Amphibolite dissolution mechanism under chlorine-rich conditions during freeze-thaw cycles

Abstract

The low-temperature weathering behavior of amphibolite is vital for revealing the cation source of groundwater and for understanding a wide range of geochemical evolution. This study aims to observe the macroscopic and microscopic characteristics of amphibolite dissolution under the freeze-thaw cycles (-25–25 °C) and chlorides (HCl, NaCl, KCl). The results show that Mg-hornblende was dissolved in chloride solutions of the same pH or concentration before albite. The change rule of the solution composition of freeze-thaw cycles is consistent with the results obtained from the dissolution experiment at room temperature. In addition, in an HCl solution of pH 1 and NaOH solutions of pH 11, 13, and 14, the dissolved amount of quartz in amphibolite can reach 11 wt %. KCl can powerfully dissolve quartz and efficiently dissolve Si in the silica-oxide tetrahedron (especially the T2 site) of Mg-hornblende. However, NaCl significantly dissolves cations in the Mg-hornblende octahedron. Analysis indicates that the leaching of Ca2+ and Mg2+ in proton-promoted dissolution strongly depended on the concentration of H+. At the same time, the release of Mg is closely related to Cl−. The results can help understand chemical element migration in the earth, especially providing a theoretical basis for groundwater cation in the Qaidam Basin.