To put it another way:

If Teck were to pay $300M at any stage past early works (which includes things like the road) we would have to pay our 25% except for the first $60M.

So $300M - $60M = $240M X 25% = $60M for our share

The first $40M comes from the cancellation of the payments due upon production decision and completion. That leaves us with the $20M owed.

$300M is not sufficient to build the mine though—we're going to need lots more money.