Pea Ridge

Location: Missouri, United States (38.124, -91.050 approx.)

Commodities: iron; magnetite; pyrite; rare earth elements

Deposit model: low Ti-Fe-oxide, Cu-Au-U-REE · volcanic-hosted magnetite

Geology

“A copy of an internal company memo, provided by Jim Kennedy (electronic commun., October, 2008), dated 11-22-88 by Larry J. Tucker (retired Pea Ridge mine superintendent) indicates that there is a combined, probable reserve for pipes X11 and X13 of approximately 250,000 metric tons of mineralized rock, grading about 13 percent REE. The reserves were calculated for the volume between levels 2275 and 2675 using a density of 2,000 pounds per 9 cubic feet (lb/ 9 ft3) [approximately 3.56 grams per cubic centimeter (g/cm3)]. The level numbers represent the depth in feet of the level below the collar of the mine shaft. Whitten and Yancey (1990) report that there are about 600,000 metric tons of REE mineralization with an average grade of approximately 12 percent rare earth oxide. It is not clear what data were used to determine the estimate of 600,000 metric tons. However, a similar, but not equal, value of 600,000 short tons occurs as a note on another internal company memo, provided by Jim Kennedy (electronic commun., October, 2008), dated 10-25-89 by Larry J. Tucker; supporting calculations for the estimate are missing. The tailings contain additional lanthanide resources, primarily because of inclusions of fine-grained, REE-bearing minerals, principally monazite and xenotime, within apatite. The apatite also contains minor amounts of REE in its structure and occurs in variable concentrations throughout the iron ore body (Vierrether and Cornell, 1993).” (Grauch and others (2010)) “The Pea Ridge deposit is a member of the diverse class of iron oxide copper-gold deposits (IOCG deposits, Williams and others, 2005). It is one of several iron deposits located in southeastern Missouri (figure 1) within the Middle Proterozoic, volcano-plutonic complex of the St. Francois terrane. Host rocks of the iron ore body are altered rhyolite tuff (Nuelle and others, 1992). The deposit area includes the following mappable units: amphibole-quartz rock, heterolithic breccia, pseudobreccia, magnetite, hematite, silicified rock, lanthanide-bearing breccia pipes, mafic dikes, and aplite dikes (Seeger and others, 2001; Seeger, 2004, Nuelle and others, 1992). There are four mapped lanthanide-bearing breccia pipes (X11, V12, X13, V14), which cross-cut the magnetite-hematite ore body and its altered rhyolite host rock (fig. 1). The pipes contain a variety of lanthanide-bearing minerals, including the principal ore minerals monazite and xenotime. Mineral paragenesis and alteration zones are described by Sidder and others (1993). Gold, tin, and silver are unevenly distributed in the breccia pipes and in both the hematite and silicified zones (Husman, 1989).” (Grauch and others (2010)) “The Pea Ridge mine site, currently inactive (2010), contains an iron mine, mill, iron-pellet-making facility, and large piles of milled iron-ore tailings resulting from its earlier operation. The property now has two large tailings lakes flanked by extensive waste and tailings piles; most have vegetation cover, and several contain smaller ponds and wetlands. There are also several small, dry tailings ponds and a variety of ore stockpiles. Tailings underlie approximately 180 acres in total. The entire property is currently owned by Jim Kennedy, the president of Wings Enterprises, Inc., in Saint Louis, Missouri (http://www.wingsironore.com/).” (Long and others (2010)) “The rare earth elements in the breccia pipes of the Pea Ridge are dominated by the light REE lanthanum (La) and cerium (Ce), but the pipes are also relatively enriched in heavy REE, including dysprosium (Dy), holmium (Ho), erbium (Er), ytterbium (Yb), lutetium (Lu), and yttrium (Y) (table 20). The REE (lanthanide) resources of Pea Ridge are proportionally more concentrated in these heavy REE than is true of most other U.S. deposits (table 21). The REE distribution in the Pea Ridge deposit was generally confirmed by a recent USGS study, which collected limited samples of tailings and drill core at the site (Grauch and others, 2010). Although the total REE oxide resource at Pea Ridge (72,000 metric tons) is very small in comparison with the Mountain Pass deposit (2.58 million metric tons), the Pea Ridge deposit may be viewed as a potential source of heavy REE as a byproduct of iron ore production.” (Long and others (2010))

Published resource estimates

As compiled by USGS USMIN from the cited studies. Resource classes follow the source; "approximate" flags values USMIN reports as approximations. These are not current company reserve statements.

Recorded production

• Pea Ridge, Pea Ridge Mine: produced 47,400,000 metric tons of magnetite (Fe3O4) at 45.6111 percent, containing about 15,700,000 metric tons Fe, 1964–2001 (Gibbs and Rance (2012), Page 18, Table 6.3)

Exploration and site history

• Exploration — Cooperative project between the USGS, the Missouri Geological Survey, and several mining companies completed an airborne geophysical survey of parts of Washington, Crawford, St. Francois, and Iron counties, 1949 (Starkey and Seeger (2016))
• Discovery — REE-bearing breccia pipes, coincident with highly radioactive areas, were first recognized in the late 1970s, 1979 (Day and others (2016))
• Active — REE not produced but stockpiled underground; Primary product was magnetite for steel production; Also coal desulfurization, concrete densification, high power magnets, iron pigments; Pyrite sold for sulfuric acid; Waste rock sold as road metal, 1963–2001 (Seeger (2013))
• Inactive — Mine production ceased in 2001 and the underground workings currently are flooded (2009), 2001–2009 (Grauch and others (2010))
• Discovery — Discovered by drilling, 1953 (Starkey and Seeger (2016))

Record imported from USGS USMIN ver. 4.0 (June 2019). Developments after that date appear on facility records, not here; see the methodology.