Origin and Circulation of Springs in the Nangqen and Qamdo Basins, Southwestern China, Based on Hydrochemistry and Environmental Isotopes

The Nangqen and Qamdo (NQ-QD) basins in China have very rich geothermal and brine resources. The origin and spatiotemporal evolutionary processes of its hot and saline springs however remain unclear. Geochemical and isotopic (18O, 2H, 3H) studies have therefore been conducted on the water from the geothermal and saline springs in the NQ-QD Basin. All saline springs in the study area are of the Na-Cl geochemical type while geothermal waters show different geochemical types. The oxygen and hydrogen isotopic compositions of the springs in the NQ-QD Basin are primarily controlled by meteoric water or ice-snow melt water and are influenced by rock-water interactions. It is found that the saline springs in the study area are derived from the dissolution of halite and sulfate that occur in the tertiary Gongjue red bed, while the hot springs in the QD Basin are greatly influenced by the dissolution of carbonatites and sulfates from the Bolila (T3b) and Huakaizuo (J2h) formations. Results from silica geothermometry and a silicon-enthalpy hybrid model indicate that the apparent reservoir temperatures and reservoir temperatures for the hot springs in the QD Basin range from 57–130°C to75–214°C, respectively. Deuterium analysis indicates that most of the hot springs are recently recharged rain water. Furthermore, the saline springs have a weaker groundwater regeneration capacity than the hot springs. Tritium data shows that the ranges of calculated residence times for springs in this study are 25 to 55 years, and that there is a likelihood that hot springs in the QD Basin originated from two different hydrothermal systems. The geochemical characteristics of the NQ-QD springs are similar to those of the Lanping-Simao Basin, indicating similar solute sources. Thus, the use of water isotope analyses coupled with hydrogeochemistry proves to be an effective tool to determine the origin and spatiotemporal evolution of the NQ-QD spring waters.

Hydrogeochemical Characteristics and Formation of Low-Temperature Geothermal Waters in Mangbang-Longling Area of Western Yunnan, China

Numerous low-temperature geothermal waters are distributed extensively in Mangbang-Longling of western Yunnan in China, whose formation mechanism has not been completely investigated yet. This study focused on the hydrogeochemical evolution, reservoir temperature, and recharge origin of geothermal waters using hydrogeochemical and deuterium-oxygen (D-O) isotopic studies. The low-temperature geothermal waters were characterized by HCO3-Na type, while shallow cold spring was of the hydrochemical type of HCO3-Ca. The hydrogeochemical characteristics of low-temperature geothermal waters were mainly determined by the dissolution of silicate minerals based on the geological condition and correlations of major and minor ions. The reservoir temperatures of low-temperature geothermal waters ranged from 111°C to 126°C estimated by silica geothermometry and the silicon-enthalpy graphic method. Low-temperature geothermal waters circulated at the largest depth of 1794–2077 m where deep high-temperature geothermal waters were involved. The data points of δD and δ18O of the hot spring water samples in the study area show a linear right-up trend, indicating the δ18O reaction between the water and rock and a possible mixture of magmatic water from below. The low-temperature thermal waters were recharged by meteoric water at the elevation of 2362–3653 m calculated by δD values. Upwelling by heating energy, low-temperature geothermal waters were exposed as geothermal springs in the fault and fracture intersection and mixed by up to 72% shallow cold waters at surface. Based on acquired data, a conceptual model of the low-temperature geothermal waters in the Mangbang-Longling area was proposed for future exploitation.

Origin of radioactive barite sinter, Flybye springs, Northwest Territories, Canada

Cold springs emerging a long the contact between Devonian limestone and shale units in the northwestern Canadian Cordillera are presently depositing a radium-enriched barite sinter. A geological cross section through the springs area shows that groundwaters could circulate through a mainly limestone aquifer to depths of approximately 2 km. Some shales and volcanic rocks associated with the aquifer contain: barium, bound in feldspars; barite, pyrite, and organic matter hosted in shale; and radium in feldspars or produced by the radioactive decay of uranium associated with organic matter hosted in shale. Spring waters are of the [Formula: see text] type characteristic of water that has equilibrated with clay minerals. A subsurface equilibration temperature of 34 °C was determined by silica geothermometry, and 31 °C by magnesium-corrected Na+–K+–Ca2+ geothermometry. Emerging waters are partly mixed with surface runoff and therefore these temperatures represent only minimum values. Assuming a normal geothermal gradient these temperatures indicate minimum groundwater percolation depths of 1 km. The δ34S values of barite sinter samples and one sample of aqueous sulphide range from + 15 to + 23‰, indicating a marine sedimentary rock source for sulphur. The corresponding δ18O values are negative, implying that the bulk of the sulphate oxygen is derived from groundwater during sulphide oxidation. These data suggest that the springs are fed by groundwaters that have percolated to depths of as much as 2 km, passing through an aquifer of Paleozoic marine sedimentary rocks and volcanic rocks. At depth these waters were reducing and probably weakly acidic. They dissolved barium, sulphur, and radium, which were transported to the surface where the water quickly oxidized and precipitated Ba(Ra)SO4.