The QB2 2016/2017 FS had an after-tax NPV (8%) of 1,253M.

In April 2018, Teck purchased 13.5% for 162.5M + 100M in options depending on copper prices when the mine enters production.  Higher copper prices would obviously increase the NAV, so it's fair play.

13.5% x 1,253M is 169M and Teck paid 162.5M.  That's pretty close to paying 100% post-tax NPV (8%).

We all know what Teck did after, but they still paid a fair price based on the information that was available at the time of the transaction.

In in the opinion that the equivalent should bring Copper Fox somewhere close to 800M for their 25%.

MoneyK