Lump of precious metal (6)
I believe the answer is:
nugget
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">lump of precious metal</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 "Small lump (of something valuable)" , "Lump (of gold, etc)" , "Rough lump of gold" , "Lump of metal, say gold" , "Piece of advice" .)