If I were you I would think about which
SM weapons already fit within your desired theme (such as the Siege drills on the centurions) and then try to find suitable alternatives for the weapons that do not fill your specifications.
I would consider each unit and what role in both combat and mining you want them to fill.
For example. Terminators could have drills instead of
PF (
CF already fit the bill as Red_Starrise mentioned) or a
PF that looks as though it's designed for lifting/breaking rocks.
I also think additional lights on some of your models wouldn't look amiss.
Another suggestion might be if you're considering Dozer Blades on your vehicles. Having large buckets similar to bulldozers that look as though they can raise them up (so attached to the chassis of the vehicle by mechanical arms)
In terms of ranged weapons there are plasma cutters on servo-harnesses that are essentially plasma pistols so any model equipped with a plasma pistol could be modeled to be wielding a plasma cutter.
I don't wanna flood you with ideas as you need to figure out what you want for yourself but these are just some concepts to help you get the ideas flowing.
I hope this helps, and if you need more help figuring out how to represent certain weapons or wargear just ask
Peace