Academic literature on the topic 'Shallow hydrothermal sources'

Iron is an essential nutrient that regulates productivity in ~30% of the ocean. Compared with deep (>2000 meter) hydrothermal activity at mid-ocean ridges that provide iron to the ocean’s interior, shallow (<500 meter) hydrothermal fluids are likely to influence the surface’s ecosystem. However, their effect is unknown. In this work, we show that fluids emitted along the Tonga volcanic arc (South Pacific) have a substantial impact on iron concentrations in the photic layer through vertical diffusion. This enrichment stimulates biological activity, resulting in an extensive patch of chlorophyll (360,000 square kilometers). Diazotroph activity is two to eight times higher and carbon export fluxes are two to three times higher in iron-enriched waters than in adjacent unfertilized waters. Such findings reveal a previously undescribed mechanism of natural iron fertilization in the ocean that fuels regional hotspot sinks for atmospheric CO 2 .

The Mesoproterozoic North American Midcontinent Rift hosts the world’s largest accumulation of native copper in Michigan’s Keweenaw Peninsula. During a regional metamorphogenic-hydrothermal event, native copper was deposited along with spatially zoned main-stage minerals in a thermal high. This was followed by deposition of late-stage minerals including minor copper sulfide. Inferences from the oxygen and carbon isotopic composition of main-stage hydrothermal fluids, as calculated from 296 new and compiled isotopic measurements on calcite, are consistent with existing models that low-sulfur saline native copper ore-forming fluids were dominantly derived by burial metamorphic processes from the very low sulfur basalt-dominated rift fill at depth below the native copper deposits. Co-variation of oxygen and carbon isotopic compositions are consistent with mixing of metamorphic-derived fluids with two additional isotopically different fluids. One of these is proposed to be evolved seawater that provided an outside source of salinity. This fluid mixed at depth and participated in the formation of a well-mixed hybrid metamorphic-dominated ore-forming fluid. Secondary Ion Mass Spectrometry in-situ isotopic analyses of calcite demonstrate a high degree of variability within samples that is attributed to variable degrees of shallow mixing of the hybrid ore-forming fluid with sulfur-poor, reduced evolved meteoric water in the zone of precipitation. The oxygen and carbon isotopic compositions of 100 new and compiled measurements on late-stage calcite are mostly isotopically different than the main-stage hydrothermal fluids. The late-stage hydrothermal fluids are interpreted as various proportions of mixing of evolved meteoric water, main-stage hybrid ore-forming fluid, and shallow, evolved seawater in the relatively shallow zone of precipitation.

Hydrothermal vents are one of the important sources of major or trace elements in the ocean. The elemental fluxes, however, may be dynamic due to coastal processes and hydrothermal plumes, especially in shallow-water hydrothermal vents. We collected water samples by using the trace-metal clean technique inside and outside two shallow-water hydrothermal vents (white vent: low temperature, high pH; and yellow vent: high temperature, low pH) off Kueishantao Islet, Taiwan, China via SCUBA divers. We analyzed these samples for their hydro-chemical parameters and dissolved elements (Fe, Mn, Mg, V, Cu, and Mo) thereafter. Our results show that dissolved metals’ concentrations were significantly different between the two vents, with higher Mn and Fe in the White Vent than in the Yellow Vent, likely due to the decreased affinity of the dissolved metals for particles in the white vent. We estimated the plume fluxes of dissolved metals from the hydrothermal mouth by multiplying in situ hydrothermal discharge flowrates with metals’ concentrations inside the vents, which were: 1.09~7.02 × 104 kg Mg, 0.10~1.23 kg Fe, 0.08~28 kg Mn, 33.4~306 g V, 2.89~77.7 g Cu, and 54.3~664 g Mo, annually. The results further indicate that such plumes probably have impacted nearby seawater due to coastal currents and particle desorption during transport. Furthermore, the concentrations of biogenic elements could be further modified in seawater, and potentially impact nearby ecosystems on a larger scale. Our study provides information with which to further understand metal redeployment in submarine shallow nearby ecosystems.

We analyzed sulfur isotopes, trace elements and chalcophile elements (Se, Te, As, Sb, and Hg) in the native sulfur matrix from the Kueishantao hydrothermal system and conducted a systematic micro-analytical investigation. The sulfur matrix lacked all measured metals (e.g., Fe, Cu) and rare earth elements (REEs) while being significantly enriched in Te, As, Se (750–1500 ppm), Sb (around 100 ppm) and some Hg. The δ34S data (0.2–2.4‰) suggest a magmatic source leached from igneous rocks and a small contribution of seawater sulfates to the sulfur in hydrothermal deposits. Correlations between Te, As, Sb, and S (r2 = 0.30–0.61) indicate that these elements behave coherently in magmatic-hydrothermal processes. The enrichment factors and content ratios of these elements demonstrate their abundance in the sulfur matrix and minor fractionation after being partitioned into the metallic melt and forming a separate vapor phase to transport. Our study focuses on the native sulfur matrix in a shallow-water volcanic hydrothermal system, to which relatively little attention has previously been paid. This will expand our understanding of hydrothermal precipitates. The study of volatile chalcophile elements in the matrix will provide significant information about their sources, distributions and other geochemical behaviors in magmatic-hydrothermal processes and help to understand the Kueishantao hydrothermal circulation better.

To elucidate the sulphur sources for chemoautotrophy by the symbiotic bacteria of a vestimentiferan tubeworm, Lamellibrachia satsuma, living in Kagoshima Bay at depths of 80–100 m, we analysed the sulphur isotopic ratios of the animal tissues and compared them with environmental sulphur species collected in the field. Animals that had been maintained in an aquarium for over a year and supplied a known sulphur source were also investigated. The gas emitted from volcanic source in Kagoshima Bay contained rather heavy sulphide (+12·7 to +22·9‰ δ34S) compared with deep-sea hydrothermal vent systems (0 to +5‰). The tissue of the tubeworms contained very light sulphide (−21·5 to −25·9‰). It is inferred from the analysis of the aquarium-maintained specimens that the fractionation by the tubeworm or its symbiont was <1·5‰. The sulphur source assimilated by the tubeworms in the field is therefore inferred to have δ ratio −19·1 to −24·6‰. This means that only 9·7 to 25·0% of the sulphur in the worm tissues can be derived from the volcanic gas and the rest must come from other sources, such as microbial activity in the bottom sediment.

The energy reserves in hot dry rock and hydrothermal systems are abundant in China, however, the developed resources are far below the potential estimates due to immature technology of enhanced geothermal system (EGS) and scattered resources of hydrothermal systems. To circumvent these problems and reduce the thermal resistance of rocks, here a shallow depth enhanced geothermal system (SDEGS) is proposed, which can be implemented by fracturing the hydrothermal system. We find that, the service life for SDEGS is 14 years with heat output of 4521.1 kW. To extend service life, the hybrid SDEGS and solar energy heating system is proposed with 10,000 m2 solar collectors installed to store heat into geothermal reservoir. The service life of the hybrid heating system is 35 years with geothermal heat output of 4653.78 kW. The novelty of the present work is that the hybrid heating system can solve the unstable and discontinuous problems of solar energy without building additional back-up sources or seasonal storage equipment, and the geothermal thermal output can be adjusted easily to meet the demand of building thermal loads varying with outside temperature.

Geogenic and anthropogenic sources of atmospheric particulate and CO2 can lead to threats to human health in volcanic areas. Although the volcanic CO2 hazard is a topic frequently debated in the related scientific literature, space and time distribution of PM2.5 are poorly known. The results of combined CO2/PM2.5 surveys, carried out at Salina, Stromboli, and Vulcano islands (Aeolian archipelago, Italy) in the years 2020–2021, and integrated with investigations on bioaccumulation of metallic particulate matter by the mean of data on the magnetic properties of oleander leaves, are presented in this work. The retrieved results indicate that no significant anthropogenic sources for both CO2 and PM2.5 are active in these islands, at the net of a minor contribution due to vehicular traffic. Conversely, increments in volcanic activity, as the unrest experienced by Vulcano island since the second half of 2021, pose serious threats to human health, due to the near-ground accumulation of CO2, and the presence of suspended micro-droplets of condensed hydrothermal vapor, fostering the diffusion of atmophile viruses, such as the COVID-19. Gas hazard conditions can be generated, not only by volcanic vents or fumarolic fields, but also by unconventional sources, such as the outgassing from shallow hydrothermal aquifers through drilled or hand-carved wells.

Dolomite bodies in the Middle Permian of the central Sichuan Basin have been reported as favorable natural gas reservoirs. The Middle Permian dolomite consists of three types of recrystallized dolomite (Rd1, Rd2, and Rd3) and one type of dolomite cement (Sd). Rd1 might be formed as the primary mineral along the calcite in the original sea-water. Its δ13C value and 87Sr/86Sr ratio, consistent with those of marine limestone and Permian seawater, support that the dolomitizing fluid for Rd1 was Permian seawater preserved in the strata. Rd2 consists of fine to medium (50 μm to 250 μm) and planar to curved crystals. Geochemical indicators (slightly high 87Sr/86Sr ratio, similar rare earth element patterns, negative δ18O, slightly high salinity) confirm that the dolomitizing fluid of Rd2 was mainly Permian seawater during shallow burial, with a small number of hydrothermal fluids. Rd3 and Sd are featured by very large (>250 μm), curved crystals, and high-temperature, high-salinity, and obviously positive Eu anomalies, suggesting that their diagenetic fluids were mainly hydrothermal fluids from deep. Additionally, inherited carbon sources and the 87Sr/86Sr ratios of some samples fall within the range of Permian seawater distribution, confirming the contribution of Permian seawater. ELIP activity caused the formation of this dolomite through the mixing of seawater and hydrothermal fluids. The main fluid circulation channels were activated basement faults, epigenetic karst pores, and shallowly buried high-permeability strata. During the peak period of ELIP activity, the continuous upwelling of deep hydrothermal fluids led to the continuous formation of Rd2, Rd3, and Sd. The dolomitization fluid of Rd2 was mainly composed of seawater and featured a certain lateral extension, which was away from faults. Rd3 and Sd are mainly distributed along the fault system, and excessive dolomitization caused by the hydrothermal activity, to some extent, inhibited the lateral movement of hydrothermal fluids. This study provides a good example for exploring the genetic mechanism and distribution pattern of structurally controlled dolomites under a volcanic activity background.

Research subject.This research study was aimed at investigating metasomatic minerals and ores in the Tamunier Deposit, which is located in the Northern Urals, at the Eastern side of the Tagil megazone within the Auerbach volcano-plutonic belt.Materials and methods.Well core samples were investigated using a complex of research methods, including optical and electron microscopy, X-ray spectral microanalysis, mineral geothermometry, thermobarogeochemistry (microthermometry, gas chromatography, determination of the salt composition of fluid inclusions in minerals) and isotope geochemistry (isotopes C, O, S, Sr, Pb).Results.A genetic model describing the formation of the Tamunier deposit was developed using the data obtained on its geological structure, mineral composition of metasomatites and ores, fluid formation mode, sources of ore matter and ore-bearing fluid. In the proposed model, the magmatogenic sodium chloride fluid carrying ore components and S is separated from the Auerbach complex at the depth of intrusion. Penetrating to the surface, this fluid interacts with the rocks of volcanic-sedimentary strata, thereby extracting a number of components, including CO2, S and Sr.Conclusion.Despite the presence of sulphide mineralization of hydrothermal-sedimentary genesis in the volcanogenic-sedimentary rock mass, the data obtained has allowed us to refer the gold-sulphide ores under study to magmatogenic-hydrothermal formations. The estimated P-T conditions (t= 100–370ºС andP= 0.4–0.6 kbar) and the shallow depth of the Tamunier field have shown its correspondence to the sub-epithermal level in the model of the porphyry-epithermal ore-magmatic system.

L’océan Pacifique Sud-Ouest a été identifié comme un point chaud de fixation de diazote (N2) par les organismes diazotrophes, arborant des taux de fixation parmi les plus élevés des océans du globe. Le succès de ces espèces repose sur les concentrations non limitantes en fer dissous (DFe) dans la couche photique de la région, dont l’origine demeure méconnue. Dans le cadre de ce travail de thèse, la distribution du DFe a été étudiée le long d’un transect de 6100 km, allant de Nouméa jusqu’aux eaux de la gyre et traversant le Bassin de Lau et l’Arc des Tonga (175 °E à 166 °W, le long de 19–21 °S). Combinées avec une analyse optimale multiparamétrique des masses d’eau, les anomalies de DFe ont été déterminées sur la zone du transect, les plus notables étant présentes le long de l’Arc des Tonga. Les résultats ont démontré que les masses d’eau d’origine lointaine alimentant le Bassin de Lau ne peuvent expliquer les concentrations observées en surface dans cette région, permettant de conclure avec certitude que le DFe provient de sources hydrothermales peu profondes présentes le long de l’arc. Bien qu’une portion non négligeable de cet apport de DFe soit transportée sur de longues distances, une large majorité est rapidement éliminée à proximité des sources sous l’action de divers processus mis en lumière à l’aide d’un modèle en boîte. Outre le fer, les fluides hydrothermaux sont enrichis en de nombreux autres métaux susceptibles d’être toxiques pour les organismes. Ces fluides, directement introduits dans la couche photique, pourraient impacter le phytoplancton. Leur effet a été évalué lors d’une expérience innovante pendant laquelle des communautés planctoniques naturelles ont été soumises à un gradient d’enrichissement en fluides hydrothermaux. Malgré un effet toxique initial de quelques jours, les apports hydrothermaux ont finalement induit des taux de fixation de N2, de productivité et d’export de matière organique deux à trois fois plus élevés que dans le contrôle non enrichi. Cet effet fertilisant résulte probablement de la détoxification de l’environnement, riche en de nombreux éléments potentiellement toxiques, par des écotypes résistants capables de produire des ligands forts, les thiols, limitant la biodisponibilité de certains métaux. L’apport additionnel d’éléments fertilisants par les fluides, en particulier le DFe, a ainsi permis la croissance ultérieure des espèces les plus sensibles. Ces résultats expérimentaux, reproduisant fidèlement les observations in-situ, confirment l’implication des fluides hydrothermaux peu profonds dans la forte productivité observée dans la région. Les sources hydrothermales ont pu être tracées à différentes échelles spatiales et temporelles par le déploiement de pièges à sédiments dérivants (durant quelques jours, le long de l’Arc des Tonga) et fixe (durant une année, le long de la dorsale de Lau) et par le carottage des sédiments du fond marin aux sites de déploiement des pièges (échelle de temps géologique). Le traçage Al-Fe-Mn a révélé que le matériel lithogénique exporté à petite et large échelle spatiale dans la région provenait de sources hydrothermales peu profondes et/ou profondes localisées le long de l’Arc des Tonga. Cette empreinte hydrothermale a également été détectée dans les sédiments, notamment à proximité de la dorsale de Lau où la présence d’une importante source active est fortement suspectée. Finalement, les dynamiques similaires observées pour l’export de particules d’origine biologique et hydrothermale suggèrent que la production de surface serait liée aux apports hydrothermaux dans la couche photique. En conclusion, ce travail de thèse a démontré l’impact de sources hydrothermales peu profondes sur le cycle des éléments traces, notamment du fer, dans la colonne d’eau et les sédiments, ainsi que leur lien avec la productivité biologique dans la région du Pacifique Sud-Ouest
The Western Tropical South Pacific Ocean has been identified as a hotspot for dinitrogen (N2) fixation by diazotrophic organisms, with some of the highest rates recorded in the global ocean. The success of these species relies on non-limiting concentrations of dissolved iron (DFe) in the photic layer of the region, whose origin remains unclear. In this thesis work, the distribution of DFe was studied along a 6100-km transect from Noumea to the gyre waters, crossing the Lau Basin and the Tonga Arc (175°E to 166°W, along 19-21°S). Combined with an optimal multiparametric water mass analysis, DFe anomalies were determined over the transect area, the most notable being present along the Tonga Arc. The results demonstrated that water masses of remote origin entering the Lau Basin could not explain the concentrations observed at the surface in this region, leading to the confident conclusion that DFe originates from shallow hydrothermal sources present along the arc. Although a non-negligeable portion of this DFe input is transported over long distances, a large majority is rapidly removed near the sources through a variety of processes highlighted by a box model. Besides iron, hydrothermal fluids are enriched in numerous other metals that may be toxic to organisms. These fluids, introduced directly into the photic layer, could have an impact on phytoplankton. Their effect was evaluated in an innovative experiment during which natural plankton communities were subjected to an enrichment gradient of hydrothermal fluids. Despite an initial toxic effect of a few days, hydrothermal inputs ultimately induced N2 fixation, productivity and organic matter export rates two to three times higher than those of the non-enriched control. This fertilizing effect probably results from the detoxification of the environment, rich in numerous potentially toxic elements, by resistant ecotypes able to produce strong ligands, such as thiols, limiting the bioavailability of certain metals. The additional supply of fertilizing elements by the fluids, in particular DFe, thus allowed the subsequent growth of the most sensitive species. These experimental results, faithfully reproducing the in-situ observations, confirm the involvement of shallow hydrothermal fluids in the high productivity observed in the region. Hydrothermal sources could be traced at different spatial and temporal scales through the deployment of drifting (for a few days, along the Tonga Arc) and fixed (for a year, along the Lau Ridge) sediment traps and through the coring of seafloor sediments at the trap deployment sites (geological time scale). Al-Fe-Mn tracing revealed that the lithogenic material exported at small and large spatial scales in the region originated from shallow and/or deep hydrothermal sources located along the Tonga Arc. This hydrothermal signature has also been detected in the seafloor sediments, particularly in the vicinity of the Lau Ridge where the presence of a major active source is strongly suspected. Finally, the similar patterns observed for the export of biological and hydrothermal particles suggest that surface production is closely linked to hydrothermal inputs into the photic layer. In conclusion, this thesis work has demonstrated the influence of shallow hydrothermal sources on the fate of trace elements, particularly iron, in the water column and seafloor sediments, and their link to biological productivity in the Western Tropical South Pacific region

Abstract Iron oxide copper-gold (IOCG) deposits are hydrothermal deposits characterized by abundant low-Ti Fe oxides, economic Cu-Au grades, structurally controlled orebodies, widespread presulfide alkaline alteration, and commonly significant volumes of breccia. They may also have elevated U, Co, Ag, and rare earth elements (REEs), and may have no clear spatial association with igneous intrusions. The IOCG sensu stricto deposits are rare in China, but the Proterozoic Fe-Cu-(Au-REE) deposits in the Kangdian region, southwestern China, have been confirmed to be of this type. Other related hydrothermal deposits, including what we could classify as Fe-Cu-Au skarn and iron oxide apatite deposits along the middle and lower Yangtze River belt, carbonatite-related Fe-REE-Nb deposits (i.e., Bayan Obo), and volcanic rock-hosted Fe-(Cu-Au) deposits in eastern Tian Shan and Altay, have been previously mentioned as Chinese IOCG deposits in some of the literature but show some important differences from IOCG deposit types. They are hence not included as IOCG deposits in this review. The Kangdian IOCG deposits are hosted in the 1.74 to 1.68 Ga metavolcanic-metasedimentary rock sequences of the Dahongshan, Hekou, and Dongchuan groups. The ore-hosting strata are fluvial to intertidal facies sedimentary-volcanic successions in a late Paleoproterozoic rift-related basin of the western Yangtze block. They comprise basal conglomerates and sandstones with minor tuffaceous and mafic volcanic rocks, grading upward to interbedded carbonate. The orebodies are generally stratabound and/or structurally controlled. They are spatially associated with 1.69 to 1.65 Ga diabase intrusions and hydrothermal breccia bodies of various sizes. The paragenetic sequence of the deposits generally includes pre-ore Na-(Ca) alteration (stage I) dominated by albite (and local amphibole); Fe-(REE) mineralization (stage II) with magnetite, siderite, and subsidiary REE-enriched apatite; and Cu-(Au-REE) mineralization (stage III) with chalcopyrite, ankerite, biotite, K-feldspar, sericite, chlorite, and local bornite and light REE minerals. Geochronological studies have shown that the Kangdian IOCG deposits formed during multiple mineralization/hydrothermal events. The most important of these was temporally and spatially associated with emplacement of 1.66 to 1.65 rift-related diabase intrusions. Another important event was related to 1.08 to 1.0 Ga rift-related magmatism in the region, but was mainly present in the deposits in the northern part of Kangdian belt. Neoproterozoic magmatic-metamorphic events (0.85–0.83 Ga) were widespread in the Kangdian region and were important for remobilization of Cu and REEs, and for upgrading the preexisting orebodies. Other hydrothermal events at 1.45 and 1.3 Ga are recorded locally and appear not to be of economic importance. Fluid inclusion, stable isotope, and radiogenic isotope studies have shown that the stage I and II ore-forming fluids were dominantly magmatic in origin, possibly derived from deep-seated magma chambers. However, nonmagmatic fluids from various sources in the shallow crust (e.g., basinal brine, meteoric water) were involved to various degrees in the formation of Cu-(Au) ores during stage III. Ore metals were largely derived from deep-seated magma chambers. Fluid-wall rock interactions and fluid mixing were important mechanisms for the precipitation of Cu sulfides. The Kangdian Fe-Cu-(Au) deposits are notably rich in REEs, and the formation of economic REE ores has a complex remobilization history. The REEs were mainly remobilized from apatite in earlier Fe oxide ores and/or country rocks and precipitated as monazite and REE-bearing carbonate minerals at a later stage of the same mineralizing event or during metamorphic-hydrothermal events hundreds of millions of years later. The IOCG deposits in the Kangdian belt formed in an intracratonic rift setting at a time when underplating of mafic magmas induced large-scale fluid circulation and pervasive Na-(Ca) metasomatism in the volcanic-sedimentary rocks. Hydrothermal brecciation of the country rocks occurred at the tops of the igneous intrusions and/or along zones of weakness within the country rocks due to overpressure imposed by the ore-forming fluids. Magnetite and hematite precipitated early along the main fluid channels, whereas Cu sulfides are mainly hosted within structures in the country rocks where sulfide saturation is favored. Such an ore-forming mechanism may be widely applicable to other IOCG deposits worldwide.

Abstract Some arc magmas lead to the formation of porphyry deposits in the relatively shallow upper crust (&lt;5 km). Porphyry deposits are major sources of Cu and an important Au source but lack significant amounts of platinum group elements (PGE). Sulfide phases control the behavior of chalcophile elements and affect the potential to form ore deposits either by remaining in the mantle residue or by fractionating from arc magmas at lower crustal levels, although in detail the role of sulfide saturation in the lower crust remains poorly understood. Lower crustal cumulate rocks from the 85 Ma Chilas Complex of the Kohistan arc, Pakistan, provide insight into processes that occur at depth in arcs. Here we provide Cu, Ni, Au, and PGE concentrations and Os isotope ratios of the Chilas Complex in order to constrain the extent of sulfide saturation in the lower crust and the effect of sulfide saturation on the metal budget of evolved melts that ascend to the upper crust. The Chilas rock suite contains less than 0.17 wt % sulfides and low PGE concentrations. In situ laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) measurements of the sulfide inclusions in silicate minerals show enrichment in several chalcophile elements (up to 34 wt % Cu, 23 ppm Au, 245 ppm Pd, and 20 ppm Pt), whereas iridium group PGE (IPGE- Os, Ir, Ru) are mainly below detection limits. The metal content of the parental melt was modeled based on the elemental concentrations of the sulfides. The modeled parental arc magmas contain 70 to 140 ppm Cu, 0.2 to 1.5 ppb Au, and 1.2 to 8 ppb Pd, but low concentrations of IPGE, suggesting that IPGE were likely retained in the mantle source. Mass balance calculations show that segregation of a sulfide melt in the lower crust could further deplete the melt by more than 95% in Pd and Pt, 33 to 85% in Au, and 13 to 60% in Cu. Thus, magmas that ascend to the upper crust would contain very low concentrations of Au (&lt; 0.2 ppb) and Pd (&lt; 0.04 ppb), but they would retain sufficient concentration of Cu (~45–57 ppm) to form porphyry Cu deposits upon emplacement in the upper crust, as is commonly observed in arc settings.

Mud volcanism can provide a mechanism for hot hydrothermal muds and brines to ascend from dehydrated, serpentinized peridotite at the mantle-crust contact (Moho). Such mud volcanism may have occurred on a regional scale across northern Europe when high to low density brines erupted as metalliferous, hot, hydrothermal, hydrocarbon-rich mud slurries. These mud-brines were delivered to the Permo-Triassic unconformity in a shallow Zechstein sea during the Pangea breakup through a series of deep-seated conduits that connected the serpentosphere to the Zechstein unconformity. A three-stage, hot, hydrothermal, mud volcanic model can explain the Kupferschiefer-Zechstein-Rote Fäule sequence of polymetallic, hydrocarbon, and saline mineralization as a consequence of a three-stage, dehydration sequence of deep serpentospheric uppermost mantle. Dehydration products of mantle-heated serpentinite were produced in three sequential stages: (1) lizardite to antigorite, (2) antigorite to chlorite-harzburgite, and (3) chlorite-harzburgite to garnet peridotite. The dehydration of serpentine correlates to three stages of Zechstein-Kupferschiefer mineralization: (1) Weissliegend-Kupferschiefer Cu-Ag-carbonaceous shale and silica sand deposits, to (2) Zechstein saline deposits, to (3) Rote Fäule hematite-Au-REE-U cross-cutting metallization.

Abstract Cripple Creek is among the largest epithermal districts in the world, with more than 800 metric tons (t) Au (&gt;26.4 Moz). The ores are associated spatially, temporally, and genetically with ~34 to 28 Ma alkaline igneous rocks that were emplaced into an 18-km2 diatreme complex and surrounding Proterozoic rocks. Gold occurs in high-grade veins, as bulk tonnage relatively low-grade ores, and in hydrothermal breccias. Pervasive alteration in the form of potassic metasomatism is extensive and is intimately associated with gold mineralization. Based on dating of intrusions and molybdenite and gangue minerals (primarily using 40Ar/39Ar and Re-Os techniques), the region experienced a protracted but intermittent history of magmatism (over a period of at least 5 m.y.) and hydrothermal activity (intermittent over the final ~3 m.y. of magmatic activity). Key factors that likely played a role in the size and grade of the deposit were (1) the generation of alkaline magmas during a transition between subduction and extension that tapped a chemically enriched mantle source; (2) a long history of structural preparation, beginning in the Proterozoic, which created deep-seated structures to allow the magmas and ore fluids to reach shallow levels in the crust, and which produced a fracture network that increased permeability; and (3) an efficient hydrothermal system, including effective gold transport mechanisms, and multiple over-printed hydrothermal events.

The Oligocene Smrekovec Volcanic Complex is a remnant of a submarine composite stratovolcano with a complex succession of lavas, autoclastic, pyroclastic, syn-eruptive resedimented volcaniclastic and siliciclastic deposits was a favourable environment for the development of peperites. Despite very complex alteration related to the stratovolcano-hosted hydrothermal system with a deep igneous source, locally elevated geothermal gradients and superimposed hydrothermal/geothermal regimes controlled by the emplacement of a shallow intrusive body, authigenic minerals in peperites - particularly pumpellyite and actinolite - show higher temperature stability ranges than those in the underlying and overlying volcanic deposits irrespectively of their lithofacies, porosity and permeability. The formation of authigenic minerals in peperites, such as laumontite, pumpellyite, epidote, prehnite or actinolite, was apparently controlled by ephemeral and localised high-temperature regimes originating from the parent lava flow. Heated pore waters in the host sediment that could have undergone local mixing with deuteric fluids circulated in peperites until thermal gradients persisted, and were the cause of alteration of juvenile clasts and the mingling sediment. The development of pumpellyite required a suitable precursor - fine-grained volcanic ash.

Abstract Carlin-type gold deposits in Nevada account for ~5% of worldwide annual gold production, typically about ~135 metric tons (t) (~4.5 Moz) per year. They are hydrothermal epigenetic replacement bodies hosted predominantly in carbonate-bearing sedimentary rocks. They are known for their “invisible” gold that occurs in the crystal structure of pyrite. Over 95% of the production from these deposits is from four clusters of deposits, which include the Carlin trend and the Cortez, Getchell, and Jerritt Canyon camps. Despite differences in the local geologic settings, the characteristics of the deposits are very similar in the four clusters. Shared characteristics include: (1) alteration characterized by carbonate dissolution, silicate argillization, and silicification; (2) ore formation characterized by auriferous arsensian pyrite, typically as rims on preore pyrite, followed by late open-space deposition of orpiment, realgar, stibnite, and other minerals; (3) Ag/Au ratios of &lt;1 in ore; (4) an As-Hg-Sb-Tl geochemical signature; (5) low temperatures (~160°–240°C) and salinities of ore fluids (~1–6 wt % NaCl equiv) and fairly shallow depths of formation (&lt;~2–3 km); and (6) lack of mineral and elemental zoning around ore. The four clusters share regional geologic controls related to formation as follows: (1) along the rifted margin of a craton, (2) within the slope facies of a passive margin sequence dominated by carbonates, (3) in the lower plate of a regional thrust fault, and (4) during a narrow time interval in the late Eocene (~42–34 Ma). The geometries and ore controls of the deposits in the four clusters are also very similar. At the deposit scale, ore and hydrothermal alteration are commonly associated with high-angle faults and preore low-angle contractional structures, including thrust faults and folds. The high-angle faults acted as fluid pathways for upwelling ore fluids, which were then diverted into lower angle favorable strata and contractional structures, where fluid-rock interaction led to replacement of carbonate and formation of ore. Rheologic contrasts between lithologies were also critical in diverting fluids into wall rocks. Common rheologic contrasts include contacts between thin- and thick-bedded lithologic units and the margins of contact metamorphic aureoles associated with Mesozoic intrusions. The similarities suggest common processes. Four critical processes are apparent: (1) development of source(s) for gold and other critical components of the ore fluids, (2) formation of fluid pathways, (3) water-rock interaction and gold deposition, and (4) a tectonic trigger, which was renewal of magmatism and a change from contraction to extension in the late Eocene. Consensus exists on these processes, except for the source of gold and other components of the ore fluid, with most models calling upon either a magmatic-hydrothermal source or a crustal source, where metals were scavenged by either meteoric or metamorphic fluids. Future research should focus on Carlin-style deposits in Nevada that exhibit epithermal characteristics and deposits that appear to have a clear genetic association with magmatic-hydrothermal systems associated with upper crustal intrusions. Rather than discrete types of ore deposits, there may be continua between Carlin-type gold deposits, epithermal deposits, and distal disseminated deposits, with the four large camps representing an end member.

This chapter argues that Earth is unique among the planets in the solar system, primarily because of its vast oceans of water. Despite decades of research, the source of much of the Earth’s water is still controversial. Many scientists today believe that life arose in a primordial pudding of clay and water. The chapter explains how shallow clay pools can promote the synthesis of macromolecules and how, at the start of life on Earth, they accumulated the building blocks of life. It explains how life arose in close proximity to hydrothermal vents, which were openings in the seafloor. Heated mineral-rich water flowed out of these vents and created the right environment for life to begin. The chapter points out that it is not an accident that life arose in association with water, whatever its origin, because this substance has several unusual properties that suit it to be the matrix of life. Among these are its thermal properties and unusual solvent characteristics. Water’s properties are directly related to its molecular structure.

Abstract This overview illustrates the processes controlling magma fertility in the formation of porphyry Cu-Au deposits. Magma fertility means all magmatic parameters (e.g., metal and volatile contents, magma and fluid volumes) that might result in higher amounts of metals, which are exsolvable from the magma. Mantle source processes seem to play a fundamental role in the enrichment of primary melts with H2O, S, and Cl, all essential ingredients to form porphyry deposits, but do not have a particular role in Cu enrichment. Cu-rich porphyry Cu-Au deposits (i.e., with Au/Cu ~4 X 10–6) are associated with large magmatic volumes accumulated in the lower thick crust of continental arcs during long-lived periods of compression in a synsubduction environment. Mineralization occurs after such accumulations have reached significant volumes and is the result of the transfer of hydrous magmas from deep to shallower crustal levels, probably favored by tectonic stress changes. Au-rich porphyry Cu-Au deposits (i.e., with Au/Cu ~80 X 10–6) are associated with magmatic systems that have evolved at overall shallower crustal levels and for this reason can be found in geodynamic settings characterized by thinner crust (e.g., island arcs with intermediate crust thickness) and/or in variably extensional settings occurring above a slab-metasomatized mantle (postsubduction setting, extensional synsubduction setting). The six largest Au-rich porphyry Cu-Au deposits (&gt;~1,300 tonnes Au) are associated with variably alkaline magmas, which are typical of postsubduction and/or extensional settings, suggesting a petrogenetic control on the Au-rich nature of these deposits.

ABSTRACT Geothermal energy and Aquifer thermal energy storage can provide beneficial ways of storing energy in excess and providing energy when needed. North Dakota's renewable energy system is impacted by its harsh winters. Geologic aquifer thermal aquifer storage system is a large scale geothermal system that can act as energy storage media. Aquifer thermal storage systems are dependent on heat conductivity of rocks, storage capacity of aquifer, fluid flow, geochemistry and geo-mechanics. The goals of the project are to 1) evaluate the amount of energy that can be stored in deep aquifers; 2) access the amount of energy that is thermally recoverable; 3) monitor changes in geo-mechanical parameters. CMG STARS, a three-phase multi-component thermal and steam additive simulator, was used for the thermal numerical simulation which takes into account the geo-mechanics (thermal dilation and re-compaction). A conventional reservoir with representative porosity and permeability is modelled in CMG and Semi Analytical Model (SAM) was used to calculate the wellbore dynamics involved with geothermal operations. This is used to calculate heat transfer to the surrounding formation and determine our heat loss. Our preliminary results show us the reservoir pore volume dilation re-compaction model changes from cold water injection. The grid block void porosity dilation re-compaction model changes are greatly influenced by grid block pressure. INTRODUCTION Geothermal Energy and Aquifer Thermal Energy Storage (ATES) Geothermal energy refers to the earth's thermal energy that can be converted into electrical energy. Emissions from the geothermal energy industry are substantially low, which is an excellent asset to reaching a low-carbon economy. Hot dry rocks and hydrothermal resources are the primary geothermal energy sources. Water from surface seeps through faults and cracks of earth and is warmed by hot rocks or water is trapped by impermeable layers to create geothermal reservoirs. Sedimentary basins have great geologic and reservoir properties for low-cost energy generation for geothermal energy. Hot water moves from deep sources to shallow reservoirs for hot water geothermal reservoirs. Hydrothermal systems use steam or water for electricity generation. Enhanced geothermal systems extract thermal energy from geothermal resources with lower permeability and fluid saturation. (Grant & Bixley, 2011)(Barbier, 2002)

New opportunities have emerged for the application of oilfield technologies transfer, such as directional drilling, to utilize base-load renewable energy. Development of geothermal resources have largely been restricted to on-shore sites, yet a major category of untapped geothermal development prospects are near-shore resources. Development of near-shore geothermal resources can provide renewable base-load electrical power options to areas that are now served by non-renewable power generation which can supply domestic, commercial, or industrial land-based and marine use. It may also support emerging technologies such as battery charging and green hydrogen generation for land-based and marine transportation or commercial applications. Additionally, the need for reliable and renewable base-load electrical power to support U.S. Naval operations has increased markedly in recent years, particularly in the western Pacific. The advantages of geothermal over other advanced renewable power sources is its base-load reliability, a relatively small footprint in terms of land use and the long-term durability of the equipment. Additionally, this generally untapped energy field provides an opportunity for oil and gas development companies to expand the application of their technology, experienced staff, and knowledge. However, as exploration and development of these geothermal resources may have substantial effects on their near-shore locations, it is important that this development recognize the commercial and environmental value of the near-shore marine environment and mitigate any effects from these activities. Many of the potential near-shore and shallow marine geothermal plays are associated with volcanic activity. However, non-volcanic structural plays also hold significant potential (figure 1). Perhaps the most dramatic and well-documented volcanic hydrothermal sites are the spectacular deep marine "black-smoker" vents associated with oceanic spreading centers. Yet, other than a few notable exceptions, such as Iceland (Atkins & Audunsson, 2013), these systems are usually located far from shore in deep marine environments (Hiriart et al., 2010) and have currently limited potential for widespread development. Other volcanic geothermal resources occurring near-shore are like structurally controlled settings observed on land. Examples include: Lihir Island, Papua-New Guinea (Peterson et.al., 2002; White, et.al., 2010); in the Mediterranean Sea (Fytikas et.al., 2005; Meteoboy, 2013) and the shores of Mexico’s Baja Peninsula (Vidal, et.al., 1978; Prol-Ledesma et.al., 2002). The western Pacific area is rife with volcanic islands. Yet only a few of these volcanoes have had geothermal resources developed for electrical production. One of the limiting features for geothermal evaluation of these volcanic islands is that, while they are often massive volcanoes, only the central top of the volcano is exposed above the water, while the bulk of the flanks are submerged beneath the sea. These volcanoes would have the same geothermal resource potential as their terrestrial counterpart but due to their partially submerged setting, they have been out of view and out of mind for the geothermal development community. With advances in directional drilling technologies over the past decades, it is now possible to develop near-shore (1~1.5 km) geothermal resources from on-shore locations, increasing the economic viability of these prospects while minimizing seafloor disturbance.

Abstract The BZ34-9 oilfield is a clastic reservoir discovered in the Oligocene strata in the southern part of the Bohai Bay Basin. The volcanic system here is intermixed with a clastic reservoir that spans more than 1000 meters. In its upper part, it overlies about 2000 meters of Miocene strata. Volcanic activity has influenced the deposition and filling of the lacustrine and played a key role in controlling the distribution of clastic reservoirs. Based on 3D seismic data and lithological data from 74 wells, four types of volcanic were identified and extracted according to seismic sequences. Establish and clearly state the reciprocal relationship between volcanism and sedimentation. The study of volcanic stratigraphic framework reflects the environmental change of volcanoes from terrestrial to marine, which is consistent with the understanding of the sedimentary environment from paleontological and sedimentary facies studies. Small-scale volcanism predates the formation of the early Oligocene strata, and a regional eruption center to the south and east of the BZ34-9 oilfield provides the tectonic setting for the basin evolution. The early Oligocene strata was deposited in a shallow lake environment, thin-bed distributary channels are developed in the near-source facies belt near the central volcano, and thick-bed mouth dams are developed in the far-source facies belt. Volcanoes of this period influenced the distribution of clastic reservoirs by the effusion facies and intrusive facies near conical craters. Water depth becomes deeper when the late Oligocene strata are deposited, thick-bed continuous underwater distributary channels and an estuary dam is developed in the sedimentary area. Volcanic activity was moderate until the last major eruption. During this period, the hydrothermal vent in the far-source facies belt is the main factor affecting the distribution of clastic reservoirs. It is of great significance for the further fine description of reservoirs and regional exploration.

ABSTRACT Important syn-rift hydrocarbon discoveries in the Tertiary East African Rift and in the South Atlantic subsalt basins have in recent years promoted renewed interest in the variability of source and reservoir rock facies in continental rifts. This talk considers several important new observations and developments in our understanding of the sedimentary evolution of lacustrine rift basins. Offshore subsalt basins in the South Atlantic demonstrate the importance of lacustrine carbonates, and especially microbialites, as reservoir facies in extensional systems. The role of rift-related magmatism is significant in these basins, both as drivers of hydrothermal systems around and within rift lakes, and as a source of solutes that facilitate carbonate accumulations. In the Tertiary East African Rift, substantial new hydrocarbon resources have been identified, including onshore siliciclastic reservoirs in remarkably young and shallow parts of the sedimentary section in the Albertine Graben. Rollover anticlines and fault-related folds serve as important structures for several new fields in the East African Rift, but larger structures affiliated with accommodation zones, in many instances located far offshore in the modern lakes, remain untested. Lacustrine source rocks that accumulated in stratified lake basins are the source of the oil and gas in these systems, however there is still much to be learned about their spatial and temporal variability. There is observed considerable variation in the character of organic matter on the floors of modern African lake basins, even adjacent ones. A number of factors likely govern the amount of total organic carbon preserved within the basins. These include 1) primary productivity; 2) degree of siliciclastic dilution, which is controlled in part by offshore slopes and the extent of onshore catchments, and 3) physical limnology, controlled by climate and basin-scale physiography, and the fetch-depth ratio of the lakes, which determines the likelihood of water column stratification. Scientific drilling in the African Rift lake basins is providing considerable information on the high temporal hydroclimate variability of the region, especially in the later Tertiary and Quaternary, which substantially controls basin lithofacies.