Columbia subject headings:
Lead ores--Congresses.
Ore deposits--Mississippi River Valley--Congresses.
Sphalerite--Congresses.
Zinc ores--Congresses.
Harvard subject headings:
Lead--Congresses.
Ore deposits--Congresses
Zinc--Congresses.
Princeton subject headings:
Lead ores--United States--Congresses.
Zinc ores--United States--Congresses.