Characterization of gas chemistry and noble-gas isotope ratios of inclusion fluids in magmatic-hydrothermal and magmatic-steam alunite

Abstract

Chemical and isotope data were obtained for the active gas and noble gas of inclusion fluids in coarse-grained samples of magmatic-hydrothermal and magmatic-steam alunite from well-studied deposits (Marysvale, Utah; Tambo, Chile; Tapajós, Brazil; Cactus, California; Pierina, Peru), most of which are discussed in this Volume. Primary fluid inclusions in the alunite typically are less than 0.2 Am but range up to several micrometers. Analyses of the active-gas composition of these alunitehosted inclusion fluids released in vacuo by both crushing and heating indicate consistent differences in the compositions of magmatic-hydrothermal and magmatic-steam fluids. The compositions of fluids released by crushing were influenced by contributions from significant populations of secondary inclusions that trapped largely postdepositional hydrothermal fluids. Thermally released fluids gave the best representation of the fluids that formed primary alunite. The data are consistent with current models for the evolution of magmatic-hydrothermal and magmatic-steam fluids. Magmatic-steam fluids are vapordominant, average about 49 mol% H 2 O, and contain N 2 , H 2 , CH 4 , CO, Ar, He, HF, and HCl, with SO 2 the dominant sulfur gas (average SO 2 /H 2 S=202). In contrast, magmatic-hydrothermal fluids are liquid-dominant, average about 88 mol% H 2 O, and contain N 2 , H 2 , CO 2 , and HF, with H 2 S about as abundant as SO 2 (average SO 2 /H 2 S=0.7). The low SO 2 /H 2 S and N 2 /Ar ratios, and the near-absence of He in magmatic-hydrothermal fluids, are consistent with their derivation from degassed condensed magmatic fluids whose evolution from reduced-to-oxidized aqueous sulfur species was governed first by rock and then by fluid buffers. The high SO 2 /H 2 S and N 2 /Ar with significant concentrations of He in magmatic-steam fluids are consistent with derivation directly from a magma. None of the data supports the entrainment of atmospheric gases or mixing of air-saturated gases in meteoric water in either magmatic-hydrothermal or magmatic-steam fluids. Thus, the oxidation of SO 2 to aqueous sulfate in the magmatic-steam fluids did not result from mixing with atmospheric oxygen. Both of the fluid types are characterized by high H 2 contents that range from 0.2 mol% to the extraordinarily large amounts (66 mol%) observed in some magmatic-steam fluids. Modeling of gas speciation using SOLVGAS requires most of the gas species to have been in disequilibrium at the time of their trapping in the fluid inclusions. The origin of such extreme H 2 concentrations, although problematic, is thought to be largely related to accumulation of H 2 from the reaction of water with ferrous iron during the rise of This article is a U.S. government work, and is not subject to copyright in the United States. magma and probably even after exsolution of fluid from a magma. The large contents of reduced gases in the inclusion fluids are far in excess of those observed in volcanic emanations, and are thought to reflect the close bsampling positionQ of ...

Seismically induced changes of the fluid signature detected by a multi‐isotope approach (He, CO2, CH4, N2) at the Wettinquelle, Bad Brambach (central Europe)

“…However, where would the CO come from and how might it be produced? In principle, CO may be formed by the catalytic reduction of CO 2 with H 2 [ González et al , 2005], but then CO may also be a component of fluid inclusions [e.g., Bergman and Dubessy , 1984; Anderson and Neumann , 2001; Landis and Rye , 2005]. An impulsive increase in the emission of reduced gas species (H 2 and CO) was also found in relation to a rapid upward migration of magma at the Etna volcano [ Pecoraino and Giammanco , 2005].…”

100th Anniversary Special Paper: Vapor Transport of Metals and the Formation of Magmatic-Hydrothermal Ore Deposits

“…13; tip of arrow "a") to form an extremely acid liquid rich in HCl and H 2 SO 4 . Such fluids are responsible for the halos of advanced argillic alteration (kaolinite, pyrophyllite, alunite) and intense rock leaching (e.g., residual vuggy quartz) observed around fumaroles (Delmelle and Bernard, 1994) and as hosts to highsulfidation epithermal Au ± Cu ± As deposits (Ransome, 1907;Brimhall and Ghiorso, 1983;Stoffregen, 1987;Landis and Rye, 2005). The magmatic vapors causing this alteration may also transport the ore metals and form economic deposits by precipitation directly from the vapor phase or after condensation into meteoric water.…”

The Spar Lake Strata-Bound Cu-Ag Deposit Formed Across a Mixing Zone Between Trapped Natural Gas and Metals-Bearing Brine

“…Methods follow previously reported QMS and noble gas techniques and applications to various types of hydrothermal ore deposits (Landis and Hofstra, 1991;Landis and Rye, 2005;. Methods follow previously reported QMS and noble gas techniques and applications to various types of hydrothermal ore deposits (Landis and Hofstra, 1991;Landis and Rye, 2005;.…”

“…Sample 31-666.4, from just outside and below the southwestern fringe of the Upper East orebody, had high concentrations (18 to >36%) of CH 4 and yielded less than 50 mol % H 2 O (nonaqueous fluid) in all three runs. In fluid inclusion gas analyses of metals deposits (Norman and Sawkins, 1985;Norman et al, , 1991Landis and Hofstra, 1991;Walder et al, 1991;Boer et al, 1995;Mavrogenes et al, 1995;Sherlock et al, 1995;Landis and Rye, 2005;Camprubi et al, 2006), only samples from orogenic gold deposits hosted in lower greenschist facies host rocks and from pre-ore paragenetic stages from Jerritt Canyon have had CH 4 concentrations greater than 10 mol %. In Figure 6, H 2 O-CO 2 -CH 4 proportions of fluid inclusion volatiles from most of the methane-rich fluid inclusions from ore deposits studied to date by quadrupole mass spectrometry are plotted for comparison with the new results from Spar Lake.…”