The article mentions that pantographs are unusable due to the number of exposed moving parts and the existence of conductive dust.

Conductive dust is evil. Even your phone will likley stop working if you get conductive dust into it. It's as bad as water, except gravity doesn't keep it pooled on the floor.

I searched a bit and found that "Trolley Assist" apparently refers to a system where large diesel-electric mining trucks use overhead lines for part of their journey. (You can do an image search for "trolley assist" and find examples.)

I guess this is the kind of thing I was looking for.

There is an example of this at the Lumawan Copper Mine in Zambia. It's trucks are powered by overhead cables and electric motors whilst driving up the fixed ramps, It then switches to diesel when moving around away from the ramp. What is really interesting is that this not only reduces fuel use but allows them to move up the ramps much more quickly and improves productivity of the mine.

Unless your vehicles are operating a very consistent route that rarely or never changes, it's likely to be cheaper to go with batteries than to build and maintain a network of overhead wires.

Depends on what you're moving, I suppose. Some materials may have gasses that don't like sparks.

I don't think that would be suitable in an underground mine due to the risk of sparks igniting flammable gases. But for open pit mines it would be OK.

Kind of but not exactly. The electric shovels are actually plugged in with large electrical cables that are routed around the dig site with tractors.

Trucks themselves wouldn't really work too well with overhead methods though.