Reconstructing the history of tight gas accumulation from the Shixi block, eastern Ordos Basin: Insights from fluid inclusion analysis.

Fate of fluid inclusions after high- to ultrahigh-temperature metamorphism and implications for multiphase fluid inclusions as a petrological tool

Fluid-rich (cloudy/fibrous) diamonds host millions of micrometric fluid inclusions that can reveal the nature of diamond-forming media. Mineral inclusions in fluid-rich diamonds are nano to micrometric making structural and chemical characterization of the different phases difficult. Consequently, limited work has been done determining the pressures, temperatures and depths at which such inclusions form. The relationship between such conditions and those of fluid-rich diamond formation remains unclear. We report the use of micro-electron diffractometry to identify and anisotropically refine the structure of a nanometric åkermanite inclusion in a fluid-rich diamond from South Africa. Additional nanometric Ba/Sr-carbonate inclusions were detected. FTIR analyses revealed a highly aggregated, gem-quality core surrounded by a rim rich in high-density fluid (HDF) inclusions from which åkermanite crystallized. Åkermanite formed during HDF depressurization due to kimberlite eruption or exhumation. In the latter scenario, åkermanite constrained diamond formation to a minimum temperature of1000 °C at ∼140 km depth (~4.6 GPa). Analysis of the HDFs reveal low-Mg carbonatitic to silicic compositions. The high BaO and Cl and the δ13C values of the diamond (-5.72 to -7.84 ‰) are attributed to formation via penetration of saline fluid into an eclogite, related to subduction of carbonated altered oceanic crust.

Fluid evolution and ore precipitation of the Shanhu quartz-vein type W-Sn deposit in South China: constraints from fluid inclusions and oxygen isotopes

Source of ore-forming fluid and metallogenic mechanism of the Lailishan tin deposit in western Yunnan, SW China: Constraints from fluid inclusions and H–O–S isotopes

This study presents a data-informed convolutional neural network (CNN) for identifying fluid-filled (e.g., water) inclusions in two-dimensional (2D) solids. To generate training data, we simulate the propagation of elastic waves in structures containing fluid inclusions using Ansys Mechanical. To provide structural details, we introduce a gridwise classification method that reconstructs the targeted domain containing arbitrary fluid-filled inclusions by creating a 2D grid-structured image. This work produces training data comprising input-layer features (i.e., measured wave responses) and output-layer features (i.e., gridwise maps labeling each grid element as solid or fluid). The CNN is trained on these simulated data sets to classify grid elements based on wave responses recorded at surface sensors, and clusters of predicted fluid grid elements are used to reconstruct fluid-filled inclusions. Numerical results show that the proposed CNN can effectively detect fluid inclusions of various locations, sizes, and shapes. We also present parametric studies of factors such as the number of sensors, the size of the training data sets, and excitation frequency, providing a comprehensive analysis of their effect on detection performance.

Removal of fluid inclusions from vein quartz by stepwise chlorination roasting and mechanism study

The Mahu Sag, a hydrocarbon-rich depression within the Junggar Basin, hosts significant petroleum resources. Here, the Permian Fengcheng Formation shale oil reservoirs have emerged as a primary exploration target. This study investigates fracture development within these alkaline lacustrine shales, a critical factor governing hydrocarbon migration and accumulation. Through integrated petrographic and geochemical analyses, we elucidate a multifactorial fracture formation mechanism driven by the interplay of alkaline minerals, stress, and fluids. Two distinct fracture types were identified: bedding-complex fracture veins (BCFVs) and Y-shaped high-angle fracture veins (Y-HFVs). Both fracture types result from alkaline fluid–rock interactions, which induce fracture opening along specific orientations, alter fracture angles, and control aperture width and final morphology. Alkaline mineral assemblages further influence fracture evolution via dissolution–precipitation cycles. Concurrently, these assemblages preserve hydrocarbons by inhibiting the thermal maturation of organic matter, as evidenced by variations in fluid inclusion fluorescence. The fracture networks act as crucial migration pathways, with the BCFV containing higher-maturity hydrocarbons (indicated by blue-green fluorescence) and the Y-HFV retaining less mature fluids (indicated by yellow-green fluorescence). This study presents the first systematic characterization of the multifactorial controls on fractures in alkaline lake environments, proposing a cooperative “alkaline minerals–stress–fluids” mechanism. These findings provide a new framework for understanding fracture development in alkaline lacustrine shales and offer valuable insights for shale oil exploration in analogous depositional settings.

The northern part of the Great Xing’an Range in China hosts a prominent Au mineralization belt, where Mesozoic clastic rock-hosted Au deposits represent the mineralization type. A study of the Baoxinggou Au deposit in this region might provide new perspectives on the mineralization mechanisms of these Mesozoic clastic-rock-hosted Au deposits. This study investigated the age of mineralization, origins and evolution of the ore-forming fluids, and sources of the ore-forming materials in this deposit. Rubidium–Sr dating of sulfides yielded a mineralization age of 119 ± 2 Ma. Fluid inclusion analyses revealed that the ore precipitated from fluids with temperatures of 105–415 °C and salinities of 4.3–8.8 wt.% NaCl equivalent. Hydrogen and O isotopic data show that the ore-forming fluids were of magmatic origin and, during mineralization, the proportion of meteoric waters increased gradually and eventually dominated the late mineralization stage. Fluid mixing was the primary ore-forming mechanism. Sulfur isotopic data for pyrite and chalcopyrite (δ34SV–CDT = −4.35‰ to −0.91‰) and Pb isotopic ratios (206Pb/204Pb = 18.429–18.477; 207Pb/204Pb = 15.581–15.591) indicate the ore-forming materials were magmatic in origin, with a similar source as an Early Cretaceous diorite and mixed crust–mantle materials. The results indicate the Baoxinggou Au deposit is a magmatic–hydrothermal deposit.

The Huoyanshan Cu-Zn volcanogenic massive sulfide (VMS) deposit, located in the North Qilian Orogenic Belt, China, is of significant economic importance. This study provides new constraints on the ore-forming processes through high-resolution in situ trace element and sulfur isotope analyses of pyrite and sphalerite using LA-(MC)-ICP-MS. Petrographic and geochemical investigations identified three distinct generations of pyrite (Py l to Py III). Early-stage Py I and Py II are characterized by high trace element contents (Au, As, Bi, Cu, Pb), elevated Co/Ni ratios (>1–10), and enriched δ34S values (+4.98‰ to +7.47‰). These signatures indicate precipitation from high-temperature, reduced magmatic–hydrothermal fluids influenced by thermochemical sulfate reduction (TSR). Late-stage Py IIl exhibits markedly lower Co/Ni ratios (<0.1) and lighter δ34S values (+3.72‰ to 3.89‰). This geochemical shift reflects a transition toward a cooler, more oxidized environment driven by the incursion and mixing of ambient seawater as the hydrothermal system waned. Trace element geochemistry of sphalerite reveals an average crystallization temperature of 265.8 °C (derived from the “GGIMFis” geothermometer), consistent with fluid inclusion data and representing a thermal “snapshot” of the waning hydrothermal stage. Systematic discriminant analysis using Ga/In, Ge/In, and Co-Ni-As systematics further confirms a strong magmatic–hydrothermal affiliation.

ABSTRACT Organic fluid activity and carbonate alteration are developed in the Lower Cretaceous uranium‐bearing red beds in the southwestern Ordos Basin. To elucidate the origin of organic‐related carbonate alteration, this study investigated the mineralisation through core alteration observations, spectral core scanning, scanning electron microscopy, and electron probe microanalysis. In addition, fluid inclusions were characterised using microscopy and microthermometry. The results indicate that: (1) Secondary carbonate alteration commonly occurs within bleached zones in mineralised sandstone intervals and surrounding rocks of the Luohe Formation, accompanied by evident hydrocarbon shows. Carbonate minerals exhibit paragenetic and associative relationships with uranium minerals and pyrite. (2) The homogenisation temperatures of organic inclusions in secondary calcite cements of mineralised sandstone range from 60°C to 165°C, with salinities between 2% and 23.18% NaCl eq. The distribution of secondary carbonate alteration is spatially correlated with organic fluid activity, and the extent of alteration shows a positive correlation with variations in the temperature–salinity conditions of the organic inclusions. It is concluded that the association of secondary carbonate alteration with organic fluids, bleaching, pyritisation, and uranium mineralisation may be attributed to the dual alteration of sandstone by moderately acidic and reducing organic fluids at low to medium temperatures.

We evaluated a microwave imaging prototype to estimate bone-marrow edema in ex vivo bovine samples, using computed tomography (CT) and injected volumes as references. Seven samples comprising distal/proximal halves of two femurs and two humeri were imaged before/after injection of iodine-enhanced gel into drilled holes (Ø 2 mm, depth 8 mm; 25.13 μL/hole). A 4 × 4 open-ended coaxial probe (OECP) array was used over 16 positions with four 90° rotations, simulating a 16 × 16 array of 256 antennas. Raw S11 scattering parameters across a 2.25-3.00 GHz sweep were calibrated and inverted using the Stuchly model with target permittivity at 2.5 GHz. Each OECP antenna was characterized to define its effective penetration depth and equivalent lateral footprint. Upscaled permittivity maps were then generated via nonlinear interpolation, while fluid estimation was computed leveraging a refractive index mixing model. Microwave estimated volumes were repeatable across the four rotations (mean coefficient of variation (CV) 2.8%; mean intraclass correlation coefficient (ICC) 0.999). Microwave estimates tracked the injected volumes with significant correlation (r = 0.81, p = 0.027) and moderate-to-good concordance (Lin's concordance correlation coefficient [CCC] 0.70), with a small bias (+12.4%; 95% limits of agreement (LoA) -17.4% to +42.2%; mean absolute percent error 12.4%). Agreement with CT-derived volumes was weaker (r = 0.58, p = 0.169; CCC 0.23) with a larger bias (+40.9%; 95% LoA -10.3% to +92.2%). Microwave imaging allowed for detecting and quantifying small, μL scale, fluid inclusions within ex vivo long-bone halves, using OECP-based arrays. Non-ionizing microwave imaging may represent a feasible complementary approach for imaging and quantitative assessment of fluid-related distributions in musculoskeletal tissues. A 16-element OECP microwave imaging array allows spatially resolved estimation of fluid-simulated inclusions in ex vivo bovine long bones. Experimental characterization of OECP antenna sensitivity enables resolution upscaling of dielectric permittivity maps. Fluid volumes derived from microwave permittivity maps show significant correlation with injected reference volumes (r = 0.81).

The Dongsheng Gas Field, a giant tight-gas field in the northern margin of the Ordos Basin in China, has the Lower Permian Shihezi Formation (P2x1) as the main gas production layer, with tight-sandstone reservoirs (average porosity and permeability of 8.6% and 0.82 mD, respectively). This study integrated basin modelling, fluid inclusion analysis, thin slice identification, and digital simulations of gas charging to explore reservoir densification, hydrocarbon charging history and accumulation dynamics. A net force concept during tight gas accumulation (Pn = Pd - Pr, where Pd is the overpressure of source rocks and Pr is the capillary force under 50% gas saturation) was established. Numerical simulations showed: Pn > 10.39MPa (rapid charging) indicates commercial gas layers; Pn < 8.88MPa (breakthrough stage) indicates dry/gas-bearing layers. The P2x1 reservoirs experienced 1 oil-gas and 2 gas charging episodes (230-180Ma, 180-120Ma, 120-80Ma), evidenced by source rocks, bitumen, inclusions and salinity variations. The 120-80Ma episode (corresponding to post-120Ma hydrocarbon peak) is the key accumulation period. During this key period, reservoirs south of the Poerjianghaizi Fault were tight, while the SGH zone had 13% porosity. Three charging stages (breakthrough: 6.81-12.83MPa; rapid: 6.02-27.46MPa; saturation: 24.86-49.96MPa) were identified. Third-stage Pn and gas saturation enable gassiness prediction. This study provides insights into tight gas accumulation mechanisms and gas distribution prediction.

Arc magmas are enriched in sulfur relative to mid-ocean ridge basalts, commonly attributed to slab-derived sulfur inputs during subduction. However, the contribution of slab fluids remains debated because sulfur concentrations in sub-arc fluids have not been directly measured. Here we quantify sulfur in slab-derived fluids preserved as multiphase fluid inclusions composed of H2O, calcite, and chalcopyrite in omphacite from ultrahigh-pressure eclogites in the Sumdo orogenic belt. Three-dimensional Raman spectroscopy reveals high sulfur concentrations averaging ~6 wt.%. Mass-balance calculations indicate that such fluids can efficiently enrich the mantle wedge and supply up to ~70% of the sulfur emitted by arc volcanism. We further suggest that chalcopyrite formed through post-entrapment reduction of oxidized sulfur species by host omphacite, followed by precipitation with co-entrapped copper and iron. Our findings identify sub-arc depths as a critical window for slab sulfur release and provide key constraints on deep sulfur cycling and copper mobilization in arc systems.

The Siahouki Cu–Au–Ag deposit is located c . 50 km NW of Bam in the southern Urumieh–Dokhtar magmatic arc. The mineralization is hosted by Eocene dacitic and andesitic tuffs that have undergone extensive silicic, argillic and propylitic alteration. Ore deposition primarily occurs in NW–SE-trending, fault-controlled quartz–carbonate ± sulfide veins. Based on field observations, petrography and microanalytical data, five hydrothermal stages are defined: stage I, early distal argillic–propylitic alteration; stage II, the principal Cu–Au–Ag stage; stage III, late Au enrichment; stage IV, mineralization dominated by calcite; and stage V, supergene oxidation and secondary enrichment. Fluid inclusions show homogenization temperatures of 112–331°C and salinities of 0.9–10.1 wt% NaCl equiv. Stable isotope constraints confirm a mixed magmatic–meteoric origin for the ore-forming fluids. The sulfur isotope compositions of pyrite, chalcopyrite and tetrahedrite ( δ 34 S = −5.4 to +0.5‰) indicate a dominantly magmatic sulfur source. The oxygen isotope values ( δ 18 O fluid = −1.4 to +1.8‰) calculated from quartz–water equilibrium indicate significant meteoric water mixing. The carbon isotopes ( δ 13 C = −0.8 to +0.0‰) from hydrothermal calcite further suggest limited carbonate wall rock interaction. Collectively, these data indicate that ore deposition was controlled by episodic boiling and fluid mixing during the transition from magmatic–hydrothermal to meteoric-dominated conditions, defining the Siahouki deposit as an intermediate-sulfidation epithermal system.

The exsolution mechanism of magmatic fluids and their metal migration capacity: example from Huanaote Pb-Zn-polymetallic deposit in Inner Mongolia, China

Genesis and quality evaluation study of high-purity quartz deposit hosted in NYF-type granite pegmatite in the Central Asian Orogenic Belt, NW China

The Bou Skour Cu–Ag deposit (Anti-Atlas. Morocco): Evidence of a porphyry copper system from mineralogy, alteration, geochemistry, isotopes, and fluid inclusions

Assessing the plausibility of direct constraints on ancient atmospheric <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"> <mml:mrow> <mml:msub> <mml:mi>P</mml:mi> <mml:msub> <mml:mrow> <mml:mi mathvariant="italic">CO</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msub> </mml:msub> </mml:mrow> </mml:math> from fluid inclusions in halite: a theoretical and experimental approach

Fluid sources and evolution in the As (±Sb) epithermal Matra deposit (Alpine Corsica, France): Constraints from fluid inclusions, gas compositions, and stable isotopes (C–O)