I live in Mackay and work in Moranbah ( I don't know if this is the one you refering to)the rentals in this particular town have been overinflated for years due to the boom, and are still over the top. But the one thing that could influence them is the impact of the new proposed mine ( name eludes me) which will require relocation of the airport etc as it that close to town, plus the fact that BMA has extended their subsidised housing scheme to the entire workforce which could give them some influence over the amount of rent that they are willing to pay. ( at the moment the most a worker has to pay is $60.00).
I've also lived in the Kimberely and NT and can honestly say that I would only invest in a mining town if I was comfortable financially and could handle the lose from an investment which could possibly turn to dust overnight.

Hope this helps