Question

The grade-tonnage distribution for the ultimate pit of a mine is given below. 

\[ \begin{array}{|c|c|} \hline \text{Cu grade (\%)} & \text{Cumulative million tonnes below the grade} \\ \hline 0.1 & 0 \\ 0.4 & 15.0 \\ 0.5 & 17.0 \\ 0.6 & 18.0 \\ 0.7 & 19.0 \\ 0.9 \text{ and above} & 23.0 \\ \hline \end{array} \] 

The mill cut-off grade is 0.5% Cu. The annual mining capacity (ore + waste) is 4.5 million tonne and milling capacity is 1.0 million tonne. Excavation is planned in such a way that either the mine or the mill runs at full capacity throughout. The planned life of the mine, in years, is \(\underline{\hspace{1cm}}\). (round off to one decimal place)

Hint:

To calculate the life of the mine, divide the total ore mined above the cut-off grade by the milling capacity per year.

Answer 1

Correct Answer: 6

The total ore mined for Cu grade above 0.5% is: \[ \text{Tonnage above 0.5% Cu} = 23.0 - 17.0 = 6.0 \, \text{million tonnes} \] Since the milling capacity is 1.0 million tonnes per year, the total life of the mine is: \[ \text{Life of the mine} = \frac{\text{Total ore mined}}{\text{Milling capacity}} = \frac{6.0}{1.0} = 6.0 \, \text{years} \] Thus, the planned life of the mine is \( \boxed{6.0} \, \text{years} \).