资料来源 : Webster's Revised Unabridged Dictionary (1913)

   3. Fig.: A rich source of wealth or other good. --Shak.

   {Mine dial}, a form of magnetic compass used by miners.

   {Mine pig}, pig iron made wholly from ore; in distinction
      from cinder pig, which is made from ore mixed with forge
      or mill cinder.

资料来源 : WordNet®

mine pig
     n : pig iron made entirely from ore