Related Clues:

• Cameo, e.g.
• See 9-Down
• It's pursued in vein
• See 63-Across
• It may be picked
• Miner's quarry
• Source of iron
• It may have a silver lining
• Tram filler
• It's fine for a refinery
• Pay dirt
• Miner's quest
• Lead ___
• Bauxite, e.g.
• Subject of testing