Since November, Teck has a plan in place to buy back 40M shares. Chances are they already purchased many shares sub $20 and in the low $20's.
Assuming both parties informally agreed to make a transaction (shares for shares) at fair value, this would mean Teck shares should be around $30 (book value).
So buying back 40M shares at (e.g. $20) and giving back 20-25-30-35M shares for Schaft Creek when they reach $30 would in a way provide them a good discount for Schaft Creek. On top of this, their shareholders might also see it as... "Wow, the sharecount is still lower compared to last year and now we have 100% of Schaft Creek that will generate crazy cash flow in a near future with QB2..."
On top of that, who knows, maybe Teck has been accumulating Copper Fox shares for years? That could provide them an additional 10% discount. Would that show anywhere in their records or nothing would be obvious until they reach a 10% ownership?
MoneyK