Empirical equations to describe trace element behaviors due to rock weathering in China

Abstract

To describe element behavior due to rock weathering, Gong et al. (2013) presented a new Weathering Index of Granite (WIG) and fitted exponential equations between trace element contents and WIG values. Five new regolith profiles developed over igneous rocks and phyllite in China are investigated along with nine other reported regolith profiles formed on multiple rocks in China to investigate the quantitative relationship between trace element contents and chemical indices of weathering. Three weathering indices of WIG, Al2O3/Ti, and K2O/SiO2 are used to quantitatively describe trace element behaviors due to rock weathering. On the basis of 13 regolith profiles developed over igneous rocks, phyllite, schist, and carbonate rocks, the equation is presented aslgc=A*1.2−WIG/100+B*lgAl2O3/Ti+C*lgK2O/SiO2+Dwhere c is the content of trace element in ng/g for Cd, Hg and μg/g for others, the content unit of Al2O3, K2O, SiO2 is weight % and the unit of Ti content is μg/g, and A, B, C, D are the fitted parameters. Empirical equations for 27 trace elements are regressed with well statistical significance, and the WIG value is limited to less than 120, SiO2 content is in the range of 14% to 80%, and the value of 10,000×Al2O3/Ti varies from ca. 8 to 160. These empirical equations have an important potential application on determining geochemical backgrounds of trace elements.