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The Snake River Plain (SRP) volcanic province overlies the track of the Yellowstone hotspot, a thermal anomaly that extends deep into the mantle. Most of the area is underlain by a basaltic volcanic province that overlies a mid-crustal intrusive complex, which in turn provides the long-term heat flux needed to sustain geothermal systems. Previous studies have identified several known geothermal resource areas within the SRP. For the geothermal study presented herein, our goals were to: (1) adapt the methodology of Play Fairway Analysis (PFA) for geothermal exploration to create a formal basis for its application to geothermal systems, (2) assemble relevant data for the SRP from publicly available and private sources, and (3) build a geothermal PFA model for the SRP and identify the most promising plays, using GIS-based software tools that are standard in the petroleum industry. The study focused on identifying three critical resource parameters for exploitable hydrothermal systems in the SRP: heat source, reservoir and recharge permeability, and cap or seal. Data included in the compilation for heat source were heat flow, distribution and ages of volcanic vents, groundwater temperatures, thermal springs and wells, helium isotope anomalies, and reservoir temperatures estimated using geothermometry. Reservoir and recharge permeability was inferred from the analysis of stress orientations and magnitudes, post-Miocene faults, and subsurface structural lineaments based on magnetics and gravity data. Data for cap or seal included the distribution of impermeable lake sediments and clay-seal associated with hydrothermal alteration below the regional aquifer. These data were used to compile Common Risk Segment maps for heat, permeability, and seal, which were combined to create a Composite Common Risk Segment map for all southern Idaho that reflects the risk associated with geothermal resource exploration and identifies favorable resource tracks. Our regional assessment indicated that undiscovered geothermal resources may be located in several areas of the SRP. Two of these areas, the western SRP and Camas Prairie, were selected for more detailed assessment, during which heat, permeability, and seal were evaluated using newly collected field data and smaller grid parameters to refine the location of potential resources. These higher resolution assessments illustrate the flexibility of our approach over a range of scales.

Play Fairway Analysis (PFA) in geothermal exploration originates from a systematic methodology developed within the petroleum industry and is based on a geologic, geophysical, and hydrologic framework of identified geothermal systems. We tailored this methodology to study the geothermal resource potential of the Snake River Plain and surrounding region, but it can be adapted to other geothermal resource settings. We adapted the PFA approach to geothermal resource exploration by cataloging the critical elements controlling exploitable hydrothermal systems, establishing risk matrices that evaluate these elements in terms of both probability of success and level of knowledge, and building a code-based ‘processing model’ to process results. A geographic information system was used to compile a range of different data types, which we refer to as elements (e.g., faults, vents, heat flow, etc.), with distinct characteristics and measures of confidence. Discontinuous discrete data (points, lines, or polygons) for each element were transformed into continuous interpretive 2D grid surfaces called evidence layers. Because different data types have varying uncertainties, most evidence layers have an accompanying confidence layer which reflects spatial variations in these uncertainties. Risk layers, as defined here, are the product of evidence and confidence layers, and are the building blocks used to construct Common Risk Segment (CRS) maps for heat, permeability, and seal, using a weighted sum for permeability and heat, but a different approach with seal. CRS maps quantify the variable risk associated with each of these critical components. In a final step, the three CRS maps were combined into a Composite Common Risk Segment (CCRS) map, using a modified weighted sum, for results that reveal favorable areas for geothermal exploration. Additional maps are also presented that do not mix contributions from evidence and confidence (to allow an isolated view of evidence and confidence), as well as maps that calculate favorability using the product of components instead of a weighted sum (to highlight where all components are present). Our approach helped to identify areas of high geothermal favorability in the western and central Snake River Plain during the first phase of study and helped identify more precise local drilling targets during the second phase of work. By identifying favorable areas, this methodology can help to reduce uncertainty in geothermal energy exploration and development.

The role of wetlands in hunter-gatherer settlement-subsistence systems has long been a topic of discussion in Great Basin archaeology. Despite clear cultural continuities between southern Idaho and the Great Basin, the role of wetland features in prehistory within the Snake River Plain has largely been overlooked. This paper will analyze surface assemblages from seasonal playas on the Orchard Combat Training Center to infer site function, mobility and general periods of occupation to provide a baseline for future research. [ABSTRACT FROM AUTHOR]

Point counts of wintering land birds using Russian Olive (Elaeagnus angustifolia) stands were conducted in 2000 and 2005 on the Snake River Plain, Idaho. The 14 most common species of the 28 recorded were found in both years, and most common species were recorded with similar frequencies between years. Thirteen bird species were observed foraging on Russian Olive fruits. Increases in recent decades in both area occupied by Russian Olive and in counts of Yellow-rumped Warblers (Setophaga coronata) and American Robins (Turdus migratorius) on Christmas Bird Counts suggest that there may be a relationship between Russian Olive expansion and abundance of these species. [ABSTRACT FROM AUTHOR]

• Play Fairway Analysis is adapted for use in geothermal exploration. • An example is developed for Snake River Plain volcanic province in southern Idaho. • Risk maps produced for heat, permeability, and seal using new and published data. • Play Fairway method is shown to be effective paradigm for discovering new resources. The Snake River Plain (SRP) volcanic province overlies the track of the Yellowstone hotspot, a thermal anomaly that extends deep into the mantle. Most of the area is underlain by a basaltic volcanic province that overlies a mid-crustal intrusive complex, which in turn provides the long-term heat flux needed to sustain geothermal systems. Previous studies have identified several known geothermal resource areas within the SRP. For the geothermal study presented herein, our goals were to: (1) adapt the methodology of Play Fairway Analysis (PFA) for geothermal exploration to create a formal basis for its application to geothermal systems, (2) assemble relevant data for the SRP from publicly available and private sources, and (3) build a geothermal PFA model for the SRP and identify the most promising plays, using GIS-based software tools that are standard in the petroleum industry. The study focused on identifying three critical resource parameters for exploitable hydrothermal systems in the SRP: heat source, reservoir and recharge permeability, and cap or seal. Data included in the compilation for heat source were heat flow, distribution and ages of volcanic vents, groundwater temperatures, thermal springs and wells, helium isotope anomalies, and reservoir temperatures estimated using geothermometry. Reservoir and recharge permeability was inferred from the analysis of stress orientations and magnitudes, post-Miocene faults, and subsurface structural lineaments based on magnetics and gravity data. Data for cap or seal included the distribution of impermeable lake sediments and clay-seal associated with hydrothermal alteration below the regional aquifer. These data were used to compile Common Risk Segment maps for heat, permeability, and seal , which were combined to create a Composite Common Risk Segment map for all southern Idaho that reflects the risk associated with geothermal resource exploration and identifies favorable resource tracks. Our regional assessment indicated that undiscovered geothermal resources may be located in several areas of the SRP. Two of these areas, the western SRP and Camas Prairie, were selected for more detailed assessment, during which heat, permeability, and seal were evaluated using newly collected field data and smaller grid parameters to refine the location of potential resources. These higher resolution assessments illustrate the flexibility of our approach over a range of scales. [Display omitted] [ABSTRACT FROM AUTHOR]

[1] This study presents paleomagnetic results from the Snake River Plain (SRP) in southern Idaho as a contribution to the time-averaged field global database. Paleomagnetic samples were measured from 26 sites, 23 of which ( 13 normal, 10 reverse) yielded site mean directions meeting our criteria for acceptable paleomagnetic data. Flow ages (on 21 sites) range from 5 ka to 5.6 Ma on the basis of Ar-40/Ar-39 dating methods. The age and polarity for the 21 dated sites are consistent with the Geomagnetic Reversal Time Scale except for a single reversely magnetized site dated at 0.39 Ma. This is apparently the first documented excursion associated with a period of low paleointensity detected in both sedimentary and igneous records. Combining the new data from the SRP with data published from the northwest United States between the latitudes of 40degrees and 50degreesN, there are 183 sites in all that meet minimum acceptability criteria for legacy and new data. The overall mean direction of 173 normally magnetized sites has a declination of 2.3degrees, inclination of 61.4degrees, a Fisher concentration parameter (kappa) of 58, and a radius of 95% confidence (alpha(95)) of 1.4degrees. Reverse sites have a mean direction of 182.4degrees declination, -58.6degrees inclination, kappa of 50, and alpha(95) of 6.9degrees. Normal and reversed mean directions are antipodal and indistinguishable from a geocentric axial dipole field at the 95% confidence level. Virtual geomagnetic pole dispersion was found to be circularly symmetric, while the directional data were elongate north-south. An updated and corrected database for the northwestern U. S. region has been contributed to the Magnetics Information Consortium (MagIC) database at http://earthref.org.

Highlights • The 1.59 Ga Gawler Range Volcanics (GRV) and Roxby Downs Granite contain clusters of touching crystals. • Clusters comprise Fe-Ti oxides, plagioclase, apatite, zircon, pyroxene, titanite and biotite. • GRV crystal clusters formed within an upper crustal magma reservoir. • Similar features in North American and Gawler Craton rocks suggest shared genetic scenarios. • Transformation of GRV-type to HS-type crystal clusters is proposed. Abstract The Roxby Downs Granite (RDG), host to the supergiant Olympic Dam deposit, and the Gawler Range Volcanics (GRV) in South Australia, both contain clusters of touching silicate and oxide minerals. Here we report on the geochemistry and petrography of these rocks and their contained mineral clusters, before comparing them to similar occurrences elsewhere in the world to gain a better understand of their genesis and the links between the RDG (and other members of the Hiltaba Suite) and the GRV. Crystal clusters in the RDG comprise magnetite + apatite ± titanite ± biotite ± zircon which are typically enveloped in a plagioclase crystal-matrix. In the GRV, crystal clusters comprise pyroxene + titanomagnetite ± plagioclase ± apatite ± zircon, display variably glomeroporphyritic, equigranular, poikilitic, and loosely packed habits, and are enclosed by texturally varied groundmass. Of the GRV lavas studied, pyroxenes and titanomagnetite show systematic trends in major and trace element compositions conformable with the stratigraphic position of their hosts. This suggests the lavas are related through differentiation in the upper crust and represent the inversion of a normally zoned reservoir. There are no compositional contrasts between phenocrysts and crystals in GRV clusters, and Mg# of pyroxenes are consistent with those predicted from whole-rock compositions, implying that all analysed crystals (including those in clusters) were formed within, or were at least equilibrated to, the host lavas' precursors. Rather than entire histories as isolated crystal clusters entrained by melt flow, intergrowth textures and mafic magmatic enclaves suggest that the majority of GRV crystal clusters were liberated from closely packed crystal masses through magma rejuvenation and associated crystal resorption. Consistent Fe-Ti oxide + apatite + zircon + plagioclase assemblages and textures in both the GRV and RDG suggest a shared genetic scenario, although an extended model is needed to account for the transformation of GRV-type to HS-type crystal clusters. For hot and dry magmas such as those that formed the GRV and RDG, cooling causes pyroxene + Fe-Ti oxide + plagioclase in GRV-type crystal clusters to react with each other and the melt, forming HS-type magnetite + titanite + biotite + feldspar crystal clusters. Rejuvenation events implicated in the liberation of GRV-type crystal clusters may be important drivers of magmatic-hydrothermal iron-oxide deposit formation. [ABSTRACT FROM AUTHOR]