Large Hydrothermal System Research Articles

El Chichón volcanic activity before and after the Mw8.2, 2017, Chiapas earthquake, México. Is El Chichón ready to erupt?

El Chichón volcano is the most active volcano in the state of Chiapas, México, and experienced its last Plinian eruption (VEI = 5) in 1982. To better assess its volcanic hazard, we studied its readiness to erupt by estimating changes in its internal stress state. These stress changes are difficult to calculate accurately, for example in the absence of focal mechanisms, but their existence can be indirectly revealed by the presence of volcano-tectonic earthquakes, for example following a large tectonic earthquake. We show that the seismic rate recorded at El Chichón volcano increased slightly after the large Mw8.2 Tehuantepec earthquake of 8 September 2017, Chiapas. However, this rate quickly returned to its background level after only 2 months, without any external volcanic manifestations, suggesting that the volcano is not ready to erupt in the near future. Previous observations of slight increases in the volcanic seismicity rate following large earthquakes have been explained by the presence of active hydrothermal systems in the vicinity of the volcano. We propose a similar explanation for El Chichón volcano which is known for its large hydrothermal system. Furthermore, the characteristics of the 2017 seismicity (spatial and magnitude distributions), and the horizontal-to-vertical spectral ratio also confirm the presence of high amounts of water near the volcano. We show that the 2017 volcano-tectonic seismicity is of hydrothermal rather than magmatic origin, in agreement with recent independent geochemical and aeromagnetic studies.

Multistage fluorite mineralization in the southern Black Forest, Germany: evidence from rare earth element (REE) geochemistry

Abstract. The Black Forest hosts a wide range of hydrothermal mineralization, including fluorite–barite vein deposits. In a detailed investigation of the Finstergrund and Tannenboden deposits in the Wieden mining district (southern Black Forest), the diversity, geochemical evolution and relative chronology of multistage fluorite precipitation is tracked on the basis of rare earth element (REE) geochemistry, geologic field relationships and crystal zoning. Geochemical discrimination and mathematical λ coefficients suggest a total of seven fluorite REE groups, at least three distinguishable post-Variscan fluid mobilization events and independent formation histories for the deposits despite their spatial proximity. Fluorite vein mineralization at the Finstergrund deposit evolved over three fluid generations, was derived from gneissic source aquifers and comprises five distinct fluorite REE groups: the first fluid generation is characterized by fluorite precipitation above 200 ∘C (“group III”), below 200 ∘C (“group I”) and after fractional crystallization (“group IV”); the second generation comprises remobilized fluorite (“group II”); and the third generation revealed fluorite precipitation by meteoric water mixing (“group V”). Fluorite vein formation at the Tannenboden deposit is associated with two distinct fluorite REE patterns derived from the same fluid generation: fluorite precipitation above 200 ∘C (“group VII”) and after cooling below 200 ∘C (“group VI”). Its fluid source aquifer lithology best matches migmatites contrary to previous models that suggest either gneissic or granitic aquifer rocks for fluorite vein precipitation in the Black Forest. The decoupled formation history between the deposits is tectonically controlled as suggested by a new genetic model for the Wieden mining district. The model argues for a change in the local fluid percolation network and the termination of hydrothermal activity at the Tannenboden deposit after the first fluid mobilization event. The geochemical evolution of multistage fluorite mineralization, as exemplified by the Tannenboden and Finstergrund deposits in combination with other fluorite mineralizations in the Black Forest, provides unique insights into the lithospheric origin and precipitation behaviour of fluorite by various fluid–rock interaction processes occurring in large hydrothermal systems. The local diversity of REE patterns emphasizes the need for detailed investigations of individual hydrothermal vein deposits.

A multidiscipline collaborative optimization approach with acceleration strategies for generator maintenance scheduling in large hydrothermal power systems considering uncertainty of natural inflows

Generator maintenance scheduling (GMS) is an important task in the dispatch and operation of hydrothermal power systems. On a long-term timescale, the uncertainty of natural inflows makes GMS essentially a stochastic optimization problem. The sample average approximation (SAA) method is used to convert the stochastic hydro and thermal generator maintenance model into a large-scale deterministic optimization problem, but it is difficult to solve. This paper proposes a multidisciplinary collaborative optimization approach with acceleration strategies (MCO-AS) for GMS, where the deterministic optimization problem is decomposed into a system-level optimization problem and discipline-level optimization subproblems through decoupling of the nonanticipative constraints and the maintenance variable consistency constraints. Three acceleration strategies, replacement and linearization, information pooling, and parallel calculation, are proposed and incorporated. Finally, computational experiments on a real large hydrothermal power system are conducted, and the results illustrate the effectiveness of the approach and acceleration strategies proposed in this paper compared to the traditional SAA method as a benchmark. • Stochastic maintenance scheduling is considered in large hydrothermal power systems. • A multidisciplinary collaborative approach is designed to decompose the problem. • Three strategies are proposed to further accelerate the solution. • Results on a real-world power system show the effectiveness of the proposed method.

Unraveling evolution histories of large hydrothermal systems via garnet U-Pb dating, sulfide trace element and isotopic analyses: A case study of Shuikoushan polymetallic ore field, South China

The Shuikoushan ore field is one of the largest Pb-Zn-Au polymetallic magmatic hydrothermal system in South China and hosts a significant metallogenic potential. In this study, detailed garnet U-Pb dating, sulfide trace element and sulfur isotopic analyses were conducted to reveal the features during ore formation. Chronologically, garnet U–Pb dating yields ore-forming ages of 158.8 ± 1.4 Ma for the Yagongtang deposit, 158.8 ± 2.5 Ma for the Kangjiawan deposit and 154 ± 18 Ma for the Laoyachao deposit, respectively. The ore formation history in the Shuikoushan ore field can be subdivided into four stages, and five types of sphalerite (Sp0 to Sp4), and three types of pyrite (Py to Py2) from early to late are identified. The distinct compostions indicate that sphalerite and pyrite were formed by different trace/minor element substitution mechanisms and oxidation state, although sulfur isotopes indicate a consistent sulfur origin. Combined with previously published studies, this work demonstrates that the Shuikoushan ore field belongs to a prolonged hydrothermal system. Its mineralization was genetically correlated with the emplacement of granodiorite, and the thermochemical sulfate reduction (TSR) process (Stage 2) and bacterial sulfate reduction (BSR) process (Stage 3) dominated the evolution of sulfur and facilitated the participation of sulfides within the Shuikoushan ore field.

Near-bottom survey of hydrothermal sulfide on an extremely magmatic accretion segment along an ultraslow-spreading ridge

An extremely magmatic accretion could exist along an ultraslow-spreading ridge that has been approved and surveyed, but less attention has been paid to its associated hydrothermal system, as it is supposed to be similar to those of fast/medium-spreading ridges. Here using an autonomous underwater vehicle and a human-occupied vehicle, a systematic investigation was conducted on the hydrothermal system of an extremely magmatic accretion segment along the Southwest Indian Ridge (50°28′ E). A collapsed chimney, microbial mat, and diffused fluid were observed in the old Duanqiao hydrothermal field (DQF), which was earlier a weakly active hydrothermal area. Notably, evident hydrothermal anomalies, including oxidation–reduction potential (ORP), turbidity, and methane, were detected above the new DQF, which lies southwest of the old DQF. Based on this investigation, we concluded that ORP is one of the most effective parameters available to identify vent location by analyzing each type of detected hydrothermal anomaly and the near-bottom magnetic inversion can image the suspected hydrothermal fluid circulation pathways. In general, we believe that the new DQF is controlled by a magmatic chamber different from those found on fast/medium-spreading ridges, and could be a large hydrothermal system.

Structural setting and fluid composition of gold mineralization along the central segment of the Keraf suture, Neoproterozoic Nubian Shield, Sudan: implications for the source of gold

ABSTRACT We provide the first large field investigation of more than 20 gold deposits and sites along the Keraf suture zone, covering an area of ~15,000 km2. The area shows diverse structural settings for gold mineralization in greenschist, amphibolite, and hornfels metamorphosed rocks. The reverse fault and dyke-hosted settings appear to be the most favourable for forming gold deposits. Two major N-S-trending, ~300-km-long corridors of deformation are delineated (West and East) but only the West seems important for gold. From fluid inclusions, 6 types of fluids are distinguished based on specific volatile contents and proportions. Most types can be related to fluid evolution by hydrothermal reactions and phase separations from a primitive fluid of metamorphic origin, containing H2O, CO2, N2, CH4, C2H6, and H2. Regional hydrothermal fields are identified based on the combinations of structural settings and fluid types. The northern field is defined as a single large hydrothermal system accounting for the mineralization of the 3 gold deposits (WG-03, UTM and Central). For sites along the West Corridor, such as Toubi, Anas, NW and Shereik, multiple and overlapping hydrothermal systems are necessary to explain the various fluid types and structural settings, even at the deposit scale (Shereik). Conversely, other sites (SW, Yasmine, Korup, Saijd, Dardora, Negeim, and SE) formed by localized individual hydrothermal systems. The documentation of fluids containing ethane at numerous sites and deposits is the most significant outcome. Such ethane-bearing fluids are generated by the metamorphism of carbonaceous-pyritic sedimentary rocks. These rocks are considered one of the best sources for providing ligands and gold for the formation of orogenic gold deposits. Consequently, the Keraf suture zone, composed mainly of carbonaceous turbidites, is interpreted to have provided such source rocks in the suture zone and below the adjacent cratons during the collision, forming orogenic gold deposits (graphical abstract).

Performance of multi-scenario equivalent hydropower models

Simulations and analysis of large hydro-thermal power systems easily become computationally heavy without simplifications of the system at hand. Hydropower, in particular, presents a challenge as complex river systems add a large amount of variables and linked constraints to the analysis. A possible simplification is to use aggregated Equivalent models for different parts of the hydrosystem which give similar results, with respect to e.g. power production, as a more detailed description of the Original system. In this paper, novel linear multi-scenario Equivalent models for hourly simulations of nonlinear hydropower systems are developed and their performance investigated. The new models consider multiple scenarios for inflow, price and start resp. end content in the reservoirs as well as reserves for balancing capacity. The performance analysis is based on case studies over Swedish hydropower systems located in the electricity trading area SE1. The average relative error in power production is 9–15% and the computation time is reduced from 9 hours to between 0.4 and 36 seconds.

Complex crater fields formed by steam-driven eruptions: Lake Okaro, New Zealand

Abstract Steam-driven eruptions are caused by explosive vaporization of water within the pores and cracks of a host rock, mainly within geothermal or volcanic terrains. Ground or surface water can be heated and pressurized rapidly from below (phreatic explosions), or already hot and pressurized fluids in hydrothermal systems may decompress when host rocks or seals fail (hydrothermal eruptions). Deposit characteristics and crater morphology can be used in combination with knowledge of host-rock lithology to reconstruct the locus, dynamics, and possible triggers of these events. We investigated a complex field of >30 craters formed over three separate episodes of steam-driven eruptions at Lake Okaro within the Taupo volcanic zone, New Zealand. Fresh unaltered rock excavated from initially >70 m depths in the base of phase I breccia deposits showed that eruptions were deep, “bottom-up” explosions formed in the absence of a preexisting hydrothermal system. These phreatic explosions were likely triggered by sudden rise of magmatic fluids/gas to heat groundwater within an ignimbrite 70 m below the surface. Excavation of a linear set of craters and associated fracture development, along with continued heat input, caused posteruptive establishment of a large hydrothermal system within shallow, weakly compacted, and unconsolidated deposits, including the phase I breccia. After enough time for extensive hydrothermal alteration, erosion, and external sediment influx into the area, phase II occurred, possibly triggered by an earthquake or hydrological disruption to a geothermal system. Phase II produced a second network of craters into weakly compacted, altered, and pumice-rich tuff, as well as within deposits from phase I. Phase II breccias display vertical variation in lithology that reflects top-down excavation from shallow levels (10–20 m) to >70 m. After another hiatus, lake levels rose. Phase III hydrothermal explosions were later triggered by a sudden lake-level drop, excavating into deposits from previous eruptions. This case shows that once a hydrothermal system is established, repeated highly hazardous hydrothermal eruptions may follow that are as large as initial phreatic events.

Development of a simulation model of HPPs chain operation

The paper presents a simulation model of a hydroelectric power plants chain. The model allows solving the problem of hydro power plants (HPPs) operation mode planning in a unified power system, taking into account the optimization of water resources. The optimal filling and decrease of storage was performed in MATLAB Simulink software. The hydraulic properties of the river flow between the stations and the corresponding time lags in the functioning of the down-river station are taken into account. The model allows continuously monitoring changes in water pressure at hydropower plants and, as a result, uses the family of flow characteristics for various water pressures. The issues of optimizing the participation of hydroelectric power stations in the regimes of large hydrothermal power systems were also raised.

Isotope geochemistry of Zn, Pb and S in the Ediacaran strata hosted Zn-Pb deposits in Southwest China

The Sichuan–Yunnan–Guizhou (SYG) area is a world-class Zn-Pb metallogenic zone and contains over four hundred of carbonate-hosted hydrothermal Zn-Pb deposits, six of which are super large-scale deposits with significant sources of Cd, Ge, and Ag, including the Huize, Wusihe, Xiaoshifang, Maozu, Tianbaoshan and Daliangzi deposits. Although previous studies focused fully on these deposits, the ore genesis of which are still in controversial. Interestedly, four of those super large scale deposits are hosted in the Ediacaran Dengying Formation, including the Maozu, Wusihe, Tianbaoshan and Daliangzi deposits. Based upon previous studies, we investigate the extent, causes and consequences of Zn and Pb isotope signatures at hand specimen scale and ore genesis of the Daliangzi and Tianbaoshan deposits, associated with published data for the Wusihe deposit. Lead isotope ratios, coupled with published data, demonstrate that Pb in the studied deposits was predominantly derived from two components: basements and sedimentary rocks. Meanwhile, a strong positive linear correlation between δ66Zn and δ34SCDT values was observed in hand specimen D-2084, suggesting the variations may be resulted by fluid mixing. Furthuremore, the Zn isotope and Cd/Zn dataset from the Tianbaoshan, Daliangzi and Wusihe deposits defines a logarithmic curve (R2 = 0.82), which, to our knowledege, is firstly reported and lies between two indentified components: a low Cd/Zn end-member with high δ66Zn values and a high Cd/Zn end-member with low δ66Zn values. Based upon previous studies, we suggest that Zn and Pb in the Wusihe and Tianbaoshan deposits were predominantly derived from basements and Ediacaran sediments; in contrast, Zn and Pb in the Daliangzi deposit were predominantly derived from Ediacaran sediments and upper sedimentary rocks, but we cannot rule out metal contributions of the basements. Furthermore, we suggest that fluid mixing is more propreate to better explain Zn isotope signatures in the studied deposits.In summary, Zn and Pb isotope ratios reflect similar ore genesis and metal sources of the Daliangzi, Tianbaoshan and Wusihe Zn-Pb deposits in the SYG area. The application to the studied deposits with the discovery of Zn, S and Pb isotope compositions for sulfides indicates the potential of Zn isotope, combined with Cd/Zn raito, as new geochemical tracers, which may be useful for distinguishing the metal sources in large hydrothermal systems as suggested previously.

Origin of the Shangfang Tungsten Deposit in the Fujian Province of Southeast China: Evidence from Scheelite Sm–Nd Geochronology, H–O Isotopes and Fluid Inclusions Studies

The Shangfang deposit is a recently discovered large-scale tungsten deposit (66,500 t at 0.23% WO3), which is located near the western boundary of the Southeastern Coastal Metallogenic Belt (i.e., Zhenghe–Dafu fault), and adjacent to the northeast of the Nanling Range Metallogenic Belt. Unlike many other W–Sn deposits in this region that occur within or near the granites, the orebodies in the Sangfang deposit all occur within the amphibolite of Palaeoproterozoic Dajinshan Formation and have no direct contact to the granite. In this study, we carry out a thermal ionization mass spectrometer (TIMS) Sm-Nd isotope analysis for the scheelites from the orebody, which yields a Sm–Nd isochron age of 157.9 ± 6.7 Ma (MSWD = 0.96). This age is in good agreement with the previously published zircon U–Pb age (158.8 ± 1.6 Ma) for the granite and the molybdenite Re–Os age (158.1 ± 5.4 Ma) in the deposit. Previous studies demonstrated that the W–Sn deposits occurring between Southeastern Nanling Range and Coastal Metallogenic Belt mainly formed in the two periods of 160–150 Ma and 140–135 Ma, respectively. The microthermometry results of fluid inclusions in scheelite and quartz are suggestive of a near-isothermal (possibly poly-baric) mixing between two fluids of differing salinities. The H–O isotope results illustrate that the ore-forming fluids are derived from magma and might be equilibrated with metamorphic rocks at high temperature. The Jurassic granite pluton should play a critical role for the large hydrothermal system producing the Shangfang W deposit. Furthermore, the negative εNd(t) of −14.6 obtained in the Shanfang scheelite suggests for the involvement of the deep crustal materials. In general, subduction of the paleo-Pacific plate caused an extensional tectonic setting with formation of the Shangfang granites and related W mineralization, the geological background of which is similar to other W deposits in the Nanling Range Metallogenic Belt.

Zinc, cadmium and sulfur isotope fractionation in a supergiant MVT deposit with bacteria

Zinc (Zn) and cadmium (Cd) are two important biological-sensitive elements, and their isotopes are strongly fractionated during biological processes. To develop the potential application of Zn and Cd isotopes for tracing the contribution of bacteria to metal mineralization, in this study we investigate for the first time the ranges and causes of isotope fractionation of Zn and Cd in a large hydrothermal system with bacteria from the world-class Jinding Zn-Pb deposit, southwest China. Extremely negative δ34SCDT values of sulfides (−48.6‰ to +7.7‰) obtained in this study and literature reveal the dominant biogenic sulfur associated with bacterial sulfate reduction. Both Zn and Cd isotope ratios are highly variable and significantly lighter compared with most of Zn-Pb ore deposits worldwide. The extremely negative δ66ZnJMC 3-0749L (down to −0.69‰) exceeds the range of Rayleigh fractionation during inorganic precipitation of ZnS. Zinc isotope ratios display a well-defined positive correlation with Zn/Cd ratios and the samples with lightest δ66Zn have lowest Zn/Cd ratios. This reflects that sphalerites formed in the early stages of mineralization already have extremely light Zn isotopic compositions. There is a negative relationship between δ34SCDT and δ66Zn, indicating that lighter Zn isotope ratios are related to stronger bacterial sulfate reduction, which results in heavier sulfur isotope ratios. Since organic compounds (e.g., Zn-carboxylate) in fluids are strongly enriched in heavy isotopes relative to free Zn2+ and Zn-sulfide, sulfides formed in the bacteria-rich hydrothermal systems would acquire light δ66Zn. Therefore, the extremely negative δ34SCDT and δ66Zn ratios demonstrate for the first time that bacterial metabolisms not only induced sulfate reduction, but also were directly involved in the formation of metals (e.g., Zn) in a large hydrothermal system. A similar process may have also partly contributed to the substantial fractionation of cadmium isotopes in the hydrothermal system. Overall, our studies show that zinc and cadmium isotopes may act as an effective tool in deciphering the specific role of organisms in formation of sulfides in hydrothermal systems and other settings.

Sources and ore-forming fluid pathways of carbonate-hosted Pb–Zn deposits in Southwest China: implications of Pb–Zn–S–Cd isotopic compositions

The Sichuan–Yunnan–Guizhou metallogenic province of Southwest China contains more than 200 Mt of Pb–Zn ore in carbonate-hosted Pb–Zn deposits, representing ~ 27% of the total Pb and Zn resources of China. Sources of metals and pathways of ore-forming fluids were elucidated through a study of the Pb–Zn–S–Cd isotopic compositions of sphalerite from the Tianbaoshan, Fusheng, Maozu, Jinshachang, and Daliangzi carbonate-hosted Pb–Zn deposits. δ34S values indicate that S in the deposits is derived mainly from evaporites in Cambrian to Triassic sedimentary strata, sulfates coexisting with sulfides, and Meso–Neoproterozoic folded basement. δ66Zn values and Pb isotopic ratios indicate that these metals originate mainly from Sinian to lower Permian sedimentary rocks and Proterozoic basement. There is a trend towards isotopically heavier Cd and Zn compositions of sphalerite from Maozu to Daliangzi, Jinshachang, and Tianbaoshan, which are all hosted in the upper Sinian Dengying Formation. Previous studies showed that there would be a trend of enrichment in heavier Zn and Cd isotopes following the migration of fluids and precipitation of minerals. The above observations suggest that the ore-forming fluids of these deposits are probably derived from the same hydrothermal fluid system. The fluids most likely flowed through Maozu first, migrating along the Xiaojiang and Anninghe fault belts and their branch faults to Daliangzi, Jinshachang, and Tianbaoshan, respectively. Zn and Cd isotopes could be useful tools in tracing the pathways of ore-forming fluids in this district, and heavier Zn and Cd isotopic compositions could provide a geochemical fingerprint for detecting remote orebodies in large hydrothermal fluid systems.

Important Issues and Results When Considering the Stochastic Representation of Wind Power Plants in a Generation Optimization Model: An Application to the Large Brazilian Interconnected Power System

Wind power has an increasing share of the Brazilian energy market and may represent 11.6% of total capacity by 2024. For large hydro-thermal systems having high-storage capacity, a complementarity between hydro and wind production could have important effects. The current optimization models are applied to dispatch power plants to meet the market demand and optimize the generation dispatches considering only hydroelectric and thermal power plants. The remaining sources, including wind power, small-hydroelectric plants and biomass plants, are excluded from the optimization model and are included deterministically. This work introduces a general methodology to represent the stochastic behavior of wind production aimed at the planning and operation of large interconnected power systems. In fact, considering the generation of the wind power source stochastically could show the complementarity between the hydro and wind power production, reducing the energy price in the spot market with the reduction of thermal power dispatches. In addition to that, with a reduction in wind power and a simultaneous dry-season occurrence, this model, is able to show the need of thermal power plants dispatches as well as the reduction of the risk of energy shortages.

Caldera unrest driven by CO2-induced drying of the deep hydrothermal system

Interpreting volcanic unrest is a highly challenging and non-unique problem at calderas, since large hydrothermal systems may either hide or amplify the dynamics of buried magma(s). Here we use the exceptional ground displacement and geochemical datasets from the actively degassing Campi Flegrei caldera (Southern Italy) to show that ambiguities disappear when the thermal evolution of the deep hydrothermal system is accurately tracked. By using temperatures from the CO2-CH4 exchange of 13C and thermodynamic analysis of gas ascending in the crust, we demonstrate that after the last 1982–84 crisis the deep hydrothermal system evolved through supercritical conditions under the continuous isenthalpic inflow of hot CO2-rich gases released from the deep (~8 km) magma reservoir of regional size. This resulted in the drying of the base of the hot hydrothermal system, no more buffered along the liquid-vapour equilibrium, and excludes any shallow arrival of new magma, whose abundant steam degassing due to decompression would have restored liquid-vapour equilibrium. The consequent CO2-infiltration and progressive heating of the surrounding deforming rock volume cause the build-up of pore pressure in aquifers, and generate the striking temporal symmetry that characterizes the ongoing uplift and the post-1984 subsidence, both originated by the same but reversed deformation mechanism.

Features of Large Magmatic–Hydrothermal Systems in Japan: Characteristics Similar to the Tops of Porphyry Copper Deposits

AbstractVolcanic complexes in Japan such as Kusatsu Shirane, Honshu, and Kuju‐Hatchobaru and Kirishima, Kyushu, host active magmatic–hydrothermal systems that are several kilometers in diameter and typically asymmetric to the intrusive center. Their heat flow is driven by multiple intrusions at <5–10 km depth over a period on the order of ~105 years. These hydrothermal systems consist of advecting fluids of magmatic origin (either vapor with acidic components condensed into meteoric water, or a subsequent liquid of varying reactivity) that interact with convecting meteoric water. The amount of the magmatic component depends on location relative to the intrusive center, local controls on permeability, and the temporal evolution of the intrusions. The proportion of meteoric water diluent typically increases from proximal to distal locations (over several kilometer distance), and with time after intrusion (> several thousands of years). Some of the neutral pH solutions in these large hydrothermal systems, up to ~5 km from volcanic vents, support geothermal energy developments, with strong structural control on fluid flow. Near active volcanic vents, the magmatic vapor component of hydrothermal systems can form acidic condensates (pH ~ 1.5) that are responsible for strong alteration of the host rock. The resulting residual quartz and advanced argillic minerals are typical of shallow‐formed lithocap alteration that is associated with deeper porphyry copper deposits in similar arc‐hosted volcanic settings. Around the world, this near‐surface lithocap alteration, influenced by structures as well as lithology, may be barren in metals, even where associated with mineralized porphyry intrusions at depth. Such intrusion‐proximal alteration is widespread in both active and extinct settings in Japan. In addition, distal geothermal hot springs typically have a magmatic water component, albeit minor, with a pH that varies from ~3 to near‐neutral; deep alteration intersected in drill holes is characterized by alunite–dickite–pyrophyllite or chlorite–wairakite, respectively. These alteration assemblages are typical of their extinct equivalents, intermediate sulfidation epithermal veins, with mineralogical complexities caused by temporal evolution as well as spatial variation (e.g. along different structures). Such active and extinct magmatic–hydrothermal systems signify the presence of shallow degassing or degassed intrusions, respectively. Where similar intrusions in volcanic arcs around the world are eroded to ~1 to 2 km depth, the tops of porphyry copper deposits are commonly exposed, marked by a transition of white mica upward to pyrophyllite‐dominant alteration. Active magmatic–hydrothermal systems on the flanks of arc volcanoes in Japan are dynamic – both cycling as well as evolving – and share characteristics with extinct systems that host epithermal and porphyry ore deposits.

Short-Term Scheduling of Integrated Power and Spinning Reserve of a Wind-Hydrothermal Generation System with AC Network Security Constraints

The world energy matrix has diversified and has become a mix of hydroelectric, thermoelectric and renewable sources, such as wind energy. However, wind power is uncertain and variable, and its random intermittence leads to great challenges in coordinating it with a large hydrothermal system, for example. These questions require increased availability of spinning reserve as a solution to reduce the risk of deficit in moments when there is no wind power generation. This spinning reserve must be appropriately allocated between the hydraulic and thermal generating units so that, when necessary, they will be available and operational. To carry out this adequate allocation, besides considering the conventional operational limits of a problem of generation dispatch, it is also necessary to take into consideration the limits of the interchange lines that connect the subsystems that compose the electric network. So, in cases of congestion of these transmission lines, the subsystem itself can supply its spinning reserve under different hydrological conditions. Thus, this work proposes a mathematical formulation to dispatch power generation and allocate spinning reserve simultaneously, considering different hydrological day-ahead conditions. To do this, a nonlinear and dynamic optimal power flow is modeled, which, in addition to performing the active and reactive power dispatch of a hydrothermal system (including electrical and energy restrictions) for a day-ahead horizon, is also capable of carrying out an optimal allocation of the spinning reserve (hydraulic and thermal). The model is tested using a system of 33 buses to represent the system of the southern region of Brazil.

Localization of magma injections, hydrothermal alteration, and deformation in a volcanic detachment (Piton des Neiges, La Réunion)

This contribution aims at understanding how magmatism, hydrothermal alteration, and deformation may have interacted to localize a detachment (a low-angle normal fault) in a basaltic volcano. Piton des Neiges, an inactive volcano of La Réunion Island, has been deeply cut by erosion, allowing its inner structure to be investigated. The deepest unit observed in the edifice is a kilometer-scale plutonic complex, the top of which is intruded by multiple sills. This zone of repeated sill intrusions has been interpreted as a detachment because it displays evidence of hydrothermal alteration in the greenschist facies linked to a brittle-ductile shear deformation. Deformation begins with cataclasis and is followed by mylonitization and chlorite crystallization, then by hydrofracturing and pumpellyite crystallization. Subsequent and post-deformation calcite crystallization occurs in voids such as fractures and vacuoles. Aluminium substitutions in chlorite suggest that the syn-deformation hydrothermal alteration did not exceed 250°C and peaked in the deformation zone. Comparison of bulk-rock major element analyses of fresh, altered and deformed rocks shows that the zone of sill intrusion and deformation localized increased concentrations of P and K otherwise depleted in the footwall and hangingwall rocks, suggesting that the detachment acted as a trap for fluids.In contradiction with proposed models of volcano spreading, it is apparent that the portion of Piton des Neiges accessible to observation did not deform by creep of a large hydrothermal system or a plutonic complex below its solidus. Instead, the interface between the already cooled plutonic complex and the host rock acted as a brittle failure zone and was repeatedly intruded by magma injections. This localized heat source promoted hydrothermal alteration and low temperature creep in and around the discontinuity. The same process of magmatism-related weakening might occur on active volcanoes; it may, for instance, explain the slow post-eruptive deformation of the eastern flank of Piton de La Fournaise (the active volcano of La Réunion) observed since the April 2007 eruption.

The Lassen hydrothermal system

The active Lassen hydrothermal system includes a central vapor-dominated zone or zones beneath the Lassen highlands underlain by ~240 °C high-chloride waters that discharge at lower elevations. It is the best-exposed and largest hydrothermal system in the Cascade Range, discharging 41 ± 10 kg/s of steam (~115 MW) and 23 ± 2 kg/s of high-chloride waters (~27 MW). The Lassen system accounts for a full 1/3 of the total high-temperature hydrothermal heat discharge in the U.S. Cascades (140/400 MW). Hydrothermal heat discharge of ~140 MW can be supported by crystallization and cooling of silicic magma at a rate of ~2400 km3/Ma, and the ongoing rates of heat and magmatic CO2 discharge are broadly consistent with a petrologic model for basalt-driven magmatic evolution. The clustering of observed seismicity at ~4–5 km depth may define zones of thermal cracking where the hydrothermal system mines heat from near-plastic rock. If so, the combined areal extent of the primary heat-transfer zones is ~5 km2, the average conductive heat flux over that area is >25 W/m2, and the conductive-boundary length <50 m. Observational records of hydrothermal discharge are likely too short to document long-term transients, whether they are intrinsic to the system or owe to various geologic events such as the eruption of Lassen Peak at 27 ka, deglaciation beginning ~18 ka, the eruptions of Chaos Crags at 1.1 ka, or the minor 1914–1917 eruption at the summit of Lassen Peak. However, there is a rich record of intermittent hydrothermal measurement over the past several decades and more-frequent measurement 2009–present. These data reveal sensitivity to climate and weather conditions, seasonal variability that owes to interaction with the shallow hydrologic system, and a transient 1.5- to twofold increase in high-chloride discharge in response to an earthquake swarm in mid-November 2014.

Cadmium and sulfur isotopic compositions of the Tianbaoshan Zn–Pb–Cd deposit, Sichuan Province, China

Although Zn–Pb deposits are one of the most important Cd reservoirs in the earth, few studies have focused on the Cd isotopic fractionation in Zn–Pb hydrothermal systems. This study investigates the causes and consequences of cadmium and sulfur isotope fractionation in a large hydrothermal system at the Tianbaoshan Zn–Pb–Cd deposit from the Sichuan–Yunnan–Guizhou (SYG) metallogenic province, SW China. Moderate variations in Cd and S isotope compositions have been measured in sphalerite cover a distance of about 78m. Sphalerite has δ114/110Cd values ranging from 0.01 to 0.57‰, and sulfides (sphalerite, galena and chalcopyrite) have δ34SCDT values ranging from 0.2 to 5.0‰. Although δ34SCDT and δ114/110Cd values in sphalerites have no regular spatial variations, the δ34SCDT values in galena and calculated ore-forming fluid temperatures decreased from 2.1 to 0.2‰ and from about 290 to 130°C, respectively, from the bottom to the top of the deposit. Heavy Cd isotopes are enriched in early precipitated sphalerite in contrast to previous studies. We suggest that Cd isotopic compositions in ore-forming fluids are heterogeneous, which result in heavy Cd isotope enrichment in early precipitated sphalerite. In comparison with other Zn–Pb deposits in the SYG area, the Tianbaoshan deposit has moderate Cd contents and small isotope fractionation, suggesting differences in origin to other Zn–Pb deposits in the SYG province.In the Tianbaoshan deposit, the calculated δ34S∑S-fluids value is 4.2‰, which is not only higher than the mantle-derived magmatic sulfur (0±3‰), but also quite lower than those of Ediacaran marine sulfates (about 30 to 35‰). Thus, we suggest that reduced sulfur of ore-forming fluids in the deposit was mainly derived from the leaching of the basement, which contains large amount of volcanic or intrusive rocks. Based upon a combination of Cd and S isotopic systems, the Tianbaoshan deposit has different geochemical characteristics from typical Zn–Pb deposits (e.g., the Huize deposit) in SYG area, indicating the unique origin of this deposit.