Today's prompt was 'bulldog'!

I need to figure out what's in my asteroid, so that I know what my Belters and Rockhoppers can access, so that I guess I want to know what has smashed into my rocks! The asteroids can be carbonaceous, with carbon and water and other volatiles, rock or metal. I forget the way this works, but I think it was 70% rock, 20% carbon and 10% metal. Obviously, any big rock will actually have been hit by a lot of smaller rocks... Therefore 'roll' up a rock and decide what The majority of the asteroid is, rolling randomly and start slicing off fractions, 50 to 100% this, then 50 to 100% of the remainder is something else, dongma? We can place an 'ore body', an impact fragment in and under a crater at some longitude and latitude. The average rock would be stone, 75% stone and then we randomly roll up additional 'hits', So we might have a massive 19% carbon fragment at 1.57 radians south and 3.14 radians west, but a truly massive crater 56% of the circumference across, and then 5% metal and the last 1% is another bit of rock, either of which may overlap the other hits, so I will want to account for that. This will be messy! I think I will want to keep it fairly simple, but we should be able to source small 'ore' bodies on any rock.