Approach a treasure box then save the game. Touch the treasure box and you will get one of several options:

100 gold or 2 leadership points.
200 gold or 4 leadership points.
300 gold or 6 leadership points.
400 gold or 8 leadership points.
500 gold or 10 leadership points.

A leprechaun willing to trade a spell if you release him.
A tribe of nomads who give you +1 to spell capacity.
Some minerals that will get a pay raise from queen.

If you do not get the desired treasure, load your game and try again. Note: Do not try for the spell capacity, as it seems to be very rare.