Vein contents (3)
I believe the answer is:
ore
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">vein contents</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for ore that I've seen before include "Mineral or metal source" , "Mineral-bearing rock" , "Small coins" , "Mineral - Scandinavian monetary unit" , "Natural minerals" .)