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 dependent 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 94% complete in February 2013. 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% 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% 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 20131 ; Kakodkar 2009)2 .
It was also reported that design studies are proceeding in India for a 200 MWe PHWR (Pressurised Heavy Water Reactor) accelerator-driven system (ADS) fuelled by natural uranium and thorium 1.
In January 2011, the China Academy of Sciences launched a research and development program on Liquid Fluoride thorium reactor (TR), known at the academy as the thorium-breeding molten-salt reactor (Th-MSR or TMSR). A 5 MWe MSR is believed to be under construction at Shanghai, with an operational target date of 2015 and a 2MWe accelerator-driven sub-critical prototype has also been reported. The US Department of Energy is collaborating with the Academy on the program, which had a start-up budget of US$350 million.
In July 2009, AECL (Atomic Energy of Canada Limited) 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 (China National Nuclear Corporation) 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 . It was reported by the World Nuclear Association that:
"In August 2012 a follow-on agreement among the parties (CANDU Energy having taken over from AECL) focused on undertaking a detailed conceptual design of the Advanced Fuel CANDU Reactor (AFCR), which is described as "a further evolution of the successful CANDU 6 and Generation III Enhanced CANDU 6, optimized for use of recycled uranium and thorium fuel." At the completion of the agreement in two years, the parties “expect to have the basis of a pre-project agreement for two AFCR units in China, including site allocation and the definition of the licensing basis." Phase one of the AECL agreement was a joint feasibility study to examine the economic feasibility of utilising thorium in the Qinshan Phase III PHWRs. (Geologically, China is better endowed with thorium than uranium.) This involved demonstration use of eight thorium oxide fuel pins in the middle of a Canflex fuel bundle with low-enriched uranium”3.
A demonstration High Temperature Reactor-Pebble Modules (HTR-PM) of 210 MWe (two reactor modules) is being built at Shidaowan in Shandong province. A further 18 units of 210 MWe each are planned and followed by increases in the size of the 210 MWe unit modules including the introduction of thorium in fuels.
At the end of December 2012, Geoscience Australia estimated that Australia's total indicated and inferred in-situ resources of thorium amounted to about 595 000 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% for mining and processing losses in the extraction of thorium, the recoverable resources of Australia's thorium could amount to about 535 500 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 and thorium. However, in current heavy mineral sand operations, the monazite is generally returned to the pit in dispersed form, as required by mining regulations. This dispersion 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 Victoria (Vic)4 . In addition, monazite and xenotime resources were also published by Australian Zircon NL for the WIM 150 and by Crossland Uranium Mines Limited for the Charley Creek deposit in the Northern Territory (NT).
Most of the known resources of monazite are in Vic and Western Australia (WA). Heavy mineral sands are being mined in the Murray basin deposits at Ginkgo and Snapper in New South Wales (NSW) and at Douglas in Vic. 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 7.8 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 by Geoscience Australia 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, Geoscience Australia estimated Australia's inferred in situ thorium resources in the mineral sands to be around 388 800 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.
In addition, monazite and xenotime was also reported by Australian Zircon NL reported to the Australian Stock Exchange on 18 July 2013 in an update of Proved and Probable Reserve totalling 24 million tonnes (Mt) of in-situ heavy minerals at 11.7% rutile, 31.7% ilmenite, 5.9% leucoxene, 21.6% zircon, 2.3% monazite and 0.4% xenotime.
Resources for a new type of placer deposit, the Charley Creek deposit in the NT, containing zircon, monazite and xenotime was reported on 15 May 2012 by Crossland Uranium Mines Ltd. The Charley Creek deposit was reported by the company as an alluvial outwash which comprises an Indicated Resource of 387 Mt 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 (REO). In addition, another 418 Mt of Inferred Resources was reported to hold about 121 000 tonnes of REO 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. On 15 April 2013, Crossland released results of a scoping study which indicated a low capital cost requirement of $156 million including contingency and project infrastructure with a payback of 2.5 years after commencing production. The project is based on a mine life of 20 years, with a drilled resource based on around 1% of the area with exploration potential. Average annual revenue of $154 million at 3645 tonnes equivalent total rare earth oxide (TREO) production.
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 northwest of Alice Springs in the NT. The mineralisation is hosted in fluorapatite veins and dykes. This deposit contains about 81 800 tonnes of thorium in 30.3 Mt of Measured, Indicated and Inferred Resources grading 2.8% REO, 12.9% P2O5, 0.02% U3O8 and 0.27% Th. Arafura is planning to establish an intermediate rare earth chemical processing plant near its Nolans Bore deposit5. In June 2012, Arafura published a revised total Measured, Indicated and Inferred Resource figure of 47 Mt grading 2.6% REO, 11% P2O5 and 0.02% U3O86. 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 120 000 tonnes.
Northern Minerals Ltd: The Wolverine deposit of the Browns Range Rare Earth group is located about 150 kilometres southeast of Halls Creek, WA. On 21 December 2012, Northern Minerals announced Indicated and Inferred Resources totalling 1.44 Mt of ore grading at 0.73% total REO (which includes 4153 parts per million (ppm) Y2O3), 26 ppm U3O8, and 28 ppm ThO2. The main ore mineral is xenotime which occurs within hydrothermal silicified and hematitic breccias. Resource drilling has outlined mineralisation over a strike length of 250 metres and a vertical depth of 250 metres. The resource has a well defined high grade (>1% total REO) central zone which is open at depth. At the cut-off grade of 0.15% total REO, the Indicated Resource has an average grade of 728 ppm Dy2O3 and 4739 ppm Y2O37.
Alkane Resources Ltd: The Toongi zirconium-niobium-rare earth element deposit occurs within a sub-volcanic trachyte horizontal intrusive body approximately 900 metres by 600 metres about 30 kilometres south of Dubbo in NSW8. The deposit has a Measured Resource of 35.7 Mt and 37.5 Mt 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 35.93 Mt 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 and uranium9. 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 1000 ktpa. 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 named Hastings) in WA. It is a large, low-grade zirconium-niobium-rare earth element (Zr-Nb-REE) deposit hosted in altered trachytic tuff of Paleoproterozoic age. On 8 September 2011, Hastings reported 36.2 Mt of Indicated and Inferred Resources grading 8.86 ppm ZrO2, 3.55 ppm Nb2O5, 182 ppm Ta2O5, 110 ppm Ga2O5, 318 ppm HfO2, 186 ppm Dy2O5, 1120 ppm Y2O3, 2102 ppm TREO and 1802 ppm 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 to 28 metres averaging from 259 to 371 ppm Th (Western Australia Geological Survey WAMEX database report A 40991).
Capital Mining Limited: The peralkaline granitic intrusions of the Narraburra Complex in NSW 177 kilometres northwest of Canberra contain anomalous amounts of zirconium, REO and low concentrations of thorium (73.2 Mt at 1250 grams per tonne (g/t) ZrO2, 146 g/t Y2O3, 327 g/t REO, 45 g/t HfO2, 126 g/t Nb2O5, and 61 g/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 18 January 2012, Lynas reported Measured, Indicated and Inferred REO resources for the Central Lanthanide deposit at a cut-off of 2.5% REO of 14.949 Mt at 9.8% REO including Y2O3. The ThO2 content of the deposit is estimated to be 712 ppm, which equates to 626 ppm 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 8.992 Mt of Measured, Indicated and Inferred Resources at 4.8% REO including Y2O3. The ThO2 content is estimated to be 441 ppm (388 ppm Th). In another part of the carbonatite complex there are 37.7 Mt 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 479 ppm (421 ppm 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 4.9 Mt at 1.74% REO, 11.2% P2O5 145 ppm U3O8 and 48 ppm 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 500 ppm Th in the top 48 metres of weathered zone in one drill hole. Thorium-rich zones of 200-400 ppm Th were intersected in two drill holes in fresh carbonatite and carbonated magnetite amphibolite to depths of 400 metres.
Hastings Rare Metals Ltd: The Yangibana ferrocarbonatite-magnetite-REE 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-REE bearing dykes occur as lenses and pods and are typically the last stage of carbonatite fractionation and are enriched in REEs, fluorite and uranium-thorium mineralisation. The Yangibana prospect has a historic (1989) recorded resource of 3.5 Mt at 1.7% REO. The rare earths are in coarse grained monazite containing up to 20% Nd2O5 and 1600 ppm Eu2O3. Whole rock chemical analyses of 21 ironstone samples collected from five prospects in the Yangibana area recorded more than 1000 ppm Th for 10 of the samples (1062 ppm to 5230 ppm Th).
There has been no widespread exploration for thorium in Australia. However, thorium is a significant component of some deposits being explored for in 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 that a low altitude airborne survey detected 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 827 ppm ThO210.
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 kilotonnes (kt) of monazite with a real export value of $284 million in 2008 dollars (Australian Bureau of Statistics 2009)11. Most of the monazite was exported to France for REE extraction, 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 a year to China from its Donald heavy mineral sand deposit. Astron also reported on 18 June that its zircon product from the Donald deposit contains about 1000 ppm U+Th which it intend to export to China where it will be leached to bring the U+Th content down to 500 ppm, raising the possibility that this process could lead to some uranium and thorium by-product12.
In 2012, the Organisation for Economic Cooperation and Development/Nuclear Energy Agency (OECD/NEA) and International Atomic Energy Agency (IAEA) 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 analysis.
OECD/NEA & IAEA (2012) has 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 65% of the known thorium resources.
Resources (In situ)*
|Total thorium for|
regions and the world
|Americas||Brazil||606 - 1300|
|Americas||United States of America||434|
|Americas||Subtotal||1536.3 - 2230.3|
|Europe||Subtotal||1316 - 1459|
|Asia||Commonwealth of Independent States
(excluding Russian Federation European part but
includes the CIS countries below)
|Asia||- Russian Federation Asian part||>100|
|Asia||Others||58.5 - 66.5|
|Asia||Subtotal||2543.5 - 2551.5|
|Africa||Others||40.5 - 50.5|
|Africa||Subtotal||649.5 - 659.5|
|World||TOTAL||6577.3 - 7432.3|
**Sources: Data for Australia compiled by Geoscience Australia; estimates for all other countries modified after OECD/NEA & IAEA, 2012: Resources, Production and Demand. OECD Nuclear Energy Agency & International Atomic Energy Agency.
|Major deposit type||World Th
Resources ('000 tonnes)