International Atomic Energy Agency IUREP N.F.S. No. 69 August 1977 Distr. LIMITED Original: ENGLISH

INTERNATIONAL URANIUM RESOURCES EVALUATION PROJECT

I U R E P

NATIONAL PAVOURABILITY STUDIES

URUGUAY

77-7711

INTERNATIONAL URANIUM RESOURCES EVALUATION PROJECT

I U R E P

NATIONAL FAVORABILITY STUDY

URUGUAY

CONTENTS

PAGE

1. INTRODUCTION 1

2. GEOLOGY IN RELATION TO POTENTIALLY 1 FAVORABLE URANIUM-BEARING AREAS

3. PAST EXPLORATION 3

4. URANIUM OCCURRENCES AND RESOURCES 4

5. PRESENT STATUS OF EXPLORATION 4

6. AREAS FAVORABLE FOR URANIUM 4 MINERALIZATION AND POTENTIAL FOR NEW DISCOVERY

7. BIBLIOGRAPHY

GEOLOGIC MAP OF URUGUAY

1. INTRODUCTION (a) Geography

Uruguay has an area of 186,926 square kilometers. Its capital is . Nearly half of the population lives in the coastal region near the capital. The country is predominantly one of gently rolling grasslands with several ranges of low hills* There are narrow coastal lowlands, many rivers, and some swamps near the eastern coast. Uruguay has no deserts or high relief. The most rugged sector is in the northwest. Part of the Rio Uruguay forms the western boundary with while the Rio de la Plata estuary lies to the south.

(b) Climate

The climate is basically temperate with rather high humidity but subtropical in the northwest. Fogs are common from May to October, especially along the coast. Strong winds are quite prevalent and cause sudden temperature changes. Rainfall is mostly adequate although occasional extreme droughts or floods occur. There is no distinct wet season.

(c) Access

Roads total 51,745 km., with the chief highway being the 634-km. Pan American between Colonia, Montevideo and the Brazilian border. Road connections between Montevideo and other commarcial centers are mostly unpaved. Other roads are being improved. Limited east-west connections are available on the almost 3,060 km. of railroad trackage. Navigable inland waterways total about 1,125 km. The Rio Uruguay is the most important. International air service operates from Montevideo airport, and the country has several other fields and landing strips.

2. GEOLOGY IN RELATION TO POTENTIALLY FAVORABLE URANIUM- BEARING AREAS Uruguay has suffered from the lack of detailed geological investigation. There have been a few reconnaissance papers printed but with little, if any, attention directed toward mineral deposits or occurrences. The geology of Uruguay is linked to that of Southern as Uruguay forms part of the southern edge of the Tarana Basin. The stratigraphic column of Uruguay is being completely revised and it appears that many of the unit names have been changed. The following column is valid in Uruguay as of 1966. This has resulted in considerable confusion, past and present, in the description of many of the various units. Harrington (1956) has divided he as follows:

Lower Precambrian

Lower Precambrian granitoid, mica, augen and foliated gneisses are found along the coast of the Rio de la Plata between Colonia and Punta de Este and between Tacuarembo and Aciqua in- the northeastern part of the country . Pegmatites and aplite dikes are common.

Middle and Upper Precambrian

The Minas Series of Uruguay rests unconformably on the early Precambrian gneisses. The rocks are massive quartzites, slates and ph}llites grading into sericitic schists, coarsely crystalline Ujnestones and conglomerates. The Minas series is intruded by many biotite and hornblende granites and alkalic rocks.

The Cambrian-Silurian is represented in the Sierra de .Animas and Piedras de Afila Formations which rest unconformably on the Precambrian metamorphics. The Piedras de Afila Formation is a series oC: sands, limestones and quartzites that have suffered either metamorphism or diagenesis. The Sierra de Animas is a geologic accident of alkaline rocks without feldspathoids but does contain alkaline amphiboles.

The Durazno Group marks the lower . It overlies the pre-Devonian (Precambrian) with an erosional disconformity. It is made up of three formations of avkoses at the base, lutites in the middle and topped by sands. Crossbedding is one of its main characteristics.

The Cordobes Formation is a fossiliferous bland micaceous lutite with a few intercalations of sand horizons.

The time between the Devonian and Permian is marked by a disconformity.

VMa \o It is believed by some that the San Gregonio - Tres Islas Formation is correlatable with the Series. Suffice <~p to say the San Gregorio is composed of glacial material such ' as tillites, varied lutites and glacial debris that lie on sands and clayey limestones of the Tres Islas.

The Permian is composed of four formations called the Caraguata Group. It lies concordant on top of the Tres Islas. The Permian group has lutites and silts at the base and gradually changes to fine green sands with some limey clay beds. The Frayle Muerto and Mangrullo are rich in pyrite. The Mangrullo also contains limestones and bituminous lutites.

The Yaguari Formation has been correlated with the Terezina Formation of Brazil (Estrada Nova of the Passa Dois series). The Passa Dois series carries uranium in the Rio Bonito Formation (middle Permian) in Brazil.

The Triassic Tacuarembo Formation overlies the Paleozoic by a disconfomiity. The Tacuarembo is a soft to hard, grey to red sand. The base is soft and friable but the top portion is hard.

The - lower is marked by enormous masses of lavas, consisting of , andesites, , and trachytes.

Sedimentation in the lower Cretaceous was lagoonal and marine with frequent deposition of conglomerates and sandy conglomerates. Sediments of the upper Cretaceous are fine- grained, clayey sands, without gravels, of various colors - white to rose.

Sed.'ments of the Cenozoic are a series of sands, cross- bedded arkoses, and clays. The is a series of argillaceous limestones and is quite widespread.

3. PAST EXPLORATION In 1965 Uruguay was surveyed for uranium by the Inter- national Atomic Energy Agency. Over 7,700 km were surveyed by carborne scintillometer and 112 radioactive anomalies were discovered. The area investigated constituted less than 1 percent of the total area of the country. Fifty anomalies were recognized in Prccambrian schists, fifty-eight in Precambrian granite gneiss and granites, one in Devonian sediments, and three in Carboniferous sediments. The anomalies discovered are almost confined to the eastern half of the country bounded by a line running north-south from near Piriapolis through Minas, Sarandi del Yi and Minas de Corrales to Rivera. Previous uranium prospecting work in Uruguay had been limited to the investigation of one small radioactivity anomaly in the batholith of Sauce de Pan de Azucar and carborne prospecting with a hand-held scintillometer in the Department of Treinta y Tres. 4. URANIUM OCCURRENCES AND RESOURCES In 1969 La Pensa reported the discovery of uranium in Tacuarembo Province, but there has been no more recent information. Other unconfirmed discoveries have reportedly been made at Amarillo in the Department of Cerro Largo. 5. PRESENT STATUS OF EXPLORATION No current uranium exploration is reported. Although Uruguay has no specific legislation on nuclear energy, its mining code authorizes expropriation of fissionable materials with payment of compensation. Foreign companies domiciled in Uruguay may engage in mineral exploration with an appropriate permit and ultimately obtain a mining concession. 6• AREAS FAVORABLE FOR URANIUM MINERALIZATION AND POTENTIAL FOR NEW DISCOVERY The geology of Uruguay is generally favorable for uranium when compared to occurrences in other parts of the world. The granitic intrusives in the Minas, Valentines and Minas de Corrales areas are considered to be most favorable among the crystalline rocks. Of the sediments,_the Dgyonian" _Gondwana area of the northeast appears to be most attractive because of the proximity to crystalline Precauibrian rocks which might have been a source of uranium. Somewhat less favorable is the extensive Cretaceous-Tertiary sedimentary area in the western part of the country. Additionally, Tertiary and Quaternary bones from the Uruguayan Pampas have been found to be radioactive and may indicate some favorability for uranium. Some of the low-grade coals of southern Brazil immediately across the border from Uruguay contain uranium and may reflect similar favorability of the Uruguayan coal beds. The Permian formations of Uruguay are believed to correlate with similar formations in Brazil which contain the uranium-bearing beds of the Rio Bonito Formation in the Figueira area. The uranium potential of Uruguay is estimated in the range of 10,000 to 50,000 tonnes.

7. BIBLIOGRAPHY ^» Bossi, J., 1966, Geologia del Uruguay: Dept. de Publicaciones, Universidad de la Republica, Montevideo, 464 p. Bossi, J., 1969, Recursos Minerales Del Uruguay: Dept. de Publicaciones, Universidad de la Republica, Montevideo, 69 p.

Bossi, J. et al., 1965, Predevoniano en el Uruguay: Fac. de Agron. de Montevideo, Bol. No. 78.

Cameron, J., 1966, Nuclear raw materials prospection mission 1965: report to the government of the Republic Del Uruguay: Internat. Atomic Energy Agency, Vienna, 50 p.

Frenguelli, Joaguim, 1930, Apunter de Geologia Uruguaya: Instituto de Geologia y Perforaciones, Bol. II, March, 47 p. Gorii, J., 1958, Consideraciones sabre la Estratigrafia del Proterozoico y Eopaleozoico Uruguayos: Bol. Soc. Bras. Geol. 7, p. 91-96.

Goni, J. et al., 1962, Estratigrafia y Geologia economica do Pre-Cambriano y Eopaleozoico Uruguaio e Sul, Rio grandense. Harrington, H.J., 1956, Uruguay, in Jenks, W.F. (ed.), HanJbook of South American Geology: Geol. Soc. America Memoir 65, p. 117-128.

Hill, W.S., 1950, Elementos radioactivos en los huesos fosiles del Terciario y del Cuaternario: Ciencia e invest. Buenos Aires 2:1. McMillan, J., 1933, Terreno precambricos del Uruguay: Montevideo, Uruguay, Inst. Geol. y Perf., Bol. No. 18, 60 p.

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Compiled fcy USERDA Augiist 1977 GEOLOGIC MAP OF URUGUAY

Legend Q Quaternary Montevideo PiriSpoiis N Tertiary Punta del Este K Cretaceous M Mesozoic Basalts T Triassic P Permian D Devonian Pe Precambrian