Geological Results from the Drilling of the Northwest Sabalan Geothermal Project

Abstract

Three deep exploration wells drilled in the Northwest Sabalan geothermal project initially encountered Quaternary terrace deposits and Pliocene trachyandesitic volcanics. The most northerly of the wells continued into a sequence of Pliocene to Neogene volcanics before drilling down the dip of a sequence of Eocene volcanics and running along a disconformity with Paleozoic meta-litharenite. Similar Eocene volcanics were encountered in the other wells, with the most southerly well penetrating a Miocene monzonite batholith and surrounding hornfels. Diorite porphyry dykes were found in the two southern wells with the youngest known dykes being found in the most southerly well. There is a complex alteration pattern produced by hydrothermal events associated with the monzonite and the two phases of dyke intrusion. Illite-rich zones around faults that are the main drilling targets in the wells represent the current alteration. New well targets off the current pads and the requirement for more southerly drilling have been identified. Two of the three wells are considered to be commercially productive and represent the first successful exploration of an intraplate trachyandesite volcano thus encouraging exploration in similar settings in Iran and elsewhere, most notably Turkey.