In the beta, I mined 6 coal ore with a Fortune lll golden pickaxe and the 6 ore dropped 1 coal, I was finding it weird, but I continued playing, just a few minutes ago, I was coming back with diamond ores mined with Silk Touch, and mined them with Fortune lll Diamond Pickaxe, and each one dropped 1 diamond, so I assumed the Fortune enchantment doesn't work on the Pickaxe