Granite alteration as the origin of high lithium content of groundwater in southeast Hungary

The study aimed to find the origin of the high lithium content of groundwater in southeast Hungary. To be concerned with assessing the economic potential of lithium in these waters, it is necessary to investigate the lithium-releasing geochemical processes. For this purpose, granite and pegmatite samples were analysed for lithium content and alteration from various Battonya Complex locations. The key alteration processes are the chloritisation of biotite and the sericitisation of feldspar, which are hypothesised to mobilise Li from minerals into the geothermal waters. Whole-rock analyses show that the 36 ppm Li concentration in one sample (S1) exceeded the average crustal Li concentration (-20 ppm), while three samples have near-average crustal con-centrations. The Li content of rock samples decreases along with the increasing intensity of alteration. The Li concentration of biotite, muscovite, chlorite, feldspar and quartz from granites and pegmatite was measured using laser-induced-breakdown-spectrometry (LIBS). A total of 180 data points were analysed. Biotite and muscovite of the relatively fresh granites contain Li up to-3800 and-2500 ppm, respectively. Chloritisation is a hydrothermal alteration process in granites that can be described by the following reaction: biotite + plagioclase -> chlorite + epidote + titanite + muscovite. As a function of chloritisation, Li concentration de-creases two-and three orders of magnitude from biotite to chlorite in the more altered cases. A similar trend is observed for muscovite in parallel. Feldspars have Li of 17-141 ppm, while there is no correlation between the Li content of feldspars and the degree of alteration. Quartz contains constant low concentrations around the 1 ppm detection limit, with one outlier value of 48 ppm. Chloritisation of biotite is a possible explanation for the high Li content of the geothermal waters in the study area and possibly elsewhere. The main Li-bearing minerals of the Battonya Complex are biotite and muscovite. Chloritisation and subordinate sericitisation result in significant lithium loss. Chlorite can incorporate Li in its crystal lattice but to a lesser degree than the other sheet silicates, like biotite and muscovite.