Origin and Evolution of Saline Spring Water in North and Central Laos Based on Hydrochemistry and Stable Isotopes (δD, δ18O, δ11B, and δ37Cl)

Xiwei Qin,Guorong Li,Qian Song,Shang Lei,Huaide Cheng,Haizhou Ma,Sha Yang,Xiasong Hu,Yongshou Li,Hongying Wang,Ziwen Jiang,Wenhua Han,Xiying Zhang,Weiliang Miao,Jibin Han

doi:10.3390/w13243568

Abstract

This paper discusses the origin and evolution of saline springs in north and central Laos, based on chemical and stable isotopes (δD, δ18O, δ11B, and δ37Cl). All the saline springs in this study are of the Na–Cl geochemical type. The geochemical and water isotope values suggest that the saline springs in this study are mainly derived from meteoric water and/or ice and snow melt from the surrounding mountains and that they also experienced strong evaporation and intense rock–water interactions. The ionic ratios, characteristic coefficients, ternary Ca–SO4–HCO3 phase diagrams, and saturation indices of minerals show that the dissolution of halite, sulfate, and carbonate rocks may be the solute sources for saline springs in this study, whereas the underground brines in the Thakhek potash mining area are geochemically influenced by the dissolution of carnallite and sylvite. The global geothermal δ11B–Cl/B relationship and δ11B values (5.50 to 36.01‰) of saline springs suggest a continental origin of B. This B is most likely derived from marine carbonate rocks and marine evaporates (gypsum and halite) of the late Cretaceous, which is similar to the saline springs of the Nangqen–Qamdo–Simao Salt Basin. The δ37Cl value (−0.12 to +0.79) and the Cl/Br ratio (4076 to 9853) show that dissolution of late cretaceous marine halite layers, atmospheric precipitation, and water–rock interactions between volcanic rocks, mudstones, and sandstone can restrict the δ37Cl values in saline springs. Results from silica geothermometry and multi–mineral equilibrium diagrams indicate that the reservoir temperatures for the saline springs range from 87–137 °C and experience deep circulation. Hydrochemical characteristic coefficients suggest that saline springs in the Muang Say basin may have leached sylvinite and carnallite and that the potash exploration prospect in this area is relatively good.

Highlights

The Khorat Plateau is one of the world’s most valuable targets for the exploitation of potassium salts, which contains Sakon Nakhon Basin and Khorat Basin.The Muang Say, Vientiane, and Khammouane salt basins, located 100–600 km north of the Khorat Plateau, include extensive and thick late Cretaceous continental red beds, evaporite deposits, and saline springs [1–5]
It can be assumed that the main recharge sources for the saline springs from north and central Laos are likely to be rainfall and/or ice or snow melt from the surrounding mountains
Based on water isotope analyses, the most likely recharge sources for saline springs in this study are rainfall and/or ice and snow melt from the surrounding mountains (Phu Bia, Phu Lay, Lao Bi, and Phu Miyang), while the Dien Bien Phu fault and other stretching tensile active faults can serve as favorable conduits for allowing groundwater circulation

Summary

Introduction

The Muang Say, Vientiane, and Khammouane salt basins, located 100–600 km north of the Khorat Plateau, include extensive and thick late Cretaceous continental red beds, evaporite deposits, and saline springs [1–5]. No detailed chemical and isotopic characteristics that can assist in determining the origin and evolution of the saline springs or for assessing the prospecting potential of these salt basins exist. It is of great theoretical and practical significance to systematically analyze the cyclic evolutionary process, recharge mechanisms, and solute sources of the saline springs, which will assist in understanding its metallogenic potential and the genesis of the evaporites

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