The Collaborative International Dictionary of English v.0.48:

Shoad \Shoad\, n. [Cf. G. schutt rubbish.] (Mining)
   A train of vein material mixed with rubbish; fragments of ore
   which have become separated by the action of water or the
   weather, and serve to direct in the discovery of mines.
   [Written also shode.]
   [1913 Webster]