Those amounts are regular income taxed at regular income rates. Your mining pool, if complying with US law, is required to report these transactions to the IRS if they exceed $600 during the year.
I don't know anything about the current mining pools, but it sounds like mining pools may now have incentive to distance themselves from the US so that they don't need to bother with US law. I really don't know how the whole thing is setup though. Regardless, it'll be interesting to see.