Australia, land of uranium - plans to supply the nuclear industry
With a growing global nuclear industry, uranium-rich Australia has a key supply role to play. Alan Eggers, CEO of Manhattan Corporation Limited, tells Michael Forrest how the company plans to access the country’s bountiful uranium deposits.
With 436 active, power-producing nuclear reactors around the world, as well as 62 under construction and a further 167 planned, nuclear energy has an undeniable role in our future. Some new plants will replace those coming to the end of their life, but the rest will add an additional 49% to the global nuclear energy supply. This increase will require a steady inflow of nuclear resources, a demand that Australia seems well equipped to meet.
Australia became the world’s third largest uranium producer (following Kazakhstan and Canada), after, in 2008, the Western Australia Liberal government rescinded the previous (Labour) government’s ban on uranium mining. Since then, exploration for the element has gathered pace. Uranium mining itself is not new to Australia, and has been taking place in some form since the Rum Jungle deposit was discovered in the Northern Territories in 1949 and subsequently mined in the 1950s. Australia hosts the world’s largest uranium mine and deposit, Olympic Dam in South Australia, but as yet no commercial production has taken place in Western Australia. ‘This might change with the Project of Manhattan Corporation,’ says the uranium exploration and resource development company’s CEO, Alan Eggers.
In terms of geological history, the landscape of area to the north east of Kalgoorlie at the edge of the Great Victoria Desert has hardly changed since the mid-Miocene (around 13Ma), when arid conditions began to prevail. Earlier in the Eocene (55–33Ma) the climate was warm and humid, resulting in the development of river channels and marshland that were infilled by sediments derived from the surrounding Yilgarn Craton. The distribution of the river channels was predetermined by differential erosion of underlying Permian-aged mudstones that rest directly on the basement. These 50-million-yearold-river channels, or palaeochannels, were then in filled with unconsolidated carbonaceous sands and organic debris 2–20m thick, subsequently overlain by 50–60m of impermeable Eocene claystone, mudstone and sandstone.
Fast forward to the present day, and Western Australia-based Manhattan Corporation now has extensive (2,600km2) 100% owned licence areas over these buried palaeochannels, which form a branched system trending NNE–SSW from the Mulga Rock uranium prospect in the north to Ponton in the south, over a distance of more than 40km. To find the deposits buried in this system, the company has been exploring using airborne electro-magnetic and magnetic surveys, combined with drilling and down-the-hole logging of gamma radiation. It is from these logs, in more than 850 drill holes along 55km of palaeochannels, that a resource estimate has been calculated using the gamma equivalent uranium (eU308), multiplied by a disequilibrium factor of 1.2 to give U308 concentrations, according to well established practice.
Manhattan has focused on eight areas of the paleochannels that define the Ponton project. These are at different stages of development, with the Double 8 uranium deposit being the most advanced, having a JORC-compliant inferred resource grading of 300ppm. This ultrafine-grained uranium mineralisation is within organic complexes found buried in the paleochannels in the form of reduced carbon-rich sands, resting upon weakly mineralised and weathered basement rocks (Archean granitic rocks and Patterson Group shales) that are overlain by Eocene clay, mud and sandstone. Preliminary mineralogical studies of the Ponton deposits indicate that the uranium is held in the minerals coffinite [U(SiO4)1-x(OH)4x] and davidite [(La,Ce,Ca)(Y,U)(Ti,Fe3+)20O38]. The element shows a strong correlation with iron affinity minerals (pyrite, rutile, ilmenite) and with carbon. The uranium-bearing sands were deposited in a reducing environment, giving rise to horizontal tabular orebodies. Taking Double 8 as standard, the mineralisation is found at depths from 30–70m and extends for several kilometres along the palaeochannel, some 3–25m thick and 200–1,500m wide.
The engineering challenge
As ever, gaining access to the uranium presents an engineering challenge. The 3D geomorphology of the deposit would allow open-pit mining but the grade, depth of overburden and sinuous nature could present difficulties. Eggers says, ‘Their shape, shallow depth, presence of a seal aquifer, permeability, porosity and mineralogy, however, does favour in-situ leaching, with impervious layers both above and below the uranium-bearing sands that have a natural porosity derived from their depositional environment.’ Uranium minerals are in the main soluble in both weakly acidic and alkali groundwater and can be recovered using a system of injection and pumping of lixiviants. This method is in-situ leaching (ISL), a well developed and mature technology that underpins the majority of uranium production in Kazakhstan (the world’s largest uranium producer), the Frome Basin in South Australia and Texas in the USA.
Unlike American uranium mines, where alkali solution systems (using oxygen and carbon dioxide dissolved in groundwater) are mainly used, ISL facilities in South Australia mostly use the acid route, as alkali solutions were found to swell clays in the orebody and consequently reduce porosity. The acid process relies on the injection and pumping of weak sulphuric acid into groundwater to give a pH in the range 2.0–2.8. Manhattan’s Ponton project proposes to use acid leach, with acid consumption estimated to be reduced due to a low carbonate content of 0.044%. As coffinite holds uranium in the tetravalent state, an oxidant will be required to obtain a solution. Furthermore, uranium in davidite can only be recovered via the acid route.
As in all ISL projects, hydrogeology is the key factor. At Ponton, in common with most of Western Australia, the groundwater is hypersaline, around five times that of seawater. Analysis from borehole samples indicates that although the groundwater is weakly acidic (around pH 5.0) it contains 10% chloride, 7.5% sodium, 1.6% sulphates, 0.75% magnesium and 0.5% sulphur for a total dissolved content in the range 70–160g/l. These dissolved salt levels will have a detrimental effect on the conventional standard resins used in ISL uranium recovery, so Manhattan proposes to apply the latest in resin technology, using resins and pulse column technology specifically designed to deal with hypersaline conditions. These are already being successfully used in the operating Honeymoon ISL uranium mine in South Australia.
The most common ISL technique for uranium recovery is ion exchange resins. Economic to use, they only require a small concentration of the uranium-containing groundwater, or pregnant liquor solution (PLS). However, in the case of high solute loading, the solutes are preferentially attached on the resin sites, therefore denying sites of attachment to the uranyl complexes, resulting in low uranium recoveries. There are a number of newer resins that can tolerate such loading, for example the Dow Chemical Ambersep 940U resin that is resistant to chloride concentration of up to 50g/l, and possibly 100g/l. Another option is to pre-treat the pumped groundwater via a reverse osmosis facility, to remove the salinity and dispose onsurface the ‘clean’ water plus lixiviant that is then being pumped into the injection borehole, thus creating clean ore ready to be leached. This method worked well at Intercontinental Energy Corporation’s Zamzow plant in Texas.
As of the end of January 2013, Manhattan has reported an inferred resource at Double 8 of 17.2Mlbs of uranium oxide. This comprises only part of the 55km of palaeochannels within the Ponton licence areas, where additional estimates of uranium content are in the range 33–67Mlbs, adding up to a resource target inventory of around 85Mlbs. Additional drilling and disequilibrium test work are likely to add to the substantial resource inventory at Ponton. A recent scoping study undertaken by engineering consultants Tetra Tech concluded that Ponton near-surface deposits have the potential to be sustainable low-cost ISL producers. ‘There is some way to go, as we need to upgrade the resources in the remaining projects and establish the final process route,’ says Eggers. The country’s strong position in the big league of uranium producers will be enhanced when recovery is secured in Western Australia.