Crustal Imaging and Characterization Team

Noble Gas Geochemistry

Task Objectives

This task has three objectives:

1. maintenance of the instrumentation and support infrastructure,
2. evolving development of new methods and techniques and calibrations appropriate for general operation of the lab, and with importance to a broad spectrum of applications originating in any Program; and
3. continued development of software enabling instrument control, data acquisition / reduction, and report generation.

Routine maintenance and repair or replacement of electronics, computers, vacuum pumps and valves, hardware development including welding and machining of parts necessary to implement new or modified procedures, and software are routine expenses in operation of this type of analyical facility that is separate from a project-specific cost. Pumps, valves, and electronics fail and must be repaired/replaced. On-going software development is improving the level of automation and ease of operation while performing very complex multi-step procedures. In addition to unforseen but predictable maintenance costs, continued development of improved automation, and of general procedures for sampling and analysis of gases/noble gases in groundwater samples will be performed this year, with creation of calibration standards and methods. Additionally, development of more efficient methods for analysis of gases extracted from fluid inclusions will be completed this year. Software for routine data reduction and reporting will be written.

Statement of Work

Analytical methodology and automation much improved for noble gas tracer and solubility studies and tritium-3He chronology of ground waters accomplished this year. Analyses for active (permanent) gas species, and concentrations and isotopic abundances for He, Ne, Ar, Kr, and Xe are somewhat routine. Attention will focus on development of improved analytical methods of fluid inclusion contained gas, with emphasis on rapid loading and exchange of samples, and programming (using C++ and Matlab)complex data reduction and interpretation of mass spectra. Calibration of volumes and mass spectrometer peak intensities and determination of best methods for gas extraction from fluid inclusions is planned. Ultimate small size and number of fluid inclusions will be determined at optimized sensitivity, with the hope of using UV laser system to analyze targeted individual fluid inclusions. These capabilities will provide major support to MRP projects, and enable novel applications in climate, ecology, and hazards studies.

Highlights & Key Findings

Major development highlight has been the implementation of complex full computer automation of feasable portions and steps of analyses. Developed new control thermocouple placement apparatus for high temperature low blank tantalum furnace. Successful design and fabrication of low blank furnace multi-sample drop loader with gate valve interlock and drop funnel-furnace blast "shutter" plate, easy sample loading while maintaining quick pumpdown and vacuum recovery. Developed inexpensive water sampling device and reliable method for attaching to gas extraction manifold, with inexpensive custom copper tube clamps. Developed new crushing device for opening fluid inclusions for active and noble gas analyses, and modified/improved design for extraction and purification of gas dissolved in water samples. Designed and fabricated super cold He cryotrap for improved selective separation of Ar, Kr, Xe for analysis and calibration of each noble gas. Concentrations and isotopes of these noble gases are now routine. In cooperation with Auslog Ltd (Australia) we have developed fully integrated sampling and logging suite of tools for discrete depth sampling and parameter measurement in water wells to depth of >3000 ft. Highlight is a sensor using a semi-permeable membrane to measure dissolved gas pressures at depth in well with fast real-time response. The total dissolved gas sensor employs a high tech space shuttle pressure transducer in a USGS designed chamber that is deployed in a conventional Auslog sonde. These tools are critical to obtaining appropriate samples and Temp. conductivity, hydrostatic pressure, and dissolved gas pressure profiles to characterize aquifer waters with depth in open well boreholes. Our recent studies illustrate that minimal water flow occurs vertically along the annulus of open water wells, minimizing the need for strategically placed packed intervals within the well.These new USGS-developed tools are applicable to hydrologic studies, investigations of coal bed methane well gases (and water geochemistry), methane hydrate studies, and 3D modeling of aquifer flow models.

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