Geothermal prospecting in the Semporna Peninsula with emphasis on the Tawau area

Abstract

Thermal manifestations in the Semporna Peninsula include hot springs, seepages, mud pools and old steaming ground. Mapping of these thermal features showed that they are structurally controlled. The chemistry of the thermal waters indicate the presence of two types of waters - near neutral sodium chloride and sulphate waters. Thermal waters from the Apas Kiri area are near-neutral sodium chloride waters and the C11B and C11F ratios suggest they have a common source of geothermal fluid. The thermal water from upper Tawau is acid sulphate type and its chemistry suggests it is steam-heated water or ground water mixed with gas (H2S). The chemistry of thermal waters from Balung and Sungai Jepun areas suggests they are acid sulphate waters which may have come from a far away source and come into contact with and neutralised by cold ground water. The upper Tawau and Balung springs may indicate the perimeter of a field centered on the Maria Volcanic Complex. The Apas Kiri area is underlain mainly by Quaternary dacitic lava, tuff and agglomerate. The surface thermal manifestations cover an area of 3 km'. The volcanic rocks are calcitised, chloritised, argillised and pyritised. Around the thermal features, the rocks are strongly argillised and calcitised. Several characteristics of the Apas Kiri thermal waters e.g. chloride contents, ClIB ratio and geothermometer suggest high subsurface temperature. The ClIB ratio also suggests the reservoir rocks are andesitic. Total heat loss from the Apas Kiri 2, Apas 5 and Sungai Jepun areas have been tentatively estimated as 28.65, 0.75 and 15.05 MW-Thermal respectively.