Who to approach depends on what his trade skills are.
It can be hard to get in with mining houses initially, so it might be better to start off approaching mining contractors, eg. Downer EDI Mining, Byrnecut, Barminco, Thiess, Macmahon. (Google "mining contractor" and a bunch will pop up).
If he's a mobile equipment boily or fitter, he could also think about mining equipment suppliers/contract maintainers, such as Komatsu and CAT.
If plant and mill maintenance and shut-downs is more up his alley, there are also specialist contractors who look after that. (Sorry - have never dealt with that side of things, so don't know any company names).
There are also some labour hire groups out there, such as Mining Employment Services, who act as a "pimp" to match suitable candidates up to contract or permanent jobs.
Finally, do a job search on Seek - there seem to be bazillions of mining job ads on there.