Pea Ridge Mine, Washington County, Missouri, USAi

Regional Level Types
Pea Ridge Mine	Mine
Washington County	County
Missouri	State
USA	Country

A former iron mine located near Meramec State Park and 13.8 km (8.6 miles) SE of Sullivan. Formerly owned by the St. Joe Domestic Metals Corp., a subsidiary of the Fluor Corp. The Meramec Mining Company (which was a partnership between St. Joe and Bethleham Steel Corporation) was the owner until 1978. Produced 1.3 million tons of ore pellets (1984). Mine was closed and flooded in 2001.

Rare earth element (REE)−bearing breccia pipes cut through the Pea Ridge massive magnetite-iron orebody. The Pea Ridge deposit is hosted by Precambrian volcanic rocks of the St. Francois terrane of southeastern Missouri. The magnetite-rich orebody is interpreted as a high-temperature, magmatic-hydrothermal deposit (Sidder and others, 1993) in ash-flow tuffs and lavas, which may have formed in the root of a volcanic caldera (Nuelle and others, 1991). Four mapped REE-bearing breccia pipes steeply crosscut the magnetite-hematite orebody and its altered rhyolite host rock. Exposed portions of the breccia pipes are as much as 60 m (197 ft) in horizontal length and as much as 15 m (49 ft) in width; the pipes extend below the mined levels to an undetermined depth (Seeger and others, 2001). Rare earth elements–bearing minerals in the breccia pipes include monazite, xenotime, and minor bastnasite and britholite. The REE concentrations reported in the breccia pipes are consistently high but variable. Nuelle and others (1992, p. A1) state, “Total REE oxide content of samples of the groundmass material, which are not diluted with lithic fragments, average about 20 weight percent.” Seeger and others (2001, p. 2) state, “Total REE oxide concentrations of grab samples range from about 2.5 to 19 weight percent.” Bulk sampling by the U.S. Bureau of Mines found REE oxide concentrations ranging from 7 to 25 weight percent and an average of 12 weight percent (Vierrether and Cornell, 1993).