SILICA-CARBONATE ALTERATION OF SERPENTINE - WALL ROCK ALTERATION IN MERCURY DEPOSITS OF CALIFORNIA COAST-RANGES

Chemical, isotopic, and thermodynamic properties have been measured of CO2-rich ground waters in the central California Coast Ranges. The acidic CO2-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 CO2 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 CO2-rich fluids react directly with peridotite or dunite, massive magnesite deposits may form. © 1973 Society of Economic Geologists, Inc.