Application of natural isotope tracers to geothermal research in Ranong fault zone (S-)

Monthon Yongprawata,b, Martin Sauter a, Bettina Wiegand a a University of Göttingen, Applied Geology, Goldschmidtstr. 3, 37077 Göttingen, Germany. b Nuclear Research and Development Division, Thailand Institute of Nuclear Technology (TINT), , 26120, Thailand 1.1. IntroductionIntroduction 4.4. MethodsMethods 2)2) Stable Stable H H andand OO isotopesisotopes Low-enthalpy hot springs in Thailand were mainly developed as local tourist Stable isotopes of hydrogen and oxygen were compared with the Global meteoric destinations (Raksaskulwong, 2004). One of the targets for geothermal utilization in the Thermal waters from six hot springs, wells and cold surface water samples were waterline (GMWL) and the local meteoric waterline (LMWL) δD = 7.97 x δ18O + 11.35 country is , where 6 hot springs are developed along an active fault collected in December 2014 and March 2016. The following parameters were (SMOW), based on daily precipitation samples from 2013 to 2015 (Hydro and Agro zone. Some of these hot springs were successfully developed and wells were drilled for investigated: Informatics Institute 2016) spa operation. Geochemical characteristic in Ranong hot springs were explored in a - Field parameters were measured on site by a portable instrument: temperature (SD number of investigations (Chaturongkawanich, 2000; Kosuwan & Nakapadungrat, +0.1 °C), pH (SD +0.005), electrical conductivity (SD +0.001 cm-1) and dissolved oxygen (1992)). (SD +0.5%). - Major ions were analyzed by standard ion chromatography (IC). - Stable isotopes of hydrogen and oxygen and chemical compositions were analyzed on hot and cool water samples by LGR (DLT-100) laser spectrometer. 2.2. GeologicalGeological setting setting - In addition, dissolved inorganic carbon (DIC) as well as d13C and 14C were analyzed by Isotopic Carbon-Analyzer (PICARRO G2121-i) and liquid scintillation technique The left-lateral strike-slip fault in Ranong in the southern part of Thailand, exposes 6 (Quantullus 1220) respectively. hot springs: Raksavarin Hot spring (RN-1), Ban Tung Yor Hot spring (RN-2), Pon Runk Hot - Very low Tritium concentration from water samples were enriched from Electrolytic spring (RN-3), Khlong Bang Rin Hot Spring Area (RN-4), Rattana Rangsan Hot spring (RN- enrichment and then were analyzed by liquid scintillation (Tricarb 3180). 5), and Ban Hat Yay Hot spring (RN-6) (Chaturongkawanich, 2000). The Ranong geothermal system is generally linked to Cretaceous granitic rocks which are comprised of 6 categories: Khlong Ban Rin granite (Kgr-br), Khlong Ngao granite (Kgr-ng), Leucocratic granite (Kgr-l), Thung Ka granite (Kgr-tk), Khao Nom Sao granite (Kgr-ns), and Haad Som Pan granite (Kgr-hsp) (Kosuwan & Nakapadungrat, (1992)) Figure 4. the stable isotope results of Ranong hot springs samples plotted with LMWL and GMWL RN6 • The stable isotope composition of surface water and hot springs plot closely to the Figure 2. the analysis Instruments; 1)14C direct absorbtion, 2) Ion chromatography (IC), 3) Laser spectrometer LMWL (Green line) and GMWL (Brown line).

• The stable isotope results of surface water samples collected in March 2016 are enriched in the heavy isotopes compared to the data from December 2014. This may RN1 5.5. Results Results be reflect evaporation and/or mixing with geothermal water. 1) Field1) sampling Field sampling and chemical and chemicalcompositions • The geothermal water results from both seasons are in the same range and have no significant oxygen-18 shift.

RN2 a) b) 3)3) Radiocarbon Radiocarbon andand Tritium Tritium dating dating • The δ13C value of DIC from hot spring water samples range from -23.55 to -25.59 ‰ PDB. RN3 • The age of hot spring waters is approximatly 3,600 years to 4,800 years. • Tritium concentrations from hot springs range from 0 to 0.1 TU. Tritium concentrations in rain water of the Nakonnayok province () were approximately 2 TU in 2012. (Yongprawat, Kamdee, and Noipow 2012).

RN5 Peripheral bicarbonate waters Thermal water samples are enriched in occur at shallow depths. Na+K and depleted in Ca and Mg 6.6. ConclusionConclusion Figure 3. the major-ion results of Ranong hot springs; a) Anions, b) Cations Figure 1. Location and geological map of Ranong hot springs applied from Imai et al., (2013) • comparing the stable isotope results with the LMWL shows that the source of and Kosuwan and Nakapadungrat., (1991) thermal water probably originates from local precipitation (Wei et al., 2018). • Temperatures of the hot springs range from 36 to 66.8 oC (the highest temperature is for RN1-1); electrical conductivities range from 256 to 339 µS/cm; pH values are • The geothermal water is dominated by Na-HCO3 type, PERIPHERAL bicarbonate between 6.97 and 7.67. waters suggesting prolonged water-rock interaction.

2- 3- 13 • Na concentrations (43.37 to 81.00 mg/l), SO4 (12.29 to 45.14 mg/l ), HCO (98.4 to • δ CPDB are from organic carbon sources but some mixture with inorganic carbon 3.3. ObjectiveObjective 167.5 mg/l), Cl (2.77 to 4.90 mg/l), Ca (9.20 to 22.06 mg/l), Mg (0.05 to 0.15 mg/l) may occur. This study aims to identify sources of the geothermal water and hydrodynamic and K (2,87 to 5.66 mg/l). processes from five hot springs along the Ranong fault zone. • Radiocarbon and Tritium show that the age of geothermal water is lower than 5,000 • Thermal water and surface water are generally dominated by the Na-HCO3 type and years. - Na-Cl-HCO3 type, respectively.

Reference •Chaturongkawanich. 2000. “The Geothermal Resources of Changwat Ranong .” Proceedings of the World Geothermal Congress: 1049-1052. •Kosuwan and Nakapadungrat. 1991. The Geology of Changwat Ranong Quadrangle ; Geological Map of Thailand Series 1:50,000. •Imai et al. 2013. “Rare Earth Elements in Hydrothermally Altered Granitic Rocks in the Ranong and Takua Pa Tin-Field, Southern Thailand” Resource Geology vol 63: 84-98. •Hydro and Agro Informatics Institute (HAII) 2016. Database of Stable Isotope in Surface Water, Precipitation and Humidity for Water Cycle Studies in Thailand. Bangkok, Thailand. •Raksaskulwong, Manop. 2004. “Geothermal Direct – Use in Southern Thailand.” the 6th Asian Geothermal Symposium: 33-37. •Wei et al, 2018. “Influences of large-scale convection and moisture source on monthly precipitation isotope ratios observed in Thailand, ”. Earth and Planetary Science Letters vol 488: 181-192. •Yongprawat, , Kiattipong Kamdee, and Nitipon Noipow. 2012. “Tritium Content in Rainfall for Mornitoring Effect from Fulkushima Accident at Ongkharak Raindall Station in Thailand.” In Environmental and Safety Technology, Nakornratchasima, Thailand: TIChE International Conference 2012.