Related Clues:

• Seam sample
• It runs in veins
• Copper container, perhaps
• Vein pursuit?
• It's picked out of a mine
• Something to be assayed
• 45D homonym
• Mined rocks
• Zincite, e.g.
• "Buried" treasure found in 17-, 27-, 44- and 59-Across
• Bauxite, for example
• Metal-in-the-rough
• Nickel in a pocket?
• Mined stuff
• Tramcar filler