GEOTHERMAL RESOURCE POTENTIAL OF THE SAFFORD-SAN SIMON BASIN, ARIZONA by James C. Witcher Arizona Geological Survey Open-File Report 81-26 Arizona Geological Survey 416 W. Congress, Suite #100, Tucson, Arizona 85701 Funded By The U.S. Department ofEnergy Contract Number DE-FC07-79ID12009 This report is preliminary and has not been edited or reviewed for conformity with Arizona Geological Survey standards NOTICE This report was prepared to document work sponsored by the United States Government. Neither the United States nor its agents, the United States Department of Energy, nor any federal employees, nor any of their contractors, subcontractors or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, products or process disclosed, or represents that its use would not infringe privately owned rights. Reference to a company or product name does not imply approval or recommen­ dation of the product by the Bureau of Geology and Mineral Technology or the U.S. Department of Energy to the exclusion of others that may be suitable. i TABLE OF CONTENTS PAGE List Of Figures List of Tables List 5f Appendices Introduction 1 Land Status 3 Previous Work 4 Regional Setting 6 Regional Stratigraphy and Structure 12 Basement structure of the northern Safford-San Simon Basin 14 Basement structure of the southern Safford San Simon Basin 19 Basin and Range 21 Basin-Fill sediments in the Safford area 23 Basin-Fill sediments in the San Simon area 27 Indian Hot Springs-Gila Valley 29 Introduction 29 Geochemistry 29 Structure 29 Geothermometry 35 Conclusion 35 Buena Vista Area 37 Introduction 37 Geochemistry 37 Geology and Reservoir Characteristics 40 Cactus Flat-Artesia Area 50 Geology 50 Temperature Gradients 53 Mercury Soil Survey 59 Ground Water Chemistry and Geothermometry 61 Conclusion 68 ii Table of Contents (cont'd.) PAGE San Simon 69 Introduction 69 Thermal Regime 69 Geology 71 Geohydrology 74 Chemistry 74 Conclusion 77 Bowie Area 78 Introduction 78 Geochemistry 78 Structure and Stratigraphy 79 Active Tectonism 85 Conclusion 86 Whitlock Mountains Area 88 Tables 89-10.9 Appendices 110-120 Bibliography 121-131 iii FIGURES PAGE FIGURE 1 Map of thermal wells and springs (pocket) FIGURE 2 Map of land status (pocket) FIGURE 3 Location map of study area and physiographic provinces 7 FIGURE 4 Regional lineaments and crustal discontinuities 9 FIGURE 5 Map of inferred Tertiary basement lithology in southeastern Arizona 15 FIGURE 6 Major geologic structure in the Safford area 30 FIGURE 7 Schlumberger resistivity profile near Safford 33 FIGURE 8 Map showing areas with low electrical resistivity and wells which encounter evaporite minerals or brine 34 FIGURE 9 Map of fluoride distribution in the Buena Vista area 38 FIGURE 10 Dissolved carbon dioxide versus excess silica for ground water in the Buena Vista area 39 FIGURE 11 Subsurface geology and stratigraphic cross section of the hot well area near Buena Vista 41 FIGURE 12 Reconnaissance geologic map of the Buena Vista geo­ thermal area 43 FIGURE 13 Temperature versus depth profile of deep well east of Buena Vista 47 FIGURE 14 Complete Bouguer gravity map of the Buena Vista area showing areas with copper mineralization 48 FIGURE 15 Reconnaissance geologic map of the Cactus Flat-Artesia area 51 FIGURE 16 Bouguer gravity map of the Safford-San Simon Basin (pocket) FIGURE 17 Aeromagnetic map of the Safford-San Simon Basin (pocket) FIGURE 18 Location map of Dipole-Dipole electrical resistivity profiles 7 and 8 54 iv FIGURES PAGE FIGURE 19 Subsurface resistivity models and pseudosections of resistivity profiles 7 and 8 55 FIGURE 20 Temperature versus depth well data in the Cactus Flat-Artesia area 57 FIGURE 21 Map showing the area of high temperature gradients in the Artesia area. 58 FIGURE 22 Map showing distribution of soil mercury in the Cactus- Flat Artesia area 60 FIGURE 23 Anion ratios versus lithium in Cactus Flat-Artesia area ground water 62 FIGURE 24 Dissolved carbon dioxide versus excess silica in Cactus Flat-Artesia area ground water 66 FIGURE 25 Temperature versus depth data for artesian wells in the San Simon area 70 FIGURE 26 Structure contour map of the base of the blue clay unit in San Simon area 72 FIGURE 27 Structure contour map of the top of the blue clay unit in the San Simon area 73 FIGURE 28 Map of water level of artesian wells in the San Simon area in 1915 75 FIGURE 29 Estimated temperature gradients of artesian wells in the San Simon area in 1915, 76 FIGURE 30 Map showing distribution of Na-K-Ca geothermometer tem- peratures in the Bowie area 80 FIGURE 31 A gravity subsurface model of the Bowie area 81 FIGURE 32 Bouguer gravity map of Bowie area compared to locations of ground-water falls 82 FIGURE 33 Topographic profiles across the San Simon Valley 83 FIGURE 34 Map of water table in the Bowie area in 1975 84 v TABLES P~E TABLE 1 Wells with measured temperatures greater than 30oC in the Safford-San Simon Basin, Arizona 89 TABLE 2 Chemical analysis of ground waters in the Safford-San Simon area. 94-103 2A Analyses of Gila Valley-Indian Hot Springs ground waters 95 2B Analyses of Buena Vista area ground waters 96 2C Analyses of Cactus Flat-Artesia area ground waters 98 2D Analyses of San Simon area ground waters 100 2E Analyses of Bowie area ground waters WI 2F Analyses of Whitlock Mountains area ground water W2 TABLE 3 Silica and Na-K-Ca geothermometers for ground water in the Safford-San Simon area. 103-108 3A Geothermometers for the Gila Valley-Indian Hot Springs area. 103 3B Geothermometers for the Buena Vista area W4 3C Geothermometers for the Cactus Flat-Artesia area 105 3D Geothermometers for the San Simon area 106 3E Geothermometers for the Bowie area 107 3F Geothermometers for the Whitlock Mountains area W8 TABLE 4 Summary table showing aquifers in the Cactus Flat area with temperatures and estimated temperature gradients 109 vi APPENDICES PAGE APPENDIX 1 Selected:dri11ers logs 110-114 APPENDIX 2 pH correction of dissolved silica 115-118 APPENDIX 3 Arizona Bureau of Mines Memorandum on the Funk 119-120 Benevolent No. 1 Fee well near San Simon vii INTRODUCTION o In the Safford-San Simon Basin, thermal water (>30 C) flows from numerous artesian wells and springs. These wells and springs are used by several min- eral baths in the Safford area. The most notable hot water occurrence in the area is Indian Hot Springs located northwest of Safford near Fort Thomas. Nearly all wells deeper than 200 meters in the Safford area flow naturally o and have discharge temperatures greater than 30 C. Deepest of these wells, the 1,148 m Underwriters Syndicate #1 Mack oil and gas test or Mary Mack well near Pima, is indicative of a substantial low-temperature geothermal resource. The well is no longer flowing and it is believed that the pressurized water broke through the shallow and deteriorated casing after the well flow was temporarily shut-in some years ago. However, in 1933, Knechtel (1938) reports o that this well had an artesian flow of2,500 gpm of 59 C, sodium chloride water with 2,251 parts per million (ppm) total dissolved solids (TDS). Figure 1 is a map showing the location of the Safford-San Simon area. Hot springs and areas with hot wells are also shown. The study area, between Fort Thomas and San Simon, straddles a valley which is drained by the Gila and San Simon rivers. The study area is bounded by rugged mountains on the south- west and northeast sides. Topography within the study area is mostly gentle and easily accessible. Agriculture is mostly confined to the Gila River flood plain between Fort Thomas and San Jose, and along Interstate 10 from Bowie to San Simon. Important geothermal anomalies occur in all these agricultural areas. Communities in the area are closely situated to the agriculture. Rising costs and supply problems for hydrocarbon fuels have intensified the need for alternative energy sources. Developing the potential geothermal resources in the Safford-San Simon basin area could reduce energy costs and assure the area of a constant energy supply. Also, new agriculture-related 1 businesses such as food processing, grain drying or ethanol production using geothermal energy are possible. This report summarizes the geologic and geohydrologic features important to the geothermal regime of the Safford-San Simon area. The purpose of the investigation is to define areas in the Safford-San Simon basin that have potential geothermal resources suitable for direct use. Several things are required to make geothermal energy feasible. The most important requirement is the availability of a suitable geothermal resource. In order to determine resource suitability for a particular application, several questions concerning the potential resource need answering before planning and development can proceed: Is the potential resource beneath land which is favorable for development; or, in other words, what is the land own­ ership, topography, and access? What depth is the reservoir? What production temperatures are likely? What is the chemical quality of the geothermal water? What are the probable reservoir rocks and their reservoir properties? What are the subsurface geologic controls on the permeability and location of the reservoir? What is the geothermal heat source and the natural heat loss of the potential resource? Direct-use applications may use geothermal water between 300 C and l800 C. The chemical quality and production requirements vary depending on the type of utilization and heat requirement. 2 Land Status Figure 2 shows land ownership in the Safford-San Simon basin, Arizona.