<strong>Rare</strong> <strong>Earth</strong> <strong>Elements</strong> <strong>Review</strong> Section 2 – Introduction to <strong>Rare</strong> <strong>Earth</strong> <strong>Elements</strong> [This page intentionally left blank.] 2-10
<strong>Rare</strong> <strong>Earth</strong> <strong>Elements</strong> <strong>Review</strong> Section 3 – Life-Cycle Stages <strong>of</strong> <strong>Rare</strong> <strong>Earth</strong> <strong>Elements</strong> Mines 3. Life-Cycle Stages <strong>of</strong> <strong>Rare</strong> <strong>Earth</strong> Mineral Mines The increasing importance <strong>of</strong> REMs for the manufacture <strong>of</strong> modern devices upon which society has become reliant, along with uncertain supplies (see Section 2), is encouraging exploration and development <strong>of</strong> new mining sites. While REMs are an important resource needed to sustain our modern technologies, the waste footprint and environmental impact from REM mining operations is expected to be as significant as current mining practices for metals and minerals. The requirements, regulations, and financial obligations and assurances for a new mine are usually complex and take years <strong>of</strong> planning. The economic feasibility <strong>of</strong> discovered deposits must be proved, and environmental effects to the local communities and habitat also must be evaluated to determine feasibility. The process <strong>of</strong> exploration, development, and construction typically required before mining can begin may exceed 10 years. Except for a few locations, known rare earth deposits in the United States are generally considered small to medium reserves. This section presents a discussion <strong>of</strong> the typical process steps used in developing a new rare earth deposit and the associated mining wastes that typically would result. It is not expected that the mining stages <strong>of</strong> a rare earth mine would be different than other hardrock or metal mining operations. Except for the radioactivity <strong>of</strong> uranium and thorium, the potential REM waste emissions would be generally comparable to a typical hardrock mine. Mining operations produce a variety <strong>of</strong> solid materials that have the potential to cause environmental contamination and require long-term remedial actions and operation and maintenance. The largest mines may generate more than a billion tons <strong>of</strong> solid wastes that may cover areas exceeding a thousand acres, and smaller operations still must handle and dispose <strong>of</strong> quantities <strong>of</strong> materials that can affect large areas (U.S. EPA, 2003). Most deposits <strong>of</strong> REE ores in the United States would be expected to require mining operations that likely would produce far less quantities <strong>of</strong> solid wastes than the largest operating mines. An example <strong>of</strong> an existing REE mine in the United States that would be considered a large mining operation, is the Molycorp Minerals rare earth mine in Mountain Pass, California (see sidebar). It would be expected that rare earth mineral mining operations developed in the United States would be similar to other large hardrock and placer mines that recover minerals containing primary metals (e.g., gold, silver, copper, zinc, lead). As examples, the mass <strong>of</strong> selected types <strong>of</strong> individual REE-containing ore deposits occurring in the United States is estimated by the USGS to be the following: • 0.2 million tons (approximate average) for thorium-rare earth vein deposits (Armbrustmacher et al., 1995) • 3.5 to 450 million tons for low titanium iron oxide deposits containing REE, with a median quantity <strong>of</strong> 40 million tons (Foose, 1995) • 6.6 to 331 million tons for minable carbonatite ore deposits (Modreski et al., 1995). These rough quantity estimates are based on known deposits, as characterized in geochemical deposit models prepared by the USGS; other deposit models may also exist other than those found and reviewed and that provide additional estimates. Averages for the The Scale <strong>of</strong> an Existing REE Mine in the United States The largest rare earth minerals mine in the United States is Molycorp Mineral’s Mountain Pass rare earth mine and site, which occupies 2,222 acres <strong>of</strong> land in San Bernardino County, California. The mine started operation in 1952, operating as an open pit lanthanide mining, beneficiation, and processing facility. The period <strong>of</strong> greatest ore production was from 1965 to 1995. Mining activities ceased in 2002, but minor milling activity continued to process stockpiled ore; and full-scale ore production may resume in 2012. When mining activities ceased, the open pit was 1,500-feet wide by 400-feet deep. Overburden materials were held on site, and numerous process water, tailings, and product storage ponds were also operated. Remaining REE reserves (relative to a 5 percent cut<strong>of</strong>f grade) at the Mountain Pass mine are estimated to exceed 20 million tons. The average REE content in the bastnasite mineral ore is approximately 9 percent. The remaining gangue minerals (calcite, barite, and dolomite) in the carbonatite igneous rock body make up approximately 91 percent <strong>of</strong> the ore-containing rock. The expected overburden produced is estimated to be 104 million tons, which will be stored at two existing storage piles. These storage piles will together cover approximately 315 acres within 30 years <strong>of</strong> the proposed period <strong>of</strong> operation through 2042 and represent approximately a 120 percent change over current stockpiles accumulated between 1950 and 2002. California Regional Water Quality Control Board, Lahontan Region (2010) 3-1
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