The Collaborative International Dictionary of English v.0.48:

Schlich \Schlich\, n. [G.; akin to LG. slick mud, D. slijk, MHG.
   sl[imac]ch.] (Metal.)
   The finer portion of a crushed ore, as of gold, lead, or tin,
   separated by the water in certain wet processes. [Written
   also slich, slick.]
   [1913 Webster]