Roosevelt Hot Springs Thermal Area Research Articles

Trace-element distribution in an active hydrothermal system, Roosevelt hot springs thermal area, Utah

Chemical interaction of thermal fluids with reservoir rock in the Roosevelt Hot Springs thermal area, Utah, has resulted in the development of characteristic trace-element dispersion patterns. Multielement analyses of surface rock samples, soil samples and drill cuttings from deep exploration wells provide a three-dimensional perspective of chemical redistribution within this structurally-controlled hot-water geothermal system. Five distinctive elemental suites of chemical enrichment are recognized, each characteristic of a particular combination of physical and chemical conditions within the geothermal system. These are: (1) concentrations of As, Sb, Be, and Hg associated with siliceous material at locations of liquid discharge, fluid mixing or boiling; (2) concentrations of Mn, Ba, W, Be, Cu, Co, As, Sb and Hg in manganese and iron oxide deposits; (3) high concentrations of Hg in argillized rock near fumaroles and lower concentrations in a broad diffuse halo surrounding the thermal center; (4) concentrations of As in sulfides and Li in silicate alteration minerals immediately surrounding high-temperature fluid flow-controlling fractures; (5) deposits of CaCO 3 at depth where flashing of brine to steam has occurred due to pressure release. The geochemical enrichments are not, in general, widespread, pervasively developed zones of regular form and dimension as are typical in many ore-forming hydrothermal systems. As the geothermal system develops, changes and eventually declines through time, the chemical deposits are developed, remobilized or superimposed upon each other, thus preserving within the rocks a record of the history of the geothermal system. Recognition of trace-element distribution patterns during the exploration of a geothermal system may aid definition of the present geometry and interpretation of the history of the system.

Roosevelt Hot Springs Geothermal System, Utah--Case Study

The Roosevelt Hot Springs geothermal system has been undergoing intensive exploration since 1974 and has been used as a natural laboratory for the development and testing of geothermal exploration methods by research organizations. This paper summarizes the geological, geophysical, and geochemical data which have been collected since 1974, and presents a retrospective strategy describing the most effective means of exploration for the Roosevelt Hot Springs hydrothermal resource. The bedrock geology of the area is dominated by metamorphic rocks of Precambrian age and felsic plutonic phases of the Tertiary Mineral Mountains intrusive complex. Rhyolite flows, domes, and pyroclastic rocks reflect igneous activity between 0.8 and 0.5 m.y. ago. The structural setting includes older low-angle normal faulting and east-west faulting produced by deep-seated regional zones of weakness. North to north-northeast-trending faults are the youngest structures in the area, and they control present fumarolic activity. The geothermal reservoir is controlled by intersections of the principal zones of faulting. The geothermal fluids that discharge from the deep wells are dilute sodium chloride brines containing approximately 7,000 ppm total dissolved solids and anomalous concentrations of F, As, Li, B, and Hg. Geothermometers calculated from the predicted cation contents of the deep reservoir brine range from 520 to 531°F (271 to 277°C). Hydrothermal alteration by these fluids has produced assemblages of clays, alunite, muscovite, chlorite, pyrite, calcite, quartz, and hematite. Geochemical analyses of rocks and soils of the Roosevelt Hot Springs thermal area demonstrate that Hg, As, Mn, Cu, Sb, W, Li, Pb, Zn, Ba, and Be have been transported and redeposited by the thermal fluids. The geothermal system is well expressed in electrical resistivity and thermal-gradient data and these methods, coupled with geologic mapping, are adequate to delineate the fluids and alteration associated with the geothermal reservoir. The dipole-dipole array seems best suited to acquire and interpret the resistivity data, although controlled source AMT (CSAMT) may be competitive for near-surface mapping. Representations of the thermal data as temperature gradients, heat flow, and temperature are all useful in exploration of the geothermal system, because the thermal fluids themselves rise close to the surface. Self-potential, gravity, magnetic, seismic, and magnetotelluric survey data all contribute to our understanding of the system, but are not considered essential to its explorati n.

Hydrothermal alteration enthalpy and heat flow in the Roosevelt Hot Springs Thermal Area, Utah

Mass abundances of hydrothermal alteration product minerals at the Roosevelt Hot Springs thermal area have been calculated using whole rock chemistry and mineral analyses. These computations together with appropriate formulation of the alteration chemical reactions have been used to estimate total enthalpy produced per unit volume of altered rock. Enthalpy of alteration varies widely depending on the model assumed for sulfate production and the intensity of alteration. Maximum enthalpy production for the most altered rock ranges from 2450 to 7070 J/cm3, depending on whether none or all of the sulfate required to produce alunite is derived from H2S oxidation. The mean enthalpies in the lower 30 m of two drill holes 60 and 66 m deep are 345 and 105 J/cm3. Approximate age and depth‐of‐alteration constraints suggest heat flow due to alteration may be as low as 4 mW/m2 or as great as 852 mW/m2 depending on alteration intensity and sulfur oxidation. Even though chemical reactions could account for a substantial fraction of measured heat flow, comparison of measured temperatures with temperature calculations indicates an insignificant contribution of alteration reactions to present‐day heat flow. The present thermal gradient is explained in terms of convective circulation with a mass flux of water of 1.3×10−6 kg/m2 s estimated from alteration mineral abundance.

On: “A summary of the geology, geochemistry, and geophysics of the Roosevelt Hot Springs thermal area, Utah,” by S. H. Ward, W. T. Parry, W. P. Nash, W. R. Sill, K. L. Cook, R. B. Smith, D. S. Chapman, F. H. Brown, J. A. Whelan, and J. R. Bowman (GEOPHYSICS, December 1978, p. 1515–1542).

I heard the initial presentation of the subject paper during the SEG Annual Meeting at Calgary in 1977 and discussed some of my following remarks with the principal author. With its appearance in Geophysics, I believe it worthwhile to call attention to certain aspects of this paper which may not be recognized by some readers. I continue to be disturbed at the tendency of the recent computer‐oriented generation of geophysicists to concentrate on their remarkable accomplishments in computation using the digital computer, while at the same time displaying a tendency to ignore accurate portrayal of the results of such work. It seems that the means now justify the end regardless of the quality of the end. No question that the means are remarkable in the power and speed which they bring to handling otherwise intractable geophysical calculations. Nevertheless, the results of such work, in many cases in the past few years, leave much to be desired in terms of faithful reproduction of data related to natural phenomena. Furthermore, the willingness of otherwise very competent authors and geophysicists to ignore the deficiencies of the published results and maps continues to puzzle me.

A summary of the geology, geochemistry, and geophysics of the Roosevelt Hot Springs thermal area, Utah

The Roosevelt Hot Springs thermal area is a newly discovered geothermal power prospect in Utah. Seven production wells have been drilled with a maximum per well flow capability averaging [Formula: see text] of combined vapor and liquid per hour at a shut‐in bottom hole temperature near 260°C. The thermal area is located on the western margin of the Mineral Mountains, which consist dominantly of a Tertiary granitic pluton 32 km long by 8 km wide. Rhyolitic tuffs, flows, and domes cover about [Formula: see text] of the crest and west side of the Mineral Mountains within 5 km of the thermal area. The rhyolitic volcanism occurred between 0.8 and 0.5 m.y. ago and constitutes a major Pleistocene thermal event believed to be significant to the evaluation of the Roosevelt Hot Springs thermal area. Thermal waters of the (now) dry spring, a seep, and the deep reservoir are dilute (ionic strength 0.1 to 0.2) sodium chloride brines.