Geothermal Surface Manifestations Research Articles

New MT surveys and 3D resistivity imaging beneath the Ngozi-Rungwe volcanoes at the triple rift junction of the East African Rift System in SW Tanzania: Support for integrated interpretations of geothermal conceptual models

The geothermal system related to the Ngozi and Rungwe volcanoes, SW Tanzania, lies at the intersection of the west and east branches of the East African Rift System and has been investigated by many geoscientists for decades. Here we present a 3D electrical resistivity model based on 190 magnetotelluric resistivity soundings that have been integrated with geochemical and geological results to support the development of the geothermal resource conceptual model presented here. The model includes two separate reservoirs, a larger system located beneath the Rungwe volcano and a smaller chloride water reservoir located under the Ngozi caldera, which contains a neutral chloride hot spring with geothermometry >230°C. An extensive conductive clay cap with variable thickness extends along the 30 km long NW-SE trending Ngozi-Rungwe Fault Zone from the Kiejo area SE of the Rungwe volcano to the Ngozi caldera. The absence of geothermal surface manifestations directly over the inferred Rungwe upflow zone is consistent with effective sealing of the proposed underlying geothermal reservoir by the clay cap. The scarcity of thermal manifestations on the up-dip margins of the low-resistivity clay cap can be explained by coincidence of the base of the clay cap with impermeable Precambrian formations and by structural boundaries. This interpretation implies that the area with the highest geothermal resource potential is the Rungwe volcano where proposed drilling sites might intersect the proposed high-temperature reservoir.

Delineation of geological structures of Arta geothermal prospect in Djibouti based on the gravity data analysis and interpretation

The Arta geothermal prospect is located in the southern part of the Gulf of Tadjoura, 45 km west of Djibouti city. This study uses 398 gravity data stations collected by the Djiboutian Office for Geothermal Energy Development (ODDEG) from February to May 2018. The geothermal activity of the Arta area is revealed by surface thermal manifestations, such as near-boiling fumaroles (98 °C). This study aims to delineate the subsurface geological structures responsible for surface geothermal manifestations and define the depth and geometry of the geothermal reservoir in the study area. A Complete Bouguer anomaly was obtained using a Bouguer density of 2.55 g/cm3, derived as an average density from the F-H, G-H and CVUR methods. A regional and residual anomaly trend separation method was applied to focus on the structures of interest in the study area, and a residual Bouguer anomaly map was obtained. Edge detection filters, including Horizontal Derivatives (HD) and an Improved Normalized Horizontal tilt angle (INH), were used to examine the gravity data for edge identification. The density was then modelled in three-dimensional (3-D), utilizing the VOXI Earth Modeling Tool performed in Geosoft Oasis Montaj. The model was constrained using estimated lower (-0.35 g/cm3) and upper (0.65 g/cm3) bound density values from the expected density values of the local geology. The Bouguer and residual anomaly maps show a high-density body in the central part, surrounded by low-anomaly structures. The high-density body is interpreted as an intrusive body covering the basement of the study area. The anomalies imaged from HD and INH indicate a significant number of high gradient anomalies trending N-S, NE-SW, and NW-SE, corresponding to the trend of the geological structures of the Arta geothermal prospect. These high-gradient anomalies can be interpreted as faults, contact zones, or geological boundaries. The 3-D model imaged a high-density anomaly trending N-S in the central part at 2 and 3 km below sea level with a volume of about 126 km3 and an average block density of 2.66 g/cm3, interpreted as magma intrusion or intrusive volcanic rocks. The 3-D vertical cross-sections revealed that the intrusion is visible at depth and that some intrusions could be seen at the surface and near surface. The findings of this gravity study will contribute to the overall and future geothermal exploration and development of the Arta geothermal prospect.

Prospective geothermal well and heat catchment locations in Nigeria: Remote sensing interpretations and field validation

Geothermal energy is a renewable energy that is environmentally friendly and will help reduce greenhouse emission resulting from the burning of fossil fuels. Nigeria has numerous geothermal surface manifestations like hot and warm springs in most parts of the country that has not been exploited or explored due to the initial high cost of exploration. Most research conducted on geothermal energy prospects in Nigeria considered specific geographical sections. Due to the geological features of Nigeria, the direct and indirect tectonic activities, there is the need to map the thermal anomalies over Nigeria to determine likely geothermal wells and ground heat catchment in Nigeria. Forty years remote sensing dataset (1980–2019), was obtained from the MERRA-2 for three hundred and two (302) locations across Nigeria. The acquired thermal parameters were processed using known models. The data was also analyzed statistically and spatially using the Statistical Package for Social Sciences (SPSS) and Quantum Geographic Information System (QGIS). The results of show that the Gummel-Kumaganum areas of chad basin, Owode-igbo ora areas of the Dahomey basin, Belli area of the basement complex in Taraba state, potiskum areas of the Upper benue Basin, Ekpoma-kwale, itu areas of the Niger delta basin are middle geothermal wells with the terrestial radiation of < −702 W/m2 while the terrestial radiation >200 W/m2 in the Gummi area of the sokoto basin, Hunkuyi area of the basement complex in the northeast, Gashua area of the chad basin, Ozubulu-idah area of Anambra basin, Atijere area of the Dahomey basin, Agbasa, Omoko, Akamkpa area of Niger delta basin, Shaki area of the southwest basement complex are heat catchment regions. Other heat catchment areas had been identified for standalone energy generation. Also, the thermal anomalies in those areas were significant. The validation of the result was achieved via benchmarking similar geothermal well around the globe and ground truthing at Ijebu-Ode Nigeria. Based on the thermal reversal depth (TRD) concept, Ijebu-Ode may have a deep geothermal well with temperatures pattern similar to geothermal wells in other parts of the globe. It is recommended that ground measurement should be carried out in the basement complex to cater for geothermal systems whose mechanism is based on conduction.

Structural Traits of Cuitzeo Lake, Central Mexico, and Areas of Geothermal Potential

Cuitzeo Lake, in the central part of the Trans Mexican Volcanic Belt, is in an extensional region associated with the Cuitzeo graben, where magmatic ascent appears to provide the heat sources for the surface, geothermal manifestations. A profuse distribution of andesitic rocks is observed throughout the study area of 50×50 km2. Gravity and magnetic field 3D inversions are calculated to obtain density and magnetic susceptibility distributions to 7000 m depth, from which we analyze N-S and E-W cross-sections and obtain density and magnetic susceptibility geosurfaces that help characterize anomaly areas of interest. We use satellite-derived gravity and magnetic data in our evaluation, owing to their high-resolution characteristics and uniform coverage of the study area. Analysis initiates with the San Agustín del Maíz region (SAM), exhibiting surface geothermal manifestations, to characterize its density and susceptibility characteristics, then the analysis is extended to the whole study area. Several outcropping, low magnetic susceptibility regions, like the one associated with SAM, are suggested as potential geothermal targets. Density geosurfaces point to two volumes where magmatic material may intrude, coinciding with active geologic faults. The analysis presented here can be extended to neighboring regions in the Cuitzeo Lake area and may constitute a fast, unexpensive exploration methodology in similar geothermal districts.

Origin and hydrogeochemical formation processes of geothermal fluids from the Kibiro area, Western Uganda

The Kibiro geothermal field, located in the western branch of the East African Rift Valley System, has many geothermal surface manifestations. Several geochemical research has already been carried out in this area. However, the sources of dissolved ions in geothermal fluids have not been assessed so far. The hydrochemical and gas isotopic characteristics have been examined in this study to identify and determine the sources of the main dissolved components and the geochemical processes involved in the formation of the geothermal fluid. Methods applied in the analysis of the genesis and hydrogeochemical evolution of geothermal fluids include isotope tracers, major ion ratios, graphical methods (stability diagrams, durov diagrams, chloro-alkaline indices, piper diagrams, and HNC-plot), and hydrogeochemical simulations using PHREEQC software. The Kibiro hot springs are high salinity Na–Cl waters. Based on δ18O and δ2H values, the geothermal waters are found to be of meteoric origin. The assessments indicate that Na+ and Cl− are derived from halite dissolution. The dissolution of dolomite, calcite, gypsum, and anhydrite is responsible for the concentration of Ca2+, Mg2+, SO42−, and HCO3−. The main source of K+ is derived from the dissolution of silicate rocks (K-feldspar). The gas isotopes analysis indicates that 97.5% of He with isotope ratio of 0.217 Ra mainly originates from crustal sources and 2.47% is derived from the mantle. 51.39% of CO2 originates from marine limestone, 46.55% from sedimentary organic carbon and 2.06% from the mantle. This evidence further confirms that there are no direct inputs of volatiles from a magma chamber below the Kibiro geothermal field. The evolution of the fluids suggests that most of the common cations and anions found in the Kibiro hot spring waters originated from high-temperature water/rock interaction.

Hydrothermal alteration of surficial rocks at Los Humeros geothermal field, Mexico: a magnetic susceptibility approach

Utility of the geothermal surface manifestations (GSMs; thermal springs, geysers, fumaroles, and zones of hydrothermal alteration) in the studies related to the geothermal exploration is widely recognized. The identification of hydrothermally altered rocks and zones of alteration is very important because their presence indicates the type and size of the geothermal reservoir and existing thermal conditions. The use of traditional methods (i.e., geochemistry, mineralogy, and petrography) requires expensive equipment, time-consuming, and laborious sample preparation methods. Some of the rock magnetic parameters, like magnetic susceptibility (χlf) and percentage of frequency-dependent magnetic susceptibility (χfd%), are potential to become effective additional tools in identification of the hydrothermal rocks during the initial stages of geothermal exploration. Three chemical methods, Chemical Index of Alteration (CIA), loss-on-ignition (LOI), and the binary plot (CaO + Na2O + K2O) vs. (Fe2O3 + MnO + MgO), along with two rock magnetic methods, χlf and the binary plot (χlf vs. χfd%), are applied to nine intensively altered andesite reference rocks. All the five methods have correctly identified that 99 out of the total 350 studied rocks are altered. More altered rocks are distributed surrounding the several faults in the study area. Various faults (e.g., Los Humeros fault and the Loma Blanca fault) favor fluid flow and present strong hydrothermal alteration at the surface. However, there are no altered rocks on the surface region between the E-W trending Las Papas and Las Viboras faults. The presence of only the deeper fluid pathway toward the east in the surroundings of these two faults result into the almost absence of hydrothermal alteration along their strike at the surface. Consequently, there are not many altered rocks observed surroundings these two faults at the surface. These features suggest that the surface hydrothermal alteration at Los Humeros Geothermal Field (LHGF) is controlled by faults. χlf and χfd% are reliable, simple to measure, fast, cost-effective, and have the potential to become reliable additional tools for future exploration studies.

Resistivity and Density Structure of Limboto Lake—Pentadio, Gorontalo, Indonesia Based on Magnetotelluric and Gravity Data

Limboto Lake—Pentadio area is located in the province of Gorontalo on the northern arm of Sulawesi Island, Indonesia, which experienced a tectonic process from the Sula Platform collision in the mid-Miocene. This tectonic process led to the westward subduction of the early Miocene and post-collision rifting and uplifting of the arc and subduction along the North Sulawesi Trench during the Late Miocene to the Quaternary periods. The rifting process of the North Sulawesi arc resulted in the formation of the Gorontalo graben zone in the W–E direction. There are geothermal surface manifestations near Limboto Lake, such as hot spring complexes, with temperatures ranging from 74.8 °C to 78.5 °C. To understand the geological structure and prospective geothermal characteristics beneath the investigated area, we performed integrated magnetotelluric and gravity surveys. The preferred 3D resistivity model confirmed the presence of a fault system and a graben system that was filled with conductive bodies (~1–15 Ωm) corresponding to alluvium deposits. This result was in accordance with the 2D density model inferred from the gravity data, where a low-density value indicates the presence of a graben zone. The conceptual model of Limboto Lake—Pentadio was constructed using the information from the MT and gravity results, and from the geological study. The conceptual model illustrates the geothermal system in Limboto Lake—Pentadio, which is controlled by the fault system and the Gorontalo graben system.

Investigasi Bawah Permukaan Pada Area Kawah Sikidang, Dieng, Jawa Tengah Menggunakan Metode Geolistrik

Sikidang crater geothermal manifestation area is located in Dieng geothermal field, Banjarnegara, Central Java Province, Indonesia. In 2019 more than 400,000 people visited Sikidang Crater tourism area. Some of the surface manifestation in this area include fumaroles, mud pools, steaming grounds, and altered ground. This research aim is to identify hydrothermal fluid below the surface and estimate the area of conductive zone using resistivity model from geoelectric data (dipole-dipole and Schlumberger configuration), surface temperature measurements, dan geological observation.Based on the results of 1D and 2D resistivity model, the low resistivity anomaly is thought to be a hydrothermal fluid that associated with surface geothermal manifestations appearence. The low resistivity anomaly also assumed to be associated with altered rocks in the study area, while the high resistivity anomaly is thought to be Pangonan andesitic lava with resistivity value above 1500 Ω.m. Several conductive zone dominantly identified in the Kawah Sikidang tourism area, however conductive zone also identified outside the tourism area.

Seismicity and 3-D body-wave velocity models across the Hengill geothermal area, SW Iceland

We image shallow crustal structures and analyze seismicity patterns in the Hengill high-enthalpy geothermal area in SW Iceland, exploiting a temporary densification of the seismic network 2018 to 2020. Using a subset of 6,300 high-quality manually picked P- and S-phases, we compute a minimum 1-D model for the region. Our results suggest that the most consistent and accurate hypocenter locations are derived from a joint inversion of P and S arrival times for the Hengill area. We demonstrate that this minimum 1-D model in combination with SeisComP detection and location algorithms can be used to produce fully-automated yet high-quality earthquake catalogs. Our analysis established that both the induced and natural seismicity in the Hengill area occurs in several distinct, spatially constrained clusters. In production and injection areas, the depth of the clusters is at about 2 km, near the bottom of the production and injection wells. These are most likely triggered by the injection and induced by the production, respectively. Outside of these clusters, the seismicity is generally deeper, with the depth of the deepest seismicity indicating the brittle-ductile transition zone. This zone is encountered at about 4 km near the center of the Hengill volcanic area and deepens with increasing distance from its volcanic center, to about 7 km in the southernmost region. A spatial analysis of b-values shows slightly increased values in areas with numerous injection wells and slightly decreased values in production areas. Three-dimensional crustal imaging of VP, VS, VP/VSshows a SE-NW trending fast velocity that extends, at 1–3 km depth between the extinct Grensdalur volcanic center and the presently active Hengill volcanic center. The fastest velocities are found in the NW corner of the Grensdalur volcanic center coinciding with a gravity high and probably reflecting dense solidified magmatic intrusion(s). This trend coincides with traces of geothermal surface manifestations, a shallow lying low resistivity anomaly and an aero-magnetic low. All these anomalies are caused by high temperature at some point in the geological history of the area and are most likely due to migration of the crustal accretion and volcanic activity between the two volcanic centers. Below-average VP/VSratios at similar depth, coincide with the main production field. We suggest that this anomaly is caused by the extensive fluid extraction, which lowers the pore-pressure in the field and consequently increases the steam dominated zone, leading to lower Vp/Vs ratios. Most of the earthquakes are within the Vp/Vs low and at the boundary of the high and low Vp/Vs anomalies, which might indicate a region of good permeability.

Interlaboratory test for chemical analysis of geothermal fluids: A new approach to determine deep geothermal reservoir fluid composition with uncertainty propagation

A representative fluid sampling of surface geothermal manifestations and its analytical data quality assurance and quality control (QA/QC) are challenging aspects of understanding the geothermal reservoir processes. To achieve these goals, an interlaboratory test for the chemical analyses of ten water samples: one synthetic water, two lake waters (i.e., duplicated), one stream water, and six water samples from two geothermal wells of Los Azufres Geothermal field (LAGF), Michoacan, Mexico, was conducted. The geothermal wells were sampled at four points: (1) total discharge of condensed fluid at the wellhead, (2) separate liquid condensed in the well separator, (3) flushed liquid at the weir box, and (4) separated vapor condensed at the well-separator (data taken from Verma et al., 2022). Sixteen laboratories from ten countries reported their results.The pH, electrical conductivity, Ca2+, Li+, SO42−, B, and Si-total measurements were 8.35 ± 0.04, 12.25 ± 0.53 mS/cm, 25 ± 1 mg/l, 18 ± 1 mg/l, 569 ± 33 mg/l, 320 ± 21 mg/l, and 20.5 ± 0.7 mg/l, which are close to the conventional true values, 8.40, 12.31 mS/cm, 23 mg/l, 19 mg/l, 647 mg/l, 330 mg/l, and 20.0 mg/l, respectively. Analytical errors for major ions, Na+, Cl− and CO2-Total are 17, 21, and 42 percent, respectively; however, the analytical uncertainties are relatively lower, except for CO2-Total (19%). Similarly, the analytical uncertainty for CO2-Total measurements of the lake water sample is 18%. Thus, the analytical method of individual laboratories for CO2-Total measurements needs revision.The NIST Uncertainty Machine web app was used for the stepwise geothermal reservoir fluid composition calculation with uncertainty propagation from the samples collected at different points of a geothermal well. The wellhead fluid sample does not represent the geothermal reservoir fluid, including the sample collected by connecting a portable separator at the wellhead. The samples collected at points 2 and 3 represent equally well for non-volatile species; however, the sample collected at point 2 is a better representative of geothermal reservoir fluid in analyzing the pH and alkalinity values. It is associated with considering the effect of non-condensable gases (CO2, H2S, etc.) liberated at the silencer of the weir box. The geothermal reservoir fluid pH uncertainty, an essential parameter for geochemical modeling, is three to four times the measured fluid pH uncertainty due to the propagation process. Thus, the alkalinity measurement and its calculation procedure of geothermal fluid need revision to understand its correction for the boric, silicic, and other alkalinities.

Origin and migration of fluoride in the area of the Aluto Volcanic Complex (Main Ethiopian Rift)

Fluoride-enriched ground and surface waters represent a major health risk for the local population in many areas along the East African Rift. The present study investigates the origin of fluoride and the reason for its accumulation in the rift waters, following two hypotheses: (i) fluid-rock-interactions release fluoride from minerals into the water and (ii) magmatic-derived fluoride-containing liquids and gases migrate along permeable fault zones until they dissolve in ground- and surface water or be released to the atmosphere.Rock-, gas, water-, soil-, and plant samples were collected from the area within and close by the Aluto Volcanic Complex, which is part of the Main Ethiopian Rift. Most analyzed waters showed fluoride concentrations above the drinking water limit (>1.5 mg/L) with the highest values in hot springs (up to 70 mg/L) and the geothermal well (76 mg/L). In the solid phase, a high fluoride content was found in acid volcanic rocks (ignimbrite: 4391 ppm; rhyolite: 3248 ppm) as well as in pumice (up to 1955 ppm). The fluoride content of soil samples collected within the volcanic complex varied between 82 and 1036 ppm, whereas former lake sediments from outside the Aluto Volcanic Complex showed higher fluoride contents ranging from 674 to 8171 ppm.Identified fluoride-rich minerals are various amphiboles (about 3 wt.-% F−), fluor-apatite (about 3 wt % F−), minerals of the fluor-caphite group (about 5 wt.-% F−), parisite (up to 9 wt.-% F−), and fluorite (CaF2). Elevated fluoride concentrations were also measured in some gas samples from fumaroles (up to 50 ppm) and in plant samples collected next to the fumaroles (up to 65 ppm). Leaching experiments of solid samples with deionized water demonstrated that fluoride can easily be mobilized from pumice and sediments but hardly from consolidated rocks. This fluoride release increased with temperature (up to 150 °C) and correlated roughly with dissolved silica indicating the binding of some fluoride to the amorphous or weakly crystalline silica fraction.Based on these results it was concluded that fluoride migrates via different pathways through the environment: At the depth of the magma chamber during magmatic differentiation fluoride enriches initially in the magmatic melt and accumulates in some late-crystallizing minerals of igneous rocks such as fluorite or mica. Upon volcanic eruption fluoride is predominantly incorporated in the glass (ignimbrite) and ash phase (pumice). On the surface, these rocks are exposed to weathering and fluoride leaches partly out into the aqueous phase. Soft and porous rocks such as pumice release fluoride first whereas hard extrusive/igneous rocks are less prone to weathering and retain the fluoride. Pumice and (lake) sediments might act both, as source and as sink for fluoride in the area. Although some fluoride might drain from the surface into the deeper subsoil, we conclude that magmatic fluids (liquid and gas) contribute more substantially to the overall fluoride ground water content because (i) of the much higher fluoride content in deep geothermal waters and hot springs as compared to surface-near waters; (ii) active geothermal surface manifestations located along fault zones indicate that fluids migrate from deep magmatic intrusions (as gas and liquid) towards the surface, where fluoride dissolves in groundwater; (iii) and the good correlation between bicarbonate (deriving from dissolution of magmatic CO2) and fluoride content in all analyzed water samples.

Assessment of geothermal power potential in the Gediz Basin, Turkey

By the end of 2020, the installed geothermal power capacity in Turkey reached 1643 MWe. Approximately one-fifth of the capacity of the installed power plants is located at the Gediz graben, which is geologically the second largest structure of the Menderes Massif. The Gediz graben has several geothermal surface manifestations and geothermal resources that have been discovered. When considering the structural/geological similarities between the Buyuk Menderes and the Gediz graben, both regions can be assessed as geothermal basins.The scope of this study is to estimate the geothermal power potential of the Gediz graben. To achieve this, a different stochastic approach is used rather than the conventional geothermal resource assessment. This approach involves using temperature depended volume distributions obtained from drilled wells, which lead to improved and solid results. Three hot anomalies that are identified from temperature dependent volumes are evaluated using the Monte Carlo Simulation technique. In these simulations, distribution data of other parameters are used along with data obtained from the drilled wells in the region.The power potential (MWe) values for three identified anomalies in terms of P10, P50 and P90 values are estimated to be 825, 1157 and 1524 MWe, respectively. Furthermore, additional geothermal potential discovery is predicted in the graben, provided that extensive efforts are exerted.

Regional thermal anomalies derived from magnetic spectral analysis and 3D gravity inversion: Implications for potential geothermal sites in Tanzania

Tanzania is one of the several countries intersected by the East African Rift System (EARS) endowed by a geothermal potential that has been explored only to a limited extent. Here we present the first heat flux map over the region based on the Curie point depth (CPD) estimation from aeromagnetic data. We have estimated the base of magnetic sources as a proxy for the CPD from the radially average power spectra of the total magnetic field using the centroid and the de-fractal methods. Our results show that the CPDs range ca. 11 to 43 km and are comparable to, but more detailed than global CPD estimates. The heat flow has then been computed assuming a constant thermal conductivity. In order to evaluate the results against crustal thickness, we have inverted the gravimetric regional field data constrained by the existing Moho depth from seismic receiver functions. Our analysis has revealed high heat flow values (over 100 mW/m2) along the EARS and at the Proterozoic collision boundaries that have been reactivated by the EARS. In general, the high heat flow anomalies coincide with known surface geothermal manifestations and shallow Moho depth in the range ca. 30 to 35 km. A high heat flow anomaly is also found in the central part of the Tanzanian craton, likely related to the mantle plume imaged by seismic tomography. The most interesting areas for geothermal exploration in Tanzania, according to our results, are the EARS triple junction in the Rungwe volcanic province, the north Tanzania divergent zone and the areas of the Proterozoic collision boundaries reactivated by the EARS.

Recognition of Geothermal Surface Manifestations: A Comparison of Machine Learning and Deep Learning

Geothermal surface manifestations (GSMs) are direct clues towards hydrothermal activities of a geothermal system in the subsurface and significant indications for geothermal resource exploration. It is essential to recognize various GSMs for potential geothermal energy exploration. However, there is a lack of work to fulfill this task using deep learning (DL), which has achieved unprecedented successes in computer vision and image interpretation. This study aims to explore the feasibility of using a DL model to fulfill the recognition of GSMs with photographs. A new image dataset was created for the GSM recognition by preprocessing and visual interpretation with expert knowledge and a high-quality check after downloading images from the Internet. The dataset consists of seven GSM types, i.e., warm spring, hot spring, geyser, fumarole, mud pot, hydrothermal alteration, crater lake, and one type of none GSM, including 500 images of different photographs for each type. The recognition results of the GoogLeNet model were compared with those of three machine learning (ML) algorithms, i.e., Support Vector Machine (SVM), Decision Tree (DT), and K-Nearest Neighbor (KNN), by using the assessment metrics of overall accuracy (OA), overall F1 score (OF), and computational time (CT) for training and testing the models via cross-validation. The results show that the retrained GoogLeNet model using transfer learning has significant advantages of accuracies and performances over the three ML classifiers, with the highest OA, the biggest OF, and the fastest CT for both the validation and test. Correspondingly, the three selected ML classifiers perform poorly for this task due to their low OA, small OF, and long CT. This suggests that transfer learning with a pretrained network be a feasible method to fulfill the recognition of the GSMs. Hopefully, this study provides a reference paradigm to help promote further research on the application of state-of-the-art DL in the geothermics domain.

Geothermal resources prospecting using magnetotelluric and magnetic methods at Al Ain AlSukhuna-Al Galala Albahariya area, Gulf of Suez, Egypt

Recently, several urban and service development projects were carried out at the “City of Al-Galala Mountain”, along the Egyptian Gulf of Suez, between Al Ain Al-Sukhuna and Al-Galala Al-Bahariya Plateau. This region is adjacent to the Gulf of Suez rift, which is an active geothermal area, as indicated by the geothermal surface manifestations, such as thermal hot springs. It is a zone between two tectonic plates, which is expected to have several geothermal reservoirs; consequently, it represents a potential area for geothermal prospecting. Aeromagnetic data interpretation was performed to define the deep and shallow structures in the study area and their distribution to select a suitable site and perform more detailed prospection. Consequently, two sites were chosen to conduct a detailed study, with land magnetic and (1D MT) to discover variations in conductivity (resistivity) and fix the depth of predicted geothermal reservoir as well as the distribution of deep and shallow faults which can facilitate geothermal solutions flow and injection to exploit the geothermal source energy. The obtained results showed that the study area is intensely faulted with major NW-SE trend and minor E-W trend. Meanwhile, the (MT) results show several conductive and resistive zones at different depths, which could be correlated with faulting zones, suitable to predict geothermal sources and aquifers.

The effects of alteration degree, moisture and temperature on laser return intensity for mapping geothermal manifestations

Understanding alteration processes in geothermal systems through remote sensing can help assess the prospectivity of a geothermal field. As a result of which, alteration detection and mapping are vital in the early exploration stage. However, many geothermal surface manifestations, which are evidence of alteration processes, often occur in densely vegetated areas, particularly in tropical regions. Current lithological mapping techniques using passive remote sensing systems can have problems with vegetation canopy completely blocking the signal. LiDAR, an active remote sensing system, can be a solution since it can (partially) penetrate vegetation canopy. It collects information from the ground in 3D-coordinated points with laser return intensity (LRI) values. In this study, we test for the first time the possibility of differentiating hydrothermally altered rocks through their LRI values in a laboratory experiment. We scanned selected altered and unaltered rocks under different moisture and temperature conditions using a terrestrial laser scanner (at 1550 nm wavelength). Our results show LRI values follow the degree of alteration: strongly altered rocks have the highest LRI, unaltered rocks are at the lowest, and weakly altered rocks show an intermediate response. Varying moisture conditions decrease LRI values for all rocks, but the relative LRI order due to alteration remains intact. We recorded no significant temperature effect on LRI values for any of the alteration stages. Our results provide the first evidence that rocks with different hydrothermal alteration phases can be distinguished by their LRI values which opens up the potential for airborne mapping of geothermal surface manifestations with LRI.

Structural control on shallow hydrogeochemical processes at Caviahue-Copahue Volcanic Complex (CCVC), Argentina

The Caviahue-Copahue Volcanic Complex (CCVC) hosts one of Argentina's most important geothermal systems. To provide new insights into origin, circulation, and residence time of fluids, the chemical and isotopic composition (3He/4He, δ2H-δ18O in H2O; δ13C-δ18O in CO2; 87Sr/86Sr) of thermal waters was measured together with the 3H and 14C activities. Water samples were collected from hot springs (LM, TC, LMM, CB and AF) representing the five major thermal zones of the CCVC and assumed to be steam-heated meteoric waters, and a well condensate (COP-2). The LMM, CB, and AF chemical composition and 87Sr/86Sr ratios show that water chemistry is acquired locally from exchange with volcanic rocks (Sr, SiO2, among others) and from steam (H2S). Two surface geothermal manifestations (LM and TC), along with the well condensate, COP-2, contain a higher contribution of deep-originating fluids, with 87Sr/86Sr indicating possible contribution from deep-seated granitoids or sediments from the underlying basement. Radiocarbon-based residence times indicate ages ranging between 13,540 and 17,520 yrs. BP, representing the minimum age for the geothermal reservoir waters. Tritium is mainly absent in hot spring waters except for LMM and CB where the activity is close to the detection limit. This indicates a minimum age older than 70 yrs. for the water circulating in the shallow circuit. This result suggests that shallow meteoric water have a more complex and/or deeper circuit, resulting in older residence times. Helium isotopes in the CCVC span a wide range, from a pure mantle-derived value, of 8.35Ra, to a more crustal radiogenic signature, of 4.6Ra. The spatial variation is explained by associating the geochemical data with the geological context, which includes the distribution of fault-fracture meshes and different sources of magmatic volatiles underlying the Copahue volcano. The first order control on helium isotope signatures observed in this study seems to be dominated by the degree of crustal assimilation of the magmatic sources, which is in turn controlled by the local arrays of faults.

Application of geothermal physics to support geotourism development in Maluku Province

This investigation aims to determine the hydrophysical gradient and the distribution of shallow surface geothermal manifestations. Geothermal manifestation data acquisition using the hydrophysical method. The manifestation of surface geothermal at the research location is only used by the local community as a place for bathing, and there is no accurate data regarding the potential of geothermal so that it can be used as a development of tourist objects (geotourism). The results showed the distribution of temperature and conductivity of surface hot springs based on hot springs around geothermal energy, consisting of two locations, namely the locations of Tulehu Village, Salahutu Subdistrict, and Nalahia Village, Nusalaut Subdistrict. The Tulehu Village location consists of two loci that are the Hatuasa locus with surface temperature values ranging from (60.1 - 80.9) °C and conductivity values ranging from (0.69 - 0.95) W/m. °C, and Talanghaha locus locations surface temperature values range from (65.5 - 67.5) °C, and conductivity values ranging from (0.68 - 0.78) W/m.°C. Whereas the location of Nalahia Village consists of the Bantang locus which has a surface temperature value of (50.1 - 61.9) °C, and the conductivity value is (0.51 - 0.71) W/m.°C. For this reason, the hydrothermal conditions of geothermal manifestations in the two research sites can be developed into geothermal hot water and maximum therapy to improve the economy of the local community and the development of the geotourism sector in Maluku Province.

Characteristics of surface hydrothermal alteration around Gunung Pancar area, West Java, Indonesia

Hydrothermal alteration is an interaction between rock and hydrothermal fluid by means changing the mineralogical composition of the rock. This process is controlled by permeability, chemical composition, temperature, pressure, and duration of the hydrothermal alteration. Gunung Pancar, located in West Java, is considered an outflow for Gunung Gede Geothermal System. Typical geothermal surface manifestations found around Gunung Pancar are hot springs, warm ground and surface alteration. Basic geological mapping was conducted followed by water and altered rock sampling. Petrographic and diffraction methods are completed to confirm altered protolith. Water analyses were conducted to determine water type and origin. Alteration zonation is then inferred based on the water type, intensity of alteration and then cross referenced with indication of structural geological features. Zonation reveals that the intensity of alteration gets weaker as it moves away from the apparent faults. The result suggested that the permeability of the host rock affects thermal fluid movement around Gunung Pancar and subsequently the local geothermal conceptual model.

Visualizing preferential magmatic and geothermal fluid pathways via electric conductivity at Villarrica Volcano, S-Chile

Preferential fluid pathways along regional fault systems are crucial for the spatial localization of volcanic and geothermal manifestations. Differences in electric properties of fluids and hydrothermal alteration products against the unaltered matrix allow for visualization of such pathways. Unfavorable geometry for 2-D inversion resulting from the fluid pathways in regional faults often being aligned along the geo-electric strike can be overcome by using 3D inversion of magnetotelluric data. For a section in the 1400 km long Liquiñe-Ofqui Fault System (LOFS), we demonstrate the potential of 3-D inversion of magnetotelluric data for visualization of fluid pathways.Six out of eight electric resistivity anomalies at intermediate depth are connected to volcanic or geothermal surface manifestations. Deep and highly conductive anomalies are detected in the vicinity of the volcanic chain and where the LOFS is crosscut by a fault that belongs to the Andean transversal fault system. The anomaly related to the fault crossing reveals a vertical pathway extending to the surface. Phase tensor analyses indicate a structural origin of the latter anomaly that may be connected to a line of volcanic cones that occurs in the NE of the Villarrica Volcano.