Geothermal Manifestations Research Articles

Geology, ore deposits and hydrothermal venting in Bahía Concepción, Baja California Sur, Mexico

Abstract Bahía Concepción is located in the eastern coast of the Baja California peninsula and it is shaped by northwestern–southeastern normal faults. These are associated with a 12–6 Ma rifting episode, although some have been reactivated since the Pliocene. The most abundant rocks correspond to the arc related Comondú Group, Oligocene to Miocene, which forms a mainly calc‐alkaline volcanic and volcaniclastic sequence. There are less extensive outcrops of sedimentary rocks, lava flows, domes and pyroclastic rocks of Pliocene to Quaternary ages. The Neogene volcanism in the area indicates a shift from a subduction regime to an intraplate volcanism related to continental extension and the opening of an oceanic basin. The Bahía Concepción area contains numerous Mn ore deposits, being the biggest at El Gavilán and Guadalupe. The Mn deposits occur as veins, breccias and stockworks, and are composed by Mn oxides (pyrolusite, coronadite, romanechite), dolomite, quartz and barite. The deposits are hosted in volcanic rocks of the Comondú Group and, locally, in Pliocene sedimentary rocks. Thus, the Mn deposits formed between the Middle Miocene and the Pliocene. The mineralized structures are associated with Miocene northwestern–southeastern fault systems, which are analogous to those associated with the Cu‐Co‐Zn‐Mn deposits of El Boleo. The Bahía Concepción area also bears subaerial and submarine hot springs, which are associated with the same fault systems and host rocks. The submarine and subaerial geothermal manifestations south of the bay are possibly related with recent volcanism. The geothermal manifestations within the bay are intertidal hot springs and shallow submarine diffuse venting areas. Around the submarine vents (5–15 m deep, 87°C), Fe‐oxyhydroxide crusts with pyrite and cinnabar precipitate. In the intertidal vents (62°C), aggregates of opal, calcite, barite and Ba‐rich Mn oxides occur covered by silica‐carbonate stromatolitic sinters. Some 10–30 cm thick crustiform veins formed by chalcedony, calcite and barite are also found close to the vents. The hydrothermal fluids exhibit mixed isotopic compositions between δ18O‐enriched meteoric and local marine water. The precipitation of Ba‐rich Mn oxides around the vent sites could be an active analog for the processes that produced Miocene to Pliocene hydrothermal Mn‐deposits.

Natural emissions of methane from geothermal and volcanic sources in Europe

It has recently been demonstrated that methane emission from lithosphere degassing is an important component of the natural greenhouse-gas atmospheric budget. Globally, the geological sources are mainly due to seepage from hydrocarbon-prone sedimentary basins, and subordinately from geothermal/volcanic fluxes. This work provides a first estimate of methane emission from the geothermal/volcanic component at European level. In Europe, 28 countries have geothermal systems and at least 10 countries host surface geothermal manifestations (hot springs, mofettes, gas vents). Even if direct methane flux measurements are available only for a few small areas in Italy, a fair number of data on CO 2, CH 4 and steam composition and flux from geothermal manifestations are today available for 6 countries (Czech Republic, Germany, Greece, Iceland, Italy, Spain). Following the emission factor and area-based approach, the available data have been analyzed and have led to an early and conservative estimate of methane emission into the atmosphere around 10,000 ton/yr (4000–16,000 ton/yr), basically from an area smaller than 4000 km 2, with a speculative upper limit in the order of 10 5 ton/yr. Only 4–18% of the conservative estimate (about 720 ton/yr) is due to 12 European volcanoes, where methane concentration in volcanic gases is generally in the order of a few tens of ppmv. Volcanoes are thus not a significant methane source. While the largest emission is due to geothermal areas, which may be situated next to volcanoes or independent. Here inorganic synthesis, thermometamorphism and thermal breakdown of organic matter are substantial. Methane flux can reach hundreds of ton/yr from small individual vents. Geothermal methane is mainly released in three countries located in the main high heat flow regions: Italy, Greece, and Iceland. Turkey is likely a fourth important contributor but the absolute lack of data prevents any emission estimate. Therefore, the actual European geothermal–volcanic methane emission could be easily projected to the 10 5 ton/yr levels, reaching the magnitude of some other natural sources such as forest fires or wild animals.

Geothermal Energy-Economy, Potential and Utilization Possibilities in Turkey

In this study, first of all, a general description of geothermal energy has been made and types of geothermal fields have been described. Later on, types of heat transfer within the Earth's crust and also various plate tectonics theories responsible for the geothermal manifestations throughout the world, have been explained. Within this context, Turkey's real geothermal energy capacity, and on the other hand, insufficient present use of this natural source, have been given. Having mentioned the general utilization possibilities of geothermal energy, its use particularly in the fields of electricity generation, greenhouse heating and central district heating in Turkey has been investigated and the problems encountered in these applications have been put forward. Consequently, a practical and economical comparison has been made among different sorts of heating sources and it has been concluded that geothermal energy acts as a clean, cheap and renewable natural source only if it is extracted and utilized prudently and necessary environmental measures are taken beforehand.

Thermal effects of massive CO2 emissions associated with subduction volcanism

Abstract Large volumes of CO 2 are emitted during volcanic activity at convergent plate boundaries, not only from volcanic centres. Their C isotopic signature indicates that this CO 2 is mainly derived from the decarbonation of subducted limestones or carbonated metabasalts, not as often admitted from magma degassing. On the example of Milos (Aegean Sea) it is argued that these fluids originate from intermediate depth in the mantle and carry sufficient heat to account for the generation of subduction-related magmas, as well as for the geothermal manifestations at the surface. The heat that is required for the decarbonation reactions is drawn by conduction from a wide zone surrounding the subducting slab and then rapidly transported upward by convection of the mixed CO 2 –H 2 O fluids that originate from the sediments in the slab. The transport takes place in a focused way through ‘chimneys’ in the upper mantle, where magmas are generated by the introduced heat and water. In the crust, the hot fluids cause thermal-dome-type metamorphism. In volcanic areas, magmas are commonly held responsible for the major part of heat transfer from the mantle to the surface. Here it is argued that most of the heat transfer is by hot gases. To cite this article: R.D. Schuiling, C. R. Geoscience 336 (2004).

Radon and helium in soil gases at Cañadas caldera, Tenerife, Canary Islands, Spain

The spatial distribution of soil radon was investigated at Cañadas caldera, Tenerife, in two surveys carried out in the summers of 1992 and 1995 by using α-particle-sensitive cellulose nitrate films (Track-Etch) and emanometry, respectively. Soil helium was studied at several transects crossing different structural features of the area. Radon concentration measured by Track-Etch ranged from 1.0 to 1990 pCi/l while that measured by emanometry ranged from 0.1 to 618 pCi/l. Soil helium concentration varied from 5250 to 15 560 ppb with an average value of 6197 ppb. The spatial distribution of soil radon correlates quite closely with structural features (fractures, emission centers, etc.), where the main geothermal manifestations (fumaroles, steam ground and high subsurface temperature and gas contents) also occur. Areas showing high soil Rn concentrations occur at the summit of Teide, Roques de Garcı́a, caldera rim and south and east off side of the caldera. High soil helium anomalies correlate well spatially with those of radon, especially at the summit of Teide where relatively high 3He/ 4He isotopic ratios occur, suggesting a deep contribution for these emanations. Data indicate that radon and helium are supplied mostly from a deep source, with a minor contribution from U- and Th-rich shallow rocks and soils.

Low- to medium-temperature geothermal reserves in Mexico: a first assessment

In this work we make a first, partial, assessment of the low- to medium-temperature geothermal reserves of Mexico. The assessment covers about 30% of the identified geothermal surface manifestations. For reserve assessment we use the volume method, supplemented by Montecarlo simulations and statistics, in order to quantify the inherent uncertainties. We estimate these reserves as lying between 7.7 × 10 16 and 8.6 × 10 16 kJ, with 90% confidence. The distribution of most likely reservoir temperatures is in the 60–180 °C range, with a mean of 111 °C. These massive amounts of recoverable energy and the associated temperatures are potentially important for the economic development of the associated geothermal localities.

First Assessment of Mexican Low- to Medium-Temperature Geothermal Reserves

In this work we make a first, partial, assessment of the low- to medium-temperature geothermal reserves of Mexico. The assessment covers about 30% of the identified geothermal surface manifestations. For reserve assessment we use the volume method, supplemented with Monte Carlo simulations and statistics, in order to quantify the inherent uncertainties. We estimate these reserves as lying between 7.7 × 1016 and 8.6 × 1016 kJ, with 90% confidence. The distribution of the most likely reservoir temperatures ranges between 60 and 180°C, with a mean equal to 111°C. These massive amounts of recoverable energy and the associated temperatures are potentially important for the economic development of the associated geothermal localities.

First Assessment of Mexican Low- to Medium-Temperature Geothermal Reserves

In this work we make a first, partial, assessment of the low- to medium-temperature geothermal reserves of Mexico. The assessment covers about 30% of the identified geothermal surface manifestations. For reserve assessment we use the volume method, supplemented with Monte Carlo simulations and statistics, in order to quantify the inherent uncertainties. We estimate these reserves as lying between 7.7 × 1016 and 8.6 × 1016 kJ, with 90% confidence. The distribution of the most likely reservoir temperatures ranges between 60 and 180°C, with a mean equal to 111°C. These massive amounts of recoverable energy and the associated temperatures are potentially important for the economic development of the associated geothermal localities.

インドネシア，フローレス島中央部イネリ力火山周辺の地熱徴候の地球化学

インドネシア，フローレス島中央部イネリ力火山周辺の地熱徴候の地球化学

Identification of the origin of salinization in groundwater using minor ions (Lower Andarax, Southeast Spain)

The study of salinization of groundwater in the Detrital Aquifer of the Lower Andarax is highly complex due to the semiarid climate, the presence of evaporites, proximity to the sea and localized geothermal manifestations in the area. The salinization has been characterized by jointly studying the content of various minor ions (B, Br and Li) and a series of ionic relationships (B/Li, SO 4/Cl, Na/Cl, Cl/B). The combined analysis of B and Li enabled the areas with a marked marine influence to be distinguished from those with an evaporite or geothermal influence. Lithium is directly related to water temperature whilst B content increases in more saline areas, since it is associated with the presence of evaporitic and/or marine influences. Bromine analysis enabled the identification of the principal processes that determine the salinity of the water along the coastal zone: the presence of Quaternary marine sediments and present-day marine intrusion. The brackish groundwaters that are related to old raised beaches showed a low Cl/Br ratio. Areas affected by marine intrusion had Cl/Br ratios similar to seawater and higher than in other areas along the coastal zone. At some points on the delta, a mixture of brackish water and recharge water was detected — the recharge water has a sulfate facies, which causes a drop in the Cl/Br ratio and changes the general character of the water in the coastal zone. The coastal zone contains silty-clay intercalations that favor processes of ion exchange, anthropogenic pollution also occurs and together these processes hamper the interpretation of all the processes.

Developing an Ecosystem Perspective from Experimental Monitoring Programs: I. Demographic Responses of a Rare Geothermal Grass to Soil Temperature

The geysers panic grass [Dichanthelium lanuginosum Spellenberg var. thermale (Bol.) Spellenberg or DILA] is exclusively associated with surface geothermal manifestations in Sonoma County, California, USA (38 degrees 46'N, 122 degrees 38'W). Steam extraction by power plants could alter the subsurface distribution of heat and water to the site, potentially impacting subpopulations of this rare plant. The purpose of this study was to use demographic monitoring to determine: (1) temporal and spatial patterns of soil temperature in relation to the distribution of established DILA individuals at Little Geysers, (2) in situ response of experimental populations of DILA to spatial variations in soil temperature, and (3) habitat requirements of DILA as an indicator of its tolerance to variations in surficial geothermal features. Thermocouple transects and a datalogger provided data for characterizing the spatial and temporal patterns of soil temperature in four microhabitats (fumarole, DILA stand, Andropogon stand, and cleared). Experimental populations were established by precisely sowing and monitoring DILA seeds in these microhabitats. The results indicated that spatial and temporal variations in soil temperature had significant effects on the processes of germination, growth, survivorship, and reproduction, thus producing a readily observed metapopulation patch dynamic in relation to geothermal activity. Seasonal depressions of soil temperature near the fumaroles by cold air and prolonged rainfall events also promoted the emergence and survival of DILA seedlings in a microhabitat that was previously too hot to occupy. Over longer periods of time, DILA metapopulation dynamism reflected climatic and geothermal variation. Drought years inhibited germination for lack of water, but more importantly for the lack of requisite soil temperature depressions in the fumarole microhabitat. Wet years promoted subpopulation expansion into transition areas that were once too hot and dry. There have also been shifts in the underground distribution of steam into areas distant from known geothermal features. The demographic responses of DILA to spatial and temporal variations in soil temperature indicate that heat is an absolutely essential component of the steam resource. In its absence, germination, seeding survivorship, growth, and maturation are significantly inhibited even if soil conditions are favorable and potential competitors are controlled. Ultimately, persistence of the species depends on maintaining the ecosystem dynamic of colonization and extirpation in response to variations in surficial geothermal features over long spatial and temporal scales. This should shift management perspective from its narrow focus on individual plants to a wider focus on monitoring the essential habitat component of steam.

Thermoluminescence as a new research tool for the evaluation of geothermal activity of the Kakkonda geothermal system, northeast Japan

The thermoluminescence glow-curve of quartz in volcanic and pyroclastic rocks of the Miocene and Quaternary in the Kakkonda geothermal field was divided into L (low), M (medium) and H (high) peaks in order of increasing temperature. Thermoluminescence emission is independent of stratigraphic boundaries but it is closely related to surface geothermal manifestations. Thermally stimulated processes of thermoluminescence caused by natural annealing occurred in the Quaternary after the eruption of the Tamagawa Welded Tuffs; radiation storage processes then began, as a consequence of the temperature drop. Thermoluminescence behavior indicates natural temperature manifestations, together with the paleo-temperature history. The H peak was thermally stable compared to the L and M peaks, and the area within which the relative intensity of the H peak is less than 5% coincides with the surface zone where dominant fluid flow is convective. In addition, L and M peaks indicate that a relatively low-temperature fluid mixes with the hot upflow around the western margin of the ascending flow zone. Thermoluminescence characteristics reflect paleo-temperature history and are related to geothermal fluid flow. Thermoluminescence is an effective exploration technique for evaluating natural temperature manifestations and subterranean heat flow in geothermal systems.

Helium and carbon isotopic compositions of hot spring gases in the Tibetan Plateau

The Tibetan Plateau is one of the most active geothermal areas in the Himalayan Geothermal Belt. However, the heat source of the geothermal manifestation is unknown because of a lack of Quaternary volcanoes in this area, except in western Yunnan and northern Tibet. In order to unravel the heat source and the origin of volatile components in hot spring gases in the southern Tibetan plateau, we have measured helium and carbon isotope ratios of hot spring gases from Yangbajain district and some northern sites. The observed helium compositions in the hot spring gases are explained by the mixing of an air component and underground components whose mean end-member 3 He/ 4 He ratio is 0.12 R atm for Yangbajain and 0.22 R atm for the northern sites, respectively. Despite the lack of Quaternary volcanism, such 3 He/ 4 He ratios are an order of magnitude higher than that of stable continental crust (0.02 R atm). These results may imply the existence of intrusive magmas that contain mantle helium in the thick Tibetan crust. The mantle helium with high 3 He/ 4 He ratio may have been diluted to the observed values by radiogenic helium produced in the crust. The observed high CO 2/ 3 He ratios of the samples (10 10–10 12) relative to that of MORB (2×10 9) indicate that most carbon dioxide in the samples is derived from crustal materials, such as organic matter and marine carbonate minerals. Regional differences are observed not only in the mean end-member 3 He/ 4 He ratios of the underground components, but also in the δ 13C(CO 2) values of the hot spring gases between Yangbajain (−9.1 to −6.3‰) and the northern sites (−4.3 to −1.0‰). These features suggest heterogeneity among basement rocks. The lower 3 He/ 4 He ratio in Yangbajain may be due to a larger addition of radiogenic 4 He from basement rocks that are enriched with uranium and thorium. The higher δ 13 C (CO 2) value of the hot spring gases from the northern sites may be due to the addition of carbon dioxide from underlying sedimentary rocks containing more marine carbonate minerals.

Diffuse emission of carbon dioxide, methane, and helium‐3 from Teide Volcano, Tenerife, Canary Islands

Diffuse emission of CO2, CH4 and ³He was investigated in the summit crater of Teide volcano, Tenerife, Canary Islands. The results indicate that Teide volcano releases abundant CO2 not only from its active crater, but also from its flanks as diffuse soil emanations. The spatial distribution of these emanations correlates quite closely with that of geothermal anomalies and manifestations. Our flux measurements indicate a total output of 380 ton·day−1 of CO2 and 1.6 on·day−1 of CH4 by diffuse degassing. From the ³He/CO2 ratios and the CO2 flux we estimate a diffuse ³He flux of 0.052 mol·year−1. Isotopic analysis of carbon in soil gas samples from sites of high soil CO2 flux indicates a magmatic origin for the CO2, also reported by high ³He/ 4He ratios of 5.50 and 5.87 Ra. The origin of methane is more uncertain with low δ13C values suggesting a biogenic contribution.

Two-dimensional magnetotelluric and gravity models of the Tuzgle volcano zone (Jujuy province, Argentina)

The Tuzgle volcano (24 ° 03′S, 66 ° 29′W) is situated in the southern part of the South American Andean Altiplano (Puna). The region has several geothermal manifestations. A 2-D magnetotelluric model of resistivity distribution and a 3-D gravity anomaly of the area have been proposed. A highly conductive and low density body is probably associated with a magma chamber surrounded by free saline fluids with its top at about 8 km depth. The release of fluids might be caused by the chemical reactions generated at the subduction plate of Nazca in contact with the South American plate.

Obligately and facultatively autotrophic, sulfur- and hydrogen-oxidizing thermophilic bacteria isolated from hot composts

A variety of autotrophic, sulfur- and hydrogen-oxidizing thermophilic bacteria were isolated from thermogenic composts at temperatures of 60–80° C. All were penicillin G sensitive, which proves that they belong to the Bacteria domain. The obligately autotrophic, non-spore-forming strains were gram-negative rods growing at 60–80°C, with an optimum at 70–75°C, but only under microaerophilic conditions (5 kPa oxygen). These strains had similar DNA G+C content (34.7–37.6 mol%) and showed a high DNA:DNA homology (70–87%) with Hydrogenobacter strains isolated from geothermal areas. The facultatively autotrophic strains isolated from hot composts were gram-variable rods that formed spherical and terminal endospores, except for one strain. The strains grew at 55–75° C, with an optimum at 65–70° C. These bacteria were able to grow heterotrophically, or autotrophically with hydrogen; however, they oxidized thiosulfate under mixotrophic growth conditions (e.g. pyruvate or hydrogen plus thiosulfate). These strains had similar DNA G+C content (60–64 mol%) to and high DNA:DNA homology (> 75%) with the reference strain of Bacillus schlegelii. This is the first report of thermogenic composts as habitats of thermophilic sulfur- and hydrogen-oxidizing bacteria, which to date have been known only from geothermal manifestations. This contrasts with the generally held belief that thermogenic composts at temperatures above 60° C support only a very low diversity of obligatory heterotrophic thermophiles related to Bacillus stearothermophilus.

Noble gases as tracers identifying geothermal components in regions devoid of surface geothermal manifestations: A case study in the Baden springs area, Switzerland

Fumaroles and drowned fumaroles are formed by steam and gas, separating from ascending geothermal fluids, whereas the residual water emerges in springs. These separated phases are tagged by specific compositions of atmospheric and radiogenic noble gases, as well as by specific values of 18O, geotemperatures and age indicators. These markers may be used to recognize geothermal components in regions with no surface geothermal manifestations. In a case study at Baden, Switzerland, a drowned fumarole is identified, containing 3.3·10 −3 cm3 He/cm 3 dry gas, He/Ne = 4900 and ( 4He/ 40Ar) radiogenic = 7.3. Residual geothermal water is recognized in the springs by significant depletions of the atmospheric noble gases (retention values of Ne as low as 35%), 9.3·10 −5 Cm3 STP He/cm 3 water, He/Ne = 1200 and (4 He/ 40Ar) radiogenic = 8.9, an 18O shift of 1%o and Si0 2 and NaKCaMg geotemperatures 80° and 74 °C respectively. Discordant tritium and 14C values of 3..6 TU and 7 pmC indicate mixing of old water with of a few percent recent water. An age beyond the 14C method is indicated for the deep old end-member.

Geothermal prospects in the central region of sucre state, venezuela

In the geothermal area of El Pilar-Mundo Nuevo, Sucre State, sampling was carried out in 36 geothermal manifestations, 18 cold springs and 10 surface runoffs. From the results of water analyses three different systems were identified: 1.(a) El Salvaje-Buena Esperanza system: acid-sulfate-calcium waters and orthorhombic sulfur, gypsum, anhydrite and low quartz deposits.2.(b) El Palmar-Aguas Calientes-Los Chirriaderos system: generally neutral, sodium chloride waters with abundant carbonate deposits.3.(c) Mundo Nuevo-Los Mereyes system: acid-sulfate-calcium waters in the higher temperature springs with low quartz and orthorhombic sulfur deposits. There are also neutral calcium bicarbonate waters, without deposits, and lower temperatures.The highest temperatures assessed from chemical geothermometers for the systems of El Salvaje-Buena Esperanza and El Palmar-Aguas Calientes-Los Chirriaderos, allow us to consider their utilization for electricity generation, exploiting the excess lower temperature fluid in fish meal and timber drying, fast drying of farm products and evaporation in sugar refining.

Evaluation of reservoir temperatures and local utilization of geothermal waters of the Konkan Coast, India

Geochemical studies on fifteen geothermal manifestations (38–70°C) from the Konkan coast geothermal province of India have been used to evaluate the reservoir temperatures. Activity studies of the minerals and the waters present in the reservoirs suggest that the thermal waters are in equilibrium with montmorillonite, kaolinite and quartz at about 100°C. Reservoir temperatures of these geothermal systems as estimated by geochemical thermometers, are 88 to 128°C, and thus too low for economic electricity production.

The shallow structure of Los Humeros and Las Derrumbadas geothermal fields, Mexico

Los Humeros caldera and Las Derrumbadas rhyolitic domes located in the State of Puebla (Mexico) are being extensively studied by Comisión Federal de Electricidad (CFE) to assess the geothermal potential of that area. Both geothermal sites have been locally studied with geological, geochemical and geophysical methods. In order to get a geological picture of the sub-surface of the area comprising both sites, a regional structural survey was conducted together with gravity and magnetics studies. These studies showed a regional weakness zone (the Libres-Oriental depression), where the volcanic activity related to the geothermal manifestations took place. The tectonic events in the area are represented by two systems of structures. The first one (N140°–N170°) gave rise to the folds and overthrusts affecting the sequence of calcareous rocks resting upon the basement. This system is affected by a second system (N40°–70°E). Regionally these tectonic events remodelled the sedimentary sequence giving rise to a series of topographic highs that constitute the core of several ranges, and to depressions that were filled with volcano-sediments during the ensuing volcanic activity. The rhyolitic domes of Las Derrumbadas are emplaced in a regional NW-SE lineament, which reflects clearly on the Bouguer anomaly, and is interpreted as a front of overthrust affecting the marine sedimentary sequence. Estimations of depths to the basement, based on magnetic data, showed that the basement under Los Humeros caldera is shallower than in Las Derrumbadas. The gravity data were interpreted in terms of tabular bodies associated to calcareous rocks, of igneous intrusions, and of depressions filled with volcano-sediments. A joint interpretation of the geological and geophysical data led to a model of the structure of the shallow crust in the area.