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722/ RME-4534( Rev.) OBE Go\\ec 04 RECONNAISSANCE FOR URANIUM IN THE TOCOPILLA AREA, PROVINCE OF ANTOFAGASTA, CHILE By William A. Bowes Paul H. Knowles Mario Serrano C. Rudolfo Grnienwald S. February 1959 Division of Raw Materials, AEC Washington, D. C. .and Instituto de Inve stigaciones Geologicas Santiago, Chile UNITED STATES ATOMIC ENERGY COMMISSION * OFFICE Of TECHNICAL. INFORMATION metadc 783694 LEGAL NOTICE This report was prepared as an account of Government sponsored work. Neither the United States, nor the Commission, nor any person acting on behalf of the Commission: A. Makes any warranty or representation, expressed or implied, with respect to the accu- racy, completeness, or usefulness of the information contained in this report, or that the use of any information, apparatus, method, or process disclosed in this report may not infringe privately owned rights; or B. Assumes any liabilities with respect to the use of, or for damages resulting from the use of any information, apparatus, method, or process disclosed in this report. As used in the above, "person acting on behalf of the Commission" includes any em- ployee or contractor of the Commission, or employee of such contractor, to the extent that such employee or contractor of the Commission, or employee of such contractor prepares, disseminates, or provides access to, any information pursuant to his employment or contract with the Commission, or his employment with such contractor. This report has been reproduced directly from the best available copy. Printed in USA. Price $0.50. Available from the Office of Technical Services, Department of Commerce, Washington 25, D. C. USAEC Office of Technical Information Extension Oak Ridge, Tennessee RME-h53h (rev.) GEOLOGY AND MINERALOGY U. S. ATOMIC ENERGY COIISSION DIVISION OF RAW MATERIALS IN COOPERATION WITH INSTITUTO DE INVESTIGACIONES GEOLOGICAS DE CHILE RECONNAISSANCE FOR URANIUM IN THE TOCOPILLA AREA, PROVINCE OF ANTOFAGASTA, CHILE By William A. Bowes, Paul H. Knowles, Mario Serrano C. and Rudolfo Grenwald S. February 1959 Santiago, Chile RECONNAISSANCE FOR URANIUM IN THE TOCOPILLA AREA, PROVINCE OF ANTOFACASTA, CHILE CONTENTS Pag ABSTRACT - * . * * . * . * * . * * * * * . * . 5 INTRODUCTION . - . 5 Geography . 7 Location and accessibility . 7 Topography, vegetation and climate . 7 Exploration and mining history . 7 Acknowledgements . 9 GENERAL GEOLOGY . * . ** , 9 Stratified rocks . 9 Intrusive igneous rocks . 9 Structure . 10 RECONNAISSANCE FOR URANIUM . 10 Tocopilla district . 11 Minita mine . * . * . .11 San Jose'mine . lb Gatico district................. 15 Guanillos district . .5 . 5 Tres Puntas - San Juan district . 1 Cerrillos district . .. .. .. 15 Other localities . 16 CONCLUSIONS . 16 REFERENCES . 17 ILLUSTRATIONS Figure 1. Index map, Tocopilla area, Province of Antofagasta, Chile 6 2. Geologic plan of portions of the Minita mine, h30 and 610 levels, showing sample localities . 13 Table 1. Radioactivity in milliroentgens per hour . 11 Plate 1. Geologic sketch, Tocopilla area, Antofagasta Province, Chile . 19 -3- RECONNAISSANCE FOR URANIUM IN THE TOCOPILLA AREA, PROVINCE OF ANTOFAGASTA, CHILE ABSTRACT In September-October 1958 a six-day reconnaissance in the Tocopilia area, Antofagasta Province, Chile, was made by members of the U. S. Atomic Energy Commission and the Instituto de Investigaciones Geologicas de Chile for the purpose of evaluating reported uranium occurrences. Bed rocks in the western part of the area are a Jurassic volcanic sequence. The eastern part is underlain by Paleozoic sediments, the two sectors being separated by a regional north-trending fault, called the Salar del Carmen fault. All subsidiary faults and fractures appear related to movement on this, or parallel, faults in the same major fault system. Both the older sediments and the volcanics are intruded by facies of the Andean diorite complex. Two principal plutons of this diorite are located, respectively, near Tocopilla and Ggtico. Uranium occurs .near Tocopilla in east- to northeast-trending tensional fractures associated with quartz, actinolite, and copper and iron minerals in veins paralleling andesite dikes. The dioritic to syenitic host rock is part of the Tocopilla pluton. The highest radiometric assays from veins were 0.09 percent equivalent uranium. In view of the persistence and character of the northeast-trending tensional structures, a limited pro- gram of more detailed geologic mapping seems warranted, as the area may possibly contain significant uranium concentrations. INTRODUCTION Reconnaissance for uranium in the Tocopilla area was performed during the winter of 1958 by geologists of the U. S. Atomic Energy Commission (USAEC) and the Instituto de Investigaciones Geol6gicas de Chile (IIG) under a cooperative agreement between the American and Chilean governments. The Tocopilla area (fig. 1) was selected for reconnaissance on the basis-of its favorable geology indicated by literature research (Hague, 1958), as well as by the presence of uranium in certain areas. Field work was accomplished in a six-day period in September and October by two field parties, each equipped with four-wheel drive vehicles. The work center was Tocopilla. Liberal use was made of aerial photographs of the U. S. Army Tri-Metrogron type (1:4O,000) and also U. S. Army Map Service (1:60,000) vertical photographs in stereoscopic pairs. The base map for plate 1 was copied from topographic maps compiled by the Instituto Geografico Mi.litar de Chile (scale 1:250,000). Both scintillation and Geiger counters were used in the investigation. R ME 4534 (rev,) To 690 680 PERU( \ 20 IQUIQU - 7 Pica 210 7) K 0 V- J .. LL 7 Son .. 220 P ro TOCOPILL * Chuq Jicomoto 00 . O O olomo 0 0 0 23 z Son Pedro de Atacomo. E w a Solar . de - ANTOFAGASTA Atocame / 0 :z 24 z w I 700 (9 6 90 .. f 680 0 100 Kilometers 0 100 Miles Frb1 Figure I- Index Map of Tocopilla area, Province of Antofogasta Chile. The scope of the work was limited to reconnaissance of the area for favorable geologic indications of uranium; this included visits to selected localities and mining districts. Geologic information thus compiled may be used in the assembly of a new geologic map of Chile, an Instituto de rnvestigaciones Geologicas project scheduled for completion two years hence. Geography Location and accessibility The Tocopilla area falls'within latitudes 21 0l5' to 220301 S. and longitudes 690h5' to 70015' W. The coastal port of Tocopilla (population, 20,000) is the capital of the Department of Tocopilla, Province of Anto- fagasta, Chile. It lies near the center of the western edge of the rectangular, north-elongated, 50- by 80-kilometer area, and is accessible by boat, rail, or auto. Access to most of the high ground east of Tocopilla is by jeep roads branching from the main east-west Chuquicamata-Tocopilla highway. Access along the coast is limited to a surfaced road south of Tocopilla, as the northern coastal road is blocked by stream washes and mud flows that occurred during freak storms in 1911. The coastal barrier is cut only rarely by valleys deep or continuous enough to make road construction possible in an east-west direction; in the area at present the only inland- coastal access is by the Tocopilla-Chuquicamata road. Much of the northern cart of the area is relatively inaccessible due to lack of access roads. Topography, vegetation and climate Elevations in the Tocopilla area range from sea level to 2,300 meters in the coast range mountains. The western slope of the coast range moun- tains is exceptionally steep; peaks as high as 1,900 meters elevation are found only 3 kilometers inland from the coastline. The coastal mountains, in an early mature stage of erosion, slope'gradually to the east and merge into the wide alluvial plains of the central.valley. The entire Tocopilla area is dry and nearly devoid of natural vegetation. Precipitation is negligible and has annually averaged 4.5 millimeters in rainfall over a period of 15 years. Drinking water is supplied by pipeline from the Andes Mountains. The climate is hot in summer and cool in winter; the coastal area is subject to frequent fogs. Rock exposures are generally good throughout the mountainous parts of the area. Exploration and mining history The city of Tocopilla has been an important copper-producing center for over a century. -'7- The rich Rosario veins in the Minita-Portezuelo Despreciada mine group, 3 kilometers northeast of Tocopilla, were worked 'until damaged by a great earthquake in 1877. Later this group of mines was consolidated into one company in the year 1920 and has since been worked more or less continuously as the Compa1 i'a Minera de Tocopilla. The Company has a sea-water flotation plant in Tocopilla which can treat up to 300 tons of the lower grade 4- to 5- percent copper ores per day. An aerial tram with a capacity of 30 tons per hour has been replaced by trucks to haul ore to the plant. This plant also treats ore from the company-owned Buena Esperanza mine located about 7 kilometers south of Tocopilla. Adjoining the Despreciada group are the Lincoln group on the north and the Sloman group on the east. The latter includes the San Jose'vein dis- cussed in another part of this report. The famous old copper mines of Gatico are situated 2 kilometers inland from the sea coast. The locality is shown in the southwest corner of plate 1, approximately 40 kilometers south of Tocopilla. The mines have been worked discontinuously from the time of the Spanish occupation. A smelter located there handled up to 200 tons of ore daily. The properties have been idle for many years, and the plant, mine buildings, and equipment are in ruins. Other important copper districts of past years include the Tres Puntas- San Juan, 10 kilometers southeast of Tocopilla, and the Guanillos, 10 kilo- meters north of Gatico. The latter district includes the Bandurrias, Gitana, San Ram'n, and Mantos de la Luna mines.

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