Title: Geochemical characterization of thermal water from Central Vietnam and Borgarfjörður W-Iceland

Abstract

The geochemistry of low-temperature geothermal water in Central Vietnam and Borgarfjördur
(W-Iceland) was studied as well as its potential utilization possibilities.
Twenty samples of geothermal water were collected in Central Vietnam and twelve samples in
Borgarfjördur in the summer of 2018. The water temperature, pH, DIC and H₂S concentrations were
measured on site and major elemental composition analysed using ICP-OES and IC at the University of
Iceland. Stable isotopes of hydrogen and oxygen (δD and δ¹⁸O) were also determined at the
University of Iceland, by IRMS. The surface temperatures of the geothermal waters in Vietnam were
42- 96°C and in Borgarfjördur they were 40-98°C.
The stable water isotope ratios, Cl and B concentrations were used to assess the water origin,
mixing and water-rock interaction. Based on the results of this analysis it was concluded that
geothermal waters in Vietnam and Borgarfjördur are of meteoric origin affected by rock leaching and
mixing with non-thermal water and with possible seawater or salt evaporaties in the case of
geothermal water in Vietnam.

The SiO₂ concentrations of the geothermal fluids in Vietnam and Borgarfjördur were 38-
138 ppm and 54-178 ppm, respectively. Using these concentrations and assuming equilibrium with
chalcedony the reservoir geothermal temperatures in Vietnam and Borgarfjördur were found to be as
high as ~120°C and ~135°, respectively. The geographical projection of the major elemental
concentrations and geothermometer temperatures revealed three geothermal anomalies in Vietnam: Le
Thuy, Quang Binh; Mo Duc, Quang Ngai; Hoi Van, Quang Binh and the highest temperatures at Haegindi
in Borgarfjördur.
Following the utilization of low-temperature waters in Borgarfjördur and elsewhere in Iceland, the
Líndal diagram suggests several utilization possibilities for the geothermal resources in Vietnam
including house heating and cooling, greenhouse farming, fish farming, swimming pools and bathing,
drying and food processing, and even electricity production for the waters with the highest
temperatures. The utilization options will, ver, largely depend on accessibility and the quantity
of geothermal water for each
location.