It depends.

Buying & selling, it's just like any other investment.

"Mining," on the other hand, probably belongs on a Sch C.

The way I think about it, if your money made (or lost) money, that's an investment.  If your time made money, that's earned income.  Next we can debate whether or not the activity rises to the level of a "trade or business" but I'd say mining probably belongs on a Sch C in most cases, subject to SE tax.

Rick