Fluid-rock Interaction Research Articles

Kyanite-muscovite-dumortierite vein mineralization mechanisms from advanced microstructural analysis using EBSD

Abstract Dumortierite, an aluminous borosilicate mineral, is relatively rare in Earth’s crust, but it is the second most abundant aluminous borosilicate after tourmaline. Boron is an element with many uses in modern societies worldwide, from health products to wind turbine blades for clean energy, but of limited availability and at future risk of supply. Only a limited number of studies have been published on dumortierite mineralization processes and the factors that control its abundance and distribution remain poorly understood. Here we present the first comprehensive electron backscatter diffraction (EBSD) study of dumortierite mineralization mechanisms in kyanite-muscovite-dumortierite veins occurring in the metapelites of the Amgaon Gneiss Supracrustals, in the Girola hill area, Sakoli region, Central India. Advanced microstructural and chemical analyses show that mixed-mode brittle-viscous deformation in kyanite, by fracturing and easy glide on (100) [001] slip system, facilitates fluid-rock interactions with reactive hydrothermal fluids rich in B, F, and K and containing Na, Ti, Mg, Fe and Pt. These interactions cause the dissolution of kyanite along fracture and cleavage surfaces and the precipitation of muscovite (F = 0.32 wt %) and topaz (F = 16.48 wt %). The motion of ripplocation defects in muscovite facilitates fluid migration along cleavage surfaces and crystallisation of dumortierite needles within these surfaces. Fluid flux removes silica in solution from the system, so reactions may continue. The observed mineral assemblage, the microstructural signature of kyanite and muscovite, the moderate fluorine content of topaz, and low fluorine content of muscovite, together suggest that dumortierite mineralization results from hydrothermal activity, possibly in a transitional magmatic-hydrothermal environment, likely at P > 2.5 kbar and 400°<T < 550°, that could be linked with granite intrusions in the area. Using EBSD we demonstrate that dumortierite mineralization is focussed along muscovite basal cleavage surfaces and dumortierite needle elongation is likely controlled by the fluid flux direction. These new results advance our understanding of dumortierite mineralization mechanisms and conditions and have important implications for our understanding of the distribution of this aluminous borosilicate mineral in muscovite-rich rocks.

In situ rubidium–strontium geochronology of white mica in young metamafic and metasomatic rocks from Syros: testing the limits of laser-ablation triple-quadrupole inductively coupled plasma mass spectrometer mica dating using different anchoring approaches

Abstract. The recent development of laser-ablation triple-quadrupole inductively coupled plasma mass spectrometry (LA-ICP-MS/MS) has revolutionized rubidium–strontium (Rb–Sr) mica dating, allowing us to obtain isotopic data within their microstructural context. While effective for old and felsic materials, this method presents challenges for young metamafic and metasomatic rocks due to limited radiogenic ingrowth associated with low Rb/Sr and young ages. We quantitatively address these limitations by combining laser-ablation ICP-MS/MS and MC-ICP-MS data for coexisting white mica and epidote, respectively, for 10 Cenozoic metamorphic rocks from Syros (Greece). White mica analyses from metamafic and metasomatic rocks yield limited Rb/Sr spread, which typically does not exceed an order of magnitude (87Rb/86Sr=14 to 231 for the combined dataset), and low radiogenic 87Sr/86Sr (generally <0.8), resulting in high age uncertainties of typically 10 to 50 % relative standard error (RSE), thus hampering robust geological interpretations. Epidote 87Sr/86Sr values range between ∼0.705 and 0.708. The former is typically expected for unaltered metamafic materials, whereas the latter is interpreted to reflect fluid–rock interaction along shear zones, with fluids derived from or having interacted with more radiogenic lithologies. These atypical values suggest that a commonly assumed value of 0.703 for mafic rocks may not always be representative. Anchoring white mica Rb–Sr to epidote 87Sr/86Sr data improves age accuracy and precision substantially (e.g., 29±17 Ma vs. 47.2±4.4 Ma for sample SYGR36). The new ages obtained in this study are consistent with multiple events previously recorded on Syros and the Cyclades blueschists unit including (i) metasomatism and metamorphism at near peak to epidote blueschist-facies conditions during early exhumation (ca. 47 to 41 Ma) and (ii) a late stage of high-pressure exhumation and metasomatism transitioning to blueschist and greenschist-facies conditions (ca. 21 to 20 Ma). Anchored white mica Rb–Sr ages in mafic rocks allow us to discriminate events of fluid–rock interactions and metasomatism associated with shear zone deformation at the subduction interface.

A rock physics modelling approach for time‐lapse monitoring and characterization of fluid–rock interactions in hydrocarbon reservoirs

AbstractOne of the research gaps is to understand the development of seismic characteristics of gas‐saturated rock along with the change in rock properties because of chemical reactions. We suggest a method to explain the change in elastic properties brought on by CO2 injection in a rock by capturing the physico‐chemical interactions observed in the laboratory in a theory of rock physics. To explain the laboratory‐measured physical characteristics and velocity of a dynamic rock–fluid system, we include a time‐dependent component in the existing cemented‐sand model. We demonstrate theoretically the rate of change of elastic moduli of the dry frame by incorporating the measured rate of change of cement due to chemical dissolution. We adapt the theory such that it can be applied to the field data and calibrate the theory using water‐saturated well log data from the Ankleshwar field, an established oil field in the Cambay basin, western India. Theoretical time‐lapse logs of velocity and density are then produced using the theory over a range of CO2 saturations, assuming cementing material in grain contacts and geochemical interactions comparable to those observed in the laboratory rock. Then, using theoretical logs, corresponding time‐lapse synthetic seismic data are produced for different saturation. These data clearly demonstrate that, for a uniform model, velocity decreases by up to 18% as CO2 saturation increases from 0% to 20% (ignoring the chemical effect), and that, for a specific saturation, say 20%, chemical effects result in a 17% decrease in velocity from the present to the end of 60 years. However, for the patchy model, velocity decreases maximum by 14% and 16% due to varying saturation and chemical reaction. Moreover, for a particular saturation of CO2, say 20%, velocity differs by 16% for different types of models. This research contributes to making strategy for CO2‐sequestration in a designated field.

Fluid–rock interaction controlled by integrated hydrothermal fluid and fault: Implications for reservoir development

Hydrothermal activity is prevalent in petroliferous basins, particularly in fractured reservoirs. Hydrothermal fluids enter the reservoirs and cause significant fluid–rock interaction, which ultimately controls reservoir development. The Mahu Sag in western China is a hydrocarbon-rich region where hydrothermal fluids and faults control the reservoirs, making it challenging to understand the development mechanism of the shale reservoirs. This study focused on the Fengcheng Formation in the Mahu Sag. Based on a range of previous lithological test results, numerical models of hydrothermal fluid charging were established to explore differences in fluid–rock interactions under varying temperature, fluid, and flow rates. Results revealed that within a specific range, increasing temperature and Mg2+ concentration promoted hydrothermal processes. The hydrothermal flow rate influenced ion accumulation on the fluid-rock contact surface, thus controlling mineral dissolution rates. In a certain range, when the flow rate is increased by 3 times, the growth rate of dolomite content is increased by more than 15 times. Hydrothermal fluid flowing near the fault underwent chemical action more readily than in other areas. The influence of hydrothermal fluid and fault on reservoir development was both constructive and destructive. The decrease and increase of porosity are 30 % and 25 %, respectively. This study could provide a theoretical basis for identifying factors influencing shale reservoir development.

Numerical simulation of a base metal deposit related to a fossil geothermal system

Fossil and active geothermal systems that produce ore deposits are sites of complex physicochemical processes and a favorable combination of factors related to the amount of metal-bearing fluid that flows through the system, ore fluid metal concentrations, depositional efficiency, and the duration of ore deposition. Of all these factors, the length of the mineralizing event is one of the least understood aspects of ore genesis.We used fluid inclusion data, chemical compositions of base metal sulfides, and fluid flow rates to constrain a reactive-transport model of a fossil geothermal system - the Patricia Zn-Pb-Ag deposit in northern Chile. The Patricia deposit consists of quartz and base metal sulfide veins of hydrothermal origin with structural control, hosted in a volcanic succession with intense propylitic alteration. The fluid inclusions are liquid-rich, with homogenization temperatures ranging from 250 to 150 °C and salinities between 22 and 1 wt% NaCl equiv., with an early fluid mixing trend and no evidence of boiling in the system. Sulfide mineralogy indicates intermediate sulfidation conditions.To identify the most relevant geochemical and transport parameters controlling the formation of this fossil geothermal system >1000 simulations were performed using the reactive-transport code TOUGHREACT. The paragenesis of the deposit is mimicked by a model of successive stages of fluid circulation consistent with the observed mineral assemblage distribution, the fluid inclusion data, and the estimated resources in the deposit.The entire geothermal activity of the system was modeled considering 10,000 years of fluid-rock interaction, with periods of circulation of metal-barren fluids followed by metal-rich fluids driving the ore formation. In the initial model, base metal solubility with predominant chloride complexing suggests that the most efficient ore-forming mechanism for the Patricia deposit was the result of the interaction of two different fluids, one fluid transporting metals and another fluid transporting reduced sulfur, mixing in a rock volume of high permeability. Mass balance estimations with this model give a period of 3500 to 5000 years for the ore stage duration in which all the ore resources of the Patricia deposit could have been precipitated by fluid mixing.In a second model, the previous estimates for the duration of the main ore stage were used to simulate the fluid-rock interaction during the ore stage for 3500 years. The results indicated the importance of the permeability of the host rock enhanced by fractures to concentrate the volume of the mineralization and the role of the hydrothermal alteration assemblage in controlling the circulating fluid acidity. A higher efficiency in forming sulfide minerals appears to coincide with pH values ranging from 5.1 to 5.3.The results of both models are validated by replicating the system evolution, reproducing the same mineral alteration assemblage, the expected base metal resource distribution, and similar amounts of ore resources to those of the Patricia deposit: a total of 52,602 tons of lead and 157,731 tons of zinc. The models indicate that the hydrothermal event might be two times longer than the ore stage.

Understanding Water–Rock Interaction in Crystalline Shield Fluids Using Calcium Isotopes

Calcium isotopes provide a potentially robust tool for understanding the evolution of crystalline shield fluids, but previous applications have focused on near surface groundwaters. The tendency of Ca isotopes to be affected by mass-dependent fractionation during processes such as water–rock interaction provides a powerful tool for studying the evolution and origin of groundwaters hosted in crystalline rocks. We report Ca isotope ratios (δ44/40Ca) of deep fluids (>300m) from across the Canadian Shield and integrate these with Sr and Br isotope values to understand long-term fluid–rock interactions in crystalline shield environments. Ca isotope ratios have a wide range of values from 0.07‰ to 0.86‰. At individual sites, δ44/40Ca values are variable whereas 87Sr/86Sr ratios are relatively constant. Sr isotope ratios (87Sr/86Sr) have a negative relationship with the Ca vs. Na content of the fluid indicating different host-minerals contributing Sr to the fluid. Ca isotope fractionation was caused by metamorphic reactions and by the growth and dissolution of Ca-rich fracture-filling minerals. The δ44/40Ca signatures of these processes are overprinted by radiogenic ingrowth of 40Ca by decay of 40K, which is expected to affect older and more K-rich rocks. At one site, δ44/40Ca and δ81Br variability reflects gas-generating reactions in the fluid and/or water–rock interaction processes. These new results demonstrate the strength of combining multiple isotope analysis to elucidate the sources of groundwater salinity and decipher the complex long-term processes that occur in crystalline shield environments.

Petrology of Tourmaline-Bearing Blueschist from SW Tianshan, China, and Its Implication in B-Rich Fluid Migration in Subduction Zone

Abstract Boron geochemistry can track fluid–rock interaction during subduction zone metamorphism. Rare tourmaline-bearing blueschists, which are associated with ultrahigh-pressure (UHP) serpentinites are first recognized in SW Tianshan, China. Detailed petrology, whole-rock and mineral chemistry, B isotope analysis, and modeling characterized two consecutive stages of tourmaline crystallization (Tur-I, Tur-II). Tourmaline included in, or intergrown with, garnet and the cores of tourmaline in rock matrixes and veins are Tur-I, which grew during prograde metamorphism at 430°C to 460°C/470°C, ~1.9–2.1 GPa. The rims of tourmaline in rock matrixes and veins are Tur-II, which formed during initial exhumation at 460°C to 490°C, ~2.1–1.7 GPa. Variable δ11B values of tourmaline (+8‰, Tur-I to −2‰, Tur-II) point to a 11B-rich signature of the fluid infiltrating at Stage I. With progressing metamorphism, δ11B decreased in the fluid. The high-δ11B Tur-I (up to +8‰) could not have crystallized from fluid released from the high-pressure metapelites (−12‰ to −7‰) and metabasites (−15‰ to −5‰) surrounding the tourmaline host rocks given the lower δ11B values. Modeling of B isotope fractionation yields the δ11B values of −9‰ to −5‰, −11‰ to −1‰, and +8‰ to +17‰ for the fluids equilibrium with the restitic metapelites, metabasites, and serpentinites, respectively. The tourmaline and whole-rock B isotope data, along with the tourmaline compositions, point to the associated serpentinites as source of the fluid that infiltrated the metamorphic rocks. This fluid was released by the partial dehydration of serpentinites through the reaction antigorite + brucite = olivine + water at forearc depth. We propose that metabasites in subduction zones can acquire 11B-rich signatures through interaction with serpentinite-derived fluids, leading to the formation of robust tourmaline minerals at shallow levels. As a new reservoir of heavy boron, these metabasites can then transport this signature to greater depths.

The role of hydrothermal alteration in uranium mineralization at the Xiaoshan uranium deposit, South China

Hydrothermal alteration can be utilized to constrain element migrations during mineralization, as it records the effects of fluid-rock interactions. Previous studies have suggested that uranium in deposits primarily originates from uranium-bearing granites; however, limited knowledge exists regarding the leaching mechamisms of this element and rare earth elements (REEs) from these rocks. In recent years, the Xiaoshan Deposit, a newly discovered medium-sized uranium deposit, has been discovered in the central part of the Lujing uranium ore field, South China. In this study, we examine this deposit to investigate hydrothermal alterations and their impact on elemental mass change. The deposit exhibits seven types of alteration including K-feldspar, albite, illite, sericite, muscovite, quartz and chlorite alteration. These alterations follow a certain sequence, starting from chlorite alteration, followed by widespread K-feldspar alteration, then to albite alteration, accompanied by muscovite alteration, and finally illite, sericite and quartz alteration. The main uranium mineralization stage was coeval with the late acid siliceous hydrothermal fluid, illite and sericite alteration. The pre-ore alkaline alteration (K-feldspar alteration) resulted in the leaching and extraction of uranium, leading to the precipitation of a significant amount of apatite in mineral interstices and initial uranium enrichment (ΔCi (U) = 16.52 ppm). This process facilitated material preparation for subsequent acidic alterations and localized ore enrichment. The original dense rock structure was disrupted, creating fractures/cavities that served as conduits for uranium mineralization. Moreover, under alkaline metasomatism, uranium and REEs was extensively leached out of uranium-bearing accessory minerals such as the apatite. According to apatite compositional variations and alteration geochemistry, these variations reveal the process of uranium dissolution, migration, and precipitation enrichment into ore bodies. Uranium was completely released during alkaline metasomatism, causing a sharp decline in U content from 53.1 ppm to 0.96 ppm. The formation of alkaline alteration fluids facilitates the extraction of uranium from the surrounding rocks (the Indosinian granite).

Geochemical signatures of forearc serpentinites from oceanic to continental subduction

In subduction systems, the forearc (FA) serpentinized mantle plays a key role as a reservoir for fluid-mobile elements, especially those prone to early mobilisation from the slab. FA serpentinites therefore provide an indication of the fluid characteristics that have been steamed out of the slab, and allow better quantification of elemental recycling and fluid flow. FA serpentinites outcropping along the Indus Suture Zone are formed by hydration of mantle peridotites by fluids derived from the Indian slab, providing a geochemical record of fluid-rock interactions during the India-Eurasia convergence. Systematic trace and multi-isotope (Sr and Pb) analyses of serpentinites from three major sites, namely Shergol-Tingdo, Kargil and Tso Morari, along the Indus Suture Zone in Ladakh (NW Himalaya) show that these rocks record a major change in the origin of metasomatic agents, from oceanic to continental subduction. The Shergol-Tingdo and Kargil FA serpentinites, formed under low temperature and pressure conditions, are characterised by high B enrichment and As and Sb depletion, high alkali/U ratios and relatively unradiogenic Sr and Pb isotope ratios. These geochemical characteristics are identical to those reported for modern oceanic subduction zones (e.g., Mariana forearc) and are consistent with input by fluids derived from subducted oceanic crust. In contrast, FA serpentinites from the Tso Morari ultra-high pressure unit show enrichment in fluid mobile elements such as As, Sb and U, low alkali/U ratios and radiogenic Sr and Pb isotopic compositions. These features suggest a change in the metasomatizing agent with a strong influence from subducted continental material. Consistent with this scenario, the Sr-Pb isotopic composition of the Kargil FA serpentinites can be reproduced by mixing between an Indian MORB-depleted mantle source and fluids derived from dewatering of blueschist facies oceanic metasediments, whereas in the case of Tso Morari a fluid end-member derived from various eclogitic continental metasediments is required. We propose that the observed geochemical signature of the Indus Suture Zone FA serpentinites can be used to reconstruct the geochemical exchanges between the slab and the overlying mantle from intra-oceanic to continental subduction. This successful systematic approach could be applied to other collisional contexts

Substantial in situ Ti isotope variations in rutile record source and fluid evolution of porphyry copper mineralization systems

Titanium (Ti) and its stable isotopes have been widely used as tracers for magmatic processes. However, our understanding of Ti isotope behavior in magmatic-hydrothermal systems remains limited. Hence, the in situ Ti isotope composition (δ49Ti) of magmatic titanite and hydrothermal rutile associated with magnetite and chalcopyrite mineralization was determined for the first time in four well-characterized porphyry copper deposits in southern Tibet. The rutile formed through the alteration of primary Ti-rich minerals during fluid-rock interaction in the early high-temperature magnetite and later moderate-temperature chalcopyrite stages of mineralization. Hydrothermal rutile, altered from magmatic titanite, exhibits δ49Ti values similar to those of residual magmatic titanite. This suggests that hydrothermal rutile inherited the Ti isotope composition of magmatic titanite. The average δ49Ti values of rutile are negatively correlated with whole-rock εNd(t) and zircon εHf(t) data, and positively correlated with whole-rock (87Sr/86Sr)i values, which suggests that the initial Ti isotope compositions of hydrothermal rutile in porphyry copper deposits primarily reflect their source. Rutile from the Qulong deposit sometimes exhibits fractionation of δ49Ti at levels exceeding 0.5‰, displaying a negative correlation with Zr and FeO, which may be attributed to the formation of magnetite and rutile at an early potassic alteration stage. Isotopically light Ti is preferentially incorporated into magnetite and rutile. Thus, the rutile associated with sulfide mineralization that formed from the remaining fluids during a later stage of phyllic alteration is enriched in heavy δ49Ti. These findings contribute to the understanding of how rutile fractionates Ti isotopes in hydrothermal systems related to porphyry copper deposits. In local contexts, the substantial crystallization of magnetite, along with the preferential incorporation of isotopically light Ti during the early stages, leads to a decrease in oxygen fugacity within the ore-bearing fluid. This, in turn, facilitates the formation of sulfides during later stages. The results of this study demonstrate the efficacy of in situ Ti isotope analysis as a powerful tool for tracking fluid and metal sources, and can be used to help interpret ore precipitation throughout different stages of magmatic-to-hydrothermal ore-forming processes.

Genesis of high-grade lode gold shoot dominated by ore fluid overprinting during a ductile-brittle shear event

Lode gold deposits hosted by ductile-brittle shear zones account for more than one-third of the world’s gold production. High-grade ore shoots from this type of deposit are the most critical exploration targets. The ore shoots can form through the post-depositional deformation of auriferous sulfides or overprinting of ore fluids accompanied by coupled dissolution-reprecipitation (CDR) reactions. However, the mechanism that dominates ore shoot genesis remains unknown, primarily due to the controversial single progressive or polyphase nature of ore-bearing shear zones. Here, we report on geological and geochemical analyses we conducted at the large Hetai goldfield, South China, to construct an accurate gold upgrading model for the formation of ore shoots. Stages 1−3 of mineralization at Hetai show features typical of ductile shearing, while Stage 4 is characterized by quartz-sulfide veinlets in brittle fractures. 40Ar/39Ar ages of ca. 184 Ma and 157 Ma for the mineralization of stages 1 and 4 overlap with the regionally dextral ductile-brittle shear that occurred during ca. 210−162 Ma. Thus, the gold event at Hetai should have been controlled by a single progressive ductile-brittle shear episode, rather than polyphase structural events. The auriferous fluids at Hetai precipitated minor invisible gold in pyrites (mean 0.173 ppm) produced during stages 1−4 through fluid-rock interaction. The systematic increase of elements Au, As, Sb, Bi, Ag, and Cu and δ34S values in ductile-deformed pyrites from stages 1−3 indicate that early invisible gold upgrading should be the result of the post-depositional remobilization of auriferous sulfides during the long-lived ductile-brittle transition. Cataclastic pyrites hosting invisible gold from Stage 4 have zoned and porous mantles with elevated invisible gold (mean 0.503 ppm) and Sb, Bi, Pb, Co, Ni, and Ti contents. These pyrites are further replaced by chalcopyrite and pyrrhotite with increasing invisible gold, Co, and Ni contents. In addition, numerous visible native gold grains in Stage 4 are included in sulfides formed by replacement and develop along the microfractures and grain boundaries of these sulfides. We suggest the late invisible and visible gold upgrading events in Stage 4 can be attributed to the auriferous fluid superposition and subsequent replacement of pyrite via CDR reactions in a brittle regime. Therefore, the gold upgrading process at Hetai is jointly caused by the early remobilization induced by ductile-brittle deformation and the late ore fluid superposition with accompanying CDR reactions within a brittle domain. As the ore fluid superposition and CDR reactions in Stage 4 produce a significant amount of visible gold, they exert a first-order control on the genesis of ore shoots at Hetai. The refined model may be widely applicable to lode gold deposits elsewhere and can be used to identify regions with promising exploration targets.

Solutions and case studies for thermally driven reactive transport and porosity evolution in geothermal systems (reactive Lauwerier problem)

Abstract. Subsurface non-isothermal fluid injection is a ubiquitous scenario in energy and water resource applications, which can lead to geochemical disequilibrium and thermally driven solubility changes and reactions. Depending on the nature of the solubility of a mineral, the thermal change can lead to either mineral dissolution or precipitation (due to undersaturation or supersaturation conditions). Here, by considering this thermo-hydro-chemical (THC) scenario and by calculating the temperature-dependent solubility using a non-isothermal solution (the so-called Lauwerier solution), thermally driven reactive transport solutions are derived for a confined aquifer. The coupled solutions, hereafter termed the “reactive Lauwerier problem”, are developed for axisymmetric and Cartesian symmetries and additionally provide the porosity evolution in the aquifer. The solutions are then used to study two common cases: (I) hot CO2-rich water injection into a carbonate aquifer and (II) hot silica-rich water injection into a sandstone aquifer, leading to mineral dissolution and precipitation, respectively. We discuss the timescales of such fluid–rock interactions and the changes in hydraulic system properties. The solutions and findings contribute to the understanding and management of subsurface energy and water resources, such as aquifer thermal energy storage, aquifer storage and recovery and reinjection of used geothermal water. The solutions are also useful for developing and benchmarking complex coupled numerical codes.

Geochemical modeling of U-Ni-Co-As transport and deposition in acidic basinal brines: Implications for unconformity-related U-(Ni-Co-As) mineralization in the Athabasca Basin (Canada)

The unconformity-related uranium (URU) deposits, which are best developed in the Proterozoic Athabasca Basin (Canada), can be divided into the monometallic (U) and polymetallic (U-Ni-Co-As) subtypes. Different models have been proposed to explain the formation of the two subtypes of URU deposits. The conventional “diagenetic-hydrothermal” model suggests that both subtypes formed from oxidizing, acidic basinal brines in a unified mineralization system, whereas a newly proposed model suggests that the polymetallic deposits formed from monometallic U deposits superimposed by Ni-Co-As mineralization. While the second model has been the subject of ongoing debates, there are also unanswered questions in the diagenetic-hydrothermal model; in particular, it remains unclear what geological factors controlled the formation of one subtype or another in a unified mineralization system. This paper aims to address this question with geochemical modeling of hydrothermal U-Ni-Co-As transport and deposition using the Geochemist's Workbench (GWB) software. The conditions for U-Ni-Co-As transport were examined with thermodynamic modeling. The results indicate that highly oxidizing (log fO2(g) > −25), acidic (pH = 3.5) brines can transport large amounts (>100 ppm) of U together with Ni-Co-As, whereas moderately oxidizing (−40 < log fO2(g) < −25), less acidic (3.5 < pH < 6) brines can transport only minor amounts (<1 ppm) of U while still capable of carrying large amounts (>100 ppm) of Ni-Co-As, and very reducing (log fO2(g) < −40) brines with pH from 3.5 to 6 can dissolve only minor amounts (<1 ppm) of U and Ni-Co-As. The mechanisms of U-Ni-Co-As deposition were examined with reaction path modeling involving fluid-rock interaction and fluid-fluid mixing. The results indicate that as a U-Ni-Co-As-bearing, acidic, oxidizing brine progressively reacts with basement rocks or mixes with a reducing fluid, U precipitates before Ni-Co-As in relation to pH increase and fO2(g) decrease. In the case of fluid mixing, while U precipitation can be caused by any of the reducing agents (CH4(aq), H2(aq), H2S(aq), and Fe2+(aq)) in the reducing fluids examined, Ni-Co-As deposition requires the participation of CH4(aq) or H2(aq). Based on the modeling results, it is inferred that U and Ni-Co-As were not transported by the same fluid, otherwise all the URU deposits would be polymetallic. The U was most likely derived from the basin rather than from the basement, because as oxidizing basinal brines infiltrate and interact with basement rocks, their ability to dissolve and transport U quickly diminishes due to fO2(g) decrease and pH increase. In contrast, as these basinal brines infiltrate the upper part of the basement, which is moderately oxidizing, they retain the ability to dissolve and transport significant amounts of Ni-Co-As, enabling the scavenging of these metals from the basement. While all URU mineralization requires U-bearing basinal brines and reducing agents, the formation of polymetallic (U-Ni-Co-As) deposits depends on the availability of Ni-Co-As-rich lithologies in the upper part of the basement, together with an ample supply of robust reducing agents, such as CH4 and H2 that were derived from the deeper part of the basement. Therefore, although the possibility that polymetallic U-Ni-Co-As deposits formed from Ni-Co-As mineralization superimposing on monometallic U deposits cannot be ruled out, the results of this study demonstrate that both polymetallic and monometallic URU deposits can be formed in a unified diagenetic-hydrothermal mineralization system in the Athabasca Basin.

Review on spontaneous imbibition mechanisms in gas-water systems: Impacts on unconventional gas production and CO2 geo-sequestration

Spontaneous imbibition, a fundamental process in porous media, involves the displacement of a non-wetting phase by a wetting phase driven by capillary pressure. It plays a key role in various applications, particularly in unconventional gas production and greenhouse gas geo-sequestration. Despite extensive research in this area, conflicting results and explanations persist regarding imbibition phenomena, particularly in gas-water systems. This paper aims to address this gap by providing a comprehensive review of basic concepts, mechanical analyses, pore-filling patterns, front evolutions, and influencing factors associated with spontaneous imbibition. Mechanical factors including capillary force, viscous force, gravitational force, hydrostatic force, inertial force, capillary back force, and dead end force, play crucial roles in water imbibition with different boundary types. The pore-filling pattern significantly affects microscopic fluid distribution and front evolution during the imbibition process. To resolve conflicting findings, we systematically analyze the influencing factors of spontaneous imbibition within gas-water systems, encompassing rock properties, fluid characteristics, rock-fluid interactions, and reservoir properties. Furthermore, we present an in-depth discussion on the imbibition and trapping mechanisms relevant to unconventional gas production and CO2 geo-sequestration, providing insights into force analyses and influencing factors. Gas production strategies and favorable conditions for CO2 capillary trapping are proposed. Finally, we outline existing knowledge gaps and suggest potential directions for future research. This review thus provides useful insights and suggestions for advancing our understanding of spontaneous imbibition within gas-water systems and optimizing unconventional gas production and CO2 geo-sequestration practices.

Modeling the impact of pH and reservoir temperature on the dissolution of quartz mineral due to oilfield chemical treatment

The petroleum industry frequently uses oilfield chemicals, such as corrosion inhibitors, scavengers, drilling fluid, and chemical enhanced oil recovery methods, to improve oil recovery. However, these chemicals can negatively impact the geochemical characteristics of the formation, potentially leading to facility failure and reservoir formation damage. A study using PHREEQC was conducted to predict the impact of reservoir temperature and pH on quartz rock dissolution under different temperatures and pH levels. The results showed consistent dissolving rates for quartz at different pH levels. The solubility of quartz minerals was slightly affected by the solution pH, suggesting that the process variable pH has little effect on the equilibrium rate. However, precipitation caused quartz to dissolve at a rate of 0.04 mmol.L−1.s−1 at 45 °C but increased to 0.07 mmol.L−1.s−1 at 65 °C in 0.8 s. As temperature increased, quartz and NaNO3 solution interaction reached equilibrium concentrations in 0.8 and 2.7 s. The study concluded that temperature significantly impacts quartz dissolution during interaction with sodium nitrate oilfield chemicals compared to pH. The PHREEQ software is a useful research tool for simulating rock-fluid interactions resulting in reservoir formation dissolution and precipitation, which can cause formation damage and sand production.

Anomalous tellurium enrichment associated with gold mineralization: A mineralogical and isotopic study of the Yongxin Te-Au deposit, northeast China

The Yongxin tellurium-gold (Te-Au) deposit, a large epithermal deposit in the Duobaoshan polymetallic metallogenic belt (DPMB) within eastern section of the Central Asian Orogenic Belt (CAOB), is mainly hosted by syenogranite and mylonite. However, the Te-Au occurrence, precipitation mechanism and genesis in this deposit remain elusive. In this study, pyrite, the primary host of Te-Au mineralization, was studied utilizing multiparametric techniques such as scanning electron microscope (SEM), electron probe microanalysis (EPMA), in-situ laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) and femtosecond laser ablation coupled multi-collector inductively coupled plasma mass spectrometry (fs LA-MC-ICP-MS). The results show that there are three generations of pyrite termed here as Py1, Py2 and Py3. The coarse euhedral Py1 and fine vein Py2 contain negligible to low contents of Te and Au, whereas the anhedral aggregated Py3 with porosity and grain boundary (GB) shows the highest concentrations of Te and Au. Representative LA-ICP-MS profiles show that Te-Au occurs either as solid solution in the Py1 and Py2 or submicroscopic Au-Ag-Te-Bi inclusions, electrum and native gold in Py3. Thermodynamic data of telluride and sulfide show that the Te-Au was deposited under relatively oxidizing conditions with values of log f Te2 ranging from −15.2 to −11.2 and log f S2 from −16.7 to −12.1. at 200 °C. We infer that fluid mixing and fluid-rock interaction were the dominant mechanisms that triggered the precipitation of Te-Au in the Yongxin Te-Au deposit. Geochemical and geochronological data indicate that the likely source of Te is Te-rich oceanic sediments originating from the Western Pacific Plate. Pyrite and telluride from the gold deposits can be potential targets for Te exploration in the DPMB.

The use of combined C[sbnd]Mg isotope compositions of carbonates from orogenic Sb[sbnd]Au deposits as a tracer of fluid interaction with sea-floor altered crust

The Mesoarchaean Murchison Greenstone Belt is composed of a strongly deformed volcano-sedimentary succession metamorphosed up to amphibolite facies and surrounded by metaluminous and peraluminous granitoids in the north of the Kaapvaal Craton of southern Africa. A circa 40 km-long shear-zone of strongly carbonatised rocks (the Antimony Line, or Sb-Line) oriented along the main trend of the greenstone belt (WSW–ENE) hosts important Sb deposits with accessory Au. These commodities mostly occur as stibnite and native gold hosted by quartz‑carbonate rocks at the centre of the Sb-Line, underlining the importance of CO2-rich fluid flow for mineralisation during deformation and metamorphism.In this study, we compare the elemental and stable isotope (C-O-Mg) composition of carbonates from the Sb-Line with regionally distributed carbonates hosted by the volcano-sedimentary succession distal to mineralisation. The carbonates of the Sb-Line and regional rocks have overlapping major element compositions. Both magnesite and dolomite in most Sb-Line samples have marked light-REE-depleted patterns with variable positive Eu anomalies. Carbon isotope ratios define two clusters, with marked δ13C peaks at ca. -5 ‰ for Sb-Line rocks and ca. -2 ‰ for regional rocks, implying separate C-sources. The peak at ca. -2 ‰ likely represents early carbonatisation through sea-floor alteration, whereas the first peak at ca. -5 ‰ is indicative of deep CO2 (mantle, or magma-derived) introduced during tectonic activity of the Sb-Line. Magnesium isotope ratios of regional rocks reveal limited fractionation (bulk δ26Mg = −0.27 ± 0.10 ‰) that overlap with mantle values, but some carbonate-bearing veins present 26Mg-depleted compositions (bulk δ26Mg = −1.91 to −0.40 ‰). Sb-Line carbonated rocks have more fractionated Mg isotope compositions (bulk δ26Mg = −0.8 to 0.0 ‰) and carbonates display marked negative 26Mg values (δ26Mg from −1.46 to −0.31 ‰). We interpret these results in terms of preferential remobilisation of isotopically light Mg during fluid-rock interaction and dissolution of carbonate in the host-rocks. The lack of correlation between δ13C and δ26Mg indicates decoupling of these isotopic systems, implying contribution from isotopically distinct sources of C and Mg to the mineralised zone.Similar to other structurally controlled AuSb mineralisation in Archaean greenstone belts, metal transport and ore deposition in the Murchison Greenstone Belt was closely related to the deep cycle of carbon, linking C-draw-down during sea-floor alteration, carbonate re-mobilisation during metamorphism and CO2 degassing from deep sources along major crustal discontinuities. In contrast to models for orogenic AuSb deposits invoking a purely intra-crustal, metamorphic origin of mineralising fluids, our results underline the importance of deep-sourced fluids originating from an external source from the volcano-sedimentary succession.

Fluid inclusion and pyrite geochemistry of the Jiapigou gold deposit, North China Craton: Implication for origin of orogenic gold deposit?

The Jiapigou auriferous belt in Jilin province has been recognized as substantial gold-producers in the North China Craton (NCC). Gold mineralization in this district mainly occurs in mineralized quartz veins and alteration zones, characterized by silicification, pyritization, and argillitization. The quartz veins contain three generations of mineralized quartz, namely, qtz1 (probably oldest), qtz2 (slightly younger), and qtz3 (probably youngest) were identified using SEM-CL. The fluid inclusions in all three generations of quartz are broadly of three types, viz., bi-phase Ia (H2O-CO2), tri-phase Ib (H2O-CO2-NaCl ± CH4), and II (H2O-NaCl).The micro-thermometric analysis of the type Ia and Ib fluid inclusion in qtz1 & qtz2 have aqueous-carbonic composition and exhibit a similar salinity of 1.1 to 7.8 wt% NaCl equivalent, whereas the homogenization temperature (Th) range varies from ∼237 to ∼350 °C. These ore-related fluid inclusions are of low to moderate salinity, and show mixture of CO2 and CH4. On the other hand, Type II fluid inclusions are dominant in qtz3. They have salinity of 3.2 to 12.7 wt% NaCl equivalent and homogenization temperature varying between 180 °C and 210 °C. These data indicate that the ore-forming fluid evolved from a CO2–H2O–NaCl ± CH4 system during the mineralization period.The X-ray elemental maps of pyrite acquired using electron microprobe analysis (EPMA) show irregular zones of Co and Ni indicating two generations of pyrite. The early-stage pyrite which occupies core portion shows high Co and Ni, whereas the later-stage pyrite occupying rim has lower Co and Ni. The laser ablation-inductively coupled plasma-mass spectrometer (LA-ICPMS) analyses of pyrite has indicated that pyrite-1 is rich in Au + Ag + Se + Cu + Co + Ni, whereas, pyrite-2 has lower concentration of these elements. A positive correlation between Fe and other chalcophile elements reported here (i.e. Au + Ag + Se + Cu + Co + Ni), might be due to fluid-rock interaction resulting into a saturated fluid that subsequently precipitated along the microfractures within earlier-formed pyrite and quartz. The in-situ δ34S values in pyrite from Jiapigou deposits overlap in the range of +4.5 to +9.6 ‰, which is consistent with the ore-forming fluids of the crustal origin input during fluid-rock interaction. The systematic pyrite compositional observations and fluid inclusions study documented here to provide new insight into the process of ore formation for the Au enrichment in the Jiapigou deposit

Characteristics of antimony mineralization in the Yangla polymetallic deposit, northwestern Yunnan, SW China: Insights from calcite Sm-Nd dating and C-O-Sr isotopes

Calcite is the main gangue mineral in antimony (Sb) deposits, and its compositions can reflect the physicochemical conditions of Sb mineralization. The Yangla is the largest Sb deposit (10 kt Sb @ 14.87 %) in the Jinshajiang suture zone (SW China), and the lode-type Sb orebodies are stratabound or developed along NE-trending fracture zones in marble. To constrain the time of Sb mineralization and establish any genetic link with the local magmatism and wallrocks, we performed calcite Sm-Nd dating and bulk C-O and in-situ Sr isotope analyses. The results show that the Sb mineralization (∼155 Ma) was considerably younger than the Cu-Pb-Zn mineralization (∼230 Ma), skarn alteration (∼234 Ma), and granitoid emplacement (∼230 Ma) at Yangla, but much older than the local W mineralization (∼30 Ma). The initial 87Sr/86Sr ratio of calcite (0.71972–0.72208) is much higher than that of the Triassic granodiorite (0.71149– 0.71990) and Carboniferous basalt (0.70562–0.70995), suggesting mixed source of calcite from the ore fluids and Devonian wallrocks. The ore-related calcite has δ13CPDB (−4.53 to − 2.33 ‰) and δ18OSMOW (+14.98 to + 16.30 ‰) values that fall between the granite and marine carbonate isotopic fields. This suggests that the ore-forming fluid may be related to the low-temperature alteration of granites and marine carbonate dissolution. Simulated precipitation temperature calculation for the ore-related calcite yielded 200–150 °C, and the calcite C-O isotopes suggest that fluid mixing, fluid-rock interactions, and CO2 degassing may have precipitated the stibnite in the fracture zones under low-temperature conditions. Our new geochemical results and published data suggest that the Yangla polymetallic mineralization was multiphase, comprising the Indosinian Cu-Pb-Zn (∼230 Ma), Yanshanian Sb (∼155 Ma), and Himalayan W-Sb (∼30 Ma) metallogenic events.

Pyrite in-situ S–Fe isotope constraints on the ore-forming sources and mineralization processes of gold and polymetallic deposits in the Liaodong Peninsula, North China Craton

Plenty of gold and polymetallic deposits are widespread in the eastern part of the North China Craton. They are associated with mafic to felsic dikes and hosted by Precambrian basement or Mesozoic granitoids. However, the sources of gold and other metals in the ore-forming fluids remain controversial. Here we present in-situ S and Fe isotopes and trace element contents of pyrites from various gold and Pb–Zn–(Ag) deposits in the Liaodong Peninsula, China. Pyrites from quartz vein-type gold deposit hosted by Mesozoic granites in the Wulong deposit have relatively homogeneous magmatic-like S isotopes (δ34S values of 0.9 ‰ to 2.5 ‰) and Co/Ni ratios, indicating derivation of sulfur and, by inference, of ore fluids/materials most likely from Mesozoic magmas. In contrast, pyrites from gold and Pb–Zn–(Ag) deposits in the Qingchengzi orefield hosted by Precambrian basement have high and variable δ34S values (9.7 ‰ to 12.7 ‰ for the Wandigou altered rock-type gold deposit and 4.7 ‰ to 8.5 ‰ for the Xiquegou Pb–Zn deposit and the Zhenzigou Pb–Zn–Ag deposit), identical to those of host rocks, indicating the important contributions of gold and other metals from wall rocks to the ore deposits. Pyrites from the various deposits have variable δ56Fe values of 0.08 ‰ to 0.63 ‰ for the Pb–Zn–Ag deposit, –0.58 ‰ to 1.23 ‰ for the altered rock-type gold deposit, and –0.68 ‰ to 0.77 ‰ for the quartz vein-type gold deposit, indicating distinct mineralization processes. Rapid precipitation of pyrites (with negative δ56Fe values) in the alteration rock and subsequent deposition of pyrites (with positive δ56Fe values) from the residual fluids in an Fe-open hydrothermal system during intensive ore-forming fluid-wall rock interaction account for the Pb–Zn–Ag mineralization, while weak fluid-rock interaction and pyrites precipitation from a Fe-closed hydrothermal system contribute to gold mineralization. Our observations provide a robust S–Fe isotope evidence for the contribution of various sources and metallogenic processes for distinct gold and polymetallic deposits.