Geology Reports⌕ Search

SEARCH · Geology Reports

Results for “Ore and Energy Resource Geology”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

1,227 records · Page 5Linked to original sources
USGS2025

Assessment of water chemistry of the Coconino aquifer in northeastern Arizona

The Coconino aquifer was investigated as a potential groundwater resource for the Hopi Tribe and Navajo Nation in northeastern Arizona. Basic groundwater chemistry, including major ions, total dissolved solids, and selected trace metal concentrations, are presented and analyzed to characterize the Coconino aquifer. The geochemical compositions of groundwater are associated with changes in geology and groundwater movement and are compared to drinking-water standards to determine suitable areas for potential groundwater resource development. Dissolved-solids concentrations in much of the Coconino aquifer water were higher than the U.S. Environmental Protection Agency’s secondary drinking-water standard of 500 milligrams per liter (mg/L) due to a buried halite body in the southeastern part of the study area. However, trace metal concentrations were generally low. Groundwater may need to be treated for high dissolved-solids concentrations before it is suitable for use as a resource for the Hopi Tribe and Navajo Nation.

Arizona↗
USGS2025

Solution-collapse breccia pipe uranium deposits of the southern Colorado Plateau, northwestern Arizona, USA

Some of the highest-grade uranium deposits in the United States occur in breccia pipes that formed by solution and collapse of sedimentary strata, which occur in the southern portion of the Colorado Plateau in northwestern Arizona. The host breccia pipes are up to 1200 m in vertical extent, average about 90 m in diameter, and can cross-cut strata from their base in the Mississippian Redwall Limestone to as stratigraphically high on some plateaus as the Triassic Chinle Formation. These uranium-base metal deposits are up to 600 m thick and formed within the breccia pipes where they transect the Permian Coconino Sandstone, Hermit Formation, and the Esplanade Sandstone. Of the hundreds of breccia pipes identified across this region, only a small percentage are known to contain mineralization. The main uranium ore mineral is uraninite that is intergrown with at least 20 base-metal sulfide minerals, which contribute Fe, Cu, Co, As, Pb, Zn, Ni, and Ag to the deposits. This study considered regional stratigraphy, sulfur isotope systematics, mineralogy, in situ dating, and compilation and analysis of previous work on the deposits. A comprehensive deposit model has not been published for these deposits. This analysis identified new additions to update the deposit model for these unusual, possibly unique deposits. Proposed modifications to the model include: (1) the source, mechanisms, timing of the base-metal sulfide mineral assemblages, and (2) the source, mechanism, and timing of the uranium mineralization. Sulfide and uranium deposition are shown to be separate mineralization events. The study proposes the possible role of gypsum as a source of sulfur for the sulfide minerals in the deposits. Groundwaters carrying uranium encountered the preexisting sulfides in breccia pipes, reducing the uranyl ions, and precipitating U oxide (as uraninite). Analysis of the regional stratigraphy recognized that numerous beds of gypsum are in the strata that lie only tens of meters above the breccia pipe deposits. In the breccia pipe region, if these stratigraphic units (Toroweap and Kaibab Formations) do not contain gypsum layers then the underlying pipes are not mineralized; where these Permian gypsum layers do occur, breccia pipes can host mineralization. This new understanding should be useful in identifying the prospective region for mineralized pipes.

Arizona↗
USGS2025

Timing of hydrothermal alteration and Au-Sb-W mineralization, Stibnite-Yellow Pine district, Idaho

The Stibnite-Yellow Pine district of central Idaho was mined from the early 1900s until the 1990s, extracting gold, antimony, tungsten, and mercury from veins and disseminated and replacement ores in mountainous terrain along the headwaters of the Salmon River. Mining during the two World Wars supplied critical antimony and tungsten to the war efforts. Recent exploration has delineated mineral resources of over 187 metric tons Au, 274 metric tons Ag, and 93,000 metric tons Sb. Mineralization is hosted in Cretaceous Idaho batholith granitic rocks and a sequence of Neoproterozoic to Paleozoic metasedimentary strata of carbonate and siliciclastic compositions. Historical studies outlined some of the complex paragenesis but debated the absolute age of mineralization. New petrographic and geochronologic work documents a sequence of five hydrothermal events in the Stibnite-Yellow Pine district. Event 1 is related to Cretaceous magmatic and hydrothermal activity and includes events ranging in age from 86 to 75 Ma, including sparse quartz-molybdenite veins dated at 86 Ma. Disseminated gold mineralization of event 2 is associated with sericitic alteration and sulfidation of igneous biotite and replacement of plagioclase by potassium feldspar, largely in granodiorite. Gold is present in zoned arsenian pyrite in both disseminated ores and in crosscutting carbonate-quartz veins containing pyrite and arsenopyrite. The large Yellow Pine deposit, localized at a dilatant bend in the Meadow Creek fault, hosts such disseminated and vein gold. Event 2 is interpreted as the major gold-forming event; 40 Ar/ 39 Ar ages of sericite and potassium feldspar alteration range, respectively, from 70 to 59 and 66 to 56 Ma. The long span is interpreted to reflect the age of gold mineralization and local overprinting by event 3. A narrower range from 66 to 61 Ma is interpreted to date the peak of gold mineralization and alteration. Event 3, tungsten mineralization with scheelite, is texturally later than event 2 gold and localized along the Meadow Creek structure. Event 3 scheelite has been dated by isotope dilution-thermal ionization mass spectrometry (ID-TIMS) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb methods at 57 Ma. Event 4, best developed in the West End area, includes gold-silver–bearing quartz-carbonate-pyrite veins and breccias with epithermal textures and potassium feldspar alteration envelopes. Adularia from event 4 yields 40 Ar/ 39 Ar plateau ages of 52 to 51 Ma. Event 5 antimony and mercury mineralization consists of stibnite veins and breccia cements at the Yellow Pine and Hangar Flat deposits as well as cinnabar veins and replacements at the peripheral Fern and Hermes deposits; it is constrained by an LA-ICP-MS U-Pb date on scheelite (ca. 47 Ma) intergrown with stibnite. Minor propylitic and argillic alteration is evident in 47 Ma igneous dikes, which do not contain economic mineralization. The Au-Sb-W ores in the Stibnite-Yellow Pine mining district formed over an extended time period from about 70 to 45 Ma in multiple pulses that were localized along the Meadow Creek fault zone. Each event corresponds to episodes of magmatism and/or hydrothermal activity in the region. Insignificant event 1 skarn and molybdenum mineralization is similar in age to the Thompson Creek porphyry molybdenum deposit in central Idaho. Event 2 gold mineralization occurred during a magmatic gap in central Idaho but was synchronous with magmatism in the Bitterroot lobe further north; event 2 is similar in age to orogenic gold-arsenic mineralization at the Beartrack mine in eastern Idaho. Event 3 scheelite mineralization coincides with tungsten mineralization at the Quartz Creek deposit, late magmatism in the Bitterroot lobe, and rapid exhumation of the Atlanta lobe of the Idaho batholith. Event 4 gold mineralization is coincident with the onset of regional Challis magmatism and extension. Event 5 antimony and mercury mineralization is time-equivalent to epithermal gold mineralization in the nearby Thunder Mountain volcanic field and the peak of Challis magmatism.

Idaho↗
USGS2025

Scoping decision-maker needs and science availability to support regional natural capital accounting in the U.S. Colorado River Basin

Natural capital accounting has the potential to yield important policy insights at multiple scales, but there remains a disconnect between regional-scale natural capital accounts and their use for informing policy. In this paper, we propose a roadmap that could lead to the creation of policy-relevant regional accounts, with steps split across an initial scoping phase and a subsequent development phase. We demonstrate the scoping steps in action with an application to the Colorado River Basin (“Basin”), a large watershed in the southwestern United States (U.S.) that has faced aridification and substantial high-profile tradeoffs around the use of its water and other natural resources. Drawing on prior U.S. Geological Survey science co-production efforts, we conducted a series of eight discussion sessions with 41 scientists and science representatives whose work is relevant to Basin water, riparian and riverine ecosystems, upland ecosystems and energy and minerals. We summarise participants' thoughts on key topics and economic linkages, their insights and questions of interest and their recommendations on existing scientific data sources and gaps. We evaluate the suitability of the available data for construction of System of Environmental-Economic Accounting (SEEA) Central Framework and SEEA Ecosystem Accounting accounts, including those for land, water, forests, energy and minerals and ecosystems (covering extent, condition and ecosystem services). We present a series of lessons learned during the scoping phase, as well as lessons that could be relevant for future practitioners engaging in the development phase. The information can help guide the development of timely and relevant regional-scale environmental-economic accounts in the U.S. and beyond.

Arizona, California, Colorado, Nevada, New Mexico,↗
USGS2026

Integrating detrital magnetite geochemistry and (U-Th)/He chronometry as a sediment provenance tool in geologic and metallogenic terranes

Magnetite is ubiquitous in porphyry Cu systems and in sediment sourcing both barren and mineralized regions, with potential as an indicator mineral in concealed and coarsely-mapped terranes. We develop and test a workflow for integrated geochemistry and (U–Th)/He (He) dating for inferring detrital magnetite (DMt) provenance in these settings. The ca. 70 Ma Taurus porphyry Cu–Mo(–Au) district in eastern interior Alaska serves as a test case. DMt from streams draining porphyry-related mineralization was characterized by geochemistry and mineral inclusion and microstructure observations, complemented by similar data for potential porphyry and host rock sources. Principal component analysis and clustering of DMt geochemical data resolve multiple populations in our samples geochemically and texturally compatible with derivation from metamorphic, porphyry-related hydrothermal, and igneous sources. Hydrothermal magnetite comprises ∼16–50% of DMt nearest porphyry mineralization but diminishes to ∼4% ∼15 km downstream. Subsampled grains within populations yield ∼160–110 Ma, ∼70 Ma, ∼55 Ma, and ∼20 Ma magnetite He date modes. Combined with provenance, He dates capture Early Cretaceous regional exhumation of metamorphic host rock and Late Cretaceous porphyry Cu mineralization. DMt grains showing partial hematite replacement yield ca. 55–20 Ma dates regardless of source, overlapping regional warm/wet climatic intervals. We interpret Cenozoic dates to reflect exhumation to near-surface oxidizing conditions and(or) supergene weathering. Magnetite is thus a promising target phase for (1) tracking the spatiotemporal distribution of porphyry systems, and (2) linking the formation and exhumation of these systems to a regional geologic history, both in Alaska and globally.

Alaska, Yukon↗
USGS2026

Revisiting the utility of regional-scale, high-quality geophysical data in mineral exploration - A case study featuring the Mammoth Magnetic Anomaly, Pinal County, Arizona

Regional aeromagnetic surveys passively measure the total magnetic intensity (TMI) and are a foundational tool used in mineral exploration (Airo, 2015). With the increased global demand and the number of critical mineral resources required for manufacturing high-tech devices, developing high-quality, regional-scale geophysical surveys could aid critical mineral exploration efforts and geologic mapping. In 2019, the U. S. Geological Survey launched the Earth Mapping Resources Initiative (Earth MRI) to modernize the geologic and geophysical mapping of regions that have the potential to contain critical mineral resources within the United States. In support of planning Earth MRI geophysical surveys, Drenth and Grauch (2019) defined five aeromagnetic data quality rankings (rank 1 through rank 5) applying them to the airborne geophysical survey inventory of the United States (Johnson et al., 2021). Rank 1 aeromagnetic surveys are of the highest quality, meeting modern standards and allowing best practices for qualitative and quantitative interpretation; whereas rank 5 aeromagnetic surveys are of the lowest quality, being useful only for qualitative interpretation of broad features. Through the Earth MRI effort, 48 high-quality, regional-scale rank 1 and 2 airborne magnetic and radiometric geophysical surveys have been planned, collected, or publicly release through May 2025 (U. S. Geological Survey, 2025). Here, a portion of a rank 1 Earth MRI aeromagnetic survey in southeast Arizona is presented and compared to a legacy rank 5 aeromagnetic survey over the Mammoth Magnetic Anomaly (MMA), demonstrating how modern, high-quality aeromagnetic data improves our view of crustal geology, aiding mineral exploration.

Arizona↗
USGS2025

Assimilation of reduced carbon triggers platinum alloy saturation in mafic and ultramafic magmas

It is generally observed that magmatic sulfide ores have higher ratios of Pd/Pt than the mantle-like values of their parental magmas. This discrepancy has defied simple explanation because the partitioning behavior of both elements between sulfide and silicate liquids is very similar. Assimilation of sulfur- and carbon-rich country rocks by mafic and ultramafic magmas is considered a critical, if not essential, step in the formation of magmatic base metal sulfide deposits. Although there is general consensus that the assimilation of external sulfur and carbon promotes sulfide saturation, the effect of carbon assimilation on the solubilities of platinum-group elements in natural S-bearing silicate melt has been overlooked. In this study, we investigate the variations of platinum and palladium solubilities during assimilation of graphite and methane through thermodynamic modeling, in comparison with data from an array of highly distinctive magmatic sulfide ore systems representing ages from Archean to Paleozoic, melt compositions from komatiite to basalt, and magmatic settings including lavas, hypabyssal intrusions, plutonic continental arc roots, and plutonic layered intrusions, namely: Raglan, Norilsk-Talnakh, Lac des Iles, and the J-M Reef of the Stillwater Complex. We model assimilation-fractional crystallization processes to estimate the reduction of oxygen fugacity ( ⁠fO2⁠ ) of the melt due to incorporation of graphite and methane. The simulations show that although Pd remains highly soluble during the progressive assimilation of reduced carbon, Pt solubility decreases significantly as the silicate melt becomes increasingly reduced. With less than 8 % of sediment assimilation, Pt alloy may saturate and then deviate from sulfide-undersaturated silicate melts, concomitantly increasing the Pd/Pt value of the remaining melts of the Raglan and Norilsk-Talnakh systems. For the Lac des Iles and Stillwater systems, a higher extent of assimilation is needed to reach Pt saturation because of the relatively carbon-poor nature of the lower crustal rocks. The assimilation of methane volatiles is shown to be more effective than graphite assimilation, and it provides a pathway to Pt alloy fractionation in the absence of detectable amounts of bulk host-rock assimilation. High Pd/Pt values have been documented in many world-class magmatic sulfide deposits whose parental magmas have demonstrably experienced crustal contamination. Our model suggests that although anomalous Pd/Pt values may be explained by other mechanisms such as incongruent melting of preexisting sulfide or differences in the diffusivities of the metals within achieving equilibration, the assimilation of graphite or methane may play an important role in the global occurrence of magmatic sulfide ores with elevated Pd/Pt values.

Economic Geology↗
USGS2025

The impact of burial diagenesis on soil-formed minerals in paleosols using stable isotopes of phyllosilicates and carbonate clumped isotopes

To understand the effects of burial diagenesis on the stable isotope geochemistry of soil-formed clay and carbonate minerals in paleosols, samples were collected from seven cores, spanning middle- to upper-Pennsylvanian strata of the Illinois Basin, with varied maximum burial depths of 1–3 km. Mixed-layer illite-smectite and kaolinite mixtures give δ 2 H and δ 18 O values of −83 ‰ to −36 ‰ and 11.9 ‰ to 21.1 ‰ (VSMOW), respectively. After carbonates were screened petrographically for diagenetic textures using transmitted light and cathodoluminescence, measured clumped isotope Δ 47 values range from 0.504 to 0.563 ‰ (I-CDES). Resulting mineral formation temperatures for phyllosilicate mineral mixtures are 28 to 66 °C (mean = 47 °C), whereas T(Δ 47 ) estimates for calcites are 36 to 61 °C (mean = 45 °C). Calculated δ 18 O water values from which phyllosilicate minerals and calcites precipitated under isotopic equilibrium ranges from −7.1 to −1.2 ‰ and − 1.4 to +4.9 ‰, respectively. Closed and open-system phyllosilicate-fluid exchange modeling indicates that phyllosilicate alteration occurred in the presence of a low temperature brine or meteoric water and is interpreted to occur in a layer-by-layer illitization transformation. Due to the lack of diagenetic textures and positively correlated T(Δ 47 ) and δ 18 O water , calcites are interpreted to have undergone solid-state bond reordering. Despite low to moderate temperatures (<125 °C) and varying depths of shallow burial (1–3 km), solid-state transformation of phyllosilicates and calcites indicates paleosols had prolonged exposure to burial conditions which has implications for the use of paleosol minerals for paleoenvironmental reconstructions.

Illinois, Indiana, Kentucky↗
USGS2025

Surficial geology and Quaternary tectonics of the Madison Valley and fault zone, Madison, Gallatin, and Beaverhead Counties, southwest Montana

The north-northwest-striking Madison fault is approximately 95 kilometers in length, lying at the confluence of the northeastern Basin and Range province and the Yellowstone tectonic parabola. The fault zone consists primarily of west-dipping normal faults that have east-dipping antithetic faults, which create the Madison Valley graben and several northeast-trending intrabasin faults. The Madison fault and associated sections discussed herein refer to the main west-dipping, range-bounding fault along the eastern side of the valley. Detailed geologic mapping (1:12,000 scale) of the entire fault zone and fault scarp profiling (total of 102 profiles) of the Madison fault reveal greater late Quaternary paleoseismic activity towards the south, including at least three paleoevents along the southern part of the fault that postdate Pinedale glaciation. Early to middle Holocene alluvial fans have vertical surface offsets that average between 2.0 and 3.0 meters and define the characteristic single-event surface offset. Pinedale lateral moraines have vertical surface offsets as great as 12.0 meters. Late Pleistocene to Holocene multiple-event fault scarps show little evidence of beveling, suggesting short seismic recurrence intervals and potential late Pleistocene and Holocene temporal clustering. Long-term average tectonic activity rates indicate slip rates ranging from 0.18–0.6 millimeters per year. Based on a comparison of fault-scarp height versus maximum slope angle of known regression lines developed from other paleoseismic investigations, the most recent event ranges from 5–1 ka. The northern section of the fault zone is defined by multiple normal faults, which detached the hanging walls of Laramide thrust faults within the Paleozoic and Mesozoic strata. This resulted in the partitioning of extension along multiple preexisting structures and less displacement along individual normal fault strands. Structural controls on lateral propagation of individual paleoevents involve the position of lateral ramps along preexisting Laramide contractional faults. This resulted in greater displacement within the larger basement-cored structures along the southern section of the fault zone, where extension is accommodated by one inferred principal basement-involved normal fault. Inferred east-northeast trending, intrabasin, normal faults within the southern half of the fault zone have no late Pleistocene displacement.

Idaho, Montana, Wyoming↗
USGS2025

Gulf Coast Basin CORE-CM initiative final report

The Bureau of Economic Geology at the University of Texas at Austin (UT-BEG) is leading the Gulf Coast Carbon Ore, Rare Earth, and Critical Minerals (CORE-CM) Initiative to assess the potential to produce critical minerals (CMs), including rare earth elements (REEs) from coal, coal ash, and produced water related to oil and gas production, and related materials (alumina processing waste [red mud], heavy mineral sands, graphite, and zeolite) within the Gulf Coast Basin. This project represents the first phase in a long-term program and provides reconnaissance data that will be foundational for future work by assessing resources and suggesting plans to be conducted in future work and expanding stakeholder engagement. The project includes several tasks designed to identify, characterize, and assess several necessary aspects for development of CMs and REEs in the Gulf Coast Basin.

Gulf Coast basin↗
USGS2025

Review and synthesis of the applications of machine learning to coalbed methane recovery

Over the last 30 years, a substantial literature has evolved on the use of machine learning (ML) to assess, predict, and improve the efficiency of coalbed methane (CBM) recovery. In the United States, the production of CBM declined as shale gas production matured, but CBM continues to be an important energy resource in other parts of the world. ML applications that have the potential to improve CBM reservoir management and production forecasts, and to increase exploration and operational efficiency, are still of significant interest. The integration of geostatistical techniques into the CBM ML applications has been largely absent but represents an opportunity for improvement. The literature demonstrates the widespread interest in, and applicability of, ML algorithms applied to CBM problems, and that they continue to result in improvements in predictive performance. However, (1) much of the research is more academic than operational, (2) many results are based on simulations, or small or proprietary datasets, (3) ML performance information can be inconsistent and sometimes entirely omitted, (4) most methodologies are unique to the specific CBM situation and likely not generalizable, (5) no standard data repositories are available to directly compare the performance of competing algorithms, and (6) the spatial component is often omitted. Finally, relatively new ML protocols involving causality analysis and reinforced learning, as well as hybrid workflows combining both supervised and unsupervised learning, are anticipated to dominate the future investigations. Integration of geostatistical and geospatial analysis with ML should enhance performance.

Book chapter↗
USGS2026

Utilization of multiple geochronology techniques to constrain the age of laterization and mineralization of the world-class Mount Weld rare earth element deposit, Western Australia

Pervasive chemical weathering on stable cratons may form thick regoliths and elemental enrichment, but constraining the age of regolith formation is challenging. In this study we utilize multiple geochronological techniques on different minerals from the world-class Mount Weld rare earth element (REE) deposit, formed by lateritic weathering of a carbonatite, to constrain the age of formation and provide insight into landscape evolution. The oldest dates, ca. 100 to 38 Ma, are from Lu-Hf dating of churchite [HREE(PO 4 )·2(H 2 O)], a heavy REE phosphate mineral. Growth bands on individual minerals show a younging outwards. 40 Ar/ 39 Ar geochronology of cryptomelane [K(Mn 4+ ,Mn 2+ )₈O₁₆] yielded dates from ca. 40 to 27 Ma. Similarly, (U-Th)/He geochronology of goethite [FeO(OH)] yielded dates ranging from ca. 45 to 19 Ma. Integrating results into regional constraints, suggests 1) churchite formed by mineral saturation in a karst-like setting below the water table from ca. 100 to 40 Ma, 2) with minor uplift and erosion, cryptomelane and goethite formed at or near the water table between ca. 45 and 19 Ma, 3) after ca. 15 to 10 Ma chemical weathering within the profile had ended. Other studies document that the region experienced minimal uplift and a wet, warm climate from ca. 100 Ma to 15 Ma. These conditions and the high carbonate content of the carbonatite promote extensive chemical weathering, a deep weathering profile, and the preservation of the weathered section. This study highlights the use of multiple geochronological techniques utilizing different minerals to provide insight into how laterites form and to constrain the timing and history of the formation of this important mineral deposit.

Western Australia↗
USGS2026

Sackung at Bald Eagle ridge, central Colorado: An updated interpretation of ridge-spreading movement, structures, and mechanisms from 50 years (1975–2025) of U.S. Geological Survey research

Slow gravitational failures of mountain peaks and ridges are poorly understood. Herein, we report on 50 years of studies at a slowly spreading castellate ridge in the Sawatch Range in central Colorado. The orientations of geomorphic-structural features indicate that the fractured Precambrian granitic rock underlying the ridge has extended and spread northwestward toward the formerly glacier-covered Busk Creek valley. Results from surveying, field-based geomorphic-structural mapping using lidar, rock mass quality measurements, a passive seismic survey, and satellite radar provide a major update to research started by U.S. Geological Survey researchers in the 1970s and 1980s. New insights include a recognition that the entire ridge has slowly moved by concurrent sliding along an inferred northwest dipping, compound basal-slip surface (or zone), and through the formation of multiple grabens by normal faulting and flexural toppling along sets of pre-existing fractures that dip moderately (∼45°) to the southeast. We were unable to distinguish the presence of a sudden and strong contrast in seismic velocity across the inferred slip surface. Movement during the 50-year study period has been episodic and gradually decreasing, in correspondence with decreasing cumulative annual precipitation and increasing mean annual air temperatures. The fastest moving area, just upslope from the glacier trimline, had an average horizontal velocity of 3 – 4 mm/yr. Evidence suggests that movement started as a paraglacial response mechanism, but because of the site’s proximity to the Rio Grande Rift, we cannot exclude earthquake shaking as a mechanism for initiation or enhancement of slope movement. An estimate of longer-term horizontal movement from the exposed basal-slip surface at the uphill side of the ridgetop graben is ∼1.1 mm/yr for the 13 – 14 ky post-glacial period. Broad implications of our work are that: (1) long-term measurements (decades or longer) of slope movement can add insights into how sackungen form and evolve through time; (2) the identification of thrust faults and toes in zones of compression near valley bottoms can be crucial for interpreting sackung failure mechanisms, and (3) the use of passive-seismic techniques to identify the depth to a slip surface may not be successful in granitic terrain dominated by planar fractures and subtle changes in rock-mass characteristics.

Colorado↗
USGS2026

Conventional hydrothermal power-producing systems of the Great Basin, USA

As part of the update to the electric-grade conventional hydrothermal assessment of the Great Basin, USA, Monte Carlo analyses of identified resources within explored regions will be performed to make estimates of discovered resources and associated uncertainty. Analyses use conditional statistics where estimates are conditioned upon a hydrothermal favorability map, allowing for the likelihood that more resources exist in regions of higher hydrothermal favorability. For these analyses, a dataset of identified hydrothermal systems is compiled, and the new compilation is described herein. Recognizing that a single hydrothermal system may be developed with multiple power plants, and that the hydrothermal upflow zone may be several kilometers across with many measurements characterizing a single hydrothermal system, a procedure was developed and employed to create clusters of points (power plants, measurements, etc.) that are associated with a single system, and a new central point was defined as the best estimator of the center of the hydrothermal system. Hydrothermal systems were uniquely identified by grouping electric-grade hydrothermal measurements and operating power plants within a distance of 10 km. Groups that are >10 km apart are assumed to be different electric-grade hydrothermal systems. While 10 km was used as the threshold, most systems were significantly further apart, and most points within groups were typically within 5 km of each other. A well measurement was considered an electric-grade measurement of a hydrothermal system if it had two properties: a measured temperature of >85 °C and evidence of hydrothermal convection. Other points that were added to the dataset are locations of operating powerplants or locations that have been classified as an electric-grade hydrothermal resource by either the U.S Geological Survey (USGS) or the Great Basin Center for Geothermal Energy. After all points are assigned to systems, new points were computed with the goal of identifying the center of the throat of the hydrothermal upflow zone. If operating powerplants exist for a system, then the arithmetic average of all power plant locations is used. Otherwise, if USGS made an estimate, that location is used. In the absence of both powerplants or USGS estimates, the arithmetic average of all electric-grade measurement locations is used. An example is shown of how these newly compiled locations might be ranked for uncertainty analyses, where higher confidence is assumed if measured temperature is higher and there are many supporting measurements indicating an electric-grade resource. In summary, 28 systems have operating power plants, an additional 78 systems are known identified electric-grade hydrothermal resources, and 99 new systems were identified as probable electric-grade systems with varying levels of confidence. These 205 locations are shown as a function of a recent hydrothermal favorability map, conceptually illustrating the conditional statistics that can be used to make estimates of the undiscovered resources of the Great Basin. An accompanying data release provides summaries of developed capacity by system and USGS estimates of likely total capacity and associated uncertainty.

Arizona, California, Idaho, Nevada, Oregon, Utah↗
USGS2024

Characterizing directivity in small (M 2.4-5) aftershocks of the Ridgecrest sequence

Directivity, or the focusing of energy along the direction of an earthquake rupture, is a common property of earthquakes of all sizes and can cause increased hazard due to azimuthally dependent ground‐motion amplification. For small earthquakes, the effects of directivity are generally less pronounced due to reduced rupture size, yet the directivity in small events can bias source property estimates and provide important insights into general regional faulting patterns. However, due to observational limitations, directivity is usually only measured and modeled for large events. As such, many studies of small earthquakes either ignore directivity altogether or assume a constant rupture direction for all events in a cluster. In our study, we apply a refined directivity fitting method constrained with two separate methods of source deconvolution to the dataset of aftershocks of the 2019 Ridgecrest earthquakes, which contain a large number of well‐recorded small‐to‐mid sized earthquakes occurring in close proximity to each other. The revealed directivity of 100+ small (M 2.4–5) earthquakes is highly heterogeneous and primarily oblique to and away from the main fault strike, suggesting a complex postseismic stress redistribution. In addition, the energy focusing effect of directivity appears to bias the selection of high‐quality data from stations in the direction of rupture, leading to average stress‐drop increases of 50% if directivity is not accounted for.

California↗
USGS2026

Multiple-well monitoring site adjacent to the Midway- Sunset and Buena Vista Oil Fields, Kern County, California

Groundwater quality in and around oil fields in the Southern San Joaquin Valley is of interest to many California residents that rely heavily on groundwater for domestic, commercial, and agricultural use. To help assess the effects of historical oil-field activities and natural geologic sources on groundwater near the southwest margins of the Kern County Groundwater Subbasin, a multiple-well monitoring site was installed near the administrative boundary between the Midway-Sunset and Buena Vista Oil Fields in Kern County, California. The installation of the Midway-Sunset Buena Vista multiple-well monitoring site (MSBV) supports regional analysis of the relations of oil and gas sources to groundwater quality by providing information about the geology, hydrology, geophysical properties, and water quality of the alluvial and upper Tulare aquifers in areas where groundwater data were limited. Data collected from the site included drill cuttings, whole core samples, sidewall core samples, mud-gas analysis, borehole geophysical logs, depth to water measurements, and water quality samples. Whole cores were scanned using dual energy computed tomography. Subsamples of selected cores were analyzed for density, porosity, specific retention, and bulk minerology. Thin sections of the subsamples were prepared, photographed, and examined. Two samples were analyzed using scanning electron microscope technology to examine the microporosity of diatomite laden sediment. Instrumentation installed in the wells collect hourly depth to water measurements. Analysis of the data show there is 355 feet of alluvium overlying the Tulare Formation at the well site. The contact between the two formations is an aquitard resulting in a perched aquifer in the alluvium and unconfined aquifer in the Tulare Formation. The alluvium is more heterogenous and finer grained than the Tulare Formation resulting in markedly higher porosity in the alluvium compared to the Tulare Formation. Higher specific retention observed in the alluvium is attributed to the finer grained sediment and greater abundance of reworked diatomite (as represented by opal-CT [cristobalite-tridymite]) compared to the Tulare Formation. Total dissolved solids (TDS) approached or exceeded 10,000 milligrams per liter (mg/L) in the alluvium from approximately 176 to 242 feet below land surface and at the top of the Amnicola clay at approximately 670 feet below land surface within the Tulare Formation. Elevated TDS, chloride, and boron concentrations in the alluvium and on top of the Amnicola clay likely reflect groundwater that is mixed with oil-field water. Water chemistry and modern-aged groundwater in the alluvial monitoring well (MSBV #3) are consistent with the oil-field water in the alluvium being derived from documented historical surface disposal of oil-field water upslope (northwest) of the site. Water chemistry and pre-modern groundwater age in the deeper Tulare monitoring well (MSBV #1) on top of the Amnicola clay are consistent with oil-field fluids derived from upslope natural geologic sources or old oil wells that leak in the subsurface. Shallow groundwater in the Tulare (MSBV #2) is not affected by mixing with oil-field sources.

EarthArXiv↗
USGS2024

Insights on gas hydrate formation and growth within an interbedded sand reservoir from well logging at the Qiongdongnan Basin, South China Sea

Although variable well log resolution and its control on saturation estimation has been studied, it has not been directly applied to a specific location to explore the nature of gas hydrate within a sand reservoir. We applied in-situ measurements of resistivities, neutron porosity, and gamma ray at two sites in the Qiongdongnan Basin, South China Sea (QDN-W05–2021 and QDN-W08–2021) to investigate the reservoir parameters of a hydrate-bearing sand reservoir. Our results show that gas hydrate is distributed in 5 zones with a total thickness of 10.7 m and an average saturation of 69% at the QDN-W05–2021 site, while they are distributed in 2 zones with a total thickness of 4.3 m and an average saturation of 49% at the QDN-W08–2021 site. We found that variances in saturations estimated from lateral-extra deep button (RX), phase shift (P40H-P40L), and attenuation (A40H-A40L) resistivities within the laterally mapped continuous sand body were affected by the nature of gas hydrate occurrences. Results indicate gas hydrate forms and accumulates at the center of the sand layer and tends to be less or not present toward the top and base. Integrated with seismic data, the in-situ measurements provide insights in the evolution of a mushroom-shaped, hydrate-gas reservoir system. In the system, free gas is likely horizontally transported from the top-center of the gas chimney to the surrounding areas in the early stage dominated by a warm-gas environment, whereas hydrate forms in the opposite pathway starting from the surrounding areas in the following stage with temperature reducing. Our study suggests that high-resolution in-situ measurements not only are a tool to identify the physical properties, but also can be used to help explain the physical process of hydrate growth and accumulation.

Marine Geology↗
USGS2025

Preliminary depth to basement modeling at Salton Sea, California

The San Andreas Fault – Imperial Fault (SAF-IF) transtensional step-over zone along the southern margin of the Salton Sea hosts substantial geothermal production and lithium brine resources. Recent volcanism at the Salton Buttes and active seismicity along the SAFIF fault system highlight active tectonic and magmatic processes that pose natural hazards and may impact energy and mineral production. Characterizing the subsurface architecture and extent of concealed alteration associated with this tectono-magmatic system enhances understanding of these active processes, associated hazards, and resources. We have compiled a gravity database, consisting of new and re-processed existing data, from which we have constructed a new isostatic residual gravity anomaly map of the Salton trough. We have used this new gravity dataset together with a compilation of publicly available borehole data to develop new depth to basement inversion models for the region. These depth to basement models help to constrain basin geometries, inform alteration mapping, and reveal variations in basement rocks. Due to the concealed nature of the complex tectonic framework at the Salton trough, it is necessary to utilize geophysical methods for subsurface characterization. These new depth to basement models are a first step toward constructing 2D and 3D geophysical and geologic models of the Imperial Valley and Salton Sea geothermal area. This analysis complements other geophysical initiatives, including magnetotelluric (MT) modeling (Tokmakoff et al., 2024), magnetic mapping (Glen and Earney, 2023, 2024) and potential field modeling, and seismic studies focused on hazard and resource investigations in the Imperial Valley.

California↗