Upflow Zone Research Articles

Regional controls on fluid flow in geothermal systems of the Taupo Volcanic Zone, New Zealand

ABSTRACT The Taupo Volcanic Zone (TVZ) provides almost 20% of New Zealand’s electricity production through seven of its 23 high-temperature geothermal systems. Fluid circulation in geothermal systems is influenced by permeable pathways, heat sources, and topography. To explore influences on systems in the TVZ, we have created regional-scale heat and fluid flow models using TOUGH2. We modelled several potential influences individually and in combination: TVZ rift boundaries, the densely faulted Taupo Fault Belt, varying thickness of volcanic cover, topographic loading, and localised heat sources inferred from magnetotelluric data. The locations of seven of the nine geothermal systems in our study area can be explained by TVZ-scale convection influenced by localised deep heat sources and hydraulic gradients due to topography. Regional-scale geology appears to be an additional influence at Rotorua and Ngatamariki, where cold recharge within the Taupo Fault Belt pushes modelled upflow towards the rift margins. At Ohaaki, modelled upflow is northwest of the system unless a dipping contact between basement and more permeable cover rocks is included. Modelled upflow zones do not correspond to geothermal systems at Te Kopia and Haroharo Volcanic Complex, which we hypothesise is related to uplift along the Paeroa Fault and shallow impermeable lava domes respectively.

Discriminating Superimposed Alteration Associated with Epigenetic Base and Precious Metal Vein Systems in the Rouyn-Noranda Mining District, Quebec; Implications for Exploration in Ancient Volcanic Districts

Abstract The Rouyn-Noranda mining district of Quebec contains 20 Cu-Zn (±Au ±Ag) volcanogenic massive sulfide (VMS) deposits, including the giant and gold-rich Quemont and Horne deposits. Mineralized epigenetic veins are also present, but their origin and relative timing remain enigmatic. The nature and extent of their alteration signatures and the effect of their superposition on district-scale alteration patterns is unknown. The VMS-related quartz-sulfide Cu-Zn-Ag veins have δ18Oquartz values of 8.5 ± 0.8‰, reflecting δ18Ofluid compositions of –0.4 to 3.1‰ (250°–350°C) that are typical of Archean seawater. They are associated with a proximal Fe-rich chlorite alteration and marginal spotted sericite-chlorite alteration with whole-rock δ18O values of 2.9 to 5.9‰ and are interpreted to have formed within the structurally controlled discordant upflow zones of a VMS hydrothermal system. Younger gold-bearing quartz-carbonate veins were emplaced along mechanical anisotropies created by mafic dikes during north-south compression and the formation of regional E-trending faults, folds, and cleavage. They are characterized by δ18Oquartz values of 11.3 ± 0.8‰, reflecting δ18Ofluid compositions of 2.4 to 5.9‰ (250°–350°C), typical of a metamorphic fluid, possibly mixed with a lower δ18O upper crustal fluid. They are associated with ankerite, calcite, muscovite, chlorite, albite, and quartz ± hematite alteration with whole-rock δ18O values of 5.8 to 10.3‰. Chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb zircon ages for two tonalite intrusions constrain the maximum age of the Cu-Zn-Ag veins to 2697.6 ± 0.7 Ma and the minimum age to 2695.3 ± 1.0 Ma, which is also the maximum age of the gold quartz-carbonate veins. Superposition of alteration related to the gold quartz-carbonate veins on previously chlorite- and sericite-altered rocks has resulted in mixed alteration signals with whole-rock δ18O values of ~6 to 8‰ that have perturbed and masked regional alteration patterns related to older VMS mineralization, such as those found in the Quemont and Horne deposits. These results indicate that defining alteration vectors in camps that have superimposed hydrothermal systems requires full consideration of the hydrothermal history of the camp, and if such constraints are lacking, whole-rock δ18O values should not be used as a stand-alone exploration method.

A critical evaluation of the role of a geothermal system in lithium enrichment of brines in the salt flats: A case study from Laguna Verde in the Atacama Region of Chile

The association between geothermal fluids and lithium-rich brines in salt flats has been evaluated in a unique natural laboratory in the Chilean Andes. The area encompasses Laguna Verde (LV), a hypersaline lake, and a salt flat (salar) within a closed basin surrounded by volcanoes. The predominant lithology consists of andesitic-dacitic rocks, with limited occurrences of rhyolitic rocks. The LV geothermal system exhibits surface manifestations, including over 20 hot springs reaching 47 °C along the lake's southern margin. The upflow zone is represented by the fumarolic field in the Nevado Ojos del Salado volcano, 25 km southwest of LV. Lithium concentrations range from 2.76 to 4.46 mg/L in thermal water and 0.59 to 0.76 mg/L in the Peñas Blancas river water, which feeds into LV after passing through a volcanic environment rich in lithium-bearing rocks. However, the thermal waters contribute over six times more lithium than non-thermal waters, highlighting their significance in releasing and transporting lithium from the source rocks to its eventual accumulation in LV. This natural laboratory at LV provides an excellent opportunity to evaluate the association between geothermal fluids and lithium-rich brines, offering valuable insights into the processes involved in lithium enrichment in similar geological and climatic conditions in other geographic areas.

Behavior of Amagmatic Orogenic Geothermal Systems: Insights From the Agua Blanca Fault, Baja California, Mexico

AbstractAmagmatic geothermal systems within regional‐scale orogenic faults are promising renewable resources for heat and possibly electricity production. However, their behavior needs to be better understood to improve their exploration and assessment of energy potential. To provide more insight, we report geochemical, geological, and geophysical studies from seven hot spring sites strung along a 90 km segment of the Agua Blanca Fault, which traverses a mountainous region of northern Baja California, Mexico. Our results show that topographic heads drive infiltration of meteoric water deep into basement rocks, where it is heated according to the local geothermal gradients. Long paths lead to long water residence times and high 3He/Hetotal fractions. The hot water ascends along preferentially permeable zones within the ABF, discharging at temperatures from 37°C in inland springs to 102°C on the Pacific coast. Higher discharge temperatures correlate positively with the degree of extensional fault displacement (a proxy for fault permeability). Correlations between hydraulic head gradients, residence times, and 3He/Hetotal of the thermal waters show that the hydraulic head gradient controls the length and depth of the flow paths, whereas the magnitudes and locations of the discharge sites are controlled by fault permeability. Optimal conditions at the coast allow the 120°C temperature threshold for electricity production to be reached at relatively shallow depths (<2 km), demonstrating the potential of orogenic geothermal systems not only for exploitation of hot discharging water but also for EGS exploitation of the hot rocks that surround the water upflow zones.

The Hydrogeochemical Model of "YR" Geothermal Field, East Java

The YR Geothermal Field is located in East Java. This field is associated with an active volcano, implying a potential for a high enthalpy geothermal system. This field is still in the exploration phase, but no drilling has been conducted yet. Thus, insights into the geothermal system are obtained through geochemical analyses of geothermal manifestations. Geochemical analyses were performed on hot spring water samples to determine the characteristics, processes, origin, and fluid flow of the geothermal system. The research results indicate that the warm springs have temperatures ranging from 29.4 to 54.8°C, with a nearly neutral pH (6.14-6.44) and high contents of HCO3 (457-1150 mg/kg), Na (77.7-255 mg/kg), and Mg (37.4-110 mg/kg). Therefore, it can be concluded that all the warm springs fall into the bicarbonate type with immature conditions, indicating no direct association with the reservoir. The upflow zone is interpreted to be at the peak of Mount 7, while the outflow zones are in areas A, B, and C. The fluids flow from the upflow zone, then condense and advectively flow down the slope, experiencing dilution and reactions with rocks before emerging as outflows in the western and north-western areas.

Analysis and Interpretation of Gravity data to modelling ‘PB’ Geothermal Field

The ‘PB’ field is located on the island of Sumatra which is related to the volcanic activity of Kaba hill which still retains residual heat from the magma. One of the geophysical methods used in this case is the gravity method where this method can be applied to determine the location of reservoirs, possible locations for reservoirs, and even to examine geological features and heat sources. In this paper, gravity data is used to interpret the structure and possibility of modelling the heat source in the ‘PB’ geothermal field. The gravity data was analyzed using integrated gradient interpretation techniques such as Horizontal Gradient (HG) and Euler Deconvolution (ED) methods. The CBA map produced shows two dominants high Bouguer anomalies underlying the ‘PB’ geothermal field associated with the presence of dacite and andesitic rocks. Analysis of fault structure based on geological data, HG and ED enhancement data on gravity anomalies was used as a reference for the initial model of subsurface conditions in the inversion model. The 2-D modelling results reflected high-density rocks associated with active ‘PB’ mountain volcanism. The conclusion obtained from the analysis and interpretation of the ‘PB’ geothermal system is that this area still has active volcanism, which is a heat source, with the presence of diatreme found through 2D gravity inversion modeling. The conceptual model results obtained by combining the integration of each reference and existing research show that the upflow zone is at the top of Kaba Hill and the outflow zone is at Babakan Bogor hot spring and Suban hot spring. Thus, these results can provide comprehensive information in analyzing and interpreting as well as the use of enhancement data gravity HG, ED and 2D slice inversion in the description of structures and modelling in the Geothermal ‘PB’ field.

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.

Geophysically guided well siting at the Aluto-Langano geothermal reservoir

Volcano-hosted high-temperature geothermal reservoirs are powerful resources for green electricity generation. In regions where such resources are available, geothermal energy often provides a large share of a country’s total power generation capacity. Sustainable geothermal energy utilization depends on the successful siting of geothermal wells, which in turn depends on prior geophysical subsurface imaging and reservoir characterization. Electromagnetic resistivity imaging methods have proven to be a key tool for characterizing magma-driven geothermal systems because resistivity is sensitive to the presence of melt and clays that form through hydrothermal alteration. Special emphasis is often given to the “clay cap,” which forms on top of hydrothermal reservoirs along the flow paths of convecting geothermal fluids. As an example, the Aluto-Langano volcanic geothermal field in Ethiopia is covered with 178 densely spaced magnetotelluric (MT) stations. The 3D electrical conductivity model derived from the MT data images the magma body that acts as a heat source of the geothermal system, controlling geothermal convection and formation of alteration zones (commonly referred to as clay cap) atop the geothermal reservoir. Detailed 3D imaging of the clay cap topography can provide direct insight into hydrothermal flow patterns and help identify potential “upflow” zones. At Aluto all productive geothermal wells are drilled into zones of clay cap thinning and updoming, which is indicative of underlying hydrothermal upflow zones. In contrast, nonproductive wells are drilled into zones of clay cap thickening and lowering, which is an indicator for underlying “outflow” zones and cooling. This observation is linked to fundamental characteristics of volcano-hosted systems and can likely be adapted to other geothermal fields where sufficiently detailed MT surveys are available. Therefore, high-resolution 3D electromagnetic imaging of hydrothermal alteration products (clay caps) can be used to infer the hydrothermal flow patterns in geothermal reservoirs and contribute to derisking geothermal drilling projects.

Investigation of deep-seated heat source through 3-D Magnetotelluric inversion in Arjuno-Welirang volcanic complex (East Java)

Arjuno-Welirang is a volcanic complex with quaternary ages in East Java Province, Indonesia. Various geothermal systems in the area might exist, from inactive to still-active hydrothermal systems and even volcanic (magmatic) hydrothermal systems. To differentiate the status of geothermal systems to be useful for further exploration programs, it is necessary to investigate the deep-seated heat source responsible for supporting heat to the existing geothermal systems. To achieve the objective, Magnetotelluric (MT) is used to image the subsurface resistivity variation down to about 20 km. A total of 117 MT stations have been included to fill the coverage area, especially in the eastern and southern regions of the research area. A series of data processing has been conducted to improve the quality of MT data, and 3-D inverse modeling has been applied after processing. In addition, the exploration is also focused on identifying the extension of the high-temperature reservoir with benign fluid. Based on the 3-D inversion of MT data, the updome of resistivity structure at the deeper level below Mt. Welirang is identified as a deep-seated heat source indication supporting the main upflow reservoir zone. A possible reservoir extension to the western side of Mt. Welirang–Mt. Kembar complex is more prominent as indicated by the resistivity pattern, supported by the Cangar and Coban hot springs occurrence as an indication of an outflow zone. This extension zone could be one of the focused areas for further exploration drilling to avoid magmatic fluid that probably exists at the main upflow zone.

Cold water injection near the magmatic heat source can enhance production from high-enthalpy geothermal fields

Although existing deep geothermal wells have confirmed that shallow magmatic intrusions heat circulating hydrothermal fluids to supercritical temperatures, successfully utilizing such fluids for power generation has proven challenging. As an alternative, using deep geothermal wells drilled into the vicinity of intrusions for injection rather than production has the potential to enhance heat extraction from the intrusion, while simultaneously providing fluid pressure support to the overlying geothermal system. However, the dynamic response of the heat source and overlying geothermal system to deep injection has not previously been investigated using numerical modelling. Here, we present numerical models showing that injection in the near-vicinity of a magmatic heat source increases the production potential of shallower geothermal wells. By locally cooling the hot rock near an intrusion, deep injection increases permeability and the rate of heat transfer across the brittle–ductile transition. The injected fluids ascend in upflow zones above the heat source and provide pressure support to shallower geothermal wells, without significantly affecting the temperature and enthalpy of produced fluids. We investigate a variety of scenarios involving only a single deep injector and a single shallower producer. Our models suggest that deep injection could increase the production potential of shallower geothermal wells by up to 10 percent after 30 years of well operation and by 20 percent after theoretical 100 years, with the magnitude of the impact increasing with continued injection over longer timescales.

The Estimation of Fracture Intensity and Pressure Distribution using Analysis of Shear Wave Splitting on “Landak” Geothermal Field

<p><em>Shear wave splitting is a study that utilizes the differences between arrival times of two shear waves (slow and fast) propagating from a source to a receiver to identify the magnitude of the anisotropic medium through which they propagate. Aside from generating a delay time between two shear waves, the anisotropic medium also shifts the polarization of fast shear wave from its initial polarization which is indicated as the main orientation of the related fracture system. The study was conducted on Landak Field, located around Bukit Besar mountain range by analyzing provided data from December 2011 to April 2012. The results of this study show that the polarizations of fast shear waves in several stations are as following; NE-SW orientation at station R09, R17, R25, and R26, N-S orientation at station R08, and NW-SE orientation at station R17. Not only do these orientations of polarization show a good correlation with structural analysis in this area, but also important to be noted that all microseismic stations encounter a wide-spreading polarization phenomenon as an effect of complex anisotropy. The delay time from all stations ranges from 0.03 to 0.07 seconds. The normalization between delay time and length of ray path for all stations results in a fracture intensity parameter ranging from 0.004 to 0.011 seconds/km. This intensity is measured in slowness parameters, which shows increased value towards the Bukit Besar area, which potentially becomes the upflow zone of the geothermal system</em>. The study shows that the distribution of fracture intensity and pressure have correlation and identical trend with temperature distribution.</p>

Analisis Karakteristik Tipe Fluida Mata Air Panas Di Hutan Pinus Lahendong Dengan Menggunakan Spektrofotometri

Pine Forest is one of the tourist attractions in Lahendong Village, which has geothermal manifestations in the form of hot springs, which shows that the area has geothermal potential. The purpose of this study was to determine the type of fluid manifested by hot springs in the Pine Forest using geochemical methods. The results of this study indicate that the temperature at the manifestation is 40°C while the degree of acidity of the pH of hot water has a value of 4 which indicates the acidity level of hot water is acidic. The type of fluid that exists in the manifestation area of hot water in the Pine Forest is the type of fluid sulphate water and sulfate water is a fluid that is formed at shallow depths and is formed as a result of the condensation process of geothermal gas towards near the surface. This is because the results of chemical analysis show that the element SO4 is the most dominant element and contains SO4 gas. Hot water that has a sulfate type is water that is formed at shallow depths and is formed as a result of the process of condensing geothermal gas towards near the surface. The geothermal gas with gas content (water and carbon) is basically dissolved in the fluid content which is located in the deep zone but separated from the chloride water. Sulphate water is usually at the boundary and not far from the main upflow zone.

Effects of structural zonation on fluids circulation of the Copahue geothermal system

The volcano-hosted geothermal system of Copahue is one of the most promising resources of renewable energy in Argentina. The associated geothermal field is bounded by a set of N60° trending normal faults to the north and by WNW-ESE trending faults to the south. This paper aims to review this first-order distribution of the structures, using previously published b-value data, and to explore the relationship between the local stress field, the superficial structural setting, the magmatic source, and the geothermal fluid flow paths related to the volcanic complex. The 2D dilation tendencies of the geomorphic lineaments is calculated, defining a structural domain with dilatant lineaments that agrees well with high b-values observed at shallow depths(2 km below the surface), and with the known extension of the geothermal field. A rough spatial correspondence is also observed between domains of unfavorable oriented to dilate lineaments and shallow low b-value areas, suggesting that these discontinuities inhibit the horizontal motion of fluids at the same structural level, and constraining the reservoir both to the northwest and to the southeast. b-value data unravels the potential magmatic plumbing system at depth, highlighting a major NW-elongated high b-value body centered at 5 km below surface, from Chancho-có hill towards the south of Maquinas fumaroles. It is coincident at surface with a high density of lineament intersections domain, which creates in depth an intense structural damage zone that may facilitate the ascent of magmatic fluids. The NW anomaly can be extrapolated to the western margin of the Caviahue lake, agreeing with the occurrence of volcano-tectonic seismic events and elevated heat flows reported in this area, and therefore suggesting the presence of the geothermal reservoir at depth. Vertical appendices branching from the b-value anomaly reach up to 3 km below Termas and Maquinitas fumaroles, outlining the possible bottom of the geothermal reservoir. The shallower one is interpreted as a blob of magma injected below the Copahue Village fault system, providing the main heat source. These findings contribute to the current understanding of the geothermal reservoir, its depth coverage and upflow zones, providing insights for future geophysical exploration stages.

Two Decades of Monitoring Hydrothermal Plumes at the Brothers Submarine Volcano, Kermadec Arc, New Zealand

Abstract Brothers volcano is arguably the most well-studied submarine arc volcano on Earth. Between 1996, when massive sulfides were first recovered by dredging, and 2018, when International Ocean Discovery Program (IODP) Expedition 376 recovered cores from as deep as 453 m below the sea floor at two chemically distinct hydrothermal upflow zones, over 60 conductivity-temperature-depth (CTD) vertical casts and tow-yo operations mapped hydrothermal plumes over and around the edifice by employing hydrothermal tracer-specific sensors. These surveys started in 1999 and were completed during nine separate expeditions at one- to three-year intervals, except for a six-year gap between 2011 and 2017. Hydrothermal plume distributions over this two-decade period show variability in the intensity and vertical rise height of plumes from the four main vent fields (Upper Cone, Lower Cone, NW Caldera, and Upper Caldera, with the latter not discovered until 2017). Upper Cone plumes were more intense than all other sites in 1999, 2002, 2007, and 2009, then significantly diminished from 2011 to 2018. The Lower Cone plume was the most intense in 2004, then the NW Caldera site became the dominant source of hydrothermal particles from 2011 to 2018. Despite the gap of six years between 2011 and 2017, hydrothermal output appears to have increased within the caldera sometime after the 2009 survey while simultaneously decreasing in intensity at the cone sites. This supports other evidence of linkages between the cone and caldera sites in the deep hydrothermal circulation system, and may be related to the predicted deepening of hydrothermal circulation, infiltration of seawater to facilitate “mining” of magmatic brines, and modulation of subseafloor mineralization processes associated with a modeled, pulsed injection of magmatic gasses. The surveys also revealed ways in which the highly variable regional hydrographic environment impacts the flux of hydrothermal products to the surrounding ocean. Plumes from sources located above the caldera rim disperse hydrothermal components without hindrance, but particles and heat from sources within the caldera become trapped and are dispersed episodically by caldera-flushing events. While on site for 18 days in 2018, repeat CTD casts into the deepest part of the caldera, which was isolated from the surrounding ocean, showed a progressive increase in temperature, representing a net heat flux of 79 MW from conductive and advective sources deeper than 1,570 m.

Hululais Field Review from Geoscientific Exploration to Exploitation Stage

Geothermal studies in Hululais carried out by Pertamina was started in 1993 with an exploration survey. The detailed geological mapping as the earliest geothermal resource assessment of Hululais was done internally by Pertamina. The geochemical study was done together with the geological study. The geophysical study was carried out using three methods. The gravity survey was run in 1993 for 320 points along 12 trace lines, while the magnetotelluric survey was conducted in 2006 and 2012 for 64 locations with 1-2 km spacing. The microearthquake survey was done in 2012 for 115 days monitoring time by six sensors in 10 km spacing and in 2019. The conceptual model as a product of the integrated study of three geoscientific surveys shows that the upflow zone is interpreted in Suban Agung – Suban Gregok in the southern area. Fumarole, mud pool and steam-heated hot spring are found in this zone. The outflow zone is interpreted towards the north in Semelako area supported by the chloride hot spring. The appearance of these manifestations is possibly controlled by fault structure in Musi Segment zone of Sumatra Fault Zone (SFZ). The heat source comes from granodiorite intrusion below Bukit Beriti Besar – Bukit Gedang Hululais. The cap rock has 500 meters thick in the upflow zone and increases to 800 meters thick towards the outflow zone in the northern part of the study area. The upflow zone was proved by two exploration wells that drilled until 3000 mMD. The first well in Suban Agung has a high temperature reach 300°C with neutral reservoir fluids and good fault structure permeability. The second exploration well that drilled towards outflow zone shows a temperature of 205°C with neutral reservoir fluids but with low permeability. In the exploitation stage, 21 development wells have been drilled for making the update conceptual model. Among them, ten wells are production wells and the remains are reinjection ones. The permeability in the reinjection wells is not so good compared to the production wells. It might be due to secondary mineral filling in the fault structure permeability zone, so this situation causes a problem in injection water to the reservoir. Investigation of the subsurface permeability distribution in the Hululais reservoir is challenging, so further research should be done to answer this challenge.

Upflow-outflow Zone Identification Based on Geochemistry Indicator and Fault Fracture Density Correlation Analysis in Mt. Gede Geothermal Case, West Java

Upflow and outflow zones in a geothermal field are very important to identifying. These two zones are very useful in running a geothermal project such as simply in determining the drill point. Mt. Gede-Pangrango is one of the interesting geothermal fields in West Java province and is still included in the category the geothermal fieldwork (WKP) has not been further investigated which is the current research area especially on Mt. Gede. The method used to identify upflow-outflow zones is to correlate fault fracture density (FFD) analysis and geochemistry indicators with the early hypothesis that the geothermal upflow zone in the Mt. Gede is most likely located in the crater area to the volcanic body. Based on the FFD analysis, areas with high density of structural lineaments with a value of >2 km/km2 tend to have a southwest-northeast pattern that describes the direction of geothermal fluid flow due to the presence of a permeable zone (fracture) from the crater area of Mt. Gede (upflow zone) towards the foot of the mountain (outflow zone) the Cipanas area, which is also supported by the presence of the bicarbonate hot spring manifestation in the area. Then based on the geochemistry indicator (HCO3/SO4, Na/K, CO2 /H2S, and Isotope 18O), it can be seen that the upflow area is in the area of the volcanic peak to the body of the volcano and the outflow is at the foot of the volcano (Cipanas Area). From these two analyzes, it can be seen that the FFD and geochemical indicators are very well correlated in identifying the upflow and outflow zones of Mt. Gede and answered the early hypothesis that the upflow area tends to be in the volcanic crater area to the volcanic body of Mt. Gede.

Lithium isotopic and fluid mobile trace element systematics of the Bay of Islands altered forearc upper to lower ophiolitic crust

Bulk rock Li isotope and select fluid mobile element traverses through the crustal section of the Late Cambrian Bay of Islands Ophiolite Complex (BOIC) in the Taconic Humber Arm Allochthon in the Newfoundland Appalachians are presented to examine the extent and conditions of alteration at different pseudo-stratigraphic levels in the ancient forearc oceanic crust that was obducted during the Middle Ordovician.N-MORB normalized enrichment factors (EFs) calculated for Li and fluid mobile elements (FMEs) show variable extents of enrichments or depletions from shallow to deep oceanic crustal sections in the BOIC that are consistent with a broad range of alteration-related δ7Li values from −2.97 to +20.69 ‰ (vs. unaltered MORB range of +1.5 to +6.1 ‰ with a mean of +3.4 ± 1.4 ‰). EFs and fluid-rock reaction modeling for Li contents and δ7Li values indicate alteration dominantly controlled enrichments and depletions of Li isotopic and FMEs systematics through all crustal levels of the BOIC ophiolite. Alteration fluids are dominated by modern seawater-like δ7Li composition rather than the recently proposed Cambrian seawater that is based on ancient carbonate shell compositions.BOIC basaltic samples proximal to the York Harbor Mine (YHM), similar to the classic mafic Cu-Zn Cyprus-type volcanic massive sulfide (VMS) deposits, show light δ7Li values of −2.97 to +1.59 ‰, but highly enriched Li contents (14.0–40.7 μg/g). Modeling results indicate that these YHM basalts were altered by metal-rich magmatic fluids, in part, derived from deeper plagiogranite intrusions near the base of the sheeted dikes that are possibly admixed with seawater-derived hydrothermal fluids below the VMS deposit. Magmatic volatile exsolution may be associated with the crystallization of directly underlying subvolcanic silicic intrusions, resulting in over-pressuring and fracturing of the carapace that may assist in localizing the high temperature (400–200 °C) upflow zones of the seafloor hydrothermal system.The BOIC layered gabbroic rocks also show evidence of variable extent of alteration as reflected by both Li content (EF both >1 and < 1) and δ7Li composition (+0.79 to +9.47 ‰), likely indicating high-temperature amphibolite (800–600 °C within the ductile deformation field) to lower temperature greenschist facies paragenesis, with down-temperature complex retrograde petrogenetic lineages. Mylonites and ductile shear zones commonly show heavier δ7Li values between +5.47 and + 18.83 ‰. We suggest that mylonite zones and coarser-grained high-strain zones allowed near-axis fluid penetration at high to lower temperatures that extended to the basal gabbroic sections in the crust during ongoing igneous activity. Shear zones were associated with rheologic weakening and initial permeable pathways for hydrothermal fluids. Shallow on-axis and deep off-axis hydrothermal circulation likely occurred at a relatively fast-spreading rate, which may account for the significant shallow to deep crustal heat extraction as predicted by the multiple sill model of lithospheric cooling.

Morphostructure and Hydrogeochemical Analysis of Geothermal Systems in Karaha Bodas and Talaga Bodas Field, West Java

The Karaha Bodas and Talaga Bodas are two geothermal fields which are located in Tasikmalaya, West Java. The Karaha Bodas and Talaga Bodas fields have geothermal prospects with the discovery of several surface manifestations in the form of hot springs, fumaroles, and acid lakes. The orientation of the structure that developed in the two fields showed a different orientation. However, no research explains the relationship between the geothermal system in the Karaha Bodas field and the Talaga Bodas field, and the potential of Cipacing and Pamoyanan. The survey location is in Garut and Tasikmalaya, West Java. The investigation method used is qualitative (morphostructure analysis) and quantitative (hydrogeochemical analysis) methods. Data processing using DEM (Digital Elevation Model) for morphostructure analysis, and water chemistry from the Karaha Bodas, Talaga Bodas, and Cipacing fields for hydrogeochemical analysis. The analysis shows that the relationship between the Karaha Bodas and Talaga Bodas geothermal systems is typical a geothermal system, with having two different heat sources, the Talaga Bodas field as an upflow zone, and the Karaha Bodas field with Cipacing and Pamoyanan potentials as an outflow zone.Keywords: Conceptual model, geothermal system, hydrogeochemical, Karaha Bodas, morphostructure, Talaga Bodas.

The implications of crustal architecture and transcrustal upflow zones on the metal endowment of a world-class mineral district

Earth’s mineral deposits show a non-uniform spatial distribution from the craton-scale, to the scale of individual mineral districts. Although this pattern of differential metal endowment is underpinned by lithospheric-scale processes the geological features that cause clustering of deposits remains enigmatic. The integration of geological and geophysical (seismic, gravity, and magnetotelluric) features has produced the first whole-of-crust image through an iconic Neoarchean volcanic complex and mineral district in the Abitibi Greenstone Belt, Superior Province, Canada. Observations indicate an asymmetry in surface geology, structure, and crustal architecture that defines deep transcrustal magmatic-hydrothermal upflow zones and the limits of the Noranda District ore system. Here, extreme volcanogenic massive sulfide (VMS) endowment is confined to a smaller area adjacent to an ancestral transcrustal structure interpreted to have localized and optimized magmatic and ore forming processes. Although lithospheric-scale evolutionary processes might act as the fundamental control on metal endowment, the new crustal reconstruction explains the clustering of deposits on both belt and district scales. The results highlight a strong magmatic control on metal and in particular Au endowment in VMS systems. Overprinting by clusters of ca. 30 Ma younger orogenic Au deposits suggest the ore systems accessed an upper lithospheric mantle enriched in Au and metals.

Ambient seismic noise monitoring and imaging at the Theistareykir geothermal field (Iceland)

In autumn 2017 a network of 14 broadband seismic stations was deployed at the Theistareykir high temperature geothermal field (NE Iceland). This experiment was conducted as part of the current efforts to characterize the field's main structures, and possible short and long term stress variations due to the ongoing fluid injection and extraction operations which started in autumn 2017. In this work, we use two years of continuous seismic records (October 2017–October 2019) to compute a 3D shear wave velocity model of the geothermal field and to detect possible crustal stress changes related to the injection and production activities. From phase cross-correlations of the vertical component recordings, we measure the Rayleigh wave group velocity dispersion curves to obtain 2D group velocity maps between 1 and 5 s. Subsequently, we use a neighborhood algorithm to retrieve the 3D shear wave velocity model of Theistareykir. Mainly, two sets of elongated high and low velocity anomalies can be observed oriented in a NW/WNW direction, parallel to the lineaments of the active Tjörnes fracture zone. Velocity reductions west of Ketilfjall and at Baerjafjall could indicate the location of upflow zones of the magmatic reservoir or hydrothermal system. We analyzed the temporal evolution of phase and amplitude of phase auto-correlations using the stretching technique and discuss their behavior in relation to the geothermal field operations. We notice a slightly stronger long-term velocity decrease in the reservoir region compared to outer regions. This could be related to the mass depletion in that area (higher fluid extraction compared to the water reinjection). In summary, our findings show how a monitoring network can be set up to enable a detailed imaging and monitoring of reservoir behavior in general.