Hydrothermal Fluid Flow Research Articles

Geological and 3D Image Analysis toward Protecting a Geosite: The Case Study of Falakra, Limnos, Greece

The Falakra geosite is located at the northern shoreline of the island of Limnos, Greece, and exhibits an array of unusual geomorphological features developed in late Cenozoic sandstones. Deposition of the primary clastic sediments was overprinted by later, low-temperature hydrothermal fluid flow and interstitial secondary calcite formation associated with nearby volcanic activity. Associated sandstone cannonballs take center stage in a landscape built by joints, Liesengang rings and iron (hydr)oxide precipitates, constituting an intriguing site of high aesthetic value. The Falakra geosite is situated in an area with dynamic erosion processes occurring under humid weather conditions. These have evidently sculpted and shaped the sandstone landscape through a complex interaction of wave- and wind-induced erosional processes aided by salt spray wetting. This type of geosite captivates scientists and nature enthusiasts due to its unique geological and landscape features, making its sustainable conservation a significant concern and topic of debate. Here, we provide detailed geological and remote sensing mapping of the area to improve the understanding of geological processes and their overall impact. Given the significance of the Falakra geosite as a unique tourist destination, we emphasize the importance of developing it under sustainable management. We propose the segmentation of the geosite into four sectors based on the corresponding geological features observed on site. Sector A, located to the west, is occupied by a lander-like landscape; to the southeast, sector B contains clusters of cannonballs and concretions; sector C is characterized by intense jointing and complex iron (hydr)oxide precipitation patterns, dominated by Liesengang rings, while sector D displays cannonball or concretion casts. Finally, we propose a network of routes and platforms to highlight the geological heritage of the site while reducing the impact of direct human interaction with the outcrops. For constructing the routes and platforms, we propose the use of serrated steel grating.

Tracking hydrothermal infiltration within light oil reservoirs using organic geochemical proxies in the Shunbei area of Tarim Basin in China

Deep oil reservoirs are becoming increasingly significant fields of hydrocarbon exploration in recent decades. Hydrothermal fluid flow is deemed as a potentially crucial factor affecting the occurrence of deep oil reservoirs, such as enhancing porosity/permeability of reservoirs, accelerating oil generation and thermal cracking, and modifying organic properties of crude oils. Understanding the interplay between hydrothermal fluids and crude oils would provide useful constraints for reconstructing hydrocarbon accumulation processes and predicting the distribution patterns of crude oils. Voluminous crude oils have been discovered in the deeply buried Ordovician carbonate reservoirs within the Shunbei area of the northern Tarim Basin. Previous studies revealed that the Early Permian Tarim Large Igneous Province (LIP) has affected the Shunbei area, whereas it is still debated whether the LIP-related hydrothermal infiltration affected hydrocarbons within the Ordovician reservoirs. To resolve this puzzle, this study was designed to unravel the potential thermal impact of hydrothermal infiltration on hydrocarbons according to molecular and stable carbon isotopic compositions of oils and associated natural gases, reflectance analysis of solid bitumen, and fluid inclusion thermometry. The studied crude oils are characterized by uniform organic indicators of paraffin, terpanes, steranes, and light hydrocarbons, implying that crude oils are derived from the same source rock. Genetic binary diagrams, such as dibenzothiophene/phenanthrene (DBT/P) vs. Pr/Ph (pristane/phytane), Pr/n-C17 alkane vs. Ph/n-C18 alkane, C31R/C30hopane vs. C26/C25tricyclic terpane (TT), and C24/C23 TT vs. C22/C21 TT, indicate that marine shales deposited in a reducing-weakly oxidized environment are major source rocks. Natural gases are associated with oil reservoirs and are mainly generated via the decomposition of kerogen and crude oil. Solid bitumen with abnormally high reflectance values (2.17–2.20%) occurred in the studied area, suggesting their formation temperatures were 252–254 °C. The abnormally high temperatures may be caused by hydrothermal infiltration related to the Tarim LIP. Hydrothermal infiltration is supported by the presence of high contents of CO2 (30–48%) with enriched δ13C ratios (between − 2.5‰ and − 2.3‰), enriched n-alkane δ13C ratios, and incongruent temperatures estimated by multiple indicators, such as light hydrocarbon compositions, homogenization temperatures of fluid inclusions, and bitumen reflectance. Outcomes of this study support the interpretation that hydrothermal infiltration indeed occurred and may have facilitated hydrocarbon generation in the Shunbei area, and possibly elsewhere in the cratonic regions of the northern Tarim Basin.

Hydrothermal fluid flow in Silurian carbonates in Lithuania and cold-water injection impact on long-term reservoir performance

Hydrothermal fluid flow in Silurian carbonates in Lithuania and cold-water injection impact on long-term reservoir performance

Brittle Regime Slip Partitioned Damage and Deformation Mechanisms Along the Eastern Denali Fault Zone in Southwestern Yukon

AbstractRare bedrock exposures of the eastern Denali fault zone in southwestern Yukon allow for the measurement, sampling, and analyses of brittle regime fault slip data and deformation mechanisms to explore relations to far field, oblique plate motions. Host rock lithologies and associated slip surfaces show episodic damage zone‐related deformation and calcite ± hematite ± chlorite related hydrothermal fluid flow. This regional scale network of asymmetric fault damage is spatially and kinematically linked to a discrete and narrow fault core. Fault network observations, orientations, slip data, and strain inversions document a slip partitioned strike‐slip fault system with locally and mutually overprinting strike‐, oblique‐, and dip‐slip components. Microstructural analyses reveal crystal plastic and co‐seismic brittle deformation mechanisms active in a narrow range of upper crustal temperature, pressure, fluid, and chemical conditions. The net damage related slip is not exclusively formed by a single kinematic system, but rather a fully partitioned, time integrated system likely operative for much of the fault's brittle regime evolution temporally constrained by previously published thermochronometric data. Although the fault slip data was collected from outcrop‐scale exposures at sites tens of kilometers apart, results show remarkable correlation between fault kinematics and plate motions along the ∼580 km long eastern Denali fault segment. End member, subhorizontal, northeast directed reverse and north directed dextral strike slip fault strain axes closely reflect relative plate motion interactions over at least the last 30 m.y. and act as a proxy for far‐field stresses compatible with the kinematics of the damage zone network.

Normal fault architecture, evolution, and deformation mechanisms in basalts, Húsavik, Iceland: Impact on fluid flow in geothermal reservoirs and seismicity

Faults within layered basaltic sequences significantly influence hydrothermal fluid flow in shallow geothermal reservoirs and potentially during CO2 sequestration and storage. Nevertheless, their characterization regarding fault zone architecture, fluid flow, deformation mechanisms, and seismic potential remains underdeveloped. This study addresses this gap by integrating structural and microstructural observations with X-ray diffraction analyses of exposed normal-transtensional faults associated with the seismically active Húsavík-Flatey Fault in the Tjörnes Fracture Zone, Northern Iceland. Our findings demonstrate that the evolution of basalt-hosted normal-transtensional faults progresses through distinct stages: (1) low-displacement fault propagation from pre-existing cooling joints; (2) fault linkage via dilational jogs; (3) damage zone/fault core growth through brecciation and cataclastic processes; (4) shear localization along sharp slip surfaces; and (5) smearing of volcaniclastic interbeds along the principal fault plane. Evidence of shear localization, truncated clasts, and hydrothermal breccias/veins suggests repeated seismic slip events facilitated by overpressured fluids. Conversely, the presence of clay-rich foliated cataclasite indicates aseismic slips during interseismic periods. Slip along fault jogs, bends, geometric irregularities, and orientation changes causes the dilatant opening of the fault planes and extensional horsetail fractures at fault tips. These structures create main tabular zones for lateral movement of hydrothermal fluids parallel to the fault strike in shallow geothermal reservoirs situated in active extensional-transtensional tectonic settings. In addition, the dilational jogs and the intersection of horsetail veins with the hosting faults may define linear zones of high structural permeability and intense localized fluid flow parallel to the σ2 paleostress orientation and finally mineral precipitation. The results of this study can be utilized to improve models of geothermal fluid flow for enhanced recovery in basaltic reservoirs and assess seismic risk in basaltic faults.

Structural controls on hydrothermal fluid flow in a carbonate geothermal reservoir: Insights from giant carbonate veins in western Germany

This study examines the impact of polyphase tectonics on the development of structurally controlled hydrothermal fluid pathways in carbonate geothermal reservoirs. Our case study focuses on hydrothermal carbonate veins and vein-filled faults in Devonian carbonates from the North Rhine-Westphalia region in western Germany, currently being explored as a potential low-enthalpy geothermal reservoir at depths of 4–5 km. These veins, which can be up to 20 m thick, are subvertical and strike NNW, N, or ESE. They exhibit pinch-and-swell undulating geometries, faulted vein-wall contacts, and occasional fillings of hydrothermal breccias. Vein-filled normal faults show hybrid shear-dilatant openings, with fault tips characterized by horsetail vein terminations. The textures, orientations, and age of the veins suggest their formation at low confining pressures and at depths < 2 km during the Post-Variscan East-West extension. Orthogonal North- and East-striking strike slip faults, inherited from the Variscan orogeny, were likely reactivated during post-Variscan extension, with a significant dilatant component that formed the observed veins. In the Ruhr Basin, the dilation tendency analysis indicates that NNW-striking veins or joints are optimally oriented for re-opening under the current strike-slip stress regime, characterized by NNW-trending maximum horizontal stress. The intersections of fractures may currently create moderately SSE-plunging linear zones of enhanced fluid flow. The main uncertainty regards the presence of similar structures at geothermal reservoir depths of ∼4–5 km in the Middle Devonian carbonates underneath the Ruhr Basin. As the study veins are likely to have formed at depths <2 km, the existence of analogous dilatant conduits at greater depths remains speculative. Eventually, we propose that zones characterized by open discontinuities and channelized fluid flow in carbonate geothermal reservoir in strike-slip tectonic settings can be: (a) dilational jogs between overlapping strike-slip faults, (b) bends along faults, and (c) strike-slip fault terminations with horsetail extensional structures. These zones can also be prone to enhanced karstification.

Thermotogota diversity and distribution patterns revealed in Auka and JaichMaa 'ja 'ag hydrothermal vent fields in the Pescadero Basin, Gulf of California.

Discovering new deep hydrothermal vent systems is one of the biggest challenges in ocean exploration. They are a unique window to elucidate the physical, geochemical, and biological processes that occur on the seafloor and are involved in the evolution of life on Earth. In this study, we present a molecular analysis of the microbial composition within the newly discovered hydrothermal vent field, JaichMaa 'ja 'ag, situated in the Southern Pescadero Basin within the Gulf of California. During the cruise expedition FK181031 in 2018, 33 sediment cores were collected from various sites within the Pescadero vent fields and processed for 16S rRNA amplicon sequence variants (ASVs) and geochemical analysis. Correlative analysis of the chemical composition of hydrothermal pore fluids and microbial abundances identified several sediment-associated phyla, including Thermotogota, that appear to be enriched in sediment horizons impacted by hydrothermal fluid flow. Comparative analysis of Thermotogota with the previously explored Auka hydrothermal vent field situated 2 km away displayed broad similarity between the two locations, although at finer scales (e.g., ASV level), there were notable differences that point to core-to-core and site-level factors revealing distinct patterns of distribution and abundance within these two sediment-hosted hydrothermal vent fields. These patterns are intricately linked to the specific physical and geochemical conditions defining each vent, illuminating the complexity of this unique deep ocean chemosynthetic ecosystem.

Time scales and mechanisms of uranium uptake in altered ocean crust; observations from the ∼15 million year-old site 1256 in the eastern equatorial Pacific

The alteration of ocean crust through hydrothermal seawater circulation facilitates chemical exchange between Earth’s surface and interior. Hydrothermal alteration leads to uranium (U) removal from seawater and net U uptake by the ocean crust, particularly during low temperature alteration that occurs on the vast ocean ridge flanks away from the spreading axes. Determining the timescales of U uptake and its associated 238U/235U signature has important implications for understanding U exchange processes during subduction and recycling into the mantle. Here we study the U systematics of ∼15 million year-old ocean crust drilled at Site 1256 on the eastern flank of the East Pacific Rise. Analysis of cores from the upper ∼1300 m of intact ocean crust at this site, reveal large variability in U concentrations and 238U/235U ratios. Many of the samples from the upper ∼600 m of extrusive lavas have elevated U concentrations and 238U/235U ratios lower than seawater, consistent with mechanisms of U uptake under relatively oxidised conditions. Samples from the underlying sheeted dikes and gabbros show evidence for hydrothermal U mobilisation, but negligible net U uptake. In contrast, in the transition zone between the extrusive lavas and the sheeted dikes, samples revealed large U enrichments and high 238U/235U ratios above seawater. This is consistent with uptake of the reduced U+4 species under relatively reducing conditions from seawater-derived hydrothermal fluids. In addition, large secular disequilibrium in 234U/238U ratios from samples in the lava-dike transition and upper sheeted dikes give evidence for U mobility within the last ∼1.5 million years, likely driven by deep channelled flow of seawater-derived hydrothermal fluids combined with preferential leaching of 234U from the rock matrix. Both the total estimated U uptake and mean 238U/235U at Site 1256 is lower than similar estimates from significantly older (>100 million years) altered ocean crusts at drill Sites 801 and 417/418. This shows the variable total U uptake and 238U/235U ratio in altered ocean crust over time, which needs to be taken into consideration when estimating global U budgets.

Impacts of temperature and fluid seepage on organic matter composition in sediments of an active hydrothermal basin

Marine sediments are one of the largest organic carbon (OC) sinks on Earth. Yet, major knowledge gaps remain in our understanding of sedimentary OC cycling, particularly regarding temperature-induced alteration processes of OC from different sources. Here, we investigate OC-rich sediments of Guaymas Basin (Gulf of California) across two hydrothermal areas, one with only conductive geothermal heating and the other additionally experiencing seepage of hydrocarbon-rich fluids from deeper layers. We use Pyrolysis-Gas Chromatography/Mass Spectrometry (Py-GC/MS) to investigate diagenetic OC changes and show that cold control sites in both hydrothermal areas are dominated by similar contributions of lipid-derived compounds, nitrogenous (likely protein-derived) compounds, carbohydrates, and polyaromatic hydrocarbons (PAHs). These OC compound groups are largely derived from phytoplankton detritus from overlying water. Conductively heated sediments, which reach in situ temperatures of ∼ 80 °C, have similar general OC compositions and contents to these cold sites, but show evidence of diagenetic modifications of individual carbohydrate groups in deeper layers. By contrast, strong decreases in carbohydrate and nitrogenous compound abundances at the seep sites indicate that these compound groups are not only modified but also selectively degraded at the higher temperatures (>80 °C) of these sites. Increases in pyrolysis products of PAHs, prist-1-ene, and alkanes with depth, moreover, show that import of OC by deep hydrothermal fluids contributes significantly to sedimentary OC pools mainly in deeper layers of these sites. Our study provides the first comprehensive analysis of major OC compound groups in Guaymas Basin sediment and indicates that the supply of OC by hydrothermal fluid flow only has minor impacts on particulate organic matter compositions at the seafloor, even at active seep sites. We furthermore show that temperatures up to ∼ 80 °C already result in thermochemical modifications of organic matter (OM) that are potentially linked to the onset of kerogen formation. The sequence and time scales of chemical modifications and activations in relation to temperature are an important subject for future investigations.

Diversity, spatial distribution and evolution of inactive and weakly active hydrothermal deposits in the TAG hydrothermal field

Introduction: Although, there is an increasing focus on inactive or extinct seafloor massive sulfide (SMS) deposits driven by the possibility of marine mining, only few studies have been devoted to them so far. The Trans-Atlantic Geotraverse (TAG) hydrothermal field is probably one of the best-studied hydrothermal systems even if the relict SMS deposits known since the mid-1980s have not been thoroughly explored.Objectives: The main objective of this study was to describe the characteristics of these so-called inactive sites.Methods: During four different expeditions, we acquired high-resolution acoustic data and performed numerous human occupied vehicle (HOV) dive operations including extensive rock sampling and in-situ temperature measurements.Results and Discussion: We discovered thirteen new hydrothermal mounds including six large (i.e. &amp;gt; 5,000 m2) deposits making the TAG hydrothermal field one of the largest accumulation of hydrothermal materials (21.1 Mt) known on the seafloor. However, copper and zinc grades of the largest SMS deposits remain low (i.e. &amp;lt; 1.4 wt%) even compared to on-land volcanogenic massive sulfide deposits. Additionally, eight areas of diffuse hydrothermal fluid flow were identified challenging the presumed inactivity of these SMS deposits and, for the first time, emphasizing the importance of low temperature (LT) hydrothermal activity in whole the TAG field. Inactive and weakly active SMS deposits exhibit a large diversity of surface mineralization (e.g. sulfides, Fe-Mn mineralization, jasper) illustrating complexity of hydrothermal activities but also different ageing history. Several mounds no longer have visible sulfide chimneys and are covered by a widespread layer of manganese and iron oxyhydroxides attesting the longevity of diffuse fluid flow at specific locations even long after last high-temperature (HT) hydrothermal activity has ceased. This contrasts with SMS deposits that are devoid of extensive LT precipitates but characterized by standing or topped sulfide chimney indicating a relatively abrupt cessation of HT hydrothermal activity.Conclusion: Together these results allow us to propose evolution models to explain the diversity of active, weakly active and inactive SMS deposits in the TAG hydrothermal field.

Physico-chemical constraints associated with hypogene hydrothermal alteration and supergene oxidation at the Farallón Negro intermediate-sulfidation epithermal Au-Ag deposit, NW Argentina

The Farallón Negro deposit is located in the Farallón Negro Volcanic Complex (FNVC; ∼9.40 to 4.88 Ma) in NW Argentina and includes intermediate-sulfidation, epithermal Au-Ag mineralization in the Alto de la Blenda deposit. Detailed mineralogical and geochemical investigations of the Esperanza-Esperanza Sureste, Cecilia veins, both hosted in the Alto de la Blenda monzonite, and the Laboreo vein, hosted in the volcaniclastic Morada Central andesitic breccia, reveal four hypogene vein stages. Each of these four stages are comprised of a texturally early quartz, followed by a sulfide-sulfosalt and a late Mn-carbonate sub-stage. Stage 1 is characterized by a quartz, base metal and Mn-carbonate sub-stage showing high δ18OVSMOW (δ18OQuartz = 13.7 ± 0.4‰ and δ18OMn-Calcite = 11.6 ± 0.2‰) and low δ13CVPDB values (δ13CMn-Calcite = –4.7 ± 0.2‰). Stage 2 includes most gold and silver minerals in a tennantite-tetrahedrite-sphalerite-pyrite-galena±electrum sub-stage. Fluid inclusions trapped in vein-anhydrite, only associated with stage 2, record the highest temperatures (TEntrapment = 327–335°C) and highest salinity (3.8NaCleq.wt.%) when compared to all other stages. Stage 2 quartz (δ18OQuartz = 9.9 to 11.9‰) and carbonate display lower δ18OVSMOW (δ18OMn-Calcite = 7.9 to 10.3‰), as well as lower δ13CVPDB values (δ13CMn-Calcite = -5.2 to 4.7‰) than all other stages. Stages 3 and 4 consist of barren quartz and carbonate sub-stages that show lower temperatures (TEntrapment = 187–262°C) and higher δ18OVSMOW (δ18OQuartz = 13.4 to 13.9‰ and δ18OMn-Calcite = 10.7 to 11.8‰) and δ13CVPDB values (δ13CMn-Calcite = –3.5 to −3.9‰) when compared to earlier stages.Petrographic, sulfide mineral chemistry, microthermometric, and stable isotope data combined with distinct alteration mineral assemblages allow the reconstruction of a model for the Alto de la Blenda deposit. During the hypogene hydrothermal fluid flow stage, around 7.16 Ma, at ∼2.2 km depth (PHYDROSTATIC = 220 bars), the high temperature alteration mineralogy, low fluid salinities and 18O and 13C isotope compositions indicate cooling of ascending magmatic-hydrothermal fluids. These fluids were derived from a contracted magmatic vapor phase that exchanged with unexposed sedimentary rocks of the Sierras Pampeanas. Hypogene quartz-R3 illite/smectite-chlorite-calcite-pyrite alteration in the andesitic-breccia and quartz-illite-R3 illite/smectite-chlorite-calcite-pyrite alteration in the monzonite are temporally and spatially to the hydrothermal vein minerals deposited between 187 and 335°C. During the post-hydrothermal supergene weathering event, around 2.70 Ma, sulfuric acids generated by meteoric fluids and supergene oxidation of hypogene sulfides, particularly pyrite, descended along normal fault zones and related vein and fracture networks to at least 450 m depth below the surface level, forming the supergene alteration assemblage of dioctahedral smectite-kaolinite-Mn-/Fe-oxides/-hydroxides-gypsum±interstratified chlorite/smectite±interstratified R1 illite/smectite in both wall rock types at temperatures <50°C.The dominant hypogene alteration assemblage, present in the monzonite and volcaniclastic andesitic breccia, may be indicative of deeper-seated, transitional magmatic-hydrothermal systems (>1 km depth), generally controlled by fluid cooling, as is the case at Farallón Negro. Pervasive supergene alteration can conceal these systems but the identified supergene alteration assemblage of dioctahedral smectite-kaolinite-interstratified chlorite/smectite-interstratified R1 illite/smectite that replaces the hypogene alteration assemblage along the permeable fault, vein and fracture zone network may present a useful vectoring tool towards concealed, deeper-seated, epithermal Au-Ag mineralization in arid climates.

Oligocene–Miocene arc magmatic activities associated with the giant Reko Diq porphyry Cu–Au deposit, western Chagai arc, Balochistan, Pakistan

The Chagai belt to the north of the Afghan block and the east of the Iranian block in the western part of Pakistan is known for occurrence of Oligocene to Miocene calc‐alkaline magmatic belt. The present study discusses the characteristics of episodic magmatic activities that contributed to mineralization for the Reko Diq porphyry complex in the western part of the Chagai belt. U–Pb dating of zircons from volcanic rocks of the Reko Diq porphyry complex yielded ages of 25.8 ± 1.8 and 12.29 ± 0.44 Ma for two phases of magmatic crystallization. Geochemical analyses of whole‐rock rhyolite and dacite indicate that the rock units are peraluminous calc‐alkaline, derived from Andean‐type subduction. The magma was formed due to partial melting of the thickened mafic lower crust in a continental arc setting in relation to the subduction of the Neotethys along the Makran subduction zone. The abundance of zircons, Hf, REE, U/Pb and Th indicates high degrees of magmatic evolution. Moreover, the Sr and Nd isotopic data indicate the fractional contribution of depleted N‐MORB mantle to the Reko Diq magmas through bulk mixing with magmas derived from the lower continental crust. Short‐lived magmatic systems repeated magma injection, and various episodes of hydrothermal fluid flow have led to the formation of porphyry mineralization. Emplacement of the Reko Diq porphyry complex and related Cu–Au mineralization is associated with a series of tectonic–magmatic events at different episodes of the Oligocene–Miocene times.

Multiple Paleokarst Events in the Cambrian Potosi Dolomite, Illinois Basin

The Cambrian (Furongian) Potosi Dolomite (100-183 m) in Illinois is part of the Cambro-Ordovician Knox Group. It is a uniformly dolomitized unit with very low intercrystalline porosity but contains very permeable vug, fracture/cavern porosity intervals. Here, we interpret the characteristics of the widespread porous zones in the Potosi as paleokarst features formed by rising hypogenic basinal/hydrothermal fluids. The conformity bounded Potosi Dolomite is characterized by massive dolomitization, overdolomitization and occlusion of previously generated intercrystalline porosity, void filling mineralization, and extensive dissolution and formation of cavity-conduit systems. The pore spaces are typically lined with drusy quartz or are characterized by partial to complete infilling with chalcedonic silica and/or dolomite cements. Clay minerals may partially fill pore spaces; physical properties and thorium-potassium crossplot suggest chlorite as the main clay mineral present. Dolomite crystals typically are planar-s or nonplanar with open-space filling, inclusion rich saddle dolomite displaying curved and zigzag crystal faces. Void filling cement does not exhibit sign of pressure solution and in places vug porosity is developed along bedding parallel stylolite indicating post burial origin of these features. Cavern reservoirs in the Potosi are laterally extensive and often stacked with intervening very low porosity dolomite; very low bulk density, excursion of caliper log signature from the baseline, and loss of fluid circulation during drilling in these intervals signify anomalously high porosity and permeability interpreted as being the result of cavern forming multiple paleokarst events. Post burial origin of cavities and void filling cements, association of saddle dolomite and chlorite, and occurrence of Mississippi Valley-type (MVT) ore deposits in Missouri suggest karstification by hypogenic warm basinal/hydrothermal fluids. Dissolution and mineralization likely occurred by flow of deep basinal formation waters and hydrothermal fluids (sourced from the crystalline basement underlying the Reelfoot Rift and the Illinois Basin) along numerous basement-rooted normal, reverse, and strike-slip faults, and the associated fold and fractures. Expansion and contraction because of fault-related seismicity likely developed fracture porosity in brittle host dolomite and possibly ruptured any underling impermeable units to enable large-scale upward and outward fluid movement. The Potosi fracture/cavern porosity intervals are confined by thick very low porosity dolomite intervals that could serve as effective seal. There is no report of any show of oil in the Potosi Dolomite, but the unit has an excellent potential to serve as a combined reservoir and seal for storing anthropogenic CO2 and waste material.

Unveiling the inherent physical-chemical dynamics: Direct measurements of hydrothermal fluid flow, heat, and nutrient outflow at the Tagoro submarine volcano (Canary Islands, Spain)

Tagoro is one of the few submarine volcanoes in the world that has been monitored since its early eruptive stage in 2011 to present day. After six multidisciplinary oceanographic cruises conducted between 2014 and 2023 to gather a comprehensive dataset of georeferenced video-imagery and in situ measurements of hydrothermal flow velocities and hydrothermal fluid samples, we provide a robust characterization of the ongoing hydrothermal fluid velocity, heat flux, and nutrient release, along with an accurate delimitation of the hydrothermal field area. Our results reveal that Tagoro hydrothermal system extends from the main hydrothermal crater up to the summit, covering an area of 7600 m2. This hydrothermal field comprises thousands of small individual vents, displaying diverse morphologies such as crevices and delicate chimney-like structures, irregularly scattered across the dominant diffuse venting surface. Hydrothermal fluid temperatures and velocities at the substratum level reveal a clustered spatial distribution, ranging from 21.0 to 33.3 °C and 1.6–26.8 cm min−1, respectively. Furthermore, our findings indicate a discernible correlation between hydrothermal fluid temperature and vent density, while significant differences were observed between velocities from diffuse and focused areas. Additionally, heat fluxes exceed 200 MW across the entire active region, with heat flux values ranging from 6.06 to 146.87 kW m−2 and dissolve inorganic nutrient concentrations exhibit significant enrichments, comparable to the magnitude of important nutrient sources in the area as upwelling systems or mesoscale structures.

Convective heat transfer of electrically conducting MHD power law fluid through annular sector duct

This study deals with the effect of Lorentz force on forced convection flow of electrically conducting magneto-hydrodynamic, (MHD) power law fluid through the annular sector duct by using finite volume method. In existence literature, hydro-thermal flow of MHD power law fluid within an annular sector duct has not been reported. The effect of Lorentz force on hydro-thermal power law fluid flow makes it very much novel in its own right. Here the main objective is to explore the effect of Lorentz force on hydro-thermal flow characteristics. The influence of uniform magnetic field is taken parallel to the radial direction. The effects of Hartman parameter, [Formula: see text] and power law index, [Formula: see text], corresponding to Lorentz force and power law fluid respectively, on the quantities of interest such as velocity and temperature profiles, friction factor and average Nusselt number [Formula: see text] are discussed for different geometric configuration parameters’ values of the annular sector duct. Computer code is developed and validated by comparing the results of limiting cases with the available literature. It has been observed that [Formula: see text] increases with the increase in [Formula: see text]. This trend is prevalent in both pseudo-plastic and dilatant fluids. The impact of [Formula: see text] is pronounced in the later case.

Temporal constraints on hydrothermal circulation associated with strike-slip faulting in the Permian Maokou carbonates, central Sichuan Basin (SW China)

Despite the ubiquity of hydrothermal fluid circulation in the crust, its timing is difficult to precisely determine using traditional thermometric dating due to strongly disturbed geothermal fields. We present a case study from the mid-Permian hydrocarbon-bearing dolostone reservoirs, situated proximally to strike-slip faults in the central Sichuan Basin (China), to highlight the utility of carbonate in-situ U-Pb geochronology in delineating the timing of hydrothermal fluid flow. Matrix and void-filling cement dolomite phases were identified in the porous Maokou Formation carbonates. Predominantly manifesting as saddle dolomites along fractures, these cements yielded statistically homogeneous U-Pb ages (242.5 ± 3.1 Ma, 238.9 ± 8.2 Ma, 244 ± 15 Ma, and 239.2 ± 6.5 Ma), slightly postdating the established stratigraphic timeline (ca. 273 to 259 Ma). The narrow temporal span suggests early emplacement following a short burial, compatible with the petrographic observation of burial stylolites crosscutting saddle dolomites. Integrating shallow emplacement depths inferred from a comparison between the dolomite U-Pb ages and a published burial history, with fluid-inclusion microthermometry, elucidates the hydrothermal system that was once present in this field. The pervasive occurrence of hydrofracturing, along with dolomite geochemical indicators represented by bell-shaped (REE + Y) PAAS patterns and elevated Y/Ho ratios, provide additional evidence for the hydrothermal fluid injection and resulting dolomitization. The dolomites' positive Eu anomalies and the parent fluids’ 18O enrichment indicate a source from deeper basinal pore waters that have interacted significantly with ambient rocks. The overlying Triassic evaporites may have provided Mg-rich brines, mixing into the circulating hot fluids responsible for hydrothermal dolomitization. Our dolomite U-Pb ages coincide with the seismically estimated timing of transtensional strike-slip fault activation. This temporal correspondence, combined with spatial associations and lateral slickensides along fracture planes, suggests that the hydrothermal fluid movement is highly relevant to the active strike-slip faults. This observation reveals a previously unrecognized early-middle Triassic, structurally controlled hydrothermal activity in the region. We propose that this episode of hydrothermal circulation was driven by extensional tectonism in response to the spreading of the Proto-Tethys Ocean. This finding is not in line with the earlier research that considered late Permian Emeishan volcanism to have been the main trigger for hydrothermal fluid influx. The long-standing view regarding hydrothermal dolomitization in this region may need to be re-evaluated.

Earlier stage, higher temperature, and deeper space facilitate indium precipitation in a skarn system, as exemplified by the Baoshan Pb-Zn polymetallic deposit, South China

Indium (In), one of the strategic critical metal elements, is preferred to be enriched in the skarn system, but the enrichment regularity in terms of temporal and spatial distribution in a specific skarn Pb-Zn deposit remains unclear. To address the problem, we conducted a systematic geological, mineralogical, and trace element geochemical investigation on the Baoshan In-rich Pb-Zn polymetallic deposit, Hunan Province. This deposit is situated in the central part of the famous Nanling W-Sn-Pb-Zn polymetallic metallogeny belt, South China. Three ore districts in the Baoshan deposit with distinct economic element associations are divided, including the Central District (dominated by Cu-Mo), West District (dominated by Pb-Zn), and North District (dominated by Pb-Zn). They comprise a typical skarn system, including the outcropped granodiorite porphyry, typical skarn mineral assemblages, and Pb-Zn-hosting Carboniferous limestone. We systematically sampled the representative Pb-Zn ores in two ore districts (West and North) and three underground levels (-270 m, −230 m, and −190 m). Four types of sphalerites with different mineral associations and mineralogical characteristics were identified, that is, Sp1a and Sp1b (formed in the early sulfide stage), as well as Sp2a and Sp2b (formed in the late sulfide stage). Our EPMA (Electron Probe Micro-Analyzer) and LA-ICP-MS (Laser Ablation Inductively Coupled Plasma Mass Spectrometer) analyses reveal the four types of sphalerite have distinct chemical compositions. Such as, the mean value of indium is 3524 ppm for Sp1a, 142 ppm for Sp1b, 48.03 ppm for Sp2a, and 87.98 ppm for Sp2b in a decreasing order, and a similar trend of calculated temperatures ranging from 336 to 135 °C using GGIMFis thermometers can be obtained. Further LA-ICP-MS trace elements mapping show that the core of Sp1a is relatively enriched in more In, Cu, Sn, and Ag contents. Spatially, the sphalerites in the deep contain a higher indium content (mean = 1581 ppm) than those in the shallow (107.20 ppm) in the vertical profile. In the planar, indium is more enriched in the West District (mean = 1090 ppm) than in the North District (60.92 ppm). The indium distribution regularity reflects that the metals-carrying magmatic hydrothermal fluids flow from Central District, through the West District, to the North District. Collectively, we conclude that indium prefers to be enriched in the earlier stages, higher temperature, and deeper space during the sphalerite crystallization in the Baoshan skarn system, and therefore highlight the deep space of Baoshan West District is a promising target for indium exploration. This new finding maybe shed light on the scientific understanding on indium enrichment and associated exploration strategies in the similar skarn Pb-Zn metallogenic systems.

Effects of Paleoregolith and Fault Offset on the Formation of Unconformity-Type Uranium Deposits

Regional paleoregolith is found to exist immediately below unconformities separating basin fills from basement rocks in sedimentary basins. However, the controlling role of paleoregolith on unconformity-type uranium mineralization has not been quantitatively addressed before. Coupled hydrothermal fluid flow and reactive mass transport modeling are therefore performed in this study by using the software TOUGHREACT. The modeling results reveal that preferential flow occurs in the regolith due to its relatively high permeability in comparison with that of the host rocks. The thicker the regolith is, the more concentrated the fluids in the footwall of a fault zone are, leading to more compact and higher-grade deposits therein, and vice versa. Also, displacement of the regolith caused by fault offset plays an important role, as it appears to control the shape of uranium deposits. When the displacement is less than 30 m, the deposits are characterized by a more compact shape. When the displacement is over 60 m, the deposits extend more laterally and even exhibit a ‘discrete’ shape due to the expelling effect of downslope flow that occurs at the fault offset site.

Deposit-scale controls of hypozonal gold mineralization in amphibolite facies metaturbidites: 3D modelling of the Twin Hills deposit, Damara Belt, Namibia

The recently discovered Twin Hills deposit is a new resource in the Pan-African Damara Belt of central Namibia, described by a finely dispersed, low-grade and high tonnage disseminated and vein-style gold mineralization. The underlying assumption of the 3D implicit modelling followed in this study is that the integration of gold grades and ore shells with structural and lithological data from oriented core logging reflects the underlying controls of hydrothermal fluid flow and mineralization at Twin Hills. The deposit comprises distinct clusters of economic-grade gold mineralization, measuring several hundred meters along strike, separated by several kilometer-long intervals of only sporadic and sub-economic gold grades. Mineralization is developed on the subvertical southern limb of a regional-scale syncline hosted in highly-strained compositionally heterogeneous, amphibolite facies metaturbidites. Additionally, the stretch of the main mineralization in the central parts of the ∼12 km long east-northeast-trending mineralized Twin Hills corridor coincides with the change of the fold vergence direction. We suggest that the steep orientation of the wall-rock strata generated high-permeability fluid conduits for focusing regional fluid flow during flexural-slip folding and associated local dextral strike-slip component of D2/3 deformation. Disseminated sulfide mineralization is mostly developed in pelitic units, whereas networks of quartz-sulfide veins and veinlets with subordinate disseminated sulfides are present in rigid psammitic beds in interbedded pelite-psammite horizons. While the wide distribution of finely disseminated sulfides point to the rather pervasive fluid flow along grain-scale permeabilities during recrystallization of mineral fabrics, the formation of fractures and resultant dilatancy in psammitic units created hydraulic gradients and focused fluid flow into the psammite horizons. High-grade ore shoots are controlled by the combination and interplay of two main factors, namely lithological contacts and subtle deflections of bedding of the highly-strained, subvertical metaturbidites. The mineralized corridor of the Twin Hills deposit is largely confined to imbricated and/or tightly folded packages of interbedded pelites-psammites within the otherwise pelite-dominated sequence. It is these units that promoted fracturing, fluid flow and the development of fine-scale vein networks as a result of pronounced strain partitioning between pelitic units (ductile) and interbedded psammites (brittle) during regional deformation. Ore shoots of higher-grade mineralization (>1.5 g/t Au) follow these main lithological contacts, but are laterally confined to subtle (5–15°) clockwise deflections of bedding (dilational jogs) from its regional east-northeast trends. Outside these deflections, gold mineralization is patchy and only sub-economic. The structural and lithological controls of the Twin Hills mineralization closely resemble those of orogenic gold deposits, whereas the fine-grained and dispersed texture of gold and associated sulfide mineralization are more reminiscent of disseminated gold deposits. We suggest that the Twin Hills deposit is an example of a hypozonal orogenic gold deposit formed under peak metamorphic amphibolite conditions.

Organic matter accumulation and hydrothermal effect of the Barney Creek formation in the Glyde Sub-basin, northern Australia

The Glyde Sub-basin is a large petroliferous unit in the McArthur Basin, northern Australia, and it is situated ∼100 km southeast to the world-class McArthur River Zn–Pb hydrothermal deposit. The Paleoproterozoic Barney Creek Formation (BCF) is the hydrocarbon source rock in the sub-basin, and also the host rock for the McArthur River deposit. The controlling factors of organic matter accumulation and the hydrothermal effects on organic matter thermal maturity are not well-constrained for the BCF in the Glyde Sub-basin, hindering petroleum and mineral explorations. To address these issues, rock eval pyrolysis, reflectance measurement, trace element analysis, Nd–Hf and Re–Os isotopic analysis were conducted for the BCF samples taken from the drill-hole GRNT-79-5 in the Glyde Sub-basin. Analysis of trace elements and Nd–Hf isotopic ratios shows that cuttings of the BCF were derived from a mafic-dominant source (La/Ni = 0.89–2.27, La/Cr = 0.63–1.04, La/Sc = 3.16–4.95, La/V = 0.23–0.81, ϵNd = −5.01 to −2.98, ϵHf = −2.27 – 1.8), which may have contributed to a pronounced phosphorous delivery to the basin, resulting in enhanced primary productivity of seawater. Therefore, the high organic matter abundance in the BCF (TOC = 0.86%–5.04%) is most likely controlled by the primary productivity of seawater. The 187Re/188Os ratios (34.954–432.95) of a suite of samples negatively correlate with proportions of kerogen in organic matter (0%–94%), suggesting that burial temperature has reset the Re–Os isotope system. Hydrocarbon generation may have been promoted by hydrothermal fluid flows which relate to the McArthur River mineralization because the Re–Os isotope data yield an isochron age similar to the age of mineralization. The Re–Os isotope data provide direct evidence that the BCF in the Glyde Sub-basin was affected by hydrothermal fluids. However, the co-variation between thermal maturity indicators (Tmax = 436–444 °C; reflectance of solid bitumen = 0.34%–0.66%) and burial depth (97–512 m) suggests that organic matter thermal maturation primarily resulted from burial diagenesis rather than hydrothermal fluid flows. This indicates that temperatures of hydrothermal fluids was not high enough to significantly alter the thermal regime of the studied region.