This is a pretty good description of what many here are thinking--at least amongst the private exchanges I have had with a dozen or so people here at AG (from explorationguy at SI):

It was probably filed on the the last day to accommodate Teck in the same way Elmer won't confirm the 120 day clock started on Feb 4 via a proper notice. I still expect we will hear from Teck on or before June 4 for the following reasons. Some have mentioned that a delay is OK because Teck must deal with a third party, or Teck's BOD needs more time, or a buyout is being prepared. I've suggested myself that all of those outcomes may happen but none of them are part of the agreement and therefore cannot be allowed to interfere with that agreement.

If June 4 passes with nothing happening then we clearly have not served notice and therefore Teck has no time limit to make a decision. It also means CUU is no longer acting in the best interests of it's shareholders because we didn't abide by the terms of the contract. In that situation the possibility of Teck walking will increase and the share will start bleeding downward in my opinion because the market will wonder why Teck can't decide they want this after 4 months or convince a third party to participate.

There seems to be a number of people who believe the CUU share value will be worth at least $ 4/ share with a Teck back-in of 75%( 70% net ownership). I haven't found any data to back that up but that's another discussion(and I'm still looking).So that gives a value of about $ 1.7 billion for CUU's 24% and about $ 5 billion for Teck's 70%.

All Teck has to do is exercise the back-in right and agree to spend $ 340 MM. Teck could also buyout CUU entirely. So what if Teck walks? Some have said no problem we'll have 94% ownership and we'll sell to the highest bidder. Really? Teck turns down a deal, in their backyard, where they get a $ 5 billion piece for no cash up front or shares and an opportunity to buyout another 24 % for $ 1.7 billion and someone thinks we can find another buyer to pay $ 6.7 billion for the 94% and then pay $ 3.2 billion to build a mine? I don't think so and that is why I believe Teck walking would be catastrophic to our share price and may be behind the strategy CUU has adopted in their dealings with Teck. Well, there are 10 more sleeps before June 4th so we'll have plenty of opportunities to revisit this discussion.