Question

Operating costs of an open cast gold mine are Rs. 4000/tonne. The recovery at the mill is 9%. At a gold price of Rs. 4550/g, the cutoff grade of gold calculated on the basis of operating cost is ________ g/tonne. \text{[round off to 2 decimal places]}

Hint:

To calculate the cutoff grade, divide the operating cost per tonne by the product of the gold price per gram and the recovery factor.

Answer 1

Correct Answer: 0.96

The cutoff grade of gold is the amount of gold (in g/tonne) that can be recovered to cover the operating costs of the mine. It is given by the formula: \[ \text{Cutoff grade} = \frac{\text{Operating cost per tonne}}{\text{Gold price per gram} \times \text{Recovery factor}} \] Given:
- Operating cost = Rs. 4000/tonne,
- Gold price = Rs. 4550/g,
- Recovery = 90% = 0.90.
Substitute the values into the formula: \[ \text{Cutoff grade} = \frac{4000}{4550 \times 0.90} = \frac{4000}{4095} \approx 0.976 \, \text{g/tonne}. \] Rounding off to two decimal places: \[ \text{Cutoff grade} = \boxed{0.96} \, \text{g/tonne}. \]