Best way to make money mining is not in the resources you collect. Its in the missions you can fill with the resources you gather.
So you need to find a good system that is offering loads of contracts for minerals. Take as many as you can get hold of. Visit all the stations in the system and surrounding systems. Then when you have a bucket load of resource jobs, then head off to a safe belt and mine.
The key to jobs is standing. So if your standing is low, the jobs won’t pay much, but fulfil the contracts and your standing improves and so does the money you earn from each mission.
Type of system and economy status of system effects the missions you get as well. But if you can find the right system, the money is there.