Borehole geology and hydrothermal alteration of well SV-14, Svartsengi, SW-Iceland

Abstract

This report describes the stratigraphic sequence and the alteration in drillhole SV-14 in the Svartsengi high-temperature field, SW-Iceland. The stratigraphic column consists of a hyaloclastite formation. This was formed under the ice sheet as a result of the quenching of magma in water. It consists consequently of a mixture of vitroclastic glass and partially crystalline basalt. The hyaloclastite formation is divided into three types, the first type, the hyaloclastite tuff, is dominantly composed of perlitic glass, the second type is the hyaloclastite breccia made up of similar amounts of perlitic glass and partially crystallized basalt and the third type is the basaltic breccia which consists of a majority of partially crystallized basalt and minor perlitic glass. Three alteration zones are divided in the well, the zeolite smectite zone, the mixed layer clay zone and the chlorite zone. Aquifers in this well were located on the basis of borehole measurements and records of circulation losses.