| Abstract |
The Casita geothermal field is held under a concession by Triton Power S.A., a 100% owned subsidiary of Polaris Energy Corporation. It is located in the eastern portion of the San Cristobal volcanic complex that is part of the Marabios Range of northwestern Nicaragua. San Cristobal located in the northwest is currently volcanically active, but Casita has no clear history of eruption. It appears erosionally older and was the site of a major catastrophic mudslide from its southern slopes during Hurricane Mitch in 1998. An even older volcanic centre occurs to the east of Casita in the form of the La Pelona caldera. Casita is a ridge, with volcanic craters along it, which is made up of pyroxene andesites with lavas predominating on its northern slopes and pyroclastics on its southern slopes as a result of the prevailing winds sorting the eruptive products. In addition to the predominance of pyroclastics in the south a further contributory cause of the 1998 mudslide was the presence of widespread hydrothermal alteration on Casita. There is also a very large area of hot and steaming ground, although actual fumarolic activity is relatively feeble. Repeated sampling and analysis of fumarole gases over time indicates the presence of a vapour-dominated reservoir at a temperature of approximately 235°C. The presence of Cl in warm surrounding ground water wells at lower elevations suggest a possible underlying neutral-Cl reservoir. Further afield, hot neutral-sulphate springs at El Bonete approximately 8 km to the north-east have an associated resistivity anomaly orientated towards Casita and have been interpreted to be an outflow of condensate from above the vapour-dominated reservoir at Casita. This interpretation has been reinforced by a recent MT survey over Casita, which shows a possible upflow zone under the Casita ridge and the link between the Casita and El Bonete resistivity anomalies. The presence of this significant condensate outflow, the extent of the thermal ground on Casita and the possibility of a major vapour-dominated zone indicate the presence of a significant geothermal resource at Casita. The concession holder has made preparations for exploration drilling. |