On the Brink of Realisation
The ore body is located on the convex margin of a major bend in the Yarramba Palaeochannel and is situated within coarse grained basal sand where it is pinched out between the overlaying clay and palaeo valley slope at a depth of about 110 m.
The Yarramba Palaeochannel is comprised of three sub-horizontal permeable sand layers, the upper, middle and basal aquifers. These are separated by clay layers, with the uranium mineralisation occurring mainly in the basal sand unit. The aquifers contain water of distinctly different composition. The upper aquifer has some potential for stock watering, but the middle and basal aquifers are unacceptable for stock due to the high sulphate, chloride and radium content.
History of the Project
Exploration for Tertiary sandstone uranium in the Southern Lake Frome Embayment was commenced in the late 1960s by Carpentaria Exploration P/L, EA Rudd Pty Ltd and Sedimentary Uranium NL. They were joined in the early 1970s by Mines Administration P/L and Teton Exploration Drilling company (the Minad Teton Joint Venture). The exploration philosophy of these groups followed that successfully employed in the Tertiary basins of Wyoming in the USA.
Regional assessment identified potentially favourable buried fluviate sands adjacent to uranium enriched source rocks. The genetic model assumed leaching from permeable sands, transport down the hydrological gradient and deposition at a reduction oxidation interface. Exploration methods employed open hole rotary drilling and wireline geophysical logging as a reconnaissance exploration method. Other methods, such as surface resistivity and gravity surveys were also used to locate and map tertiary palaeochannels.
In 1970, Sedimentary Uranium discovered the East Kalkaroo deposit and the Yarramba deposit. By November 1972 the Minad Teton JV had discovered Honeymoon, and by 1973 the Goulds Dam deposit had been identified. Because of the size, grade and configuration of the Honeymoon deposit, it was decided that the key to the development of these deposits was the successful demonstration of the in situ leaching technique to recover uranium oxide.
From here on the project went through a number of stages as data were acquired, the ore body delineated and feasibility studies concluded. The project was now run by a joint venture consisting of two major Australian companies and a small North American exploration group, and it would be fair to say that progress was slow due to problems associated with one of the partners' financial situation. The delays that this situation caused were quite important in the project missing the window of opportunity to commence operations. Key events were as shown in Table 2.
In the period from 1983 until 1996 the Labor Party remained in power
in Australia and the uranium industry remained in the doldrums. With the
change in government in March 1996 and the abandonment of the Three Mine
Policy, companies were able to dust off the old files and to look at what
was happening in the world of uranium.
In May 1996 Sedimentary Holdings, now a gold mining company, commissioned a study into the significance of its uranium interests in area EL 2310. The study concluded that whilst ISL treatment of the uranium at East Kalkaroo was feasible, there was a strong case for amalgamating the uranium interests in the area. Accordingly a strategy was implemented resulting in the consolidation of the Honeymoon, Goulds Dam and tertiary uranium in EL 2310 under the ownership of Southern Cross Resources Australia P/L, which is wholly owned by Southern Cross Resources Inc of Canada. Sedimentary Holdings owns some 35% of Southern Cross Resources Inc. Southern Cross Resources took possession of the Honeymoon and Goulds Dam properties, and the balance of the EL 2310 deposits, from former owner MIM on 15 May 1997.
Present Plans
The present plans for the development of the Honeymoon property are similar to those that were outlined in the environmental impact statement (EIS) that was approved back in 1981, utilising the plant, albeit rehabilitated, that was built in 1982.
It is anticipated that the development will proceed in three stages:
Whilst there has been some wear and tear as a result of the passage of time, the main effort required to bring the plant up to operational standard is the reinstallation of those items of equipment that were removed as part of the mothballing process. These are the camp and accommodation buildings, the water supply, the power supply and other services, along with miscellaneous equipment and transport. It is anticipated that the plant refurbishment will be sufficiently advanced to commence commissioning the plant for the demonstration phase in December 1997.
The demonstration phase of the programme will involve running the plant at a rate of 25 litres per second for a period of approximately 18 months, during which time the operators and Southern Cross Resources technical staff will develop an understanding and an appreciation of the subtleties of ISL operations.
During this period a revised EIS will be submitted to the state and federal authorities to cover the operations as they develop at Goulds Dam, Honeymoon and in EL 2310. The exact duration of the demonstration phase will to some extent be dependent upon what is found to be of significance in terms of well field management and the rate of extraction of uranium.
The commercial operation phase of the programme will follow a plant expansion to lift production to approximately 100 litres per second (equivalent to 460 t U3O8 per year) or higher, depending upon the results of the demonstration phase and the market situation. It is anticipated that the commercial process plant will be an extension of the existing demonstration plant, incorporating some more up to date high capacity mixer settler combinations and vacuum drying of the yellowcake product.
The Production System
The production system to be employed at Honeymoon is the solution mining technique that has come to be known generally in the uranium production industry as in situ leaching (ISL). This technique was developed in the United States and now accounts for around 95% of all US uranium production.
To be amenable to solution mining a uranium deposit must have the following characteristics:
In the solvent extraction section the uranium is concentrated in an organic phase from where it is stripped to a final aqueous phase from which it is precipitated with a combination of sodium carbonate and hydrogen peroxide as uranyl peroxide. This product is dried and shipped as a traditional yellowcake product to the conversion facility. A diagrammatic flowsheet of the in situ leaching system is shown as Figure 2, and a detailed flowsheet of the extraction plant is shown as Figure 3.
The Honeymoon deposit has the desirable characteristics for an in situ project, as indicated in Table 3. These are shown in comparison with similar operating mines in the United States.
Conclusion
It is now 26 years since the discovery of the Honeymoon and associated uranium deposits in the Curnamona Province of South Australia, and the project has yet to be commercialised. Later and larger discoveries such as Olympic Dam have been developed during a period when the impediments to uranium mining were the politics of Australian uranium policy. With the end of the Cold War and the significant reductions now under way in weapons stockpiles, the agreement of the nuclear test ban treaty and the perceived reduction in the threat of nuclear war, there appears to be a reduction in the opposition to nuclear power.
Superimposed on this scenario is the perception that greenhouse gas emissions from conventional thermal power stations are contributing to climate change. One feels that in some areas the nuclear power option will achieve higher levels of production in the coming century. Southern Cross feels that the sentiment towards uranium mining has changed in Australia, although the regulatory and environmental controls are tending to get tighter rather than more relaxed.
Southern Cross is optimistic that it will be able to negotiate the barriers that face all potential uranium producers, that the demonstration stage of the Honeymoon operation will commence operations in January 1998, and that the project will be in operation on a commercial basis by the millennium. We expect that the operation has the potential to rank in the bottom quartile of world wide uranium production costs.
Refurbishment of the existing facilities has commenced, with the appointment of Ausenco Limited as engineers for the plant refurbishment programme. The initial site assessment has been completed with the plant being considered to be in remarkably good condition for its age.
Basically the technique involves the recirculation of treated groundwater through the uranium bearing sandstone formation to oxidise the uranium and put it into a solution, which is pumped to the extraction plant where the uranium is removed from the leach solution by solvent extraction. The stripped solution is recharged with oxidant and recirculated back to the ore body.