Geochemical and geochronological characteristics of basalts in the Tianxinggang area within the Jitai Basin, Jiangxi Province, and their implication for lithium-rich brine deposits

The Jitai Basin in Jiangxi Province has an important potential of brine-type lithium resource, yet the basic geological study is very limited at present. The recently discoved basalt in the Tianxinggang area in the southern part of the Jitai Basin provides important scientific information for understanding the tectonic evolution and deep geological processes of the basin. In this study, we have carried out the petrographic, major and trace element geochemical, and LA-ICP-MS zircon U–Pb chronological studies of the basalt in the Tianxinggang area in order to explore its origin and geological significance. The basalt in the Tianxinggang area is trachybasalt. It is mainly composed of plagioclase and clinopyroxene with small amount of olivine and amphibole. It belongs to the shoshonite series with high alkaline and potassic properties. Its samples are characterized with relatively low SiO2 contents (47.72%-48.38%), high MgO contents (6.27%-7.20%), high total alkali contents (5.24%-5.68%), and Mg# values ranging from 34.71 to 37.70. The basalts are relatively enriched in elements of Rb, Ba, Sr, and U, and relatively depleted in elements of Pb, Sm, Y, with a clear fractionation of light and heavy rare earth elements and with no obvious Eu and Ce anomalies. It is suggested that the basalt in the Tianxinggang area was formed by magma derived from the partial melting of garnet spinel lherzolite through the minimal crustal contamination and insignificant magmatic crystallization differentiation processes. As an intraplate basalt, its magma could have provided the energy and material substrates for the formation of lithium-rich brine in the basin. The area nearby has potential for exploring lithium-rich brine resources. The zircon U–Pb age of (73.6±1.3) Ma of the basalt indicates that the Jitai Basin was in an extensional and subsiding tectonic environment at that time of basaltic magam eruption and was limitedly affected by the subduction of the western Pacific plate.