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Fluid inclusion studies of calcite veins from Yucca Mountain, Nevada, Tuffs: Environment of formation

Conference ·
OSTI ID:60925
 [1];  [2];  [3]
  1. Harvard Univ., Cambridge, MA (United States)
  2. Geological Survey, Denver, CO (United States)
  3. Los Alamos National Lab., NM (United States)
Calcite vein and vug fillings at fourth depths (130-314m), all above the present water table in USW G-1 bore hole at Yucca Mountain, Nevada, contain primary fluid inclusions with variable vapor/liquid ratios: most of these inclusions are either full of liquid or full of vapor. The liquid-filled inclusions show that most of the host calcite crystallized from fluids at <100{degrees}C. The vapor-filled inclusions provide evidence that a separate vapor phase was present in the fluid during crystallization. Studies of these vapor-filled inclusions on the microscope crushing stage were interpreted in an earlier paper as indicating trapping of an air-water-CO{sub 2} vapor phase at {open_quotes}100{degrees}C{close_quotes}. Our new studies reveal the additional presence of major methane in the vapor-filled inclusion, indicating even lower temperatures of trapping, perhaps at near-surface temperatures. They also show that the host calcite crystals grew from a flowing film of water on the walls of fractures open to the atmosphere, the vapor-filled inclusions representing bubbles that exsolved from this film onto the crystal surface.
Research Organization:
American Society of Civil Engineers, New York, NY (United States); American Nuclear Society, La Grange Park, IL (United States)
OSTI ID:
60925
Report Number(s):
CONF-940553--Vol.4
Country of Publication:
United States
Language:
English