Describing geochemical backgrounds of lithium in rock-soil-sediment systems

Abstract

An empirical equation has been proposed to describe geochemical backgrounds of trace elements during rock weathering on weathering and lithological indices. However, with respect to lithium, the equation was derived on only 9 regolith profiles in China and was not applicable to carbonate-bearing materials with WIG (weathering index of granite) larger than 120. To derive a robust and widely used equation on geochemical backgrounds of lithium, 851 elemental abundance data including 379, 280, and 192 records of rocks, soils, and stream sediments, respectively, were used to fit the new equation.lgc = −0.02630xy2z + 0.03000xyz2 + 0.03540xy + 0.6425y + 3.288 for WIG<20 （1）lgc = 0.00001579x2yz + 0.001141y2xz - 0.9445y + 0.3650z for 20≤WIG<120 （2）lgc = 0.1849xy2z + 0.03382xyz2 + 0.6839xyz - 09414x - 1.471y + 1.070z for WIG≥120 （3）where c is the calculated geochemical background of Li in μg/g. WIG is the weathering index of granite. The x in Eq. (1) and Eq. (2) is WIG and is lg(WIG) in Eq. (3). The y is lg(Al2O3/Ti) where Al2O3 and Ti represent their contents with units of wt% and μg/g respectively. The z is lg(K2O/SiO2) where K2O and SiO2 represent their contents in wt%. The fitting data of Li, WIG, Al2O3/Ti, and K2O/SiO2 are 3.5–70 μg/g, 6.9–9400, 0.0003–0.0356, and 0.0006–0.1410, respectively. By comparison with the previous equation in a linear fitting, the newly presented equation in a nonlinear fitting is applicable to geological materials without WIG limitations. However, to the materials with WIG ranging from 0 to 120, the fitted results between the previous and the newly presented equations are generally similar. In summary, the new equation works well to describe lithium geochemical backgrounds of geological materials and could play an important role in environmental and exploration geochemistry. In mineral exploration, the method of seven levels' classification of geochemical anomaly can be improved on this newly presented equation and has been validated in the Tieshanlong tungsten deposit area in Southeastern China.