there are likely a number of factors that could possibly explain the difference.  Here are a few imo

On the CF side of the reported C1:

- LT commodity prices used were lower? 
- CF has to be very careful and conservative with what they publish about Teck's project.
- The referenced $1 C1 figure comes from our PEA (?, not sure).  A PEA would use a rudimentary and conservative approach to estimating economics
- The $1 figure is in Cdn $?  If so then its equal to $0.72 USD

On the Teck side of the reported C1:

- LT commodity prices used were higher?
- The $0.50-0.60 figure comes from an analysis that has been (marginaly) oprtimized for ten years?
- The figure is in USD so $0.60 USD for example equals $0.82 Cdn (just an 18 cent difference w/$1 Cdn)
- Teck's fine print indicates that all resources, i.e. M,I and also Inferred are used in their economic analyses which BTW is not 43-101 compliant reporting and CF would never do that

I can only imagine how amazing the C1 cash cost really is with a legitimate optimization.

JMHO