Geothermal Manifestations Research Articles

The Correlation Between P-Wave Velocity Value With Pathways Of Geothermal Manifestation In The Area Ie Jue, Aceh Besar As Hazardous Side Study

Refraction seismic survey has been carried out in the manifestation area of Ie Jue, Seulawah Agam Volcano Region, Seulimuem, Aceh Besar Regency. This research aims to identify weak zones related to channel of geothermal outflow that would bring about a potential hazard for human activity and that goal is obtained by exstracting information from P-wave velocity. The data acquisition was conducted for two seismic lines located near to the geothermal manifestation area of Ie Jue. Both of the seismic lines were set up by linking the 24 geophones to the Seismograph PASI 16S and placing them in three meters spacing of each other. The offsets either left or right were laid out at 35 meters from first and last geophones, so the total spread length of each seismic line is 139 meters. The data recorded by the tool then were processed by using ZONDST2D and finally, the 2D velocity profile was obtained. The results show that the 2D velocity profiles illuminate us to potray and interpret the features figured out. The most valuable information provided by the profile is the existance of such the weak zones of the first and second seismic lines at relatively near-surface depth. These weak zones were suspected as the fractured or low-velocity zones, where their velocity ranges approximately at 0.2 - 1.2 km/sec. These low-velocity layers are strongly predicted as the pathways or channels of the geothermal fluids that appears to the surface. The shallow weak zones are potentially to become the hazard grounds because they are regularly traversed by timber trucks from which the dynamic load will be pushing them down. As consequence, the ground surfaces could gradually become a land subsidence endangering human activity within the vicinity of the area.

Geochemistry of Sulphate spring in the Ie Jue geothermal areas at Aceh Besar district, Indonesia

Geochemical studies of geothermal manifestations in the Northern Zone of Mt. Seulawah Agam, one of which is Ie Jue manifestation, has been conducted. In this study, water geochemical analysis of cations and anions content was performed to observe the surface characteristics of manifestations, the type of water manifestation, the water balance of reservoir depth and to estimate depth temperature using geothermometer equations. Cations and anions measurements were conducted using atomic absorption spectroscopy, UV-Vis spectrophotometer and acid-base titration. The data analysis was determined using spreadsheet version 3 Powell Geoscience Ltd.3 September 2012 by Powell & Cumming. The geothermal water Ie Jue manifestation was acidic pH, water sulphate type was obtained from the geoindicator Cl-SO4-HCO3 and the immature water was based on plot Na-K-Mg ternary diagram. Its reservoir temperatures ranged from 690 °C to 761 °C in accordance with Na/K geothermometer equations based on results of Na/K Giggenbach and Fournier. The Ie Jue manifestations indicated a high-temperature geothermal system (high enthalpy) that could be characterized when the average temperature reached higher than 225 °C and suitable for power plant development.

3D Gravity Data Modelling for Determining a Subsurface structure of The SDP Geothermal Field

The SDP geothermal research area geographically located in eastern Indonesia where there are geothermal manifestations of hot springs. 3D modeling and vertical-horizontal gradient analysis are used to determine the presence of subsurface structures of the study area. Separation of complete Bouguer anomaly data to obtain regional and residual anomalies has been done by upward continuation. The results of the horizontal and vertical gradients indicate that the presence of the geothermal manifestation of MAP 1 hot spring is controlled by the presence of trending northwest-to-southeast fault. We interpret the emergence of manifestations due to the presence of a permeable zone in the form of the fault structure. 3D modeling shows the existence of alluvium sediment, sedimentary rocks, limestones, ultrabasas (peridotite), granite, metagranite, gneiss and the presence of trending northwest trending to the southeast fault.

Identifikasi Manifestasi Panas bumi Berdasar Interpretasi Citra di Daerah Manokwari, Provinsi Papua Barat

Penginderaan Jauh adalah ilmu atau seni untuk memperoleh informasi tentang suatu objek, daerah maupun fenomena melalui analisa data yang diperoleh dengan suatu wahana tanpa kontak langsung dengan objek, daerah maupun fenomena tersebut. Dengan demikian untuk fenomena seperti manifestasi panasbumi dapat memanfaatkan kemampaun penginderaan jauh menggunakan satelit yang datanya berupa citra satelit. Penelitian dilakukan di daerah Kebar, Kabupaten Manokwari, Provinsi Papua Barat. Pada penelitian ini citra satelit digunakan untuk menemukan potensi panasbumi baru berupa manifestasi panasbumi di sekitar Distrik Kebar. Data yang digunakan dalam penelitian ini adalah Citra ASTER L1B, Citra SRTM dan Peta RBI. Pengolahan data diawali dengan proses deliniasi, analisa NDVI, analisa pelamparan temperatur permukaan dan proses klasifikasi. Dari hasil pengolahan data ditemukan bahwa terdapat beberapa kemungkinan manifestasi panasbumi baru di Distrik Kebar, Kabupaten Manokwari, Provinsi Papua Barat.

Detection of ground thermal anomaly under dense vegetation based on ASTER TIR images

Ground thermal anomalies associated with geothermal surface manifestations such as hot springs, fumaroles, altered surfaces, and steaming grounds serve as crucial indicator for geothermal explorations. In order to highlight the ground thermal anomalies, this study was raised to use the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data to estimate surface temperature under condition of dense vegetation. This study was focused to exploit the ASTER Thermal Infrared Radiometer (TIR) under lab and field scale conditions. The ASTER TIR bands were used to extract the Land Surface Temperature (Ts) from radiances by excluding surface emissivity (εs). The ε is a surface parameter dependent to the surface materials. In this paper, we demonstrated the performance of the Normalized Emissivity Method (NEM) to calculate the Ts by estimating the ε under condition of dense vegetation. The Patuha and Wayang Windu Geothermal field in West Java (Indonesia) were selected as study site due to existence of surface manifestations under canopy vegetation and open area. According to the method, we identified that the ground thermal anomalies are located at surface manifestations. Due to the different spatial scales of satellite and surface measurements and the lack of homogeneous areas, which are representative for low resolution pixels and ground measurements, ground-validation is necessary. The consistency between ASTER data and location of geothermal manifestations indicated that thermal remote sensing data integrated with a spatial-based model, provides an effective means for identifying geothermal potential.

Delineation of Recharge and Discharge Area for Geothermal Energy in Natar

Geothermal is one of the renewable energies which is abundant in Indonesia (∼29 GW). Lampung has several potential areas of the geothermal energy, such as Way Panas, Rajabasa, Sekincau, Way Ratai, Natar, etc, 110 MW potential in total. Natar hot spring is one of the geothermal manifestations located in Natar, South Lampung and included in Metro-Kotabumi Groundwater Basin. This indicates that Natar has potential in geothermal energy. Geothermal energy is known as renewable energy, if only the system can be maintained. One component that can be maintained is presence of water in the reservoir. To maintain this component, recharge area must be known. This paper, provide analysis recharge area delineation based on topographic and geological map. Based on topographic map, recharge area is located at western and at southern part of Metro-Kotabumi Groundwater Basin. The recharge area is located in high terrain topography and covered by volcanic product (intercalation between tuff, lava, and volcanic breccia). Ratio value between recharge and discharge area is 0.17. Due to the recharge area is very small compared to discharge area, it is need to conserve recharge area seriously hence Natar hot spring can be sustainable.

Structural model and slip-dilation tendency analysis at the Copahue geothermal system: Inferences on the reservoir geometry

The Copahue volcano host one of the most attractive geothermal resources of Argentina. Several studies focused on both the volcanic activity and the related geothermal manifestations, including a feasibility report during the '90s. However, limited, unclear and usually contradictory structural interpretations are found in the literature, and the role of the main faults over the geothermal system remains thus unsolved. This paper provides the first structural characterization and role assessment of the faults over the fluid flow and the reservoir geometry. A 3D structural model has been constructed to achieve this goal, and a fault-plane striations survey has been carried out at Anfiteatro, Termas and Maquinitas hydrothermal zones. Using this dataset, a slip and dilation tendency analysis over the main structures have been performed. The 3D structural model indicates that the Copahue geothermal field is bounded by an N60°-trending fault set and constrained to the north by the Trolope fault and to the south by the Chancho-Co fault, both with WNW-ESE trend. The collected fault-plain striations data was inverted to obtain the paleostress tensor related to the formation of the Copahue village fault system (CVFS), the structure that controls the hydrothermal areas. The subvertical maximum principal stress axis obtained defines a well constrained tensional regime, with a subhorizontal NW-SE minimum principal stress, consistent in all the surveyed locations. Both the 3D model and the inverted paleostress tensor indicate that the geothermal field, and probably the entire northeastern slope of the volcano, is subjected to an extensional faulting regime. Our analysis shows that the N°60-trending fault set is critically stressed for dilation and probably behaves as an active hydrological fault system, whereas the N105° and N135° fault sets have intermediate and low dilation tendency, respectively. These tendencies might lead to a northeast-trend fluid path between the Chancho-co and the N135° faults and might define the extension of the steam cap. We propose a compartmentalized reservoir model made up by three fault segmented blocks. While a steam cap over a deeper reservoir controlled by the CVFS characterizes the central segment, a pressurized liquid-dominated reservoir could prevail to the west of Termas and the east of Maquinas hydrothermal zones. This model explains the differences between the fumaroles inside the CVFS (i.e., Termas to Maquinas fumaroles) and outside this structural system (i.e., Anfiteatro), is consistent with the steam cap identified by the exploration boreholes and is consistent with the 3D structural framework proposed. Also, the model suggests that the collapse of the eastern slope of the Chancho-co hill might constitute the initial state of the current configuration of the geothermal system. Additional studies are needed to verify the proposed reservoir model before defining deep exploration targets, including magnetotellurics, discrete fracture network analysis, and preliminary thermodynamical models.

Geothermal Exploration in Some Interest Geothermal Area in Republic of Yemen

The first geothermal area (Al Lisi–Isbil Geothermal field) is located about (100) km from Sana’a capital city of Republic of Yemen, and the second geothermal area (Alsyani – Algandeah Geothermal field) is located about (250) km from Sana’a capital city of Republic of Yemen. In addition, the third geothermal area (Red Sea geothermal area) is located about (290) km from Sana’a capital city of Republic of Yemen. The geothermal mapping was carried out in (Al Lisi and Isbil and Alsyani – Algandeah Geothermal field) in the western area of Yemen.The rocks type in Al Lisi–Isbil Geothermal area was classified To six group, trap series, the post trappic volcanic activity, Isbil volcanic complex, Al Lisi volcanic complex, Basaltic Fissure volcanism and recent and active sedimentary deposits, The main structural feature are trend (NNE-SSW), (NE-SW),The rocks type in the second geothermal area Alsyani – Algandeah Geothermal area was classified to (4) type of Rocks, Tertiary Volcanic (Basalt, Rhyolite, and Tertiary intrusive rocks), Tawilah Sandstone Group, Medj-Zir Sandstone and Quaternary Deposits. The main structural feature is trend (NE-SW). In Al Lisi and Isbil Geothermal area The Geothermal manifestations (steam, clay alteration and slight alteration)common in many deferent site in the Geothermal area, two types of alteration zones are distinguished slight alteration mostly characterized by slight color change of the Brownish, reddish, yellowish to white colors and also involving some silica minerals (opal) and calcite veins and the some altered rocks assume a whitish color due to the presence of opline silica, clay minerals and iron oxides. In addition, the Albit, Montomornillonite, Biotite, Kaolinite, Chlorite Quartz, and Calcite are the individual minerals obtained by analysis (X-Ray) for samples taken from Al Lisi and Isbil Geothermal area. The temperatures of steam that exceed 92°C and They are 118 hot well in the area the temperature between (25°C) to (59°C).And the Geothermal manifestations(slight alteration)In Alsyani–Algandeah Geothermal area are common in many deferent site in the Geothermal field, one types of alteration zones are distinguished slight alteration mostly characterized by slight color change of the Brownish, reddish, to yellowish colors and also involving some silica minerals (opal) and calcite veins and the some altered rocks assume a Brownish, reddish and yellowish color due to the presence of opline silica, calcite veins, clay minerals and iron oxides. In addition, the limonite, Heulandite, Quartz, and Calcite are the individual minerals obtained by analysis (X-Ray) for samples taken from Alsyani–Algandeah Geothermal area.They are (42) hot well in the area the temperature between (27°C) to (75°C), the thermal wells to 340 meters deep (75°C), are in the area.Also The Red Sea geothermal area is located in west area of western Yemen volcanic part, was covered by drilling is does not exceed 3000 km2,but data from several areas throughout the world, including neighboring countries such as Ethiopia yielded similar temperatures and geothermal gradients. In the Present, the temperature logs from the boreholes show temperatures of 190°C at 2458 m depth in the Red Sea geothermal area.

PRELIMINARY DETECTION OF GEOTHERMAL MANIFESTATION POTENTIAL USING MICROWAVE SATELLITE REMOTE SENSING

The satellite technology has developed significantly. The sensors of remote sensing satellites are in the form of optical, Microwave, and LIDAR. These sensors can be used for energy and mineral resources applications. The example of those applications are height model and the potential of geothermal manifestation detection. This study aims to detect the potential of geothermal manifestation using remote sensing. The study area is the Northern of the Inverse Arc of Sulawesi. The method used is remote sensing approach for its preliminary detection with 4 steps as follow (a) mining land identification, (b) geological parameter extraction, (c) preparation of standardized spatial data, and (d) geothermal manifestation. Mining lands identification is using Vegetation Index Differencing method. Geological parameters include structural geology, height model, and gravity model. The integration method is used for height model. The height model integration use ALOS PALSAR data, Icesat/GLAS, SRTM, and X SAR. Structural geology use dip and strike method. Gravity model use physical geodesy approach. Preparation of standardized spatial data with re-classed and analyzed using Geographic Information System between each geological parameter, whereas physical geodesy methods are used for geothermal manifestation detection. Geothermal manifestation using physical geodesy approach in Barthelmes method. Grace and GOCE data are used for gravity model. The geothermal manifestation detected from any parameter is analyzed by using geographic information system method. The result of this study is 10 area of geothermal manifestation potential. The accuracy test of this research is 87.5 % in 1.96 σ. This research can be done efficiently and cost-effectively in the process. The results can be used for various geological and mining applications.

Geochemical studies of thermal waters from Kanlaon Volcano, Negros Island, Philippines

Kanlaon is a stratovolcano situated in central Negros Island, Philippines. It has a record of 30 eruptions since 1866 ranging from phreatic to phreatomagmatic (VEI = 1–2) events. Geothermal manifestations in Kanlaon Volcano are evidenced by the presence of hot springs, boiling mud pools, and warm rivers with temperatures up to 95 °C. It has developed a significant hydrothermal system within the volcanic edifice. Through time, it evolved into two distinct hydrothermal systems independent of each other. A mature hydrothermal system, represented by Pataan thermal area is characterized by neutral Na + K chloride (bicarbonate) fluids and an immature system, represented by Hagdan spring is characterized by the presence of acid-sulfate waters.Representative water samples were collected between 2014 and 2017 to further characterize the two systems. Chemical and sulfur isotopic analyses were performed on thermal waters to classify the samples that are linked to the co-existence of these two hydrothermal systems. Results show that thermal spring's pH ranges between 2.5 and 8.1 and conductivity ranges between 88 μS/cm to 3930 μS/cm. Based on their Cl-SO4-HCO3 relative abundances, the thermal waters are classified as acid sulfate, acid-sulfate chloride, neutral chloride and neutral bicarbonate waters.Temperatures of deep-water hydrothermal reservoirs were calculated using fluid-mineral geothermometers and correlated with available borehole temperatures. The Na-K-Mg geothermometer was used to evaluate equilibrium between water and reservoir rocks. Results show that the samples are not in equilibrium with the minerals in the reservoir. Temperature of equilibrium for the mature hydrothermal system was extrapolated to 270 °C based on available borehole temperatures. The linear trend towards the equilibrium temperature in the Na-K-Mg geothermometer can be explained by either groundwater/meteoric dilution. This is consistent with the light sulfur isotopic signatures between δ34S = −3.4‰ and + 1.2‰ of the mature hydrothermal system (Mambucal), which imply that the origin of sulfates is linked to surficial oxidation of H2S or dilution and mixing of meteoric water. On the other hand, immature hydrothermal system (Hagdan) shows a significantly higher sulfur isotopic composition (δ34S = +8.2‰), which could either result from the disproportionation of magmatic SO2 or from the hydrolysis of elemental sulfur at high temperature between 100 and 350 °C.

Geologi Daerah Geothermal Pangi Kabupaten Bone Bolango Provinsi Gorontalo

Geothermal is associated with volcanic that still has heat energy below the surface. Indonesia is a country with geothermal energy reserves of around 40%. There are 256 potential geothermal areas and only 7 locations have been utilized. Gorontalo has several geothermal manifestations, such as Lombongo, Pangi, Libungo, and Hungayono. The purpose of this study was to study the geology of the geothermal manifestations of Pangi, East Suwawa District, Bone Bolango Regency, Gorontalo Province. The research method is divided into field observations, laboratory analysis, and studio analysis. The results of this research show that the geomorphology in the study area is divided into 3 units, namely the Fluvial Plain, the Volcanic Hills, and the Structural Use Landscape. Alluvial Deposition Unit, Volcanic Breccia Unit, Tuff Lapili Unit, Andesite Unit, Granodiorite Unit, and Porphyry Diorite Unit.

Fluid-Rock Interaction During Hydrothermal Alteration at Parangtritis Geothermal Area, Yogyakarta, Indonesia

DOI: 10.17014/ijog.6.1.29-40Parangtritis Volcano is part of the Tertiary magmatic belt in Java, which was tectonically formed by collisions between the Eurasian Continental Plate and Indo-Australian Oceanic Plate. The collisions have taken place since Late Cretaceous and still continue until today. In that period, the magmatic belt in Java Island was formed and produced mineralization and geothermal. The characterization of geothermal in Tertiary volcanoes differs from the geothermal system that is on Quaternary volcano alignment in the middle of Java, such as: Awibengkok, Wayang Windu, Darajat, and Kamojang which have a high temperature. The purpose of this research is to study the mobilization elements due to interaction of hydrothermal fluids with wall rocks in low enthalpy geothermal regions of the Tertiary magmatic arc in Parangtritis. Identification of minerals and chemical element changes is approached by methods of petrographic and scanning electron microscope (SEM) analyses. As for knowing the composition and the origin of hydrothermal fluids, it used analyses of cations, anions, and isotope δ18O and δD of hot water manifestation. The occurrence of geothermal manifestations in Parangtritis, such as hot water and rock alteration, reflects the interaction of hydrothermal fluids with wall rocks which generates an argillic zone with mineral alteration such as quartz, calcite, montmorillonite, and hematite. The presence of alteration mineral montmorillonite replacing pyroxene provides an evidence that there have been interactions between the fluids and rocks. This interaction is as a process of element mobilization. Decrease in elements Si, Ca, Mg, and Fe is accompanied by an increase of Al during the replacement of pyroxene into montmorillonite. The mobility of this element occurs due to acid fluids. However, the hydrothermal fluid composition of the current hot water manifestation is neutral chloride water type composition, and the origin of the fluids is meteoric water (δ18O: -4.20 ‰ and δD: 23.43 ‰).

Gridded maps of geological methane emissions and their isotopic signature

Abstract. Methane (CH4) is a powerful greenhouse gas, whose natural and anthropogenic emissions contribute ∼20 % to global radiative forcing. Its atmospheric budget (sources and sinks), however, has large uncertainties. Inverse modelling, using atmospheric CH4 trends, spatial gradients and isotopic source signatures, has recently improved the major source estimates and their spatial–temporal variation. Nevertheless, isotopic data lack CH4 source representativeness for many sources, and their isotopic signatures are affected by incomplete knowledge of the spatial distribution of some sources, especially those related to fossil (radiocarbon-free) and microbial gas. This gap is particularly wide for geological CH4 (geo-CH4) seepage, i.e. the natural degassing of hydrocarbons from the Earth's crust. While geological seepage is widely considered a major source of atmospheric CH4, it has been largely neglected in 3-D inverse CH4 budget studies given the lack of detailed a priori gridded emission maps. Here, we report for the first time global gridded maps of geological CH4 sources, including emission and isotopic data. The 1∘×1∘ maps include the four main categories of natural geo-CH4 emission: (a) onshore hydrocarbon macro-seeps, including mud volcanoes, (b) submarine (offshore) seeps, (c) diffuse microseepage and (d) geothermal manifestations. An inventory of point sources and area sources was developed for each category, defining areal distribution (activity), CH4 fluxes (emission factors) and its stable C isotope composition (δ13C-CH4). These parameters were determined considering geological factors that control methane origin and seepage (e.g. petroleum fields, sedimentary basins, high heat flow regions, faults, seismicity). The global geo-source map reveals that the regions with the highest CH4 emissions are all located in the Northern Hemisphere, in North America, in the Caspian region, in Europe and in the East Siberian Arctic Shelf. The globally gridded CH4 emission estimate (37 Tg yr−1 exclusively based on data and modelling specifically targeted for gridding, and 43–50 Tg yr−1 when extrapolated to also account for onshore and submarine seeps with no location specific measurements available) is compatible with published ranges derived using top-down and bottom-up procedures. Improved activity and emission factor data allowed previously published mud volcanoes and microseepage emission estimates to be refined. The emission-weighted global mean δ13C-CH4 source signature of all geo-CH4 source categories is about −49 ‰. This value is significantly lower than those attributed so far in inverse studies to fossil fuel sources (−44 ‰) and geological seepage (−38 ‰). It is expected that using this updated, more 13C-depleted, isotopic signature in atmospheric modelling will increase the top-down estimate of the geological CH4 source. The geo-CH4 emission grid maps can now be used to improve atmospheric CH4 modelling, thereby improving the accuracy of the fossil fuel and microbial components. Grid csv (comma-separated values) files are available at https://doi.org/10.25925/4j3f-he27.

Delineation of Geothermal Manifestation in Sangubanyu Area Based on Microtremor HVSR Method

The aims of this study is to describe the distribution of P wave velocity and S wave velocity value and Vp/Vs ratio based on microtremor HVSR method and its relationship with the appearance of hot spring at Sangubanyu Village. Geothermal manifestations in the Sangubanyu area are located in Bawang sub-district, Batang regency, and Plantungan sub-district, Kendal regency, Central Java province. HVSR method is used to process microtremor data which produces the dominant frequency value and amplification factor then do inversion on the H/V curve to get the value of the Vp and Vs. The results of the microtremor HVSR processing obtained the distribution of the dominant frequency values in the study area between 0.62 to 0.73 Hz and amplification factor values 1.09 to 1.39, the inversion results on the H/V curve obtained the distribution of Vp values between 131.76 m/s to 2181.19 m/s, Vs values between 76.61 to 1129.42 m/s, Vp/Vs ratio 1.64 – 3.35. Based on the results of the analysis and wave velocity interpretation, the subsurface structure of manifestation area of Sangubanyu is composed of tuffaceous sandstone and volcanic breccia, the normal faults with southern blocks relatively downthrown, that cause the appearance of hot springs.

Global geological methane emissions: An update of top-down and bottom-up estimates

A wide body of literature suggests that geological gas emissions from Earth’s degassing are a major methane (CH4) source to the atmosphere. These emissions are from gas-oil seeps, mud volcanoes, microseepage and submarine seepage in sedimentary (petroleum-bearing) basins, and geothermal and volcanic manifestations. Global bottom-up emission estimates, ranging from 30 to 76 Tg CH4 yr–1, evolved in the last twenty years thanks to the increasing number of flux measurements, and improved knowledge of emission factors and area distribution (activity). Based on recent global grid maps and updated evaluations of mud volcano and microseepage emissions, the global geo-CH4 source is now (bottom-up) estimated to be 45 (27–63) Tg yr–1, i.e., ~8% of total CH4 sources. Top-down verifications, based on independent approaches (including ethane and isotopic observations) from different authors, are consistent with the range of the bottom-up estimate. However, a recent top-down study, based on radiocarbon analyses in polar ice cores, suggests that geological, fossil (14C-free) CH4 emissions about 11,600 years ago were much lower (<15 Tg yr–1, 95% CI) and that this source strength could also be valid today. Here, we show that (i) this geo-CH4 downward revision implies a fossil fuel industry CH4 upward revision of at least 24–35%. (ii) The 95% CI estimates of the recent radiocarbon analysis do not overlap with those of 5 out of 6 other bottom-up and top-down studies (no overlap for the 90% CI estimates). (iii) The contrasting lines of evidence require further discussion, and research opportunities exist to help explain this gap.

The application of geochemistry to bicarbonate thermal springs with high reservoir temperature: A case study of the Batang geothermal field, western Sichuan Province, China

The Batang geothermal field, located at the north-eastern margin of the Qinghai-Tibet Plateau, is a high-temperature geothermal system with two main geothermal areas, namely Bogexi and Rekeng. The Rehai geothermal field is also a high-temperature geothermal system, with a magmatic heat source which shows geothermal manifestations similar to those in Batang, especially in the Rekeng area. In this study, we compared the chemical compositions of different thermal springs in the Batang geothermal field with those in the Rehai geothermal field, to ascertain whether the thermal spring waters in Batang are also influenced by magma degassing or not. Further, we investigated the hydrogeochemical processes involved in forming the various thermal springs in the Batang geothermal field. We find that the thermal waters in the Batang geothermal field are not influenced by magma degassing. Although inorganic carbon, including HCO3− and CO32−, is the dominant anion component of most of the thermal waters in the Batang geothermal field, SO42− is present in variable amounts. In this area, the mixing of the thermal waters with steam containing some amount of H2S generated by metamorphism probably causes the relatively high SO42− concentration in the neutral thermal springs. Also, beneath the Rekeng area, there is a deep reservoir with the temperature of about 180 °C; a shallow reservoir of a relatively low temperature of about 75 °C was also identified in the eastern part. About half of the thermal spring waters in Rekeng directly originate in the deep reservoir, mixing with little or no snow-melt water and steam. Conversely, no steady reservoir exists beneath the Bogexi area. We attribute the high levels of Ca2+, Mg2+ and TIC (total inorganic carbon) in the thermal spring waters in the Bogexi area to the carbonate geologic stratum distributed at the outlets of the springs.

Determining Upflow/Outflow Zone and Fluids Flows in Geothermal Prospect Area Based on Geoindicator Comparison Value: A Case Study of Mt. Telomoyo, Central Java, Indonesia

Mt. Telomoyo is situated in Magelang Regency, about 400 kilometers from Jakarta. In the studied area, eight geothermal surface manifestations were found, consist of four hot springs and four cold springs. This research aims to identify upflow and outflow zones of geothermal area using compared value of geoindicator and tracer obtained from sampled of geothermal surface manifestations, and also to identify fluids flow of Mt. Telomoyo geothermal system. The method used in this research is to compile geoindicator comparison results, which are B/Li, Cl/B, Na/Ca, Cl/SO4, SO4/HCO3, and Na/K. Comparison results are then converted into geoindicator comparison maps. Fault and fracture is used to identify density of lineament, also direction of lineament where manifestation found. Afterward overlayed geoindicator maps and FFD maps is correlated to identify upflow/outflow zone and flow trend of geothermal fluid. The result of this research shows that the upflow zone in study area is located beneath Mt. Telomoyo, the upflow zone has high density of lineament. Furthermore, the outflow zones are found with two tendencies.The major trend of outflow is directed toward the western part of upflow zone, where geothermal manifestation APPD and APCU were found in ENE-WSW direction. The other outflow trend is directed toward the northeastern part of interpreted upflow zone, where geothermal manifestation APCD-1 and APCD-2 were found in NNW-SSE direction.

Possible generation and existence of quartz veins at Cisolok Geothermal Area

Cisolok area located at Southern West Java shows various geothermal manifestations. The igneous and volcanic rocks forming the main component of lithology in the area contains quartz veins. This indicates the rocks units in the area may have a close relation to the widely known Cikotok Fomation containing valuable minerals. Macroscopic description of Cisolok quartz vein samples show pyrite and possibly other heavy metal minerals in the veins. Geological condition shown close relation of Cikotok Formation having older geological age to dasitic volcanic rocks extrusted in Cisolok geothermal area. Further and detail research of quartz veins in Cisolok geothermal area will provide relationship to the Cikotok Formation, possible generation and component of valuable heavy minerals. This paper discusses the case condition under lithological and stratigraphic analysis of the volcanic and igneous rocks having quartz veins at Cisolok geothermal area.

Structural Geology Analysis Using Remote Sensing Method and its Correlation to Geothermal Occurence in Bayah District, Banten

Research area is located in Bayah District, Lebak Regency, Banten Province. The research location is located approximately 80 kilometers southwest of Jakarta. This area has a complex geological structure, as well as found many intrusive and metamorphic rocks. In this research area, geothermal manifestations were found in the form of four hot springs (APPC-1, APPC-2, APPC-3, and APC) as well as two cold springs (ADC-1 and ADC-2). This study aims to identify the relationship of geological structure control with the occurence of manifestations in the research area, as well as to determine the Bayah non-volcanic geothermal prospects. The method used is Fault and Fracture Density analysis for structural analysis of research area and magnetic map analysis for interpretation of geothermal prospect prospect. Structural analysis methods performed in the form of lineament delineation, determination of lineament density and major trends, and application of structural sequence model. The results of structural analysis will be correlated with the occurences of geothermal manifestations with the aim of identifying the most influential structural patterns as the pathway for geothermal fluid to reach surface in the study area. Magnetic data is also used to determine the possibility of Bayah non-volcanic geothermal prospects. The developing structure in the research area has NE-SW and NW-SE directions. The FFD analysis shows that high-density lineament is located in the southeast of research area where 3 hot springs manifestation APPC-1, APPC-2, APPC-3 are present. This manifestation appears in the lineament with NE-SW direction. Magnetic data also obtained negative magnetic anomalies in the southeast of the study area. It can be concluded that the lineaments with NE-SW direction influence the fluid outflow the most, and Bayah non-volcanic geothermal prospect areas are located around APPC manifestations.

Overview of the petrophysical and geochemical properties of the Ungaran Quarternary Volcano in relation to geothermal potential

Ungaran geothermal field is estimated to have a potential of 15 MWe. The volcano is located in the middle of Java Island which is a range of Quaternary volcanoes. As in other islands in Indonesia that indicate that this volcano has a potential energy of geothermal. This volcano is a strato volcano with andesitic composition. The Ungaran volcano geothermal system is located within a young cone depression, overgrown by Mount Gugon and Mount Megi that form the depressive ring. Geothermal manifestations contained in Gedongsongo include: fumarola, hot springs, travertine, steaming ground and alteration rocks. The temperature of the hot springs is about 50°C, the pH of hot water is acidic (ranging from pH 1.5 to 5.5), bubble gas and around fumarola are found sublimation of sulfur and pyrite.This research uses analytical methods of geochemistry (water and rock), petrography and petrophysics. Based on geothermometer analysis shows that the reservoir temperature is 300°C. The composition of fumaroles is strongly influenced by magmatic elements with temperatures greater than 300°C. While petrography analysis yields that the material of Ungaran volcano rock is andesite-basaltic. Knowing the geothermal potential of this area is expected to increase the Java-Bali power supply.