Petrography Analysis At Valles Caldera - Sulphur Springs Geothermal Area (Armstrong, Et Al., 1995)

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Exploration Activity: Petrography Analysis At Valles Caldera - Sulphur Springs Geothermal Area (Armstrong, Et Al., 1995)

Exploration Activity Details
Location Valles Caldera - Sulphur Springs Geothermal Area
Exploration Technique Petrography Analysis
Activity Date 1988 - 1992
Usefulness not indicated
DOE-funding Unknown

Exploration Basis
The goal of this study was to compare Paleozoic carbonate and siliciclastic rocks collected from the Valles caldera VC-2B core hole with equivalent rocks from the Socorro caldera to better understand the controls on hydrothermal alteration and mineralization observed in the samples.
Samples were collected at 3 m intervals from the CSDP VC-2B core hole, totaling 103 samples from the Pennsylvanian Madera Limestone and underlying Sandia Formation intersected between 1296.1 and 1556.9 m depth. Polished thin sections prepared from these samples were examined using petrographic, cathodoluminescence, and scanning electron (SEM) microscopy. These investigations revealed that hydrothermal alteration in these rocks (and by association, permeability and fluid flow) is controlled by lithology and by the distribution of fractures, breccias, karsts, and shear zones in the host rocks. The matrices of poorly cemented quartz sandstones and siltstones were highly to moderately altered to quartz, chlorite, and sericite. These rocks retained much of their original permeability, whereas claystones, coarse-grained packstones and grainstones exhibited only moderate to low permeability. Micritic limestones were virtually impermeable to hydrothermal fluids, except where they are cut by small fractures filled with and bordered by envelopes of alteration minerals.

Additional References