A Reconnaissance Geochemical Study Of La Primavera Geothermal Area, Jalisco, Mexico

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Journal Article: A Reconnaissance Geochemical Study Of La Primavera Geothermal Area, Jalisco, Mexico

The Sierra La Primavera, a late Pleistocene rhyolitic caldera complex in Jalisco, Mexico, contains fumaroles and large-discharge 65°C hot springs that are associated with faults related to caldera collapse and to later magma insurgence. The nearly-neutral, sodium bicarbonate, hot springs occur at low elevations at the margins of the complex, whereas the water-rich fumaroles are high and central. The Comision Federal de Electricidad de Mexico (CFE) has recently drilled two deep holes at the center of the Sierra (PR-1 and Pr-2) and one deep hole at the western margin. Temperatures as high as 285°C were encountered at 1160 m in PR-1, which produced fluids with 820 to 865 mg/kg chloride after flashing to one atmosphere. Nearby, PR-2 encountered temperatures to 307°C at 2000 m and yielded fluids with chloride contents fluctuating between 1100 and 1560 mg/kg after flashing. Neither of the high-temperature wells produced steam in commercial quantities. The well at the western margin of the Sierra produced fluids similar to those from the hot springs. The temperature reached a maximum of 100°C near the surface and decreased to 80°C at 2000 m. Various geothermometers (quartz conductive, Na/K, Na-K-Ca, Δ18O(SO4-H2O) and D/H (steam-water) all yield temperatures of 170 ± 20°C when applied to the hot spring waters, suggesting that these spring waters flow from a large shallow reservoir at this temperature. Because the hot springs are much less saline than the fluids recovered in PR-1 and PR-2, the mixed fluid in the shallow reservoir can contain no more than 10-20% deep fluid. This requires that most of the heat is transferred by steam. There is probably a thin vapor-dominated zone in the central part of the Sierra, through which steam and gases are transferred to the overlying shallow reservoir. Fluids from this reservoir cool from ~170°C to 65°C by conduction during the 5-7 km of lateral flow to the hot springs.

Gail A. Mahood, Alfred H. Truesdell and Luis A. Templos M

Published Journal 
Journal of Volcanology and Geothermal Research, 1983

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Gail A. Mahood,Alfred H. Truesdell,Luis A. Templos M. 1983. A Reconnaissance Geochemical Study Of La Primavera Geothermal Area, Jalisco, Mexico. Journal of Volcanology and Geothermal Research. (!) .