Hickson, Catherine J.

Geothermal exploration relies in part on the gas geochemis- try of fumaroles, bubbling springs and steaming ground to offer insight into the nature of the fluids at depth, processes affecting them when rising to the surface, and provide estimates of the temperature of last equilibration of the gases within the reservoir. Traditional measurements involve direct sampling of the gases in pre-evacuated Giggenbach glass bottles before laboratory chemical analysis. Gas component analysis, combined with the isotope ratios of certain components (e.g., CO2, He), provides insight into the proportion of magmatic, crustal, meteoric and atmospheric components in the fluid, and the state of equilibrium and temperature of these fluids at depth. The Multi-component Gas Analyzing System (MultiGAS) was developed by the volcanological community over 10 years ago as a field-portable instrument for in-situ analysis of the major volcanic gas components in diffuse and dilute gas emissions. No two instruments are identical but all consist of various sensor types now capable of simultaneously analyzing for H2O, CO2, CO, SO2 and H2S. In geothermal systems, surface manifestations are often com- prised of gas emissions. In some cases, low temperatures and/or low flow rates make traditional sampling of fumaroles difficult, due to rapid vapor condensation (in water-rich fumaroles) and atmospheric contamination. The MultiGAS is best suited to these types of manifestations, providing a tool that can be used at a wide variety of locations with differing gas emission styles. The MultiGAS has been field-tested in two very different geothermal prospect areas: one characterized by cold, CO2-rich gas seeps and bubbling springs, and the other characterized by steaming ground and fumaroles with temperatures near the boiling point of water. Results of the MultiGAS analysis are compared with the equivalent ratios obtained from traditional sampling and analytical procedures (where possible), in order to identify the ad- vantages and disadvantages of this new technique. The MultiGAS allows for the rapid characterization of the gas geochemistry in the field, aids in mapping/targeting of fumaroles in a large field, and allows for the selection of the most ideal fumaroles to sample using the traditional Giggenbach method.

Chapter: This field guide describes a three-day trip from Vancouver, British Columbia, to the Wells Gray–Clearwater volcanic field (WGCVF) in east-central British Columbia. The WGCVF is the site of transitional to alkali olivine basaltic volcanism erupted over the last three million years. The small volume magmas (<1 km3) erupted along preexisting normal faults related to the late stages of Cordilleran terrane amalgamation, along the boundary between the miogeoclinal and pericratonic rocks of the Kootenay terrane and the allochthonous Slide Mountain and Quesnellia terranes west of ancestral North America. The magmas are highly enriched in incompatible elements, especially large-ion lithophile elements, and are interpreted as the result of low degrees of partial melting of a heterogeneous, metasomatized mantle. Upon ascent through the crust, they carried up both crustal and mantle xenoliths. During the eruptive period of the WGCVF, at least four glacial periods have occurred. The interplay between volcanism and glaciation is captured in the wide range of volcanic features found in the region. Field trip participants will view numerous diverse volcanic landforms and deposits: from tuyas to ice-marginal valley-edge deposits, volcanoclastic-lacustrine deposits, and associated pillow lavas and hyaloclastites. <p>Book: This volume, prepared for the 126th GSA Annual Meeting in Vancouver, Canada, offers guides to trips in the Cascadia subduction zone. The active tectonism of the region has had a profound effect on the bedrock and surficial geology of the area, and on human interactions with the geologic environment. These themes are reflected in the trips associated with the meeting. Trip topics relate to bedrock geology, volcanism and Cordilleran glaciation and deglaciation, as well as human interaction with the natural environment. The trips that discuss human interaction cover archaeology, natural hazards and the urban environment, as well as the role that local geology and tectonism have played in shaping colonization of the region since the last glaciation. The field guide volume has something for everyone! --From publisher description.