Assayers' samples (4)
I believe the answer is:
ores
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">assayers' samples</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for ores that I've seen before include "Mined minerals" , "Sources of metal" , "Bauxite, haematite etc" , "Rocks or minerals containing metals" , "Metal-bearing minerals" .)