Mt Adams

From Wikipedia:

In 1929 and 1931 Wade Dean filed mining claims to the sulfur on Adams' 210-acre (0.8 km2) summit plateau. After building a horse and mule trail, he had a diamond-tipped drilling machine moved to the summit area and test pits were drilled. Although sulfur sludge was found, the amount and quality of the ore was never good enough to make the venture profitable and the project was abandoned in 1959. Adams is the only large Cascade volcano to have its summit exploited by commercial miners.