Luis López reports that historically, uranium resources in Argentina have been classified and reported according to the Organisation for Economic Co-operation and Development (OECD) Nuclear Energy Agency (NEA)/IAEA resource reporting scheme (the ‘Red Book’) [3] In 2011, the National Atomic Energy Commission of Argentina (CNEA) reported about 20,000 t of uranium (tU) as identified resources (reasonably assured resources + inferred resources) for the production cost category <US $130/kgU. In addition, about 11,000 tU of Canadian National Instrument 43-101 [10] certified resources have been reported in recent years by public mining companies [11, 12] (Figure 2). The total uranium resources of Argentina are thus approximately 31,000 tU in the aforementioned identified resources category (Table 6).
UNFC-2009 allows the documentation and reporting of these uranium resources of the country. UNFC-2009, in addition to providing the project maturity of resources, considers social and economic issues, including regulatory, legal and market conditions imposed by governments and markets, domestic demand, technological and industrial progress and the ever-present uncertainty.
For the uranium resources of different projects of the CNEA and mining companies, the criteria of UNFC-2009 concerning social and economic viability (E), technical feasibility (F) and geological knowledge (G) were defined at the sub-category level and grouped into major classes considered in this classification system, as shown in Table 7 [2].The identified uranium resources in Argentina are mostly located in the provinces of Chubut and Mendoza. These are areas where no metallic mineral mining projects are in operation. In addition, legislation is in place that markedly restricts uranium production, which needs to be taken into account when studying the social viability of the projects. In Chubut, projects need to wait for the Chubut provincial territory zoning provisions of Law 5001/2003, as well as the introduction of a mining regulatory framework for this jurisdiction [13]. Moreover, the operation of uranium mining and processing in Sierra Pintada will require major changes to the legislation, such as permitting of open pit mining and the use of sulphuric acid, which is currently forbidden by Law 7722/2007 [14].
To define the economic feasibility of the CNEA’s projects, uranium prices in the international market are taken as a reference, not as a determining factor, considering that the raw material has a bearing of 5 to 7 per cent in the total cost of nuclear energy in the country. Argentina so far has not pursued the objective to obtain dividends from the sale of uranium in international markets. For domestic use uranium is imported, which has implications for security of supply.
In recent years, an increase in exploration efforts has led to a significant increase in uranium resources and their level of knowledge, especially in the San Jorge Basin, which extends over about 180,000 km2 and hosts not only important uranium deposits, but also oil and gas resources. In the Cerro Solo Deposit (Chubut Province), tonnage and grade estimated is expected to ensure sustained uranium production in the future. This blind deposit was discovered in 1971 and since then, exploration and evaluation drilling programmes have amounted to 100,700 metres. It is located in Cretaceous fluvial sandstones and conglomerates of the Chubut Group. In this paleochannel structure, the mineralized levels are 0.5-6 metres wide and 50-130 metres deep. The identified resources are 9,230 tU at approximately 0.2 per cent U, included in the <US $130/kg U production cost category (cost category as applied in [2]). The reported resources correspond to the two most studied mineralized bodies and the available geological knowledge indicates very good perspectives to develop new uranium resources in this mining property [15, 16, 17, 18] (Figure 3).
Currently, a program to complete the feasibility study of the Cerro Solo Deposit is being carried out. As background, in 1997 the CNEA retained NAC International to complete a pre-feasibility study of the Cerro Solo uranium Deposit, including geological model revision and ore reserves estimate, mining and milling methods and their costs, cash flow and risk analysis [19]. Also, the social-environmental baseline is being surveyed in cooperation with national universities and research councils.
Regarding by-products, it can be mentioned that though economic recovery of molybdenum has not been defined for the Cerro Solo Deposit, the potential economic benefits of income from this process justify further research and evaluation in both the extent of molybdenum reserves and its recovery. In addition, anomalous assays of rhenium were detected in Cerro Solo, and its potential should be the subject of further research.
T
he Sierra Pintada uranium Deposit (Mendoza Province) belongs to the volcanic-related model, where mineralization is localized in Permian formations associated with synsedimentary acid volcanism [20, 21]. The level of uncertainty in the estimation of remaining resources in Sierra Pintada is medium to high, which are evaluated to be 10,010 tU recoverable at a production cost below US $130/kg U [22].
This deposit has been the focus of the most important uranium exploitation in the country, with a total production of 1,600 tU from 1975 to 1997, when the mining-milling facility was put in stand-by status for economic reasons. Therefore, feasibility has been partially demonstrated by the fact that this deposit was previously in operation, using an acid heap-leaching mining method. However, other alternatives have been considered for possible future production, including the use of alkaline leaching [23], bioleaching [24] and vat leaching [25] (Figure 4).
The Laguna Salada project (Chubut Province) includes the Guanaco and Lago Seco areas, corresponding to a surficial uranium-vanadium deposit. Mineralization occurs within 3 metres from the surface in soft, unconsolidated gravel. Uranium identified resources have been evaluated at 3,880 tU at grades ranging between 55 and 72 ppm U, while vanadium identified resources have been evaluated at 21,330 tV at grades ranging from 308 to 330 ppm V. Initial metallurgical results show uranium and vanadium grades are increased between 3 and 11 times by simple screening, followed by rapid uranium-vanadium extraction using alkaline leaching in the Guanaco area of the deposit, while acid leach is very effective in the Lago Seco area.
Recently, U3O8 Corporation has reported a favorable preliminary economic assessment (PEA) for the Laguna Salada Deposit (Figure 5), based on previous NI 43-101 report, taking into consideration U-V comprehensive extraction. However, it can be considered that the PEA includes around 40 per cent inferred resources; to the extent that follow up exploration activities can increase resources and their geological knowledge, the project could move to a UNFC-2009 Class of “potentially commercial projects” [26, 27].
Meseta Central project (Chubut Province) is located in the vicinity of Cerro Solo and comprises the Graben, Plateau West and Plateau East Deposits. Uranium mineralization is hosted by siltstones, sandstones and conglomerates of the fluvial and lacustrine origin of the Cretaceous-aged Los Adobes Formation. Mineralized layers lie between 40 and 140 metres beneath the surface, are flat-lying or very gently dipping, and are up to 15 metres in thickness [28]. The total inferred resources for the project are 7,350 tU at an average grade of 260 ppm U. These resources used data from two drilling campaigns comprising 178 boreholes for a total of 21,450 metres of drilling. Boreholes are mostly on a 200 by 200 metres grid. As reported by UrAmerica Ltd., about 75 per cent of the uranium resources evaluated are placed in confined aquifers layers. Therefore, further geological and hydrological studies will be addressed to determine the amenability to in situ leaching mining. The results of these studies could play a relevant role regarding the socio-economic viability of this project (Figure 6).
The Don Otto (Salta Province) uranium Deposit is a tabular U-V subtype, occurring in the Cretaceous Yacoraite Formation of the Salta Basin; this basin covers approximately 150,000 ha, and is also known for its oil and gas potential. Don Otto was in operation from 1963 to 1981 and produced 201 tU at 0.1 per cent-0.2 per cent U grade [29, 30]. When mapping to the E, F and G axes, the Don Otto Deposit is classified as a “non commercial project” where development is not clarified. However, it should be highlighted that as this deposit was previously in operation and current exploration/evaluation studies yielded very encouraging results, it could be possible in the future to move the project to a higher UNFC-2009 Class. Additionally, enlargement of the mining property and resource augmentation are considered key factors to ensure the project feasibility. A comprehensive study that includes updating environmental impact assessment (EIA) reports, block-leaching research and development studies, feasibility of underground extraction, use of mobile ionic exchange plant, and uranium recovery from the former heaps and remediation of the site, are all factors that would aim in the same direction of increasing project viability [31, 32] (Figure 7).
The limited resources of Laguna Colorada (Chubut Province) [16] make it difficult to envisage extraction at present, unless the characteristics of the ore will allow treatment in a plant that may in the future be located in the area of Cerro Solo (Figure 8).
Ultimately, the Cerro Solo project appears to be the most promising uranium project in Argentina, and with realistic assumptions of possible market conditions and obtaining social license, there are prospects for extraction in the near future.
The application of UNFC-2009 as a complement to the NEA/IAEA classification contributes to both a better understanding of the availability of reliable resources in Argentina as well as how these resources can contribute to the national nuclear energy program.
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