Lithium (Li) isotopes have been shown to be fractionated significantly during chemical weathering of silicate rocks. However, previous research has mainly been focused on basalt weathering, whereas the behavior of Li isotopes during the weathering of granite remains unclear. The Li isotopic compositions in the saprolite profile developed on granite was analyzed, as well as several individual primary minerals (K-feldspar, plagioclase, quartz and biotite) in the parent granite. Lithium concentration and the isotopic compositions of the individual primary minerals appear to be heterogeneous. Biotite is rich in Li (369.4 mg/kg), but the Li concentration is very low in other minerals (1.3-11.3 mg/kg). Quartz has the highest delta Li-7 value (+19.9 parts per thousand); other minerals contain delta Li-7 within a fairly narrow range (+5.8 parts per thousand to +9.0 parts per thousand). The saprolite samples were mainly composed of primary minerals and were characterized by low weathering intensity (CIA = 52-60). Lithium was distinctly lost in the sapmlites relative to parent granite. Meanwhile, delta Li-7 values of saprolites were all lower than those of parent granites (-2.0 parts per thousand to +3.9 parts per thousand vs. +7.1 parts per thousand, respectively), which systematically decreased with increasing weathering intensity. The mineralogical composition and Sr-87/Sr-86 ratio in the saprolites suggest that the biotite was preferentially weathered below 120 cm depth in the examined profile, whereas plagioclase weathering mainly occurred above 120 cm depth. The Li released during granite weathering was characteristically different from the isotopes in the primary minerals. Lithium isotopic fractionation during granite weathering is affected by adsorption and/or incorporation of Li by secondary minerals (or clay minerals), and the release of Li from biotite. This study highlights the fact that significant Li isotope fractionation occurs during Li leaching (relatively higher Li-7/Li-6 ratios) from biotite in the incipient stage of granite weathering, which may help to explain the higher delta Li-7 values found in the dissolved load from the catchments of low weathering intensity.

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