$0.30 party, page-26

A simplistic illustration:

Imagine a concrete slab with $100 of $1 coins scattered through it like a choc chip muffin vs a concrete slab of the same volume with 5x$20 notes within it. For each chunk you remove from the first slab, you can sell as it has a couple of dollars contained within, whilst in the second example, you’ve got a lot more waste which is of no value that you must get through before striking your high grade. Now imagine that the coins basically start from the surface of the concrete vs the notes which are held deeper within the slab, and you can see why a low grade deposit starting from the surface can not just be economic, but preferable.