Hydrothermal alteration in well Baca 22, Baca geothermal area, Valles Caldera, New Mexico

A number of exploration wells were drilled to supply steam for a proposed electric generating plant. Drill cuttings from one of these wells, Baca 22, were studied with a petrographic microscope and by x-ray diffraction to determine the nature of the original rocks and of the hydrothermal alteration. The hydrothermal alteration is used to determine the temperatures of alteration which can then be compared with borehole temperatures to determine if the mineral assemblages are compatible with present day temperatures. It is shown that there is evidence indicating that the upper 2000 feet of borehole is cooler now than it has been in the past. Sample sizes were limited in this study (usually less than 5 grams). In most cases, one quarter of the sample was used to make the thin section while the remainder was reserved for x-ray analysis. Samples were mounted in epoxy and cut to a thickness of 30 microns for petrographic study. X-ray diffraction patterns were obtained using a Debye-Scherrer camera and Fek..cap alpha.. radiation