My logic is based on the fact that I don't think we have enough info to make a construction decision yet. Backing in for 20% allows Teck to explore improvement opportunities without committing to construction. Essentially it delays their decision and allows them to improve the project.

But they'd then have to pay 4 times more to get the rest... Well, more assuming everything they did (upgraded metallurigical tests, updated RE etc.) didn't make buying SC vastly more expensive. They're also leaving CUU, a non-miner in charge by doing so. A partner that, if they don't sell for what Teck wants at a later time will then sell to someone else and be in this project for much less than they wanted and with a partner that would be setting terms instead of them.