Heh got me the first time as well, The mines are on the same island as Redbeard (Just go up the hill). It one of the top islands on the second map
Yup he wants a 100k but you can play a double, no triple cross on the pirates. Deliver the black mark for redbeard, spooks James out, he counter offers and asks you to kill Redbeard and will waver the gold for the map.
Return to Redbeard, finish the black mark quest and tell him you won't kill him. Then click on him and tell him you changed your mind. Kill him, return to James, finish his quest and kill him!
Not very becoming a Paladin