Thorium

Content maintained by Yanis Miezitis

• Thorium
• Resources
• Exploration
• Production
• World Ranking

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, welding electrodes and in heat resistant ceramics.

Thorium also can be used as a nuclear fuel through breeding to U²³³. Several reactor concepts based on thorium fuel cycles are under consideration, but much development work is required before it can be commercialised. Early in April 2008, India commissioned a critical facility designed to conduct experiments to validate reactor physics for a 300 megawatt electric (MWe) technology demonstrator thorium-fuelled Advanced Heavy Water Reactor (AHWR). The facility was fuelled with natural uranium and went critical in early April 2008. Natural uranium fuel will be used to simulate Pressurised Heavy Water Reactors and thorium-uranium 233 fuel will be used to simulate the AHWR. However, full commercialisation of the AHWR is not expected before 2030.

The critical facility can be used also for experiments to simulate an Accelerator Driven System which can be used to burn thorium.

A research program at Moscow's Kurchatov Institute involves the United States company, Thorium Power Ltd, and is supported by United States Government funding to develop thorium-uranium fuel for the existing Russian Vodo-Vodyanoi Energetichesky (VVER-1000) reactors. While normal fuel uses enriched uranium oxide (UO₂), the new design has a demountable centre portion and blanket arrangement, with plutonium fuel in the centre surrounded by a blanket of thorium uranium fuel. The Th²³² becomes U²³³, which is fissile, as is the core Pu²³⁹. Blanket material remains in the reactor for nine years but the centre portion is burned for only three years (as in a normal VVER) (World Nuclear Association Information Paper - Thorium, March 2008).

One of the main objectives of this program is to eliminate weapons grade plutonium by using it as thorium-plutonium fuel in nuclear reactors. More recently, (Platts Nuclear Fuel 19 November 2007), Thorium Power Ltd stated that it was shifting the emphasis of its thorium fuel development to commercial deployment of thorium-based fuel in the United States.

Thorium Power Ltd has successfully completed a three year test of experimental thorium fuel rods and is planning further testing to qualify the fuel for widespread use, initially in VVERs, then in other current light water reactors (World Nuclear News, 22 March 2007).

The company says that because parts of fuel assemblies can remain in a reactor for up to nine years, more of the highly-radioactive actinides produced by fission are burnt, resulting in a 50% reduction in waste volume and a 90% reduction in waste toxicity. As a result, waste storage time is reduced to between 100 and 800 years. There also is a 10-20% improvement in fuel savings versus a conventional uranium fuel cycle (personal communication Dr A. Mushakov, Thorium Power Ltd, October 2007).

Thorium Power Ltd is planning further testing to qualify the fuel for widespread use - first in VVERs, then in other current light water reactors. The research program is on track for deployment of lead test assemblies within three years.

Atomic Energy of Canada Limited (AECL) claims that its Advanced CANDU Reactor (ACR) 1000 reactors of 1080 to 1150 MWe will have the flexibility to use a variety of fuels including natural uranium, low enriched uranium, thorium and DUPIC (Direct Use of Spent Pressurised Water Reactor (PWR) Fuel). AECL noted that it is moving towards certification of ACR 1000 in Canada and the earliest in-service date for an ACR 1000 (Generation III+ 1200 MWe) unit is 2016. However, it is anticipated that use of thorium fuel will be in a later stage. In the shorter term, some jurisdictions are assessing the use of thorium cycles in existing CANDU 6 (700 MWe class) reactors.

There are no comprehensive detailed records on Australia's thorium resources because of the lack of large-scale commercial demand for thorium 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 dispersed back through the original host sand (to avoid the concentration of radioactivity) when returning 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.

Most of the known resources of monazite are in Vic and WA. Mining of heavy mineral sands has begun in the Murray basin deposits at Ginkgo in NSW and at Douglas in Vic while construction of another inland heavy mineral mine is well under way at Mindarie in SA.

Using available data, Geoscience Australia estimates Australia's monazite resources in the heavy mineral deposits to be around 6.2 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:

• Analyses for monazite and thorium in published and unpublished reports;
• published and unpublished analyses of thorium content in exported monazite concentrates; and
• monazite and thorium analyses on heavy mineral sand deposits in company reports on open file available at some State Geological Surveys.

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 was not available, regional data were applied to individual deposits to estimate their monazite and thorium resources. Using this information, Australia's inferred thorium resources in the mineral sands were estimated to be around 376,000 t.

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. A significant example is the Nolans Bore rare earth, phosphate uranium deposit in NT, which is in fluorapatite veins and dykes This deposit contains about 60,600 t of ThO₂ (53,300 t of Th) in 18.6 Mt of indicated and inferred resources grading 3.1% rare earth oxides, 14% P₂O₅, 0.021% U₃O₈ and 0.326% ThO₂.

In NSW, the Toongi alkaline trachyte plug is located 30 km south of Dubbo and hosts 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 t contained Th.

Similarly the peralkaline granitic intrusions of the Narraburra Complex 177 km north west of Canberra contain anomalous amounts of zirconium, REO and low concentrations of thorium (55 Mt at 1000 g/t ZrO2, 60 g/t Y₂O₃, 300 g/t REO, 40 g/t HfO2, 80 g/t NbO2, and 50 g/t ThO₂).

Other alkaline complexes with known rare earth and thorium mineralisation include Brockman in WA. It is a large low-grade Zr-Nb-REE deposit hosted in altered trachytic tuff of Palaeoproterozoic age containing mineralised material of 50 Mt at 4400 ppm Nb, 270 ppm Ta, 1.04% Zr, 1240 ppm Y, 350 ppm Hf, 110 ppm Ga and 900 ppm REE (Aztec Resources Ltd, 2004 Annual Report). 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 16m to 28m averaging from 259 to 371 ppm Th (Geological Survey of Western Australia WAMEX database report A 40991).

Data on the thorium content of carbonatite intrusions in Australia is sparse. Mt 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.

The Mt Weld deposit in WA occurs within the regolith profile developed over the carbonatite and has a resource of 273 Mt at 0.9% Nb₂O₅. Tantalum is usually, but not always, associated with niobium, and the estimated resource amounts to 145 Mt at 0.034% Ta₂O₅. The typical thorium content is reported to be about 600 ppm Th (~0.069% ThO₂ - Carr Boyd Minerals Limited, Mt Weld project promotion brochure, April, 1991). More recently Lynas Corporation Ltd quoted an REO resource of 7.7 Mt at 12% REO with a ThO₂ content of 44ppm per 1% REO which works out about 464 ppm Th. (Investor Presentation: January 2008).

In March 2008, Navigator Resources Ltd reported inferred resources for Cummins Range in WA carbonatite deposit of 3.55 Mt at 2% REO, 11.2% P₂O₅ 216ppm U₃O₈ and 36 ppm Th. However in other parts of the deposit, 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 48m of weathered zone in one drill hole. Thorium-rich zones of 200 to 400 ppm Th were intersected in two drill holes in fresh carbonatite and carbonated magnetite amphibolite to depths of 400 m.

The Yangibana ferrocarbonatite-magnetite-rare earth-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-bearing dykes occur as lenses and pods and are typically the last stage of carbonatite fractionation and are enriched in REEs, fluorite and U-Th mineralisation. The Yangibana prospect has a recorded resource of 3.5 Mt at 1.7% REO. The rare earths are contained 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).

Australia's total indicated and inferred resources amount to about 485,000 t Th.

As there is no established large scale demand and associated costing information for thorium, there is insufficient information to determine how much of Australia's thorium resources are economically viable for electricity generation in thorium nuclear reactors.

There has been no widespread exploration for thorium in Australia apart from two exploration licences which have been reported as being primarily for thorium exploration in Qld.

However thorium is a significant component of some deposits being explored for other commodities. As mentioned above, thorium is present in the Nolans Bore deposit and in the Toongi intrusives complex. Heavy mineral concentrations within the King Leopold Sandstone and the Warton Sandstone, which constitute the Durack Range uranium project, also contain up to 2% thorium in the heavy mineral concentrate (Northern Mining Limited - announcement to the Australian Stock Exchange 21 March, 2007).

There is no production of thorium in Australia, but it is present in monazite currently being mined with other minerals in heavy mineral beach sand deposits. Prior to 1996, monazite was produced from heavy mineral sand operations and exported for extraction of rare earths but is no longer considered to be a commercially viable source of rare earths because of the disposal costs associated with the radioactive material containing thorium.

OECD/NEA (2006) has compiled estimates of thorium resources on a country-by-country basis. The OECD/NEA report notes that the estimates are subjective due to variability in the quality of the data, a lot of which is old and incomplete. Table 1 has been derived by Geoscience Australia from information presented in the OECD/NEA analysis. The total identified resources refer to RAR plus inferred resources recoverable at less that US$80/kg Th. The table below includes quantitative estimates of some countries undiscovered thorium resources.

Table 1. Estimated thorium resources by country

Sources: Data for Australia compiled by Geoscience Australia; estimates for all other countries are from: OECD, 2006: Red Book Retrospective. A review of Uranium Resources, Production and Demand from 1965 to 2003.

OECD/NEA & IAEA (2006) 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 world total.

Table 2. World and Australia's thorium resources according to deposit type (modified after OECD/NEA & IAEA (2006))

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 is located in placers where the heavy mineral sand deposits account for about 80% of the known thorium resources in Australia.