Exploring the formation mechanism of cold mineral springs in the potassic basaltic region of Wudalianchi, Northeast China

The groundwater chemistry is determined by the complex interaction between temperature-water-rock-gas. Therefore, it is a great challenge to study the formation mechanism of cold mineral spring-Erlongyan Spring, which is located in the Wudalianchi Global Geopark in Northeast China. A multiphase reactive transport model that integrated with fluid, heat transfer, and chemical reaction was employed to simulate the evolutions of water heat and water chemistry in Erlongyan Spring. Firstly, the mechanism of water migration-heat transfer was established. The low temperature rainfall penetrated into the basalt aquifer with relatively high temperature, and through heat transfer, the temperature of Erlongyan Spring reached 3.8 °C. Secondly, the source of CO₂ was determined. CO₂ from the magma chamber of the upper mantle escaped into basalt aquifers via volcanic eruption channels to participate in water evolution. By comparing the maximum weathering amount of minerals at the bottom of aquifer with or without CO₂ injection, it can be seen that the growth rate of mineral weathering in the presence of CO₂ was forsterite (411 %) > ferrosilite (260 %) > albite (242 %) > K-feldspar (222 %) > diopside (100 %). Finally, based on the coupling simulation of heat-water chemistry, the weathering and precipitation of minerals, the migration of ions at low temperature were analyzed. The presence of CO₂ enhanced the mineral weathering, but the contents of $M{g}^{2+}$, $N{a}^{+}$ and $K^{+}$ in the groundwater failed to increase. The main reasons for this phenomenon were that secondary clay minerals were more likely to be generated and remain stable in cold environment, thereby consuming these ions through chemical reactions and adsorption, and reducing the release of ions into the fluid through inhibiting the mineralization of clay minerals. However, the participation of CO₂ leaded to the increase of $H_{2}Si{O}_4^{2-}$ and $C{a}^{2+}$ in groundwater, which is consistent with the actual situation (How metasilicic acid mineral water got its name and no carbonate was found in SEM observations). The cold environment, CO₂ gas and secondary clay minerals together create unique water chemistry of Erlongyan Spring. This study provides scientific guidance for predicting the response of heat-water chemistry system under changing environment and protecting rare cold mineral springs.