Search

In the complex fluid environment of subterranean rocks, some mineral components are easily hydrated, which hinders the accumulation and utilization of hydrocarbon. However, the nature and distribution of these key substances remain unclear. This study aims to provide a fresh perspective on the substances that impede the storage and extraction of hydrocarbon of the world's largest conglomerate oilfield. Using a variety of qualitative, semi-quantitative, and quantitative methods, including X-ray diffraction, secondary electron imaging, elemental spectroscopy, and Tescan-Integration-Mineral-Analyzer (TIMA), our experimental results show: (1) For the first time, water-sensitive clay minerals on the surfaces of gravel particles in tight conglomerates in China have been identified. Although the matrix composition contains less than 4.2% clay minerals on average, certain gravels contain over 72.7% clay minerals. These clay minerals are primarily composed of smectite, which is highly water sensitive, followed by chlorite, which poses significant challenges to hydrocarbon extraction; (2) The distribution of clay minerals on a single gravel surface is relatively uniform, enabling their interaction with fracturing fluid and exacerbating reservoir degradation. The total content of the illite-smectite mixture in the conglomerate can reach approximately 12%, with skeleton particles (gravel) containing more than 30% of this mixture. There are significant differences in the degree of clayiness among different types of gravel, which can be classified as high clayey, medium clayey, or low clayey. The evenly distributed illite-smectite mixed layer on the gravel surface allows complete contact with the fracturing fluid, resulting in severe reservoir damage; (3) Gravel particles with a size range of 8.88 μm–10.73 μm contain the highest concentration of illite-smectite mixture, which is identified as a major factor contributing to reservoir damage. • The storage and mobility of hydrocarbon in the subsurface are intricately linked to mineralogy. • The illite-smectite mixtures significantly impede the oil exploitation in tight conglomerates. • The proportion of illite-smectite mixture on skeleton particles, commonly referred to as gravel, can exceed 30%. • Gravels ranging in size from 8.88 μm to 10.73 μm exhibit the highest concentration of illite-smectite mixture. [ABSTRACT FROM AUTHOR]

Landfill leachate is a complex liquid waste, considered a significant problem for the environment. Microalgae are presented as an alternative for the treatment and use of wastewater, thanks to its adaptive capacity, being a viable option for its use in leachates. This contribution presents a bibliometric description of the investigations indexed in the SCOPUS database related to microalgae and leachates from landfills. Based on this, the relevance of treatment with microalgae was identified both in wastewater in general and in leachate, in order to know the progress ratio between the two. 88 articles related to microalgae and leachates were found, with China being the most productive country in terms of number of publications. This study showed that the use of microalgae in leachates is a subject in development and is focused on the treatment of this residue, with limited use and bioproduct production studies. [ABSTRACT FROM AUTHOR]

Dolomite is the most important component of the prolific reservoirs in the Ma55 to Ma51 submembers of the Ordovician Majiagou Formation in the central Yishan Slope, Ordos Basin. However, the origins of the different types of dolomite are unclear because of the different diagenetic environments and complex diagenetic fluids. This paper mainly focuses on the diagenetic environment and diagenetic fluid associated with the dolomite. The petrographic features of the dolomite were studied on the basis of core observation and thin section identification. Geochemical characteristics were analyzed according to the O, C and Sr stable isotopes and major and trace elements. The results demonstrate that, petrographically, the dolomite can be divided into four types, namely, type 1, type 2, type 3 and type 4. Type 1 is mainly characterized by dolomite with gypsum and salt dissolution as well as breccia structures with no clay minerals filling between breccia clasts. Type 2 is characterized by powder-fine crystalline dolomite with apparent residual textures and residual intergranular and intercrystal pores. Type 3 is characterized by leopard limestone or dolomite with leopard textures and massive bioborings. Finally, type 4 is characterized by karst breccia dolomite with many fractures and caves filled by abundant terrigenous clay minerals. In combination with the petrographic data, analysis of the geochemical data reveals that the type 1 dolomite formed in an early near-surface diagenetic environment and the diagenetic fluid might have been early freshwater. Type 2 and type 3 dolomite formed in a shallow-burial diagenetic environment. The diagenetic fluid of type 2 dolomite might have been hypersaline brine that was influenced by freshwater, but that of type 3 dolomite might have been a mixed fluid consisting of seawater and freshwater, which was less saline than the type 2 dolomite fluid. Type 4 dolomite formed in an epidiagenetic near-surface environment and the diagenetic fluid might have been superficial freshwater carrying abundant terrigenous clay minerals. The study shows that the analysis of the diagenetic environment and fluid of dolomite has great significance for research on dolomite origins. The porosity and permeability values of the four types of dolostone reservoirs indicate that type 1 dolomite reservoirs are the best reservoir, type 2 dolomite reservoirs have good physical properties, type 4 dolomite reservoirs are relatively good reservoirs, and the worst reservoir is the type 3 dolomite reservoirs. [ABSTRACT FROM AUTHOR]

In this study, we performed an integrated investigation of K and Mg isotopes in hydrothermally altered rocks from the giant Dexing porphyry Cu deposit in China. Both the altered porphyry intrusion and the surrounding wall rocks exhibit large variations in K and Mg isotope compositions, with δ41K values ranging between −1.0296‰ and 0.38‰, and δ26Mg values ranging between −0.49‰ and 0.32‰. The δ41K and δ26Mg values of the majority of altered samples are higher than the isotopic baseline values for upper continental crust. We attribute the general increase in δ41K and δ26Mg in altered rocks to hydrothermal alteration, which caused preferential incorporation of heavy K and Mg isotopes in alteration products, particularly phyllosilicates. However, a few altered samples show anomalously low δ41K and δ26Mg values. The δ41K and δ26Mg values do not correlate with K and Mg concentrations, or mineralogy of altered samples. The variable K-Mg isotope data likely reflect fluids of different physical-chemical properties, or different isotopic compositions. Based on the combined K-Mg isotope data, at least three groups of hydrothermal fluids are distinguished from the Dexing porphyry deposit. Therefore, K-Mg isotopes are potentially a novel tracer for fingerprinting fluids in complex hydrothermal systems. [ABSTRACT FROM AUTHOR]

Carbonate cementation of sandstones at channel bases is commonly interpreted to be a result of solutes generated from surrounding rocks in a burial-diagenetic regime. However, in rapidly buried and under-compacted conglomerates presented in this study, we interpret carbonate cements formed during early-diagenesis (1000–1600 m) to be precipitated directly from Ca- and CO 2 -rich saline formation water, derived from hypersaline lake water and driven by gravity and compaction. In the Bayindulan Sag of the Er'lian Basin, which is a continental rift basin, the sandstones and conglomerates of the A'ershan Formation (K 1 b a) were deposited in fan delta front settings during the syn-rift phase. Within these, tightly non-ferroan calcite-cemented conglomerates are present at the bases of distributary channels. In addition, some Fe-dolomite cements are present in sandstones with high present-day porosity, which are located in the upper parts of distributary channels. A petrographic analysis and fluid-inclusion microthermometry study show that the calcite cement predates the Fe-dolomite. Stable isotopic values indicate that both calcite and Fe-dolomite are characterized by enrichment of 13C and depletion of 18O (δ18O V-PDB : −15‰ to −8‰), and the value of δ13C V-PDB in calcite (+1.6‰ to +3.8‰) is less positive than that in Fe-dolomite (+3.1‰ to +8.4‰). Integrated analyses imply that the studied carbonate cements were probably formed within an open diagenetic system and were influenced by multiple diagenetic fluids. During deposition of the A'ershan Formation (K 1 b a), the lake water was brackish to hypersaline (Sr/Ba>1 and Sr content > 300 ppm). During deposition of the Tenggeer Formation (K 1 b t), the K 1 b a progressed rapidly into a deep burial phase (90 m/Ma), diagenetic fluids were controlled by hypersaline lake water, incursion of meteoric water occurred along faults, and methanogenic fermentation. Calcium was probably derived from the saline formation water and the transformation of smectite to illite in associated mudstones, leading to the precipitation of calcite (54–78 °C). In the Saihantala period, the K 1 b a experienced a slight uplift, the fault activity ceased, and the diagenetic fluids were derived from the saline formation water and were influenced by methanogenic fermentation, and Fe-dolomite began to precipitate. In deeper burial detrital feldspar grains and some calcite cement were probably dissolved by organic acid discharged from mudstones. In conclusion, the early diagenetic characteristics in the continental rift basins were controlled by the composition of the depositional waters and tectonics that controlled the opening and closing the diagenetic system thus influencing fluid composition. • Complex diagenetic fluids within a fan delta front in a continental rift basin. • Carbonate cementation in the rapidly buried and undercompacted conglomerates. • Ca, Mg, and Fe derived from the transformation of smectite to illite in mudstones. • Enrichment of 13C and depletion of 18O caused by microbial methanogenesis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two generations of pyrite show distinguished textures and chemical compositions. • These generations likely record an evolution from non-immiscibility to immiscibility. • The key factor for the Au precipitation is fluid immiscibility in the second stage. • The immiscibility is responsible for the unusual decoupling of Au and As in pyrite. Pyrite, as one of the most important Au carriers, can well document ore-forming processes. In this study, we select the Hekou gold deposit (HKGD), a newly discovered deposit in the North China Craton (NCC), to rebuild its ore-forming process and gold precipitation mechanism with pyrite. The gold-bearing pyrite was used to perform a combined micro-textural petrography, elemental and S isotope analyses. The micro-textural petrography reveals two distinguished generations of pyrite, including coarse-grained euhedral Py1 and fine-grained xenomorphic Py2. The fine-grained xenomorphic Py2 likely results from a fast nuclear rate responding to the rapid thermochemical changes of hydrothermal fluid. Trace elements of pyrite constrained by LA-ICP-MS reveal that the concentrations of metals such as Au, Ag, Cu, and Pb dramatically increase from Py1 to Py2, suggesting that the fluid evolved to oversaturation. The concentrations of As notably decrease from 284.35 to 23.27 ppm from Py1 to Py2, supporting that As escape from the ore solutions. Moreover, the in situ S isotopes by LA-MC-ICP-MS reveal a minor δ34S fractionation between Py1 (6.29±0.22‰, 2SD) and Py2 (5.95±0.22‰, 2SD), which also agree with the isotopic behavior of H 2 S escape. All of them, together with fluid inclusion observation, we explain that the two-stage pyrite formation in the HKGD records a hydrothermal system evolution from non-immiscibility (Py1) to immiscibility (Py2). Fluid immiscibility likely effectively facilitated the Au precipitation in the HKGD, via significantly destabilizing the Au-HS complex in fluid and incorporating Au into pyrite. Meanwhile, it also led to an unusual decoupling of Au and As in pyrite. This study highlights that the pyrite texture and chemistry can be excellent tools to reveal trace hydrothermal system evolution and gold precipitation mechanism. [ABSTRACT FROM AUTHOR]

The knowledge of fluids derived from the subducting slab is important to constrain the mass transfer in subduction zones, which is important to understand arc magma characteristics. The varying scales of veins in subduction-zone metamorphosed rocks reflect different scales of previous fluid flow. Metamorphic rocks from (ultra-) high pressure (UHP) metamorphic belt of Southwestern Tianshan orogen, China, developed various large-scale veins, which indicate complex mass transfer processes in subduction zones. To further understand the complex geochemical processes and constrain the slab-released fluids in subduction zones, we investigated two rock blocks (13TS-I and 13TS-VI) in this study, which developed different types of veins. The glaucophane-rich breccias and common presence of garnet and omphacite in the vein of rock block 13TS-I reflect a significant dehydration process, while the rock block 13TS-VI with garnet-dominated selvage and epidote-dominated veins reflect a strong fluid-rock interaction process. Although both of these rock blocks were affected by external fluids, they have experienced different metamorphic processes. Compared to the Sr Nd isotope mixing curve with different potential fluid endmembers, the external fluids for 13TS-I and 13TS-VI under eclogite-facies metamorphic conditions are derived from pelagic sediments and altered oceanic crust, respectively. The different metamorphic processes (e.g., dehydration, fluid-rock interactions) and different sources for fluids (e.g., pelagic sediments or altered oceanic crust) lead to the development of various veins in subduction-zone metamorphic rocks, which reflect complex geochemical processes in subduction zones. • Two types of meta-basalts containing different veins were investigated. • Meta-basalts have similar protoliths but experienced different metamorphic processes. • Infiltration of fluids control the element geochemical behaviors of veins in metabasalts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Texture and micro-zone analysis of sulfides are the best indicators to judge the genesis of hydrothermal gold deposits. • The hydrothermal gold deposits, located along the Anqi fault (west Junggar, NW China), formed at ∼300 Ma. • Framboidal pyrite participates in the ore-forming process in the Huilvshan gold deposit. Hydrothermal gold deposits commonly form during protracted multistage ore-forming processes, however, discriminating among different ore-forming fluids and tracing their origin to unique or different repositories is a challenging task. The Huilvshan gold deposit in West Junggar (Xinjiang province, NW China), was affected by three hydrothermal stages and thus provides an opportunity to examine complex ore-forming processes. The deposit consists of gold-bearing quartz-sulfide veins and disseminated sulfides, hosted within Early Carboniferous basalts and tuffs. Three stages of hydrothermal pyrite (Py1, Py2, and Py3) were identified. Gold is only present in Py2 where it occurs as native gold inclusion and in invisible form. Anhedral Py1, disseminated in the altered basalt, is characterized by higher Ni (13.7 to 635 ppm) concentrations than Py2 and Py3. Euhedral-subhedral Py2 is the richest in Au (1.46 to 25.7 ppm) among three stages of pyrite. Py3 is subdivided into grains with zonal texture (Py3a) and irregular grains (Py3b). Both sub-types have high Sb (56.8 to 1599 ppm) and Tl (0.02 to 68.7 ppm) concentrations. In situ δ34S values of Py1 (-6.0 to 2.7 ‰) are similar to those of Py2 (-5.9 to 3.9 ‰), whereas Py3 has extremely negative δ34S values (-44.3 to-18.0 ‰). Ar-Ar ages of hydrothermal muscovite coexisting with Py2 indicate that the Huilvshan gold deposit formed at ∼300 Ma. The sulfur isotopic systematics of Py1 and Py2, close spatial and temporal relationship between the Huilvshan gold deposit and adjacent felsic intrusions, and paucity of regional metamorphic rocks in the region all suggest that hydrothermal fluids in stage I (Py1) and II (Py2) were derived from magmatism. On the other hand, stage III pyrite and associated sulfides more likely precipitated from a hydrothermal fluid that circulated in tuffs, based on the extremely negative δ34S values of Py3, similar to those measured from framboidal pyrite in the host tuffs. Therefore, textural, trace elemental and sulfur isotope data from pyrite suggest different sources for the hydrothermal fluids in the Huilvshan gold deposit, and that magmatic activity may have contributed the most to the main ore-forming stage. The genesis of this Huilvshan gold deposit could provide significant insights into the origin of other hydrothermal gold deposits that show multiple sulfide generations. [ABSTRACT FROM AUTHOR]

[Display omitted] • Siderite-related gold precipitation is more efficient than that related with pyrite at Jiudian. • The fluid of the second ore stage is independent from the previous stage. • Fluid immiscibility occurred in both ore stages, but more intense in the second stage. • Siderite replacement and fluid immiscibility contribute to the high-efficiency gold precipitation. Pyrite (FeS 2) is a common host for gold in various hydrothermal gold deposits, but the close relationship between siderite (FeCO 3) and gold is rarely reported. Furthermore, the gold precipitation mechanism is also poorly understood. In the Jiudian gold deposit of the world-class Jiaodong gold province (eastern China), two gold ore stages were identified: pyrite-smoky grey quartz (the first ore stage), quartz-siderite-polymetallic sulfide (the second ore stage). Gold occurs as visible electrum with minor native gold in both ore stages. The latter stage ores have higher gold grade, indicating gold precipitation associated with second-stage siderite is more efficient than that associated with first-stage pyrite. An integration of mineral texture and composition and fluid inclusion evidence demonstrates that gold deposition in the first ore stage was formed by fluid immiscibility, which destabilized the Au (HS)2− complex in the ore-forming fluid. Fluid immiscibility (boiling) also occurred in the second ore stage, resulted from the abrupt drop of pressure and temperature due to the fracturing of the ore-controlling faults during seismic activity and mixing with cold oxidized meteoric water, and then the polymetallic sulfide precipitation was triggered. The presence of CH 4 in the hydrothermal fluid of the second ore stage may have also promoted the fluid unmixing. Subsequently, the metasomatic reactions of pre-existing pyrite into marcasite and siderite occurred successively, and further facilitated with fluid immiscibility mutually by building a positive chain circuit. These complex processes may have formed a highly drastic and disequilibrated fluid system, in which the crystallized pyrite is featured by the decoupling of As and Au, which is different from the common early-ore Au-As association. The abnormal hydrothermal physicochemical perturbance may have triggered high-efficient gold precipitation associated with siderite. [ABSTRACT FROM AUTHOR]

After long-term water injection, many developed oilfields in the Ordos Basin, China, have entered a period of the high water-cut stage. In waterflooded layers, formation water is a mixture of injected water and primary formation water. The variation of formation water salinity will significantly affect the evaluation of reservoirs using resistivity logging curves while having little effect on the NMR response. It lays a foundation for identifying fluid type and evaluation of waterflooding grade by NMR logging. However, in waterflooding layers with mixed wettability, the NMR T 2 responses are still complicated and unclear. In this paper, the tight sandstone samples with different wettability of Chang 6 and Chang 8 members of Triassic Yanchang Formation in the Ordos Basin are used to investigate the NMR experiments under three saturation states: water-saturated state, oil displacing to bound water state (abbreviated as oil flooding) and water flooding to the residual oil state (abbreviated as water flooding). Results show that the distributions of standard T 2 spectra, without an external gradient magnetic field, of the water-saturated state in mix-wetted samples is very close to that of after oil flooding. Thus, the standard T 2 spectra will be hard to distinguish the oil layer, water layer, and waterflooded layer of mix-wetted reservoirs. The diffusion coefficients of water and oil in pores differ, resulting in different shift T 2 spectra results under gradient magnetic field. Therefore, the shift T 2 spectra with the external gradient magnetic field and different echo time TEs were calculated and measured. When the echo time TE = 3.6 ms is adopted, the T 2 signal of water-saturated tight rock samples will be nearly distributed less than 100 ms with magnetic field gradient G = 18 G/cm, rather the T 2 signal greater than 100 ms is the oil signal. This characteristic makes the shift T 2 spectra outstanding in the fluid identification of tight reservoirs with complex wettability. Finally, based on this experiment, a residual oil index based on the shift T 2 spectrum is constructed to evaluate the flooded grades of tight waterflooding reservoirs. The evaluation results are consistent with the core description and oil test results in the study infilled wells. • The NMR experiments of mixed wetting and water wetting tight rock samples are performed and analyzed. • The standard T 2 spectra have difficult in distinguishing the oil and water layer of the mixed wetting reservoir. • Shift T 2 spectra have an excellent effect in identifying and evaluating fluid properties in complex wettability reservoirs. • The residual oil index is constructed by shift T 2 spectra to evaluate the waterflooded grades. [ABSTRACT FROM AUTHOR]

• Pd/Pt contents of PCDs in intracontinental extensional environment are much lower. • Pd is more abundant than Pt in PCDs. • Oxidized, mantle–derived parental magmas are prerequisite for precious metal. • Pd transport/precipitation as chloride-/bisulfide- complexes in hydrothermal fluids. • Behavior of sulfur is important for PGE and Au captured and preserved. The Tongshankou deposit is located in the southern part of the Edong district in the late Mesozoic Middle–Lower Yangtze River Metallogenic Belt, Eastern China. Alterations related to the porphyry and skarn mineralization are pervasive and intensive. Based on the ore metal contents, four groups of ores/mineralized-rocks are divided: Cu–Mo mineralized rock, Cu–Mo ore, Cu–Mo–W ore and Cu ore. The former two groups are porphyry related, and the latter two groups are skarn related. The average grades of Au, Pt and Pd in the ores are hundreds ppb, ~2.3 ppb, and ~10 ppb, respectively. While they are ~340 ppb, ~29.3 ppb, and ~14.4 ppb in the flotation concentrations, respectively. Considering the similar geological characteristics and tectonic setting (intracontinental extensional environment (IEE)) for the Tongshankou and Fengshan PCDs, they are compared with the PC]Ds that formed in an island arc environment (IAE). Our data show that: (1) Pd and Pt contents of PCDs in IEE are much lower than those of PCDs in IAE; (2) Pd is more abundant than Pt in PCDs. Critical controlling factors for Pt–Pd enrichments in PCDs include: (1) Oxidized, mantle–derived parental magmas, which also explain why PCDs in IAE have higher Pt–Pd contents than PCDs in IEE; (2) Modes of PGE transport and precipitation (as chloride- or bisulfide- complexes) in late-stage hydrothermal fluids; (3) Behavior of sulfur during the magmatic evolution, since PGE and Au could be captured and preserved in magma due to sulfur undersaturation. [ABSTRACT FROM AUTHOR]

• Quartz-stibnite ores have the same zircon U–Pb age ranges as the Banxi host rocks. • Highly radiogenic Hf isotopes suggest a crystalline basement-derived fluid. • Deep-sourced fluid mixed with meteoric water resulted in Sb precipitation. • Changing of Lu–Hf systematics is ascribed to lattice breakdown of old zircons. Fluid-zircon interaction in hydrothermal systems may provide key information on fluid characterization and ore precipitation. In this study, in situ analyses of Hf isotopes in zircon, combined with U–Pb ages and major and trace element data, provide new insights into fluid genesis at the Banxi antimony deposit. The zircons separated from typical quartz-stibnite ores and altered wall rocks have undergone fluid modification to different degrees, showing hydrothermal overprints in reflected/transmitted light, back scattered electron (BSE) and cathodoluminescence (CL) images and variable concentrations of Si, Zr, Hf, U, Th, Pb, Ti, Nb, Ta, P, F, Y and rare earth elements. They possess identical U–Pb ages to the Banxi Group and underlying Lengjiaxi Group clastic rocks but distinct 176Hf/177Hf, 176Lu/177Hf and 176Yb/177Hf ratios, indicating the possible changing of Lu–Hf systematics during the hydrothermal alteration. The evidence suggests a contribution of ore material from the Banxi Group and a deeper fluid source, derived from the Lengjiaxi Group and the crystalline basement beneath it. A fluid mixing model is proposed wherein the deep-sourced, high radiogenic Hf fluid mixed with circulating near-surface meteoric component-dominated fluid, triggering antimony precipitation. The U–Pb chronometer was not reset during this low-temperature mineralization event whereas the Lu–Hf systematics in the fluid-altered zircons show evidence of lattice breakdown of the old zircons during fluid mixing, coupled with external input of highly radiogenic Hf from the crystalline basement. This research highlights the potential to use zircon structure and geochemistry in tracing complex fluid evolutionary processes. [ABSTRACT FROM AUTHOR]