Content maintained by Yanis Miezitis
Content maintained by Yanis Miezitis
Thorium oxide (ThO2) has one of the highest melting points of all oxides (3300°C) and has been used in light bulb elements, lantern mantles, arc-light lamps and welding electrodes as well as in heat resistant ceramics.
Thorium can be used as a nuclear fuel through breeding to 233U. There is no significant demand for thorium resources currently and any large scale commercial demand is expected to be dependant on the future development of thorium fuelled nuclear reactors. Several reactor concepts based on thorium fuel cycles are under consideration, but a considerable amount of development work is required before it can be commercialised.
India has been developing a long-term three stage nuclear fuel cycle to utilise its abundant thorium resources. The construction of a 500 megawatt electric (MWe) prototype fast breeder reactor at Kalpakkam, near Madras, was about 81 per cent complete in November 2011. It will have a blanket with thorium and uranium to breed fissile 233U and plutonium respectively. Six more such fast breeder reactors have been announced for construction and this project will take India's thorium program to stage 2.
In stage 3, Advanced Heavy Water Reactors (AHWRs) burn 233U and plutonium with thorium to derive about 75 per cent of the power from thorium. For each unit of energy produced, the amount of long-lived minor actinides generated is nearly half of that produced in current generation Light Water Reactors. In mid 2010, a pre-licensing safety appraisal had been completed by the Atomic Energy Regulatory Board (AERB) and site selection was in progress. Construction of the AHWR is anticipated to commence in 2014, but full commercialisation of thorium reactors is not expected before 2030. The AHWR can be configured to accept a range of fuel types, including enriched U, U-Pu MOX, Th-Pu MOX, and 233U -Th MOX in full core.
In September 2009, India announced an export version of the AHWR, the AHWR- Low Enriched Uranium (LEU) version. This design will use LEU plus thorium as a fuel, dispensing with the plutonium input. About 39 per cent of the power will come from thorium (via in situ conversion to 233U). This version can meet the requirement also of medium sized reactors in countries with small grids along with the requirements of next generation systems (World Nuclear Association 20111; Kakodkar 2009)2.
In January 2011, the China Academy of Sciences launched a research and development program on Liquid Fluoride TR, known at the academy as the thorium-breeding molten-salt reactor (Th-MSR or TMSR). A 5MWe MSR is believed to be under construction at Shanghai, with an operational target date of 2015.
Atomic Energy of Canada Ltd (AECL) has reported that some countries are assessing the use of thorium fuels in existing CANDU 6 (700MWe class) reactors. In July 2009, AECL signed a second phase agreement with four Chinese entities to develop and demonstrate the full-scale use of thorium fuel in the CANDU 6 reactors at Qinshan in China. This was supported in December 2009 by an expert panel appointed by CNNC and comprising representatives from China's leading nuclear academic, government, industry and research and development organisations. The panel also recommended that China consider building two new CANDU units to take advantage of the design's unique capabilities in utilising alternative fuels3. A demonstration 'High Temperature Reactor-Pebble Modules' (HTR-PM) of 210MWe (two reactor modules) is being built at Shidaowan in Shandong province. A further 18 units of 210MWe each are planned and followed by increases in the size of the 210MWe unit modules including the introduction of thorium in fuels.
At end of December 2011, Australia's total indicated and inferred in-situ resources of thorium amounted to about 532 000 tonnes. Because there is no publicly available data on mining and processing for these resources, the recoverable resource of thorium is not known. However, assuming an arbitrary figure of 10 per cent for mining and processing losses in the extraction of thorium, the recoverable resources of Australia's thorium could amount to about 478 800 tonnes.
Because there is no established large scale demand and associated costing information, there is insufficient information to determine how much of Australia's thorium resources are economically viable for electricity generation in thorium nuclear reactors.
There are no comprehensive detailed records on Australia's thorium resources because of the lack of large-scale commercial demand and a paucity of the required data.
Most of the known thorium resources in Australia are in the rare earth-thorium phosphate mineral monazite within heavy mineral sand deposits, which are mined for their ilmenite, rutile, leucoxene and zircon content. Prior to 1996, monazite was being produced from heavy mineral sand operations and exported for extraction of rare earths. However, in current heavy mineral sand operations, the monazite is generally returned to the pit in dispersed form, as required by mining regulations. This dispersment is carried out to avoid a concentration of radioactivity when rehabilitating the mine site to an agreed land use. In doing so, the rare earths and thorium present in the monazite are negated as a resource because it would not be economic to recover the dispersed monazite for its rare earth and thorium content. The monazite content of heavy mineral resources is seldom recorded by mining companies in published reports. However, in June 2012, Astron Corporation Ltd noted in an investor presentation that it intends to export 10 000 tonnes of monazite per year to China from its Donald heavy mineral sand deposit in Victoria4.
Most of the known resources of monazite are in Victoria and Western Australia (WA). Heavy mineral sands are being mined in the Murray basin deposits at Gingko and Snapper in New South Wales (NSW) and at Douglas in Victoria. In WA, mining of heavy minerals is taking place at Eneabba, Cooljarloo, Dardanup and Gwindinup.
Using available data, Geoscience Australia estimates Australia's monazite resources in the heavy mineral deposits to be around 7.4 million tonnes (Mt). The data on monazite and the thorium content in the monazite in the mineral sand resources is very variable, but the available sources include:
Information from these sources was applied to resource data on individual heavy mineral sand deposits to estimate the thorium resources in these deposits. Where local data on the monazite and thorium were not available, regional data were applied to individual deposits to estimate their monazite and thorium resources. Using this information, Australia's inferred in situ thorium resources in the mineral sands were estimated to be around 371 000 tonnes. The regional distribution of monazite in heavy mineral sands is shown in figure 1 and the location of various types of deposits containing thorium and the regional distribution of estimated thorium resources is shown in figure 2.
Resources for a new type of placer deposit, the Charley Creek deposit, containing zircon, monazite and xenotime was reported on 15 May by Crossland Uranium Mines Ltd. The Charley Creek deposit was reported by the company as an alluvial outwash with comprises an Indicated Resource of 387Mt containing 27 000 tonnes of xenotime, 161 000 tonnes of monazite and 196 000 tonnes of zircon. The xenotime and monazite were stated to contain about 114 000 tonnes of total rare earth oxides. In addition, another 418Mt of Inferred Resources was reported to hold about 121 000 tonnes of rare earth oxides in about 31 000 tonnes of xenotime and 167 000 tonnes of monazite as well as 220 000 tonnes of zircon. The thorium content in the xenotime and monazite was not stated.
Apart from heavy mineral sand deposits, thorium can be present in other geological settings such as alkaline intrusions and complexes, including carbonatites, and in veins and dykes. In these deposits, thorium is usually associated with other commodities such as rare earths, zirconium, niobium, tantalum and other elements. The more significant deposits are described in the following sections.
Arafura Resources Ltd: Nolans Bore rare earth element-phosphate-uranium-thorium deposit is located 135 kilometres (km) northwest of Alice Springs in the Northern Territory (NT). The mineralisation is hosted in fluorapatite veins and dykes. This deposit contains about 81 800 tonnes of Th in 30.3Mt of Measured, Indicated and Inferred Resources grading 2.8% rare earth oxides (REO), 12.9% P2O5, 0.02% U3O8 and 0.27% Th. Arafura is considering processing the rare earth-phosphate-uranium-thorium ore concentrate from the Nolans Bore deposit at Whyalla in South Australia. The thorium content in the concentrate will be separated as an iron thorium precipitate and transported back to the Nolans Bore mine site for long-term storage as a possible future energy source. In June 2012, Arafura published a revised total Measured, Indicated and Inferred Resource figure of 47Mt grading 2.6% REO, 11% P2O5 and 0.02% U3O8. The thorium grade was not published but assuming a similar thorium grade of 0.27% Th, the upgraded resource could contain thorium in the order of 127 000 tonnes.
Alkane Resources Ltd: The Toongi zirconium-niobium-rare earth element deposit occurs within an alkaline trachyte plug about 30km south of Dubbo in NSW. The deposit has a Measured Resource of 35.7Mt and 37.5Mt of Inferred Resources grading 1.96% ZrO2, 0.04% HfO2, 0.46% Nb2O5, 0.03% Ta2O5, 0.14% Y2O3, 0.745% total REO, 0.014% U3O8, and 0.0478% Th, giving a total of about 35 000 tonnes contained Th. In November 2011, Alkane announced Proved and Probable Reserves for the deposit of 35.93Mt grading 1.93% ZrO2, 0.04% HfO2, 0.46% Nb2O5, 0.03% Ta2O5, 0.14% Y2O3, and 0.73% total REO. The company also released results of a definitive feasibility study for the project that excluded the production of thorium. The financial analysis indicated a net present value for the project of $181 million at a processing rate of 400 kilotonnes per annum (ktpa) and $1.207 billion at a processing rate of 1000ktpa. In July 2012, Australian Zirconia Limited (AZL), a wholly owned subsidiary of Alkane Resources Ltd, signed a Memorandum of Understanding with Japan's Shin-Etsu Chemical Co Ltd to produce a suite of separated heavy and light rare earths using the rare earth concentrates from the Dubbo Zircon Project.
Hastings Rare Metals Limited: Other alkaline complexes with known rare earth and thorium mineralisation include Brockman (now renamed 'Hastings') in WA. It is a large low-grade zirconium-niobium-rare earth elements (Zr-Nb- REEs) deposit hosted in altered trachytic tuff of Paleoproterozoic age. On 8 September 2011, Hastings reported 36.2Mt of Indicated and Inferred Resources grading 8.86 parts per million (ppm) ZrO2, 3.55ppm Nb2O5, 182ppm Ta2O5, 110ppm Ga2O5, 318ppm HfO2, 186ppm Dy2O5, 1120ppm Y2O3, 2102ppm total REO and 1802ppm heavy REO. Historic company reports on open file on the Geological Survey of Western Australia WAMEX database show analyses for thorium in six separate drill hole intersections (in tuffs) of 16 metres (m) to 28m averaging from 259-371ppm Th (Western Australia Geological Survey WAMEX database report A 40991).
Capital Mining Limited: The peralkaline granitic intrusions of the Narraburra Complex 177km northwest of Canberra contain anomalous amounts of zirconium, REO and low concentrations of Th (73.2Mt at 1250 grams per tonne (g/t) ZrO2, 146g/t Y2O3, 327g/t REO, 45g/t HfO2, 126g/t Nb2O5, and 61g/t ThO2, Capital Mining Limited Prospectus 2006). The thorium oxide (ThO2) content amounts to 4465 tonnes (2420 tonnes Th). In the March quarterly report in 2010, Capital Mining reported that it was conducting metallurgical test to recover hafnium (Hf), Th, tantalum (Ta), niobium (Nb), neodymium (Nd) and cerium (Ce).
Data on the thorium content of carbonatite intrusions in Australia is sparse. Mount Weld and Cummins Range in WA have the most significant rare earth resources reported for carbonatites in Australia to date, with both having some thorium content.
Lynas Corporation Ltd: The Mount Weld deposit in WA occurs within a lateritic profile developed over an alkaline carbonatite complex. On 12 January 2012, Lynas reported Measured, Indicated and Inferred REO resources for the Central Lanthanide deposit at a cut-off of 2.5% REO of 14.949Mt at 9.8% REO including Y2O3. The ThO2 content of the deposit is estimated to be 712ppm, which equates to 626ppm Th (personal communication B Shand, Lynas Corporation Ltd (Lynas) 17 June 2009).
An updated resource for the Duncan Deposit in the weathered carbonatite complex stands at 8.992Mt of Measured, Indicated and Inferred Resources at 4.8% REO including Y2O3. The ThO2 content is estimated to be 441ppm (388ppm Th). In another part of the carbonatite complex there are 37.7Mt of mostly Inferred Resources grading 1.07% Nb2O5, total lanthanides at 1.16% and 0.09% Y2O3, 0.3% ZrO2, 0.024% Ta2O5, 7.99% P2O5 and a ThO2 content of 479ppm (421ppm Th).
Kimberley Rare Earths Ltd: On 13 February 2012, Kimberley Rare Earths Ltd announced a revised Inferred Resource for the Cummins Range in WA carbonatite deposit of 4.9Mt at 1.74% REO, 11.2% P2O5 145ppm U3O8 and 48ppm Th. The resource was calculated at a cut-off grade of 1% REO. In other parts of the deposit historic sample analyses recorded in open file report A16613 in the Geological Survey of Western Australia WAMEX database averaged about 500ppm Th in the top 48m of weathered zone in one drill hole. Thorium-rich zones of 200-400ppm Th were intersected in two drill holes in fresh carbonatite and carbonated magnetite amphibolite to depths of 400m.
Hastings Rare Metals Ltd: The Yangibana ferrocarbonatite-magnetite-rare earth element bearing dykes in WA (termed ironstones) crop out over an area of 500 square kilometres and form part of the Gifford Creek Complex. The dykes are part of a carbonatitic episode which intrudes the Proterozoic Bangemall Group. The ferrocarbonatite-magnetite-rare earth element bearing dykes occur as lenses and pods and are typically the last stage of carbonatite fractionation and are enriched in rare earth elements, fluorite and uranium-thorium mineralisation. The Yangibana prospect has a historic (1989) recorded resource of 3.5Mt at 1.7% REO. The rare earths are in coarse grained monazite containing up to 20% Nd2O5 and 1600ppm Eu2O3. Whole rock chemical analyses of 21 ironstone samples collected from five prospects in the Yangibana area recorded more than 1000ppm Th for 10 of the samples (1062ppm to 5230ppm Th).
There has been no widespread exploration for thorium in Australia. However, thorium is a significant component of some deposits being explored for other commodities. Thorium is present in the Nolans Bore deposit in the NT and in the Toongi intrusives complex in NSW. In April 2011, Centius Gold reported low altitude airborne thorium and uranium anomalies over the northern rim of its Bethungra Caldera prospect which was claimed to resemble similar airborne radiometric anomalies over Alkane's Dubbo (Toongi) zirconium-rare earth project to the north. Drilling by Chinalco Yunnan Copper Resources Ltd at the Elaine deposit copper-cobalt-gold south of Mary Kathleen deposit in Queensland has intersected up to 827ppm ThO25.
There is no production of thorium in Australia, but it is present in monazite being mined with other minerals in heavy mineral beach sand deposits.
Between 1952 and 1995, Australia exported 265 kilotonne (kt) of monazite with a real export value of $284 million in 2008 dollars (Australian Bureau of Statistics 2009)6. Most of the monazite was exported to France for extraction of rare earth elements, but the monazite plant in France was closed because its operators were unable to obtain a permit for the toxic and radioactive disposal site.
In current heavy mineral sand operations, the monazite fraction is returned to mine site and dispersed to reduce radiation as stipulated in mining conditions. However, in June 2012, Astron Corporation Ltd indicated in an investor presentation that it intends to export 10 000 tonnes of monazite per year to China from its Donald heavy mineral sand deposit4. Astron also reported on 18 June that its zircon product from the Donald deposit contains about 1000ppm U+Th which they intend to export to China where it will be leached to bring the U+Th content down to 500ppm raising the possibility that this process could lead to some uranium and thorium by-product7.
The Organisation for Economic Cooperation and Development/Nuclear Energy Agency (OECD/NEA) and International Atomic Energy Agency (IAEA) (2012) have revised estimates of thorium resources on a country-by-country basis. The OECD/NEA report notes that the estimates are subjective as a result of the variability in the quality of the data, much of which is old and incomplete. Table 1 has been derived by Geoscience Australia from information presented in the OECD/NEA & IAEA analysis.
OECD/NEA & IAEA (2012) have grouped thorium resources according to four main types of deposits as shown in Table 2. Thorium resources worldwide appear to be moderately concentrated in the carbonatite type deposits, accounting for about 30% of the total. The remaining thorium resources are more evenly spread across the other three deposit types in decreasing order of abundance in the placers, vein type deposits and alkaline rocks. In Australia, a larger proportion of resources are located in placers where the heavy mineral sand deposits account for about 70% of the known thorium resources.
|Region||Country||Identified Thorium Resources (In situ)* ('000 tonne Th)||Total thorium for regions and the world ('000 tonne Th)|
|United States of America||434|
|Commonwealth of Independent States (excluding Russian Federation European part but includes the CIS countries below)||1500|
|- Russian Federation Asian part||>100|
*Sources: Data for Australia compiled by Geoscience Australia; estimates for all other countries are from: OECD/NEA & IAEA, 2012: Resources, Production and Demand. OECD Nuclear Energy Agency & International Atomic Energy Agency.
|World deposit In situ||Australian deposits In situ (recoverable)|
|Major deposit type||Resources (1000 tonnes Th)||Percentage||Resources (1000 tonnes Th)||Percentage|
|Placer deposits||1500||24.7||371 (334)||69.7|
|Vein-type deposits||1300||21.4||81.5 (73)||15.3|
|Alkaline rocks||1120||18.4||51 (46)||9.6|