Clause 15.1 of the agreement states that no later than 60 days after delivery of a Feasibility Notice, Teck shall prepare a "definitive option join venture agreement" embodying all the terms and conditions of this agreement. The new agreement will replace and supercede the current agreement, and they have to use best efforts to settle in good faith.

(Thanks to Canadagrant for getting me to read further down the page.)

Anyway, if they had to negotiate a brand new agreement within two months of releasing the Feasibility, as this says, that might put them into blackout. It complicates the 120 day period whereby Teck is trying to decide whether to back-in or not.

This clause might also explain why a couple of people have said that either CUU or Teck wanted to re-open the agreement.