Gamify Mining/Mining mini game ideas

I'm planning to have a mining side quest coming up, and want to "gamify" it a bit. The idea is to make it sort of a challenge to get the proper minerals, without making it just a dice roll every time. Ideally whoever gets the most minerals will get an additional reward or it could be a ranking system of 1st-last with diminishing rewards for placement.

I have a plan for how this plugs into a greater story and how dangers of the mine work in, as well as monsters. My other thoughts are to give players a task that could rotate among players(like one player is on guard duty, one player mines while the other hauls the cart to make it a bit of cooperation).

Was hoping to get any feedback or ideas on a mining mini game and how to make mining a contest.