Silica-carbonate alteration of serpentine: Wall rock alteration in mercury deposits of the California Coast Ranges

Chemical, isotopic, and thermodynamic properties have been measured of CO ₂-rich ground waters in the central California Coast Ranges. The acidic CO ₂-rich waters react with serpentine to form silica-carbonate rock, the host rock of many mercury deposits in the Coast Range of California. In part the waters are of a metamorphic origin and in part the waters are locally derived meteoric waters. The CO ₂ is entirely derived from metamorphic reactions at depth. Depending on the relative importance of several reactions, the relative abundances of silica and carbonate minerals vary in the silica-carbonate rock. If the CO ₂-rich fluids react directly with peridotite or dunite, massive magnesite deposits may form. © 1973 Society of Economic Geologists, Inc.