Republished from: The Principal Rare Earth Elements Deposits of the United States, USGS Scientific Investigations Report 2010-5220
By Keith R. Long, Bradley S. Van Gosen, Nora K. Foley, and Daniel Cordier. USGS
Locating a Deposit - Exploration
The first step in developing a new REE mine is to locate a suitable REE deposit. Exploration for new deposits may be in either of two contexts: greenfield exploration to find new deposits in areas not previously mined and brownfield exploration in and adjacent to current and past mining activity.
Greenfield exploration may target frontier areas with no previous exploration or may follow up on past exploration results. Brownfield exploration includes searching for extensions to known reserves and resources within or near a mine as well as new deposits in the vicinity of existing operations. The latter may extend the life of an existing mine or result in the complete redevelopment of a former mine.
Exploration is an uncertain process conducted with limited capital. An explorer's objective is to find a deposit of the targeted type, size, and quality with the least amount of expense. Thus, any particular location of merit is rarely exhaustively explored. Exploration will proceed on the basis of favorable indicators so long as objectives are met within budget. An exploration project will be curtailed if evidence is found that contraindicates the prospectivity of the target or if results are insufficient to justify further work.
Market Price Influence on Exploration Budgets
Exploration commonly runs in cycles, prompted by short- to medium-term increases in mineral prices. The low side of a price cycle may prompt little or no exploration activity. Any particular prospect may undergo many episodes of exploration by different parties during many decades; the exploration episodes are motivated by price cycles, new cost-saving technology, improved exploration concepts and methods, and the vagaries of land access and exploration management.
The Current REE Exploration Boom
In the case of REE, very little exploration has ever been done and the most intense period ever of direct exploration for REE is currently underway (2010). Many important past discoveries have been serendipitous-the world's largest REE mine, Bayan Obo in China, was first mined for iron ore. The "funny" steel produced from this ore was investigated and found to be contaminated with REE (Laznicka, 2006). Mountain Pass, California, was found in the course of a U.S. Geological Survey radioactivity reconnaissance project that expected to find uranium. Many REE-bearing carbonatite deposits were initially explored as a source of niobium or phosphates.
Proving The Deposit
The discovery of a REE deposit must be proved by extensive trenching, drilling, and sampling. Drilling will initially be on a widely spaced grid to evaluate the extent and richness of mineralization. If results are favorable, the deposit will be drilled on progressively narrower spacing until a measured resource of adequate size is established. Concurrently, baseline environmental studies will be completed and bulk samples obtained for metallurgical testing.
Mining and Metallurgical Planning
A conceptual mine plan and metallurgical plan will be engineered and a preliminary economic feasibility study undertaken. If the results of these studies are favorable, further work will develop an optimized mine plan, validate metallurgical processing on a pilot plant scale, begin application for permits, and conduct a definitive economic feasibility study.
Permitting the Mine
If the results of the feasibility study are positive, financing will be sought and permitting further advanced along with detailed plant engineering. Permitting will typically require an approved plan of operations, a positive environmental impact study, and some kind of final permission by a government agency. If external financing is required, an independent due diligence study will verify the results of the feasibility study.
Construction of Mine and Plant
Once financing and regulatory approval are in place, a construction decision will be announced. Ongoing detailed engineering design will be completed, long lead-time items will be ordered, construction work will be bid on, and contracts will be awarded. Construction begins as soon as possible and is executed quickly to minimize interest and opportunity costs.
As mine components are completed, they will be tested and placed in operation with a ramp-up period until full commercial production at the planned output rate is achieved. The ramp-up process may be completed smoothly in a matter of months or may encounter unanticipated difficulties that require an extended period of time to solve. Some mines have failed at this stage because of ore grades that are lower than expected or metallurgical processes that do not work as planned.
Enormous Expenses and Sources of Capital
Up to this point, a mining company has been spending large amounts of money without any revenue from mineral sales. Capital must be supplied internally, from net revenues of a mining company's other operations, or externally from banks or investors. The cost of borrowing these funds is considerable and repayment cannot even start until a mine goes into production. The largest of currently (2010) proposed new REE mining operations, including Mountain Pass, California, have reported premining capital requirements of a half a billion dollars or more.
Operation, Reclaimation & Closure
A mine will operate until reserves are exhausted. Today, mine closure and reclamation are planned before a mine is built; reclamation is undertaken concurrent with operations wherever possible. Mobile equipment and structures are removed. Roads, waste stockpiles, tailings, and surface facilities are also reclaimed in an attempt to restore the land to its previous use and appearance. Large open pits are not typically backfilled because of the large energy and CO2 emissions costs of doing so. Instead, to minimize environmental impact they are reclaimed as landscape features.
Only one REE mine, at Mountain Pass, California, has ever been developed in the United States. That occurred in the early 1950s and is not illustrative of what is required to develop such a mine today. Nickel laterite deposits were suggested above as a useful analog for the development of a new REE mine.
This comparison is particularly apt for a REE laterite deposit, such as Mount Weld, Australia. Niobium-bearing carbonatites are another close analog. These two deposit types share complex and difficult metallurgy and typically require extended periods of time to develop.
The time that was required to bring into production recently developed nickel laterite mines and most niobium carbonatite mines is shown in Table 2. All of these mines were developed outside of the United States and the permitting delays noted in Table 1 do not pertain in this case.
Lead Time To Production
The time from discovery to initial production for the mines listed in Table 2 range from 5 to 50 years, permitting to initial production 1 to 7 years, and ramp-up times were 3 to 42 months, except in the case of Araxá, Brazil, which suffered some unusual political delays. These development times are in line with the results of Peters (1966) and indicate that in some instances a relatively rapid pace of development can be obtained.
It should be noted, however, that the most advanced REE projects other than Mountain Pass, California, namely Mount Weld and Dubbo in Australia, have required years of metallurgical testing and development and fall into the fourth, 7-year-or-more category of Peters (1966).
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"US Seeks Rare Earth Elements" reviews the importance of rare earth elements and features a video visit to the Mountain Pass Mine in California. At one time Mountain Pass was the leading source of rare earth elements for the world. Then low-cost supplies from China rendered it uncompetitive. The Mountain Pass Mine has the potential to produce rare earths at a competitive price and supply about 25% of world demand for several key elements. Video by the Al Jazeera English Channel.
Northwest-facing view of Iron Hill, Gunnison County, southwestern Colorado. Iron Hill is formed by a massive carbonatite stock that forms the center of an alkaline intrusive complex. This complex hosts many mineral resources, including titanium, niobium, rare earth elements, and thorium (Van Gosen and Lowers, 2007). The carbonatite stock is estimated to consist of 655.6 metric tons of carbonatite containing 2.6 million metric tons of rare earth elements oxides, 28,200 metric tons of thorium oxide, and 373,700 metric tons of niobium oxide (Staatz and others, 1979, p. 30).
Generalized geologic map of most of the Mountain Pass rare earth element district, southern California.
Only a representative minority of the hundreds of shonkinite, syenite, and carbonatite dikes are shown. Widespread andesitic and rhyolitic dikes, of Mesozoic or Tertiary age, are
not shown. From USGS Open-File Report 2005-1219
Schematic flow diagram of REE ore processing at Mountain Pass, as outlined in the text. Bold type indicates
final products or groups of products. From USGS Open-File Report 2005-1219
Table 1: Time required to get permits, construct, and commission recent metal mines in the U. S.
Alta Mesa, Texas
Arizona 1, Arizona
Ni Cu Co PGE
East Boulder, Montana
Lisbon Valley, Utah
Pend Oreille, Washington
Rock Creek, Alaska
Rossi (Storm), Nevada
2nd half 2008
Turquoise Ridge, Nevada
[NYA, not yet achieved, production not yet begun or commercial operations not achieved; PGE, platinum group elements. Yes, long permitting and development delays because of litigation by government agencies and nongovernmental organizations]
Table 2: Time required to develop selected mines outside of the United States.
Commercial Operations Began
Barco Alto, Brazil
Catalão I, Brazil
Goro, New Caledonia
Murrin Murrin, Australia
Onça Puma, Brazil
Urumu Utsumi, Brazil
[These mines selected as close analogs of the mining and metallurgical methods required by a rare earth elements mine. NYA, commercial production not yet achieved]