I'd expect at least half of the 77 new locomotives to be standard gauge, particularly since it looks like all of the ex WAGR L class seem to be listed for withdrawal and something will need to do all the jobs they are doing now....
Aurizon mentions 77 new locos, most probably PH37's and Siemens 3800's. I think the heavy hauling will be far more likely to survive. There was an article in the Courier Mail a week or so back that said Gina Rhineharts Alpha coal lines will work "in conjunction with existing infrastructure". Maybe this line will be an extension of the existing 3' 6" rather than a totally new (and long) 4' 8" which would require new unloading facility and associated infrastructure.
M636C