Distribution and significance of hydrothermal alteration minerals in the Tuzla hydrothermal system, Canakkale, Turkey

Hydrothermal alteration zones have been investigated by X-ray diffraction, mineralogical-petrographical techniques, and geochemical analysis. Examination of cores and cuttings from two drill sites, obtained from a depth of about 814-1020 m, show that the hydrothermal minerals occuring in the rock include: K-feldspar, albite, chlorite, alunite, kaolinite, smectite, illite, and opaque minerals. In the studied area, silicified, smectite, illite, alunite, and opal zones have been recognized. These alteration mineral assemblages indicate that there are geothermal fluids, which have temperatures of 150-220 degrees C in the reservoir. The distribution of the hydrothermal minerals shows changes in the chemical composition of the hydrothermal fluid, which are probably due not only to interaction with host rock, but also to dilution of the Na-K-Cl-rich hydrothermal fluid of the deep reservoir by cold sea water at shallow levels. Geochemical analyses of the solid and liquid phases indicate that the hydrothermal fluids of the Tuzla geothermal system are in equilibrium with alteration products. The tectonic structure of the studied area is caused by NW-SE and NE-SW directional forces. The volcanic rocks where hydrothermal zones are observed in the studied area are of Lower-Middle Miocene age comprise latite, andesite, dacite, rhyolite-type lavas, tuff, and ignimbrites. (C) 2000 Elsevier Science B.V. All rights reserved.