Cathy Janik Lynne Fahlquist Linda S. Johnson Jacob B. Lowenstern 1999 We present 45 chemical and isotopic analyses from well discharges at The Geysers geothermal field and summarize the most notable geochemical trends. H₂ and H₂S concentrations are highest in the Southeast Geysers, where steam samples have δD and δ¹⁸O values that reflect replenishment by meteoric water. In the Northwest Geysers, samples are enriched in gas/steam, CO₂, CH₄, and N₂/Ar relative to the rest of the field, and contain steam that is elevated in δD and δ18O, most likely due to substantial contributions from Franciscan-derived fluids. The δ13C of CO₂, trends in CH₄ vs. N₂, and abundance of NH₃ indicate that the bulk of the non-condensable gases are derived from thermal breakdown of organic materials in Franciscan meta-sediments. application/pdf en Geothermal Resources Council Compilation of gas geochemistry and isotopic analyses from The Geysers geothermal field: 1978-1991 article