The Rare Earth Minerals (REM) have piqued the interest of many people in the last few years since China, the world’s largest supplier, reduced the amount of exports. Since the REM contain elements vital to much of the electronic industry (including military components), there has been a large effort to locate new resources, not only in the U.S. but in other industrialized nations such as Brazil, Canada, India, Japan, and the European Union (I know, not a “real” country).
Just what are the REM? The simplest answer is they contain different concentrations of the rare earth elements (REE): yttrium (Y atomic number 39), the 15 lanthanides (lanthanum, La #57 to lutetium, Ln #71), and scandium (Sc #21). All of these elements with the strange names are metals, and all have similar chemical and physical properties. Although they are called “rare” some of the elements are really fairly common. For example, cerium (Ce #58) is about as common (25th most abundant element) in rocks of the earth’s crust as is copper. However, it is somewhat tough to locate concentrations of REE suitable for commercial mining, hence the moniker “rare”.
I became interested in REM/REE when I read comments in the tome Minerals of Colorado (Eckel and others, 1997) that the radioactive (because of thorium) phosphate mineral monazite-Ce [(Ce,La,Nd,Th)PO4] is a REM and may be found in virtually every mountain county in the state—either as placer deposits or enclosed in various igneous or metamorphic rocks (note that many REM are listed with the dominant REE as part of the mineral name). The problem was that most likely I could not identify a REM/REE if it hit me in the head (just a small hit). However, in the last few months one of those serendipitous moments showed up. At an auction last fall I acquired a specimen of bastnäsite in a flat of mixed minerals; Mr. Rockhounding the Rockies sent me home with a specimen of euxenite; and my friends at Ackley’s Rock store supplied me with a specimen of fluocerite. So, now I had three different samples of REM but still could not really identify any of them without some help!
Bastnäsite [(Ce,La)(CO3)F] is a fluorocarbonate that is divided into three minerals depending upon the predominant REE; all have cerium present. Therefore, there is bastnäsite-Ce [(Ce,La)(CO3)F], bastnäsite-La [La,Ce)(CO3)F], and bastnäsite-Y [Y,Ce )(CO3)F]. It appears that most bastnäsite in Colorado is the cerium variety (Eckel and others, 1997). Of the REE, bastnäsite may be the easiest to identify if crystals are present—tabular, hexagonal, greasy to vitreous luster, honey-brown to red-brown color, mostly translucent, and fairy soft at 4-5 (Mohs). The specimen I acquired is a tiny crystal situated in an amazonite-quartz pegmatite collected from Park County, probably from a unit in the Precambrian Pikes Peak granite. Information from Eckel and others (1997) would suggest a collecting site at Crystal Peak.
Euxenite, an oxide REM, is usually written as
euxenite-Y and contains yttrium, calcium, cerium, uranium, thorium, niobium,
tantalum, titanium and maybe a few other metallic elements:
[(Y,Ca,Ce,U,Th)(nb,Ta,Ti)2O6]. Although Eckel and others
(1997) noted some crystals may be several inches long, small masses or disseminated
grains appear to be more common in the rock record. The specimen was originally acquired at a
local auction, with a notation of collecting at the “Guffey District” (Park
County). It displays small amounts of
black, glassy, “globs” that have not formed into crystals or at least any than
I can observe. It is harder than bastnäsite
at ~6 (Mohs). I cannot identify the host
rock, perhaps monazite or feldspar with some minor quartz. The Colorado Geological Survey (www.geosurvey.state.co.us)
noted that REM at Guffey came from a Proterozoic gneiss or pegmatite.
Amazonite-quartz pegmatite with small crystal of red bastnäsite ~ 3 mm.
Photomicrograph of bastnäsite crystal ~3mm.
Photomicrograph of black “smears” non-crystals) of euxenite. Largest area ~2mm.
Photomicrograph of black “smears” (non-crystals) of euxenite. Width of smear ~2mm.
The third REM I acquired is fluocerite-Ce [(Ce,La)F3], named from its major components FLUOrine and CERium. The mineral is sort of non-descript, translucent, yellow- to red-brown in color. If crystalline, the individuals are slender prisms. In addition, fluocerite is quite brittle, a characteristic for which I can attest. The specimen is marked as being collected from “St. Peters Dome, CO”. One of the units of the Precambrian Pikes Peak granite evidently produced the REM.
Most causal readers and citizens are unaware of the REM/REE and simply tend to ignore them. After all, who wants to strike up a conversation about the physical properties of Erbium (Er #68)? That would be a real party killer! However, the REE make up a critical part of our daily life as they are used in smart phones, rechargeable batteries (especially those for electric and hybrid vehicles), weapon components for the military, cell phones, catalytic converters, night-vision goggles, clean energy technology, and a wide variety of other common products (Cerium is the “flint” in cigarette lighters). The problem with REM, as now being defined, is that China controls about 97% of the current world supply. The United States, and virtually every other country, is therefore heavily dependent upon a single country for the import of a vital manufacturing product. All has been “OK” in past years; however, Chinese officials in 2009 announced the restriction of REM exports by 35 percent! That announcement reverberated from Pentagon defense industries to clean-industry manufacturing plants.
Since the Chinese annulment, numerous countries have ramped up their exploration, planned mining, and REE extraction; however, the entire process from locating minable REM to producing an end product is agonizing slow.
Is all hopeless then? Probably not since REM are really not as "rare" as many other minerals, gold for example. And, REM are found in rocks cropping out in many parts of the western United States, including Colorado. In fact, agencies such as the USGS and the Colorado Geological Survey, along with various mining companies are exploring and locating RMM deposits, and planning for future mining operations. The USGS believes that, although mining for REM in the US is currently insignificant, the country may have reserves of about 13 million metric tons (as compared to China's 36 million), still a significant number. USGS data also suggest that two identified sites in Colorado, in the San Juan Mountains (Iron Hill Carbonatite Complex) and the Wet Mountains (pegmatites in Chaffee and Fremont Counties), contain 3 million tons of identified REM resources. In 2012 Denver-based Molycorp reached “start-up” status on reopening the Mountain Pass Mine near Las Vegas (but in California)—once the major U.S. producer of REM/REE. Rare Elements Resources is planning to mine 17.5 million tons of REM in Wyoming northwest of the small community of Sundance in the Bear Lodge Mountains. These mountains are actually part of the Black Hills (Laramide Orogeny) but contain several Eocene intrusions such as Devils Tower (see postings August 14, 2012, Crow Peak: A Pocket Laccolith and June 19, 2012, Bear Butte: A Laccolith on the Prairie). The Bear Lodge Complex is one of these intrusions consisting mainly of the rocks trachyte and phonolite. According to Rare Elements Resources, these alkali rocks contain base metals as well as REE.
But, there may be a downside to new mining in the U.S. for REM. The mining, refining and extraction have the ability to produce radioactive slurries and toxic acids, the basis for a possible environmental disaster. It appears that China has relied on open-pit mines and has produced environmental problems that may never disappear. With these known difficulties for REM mining one can imagine that the permitting process in the U.S will take years or even decades to complete.
So, big decisions are in the future for REM mining in the U. S. If citizens want "green technology" as a part of our "future", we must remember that every hybrid car takes a few pounds of REE, and that mining and refining of REE does/might produce some nasty byproducts. What is a person to do? That question is sort of like the fracking discussions here in El Paso County, Colorado. Many citizens want to drive their big cars and vans and live several miles distant from their work place; however, they tend to overlook the vast need for petroleum products. We want the gasoline and oil available at a reasonable price but prefer the petroleum to be pumped and refined elsewhere. And, we especially are afraid that fracking may cause environmental problems down the road. To me, this is a classic case of NIMBY. On the other hand, I prefer active citizens rather than passive consumers and there is much food for thought in the world of REM/REE. Whatever the case, these decisions are likely to be made at a pay grade higher than mine!
One final thought---the magma responsible for the Precambrian Pikes Peak granite must have been an interesting mix. The rocks contain such a variety of interesting gemstones (i.e amazonite and topaz), numerous concentrations of REM/REE, and minerals not very common at other locations: i.e riebeckite (June5, 2012), astrophyllite (June12, 2012), large zircons (June 7, 2012) and laihunite (April 24, 2013), and a host of others.
Eckel, E. B. and others, 1997, Minerals of Colorado: Denver Museum of Nature and Science and Fulcrum Publishing.