The actual vehicles needed on a placer mining site is pretty much limited to bulldozer, front end loader, backhoe and excavator. Each has a specific purpose (and price point) and I intend to represent each in my game.
Bulldozer. A bulldozer can be used to clear the trees and brush from the land before the real digging can begin. It can also be used to level/grade land/roads so that other equipment (like wheeled equipment) can traverse to various areas of the minesite. It is also used to push loose dirt into larger piles so that other equipment can easily access it. Lastly, it is often used to move/extract LARGE rocks. The tracks give is lots of traction and ability to handle wet terrain and steep inclines. Some bulldozers also have a 'ripper' on the back..used to 'rip' up hard earth (like Klondike permafrost) to make it easier for other equipment to dig and move. My intention for the bulldozer (at the moment) is for the tree clearing and some grading/pushing activity. At the moment, I don't intend to have large rocks/boulders represented in the game...but who knows. I've still got to experiment with actually pushing the dirt that the dozer manipulates in 'front' of the dozer (and maybe off to the side a bit). It's actually next on my list. I have to tweak my texturing code so that when I raise the level of the ground, that I don't simply use my 'normal' height based texturing, otherwise I could end up adding grass to already dug dirt. I've got the tree 'knockdown' complete...at the moment, I don't intend to have you 'push' the fallen trees out of the way...I don't want to introduce any additional objects/meshes that will decrease my frame rate (at this point) or have to deal with any more complex physics. I DO intend to implement some sort of ripping mechanism/simulation I cannot find a low-poly (free) model for an bulldozer as yet.
Front End Loader. Used for scooping up large quantities of loose, piled dirt (and rocks) and either depositing in the washplant or in a dump truck or simply moving to another location on the minesite. While this is the current low-poly model I am using for testing, I have no prototype functionality for this as yet. I'm a 'little' worried that the loader essentially grabs dirt 'from the side' of a pile and my terrain deformation is really only surface simulated, I'll have to see how this goes. It's all about suspending reality and making the user see what I want them to see.