MNE - Mill Allotment Update, page-53

As a comparison, a gravel quarry sells road base gravel for around $20 per tonne to make a profit.
This after blasting, excavating, trucking, crushing and screening costs. So $399 per tonne for unprocessed ore is significantly better than $20 for a tonne of processed gravel.

The big difference is the volumes produced. A typical gravel quarry produces 200,000 plus tonnes a year.

The other difference is the higher cost of under ground mining.

Still, a price of over $300 per tonne is impressive if the production costs are less than $50 per tonne.