PROCEEDINGS, 43rd Workshop on Geothermal Reservoir Engineering Stanford University, Stanford, California, February 12-14, 2018 SGP-TR-213 1 Strategic and Critical Elements in Produced Geothermal Fluids from Nevada and Utah Stuart F. Simmons 1,2 , Stefan Kirby 3 , Philip Verplanck 4 and Karen Kelley 4 1 EGI, University of Utah, 423 Wakara Way, Ste 300, Salt Lake City, UT 2 Department of Chemical Engineering, University of Utah, 50 S. Central Campus Dr., Salt Lake City, UT 84112 3 Utah Geological Survey, 1594 W. North Temple St., Salt Lake City, UT 84114 4 US Geological Survey, Box 25046, MS-973, Denver Federal Center, Denver, CO 80255 ssimmons@egi.utah.edu Keywords: critical elements, geothermal, hydrocarbons, produced water geochemistry ABSTRACT Herein we summarize the results of an investigation dealing with the concentrations and inventories of strategic, critical and valuable materials (SCVM) in produced fluids from geothermal and hydrocarbon reservoirs (50-250° C) in Nevada and Utah. Water samples were collected from thirty-four production wells across eight geothermal fields, the Uinta Basin oil/gas province in northeast Utah, and the Covenant oil field in southwestern Utah; additional water samples were collected from six hot springs in the Sevier Thermal Belt in southwestern Utah. Most SCVM concentrations in produced waters range from <0.1 to 100 g/kg; the main exception is lithium, which has concentrations that range from <1000 to 25,000 ug/kg. Relatively high concentrations of gallium, germanium, scandium, selenium, and tellurium are measured too. Geothermal waters contain very low concentrations of REEs, below analytical detections limits (0.01 g/kg), but the concentrations of lanthanum, cerium, and europium range from 0.05 to 5 g/kg in Uinta basin waters. Among the geothermal fields, the Roosevelt Hot Spring reservoir appears to have the largest inventories of germanium and lithium, and Patua appears to have the largest inventories of gallium, scandium, selenium, and tellurium. By comparison, the Uinta basin has larger inventories of gallium. The concentrations of gallium, germanium, lithium, scandium, selenium, and tellurium in produced waters appear to be partly related to reservoir temperature and concentrations of total dissolved salts. The relatively high concentration and large inventory of lithium occurring at Roosevelt Hot Springs may be related to granitic-gneissic crystalline rocks, which host the reservoir. Analyses of calcite scales from Dixie Valley indicate enrichments in cobalt, gallium, gold, palladium, selenium and tellurium, and these metals appear to be depositing at deep levels in production wells due to boiling. Comparisons with SCVM mineral deposits suggest that brines in sedimentary basins, or derived from lacustrine evaporites, enable aqueous transport of gallium, germanium, and lithium. 1. INTRODUCTION This project deals with resource assessment of strategic, critical and valuable materials (SCVM) in production fluids and reservoirs across several western states. SCVM comprise a wide range of diverse elements (e.g., Critical Metals Strategy, DoE, 2011; Energy Critical Elements, American Physical Society and Materials Research Society, 2011), including an alkali metal (Li), noble gases (He, 3 He), metals and metalloids (Ag, Co, Ga, Ge, In, Ir, Nb, Os, Pd, Pt, Re, Rh, Ru, Se, Te), and rare earth elements (REEs: Ce, Dy, Er, Eu, Gd, Ho, La, Lu, Pr, Nd, Sc, Sm, Tb, Tm, Y, Yb). Previous work has been directed at targeted studies of subsets of SCVM, typically REEs, primarily in high temperature geothermal fluids from just a few sites in the USA. Accordingly, the aqueous concentrations of REEs are less than a few g/kg, whereas some metals (Te and Ag) can reach mg/kg level, and aqueous Li can exceed 100 mg/kg (e.g., McKibben and Hardie, 1997; Simmons et al., 2016; Neuapane and Wendt, 2017). This report describes new data obtained from geothermal and oil/gas fields in Nevada and Utah (Fig. 1). Production fluids and rocks from a number of fields, with reservoir temperatures ranging from 50-250° C, were sampled and analyzed. The results have been used to calculate the grades and inventories of SCVM in reservoirs, and the numbers reported herein are provisional. The results are discussed in the light of the chemical, thermal, and geological controls on hydrothermal transport of SCVM. They are also compared to geological information of known SCVM deposits in the USA. 2. SAMPLING Hot springs (37-83°C) and production wells were sampled for waters, and a subset of these sites was sampled for gases, but only the helium isotope data are reported herein. The methodology for acquiring fluid samples from geothermal wells depended on several factors, including the location(s) and availability of pipeline sample ports and temperature-pressure conditions. Where the wells are pumped to produce geothermal fluid (Blue Mountain, Patua, San Emidio, Soda Lake), samples were acquired with stainless steel coiled tubing submerged in an ice bath to prevent gas phase separation. Where the wells are self-flowing and fluid production is two-phase