The massive dump-trucks and drill rigs are going autonomous, with anywhere between 10% and 100% (depending on the site) of the heavy vehicles are now driverless.
The routes can be easily predefined, they are relatively short and you can add additional beacons / markers that make things much easiser.
I think the problem with trains outside of say closed loop underground trains that you have a lot of tracks in varying conditions, you can have track abstractions you have a multi agent environment with crossing and that at least as far as cargo trains go the engineer does more than just drive the train they handle many more operations.
Mine site are open cast, mine large tonnage and have long mine lives justifying the large initial investment.
Australian mining operations are also very dry, which helps a lot. Rain introduces a lot of variables.
Large scale automation is particular to the Australian mining industry at this point.
South African deep level gold mines have been working on this for many years with little success, and I think they have mostly given up.
Train drivers do more than just drive a train. They also have to deal with dropping off and picking up cars from the consist. They also need to monitor track conditions that aren't necessarily easy to pick up from track circuits, such as deep snow (https://www.youtube.com/watch?v=Yja2VmZOfdA shows you how some trains deal with snow).
In general, the costs of upgrading track to be able to support autonomous driving aren't worth the savings you get from eliminating driver. The main counterexception to this is Western Australia, where everything of value is 1,000 miles away from where anybody lives (and is transported by trains to the coasts for export), and so railroads face tremendous costs actually getting their drivers to their trains. Unsurprisingly, the mining companies in Australia who own/run their own railroads have invested heavily in autonomous trains.