Related Clues:

• Copper containers
• They're found in the ground
• Mined-over matter
• Raw material
• Cinnabar et al.
• Smeltery input
• Some train cargoes
• They lack refinement
• Smelter's stuff
• Products of a 16-Across
• Metallurgists' studies
• Sourdough's find
• Rock group?
• Cinnabar, taconite, etc.
• Metallurgist's stock