Natural systems evidence for the alteration of clay under alkaline conditions; An Example from Searles Lake, California

Savage, D.*; Benbow, S.*; Watson, C.*; Takase, Hiroyasu*; Ono, Kaori*; Oda, Chie  ; Honda, Akira

Mudstones containing smectite have been altered under mildly alkaline conditions (9 pH 10) at Searles Lake, California over a 3 million-year time period. This natural alteration has been simulated incorporating time-dependent boundary conditions of sedimentation and fluid composition, a Pitzer model for activities of aqueous species, and a coupled hydrogeological model for time-dependent flow in the sediment layers. Kinetic dissolution of detrital smectite under alkaline conditions was described using one of two models based on departure from thermodynamic equilibrium or by an empirical rate dependent upon aqueous Si concentrations. The zonal pattern of smectite dissolution observed at Searles Lake was reproduced reasonably well by the "Cama-TST" model of montmorillonite dissolution. This assessment provides a test of the accuracy and reliability of published data in the application of models of smectite dissolution in the long-term.