Hydrothermal alteration of graywacke and basalt by 4 m NaCl

U. S. Geol. Surv., Menlo Park, CA, United States

Separate experiments at 350 degrees C and 500 bars at a rock/fluid ratio of 1/10. Illite, dolomite, and quartz amounting to 67 percent of the original graywacke, were converted to albite and smectite. The rock gained Na and released Ca, K, heavy metals, and CO ₂ to solution. In sharp contrast, the reaction of 4 m NaCl with basalt produced only minor alteration. Albitization of graywacke produces H (super +) whereas albitization of basalt apparently consumes H (super +) . All experiments to date that have reacted basalt with sea water, natural brine, and fully saturated NaCl over a variety of conditions have been unsuccessful in producing a spilite alteration assemblage.--Modified journal abstract.

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