[Anthony]

Realistically this is going to be super boring (the geological processes that create concentrated veins of ore don't exist in asteroids, so much a question of whether it's mostly silicates or mostly nickel-iron, plus ice in the outer system), but that doesn't make for much of a game.

I would avoid using random tables, though, because the interesting thing from a campaign standpoint isn't the mining itself, it's the shenanigans around the mining (claim jumping, etc).