why the First Nation is upset:if you read page 4 of the July 28th Tl'azt'en document (it is a web-available pdf that an earlier commenter mentioned), you'll see that it specifically mentions protection of Mt. Sidney Williams. I looked that up on google maps and compared it to maps for Deccar on FPX Nickel's website. They loo to be on top of each other.
I didn't look further, for more detailed maps of the MRE outline or proposed mine layout - and those details might not matter to the First Nation anyway.