MNE - Mill Allotment Update, page-51

Wabbit, I suggest you read the following closely.
Copper is currently selling for $7,125 per tonne. The mill does not buy copper at $399 per tonne and keep the $6725 in profit for itself. The mill buys ore, grading 7.5% copper at $399 per tonne. This ore costs us $34/t to mine, so we make $365/t on this grade ore sold to the mill. Yes the mill buys waste. In fact it is 92.5% waste on 7.5% grade copper ore. If you do the sums then 7.5% of $7,125 is $534 of contained copper. The mill buys for $399 which leaves $135 to cover its processing costs and to make a profit.
i hope this is clear .