| Title | FLUID-INCLUSION GAS CHEMISTRY OF THE DIXIE VALLEY (NV) GEOTHERMAL SYSTEM |
|---|---|
| Authors | Susan Juch Lutz, Joseph N. Moore, Nigel J.F. Blamey, and David I. Norman |
| Year | 2002 |
| Conference | Stanford Geothermal Workshop |
| Keywords | Dixie Valley, fluid inclusions |
| Abstract | Hydrothermally altered samples from outcrops along the eastern Stillwater Range (NV), and scale and vein samples from Dixie Valley geothermal wells were collected for fluid-inclusion analyses. Fluid-inclusion microthermometry and gas analysis by quadropole mass spectrometry were applied to establish the chemistry of the fluids trapped during alteration. Relationships between CO2/CH4, N2/Ar, and H2S were used to evaluate the origins of the inclusion fluids. Most geothermal vein samples from the wells are interpreted as mixtures of shallow meteoric and evolved meteoric ("crustal") fluids. Fluid-inclusion gases from epidote-bearing fault gouge appear to have a strong crustal signature (with low CO2/CH4 ratios). Hematite-bearing vein assemblages exhibit gas compositions that are oxidized (with high CO2/CH4 ratios), and meteoric (N2/Ar = 50-100) in origin. Analyses with high N2/Ar ratios (up to 300) indicate a magmatic origin for some fluid-inclusion gases. Actinolite-bearing veins associated with Miocene-age basaltic dikes contain mixtures of magmatic and meteoric gases. There also appears to be a small magmatic component to the gases in quartz-calcite veins from production wells. This result was unexpected because the Dixie Valley system is thought to be a deep-circulation, nonmagmatic geothermal system. However, vapor-rich fluid inclusions in production well scales and production fluids also contain some magmatic helium, and have slightly higher N2/Ar ratios than gases with a purely meteoric origin. . |