Metallurgy, page-12

Yep, to be visible, the grade generally has to be up around the 90-100 g/t mark.

Even then you might end up with a low end of 60% recoverable by gravity even if the main part of the gold is refractory.

It all depends upon the scale of the orebody and hence the operation, but it does open up the option of having a Stage 1 plant operating on a gravity basis, with the tails stored for retreatment in a Stage 2 refractory facility which can be constructed at a later stage.