| Abstract |
Four geothermal resources in Changwat Ranong, an important province along the west coast of southern Thailand, have been investigated. They are: Wat Thapotharam Hot Spring Area (RN1), Ban Thung Yo Hot Spring Area (RN2), Ban Porn Rang Hot Spring Area (RN 3) and Khlong Bang Rin Hot Spring Area (RN4) Stratigraphically, the oldest rock unit is composed of pebbly sandstone, greywacke, arkose, siltstone, mudstone, conglomeratic sandstone of Carboniferous-Permian age, and locally gneiss, schist, quartzite and hornfels. Quaternary alluvial deposit of gravel, sand, silt and clay and the recent nearshore sediment deposits of sandy clay and clay, are distributed on the western part of the study area. The batholith of granitic rocks in Cretaceous age are of 2 types: porphyritic, two-mica, tourmaline, granite and leucocratic granite. Andesitic dykes extruded along the fracture planes in granitic rocks.The faults and joints are observed in NW-SE, E-W and N-S directions. which are the main conduits for hot water transmission from deep - seated reservoir to the surface. All four hot springs are associated with Cretaceous granite. The natural surface manifestation are seepages and hot pools. The hot water is clear, pH 8.3-8.4, some CO2 bubbles, very little H2S, minor algae and alteration mineral of calcite. The general chemical constituents are as follows : TDS 320-330, Na 46.1- 48.4, K 2.8-3.2, Ca 41.3-44.8, Mg 0.01-0.03, Fe 0, Mn 0-0.01, HCO3 182-219, F 5.2-7.5, SO4 19.3-45.3, Cl 4.8-11.0, SiO2 72.0-81.3 mg/l. The subsurface temperature calculated by SiO2 geothermometer is about 120o-126? C. The high potential hot spring area is Wat Thapotharam, due to its high flow rate (about 600 m3 /day) and high surface temperature (65? C). |