Lump of gold (6)
I believe the answer is:
nugget
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">lump of gold</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for nugget that I've seen before include "Lump of, eg, gold" , "Lump of valuable metal" , "Lump sought by the prospector" , "small, valuable item" , "Small lump (of something valuable)" .)