Information about rare earth elements can be downloaded as a pdf: M28 Rare Earth Elements (PDF 1.1 Mb)
Rare earths were named by Johann Gadolin in 1974 for a group of chemically similar, metallic elements with atomic numbers 57 through to 71.
In order, these are lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu).
These elements are commonly known as the lanthanide series and are divided into light rare earths (lanthanum–gadolinium) and heavy rare earths (terbium–lutetium). Scandium (Sc, atomic number 21), yttrium (Y, atomic number 39) and thorium (Th, atomic number 90) are also generally included in the rare earth group because of their similar chemical properties.
The rare earths were originally thought to be rare in crustal abundance but this is now recognised not to be the case and they have a similar crustal abundance to elements such as nickel, copper, silver, lead and tin. However, mineable concentrations are less common than for most other ores. The main economic minerals exploited for their rare earth content are:
- Bastnaesite (CeFCO3)
A fluoro-carbonate of cerium containing 60–70% rare earth oxides (REO) including lanthanum and neodymium. Bastnaesite is the world’s major source of rare earths. Host rocks include carbonatite, dolomite breccia with syenite intrusives, pegmatite and amphibole skarn.
- Monazite ((Ce,La,Y,Th)PO4) A rare earth phosphate containing 50–78% REO. It is recovered as a component of heavy mineral sands and is a major source of thorium which imparts radioactive properties to the mineral.
- Xenotime (YPO4)
A yttrium phosphate containing 54–65% REO including erbium, cerium and thorium. It is often a component of heavy mineral sands, pegmatite and igneous rocks.
Other rare earth minerals include:
- Allanite, a complex calc-silicate containing 5–20% REO including cerium and yttrium
- Apatite, a calcium fluorophosphate with cerium
- Zircon, a zirconium silicate with thorium, yttrium and cerium.
Most commercial products are mixed rare earth concentrates, accounting for approximately 95% of usage.
Uses include automotive catalytic converters (35%) with demand expected to further increase with the predicted expansion of hybrid vehicles; glass polishing, colouring and optical lenses (27%); metallurgical additives and alloys including strengthening and hardening of magnesium and aluminium alloys (14%); petroleum refining catalysts (10%); permanent magnets (5%); ceramics, colourants for glazes, coatings, refractories and stabilisers (4%); and phosphors for televisions and energy efficient light globes (3%). Other uses include nuclear control rods, nuclear detectors and counters, lasers, electronic components, jewellery, cigarette lighters, automatic gas lighting devices, flares, paint, lubricants and tracer ammunition.
The production of mischmetal is the oldest application of rare earths. This alloy, composed of 51–53% Ce, 22–25% La, 15–17% Nd, 3–4% Pr, 2–3% Sm, 3% Tb, 3% Y and 5% Fe, has metallurgical applications in the production of high-strength, low-alloy (HSLA) steel, high carbon steel, superalloys, stainless steel and armour plate. It is pyrophoric and when scratched gives off a spark and is used in cigarette lighters, automatic gas lighting devices, miners’ safety lamps, flares and tracer ammunition.
World production in 2013 of rare earth oxides was 110,000 tonne, with main production from China of 100,000 tonne, USA at 4,000 tonne and Australia at 2,000 tonne, mainly from the Mount Weld deposit in Western Australia. World resources are dominated by deposits rich in the minerals bastnasite, and monazite., with the largest resources of these minerals in China and the USA.
South Australian resources
Currently, South Australia has no rare earth production but an estimated 1500 t of rare earths comprising the oxides of scandium (3%), yttrium (16%), lanthanum (38%), cerium (24%), praseodymium (0.7%), neodymium (1.8%), samarium (0.2%), europium (0.07%), gadolinium (0.4%), terbium (0.5%), dysprosium (3.3%), holmium (0.7%), erbium (3.8%), thulium (0.7%), ytterbium (6.5%) and lutetium (0.6%) remain in uranium tailings at Port Pirie where davidite concentrates, produced at the Radium Hill Mine between 1954 and 1961, were treated.
This purpose-built Port Pirie treatment plant used an acid leach and ion exchange process to produce yellowcake from concentrated ore railed from the Radium Hill mine from 1955–62. Following decommissioning of the site in 1962, a number of smaller concerns have used the property for various operations including the extraction of Rare Earth Elements (REE). All original infrastructure related to the site was demolished in 2006.
Some South Australian Iron oxide-Copper-Gold (IOCG)-type deposits carry REE below economic levels. Future discoveries of IOCG-type deposits may carry elevated REE values. Exploration drilling at Ketchowla has identified elevated values for REE associated with secondary iron and manganese oxides.
Rare earth prospects and deposits in South Australia
Hematite breccias, the host rocks to Cu-U-Au-Ag ore at the Olympic Dam deposit, occur as steeply dipping, northwest-striking, dikelike bodies within fractured granite. The breccias are highly enriched in light (LREE) and heavy rare earth elements (HREE).
Five hydrothermal REE phases have been identified: bastnaesite, florencite, monazite, xenotime and britholite. Lanthanum and cerium are the main REE.
Located approximately 25 km SW of the Olympic Dam Deposit and targeted for IOCGU (REE).
Mineralisation occurred within basement rock, beneath metasediment of the overlying Stuart Shelf. Initial reconnaissance outlined sub-economic Fe-Cu-(U-Au) mineralisation.
Surface rock chip sampling identified anomalous uranium to maximum 1200 ppm U3O8. Follow up RC percussion
drilling returned anomalous values for U and REE (Ce, La, Y).
RC09BEC008 from 40–88 m, 48 m at 340 ppm U3O8, 367 ppm Ce, 365 ppm La, and 107 ppm Y.
First targeted as a possible IOCG. Geochemistry results were anomalous in REE (Ce and La almost to 1%), Cu (4000 ppm), Pb (1500 ppm), and Zn (5500 ppm).
Hole NC9202 results were:
134 m (96–230m), @ 626 ppm Cu, 256 ppm Pb, 593 ppm Zn, including 28 m (168–196 m) @ 1428 ppm Cu, 614 ppm Pb, 2330 ppm Zn, 2 ppm Ag, and almost up to 1% La + Ce.
Identified as being IOCG (REE)-style mineralisation in hematitic breccia host.
Assay results indicated 73 m @ 2.89% Cu and 0.4 g/t Au from 476–549 m (0.7% cut-off), 58 m @ 0.94% Cu from 549– 607 m, and 13.2 m @ 0.65% Cu from 607–654.2 m.
Overall assay for the interval 476–654.2 m (178.2 m) was 1.83% Cu, 0.64 g/t Au, 0.21% Ce, and 0.13% La.
Edward Creek – Victory Prospect
Results from surface rock chip and soil sample analysis indicate anomalous uranium.
Best results include 412 ppm U and 3.92% total REE (+Yttrium).
Other results include elevated copper-uranium (1320 ppm Cu, 60.3 ppm U, 1250 ppm Co, 361 ppm Zn, 7.87% Mn, 0.56% TREE+Y).
Gunsight Prospect (Mount Painter District)
From limited drilling mineralisation appeared to be dispersed over wide intervals in sub-economic concentrations. In the western portion of the prospect, surface gossans of a similar appearance were related to lenses of more massive sulphides, within which the Cu-U mineralisation approached ore grade.
Victory Downs Occurrence
Stream sediment sampling returned heavy mineral contents high in rare earths. These heavy mineral fractions averaged 38% of
the total, with zircon content to 1.6–8.6 %, TIO2 content 1.5–8.9%.
Assays of REE gave yttrium at 100 ppm, cerium at 800 ppm, and lanthanum at 600 ppm.
Vulcan IOCGU Project
The Vulcan gravity anomaly located approximately 40 km north of Olympic Dam is subject to ongoing exploration. IOCGU Mineralisation has been intersected in a number of drill holes.
Anomalous rare earth concentrations has also been intersected in VUD 002, with one five metre zone (from 947 m to 952 m down hole) averaging 0.29% cerium and 0.18% lanthanum.
Further drilling will commence in January 2011.
Winjabbie Dam Prospect
Recognised low-grade copper sulphide and rare earth mineralisation at a depth of 864 m.
Additional Reading on Rare Earths
Blissett, A.H., 1976. Rare Earths — South Australia. In: Knight, C.L. (Ed.), Economic geology of Australia and Papua New Guinea, 4, Industrial minerals and rocks. Australasian Institute of Mining and Metallurgy. Monograph Series, 8:329-330
Drexel, J.F. and Major, R.B., 1990. Mount Painter uranium–rare earth deposits. In: Hughes, F.E. (Ed.), Geology of the mineral deposits of Australia and Papua New Guinea. Australasian Institute of Mining and Metallurgy. Monograph Series, 14:993-998.
Harben, P.W. and Kuzvart, M., 1997. Industrial minerals — a global perspective. Industrial Minerals Information Ltd, Surrey, UK, pp.330-340.
Reeve, J.S., Cross, K.C., Smith, R.N. and Oreskes, N., 1990. Olympic Dam copper–uranium–gold–silver deposit. In: Hughes, F.E. (Ed.), Geology of the mineral deposits of Australia and Papua New Guinea. Australasian Institute of Mining and Metallurgy. Monograph Series, 14:1009-1035.
Robertson, R.S., Preiss, W.V., Crooks, A.F., Hill, P.W. and Sheard, M.J., 1998. Review of the Proterozoic geology and mineral potential of the Curnamona Province in South Australia. AGSO Journal of Australian Geology and Geophysics, 17(3):169-182.