Just a reminder:

20% back-in = Teck must spend $85M

40% back-in = Teck must spend $256M

75% back-in = Teck must spend $341M

The 40% and 75% back-in amount can really only be achieved if a mine is built. That's a multibillion dollar commitment from Teck. (Remember, Teck only obtains the back in amount after the full spending is reached. If they back in for 75% and only spend $300M, then they will not have achieved any back-in interest yet. Correct?)

The 20% back-in allows Teck to optimize the project and obtain an interest without committing huge amounts of money ($85M). There is a risk that the remaining 80% is sold to someone else, but Teck has the advantage of having inside information on things like the environmental assessment, drilling results, feasibility updates, etc. If they like what they see, they can use their inside knowledge to buy out the rest of the project. If they don't like what they see, they can spend their $85M and will at least have obtained an interest in the project that they can sell to someone else down the road. Seems pretty logical to me.