Depends completely on the scale you are talking about.
If you are looking for the hand-push cars that were used in the minds, you might want to try taking an HOn30 car and use it as an On18 cart, or take an On30 car and use it as a Gn15 model.
I think someone makes stationary models of hand-push carts in several scales.
As for rolling models, that will again depend on the scale you are talking about. Hoppers meant to be towed behind a locomotive can be found in HOn2, HOn30, HOn3, On2, On30, On3, Gn15, and 1:20.3 (Fn3) scales.
Someone I'm sure can provide a list of the different manufacturers, but that's the best I can do for you at the moment.
Frank, given this is the standard gauge O folder you might be better served posting in the mining and logging section.
As stated, telling us the scale you are after would assist greatly in sending you to a possible solution.