The Collaborative International Dictionary of English v.0.48:

Stockwork \Stock"work`\, n. [G. stockwerk.]
   1. (Mining) A system of working in ore, etc., when it lies
      not in strata or veins, but in solid masses, so as to be
      worked in chambers or stories.
      [1913 Webster]

   2. (Geol.) A metalliferous deposit characterized by the
      impregnation of the mass of rock with many small veins or
      nests irregularly grouped. This kind of deposit is
      especially common with tin ore. Such deposits are worked
      in floors or stories.
      [1913 Webster]