Geology of the tengchong geothermal field and surrounding area, West Yunnan, China

This paper describes the regional tectonics, active structures and thermal springs of the Tengchong geothermal field and surrounding area. Regional tectonic evidence shows that Tengchong and the surrounding area was a microcontinent between the Gondwanaland and Eurasian plates. The distribution of the thermal springs is controlled by active faults in the “arched” and circular structures. The majority of the thermal areas have a deep circulation within the fault system. Only a few high-temperature hydrothermal systems issuing sodium chloride may be heated by a local magmatic source.     

Geothermal energy potential related to active volcanism in Indonesia

About 90 thermal areas in Indonesia are indicated, most of which could be grouped into hyperthermal areas located in active volcanic belts. The thermal manifestations are fumaroles, geysers, hot springs and hot mud-pools with surface temperatures generally at boiling point or more than 70°C. A tentative evaluation has been made of the potential of 54 thermal areas with a view to their further development for electrical power. The successful results of these studies in several thermal areas suggest that these volcanic geothermal systems have a high energy potential of about 13,000 – 14,000 MW.The Kawah Kamojang geothermal field in West Jawa is the first promising attempt at utilizing this geothermal energy for electrical power; a 30 MW geothermal power plant has already been installed, and a further 3 units totalling 165 MW are planned.     

Correlation between the silica concentration and the orifice temperature in the warm springs along the jordan-dead sea rift valley

Analysis of twenty-one thermal springs emerging along the Jordan-Dead Sea Rift Valley in Israel indicates a very good correlation between the concentration of dissolved silica and the temperature of the spring orifice. Dissolution of quartz was identified as the apparent source of the silica in the water. Application of the silica geothermometer for mixed systems suggests that the springs in the Tiberias Lake Basin are supplied with hot water from deep reservoir (or reservoirs) at a temperature of 115°C (239°F). The same temperature was postulated earlier by the application of the Na-K-Ca hydro-geothermometer to a group of thermal springs in the same basin. The temperature of the reservoir supplying hot brines to the springs emerging along the western shore of the Dead Sea is estimated at 90°C (194°F).     

Application of chemical geothermometers to thermal springs of the Maghreb,North Africa

In order to assess the geothermal potential in the Maghrebian region, several studies have been undertaken in the three countries concerned, Morocco, Algeria and Tunisia, during the past decade. Research programmes have considered the surface evidence (thermal springs) and underground thermal information from deep and shallow wells. The main chemical characteristics of the sampled thermal springs and the results of the application of geothermometers as result from these studies are presented. Of the 238 inventoried thermal springs, 169 have been selected, on the basis of complete water analyses and acceptable ionic balances. Measured temperatures range from 22.5 to 98°C, thermal indexes from 0.5 to 78°C and salinities from 0.13 to 52.5 g/L. Most studied springs are sodium-chloride type waters. These basic data allow identification of the main thermal anomalies in the Maghrebian zone, which are located in regions of the Libyan-Tunisian, Algerian-Moroccan and Algerian-Tunisian frontiers, of northern Tunisia, the Eastern Rif and the northern part of the Saharan Atlas.Several chemical geothermometers have been applied to selected springs: NaK, NaKCa, NaKCaMg, Na/Li, Mg/Li, K²/Mg, quarts, chalcedony (Fournier) and chalcedony (Arnorsson). The NaK, NaKCa, NaKCaMg, Na/Li and Mg/Li geothermometers seem to give unreliable results, while K²/Mg and silica temperatures are apparently reasonable. However, dissolved silica seems to be governed by quartz solubility for some thermal springs and by chalcedony solubility for others. The results are tentatively compared with known geothermal gradients and geological features.     

Geothermal resources in Algeria

The geothermal resources in Algeria are of low-enthalpy type. Most of these geothermal resources are located in the northeastern of the country. There are more than 240 thermal springs in Algeria. Three geothermal zones have been delineated according to some geological and thermal considerations: (1) The Tlemcenian dolomites in the northwestern part of Algeria, (2) carbonate formations in the northeastern part of Algeria and (3) the sandstone Albian reservoir in the Sahara (south of Algeria). The northeastern part of Algeria is geothermally very interesting. Two conceptual geothermal models are presented, concerning the northern and southern part of Algeria. Application of gas geothermometry to northeastern Algerian gases suggests that the reservoir temperature is around 198 °C. The quartz geothermometer when applied to thermal springs gave reservoir temperature estimates of about 120 °C. The thermal waters are currently used in balneology and in a few experimental direct uses (greenhouses and space heating). The total heat discharge from the main springs and existing wells is approximately 642 MW. The total installed capacity from producing wells and thermal springs is around 900 MW.     

Spatial data analysis and integration for regional-scale geothermal potential mapping,West Java,Indonesia

Conceptual modeling and predictive mapping of potential for geothermal resources at the regional-scale in West Java are supported by analysis of the spatial distribution of geothermal prospects and thermal springs, and their spatial associations with geologic features derived from publicly available regional-scale spatial data sets. Fry analysis shows that geothermal occurrences have regional-scale spatial distributions that are related to Quaternary volcanic centers and shallow earthquake epicenters. Spatial frequency distribution analysis shows that geothermal occurrences have strong positive spatial associations with Quaternary volcanic centers, Quaternary volcanic rocks, quasi-gravity lows, and NE-, NNW-, WNW-trending faults. These geological features, with their strong positive spatial associations with geothermal occurrences, constitute spatial recognition criteria of regional-scale geothermal potential in a study area. Application of data-driven evidential belief functions in GIS-based predictive mapping of regional-scale geothermal potential resulted in delineation of high potential zones occupying 25% of West Java, which is a substantial reduction of the search area for further exploration of geothermal resources. The predicted high potential zones delineate about 53–58% of the training geothermal areas and 94% of the validated geothermal occurrences. The results of this study demonstrate the value of regional-scale geothermal potential mapping in: (a) data-poor situations, such as West Java, and (b) regions with geotectonic environments similar to the study area.     

Hydrogeochemistry and geothermometry of Changal thermal springs,Zagros region,Iran

This study addresses the hydrogeochemistry of thermal springs that emerge from the Asmari limestone in a gorge at Changal Anticline in the vicinity of the Salman-Farsi dam. The Changal thermal springs vary in temperature between 28 and 40 °C. Chemical and isotopic compositions of the thermal waters suggest two distinct hydrogeological systems: a deep, moderate-temperature (∼40 °C) geothermal system recharged by deeply circulating meteoric waters, and a shallow cold aquifer system related to local groundwater. The source geothermal fluid temperature was calculated using different geothermometers and mineral saturation indexes. Based on chemical and isotopic data, it is hypothesized that: (1) mixing occurs between the ascending geothermal water and shallow cold water; (2) the resulting thermal waters reaching surface are a mixture of 80% local, shallow meteoric water and 20% geothermal water; and (3) the circulation depth of the meteoric water is about 1500 m. The thermal reservoir temperature is estimated to be between 70 and 80 °C according to calculations using different geothermometers and computation of saturation indices for different solid phases.     

Assessment of reservoir temperatures of thermal springs of the northern areas of Pakistan by chemical and isotope geothermometry

Chemical and isotope geothermometers, i.e. the Na–K, K–Mg, quartz and δ¹⁸O(SO₄–H₂O), have been applied to estimate the reservoir temperature of the thermal springs in the northern areas of Pakistan. The chemical types of the thermal waters and the effects of mixing of shallow cold water with the thermal end-members are discussed. These waters are neutral to slightly alkaline and have low dissolved contents. Sodium is the dominant cation in almost all the cases. In terms of anions, the hot waters of Budelas are of the SO₄ type, those of Tatta Pani are of mixed character (SO₄ and HCO₃), and the waters from the remaining areas show HCO₃ domination. An absence of tritium in Tatta Pani and Tato thermal springs indicates that they do not have any contribution of shallow young water. In the case of the Murtazabad springs, the wide range of tritium concentrations, negative correlations with surface temperature and Cl, and positive correlation between Na and Cl show that the shallow cold groundwater is mixing with thermal water in different proportions. For the mixed water of Murtazabad thermal springs, ‘isochemical modelling’ using the Na–K, K–Mg and quartz geothermometers indicates an equilibrium temperature in the range 185–200 °C. The δ¹⁸O(SO₄–H₂O) geothermometer gives relatively low temperatures for three springs, whereas two samples are close to the 185–200 °C temperature interval. The reservoir temperatures of Tatta Pani springs (100–120 °C), determined by Na–K and quartz geothermometers, are in good agreement. The δ¹⁸O(SO₄–H₂O) geothermometer gives a relatively higher range (140–150 °C) for most of the Tatta Pani springs. For Tato spring, the isotope and chemical geothermometers (except for the K–Mg) agree on an equilibrium temperature of about 170 °C. Reservoir temperatures of the remaining minor fields are not conclusive due to the lack of sufficient data.     

Development and role of geothermal resources in India

The geothermal resources discovered in India consist of warm/hot water systems. Medium-temperature waters and reversal of temperature at depth were observed in Puga, Manikaran and the West Coast geothermal areas after exploratory drilling. Such resources can be utilized only for non-electrical applications after detailed technical—economic feasibility studies. The presence of medium-temperature (90–140°C) springs in the cold, remote and steep Himalayan terrains and of lower temperature springs (100°C) in the hot and variable climate of the Peninsular and Coastal regions further restrict full utilization of these resources, with the exception of Cambay, West Coast and Tatapani—Jhor areas. After careful study a list of direct utilizations is proposed for future consideration and the development of the main geothermal resources in India.     

南方电网水火调剂运行模式探讨

为优化利用云南清洁水电资源、提高南方电网西电东送通道资源的利用率,在分析云南、贵州外送电力特性和广东电力负荷需求特性的基础上,探讨了南方电网水火调剂运行的可能模式。结果表明,在南方电网内通过优化云南、贵州向广东的送电曲线,可以以广东电网为平台,实现云、贵间的水火互济运行;丰水期由水电比重大的云南电网替代火电比重大的贵州电网向广东供应部分电力,获得节约燃煤的效益,枯水期则由火电比重大的贵州电网向广东多送电,补偿云南枯水期水电出力的不足。这一运行模式也可实现南方电网内的资源优化配置。     

Geothermal manifestations in Nepal

A number of thermal springs have been located in different parts of Nepal. As very few systematic studies have been carried out so far very little is known on their chemistry and genesis. Talalov (1973) and Bhattarai have made an inventory of the thermal springs of Nepal and have provided some relevant information on about forty of them. Dikshit and Bhattarai and Bashyal have made preliminary investigations of some thermal springs of Dhawalagiri and Karnali Zone, and Lumbini Zone respectively. The present paper deals with some of the geological and chemical studies of the thermal springs undertaken by the author.     

The thermal springs of bockfjord, svalbard: occurrence and major ion hydrochemistry

The Troll and Jotun thermal springs of northern Svalbard, with temperatures of up to 25.6°C, are derived from a major fault forming the junction between Devonian sandstones and Proterozoic marbles, mica schists and gneisses. The Troll waters are dominated by Na–HCO₃ compositions and the Jotun waters by Na–Cl compositions. The pristine thermal water source has a sub-neutral pH and is highly reducing. Taken at face value, common geothermometers suggest temperatures at depth of 130–180°C for the Troll springs (corresponding to a depth of 1.6–2.3 km), with 10–30% thermal water diluted by 70–90% cold water. Such geothermometers may, however, be inappropriate to the cool, high CO₂ waters of Bockfjord, and real temperatures at depth and dilution factors are probably considerably lower. The salinity of the thermal water appears to be only partially derived from water–rock interaction; Br\Cl ratios suggest that seawater or possibly evaporites may be a source of chloride salinity.     

Hot springs and geothermal gradients in northern Thailand

Chemical geothermometry of hot springs in northern Thailand indicates that many have reservoir temperatures in excess of 150°C and some in excess of 180°C. Measurements of temperatures in abandoned oil wells in Fang Basin indicate geothermal gradients of 70 – 130 mK/m. The high geothermal gradient may be the result of extensional tectonics in northern Thailand, caused indirectly by sea-floor spreading in the Andaman Sea. Relatively high reservoir temperatures and shallow reservoir depths suggest that hot spring areas in northern Thailand may be potential sources of geothermal energy.     

Chemical patterns of thermal aquifers in the volcanic islands of the Aegean Arc, Greece

Thermal spring waters and associated gases discharging on several volcanic islands and on mainland Greece along the Hellenic Volcanic Arc (HVA) in the south Aegean sea have been investigated. The chemical characteristics of most of the spring waters suggest that the water in their feeding aquifers is largely derived from seawater that enters the hydrological circuits and mixes with local neutral low-salinity bicarbonate waters. There are however discrepancies between the simple theoretical mixing line between local meteoric waters and seawater, and the actual mixing line. This mixing is accompanied by partial Mg and SO₄ precipitation to secondary minerals and by the addition of K, Ca, HCO₃, B, NH₄, and SiO₂ to the solutions as a result of water-rock interaction processes.At Milos and Nisyros, where active hydrothermal systems are present at shallow depth, the silica content of the thermal springs is much higher than that of springs on the other islands and mainland Greece. This suggests higher thermal gradients at depth there, and the ascent of geothermal fluids to the surface along fractures prevalently located in the fumarolic fields within the latest eruptive centers and calderas. The fact that the springs are anomalously enriched in silica only at Milos and Nisyros suggests indirectly that, apart from Santorini island, where steam vents are present at the surface, the fluids from the active high-enthalpy geothermal systems do not rise to the surface anywhere else along the HVA. If present, they are well confined under thick and impermeable covers.     

Geothermal areas in Pakistan

In this paper an attempt has been made to correlate the tectonic and geologic features with surface manifestations of geothermal activity in Pakistan to delineate prospective areas for exploration and development of geothermal energy. Underthrusting of the Arabian plate beneath the Eurasian plate has resulted in the formation of Chagai volcanic arc which extends into Iran. Quaternary volcanics in this environment, along with the presence of thermal springs, is an important geotectonic feature revealing the possible existence of geothermal fields. Geothermal activity in the northern areas of Pakistan, as evidenced by thermal springs, is the likely result of collision and underthrusting of the Indian plate beneath the Eurasian plate. Numerous hot springs are found along the Main Mantle thrust and the Main Karakorum thrust in Chilas and Hunza areas respectively. The concentration of hot springs in Sind Province is also indicative of geothermal activity. A string of thermal seepages and springs following the alignment of the Syntaxial Bend in Punjab Province is also noteworthy from the geothermal viewpoint.In Baluchistan Province (southwest Pakistan), Hamun-e-Mushkhel, a graben structure, also shows geothermal prospects on the basis of aeromagnetic studies.     

Geochemistry of thermal springs around Lake Abhe,Western Djibouti

The Republic of Djibouti, occupying an area of 23,180 km², falls within the arid zone of East Africa and is located above the ‘Horn of Africa’, adjacent to the Red Sea. This country has several thermal springs and fumaroles distributed over three regions – Lake Assal, Lake Hanle and Lake Abhe. The most characteristic feature of Lake Abhe is the presence of several linear chains of travertine chimneys. The thermal waters are typical of the Na-Cl type near neutral waters rich in CO₂. These waters show an oxygen shift, indicating reservoir temperatures>200°C. The chemical signature of the thermal springs and the geology of the Lake Abhe region are very similar to the Tendaho geothermal area of Ethiopia. The geology, temperature gradient and its proximity to Damah Ale volcano make the Lake Abhe region a potential site for geothermal power development.     

Isotopic and chemical evidence for water sources and mixing in the Cerro Pando geothermal area, Republic of Panama

The Cerro Pando geothermal area in Chiriqui Province is situated just to the south of the continental divide in western Panama. Three groups of thermal springs are associated with lineations in a complex of late Tertiary and Quaternary extrusives. Spring temperatures reach maximum values of 66°C at Los Pozos, 67°C at Cotito and 41°C at Catalina; flow-rates are low, ranging up to 1.5 l/s. However, total heat output is estimated at around 7 MW from calculations incorporating measured spring discharges with river-bed discharges inferred from stream conductivity anomalies. In all cases the spring hydrochemistries become of a more dominantly Na-Cl character as mineralization increases; the highest salinities are found in samples from test boreholes in which 4500 mg/l Cl⁻ has been measured. ¹⁸O/¹⁶O and ²H/¹H data for all thermal springs are roughly colinear, plotting on the δ-diagram with a slope around 3.6 and intersecting the meteoric water line within the compositional range of local surface water. Moreover, δ¹⁸O data are found to correlate with Cl⁻ concentrations, although separate linear trends represent the Los Pozos/Cotito and the Catalina groups of springs. These data are interpreted as indicating that deep thermal ground water feeds the thermal spring systems, with differing isotopic compositions and/or salinities in the Los Pozos/Cotito and Catalina groups. These end-member compositions have evolved by sub-surface steam loss, possibly without any δ ¹⁴O shift due to water - rock exchange. The observed spring compositions are all mixtures between the deep thermal and shallow cool end-member ground waters. The importance of resolving mixing relationships before applying geothermometric calculations is illustrated.     

Response of Bao-Banati thermal area to development of the Tongonan geothermal field, Philippines

During the first six years of commercial operations at Tongonan-1, the chloride contents, flow rates, and quartz geothermometer temperatures of the Bao-Banati springs generally declined. Geysering ceased, and some springs were reduced to non-flowing pools. The total flow decreased from 85 (1983) to 10 kg/s (1992), due to a reduction in the contribution of deep reservoir fluids to the surface discharges resulting from an exploitation-induced decline in reservoir pressures. There was no reinjection fluid breakthrough from Tongonan-1 to the springs during this period. In 1982–83, test reinjection into well 5RD1 in the Malitbog sector resulted in increased thermal activity of the springs, but a tracer test had negative results. A further reinjection test in 1983 caused a brief increase in chloride content and flow rate, but these resumed their decline after the test ended. Similar responses occurred during pre-commissioning trials for the Malitbog plant in 1996. Activity increased again when the plant was commissioned in 1997. A tracer test, using Na-fluorescein, confirmed communication between 5R1D and the hot springs.     

The thermal springs of Bockfjorden, Svalbard: II: selected aspects of trace element hydrochemistry

Waters from the Trollkjeldene (Troll springs) and Jotunkjeldene (Jotun springs) thermal springs on northern Svalbard have been analysed by ICP-AES, ICP-MS and IC techniques for a wide range of major and trace elements. Although it is plausible that the thermal waters originate from a deep reservoir in siliceous rocks, it appears that a significant component of their hydrochemical signature is derived from dissolution of higher-level Hecla Hoek marbles. Rare earth elements (REEs) show some degree of enrichment of heavy REEs in the water phase, relative to the marbles and to the travertines that precipitate from the waters. A strong positive Eu anomaly is also observed in the waters, suggesting preferential mobilisation of Eu under reducing conditions. The ratio Nb/Ta is rather well-preserved between the marbles, the waters and the travertines.     

Chemical study of geothermal waters of Central Tibet (China)

Thirteen of about 300 areas of thermal springs in Tibet have been studied in detail. The springs fall into four groups, the most important and interesting of which produces silica, boron, lithium and cesium-rich waters. Chemical geothermometers agree within a few degrees in the range 200–220°C. A second group includes waters of the same type, but secondary reactions decrease the silica concentrations and increase the Ca and Mg contents. The third and fourth groups are similar to Pyrenean alkaline waters and to CO₂-rich waters from Massif Central respectively; deep temperatures are low to moderate.