan and Whittle (1996) developed a<br />

heuristic method to combine pit and blend<br />

optimization. Their method iteratively<br />

changes the price of each ore type until the<br />

quality of ore types mined is equal to the<br />

blending requirements.<br />

Osanloo and Rahmanpour (2012)<br />

developed an approach based on a<br />

combination of Binary integer programming<br />

(BIP) and network flow. In this method,<br />

those blocks that meet the blending<br />

requirements are selected using BIP. Then<br />

applying maximum flow technique, the final<br />

pit limit of the mine considering blending<br />

options is determined. This approach<br />

iteratively uses BIP to select the ore blocks<br />

that meet the blending requirements, which<br />

is quite time consuming. Therefore, there is a<br />

need for some fast algorithms in order to<br />

optimize the blending and pit design. This<br />

will enable the planner to compare any<br />

blending options to select the most suitable<br />

and profitable case.<br />

Section 2, briefly reviews the available<br />

methods for open pit design. Section 3,<br />

provides a general mathematical model for<br />

blend optimization. In section 4, the<br />

combined approach introduced by Osanloo<br />

and Rahmanpour (2012) will be described.<br />

Then a self-adapting differential evolutionary<br />

algorithm is developed for blend<br />

optimization. The proposed algorithm is<br />

applied to determine the final pit limit for<br />

Gol-E-Gohar iron ore mine which is<br />

discussed in section 5. Section 6 gives the<br />

final remarks of the paper.<br />

2 <strong>PIT</strong> OPTIMIZATION<br />

The aim of pit optimizing is to designs a pit<br />

in which (1) pit slope constraints are obeyed,<br />

and (2) total value (profit) of the pit is<br />

maximized. Pit value is the summation of<br />

those block-values that are included in the<br />

final pit. BEVs are normally calculated via<br />

equation 1. After the calculation of BEVs<br />

and developing an economic block model,<br />

the ultimate pit limit of the mine can be<br />

determined. Various techniques are available<br />

to determine the ultimate pit limit. When the<br />

ultimate pit limit is determined it means that<br />

the value of ore blocks (income) can pay the<br />

costs of removing the overlaying waste block<br />

(costs). Inside the pit limit, mining<br />

operations is economic with the highest<br />

profit, and outside the pit limit, open pit<br />

mining is not likely to be profitable.<br />

Optimum pit design methods are divided<br />

into Heuristic and Rigorous methods (Kim,<br />

1979). Heuristics are short cuts to solve the<br />

ultimate pit limits problem and heuristics<br />

such as moving cone technique are not likely<br />

to determine the optimum solution of the<br />

ultimate pit limit problem. On the other<br />

hand, these methods are easy to implement<br />

but it should be noted that they lack the<br />

rigorous mathematical proof. Pana (1965)<br />

introduced the moving (floating) cone<br />

technique. This technique creates a cone for<br />

120

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