Hydrothermal alteration in Oregon's Newberry Volcano No. 2: fluid chemistry and secondary-mineral distribution
Newberry 2 was drilled in the caldera floor of Newberry Volcano, Oregon, by the US Geological Survey during 1979-81. The maximum temperature measured was 265C at the bottom of the hole, 932 m below the surface. Rocks recovered fr9om the drill hole are divided into three intervals on the basis of hydrothermal alteration and mineral deposition: (1) 0-290 m consists of unaltered, largely glassy volcanic material, with present temperatures ranging from 20 to 40C; (2) 290-700 m consists of permeable tuff layers, tuff breccia units, and brecciated and fractured rhyodacitic to dacitic lava flows, with temperatures ranging from 40 to 100C; (3) 700-932 m consists of impermeable andesitic to basaltic lava flows that generally show little effect of alteration, interlayered with permeable hydrothermally altered flow breccia, with temperatures gradually increasing from 100 at 700 m to 265C at 932 m. Hydrothermal alteration throughout the system is controlled by rock permeability, temperature, composition of geothermal fluids, and composition and crystallinity of host rocks. Rock alteration consists mainly of replacement of glass by clay minerals and, locally, zeolites, partial replacement of plagioclase phenocrysts by calcite +/- epidote +/- illite, and whole-rock leaching adjacent to fluids channels. Open-space deposition of hydrothermal minerals in fractures, vesicles, and interbreccia pore space is far more abundant than replacement. A cooling shallow convection system in the upper 700 m is indicated by the occurrence of hydrothermal minerals that were deposited in a slightly higher temperature environment than presently exists. Below 700 m, the heat flow is conductive, and fluid flow is controlled by horizontal lava flows. Homogenization temperatures of secondary quartz fluid inclusions were as high as 370C.
- Research Organization:
- Geological Survey, Menlo Park, CA
- OSTI ID:
- 6137676
- Journal Information:
- Bull., Geotherm. Resour. Counc. (Davis, Calif.); (United States), Vol. 13:4
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
HYDROTHERMAL SYSTEMS
MINERALS
ROCKS
HYDROTHERMAL ALTERATION
OREGON
CHEMICAL COMPOSITION
GEOLOGY
GEOTHERMAL FIELDS
GEOTHERMAL FLUIDS
GEOTHERMAL RESOURCES
RESOURCE DEVELOPMENT
ENERGY SYSTEMS
FEDERAL REGION X
FLUIDS
GEOTHERMAL SYSTEMS
NORTH AMERICA
RESOURCES
USA
152003* - Geothermal Data & Theory- Rock-Water-Gas Interactions