Search Results (196)

Numerical simulations enable us to couple multiphase flow and geochemical processes to evaluate how sequestration impacts brine chemistry and reservoir properties. This study investigates these impacts during CO₂ storage at the San Juan Basin CarbonSAFE (SJB) site. The hydrodynamic model was calibrated through history-matching, utilizing data from saltwater disposal wells to improve predictive accuracy. Core-scale simulations incorporating mineral interactions and equilibrium reactions validated the model against laboratory flow-through experiments. The calibrated geochemical model was subsequently upscaled into a field-scale 3D model of the SJB site to predict how mineral precipitation and dissolution affect reservoir properties. The results indicate that the majority of the injected CO₂ is trapped structurally, followed by residual trapping and dissolution trapping; mineral trapping was found to be negligible in this study. Although quartz and calcite precipitation occurred, the dissolution of feldspars, phyllosilicates, and clay minerals counteracted these effects, resulting in a minimal reduction in porosity—less than 0.1%. The concentration of the various ions in the brine is directly influenced by dissolution/precipitation trends. This study provides valuable insights into CO₂ sequestration’s effects on reservoir fluid dynamics, mineralogy, and rock properties in the San Juan Basin. It highlights the importance of reservoir simulation in assessing long-term CO₂ storage effectiveness, particularly focusing on geochemical interactions. Full article

The global energy sector is aiming to substantially reduce CO₂ emissions to meet the UN climate goals. Among the proposed strategies, underground storage solutions such as radioactive disposal, CO₂, NH₃, and underground H₂ storage (UHS) have emerged as promising options for mitigating anthropogenic emissions. These approaches require rigorous research and development (R&D), often involving laboratory-scale experiments to establish their feasibility before being scaled up to pilot plant operations. Microorganisms, which are ubiquitous in laboratory environments, can significantly influence geochemical reactions under variable experimental conditions of porous media and a salt cavern. We have selected a consortium composed of Bacillus sp., Enterobacter sp., and Cronobacter sp. bacteria, which are typically present in the laboratory environment. These microorganisms can contaminate the rock sample and develop experimental artifacts in UHS experiments. Hence, it is pivotal to sterilize the rock prior to conduct experimental research related to effects of microorganisms in the porous media and the salt cavern for the investigation of UHS. This study investigated the efficacy of various disinfection and sterilization methods, including ultraviolet irradiation, autoclaving, oven heating, ethanol treatments, and gamma irradiation, in removing the microorganisms from silica sand. Additionally, the consideration of their effects on mineral properties are reviewed. A total of 567 vials, each filled with 9 mL of acid-producing bacteria (APB) media were used to test killing efficacy of the cleaning methods. We conducted serial dilutions up to 10⁻⁸ and repeated them three times to determine whether any deviation occurred. Our findings revealed that gamma irradiation and autoclaving were the most effective techniques for eradicating microbial contaminants, achieving sterilization without significantly altering the mineral characteristics. These findings underscore the necessity of robust cleaning protocols in hydrogeochemical research to ensure reliable, reproducible data, particularly in future studies where microbial contamination could induce artifacts in laboratory research. Full article

Groundwater sustains ecosystems, agriculture, and human consumption; therefore, its interaction with hydrocarbons is an important area of research under the umbrella of environmental science and resource exploration. Naturally occurring or anthropogenically introduced hydrocarbons can significantly impact groundwater through complex geochemical processes such as dissolution, adsorption, biodegradation, and redox reactions and can also affect groundwater chemistry in terms of pH, redox potential, dissolved organic carbon, and trace element concentrations. Accurate determination and identification of hydrocarbon contaminants requires advanced analytical methods like gas chromatography, GC–MS, and fluorescence spectroscopy, complemented with isotopic analysis and microbial tracers, which provide insights into sources of contamination and biodegradation pathways. The presence of hydrocarbons in groundwater is a matter of environmental concern but can also valuable data for petroleum exploration, tracing subsurface reservoirs and seepage pathways. This paper refers to the basic need for geochemical investigations combined with advanced detection techniques for successful regulation of thermal–mineral groundwater quality. This contributes towards successful sustainable hydrocarbon resource exploration and water resource conservation, with emphasis on the relationship between groundwater quality and hydrocarbon exploration. The study points out the significance of continuous observation of thermal mineral waters to identify their connection with the specific hydrocarbons of each study area. Full article

The Sanandaj–Sirjan Zone and Zagros Fold–Thrust Belt in Iran host numerous Mediterranean-type karst bauxite deposits; however, their formation mechanisms and critical raw material potential remain ambiguous. This study combines mineralogical and geochemical analyses to explore (1) the formation of authigenic minerals, (2) the role of microbial organic processes in Fe cycling, and (3) the assessment of their critical raw materials potential. Mineralogical analyses of the Late Cretaceous Daresard and Middle–Late Permian Yakshawa bauxites reveal distinct horizons reflecting their genetic conditions: Yakshawa exhibits a vertical weathering sequence (clay-rich base → ferruginous oolites → nodular massive bauxite → bleached cap), while Daresard shows karst-controlled profiles (breccia → oolitic-pisolitic ore → deferrified boehmite). Authigenic illite forms via isochemical reactions involving kaolinite and K-feldspar dissolution. Scanning electron microscopy evidence demonstrates illite replacing kaolinite with burial depth enhancing crystallinity. Diaspore forms through both gibbsite transformation and direct precipitation from aluminum-rich solutions under surface conditions in reducing microbial karst environments, typically associated with pyrite, anatase, and fluorocarbonates under neutral–weakly alkaline conditions. Redox-controlled Fe-Al fractionation governs bauxite horizon development: (1) microbial sulfate reduction facilitates Fe³⁺ → Fe²⁺ reduction under anoxic conditions, forming Fe-rich horizons, while (2) oxidative weathering (↑Eh, ↓moisture) promotes Al-hydroxide/clay enrichment in upper profiles, evidenced by progressive total organic carbon depletion (0.57 → 0.08%). This biotic–abiotic coupling ultimately generates stratified, high-grade bauxite. Finally, both the Yakshawa and Daresard karst bauxite ores are enriched in critical raw materials. It is worth noting that the overall enrichment appears to be mostly driven by the processes that led to the formation of the ores and not by the chemical features of the parent rocks. Divergent bauxitization pathways and early diagenetic processes—controlled by paleoclimatic fluctuations, redox shifts, and organic matter decay—govern critical raw material distributions, unlike typical Mediterranean-type deposits where parent rock composition dominates critical raw material partitioning. Full article

The Paleoproterozoic Kovdozero complex, one of largest in the Fennoscandian Shield, was emplaced in a peripheral region of the SB–TB–LBB (Serpentinite Belt–Tulppio Belt–Lapland–Belomorian Belt) megastructure. Coronitic rocks of ultrabasic–basic compositions, investigated along a cross-section in the Gabrish area, are members of a cryptically layered series. They crystallized from the northern margin inward, as indicated by variations in mineral compositions and geochemical trends. Unsteady conditions of crystallization arose because of uneven cooling of the shallowly emplaced complex. Rapid drops in temperature likely caused the forced deposition of different generations of variously textured pyroxenes and chromian spinel or resulted in the unique development of narrow recurrent rims of orthopyroxene hosted by olivine. The unstable conditions of crystallization are expressed by (1) textural diversity, (2) broad variations in values of Mg#, and (3) virtual presence of double trends of Mg# as a function of distance. The coronitic textures are intimately associated with interstitial grains of plagioclase (An_≤65), also present as relics in a rim of calcic amphibole. The coronas are results of (1) rapid cooling leading to unsteady conditions of crystallization, which caused the sudden cessation of olivine crystallization and the development of an orthopyroxene rim on olivine and (2) an intrinsic enrichment in H₂O (and essential Cl in scapolite) coupled with a progressive accumulation of Al and alkalis, giving rise to fluid-rich environments in the intercumulus melt at advances stages of crystallization. These processes were followed by deuteric composite rims of calcic amphibole and reaction of fluid with early rims or grains of pyroxenes and late plagioclase. The coronitic sequences Ol → Opx → Cpx → calcic Amp → Pl (plus Qz + Mca) observed at a microscopic scale reproduce, in miniature, the normal order of crystallization in an ultrabasic–basic complex. A composite orthopyroxene + calcic amphibole corona resembles some rocks in complexes of the Serpentinite Belt. The prominence of such coronas may well be characteristic of the crystallization of komatiite-derived melts. Full article

A thorough understanding of the chemistry involved in reinjecting heat-depleted geothermal water into poorly consolidated sandstone is vital for the effective design of treatments targeting subsurface rock formations. The intricate chemical interactions occurring within sandstone systems can result in the dissolution of certain minerals and the subsequent precipitation of others, which may significantly contribute to damage within the formation. This process can alter the physical properties of the rock, potentially leading to reduced permeability and other challenges in resource extraction. Thus, it is imperative to monitor not only the concentration of various chemical species present in the geothermal water and sandstone, but also the spatial distribution of these geochemical reactions. By doing so, we can better predict and mitigate their potential adverse effects on rock formations, ensuring the long-term success and efficiency of geothermal energy extraction and other subsurface activities. In this study, we conducted laboratory experiments using both model and natural formation waters, as well as rock samples, to investigate water–rock interactions in a sandstone reservoir in the Szentes area of Hungary. Geochemical models were run with two different thermodynamic databases to simulate laboratory experiments, predict the effects of heat-depleted geothermal water reinjection into the reservoir, and assess predictions of different geochemical databases. Our study shows that calcite dissolves while quartz, kaolinite, and dolomite form. Other mineral reactions, however, remain less certain. The PHREEQC database indicates chlorite dissolution along with the formation of small amounts of feldspars and hematite, whereas the Thermoddem database predicts montmorillonite dissolution and chlorite precipitation. The reservoir porosity and permeability are expected to change over time as a result of mineral reactions. Modeling results, however, indicate negligible porosity changes as the reservoir reaches equilibrium state. The general concept proposed here, which focuses on the geochemical properties of the reinjected water and reservoir, provides a framework for detailed analysis of the geothermal system—a critical step for ensuring sustainable geothermal operations. Full article

Metabolism, the network of biochemical reactions that powers life, arose under conditions radically different from those on Earth today. Investigating its origins reveals how initially simple chemical processes gradually integrated nucleic acid and then protein catalysts, becoming progressively more complex and regulated until they evolved into the enzyme-rich systems observed in modern organisms. Here, we integrate multiple perspectives on the origin of metabolism, focusing primarily on an evolutionary trajectory from an RNA-based world, where ribozymes, metal ions, coenzymes, small peptides, and other small organic molecules worked in concert, to enzyme-driven metabolic networks. We also address the longstanding debates on whether these early metabolic pathways were largely autotrophic or heterotrophic, and consider so-called “pre-metabolisms” (non-enzymatic networks) as an alternative conceptual framework. We discuss key examples such as the Wood–Ljungdahl (W–L) pathway and the reverse tricarboxylic acid (TCA) cycle, both posited to function under early Earth conditions. Finally, we examine how the environment (e.g., minerals, clays, hydrothermal vents) shaped early metabolism, describe unresolved questions about the Last Common Ancestor’s catalytic repertoire and propose future directions that link geochemical insights with molecular biology and synthetic approaches. Full article

The degradation of deadwood is a vital ecological process for geochemical cycling and biodiversity conservation, with two main routes of fungal degradation: brown and white rot. Brown rot fungi cause severe destruction of wood cellulose and lead to brown and modified lignin residue. Fomitopsis pinicola is a typical brown rot fungus with a distinct host preference for coniferous trees. The mechanisms through which this fungus degrades coniferous and broadleaf wood remain poorly understood. Therefore, in this study, a 60-day cultivation experiment involving F. pinicola growing on deadwood strips of Pinus koraiensis and Betula platyphylla separately was performed. A comparative transcriptome analysis was carried out to explore the mechanisms underlying the differences in degradation, in terms of both physicochemical properties and transcriptomic data. The findings revealed that the host preference of F. pinicola resulted in the more efficient degradation of coniferous wood than broadleaf wood, accompanied by higher gene expression levels. GO enrichment analysis indicated that this preference was primarily associated with the hydrolytic enzyme family and processes related to the Fenton reaction, which is characteristic of brown rot fungi. Furthermore, the KEGG pathways showed that the DEGs were enriched in mainly included histidine metabolism, fatty acid degradation, and so on, indicating underlying carbohydrate and lipid metabolism processes. These results support P. pinicola’s strong ability to degrade the deadwood lignin of P. koraiensis, reflecting its adaptive evolution in host selection and choice of different ecological niches. Full article

Gejiu, a prominent tin–polymetallic ore district, is distinguished by its diverse mineral complexes. However, the genesis of these complexes and their relationship with mineralization remain inadequately studied. This study utilized whole-rock geochemical analyses to investigate the magmatic sources and petrogenesis of different complex types, aiming to elucidate their implications for tin–polymetallic mineralization. The results indicate that gabbro, monzonite, diorite, and syenite are derived from enriched mantle-derived magmas and have undergone limited crustal contamination. Granites are formed by the mixing of mantle- and crust-derived magmas, involving both physical mixing and chemical diffusion. Major and trace element characteristics suggest that the Gejiu granites predominantly exhibit features of both A-type and I-type granites. Harker diagrams and whole-rock indicators, such as Nb/Ta and Zr/Hf, suggest that granites experienced a two-stage fractional crystallization process, ultimately forming highly evolved biotite monzogranite. Fractional crystallization is the dominant mechanism controlling magmatic evolution, while high-temperature melting and biotite decomposition reactions are critical for the formation of the world-class Gejiu tin deposit. Full article

The Mesoproterozoic alkaline Grønnedal-Íka complex (1325 ± 6 Ma) is intruded into old Archean gneissic bedrock between Ikka Fjord and Kangilinnguit (Grønnedal) by Arsuk Fjord in Southwestern Greenland. This 8 × 2.8 km oval-shaped complex constitutes the oldest part of the Gardar Province, representing a failed continental rift across southern Greenland. It comprises outer rings of mainly nepheline syenites with a central plug of Fe- and Ca-rich carbonatites. Here, we present petrological data on the syenites and carbonatites combined with geochemical modelling of groundwater percolating through the Grønnedal-Íka complex and the secondary minerals and fluid chemistry arising from these fluid–rock reactions. The results show that modelling using input data of (1) meteoric water in a closed system with respect to atmospheric CO₂ can (2) dissolve the primary minerals of the syenites and carbonatites and (3) simulate the fluid chemistry of the natural sodium carbonate springs of 3–4 °C and pH 10–11 seeping up through fractures at the bottom of Ikka Fjord, which (4) leads to the deposition of nearly a thousand tufa columns of the cold carbonate mineral ikaite (CaCO₃•6H₂O). Our results thereby support the geochemical relationship between fluid–rock reactions inside the Grønnedal-Íka alkaline complex and the precipitation of ikaite in the shape of submarine tufa columns in Ikka Fjord. The modelling indicates that the groundwater itself can be supersaturated with respect to ikaite and provide the seed crystals that lead to the columnar growth of ikaite up to 20 m tall in the seawater of Ikka Fjord. Full article

The Luhai uranium deposit is a large-scale uranium deposit newly discovered in recent years through comprehensive prospecting methods. It is located in the Basaiqi Paleochannel Uranium metallogenic belt of the Erlian Basin and is characterized by its shallow burial and large scale. This paper provides new data on the genetic processes of sandstone-type uranium mineralization through sedimentological and geochemical environmental indicators (such as Fe³⁺/Fe²⁺, organic carbon, total sulfur, etc.), analysis of C-O isotopes of carbonate cements and H-O isotopes of groundwater, and geochemical and mineralogical studies of uranium minerals, iron–titanium oxides (involving backscatter analysis, micro-area chemical composition determination, and elemental surface scanning), and organic matter. Sedimentological analysis shows that the ore- bearing layer in the upper member of the Saihan Formation developed a braided channel within floodplain subfacies, which control the distribution of uranium ore bodies. Uranium mineralogical observations, geochemical environmental indicators, and organic geochemical data indicate that the main reducing agents related to mineralization are pyrite, terrestrial plants, and deep-sourced oil and gas. The δD values of groundwater in the ore-bearing layer range from −95.34‰ to −90.68‰, and the δ¹⁸O values range from −12.24‰ to −11.87‰. For calcite cements, the δ¹⁸O_V-PDB values range from −24‰ to −11.5‰, and the δ¹⁸_OV-SMOW values range from 6.2‰ to 19‰. It was determined that the ore-forming fluid is mainly surface fresh water that entered the strata during the tectonic uplift stage, with local mixing of deep-sourced brine. Based on these data, the main modes of uranium mineralization in the paleochannel were obtained as follows: (1) Redox mineralization occurs due to the reducing medium within the sand body itself and the reduction caused by deep- sourced oil and gas generated from the Tengge’er and Arshan Formations. (2) Mineralization is achieved through the mixing of fluids from different sources. Furthermore, a genetic model related to uranium mineralization in the paleochannels of the Luhai area has been established: favorable uranium reservoirs were formed during the sedimentary period, and during the post-sedimentary stage, reverse structures promoted redox reactions and fluid-mixing-induced mineralization. The research findings can provide guidance for the exploration of paleochannel sandstone-type uranium deposits in other areas of the Erlian Basin. Full article

This study investigates the combined effects of impurities in CO₂ stream, geochemistry, water salinity, and wettability alteration on oil recovery and CO₂ storage in carbonate reservoirs and optimizes injection strategy to maximize oil recovery and CO₂ storage ratio. Specifically, it compares the performance of pure CO₂ water-alternating gas (WAG), impure CO₂-WAG, pure CO₂ low-salinity water-alternating gas (LSWAG), and impure CO₂-LSWAG injection methods from perspectives of enhanced oil recovery (EOR) and CO₂ sequestration. CO₂-enhanced oil recovery (CO₂-EOR) is an effective way to extract residual oil. CO₂ injection and WAG methods can improve displacement efficiency and sweep efficiency. However, CO₂-EOR has less impact on the carbonate reservoir because of the complex pore structure and oil-wet surface. Low-salinity water injection (LSWI) and CO₂ injection can affect the complex pore structure by geochemical reaction and wettability by a relative permeability curve shift from oil-wet to water-wet. The results from extensive compositional simulations show that CO₂ injection into carbonate reservoirs increases the recovery factor compared with waterflooding, with pure CO₂-WAG injection yielding higher recovery factor than impure CO₂-WAG injection. Impurities in CO₂ gas decrease the efficiency of CO₂-EOR, reducing oil viscosity less and increasing interfacial tension (IFT) compared to pure CO₂ injection, leading to gas channeling and reduced sweep efficiency. This results in lower oil recovery and lower storage efficiency compared to pure CO₂. CO₂-LSWAG results in the highest oil-recovery factor as surface changes. Geochemical reactions during CO₂ injection also increase CO₂ storage capacity and alter trapping mechanisms. This study demonstrates that the use of impure CO₂-LSWAG injection leads to improved oil recovery and CO₂ storage compared to pure CO₂-WAG injection. It reveals that wettability alteration plays a more significant role for oil recovery and geochemical reaction plays crucial role in CO₂ storage than CO₂ purity. According to optimization, the greater the injection of gas and water, the higher the oil recovery, while the less gas and water injected, the higher the storage ratio, leading to improved storage efficiency. This research provides valuable insights into parameters and injection scenarios affecting enhanced oil recovery and CO₂ storage in carbonate reservoirs. Full article

Presently, geothermal resources have been globally recognized as an indispensable component of the energy system due to their sustainability. However, previous studies on geothermal reservoirs focus primarily on single reservoirs, lacking a systematic investigation of composite geothermal reservoirs. The geothermal reservoirs in the northwestern Shandong geothermal area in China are primarily of sandstone and karst types, characterized by extensive distributions, shallow burial depths, high water temperatures, and high water abundance, holding considerable potential for exploitation. This study explored the hydrochemical, isotopic, and circulation characteristics of geothermal fluids in the composite geothermal reservoirs in the study area using methods like hydrogeochemistry and geothermal geology. The purpose is to determine the geochemical differences in geothermal fluids across the composite geothermal reservoirs and provide scientific support for subsequently efficient and sustainable exploitation and utilization of geothermal resources in the study area. The composite geothermal reservoirs in the study area are composed of porous sandstone geothermal reservoirs (also referred to as sandstone reservoirs) in the upper part and karst-fissured geothermal reservoirs (also referred to as karst reservoirs) in the lower part. The results show that the geothermal fluids in the sandstone and karst reservoirs are primarily of Na-Cl-SO₄ and Na-Ca-Cl-SO₄ types, respectively. The hydrochemical composition of geothermal fluids in the karst reservoirs is principally influenced by the precipitation–dissolution equilibrium of carbonate and sulfate minerals, while that in the sandstone reservoirs is predominantly influenced by the precipitation–dissolution equilibrium of carbonate and silicate minerals, as well as cation exchange reactions. The temperatures of the karst reservoirs were calculated at 52.9–82.09 °C using geothermometers. Given the cold-water mixing ratios range from 89% to 96%, the corrected reservoir temperatures vary from 200 to 225 °C. In contrast, the temperatures of the sandstone reservoirs were calculated at 60.54–85.88 °C using geothermometers. These reservoirs exhibit cold water mixing ratios ranging from 85% to 90%, and their corrected reservoir temperatures vary from 150 to 200 °C accordingly. The circulation depths of geothermal fluids in the karst and sandstone reservoirs range from 1107.28 to 1836.69 m and from 1366.60 to 2102.29 m, respectively. The study area is primarily recharged by meteoric water from Mount Tai and the Lushan and Yishan mountains (collectively referred to as the Tai-Lu-Yi mountains) to the southeast of the study area. Investigating the differences in geochemical characteristics of geothermal fluids in composite geothermal reservoirs in the study area is significant for balancing the exploitation and supply of geothermal resources, optimizing the exploitation and utilization modes, and promoting the efficient and sustainable exploitation and utilization of geothermal resources in the study area. Full article

This research evaluates the mineral ions and their concentrations in formation water from five well samples of the Bibi Hakimeh oil field (Iran). The analysis reveals the presence of calcium (Ca²⁺), sodium (Na⁺), and magnesium (Mg²⁺) cations, as well as sulfate (SO₄²⁻), bicarbonate (HCO₃⁻), and chloride (Cl⁻) anions, which are soluble in water within the Bibi Hakimeh oil formation. Furthermore, mineral deposits of CaSO₄, CaSO₄.2H₂O, CaCO₃, and MgCO₃ are investigated and predicted using StimCADE 2 software. The findings highlight the significant chemical precipitation of calcium sulfate and calcium carbonate mineral deposits under the operating conditions of the Bibi Hakimeh oil well. The geochemical composition of the formation waters is discussed to understand the equilibrium conditions and possible influence of the physical parameters. Additionally, this study examines the interaction between rock and water of the Bibi Hakimeh formation, revealing a notable correlation between the concentration of calcium and magnesium ions and the water–rock reaction in this field. Full article

The Biggenden gold-bearing Fe skarn deposit in southeast Queensland, Australia, is a calcic magnetite skarn that has been mined for Fe and gold (from the upper portion of the deposit). Skarn has replaced volcanic and sedimentary rocks of the Early Permian Gympie Group, which formed in different tectonic settings, including island arc, back arc, and mid-ocean ridge. This group has experienced a hornblende-hornfels grade of contact metamorphism due to the intrusion of the Late Triassic Degilbo Granite. The intrusion is a mildly oxidized I-type monzogranite that has geochemical characteristics intermediate between those of granitoids typically associated with Fe-Cu-Au and Sn-W-Mo skarn deposits. The skarn mineralogy indicates that there was an evolution from prograde to various retrograde assemblages. Prograde garnet (Adr_11-99Grs_1-78Alm_0-8Sps_0-11), clinopyroxene (Di_30-92Hd_7-65Jo_0-9), magnetite, and scapolite formed initially. Epidote and Cl-bearing amphibole (mainly ferropargasite) were the early retrograde minerals, followed by chlorite, calcite, actinolite, quartz, and sulfides. Late-stage retrograde reactions are indicated by the development of nontronite, calcite, and quartz. Gold is mainly associated with sulfide minerals in the retrograde sulfide stage. The fluids in equilibrium with the ore-stage calcites had δ¹³C and δ¹⁸O values that indicate deposition from magmatically derived fluids. The calculated δ¹⁸O values of the fluids in equilibrium with the skarn magnetite also suggest a magmatic origin. However, the fluids in equilibrium with epidote were a mixture of magmatic and meteoric water, and the fluids that deposited chlorite were at least partly meteoric. δD values for the retrograde amphibole and epidote fall within the common range for magmatic water. Late-stage chlorite was deposited from metasomatic fluids depleted in deuterium (D), implying a meteoric water origin. Sulfur isotopic compositions of the Biggenden sulfides are similar to other skarn deposits worldwide and indicate that sulfur was most probably derived from a magmatic source. Based on the strontium (⁸⁷Sr/⁸⁶Sr) and lead (²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb) isotope ratios, the volcanic and sedimentary rocks of the Gympie Group may have contributed part of the metals to the hydrothermal fluids. Lead isotope data are also consistent with a close age relationship between the mineralization at Biggenden and the crystallization of the Degilbo Granite. Microthermometric analysis indicates that there is an overall decrease in fluid temperature and salinity from the prograde skarn to retrograde alterations. Fluid inclusions in prograde skarn calcite and garnet yield homogenization temperatures of 500 to 600 °C and have salinities up to 45 equivalent wt % NaCl. Fluid inclusions in quartz and calcite from the retrograde sulfide-stage homogenized between 280 and 360 °C and have lower salinities (5–15 equivalent wt % NaCl). In a favored genetic model, hydrothermal fluids originated from the Degilbo Granite at depth and migrated through the shear zone, intrusive contact, and permeable Gympie Group rocks and leached extra Fe and Ca and deposited magnetite upon reaction with the adjacent marble and basalt. Full article