Doctor

Ducci et

THE PREFEASIBILITY STUDY OF THE S A N MARCOS GEOTHERMAL AREA, GUATEMALA
Enzo Ducci , Otto
European Co-Director, Geotermica Italiana Pisa, Italy and Julio Coordinator, National Co-Director

INDE, Unidad de Desarrollo Guatemala City, Guatemala

ABSTRACT
The Geotergua project is a joint venture between the European Community and INDE. Its objective is the prefeasibility study ofthe San Marcos geothermal area. The area is located near the Mexican border, 250 km west from Guatemala City and is sited in lower a calderic depression originated in the late tertiary Pleistocene age as a result of various strong pyroclastic eruptions. Numerous thermal springs with a temperature ranging from 23°C to boiling point have been found. The great majority of these springs are along ornear the Palatza and the Naranjo rivers, they are isotopically heavy. The geothermometry indicates temperatures of for the main reservoir, probably located within the dioritic basement. In order to evaluate all possible electrical production scenarios, different ranges of temperature, depth and flow of the wells, and discount rate were considered. The result of the economic evaluation provides, forthe different types of plant evaluated, average costs lower than those of alternative energy sources in Guatemala (Thermal and Hydro). The study indicates the existence, in the San Marcos area, of a geothermal field suitable for electric production, of industrial capacity, and of economic value. Key Words: Geotergua, Geovulcanology, Conceptual Geothermal Model. 1. Geochemistry,

SAN MARCOSGEOTHERMAL AREA

1 Geotergua project location map.

INTRODUCTION 3. GEOVULCANOLOGY

The Geotergua project is a joint venture between the European Community and INDE, the national utility company of Guatemala. Its objetive is the prefeasibility study of the San Marcos geothermal area. The work carried out to date includes: geo-vulcanology, geochemistry, a limited geo-electric survey, anenvironmental impact evaluation, and a technical-economic study. The program was undertaken by the below mentioned personnel of INDE and the EC contractor Geotermica Italiana: Ing. Julio Palma National Co-Director, Ing. Otto Garcia-Coordinador, Ing. Victor Ing. Carolina Ortiz-Geologist, Ing. Alfredo Tech. Grajeda-Geochemist, Techn. Hugo Rosas-Geophysicist, Tech. Franklin Escobar-Computer Analyst, Dr. EnzoDucci-European Co-Director, Dr. Antonio Frullani-Geovulcanologist, Dr. Marcello Ghigliotti Geovulcanologist, Dr. Milletto-Geophysicist, Dr. Luigi Marini-Geochemist, Dr. Massimo Guidi-Geochemist, Dr. Roberto Cioni-Chemist, Ing. Riccardo Corsi-Environmentalist. Ing. Giuseppe Valleggi-Economist. This paper is the result of their work. 2.

The main geological characteristics of the San Marcos areaare described here. The stratigraphic series includes an intrusive regional basement made up of diorite and an overlying pile of volcanites of tertiary and quaternary age. (Fig. 2) The dioritic basement outcrops 10 km to the west of the city of San m and can be Marcos, at an average height of found at a depth of kilometres below the San Marcos depression (exact depth unknown). The tertiaryvolcanites are mainly made up of andesitic-basaltic and basaltic flows with subordinate pyroclastites aglomerates and lahares. The thickness of this series varies considerably and could range from several hundreds to thousands of metres. The overlying quaternary volcanites are mainly pyroclastics (ignimbrites and lahares) and breccias reaching a thickness of several hundred metres in the centre of the SanMarcos depression, according to an overall interpretation from vertical electrical soundings and geological field data. The San Marcos depression is the main structural and morphological feature present in the studied area and is considered to be a caldera. It is an eliptical depression with axes approximately 13 and 9 km wide. This caldera originated in the late tertiary lower-Pleistocene age...