Valles Caldera geothermal systems, New Mexico, U.S.A.

Abstract

Valles Caldera is part of a Quaternary silicic volcano in northern New Mexico that possesses enormous geothermal potential. The caldera has formed at the intersection of the volcanically active Jemez lineament and the tectonically active Rio Grande rift. Volcanic rocks of the Jemez Mountains overlie Paleozoic—Mesozoic sediments, and Precambrian granitic basement. Although the regional heat flow along the Rio Grande rift is ~2.7 HFU ∗ ∗ 1 HFU (heat flow unit) = 1 μcal. s −2 cm −2 = 41.67 mW m −2. , convective heat flow within the caldera exceeds 10 HFU. A moderately saline hotwater geothermal system ( T > 260° C, Cl ⋍ 3000 mg/ l ) has been tapped in fractured caldera-fill ignimbrites at depths of 1800 m. Surface geothermal phenomena include central fumaroles and acid-sulfate springs surrounded by dilute thermal meteoric hot springs. Derivative hot springs from the deep geothermal reservoir issue along the Jemez fault zone, 10 km southwest of the caldera. Present geothermal projects are: (1) proposed construction of an initial 50-MW el power plant utilizing the known geothermal reservoir; (2) research and development of the prototype hot dry rock (HDR) geothermal system that circulates surface water through deep Precambrian basement (∼5MW th); (3) exploration for deep hot fluids in adjacent basin-fill sediments of the Rio Grande rift; and (4) shallow exploration drilling for hot fluids along the Jemez fault zone.