About uranium favourability of the basin

From the point of view of the uranium favourability, the geologic-economic model that was developed through the Cerro Solo's investigation provided a useful guide to the exploration of the San Jorge Gulf Basin as a whole, considering that the Chubut Group is widely distributed in this area, covering a total area of 170,000 sq. km (68,000 sq. miles).

Figure 4 represents a map, that indicates the known and inferred development of the fluvial and the tuffaceous systems of the Chubut Group. It also shows the position of the main deposits and group of anomalies that have been studied to some extent [3, 4, 5].

FIG. 4. Main areas of anomalies and deposits.

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REFERENCES

[1] NAVARRA, P., The Cerro Solo Project, IAEA-TECDOC-650, 1992.

[2] NAVARRA, P., BENITEZ, A., Development of the Cerro Solo deposit and Uranium Favourability of the San Jorge Gulf Basin. Province of Chubut. IAEA Tech. Comm.

Meeting, Kiev, 22-26 May. 1995.

[3] FUENTE, A., GAYONE, R., BIANCHI, R., MARVEGGIO, N., PAEZ, M. 1993.

Chubut Group, Cretaceous sedimentites. Unit XLVI. CNEA, Internal Report.

[4] Uranium Geology Working Group, CNEA. Endowment Assessment of Cretaceous Chubut Group Basin. Patagonia Region. Internal Report, 1995.

[5] NAVARRA, P., BENITEZ, A., Eventos en la exploración por uranio de la Cuenca del Golfo de San Jorge, Prov. del Chubut, V Congreso Nacional de Geología Económica, San Juán, 18-22 Setiembre, 1995.

[6] BENITEZ, A., Avances en la exploración del Flanco Oriental de la Sierra de Pichiñán, Internal Report, 1997.

[7] SARDIN, P., URQUIZA, L., Yacimiento Co. Solo. Estimación de recursos uraníferos, análisis económico financiero y alternativa de explotación combinada. CNEA, Internal Report, 1997.

[8] TOMELLINI, G., LUCONI, O., SALDAÑO, R., CARRION, R., ORTEGA, R., Ensayos de lixiviación convencional a testigos de Cerro Solo. CNEA, Internal Report.

1997.

[9] TOMELLINI, G., LUCONI, O., SALDAÑO, R., CARRION, R., ORTEGA, R., Informe de lixiviación estática ácida a testigos chancados del yacimiento Cerro Solo.

CNEA, Internal Report, 1997.

[10] BENITEZ, A., FUENTE, A., MALOBERTI, A., LANDI, V., BIANCHI, R., MARVEGGIO, N., GAYONE, M., Evaluación de la Mina Nuclear Cerro Solo, Prov.

del Chubut. Parte 1: Características geológicas del yacimiento y de la cuenca. XII Congreso Geológico Argentino, Actas T.V: (272-278), 1993.

[11] MARVEGGIO, N., O'CONNOR, E., Estudio estadístico del Miembro Arroyo del Pajarito, para el Sector C del Yacimiento Cerro Solo, Pcia. del Chubut. CNEA, Internal Report, 1995.

BIBLIOGRAPHY

OLSEN, H y BERIZZO, J., El potencial uranífero del Cretácico Continental en la Patagonia Extrandina de la República Argentina. Uranium Evaluation and Mining Techniques, IAEA-SM-239/35, 1980.

SARDIN, P., Approach to the resource estimation of the Cerro Solo uranium ore deposit using geoestatistical methods. Tech. Comm. Meeting, Computer Application in Uranium Exploration and Production, IAEA, Vienna, 15-18 November 1994.

SARDIN, P., URQUIZA, L., Estimación de reservas y análisis económico del cuerpo C1, Yac. Co. Solo, Prov. del Chubut. V Congreso Nacional de Geología Económica, San Juán, 18-22 de setiembre, 1995.

McARTHUR RIVER PROJECT, SASKATCHEWAN, CANADA G.D. POLLOCK

Cameco Corporation,

Saskatoon, Saskatchewan, Canada

Abstract

The McArthur River uranium deposit contains an estimated 416 million pounds at an average grade of 15%

U3O8. Cameco, on behalf of joint venture partners Uranerz and Cogema, plans to develop an underground mine with ore to be transported 80 kilometres for processing at the Key Lake mill and tailings facility. The planned production of 18 million pounds per year will be achieved by mining only 125 tonnes of ore per day. This allows for a high degree of engineering control of the extraction process to ensure the health and safety of employees and protection of the environment. Three remote mining methods have been considered: raiseboring, box hole boring, and remote box hole stoping. All three are compatible with grouting or freezing to control water flow and ground conditions. Raiseboring has been selected as the primary method in the first phase of production.

Crushing and grinding will be carried out underground and thickened slurry will be pumped to surface. Public review of the environmental impact statement was completed in 1996, the review panel issued a favourable report in March, 1997 and government approvals were received in May, 1997. Subject to receipt of licenses and permits, production is planned in 1999 when it will replace the depleted mine production from Key Lake.

1. INTRODUCTION

The development of the McArthur River and Cigar Lake mines will represent a new generation of large, very high grade, underground uranium mines in Saskatchewan. Subject to approvals and licensing, production from these mines is planned in 1999 for McArthur River and 2000 for Cigar Lake. This will replace production from Key Lake which will be depleted, and from Rabbit Lake, to be depleted a few years later. These developments are important for the Canadian uranium production industry and for Cameco which is the largest owner and will be the operator of both mines. This paper describes recent activities and the current status at one of these, the McArthur River project.

McArthur River is in the eastern part of the Athabasca Basin in northern Saskatchewan. It is located about 70 kilometres northeast of Key Lake and 40 kilometres southwest of Cigar Lake. In the case of both McArthur River and Cigar Lake the ore will be transported by road to off-site mills; McArthur River ore will be milled at Key Lake and Cigar Lake ore at the JEB mill at McLean Lake (see Fig. 1). The McArthur River project is owned by Cameco 55.844%, Uranerz 27.922% and Cogema 16.234%.

2. GEOLOGY

The large and high-grade Saskatchewan uranium deposits occur at or close to the unconformity which separates the generally flat-lying, unmetamorphosed middle Proterozoic sandstones of the Athabasca Group from folded and metamorphosed lower Proterozoic and Archean rocks beneath. At McArthur River this unconformity is at a depth of 500 to 600 metres. The mineralization at McArthur River is associated with a northeast-trending, southeast-dipping zone of reverse faulting along which the unconformity is displaced vertically 60 to 80 metres. The individual faults tend to be rather narrow in the basement rocks, expanding to form extensive zones of mylonitization, fracturing and brecciation in the

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overlying sandstone. The lower Proterozoic basement rocks at McArthur River include significant quartzite units. The alteration is characterized by intense silicification of the sandstone with weak development of clay alteration. This is in contrast with the strong bleaching and clay alteration generally found around other Athabasca deposits. The mineralization is largely pitchblende without the associated cobalt-nickel-arsenic minerals which are present at Key Lake and Cigar Lake.

FIG. 1. McArthur River location map.