In reality most of us know as much as you do.
What I would recommend as a starting point is to look at some of the NT/SA/Qld transport plans and see what they say about traffic volumes and types. Then look at RDA and council commissioned reports to see what might be possible in the area. A few good google searches should help you out. Also have a look at the Queensland rail information packs on the Mt Isa line, and the work being done by the Mt Isa-Tennant Creek economic development zone. Some mining companies might have some info. Finally press and newspaper articles might be useful to understand. There is some of this discussed here on RP (eg the phosphate mining near Tennant Creek that looks to have not eventuated) but I'm sure you might find some things that might not be discussed.
Have a look around and see what you find.