Li Distribution between Chlorite and Albite in a Common Vapor Phase

Abstract

<p>This study attempted to examine the process of Li enrichment in spilites by testing the hypothesis that Li is concentrated in metamorphosed basalts from hydrothermal solutions in the temperature range 400º to 700ºC and at a 1.5 kb pressure. Using a double-capsule technique Li was partitioned between albite and chlorite in a common vapor phase. These minerals were used since they are commonly found in the greenschist facies and chlorite is suspected to be the main Li host. The chlorite (clinochlore) and albite were grown from synthetic gels. A few experiments were also attempted with a natural albite and natural Fe-chlorite. Li analysis was carried out by atomic absorption and neutron activation.</p> <p>A variation between temperature and the partition coefficient of Li between albite and chlorite could not be resolved. Therefore, the average partition coefficient from all synthetic experiments was D^(alb-chl) = 0.56 ± .06. The partition coefficient in the natural system was not significantly higher, (D^(alb-chl ± 0.81 ± .46). Considerable doubt exists as to the accuracy of the vapor-mineral partition coefficients because of the poor Li mass balance. A range of possible vapor-mineral distributions was obtained:</p> <p>measured predicted from Li mass balance</p> <p>D^(vap-alb) 2.77 ± 6.45 5.97 ± 7.99</p> <p>D^(vap-chl) 1.10 ± 2.31 2.89 ± 3.34</p> <p>The measured Li partition coefficients do not explain the behavior of Li in spilites because too much Li went into the albite, and the D^(vap-chl) was not less than 1,000 so that most hydrothermal waters do not contain enough Li to produce the observed enrichment in spilites. Lithium may be precipitated in spilites at lower temperatures of pressures than those in this study.</p>