Behavior of Li, Rb and Cs during basalt glass and olivine dissolution and chlorite, smectite and zeolite precipitation from seawater: Experimental investigations and modelization between 50° and 300°C

This study investigates experimentally the behavior of Li, Rb and Cs during the hydrothermal alteration of a basalt glass and of forsterite. The behavior of trace alkalis during the dissolution of a basalt glass and forsterite has been followed between 150° and 300°C: Rb and Cs are preferentially leached from the glass while Li exhibits a stoichiometric release with respect to silica. On the other hand, incongruent loss of Li relative to Si during forsterite dissolution reflects a crystallographic (site energy) control of the release of trace elements from crystalline silicates. The partitioning of Li, Rb and Cs between hydrothermal solutions and chlorites, smectites and zeolites has been experimentally investigated between 50° and 260°C. The alteration phases were synthesized by altering silicate glasses in solutions containing the trace alkalis. The lower the temperature, the higher the exchange capacity of the mineral or the lower the ionic hydration energy, then the more the element is incorporated into the solid phases. Computer simulations generated with the EQ3/6 software package and our experimental data on distribution coefficients account for the behavior of alkali trace elements during the alteration of basalt glasses by seawater at mid-ocean ridges.