Lithium isotopes in the system Qz-Ms-fluid: An experimental study

The fractionation of lithium isotopes among quartz, muscovite, and a chloride-bearing aqueous fluid has been investigated experimentally at 400 degrees-500 degrees C and 50-100 MPa. Experiments were performed for 15-60 days in cold seal vessels with natural mineral specimens. Lithium was introduced primarily through the fluid, which also contained KCl and HCl. In most runs, the fluid was prepared with the L-SVEC standard (delta(7)Li = 0) and was 1 M in total chloride with K/Li/H = 100/10/1. In two experiments, a Li-6 spike was employed. The experiments demonstrate that quartz and muscovite are susceptible to pronounced, rapid shifts in Li isotopic composition by diffusion through interaction with a Li-bearing fluid, particularly at 500 degrees C. At 500 degrees C, fractionation factors were determined to be Delta(quartz-aqueous) congruent to +8 to +12 parts per thousand and Delta(muscovite-aqueous) congruent to +18 to + 20 parts per thousand. An intermineral fractionation factor is given by Delta(muscovite-quartz) approximate to +9 parts per thousand. At 400 degrees C, the results suggest Delta(quartz-aqueous) approximate to +4 to + 6 parts per thousand. The study provides evidence of systematic fractionation in lithium isotopes at the temperatures of some magmatic processes, such as those associated with porphyry-type ore systems and pegmatites. Copyright (C) 2005 Elsevier Ltd.