Fluid Source Research Articles

The magmatic-hydrothermal transition in P-rich pegmatitic melts: Crystal-melt-fluid interactions recorded by phosphate minerals

Rare-element pegmatites are the crystallization product of melts strongly enriched in incompatible elements. Some of these elements, e.g., Li, B, P, F, and H2O, function as melt structure modifiers, allowing such melts to reach unusually low crystallization temperatures and regulating the saturation of aqueous-carbonic fluids from the melt. However, the timing of fluid saturation is highly debated, and the processes that mark the magmatic-hydrothermal transition in rare-element pegmatites are still elusive. The crystallization sequence of phosphate minerals can be used to assess the timing and nature of fluid-related processes in pegmatitic systems. In the Buranga pegmatite, western Rwanda, magmatic phosphates are replaced by (hydrous) alkali-rich phosphates and later by strongly hydrated phosphates as the dike cools. This reaction series indicates a disequilibrium in the crystal-melt-fluid system and records complex fluid-rock interactions during dike consolidation. This contribution compares these interactions with the fluid record preserved in fluid inclusions in the main phosphates of the crystallization sequence. Three major fluid inclusion types are observed, aqueous-carbonic (mostly-two-phase, L-V), carbonic-aqueous (two-phase, V-L, or three-phase, L-L-V), and crystal-rich inclusions (multiphase, L-V-Solids). Crystal-rich fluid inclusions in trolleite [Al4(PO4)3(OH)3], the last primary phosphate to precipitate from the melt, show a paragenesis of solid phases similar to the secondary phosphates observed in the dike. LA-ICPMS analyses of individual fluid inclusions show high concentrations of Na and K, with some content of Li, Rb, Cs, B, Fe, and Mn in the fluid. A similar composition is present in all inclusion types within the same mineral. Crystal-rich fluid inclusions demonstrate that during the magmatic-hydrothermal transition, primary phosphates react with the fluid in the presence of melt to generate secondary phosphates. No evidence of external fluid sources has been observed during the magmatic-hydrothermal transition. The fluid inclusion record shows that the fluid salinity is kept constant due to fluid-mineral interactions and corroborates the hypothesis that fluid-soluble elements are internally remobilized in the melt-crystal-fluid system during the magmatic-hydrothermal stage. These interpretations have implications for the general evolution of P-rich pegmatitic melts and the mineralization of Nb and Ta in these systems.

Role of aspirin, beta-blocker, statins, and heparin therapy in septic patients under mechanical ventilation: a narrative review.

Sepsis is the main cause of death among patients admitted to intensive care units. Management of sepsis includes fluid resuscitation, vasopressors, intravenous antimicrobials, source control, mechanical ventilation, and others. New insights into the potential benefits of non-antimicrobial drugs in sepsis have evolved based on the pathophysiology of the disease and the mechanism of action of some drugs, but the findings are still controversial. In this study, we aimed to evaluate the effect of beta-blockers, aspirin, statins, and heparin as adjunctive treatments in septic patients under mechanical ventilation with non-cardiovascular diseases and their effect on mortality. We searched PubMed with relevant keywords (beta-blockers, aspirin, statins, or heparin, and critically ill or sepsis) for the last 10 years and some personal collection of relevant articles, and then we assessed studies according to prespecified inclusion and exclusion criteria. Our results show that beta-blockers, aspirin, and heparin may have promising feedback on reducing mortality. However, new well-controlled, randomized, multicenter studies are needed to confirm that, and multiple issues regarding their usage need to be addressed. On the other hand, the feedback regarding the effectiveness of statins was not as strong as that of the other drugs studied, and we suggest that further research is needed to confirm these results.

The B isotopic signature of serpentine from obducted ophiolites: Mixing of fluids and tectonic implications

Obducted ophiolites expose oceanic lithosphere slivers in suture zones. The few previous studies focusing specifically on the serpentinization of the ultramafic part of ophiolites mostly concluded that serpentinization was driven by seawater. Recent developments in B isotope geochemistry have enabled the tracking of fluid source(s) in serpentinites, suggesting δ11B values above +10‰ mostly reflect seawater hydration and δ11B values below +10‰ mostly reflect hydration by subducted crust-derived metamorphic fluids. In this study, we further investigate the fluid sources recorded by ophiolitic serpentinites by presenting B isotopic geochemistry for seventeen samples from well-characterized ophiolites in Guatemala, Iran, and Brazil. The samples from Guatemala and Iran are from fossil Supra Subduction Zones (SSZ), while samples from Brazil represent a fossil Ocean-Continent Transition (OCT). Most of the samples display the pseudomorphic mesh matrix and bastite microtexture typical of serpentinites. Nine of the samples are either totally (both microtextures) or partially (one microtexture only) out of isotopic equilibrium, with δ11B variations of up to 18‰ within individual samples/textures. Among the samples with a narrow δ11B range (i.e., at isotopic equilibrium), those from a fossil OCT ophiolite have δ11B ranging from +3.8 to +23.2‰, which is broadly consistent with serpentinization by seawater. In contrast, serpentinites from fossil SSZ ophiolite have δ11B straddling 0‰, ranging from −7.7 to +13.5‰. These data indicate that seawater alone cannot be responsible for serpentinization of these ultramafic rocks, but rather either subducted crust-derived metamorphic fluids, or a mixture of seawater and subducted crust-derived metamorphic fluids. This interpretation agrees with the recent suggestions that SSZ ophiolites possibly represent fossil forearc lithosphere.

Soft computing-based predictive modeling of flexible electrohydrodynamic pumps

Flexible electrohydrodynamic (EHD) pumps have been developed and applied in many fields due to no transmission structure, no wear, easy manipulation, and no noise. Physical simulation is often used to predict the output performance of flexible EHD pumps. However, this method neglects fluid–solid interaction and energy loss caused by flexible materials, which are both difficult to calculate when the flexible pumps deform. Therefore, this study proposes a flexible pump output performance prediction using machine learning algorithms. We used three different types of machine learning: random forest regression, ridge regression, and neural network to predict the critical parameters (pressure, flow rate, and power) of the flexible EHD pump. Voltage, angle, gap, overlap, and channel height are selected as five input data of the neural network. In addition, we optimized essential parameters in the three networks. Finally, we adopt the best predictive model and evaluate the significance of five input parameters to the output performance of the flexible EHD pumps. Among the three methods, the MLP model has exceptionally high accuracy in predicting pressure and flow. Our work is beneficial for the design process of fluid sources in flexible soft actuators and soft hydraulic sources in microfluidic chips.

Discovery of the large-scale Eocene Xiwu Pb–Zn–Ag deposit in the Tethyan Himalaya: Geochronology, geochemistry, and C–H–O–S–Pb–Sr–Nd isotopes

The known Pb–Zn–Sb–Au polymetallic deposits in the Himalaya mainly formed during the main-collisional convergence (65–41 Ma) and post-collisional crustal extension (25–0 Ma) tectonic settings. Here, we report the discovery and genesis of the large-scale Eocene Xiwu Pb–Zn–Ag deposit that formed during the late-collisional tectonic transition stage (40–26 Ma) in the eastern Himalaya. The surrounding ore-hosting rocks are mainly low-grade metamorphosed Jurassic clastic rocks and Early Cretaceous diabase. The most important ore-controlling structures are NE–SW thrust faults. The ore minerals include large amounts of galena, sphalerite, tetrahedrite and siderite, with minor chalcopyrite, pyrite, arsenopyrite, calcite and quartz. In this contribution, we analyzed the S–Pb isotopes of sulfides, fluid inclusions and the C–H–O–Pb–Sr–Nd isotopes of nonmetallic minerals. The results indicate that the ore-forming materials originated from deeper metamorphic rocks of the Greater Himalayan Crystalline Complex. This study infer that the source of ore-forming fluids was mainly metamorphic fluids with moderate temperatures and salinities, and S and C were mainly derived from microbial sulfate reduction and the decarboxylation of organic matter, respectively. The main ore-forming mechanism is fluid mixing between the deep ore-bearing metamorphic fluids and shallow formation waters. The Sm–Nd isotopic age of siderite is 37.4 ± 1.1 Ma, which is slightly younger than the zircon U–Pb age of the Zhunba leucogranite (38.9 ± 0.4 Ma) but is consistent with the main epoch of early prograde metamorphism (43–36 Ma) in the Himalaya. We propose a new metallogenic model for Himalayan Pb–Zn–Ag deposits that can greatly promote ore prospecting. The genetic type of the Xiwu deposit is a clastic-dominated subtype of sediment-hosted Pb–Zn deposits.

Fluid evolution and metallogenesis of the Zhangjiapingzi gold deposit in mianning, Sichuan province: constraints from fluid inclusion studies

Introduction: The Zhangjiapingzi gold deposit, located at the western margin of the Yangtze Craton and controlled by the Jinhe-Chenghai deep fault, is a newly discovered super-large gold deposit in the Danba-Mianning metallogenic belt. The gold ore bodies are hosted in the Middle Triassic (T2) altered dolomite (Dm), and have two types of mineralization: altered rock type and quartz vein type. Previous studies on this deposit are rare, especially on the ore-fluid characteristics, which limit the understanding on the ore genesis.Methods: This study focused on fluid inclusions in quartz from altered rocks, and used microthermometry and laser Raman spectroscopy to investigate the properties and sources of ore-forming fluids, and to determine the ore genetic type.Results and discussion: The results show that the fluid inclusions are mainly CO2-H2O-NaCl inclusions, with medium temperature (220–300°C), low salinity (<10%), medium-low density (0.79–1.01 g/cm3) and high contents of CO2 and CH4, resembling typical orogenic gold ore fluids. We suggest that the Zhangjiapingzi is best classified as orogenic type, and our findings provide new insights into the fluid origin and metallogenesis of orogenic gold deposits in the Danba-Mianning metallogenic belt.

Stratigraphic and mineralization age, Sr–Nd isotope constraints on the source of fluids in the Yindonggou Ag–Au(–Pb–Zn) deposit, Qinling Orogen, China

The Yindonggou deposit, located in the northwestern margin of the Wudang Block, is the largest Ag–Au deposit (reserves: 2000 t Ag and 20 t Au) in the area. Quartz vein- and altered rock-type orebodies are hosted in the meta-volcanic rocks of the Wudang Group, and are controlled by the Yindongyan anticline and ductile shear zone along the anticlinal axis. The metamorphosed quartz keratophyre tuff from the Wudang Group yield LA-ICP-MS zircon concordant 206Pb/238U age of 738.30 ± 5.90 Ma, indicating a Neoproterozoic volcanic event. Four stages of mineralized quartz veins were found in the deposit. One hydrothermal sericite sample collected from the stage 2 smoke-gray quartz Ag–Au veins yield a well-defined 40Ar/39Ar isotopic plateau age of 234.65 ± 3.51 Ma, and 39Ar/36Ar-40Ar/36Ar normal isochron age of 220.11 ± 14.32 Ma, suggesting a Middle to Late Triassic (ca. 234 Ma) mineralization at Yindonggou. The difference between diagenetic and mineralization ages indicates that the Yindonggou deposit is not a volcanic eruption-related deposit, but a vein type epigenetic ore deposit. Five wall-rock samples from the Wudang Group of the Yindonggou deposit yield ISr(234 Ma) ratios of 0.714890–0.723704, averaging 0.719938; the (143Nd/144Nd)i values ranging from 0.512018 to 0.512078, averaging 0.512055, with the εNd(234 Ma) values of −6.22 to −5.05. Galena from stage 1 have ISr(234 Ma) values of 0.710801–0.718999, (143Nd/144Nd)i values of 0.511954–0.512234, and εNd(234 Ma) values of −7.47–2.01. Pyrite and sphalerite from stage 2 yield ISr(234 Ma) ratios of 0.704389–0.719884, (143Nd/144Nd)i values of 0.511920–0.512402 and εNd(234 Ma) values of −8.13 to 1.28. Both εNd(234 Ma) and ISr(234 Ma) values of the sulfides indicate that the ore-forming fluids were contaminated by wall rocks from the Wudang Group. The early stage sulfides are representative of the initial ore-forming fluids, which is similar to metamorphosed basic rocks and Mian-Lue ophiolite. This indicates that the deep-sourced initial ore-forming fluids with high εNd(234 Ma) and low ISr(234 Ma) were derived from the metamorphic devolatilization of the subducted oceanic crust. The Yindonggou is an orogenic-type deposit formed in Triassic oceanic subduction-related accretionary orogeny.

Genesis of ferromanganese nodules associated with mud volcanoes in the southeastern Dongsha waters of the northern South China Sea: Implications for regional deep Mesozoic hydrocarbon prospects

The Dongsha waters of the South China Sea are the location of thick Mesozoic deposits and many mud volcanoes that suggest hydrocarbon accumulation. Knowledge of the mechanism, fluid source and evolution of these mud volcanoes, however, remains inadequate. Ferromanganese nodules have been sampled from several deep-water mud volcanoes in waters around Southeast Dongsha island and provide a unique opportunity to study the fluid origin and evolution of the mud volcanoes in the area. In this contribution, the petrology, geochemistry and C–O isotopes of fluid inclusions in the nodules have been analyzed. The ferromanganese nodules are composed of distinct black Fe–Mn crust layers and light-yellow nucleus that contain quartz that hosts fluid inclusions. The outermost layers mainly consist of iron manganese minerals with high Mn/Fe ratios (0.9∼1.57), whereas the nucleus are dominated by siliceous debris. Positive Ce anomalies (δCe: 1.45∼2.13) and negative Y anomalies in growth layers indicate an anoxic environment, which is conducive to hydromanganite precipitation. In contrast, negative Ce anomalies (δCe: 0.27∼0.96) and positive Y anomalies in the nucleus suggest oxidized conditions. The absence of obvious Eu anomalies may be related to low-temperature hydrothermal conditions. The nucleus is enriched in δ13C (−2.59∼1.09‰) and weakly depleted in δ18O (−4.94∼0.89‰), whereas the growth layers are strongly depleted both in δ13C (−16.94∼–12.57‰) and δ18O (−23.05∼–17.48‰). These values indicate that carbon in the nucleus is mainly inorganic carbon from volcanism, whereas the carbon in the growth layers is related to the leakage of deep old hydrocarbon. The fluid inclusions in the quartz from the nucleus show records of at least two periods of CO2-rich hydrothermal activity and an origin from deep Mesozoic strata before release by mud volcanism. Given the widespread mud volcanism, the quartz from the nucleus may come from debris carried by mud volcano eruptions; the quartz also experienced diagenesis related with micro-organisms. The growth layers are considered to be hydrogenic and affected by the leakage of mature thermogenic hydrocarbons from deep old strata. These findings provide insights into deep mature hydrocarbon sources and thermogenic activity and improve understanding of mud volcanism and deep oil and gas resources in the southeastern Dongsha waters.

A metasedimentary origin for gold deposits in the Dian-Qian-Gui “Golden Triangle” of Southwest China

The Dian-Qian-Gui “Golden Triangle” area of Southwest China hosts a large number of Au deposits. However, the sources of the ore-forming fluids are still controversial, hampering the formulation of a sound genetic model and effective ore prospecting. Here we investigate the sources of ore-forming fluids by an integrated study of in-situ sulfur isotope analyses and available trace element (e.g., Co and Ni) data for the pyrite in the “Golden Triangle” area. We find that the ore stage pyrites are featured by low Co/Ni ratios (mostly < 2), which is distinct from pyrite formed in magmatic-hydrothermal systems but resemble typical sedimentary pyrite. In addition, the significant variation (from −7.5 to +20.0‰) in sulfur isotopes (δ34S) of the ore stage pyrite in these deposits also support a sedimentary origin of the ore-forming fluids. Considering the difference in sulfur isotopic compositions of ore-stage pyrite and the sedimentary host rocks, we suggest the metasedimentary basement rocks (>500 Ma) in the area may have supplied most of the sulfur and gold for the ore-forming fluids during the Triassic orogenesis in the Dian-Qian-Gui “Golden Triangle” area of Southwest China.

Basin scale evolution of zebra textures in fault‐controlled, hydrothermal dolomite bodies: Insights from the Western Canadian Sedimentary Basin

AbstractStructurally controlled dolomitization typically involves the interaction of high‐pressure (P), high‐temperature (T) fluids with the surrounding host rock. Such reactions are often accompanied by cementation and recrystallization, with the resulting hydrothermal dolomite (HTD) bodies including several ‘diagnostic’ rock textures. Zebra textures, associated with boxwork textures and dolomite breccias, are widely considered to reflect these elevated P/T conditions. Although a range of conceptual models have been proposed to explain the genesis of these rock textures, the processes that control their spatial and temporal evolution are still poorly understood. Through the detailed petrographical and geochemical analysis of HTD bodies, hosted in the Middle Cambrian strata in the Western Canadian Sedimentary Basin, this study demonstrates that a single genetic model cannot be applied to all the characteristics of these rock textures. Instead, a wide array of sedimentological, tectonic and metasomatic processes contribute to their formation; each of which is spatially and temporally variable at the basin scale. Distal to the fluid source, dolomitization is largely stratabound, comprising replacement dolomite, bedding‐parallel zebra textures and rare dolomite breccias (non‐stratabound, located only proximal to faults). Dolomitization is increasingly non‐stratabound with proximity to the fluid source, comprising bedding‐inclined zebra textures, boxwork textures and dolomite breccias that have been affected by recrystallization. Petrographical and geochemical evidence suggests that these rock textures were initiated due to dilatational fracturing, brecciation and precipitation of saddle dolomite as a cement, but significant recrystallization occurred during the later stages of dolomitization. These rock textures are closely associated with faults and carbonate‐hosted ore deposits (e.g. magnesite, rare earth element and Mississippi Valley–type mineralization), thus providing invaluable information regarding fluid flux and carbonate metasomatism under elevated P/T conditions.

Melt-fluid interaction in the formation of peralkaline granite: Evidence from the Baiyinwula intrusion, Inner Mongolia, China

The genesis of peralkaline granites (with molar (Na + K)/Al > 1) remains a conundrum, particularly their emplacement accompanied by contemporaneous calc-alkaline rhyolites rather than peralkaline rocks. In this study we present a petrogenetic comparison of calc-alkaline rhyolites (296–293 Ma) and subsequent peralkaline granites (291 Ma) in Baiyinwula, Inner Mongolia of north China. The calc-alkaline rhyolites display a narrow variation of GdN/YbN (1.0–1.4) with increasing Zr/Sm (29–79) and positive correlation of εNd(t) (+ 1.5 to +5.1) versus 1/Nd (0.02–0.08). Accordingly, their formation is interpreted to have involved partial melting of juvenile crust, followed by feldspar-dominant fractionation and crustal contamination. The peralkaline granites exhibit roughly constant variations of MgO (0.06–0.24 wt%), Na2O (4.05–4.89 wt%), K2O (3.77–4.61 wt%) and increasing peralkalinity (0.97–1.12) and Fe-index (0.90–0.97) with increasing Zr (350–1022 μg/g) and Zr/Sm, precluding their genesis from calc- or per-alkaline parental magmas through high degree of fractionation. Interestingly, the mixing hyperbola (R2 = 0.85) of GdN/YbN (0.5–1.2) and Zr/Sm (50–240) for peralkaline granites indicate interaction between magmas and alkali-rich fluids, but is distinctly different from those derived by partial melting of metasomatized sources which exhibit a trend of partial melting. Simulation based on two-component (calc-alkaline rhyolitic melts and alkali-rich fluids) mixing yields highly consistent inference. Both magmatic albite in peralkaline granites and dissolved morphology of zircons from calc-alkaline rhyolites are indicators for onset of melt and fluid interaction. Combining the modelling results with positive correlation between εNd(t) (+ 5.6 to +6.6) and Zr/Sm, we infer that the potential end-member source of alkali-rich fluids is from mantle alkali-magmas or degassing. Considering the petrogenesis of peralkaline granites and their occurrences in the Uliastai Continental Margin (UCM) distributed along the major strike-slip fault, and temporally marking the final stage of the Late Palaeozoic magmatism, we propose a model for the magmatic transition from calc- to peralkaline magmas in an extensional setting during the culmination of the magmatic event. Subsequently, the calcalkaline melts began to wane, corresponding to the gradual weakening of the geothermal gradient in the lowermost crust. In contrast, the activities of mantle degassed fluids became more intense and migrated through the major fault, metasomatizing crustal rocks or injecting into and interacting with the pre-existing calc-alkaline magmas in the roof of the magma chamber.

Dark energy nature in logarithmic f(R,T) cosmology

This research paper is an investigation of dark energy nature of logarithmic [Formula: see text]-gravity cosmology in a flat FLRW space–time universe. We have derived modified Einstein’s field equations for the function [Formula: see text] where [Formula: see text] is the Ricci scalar curvature, [Formula: see text] is the trace of the stress energy momentum tensor, and [Formula: see text] is a model parameter. We have solved field equations in the form of two fluid scenarios as perfect fluid and dark fluid, where dark fluid term is derived in the form of perfect fluid source. We have made an observational constraint on the cosmological parameters [Formula: see text] and [Formula: see text] using [Formula: see text] test with observational datasets like Pantheon sample of SNe Ia and [Formula: see text]. With these constraints, we have discussed our model with deceleration parameter [Formula: see text], energy parameters [Formula: see text], EoS parameter [Formula: see text], etc. Also, we have done Om diagnostic analysis. The derived [Formula: see text] model shows a quintessence dark energy model [Formula: see text] and late-time universe approaches to [Formula: see text] CDM model.

The genetic association between vein and skarn type tungsten mineralization in the Yaogangxian tungsten deposit, South China: Constraints from LA-ICP-MS analysis of individual fluid inclusion

The large-scale Yaogangxian W deposit, located in central of the Nanling metallogenic belt, South China, comprises independent quartz vein-type and skarn-type W mineralization. Wolframite-bearing quartz veins occur invariably in metasandstone and slate to the northwest of the Yaogangxian granitic intrusion, whereas scheelite-skarn are mainly hosted by the limestone to the east. The vertical extension of single wolframite-bearing quartz vein can reach up to 1000 m and we focused on the vein samples collected from the deepest level (26 level) which likely recorded early magmatic fluids. For skarn mineralization, two scheelite precipitation stages were recognized, namely scheelite-1 in retrograde stage and scheelite-2 from sulfide-stage. To reveal the fluid sources and characteristics of two mineralizing systems, detailed petrography and microthermometry analyses were carried out on fluid inclusion assemblages (FIA) in scheelite, wolframite and their coexisting quartz. Fluid compositions were obtained from individual fluid inclusion (FI) in ore and gangue minerals via laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis. These data aid elucidation on the source and nature of fluids in the two distinct W mineralization styles. The chemical compositions of FIs hosted in wolframite and scheelite points to a common magmatic source. The fluid in the scheelite ore section exhibits lower As and B than the wolframite ore section, indicating that boiling may have occurred at early skarn stage. Fluid evolution in the two mineralizing systems suggest that formation of diverse W mineralization styles is mainly controlled by different host lithology and fluid processes. In the wolframite ore section, ore-forming fluid recorded in the deepest level of vein show elevated As, B, K and Rb contents than previously reported ore-forming fluid obtained from the tip of the vein. This likely indicate absence of intensive fluid immiscibility in the deep during wolframite formation, which may rather be accompanied by fluid-rock interaction. In the scheelite ore section, constant injection of meteoric water is revealed. FI hosted in scheelite-1 and 2 exhibit similar compositions, and the lower K content in scheelite-2 fluid is thought to be caused by sericitization in the retrograde stage skarn. The Mo content of scheelite decreased from the retrograde stage to sulfide-stage, indicating a decrease in oxygen fugacity. Based on these conclusion and previous geological and geochronological studies, we propose a metallogenic model of the coupled wolframite-quartz vein and scheelite-skarn mineralization.

Trace element geochemistry of magnetite from Mabianshan skarn iron deposit in the Lu-Zong volcanic basin, Eastern China

The composition of host rocks is essential in determining the composition of hydrothermal magnetite formed via fluid-rock interactions in skarn deposits. The HuangLong ore field in the Luzong volcanic basin, Eastern China, hosts several stratabound iron (Fe) skarn deposits, including Mabianshan and Longqiao. In this paper, we analyse the composition of different lithologies of carbonate strata and trace element concentrations in magnetite from Mabianshan, which has complex lithology carbonate strata, and compare it with magnetite from Longqiao, which has uniform lithology carbonate strata. The objective is to investigate the influence of lithology variation on magnetite trace elements and enhance the indicative significance of magnetite trace elements in prospecting and exploration. Our results demonstrate that the lithology of ore-bearing carbonate strata varies greatly due to inversion and different degrees of denudation in the ore field, resulting in variations of Al, Si, Mg, Mn, and Ca in the protolith across different areas. The alteration mineral assemblage of the Mabianshan deposit primarily included epidote, chlorite, and magnetite, while only a few diopside-magnetite relatively high-temperature assemblages developed in the southeastern part of the deposit. Moreover, higher concentrations of Ti and V in magnetite samples from the southeastern area of the deposit suggest that the heat sources related to Fe mineralization may be located there. Compared with the regular spatial variations of Mg, Mn, Al, and Si in the magnetite from Longqiao, the magnetite from Mabianshan does not show evident spatial variations due to the complex lithology of the magnetite protolith in different regions. The protolith lithology of magnetite from Longqiao is relatively stable, mainly dolomitic limestone. However, the protolith lithology of magnetite from Mabianshan is complex and includes dolomitic marlstone, dolomitic limestone, dolomite, and Fe-Mn bearing dolomite, resulting in a significant increase of Si, Al, Mg, and Mn in magnetite. Therefore, it is difficult to effectively trace the temporal-spatial evolution of the hydrothermal fluids using these elements in magnetite. Special attention should be paid to the uniformity of the protolith lithology of the ore when using these elements in magnetite to trace the fluid source.

Ore‐forming process within the Hongyuan reduced porphyry Mo–Cu deposit, West Junggar, NW China

The Hongyuan porphyry Mo–Cu deposit (PMCD) is a rare example of a “reduced” deposit, in contrast to classical oxidized porphyry Cu or Mo–Cu deposits. It is characterized by an ilmenite–series I–type felsic granitoid intrusion, reduced ore‐forming fluids with methane‐rich fluid inclusions, and widely distributed primary pyrrhotite. Mo–Cu mineralization in the Hongyuan PMCD occurs as disseminated in porphyry, granular in miarolitic cavity, and vein‐type in the quartz vein. These three types of mineralization are generally produced in the late magmatic period, magmatic‐hydrothermal transition period, and hydrothermal period, respectively. Molybdenite from miarolitic cavities shows a greater contribution from mantle fluid, as evidenced by mantle He proportions of 37.6%–16.8%. Molybdenite in quartz veins has relatively lower mantle He proportions of 1.63%–10.5%, indicating a predominantly crustal fluid source. The 3He/4He variations of these two groups of molybdenite illustrate an increasing input of crustal fluid during the magmatic to hydrothermal transition. Molybdenite samples from miarolitic cavities and quartz veins yield a Re‐Os model age of 300.5 ± 3.7 Ma, which is consistent with the U–Pb ages of zircons in the wallrock porphyries (300–302 Ma). This further indicates simultaneous diagenesis accompanied by mineralization. The Sr–Nd isotopic compositions (initial 87Sr/86Sr: 0.703404–0.703552; initial 143Nd/144Nd: 0.512585–0.512655; εNd[t]: +6.56 to +7.90) and young T2DM model ages (421–531 Ma) of the Hongyuan porphyries suggest that these rocks were derived from partial melting of the basaltic lower crust. We propose that mantle‐derived fluids rose up and mixed with fluids from the lower crust under an extensional tectonic setting, forming mantle‐like Sr–Nd–He–Ar isotopic compositions. The pre‐mineralization stage of the Hongyuan reduced PMCD is marked by quartz‐molybdenite ± K‐feldspar ± pyrite veins or veinlets and miarolitic cavities in the intensively potassic alteration zone. These veins formed at high temperatures (400–476°C) and high salinities (47.5–56.6 wt.%). The syn‐mineralization stage is the main metallogenic stage represented by numerous quartz‐molybdenite ± pyrrhotite veins associated with moderate to high temperatures (248°C–424°C) and low to high salinities (1.57–50.1 wt.%). The post‐mineralization stage is characterized by low temperatures (104–270°C) and low salinities (0.35–8.81 wt.%). Fluid immiscibility, mixing with meteoric water, ore fluid‐wall rock interactions, and decreasing temperature and salinity have played important roles during molybdenum mineralization.

Sudden shock waves in modified gravity

We construct a generic asymptotic solution for modified gravity near a sudden singularity. This solution contains a fluid source with no equation of state and is function-counting stable, that is it has eleven independent arbitrary functions of the spatial coordinates as dictated by the Cauchy problem of the theory. We further show that near the sudden singularity the solution has a shock wave character with the same number of free functions in the Jordan and Einstein frame.

Origin and Evolution of Ore-Forming Fluids at the Small-Sized Gold Deposits in the Khudolaz Area, Southern Urals

Lode gold deposits are widespread in orogenic belts of various ages and are a valuable gold source, but their genesis remains debatable. The close relationship between native gold and quartz was considered a reason to search for acid-magmatic sources of heat and fluids (i.e., granite intrusions), while small gabbro bodies were often ignored. Six minor gold deposits associated with NE-strike faults were studied in the Khudolaz area of the South Urals (Tukan, Bilyan-Tau, Fazly-Tau, Muildy-Tamak, Alasiya-II and Isyanbet-I). It was established, for the first time, that all of the studied deposits are similar geologically but differ in mineralogical diversity of ore-bearing quartz veins, which is due to the different composition of host rocks and ore-bearing intrusions of the Khudolaz (325–329 Ma, U-Pb) and the Ulugurtau (321 ± 15 Ma, Sm-Nd) ultramafic-mafic complexes. Results of the geochemical study of quartz veins (ICP MS) and their fluid inclusions (microthermometry, gas chromatography) showed that native gold was mostly precipitated at temperatures of 230–330 °C from a low- to moderate-saline (8–12 wt.% NaCl-eq.) H2O–CO2–CH4-bearing fluid, when weakly oxidized or near-neutral conditions, were replaced by reducing ones. No significant differences between barren milky white and ore-bearing brownish quartz veins were defined, which indicates their common formation settings and an impulse pattern of vein injection. The stable pattern of the fluid salinity, along with low hydrocarbon and N2 contents, as well as a narrow range of δ18O values, indicate a prevailing magmatogenic source with a certain influence of host rocks but without the influence of meteoric waters. Based on the presented data, the studied deposits were attributed to the epizonal orogenic type. This study shows the formation of lode gold deposits is possible without the participation of granite massifs.

Ore-forming processes of the Baisong carbonate-hosted Pb-Zn deposit, SW China: Constraints from in-situ sphalerite trace element and sulfide S-isotopic compositions

The western Hunan-eastern Guizhou (WHEG) Pb-Zn ore belt in the southwestern Yangtze block is a main Pb-Zn province in China. The metallogenic characteristics of this ore belt were widely reported, but the ore-forming process is still poorly understood. The lower Cambrian carbonate-hosted Baisong deposit is a representative Pb-Zn deposit in the southern WHEG belt. Sphalerite trace elements and sulfur isotopic compositions from the Baisong Pb-Zn deposit could reveal the ore-forming fluid source and metallogenic processes. Four types of sphalerites have been distinguished (black colloidal sphalerite (Sp) I, light-colored sector Sp II, red zoned Sp III and brown zoned Sp IV, indicating four sulfide mineralization stages from the early ore phase. Sp I (66-117℃, δ34S: +24.8 to + 27.8‰) has the highest Cd-Ga-Ag-Cu contents among the four sphalerite types, and commonly overgrow with marcasite. This suggests that Sp I was formed from acidic fluids under high precipitation rate. The trace elements and sulfur isotopic compositions of Sp II (80-128℃, δ34S: +26.5 to + 28‰) are similar to Sp I. Sp II was likely formed by a decrease in oversaturation and precipitation rate with fluid pH increase. Sp III (127-164℃, δ34S: +31 to + 32.5‰), commonly overgrow on pyrite (Py I), has higher Mn-Fe-Ge but lower Cd-Cu-Ga-Ag contents and heavier sulfur isotopes than Sp II. Changes in precipitation environment and fluid compositions are likely major factors in forming Sp III (temperature increase, pH increase and more reduced). The forming of Sp III and Py I likely consumed the Fe and Ge in the fluid, depriving those elements from the later-formed Sp IV (97-141℃, δ34S: +25.7 to + 29.8‰). The sulfide δ34S value (+22.5 to + 46.3‰) implies that the S2- at Baisong was sourced from seawater sulfates via thermochemical sulfate reduction (TSR). Sphalerite trace element features reflect that the Baisong is an MVT deposit.

Apatite U-Pb geochronological and geochemical constraints on the Mazhala Au-Sb deposit in South Tibet, China

Due to lack of suitable datable minerals, timing of the Mazhala Au-Sb deposit in South Tibet remains unresolved. Also, previous geochemical studies suggest an ambiguous conclusion on the source of ore-forming fluid, with diverse viewpoints of magmatic water, mixed magmatic–meteoric water or mixed metamorphic-meteoric water, respectively. In this study, hydrothermal apatite U-Pb dating constrains the Mazhala Au-Sb deposits to have formed at ca. 35 Ma, consistent with the timing of Eocene leucogranite intrusions in South Tibet. The Mazhala Au-Sb mineralization occurred during the main collision stage to late collision stage in Eocene to Oligocene, and predates the Cuonadong Sn mineralization in South Tibet which occurred during the crustal extension stage in Miocene. An EPMA analysis shows the apatite belongs to fluorapatite that have F contents in the dominant range of 2–4%. The Mazhala apatite displays an overall MREE enrichment and LREE- and HREE depletion distribution pattern with positive Eu anomalies, and have δ18O values dominantly in the range of 16-19‰ with a mean δ18O‰ value of 17.74 ± 0.15‰ (2σ), which suggest a relatively homogenous chemical composition for the ore forming fluids with a relatively stable temperature regime. In combination with previous temperature estimates, the ore forming fluids are inferred to have a dominant δ18Ofluid value of 13-16‰, which overlap with metamorphic water.The combined age and geochemical data suggest Eocene leucogranite intrusion induced metamorphic fluid circulation within Paleozoic-Mesozoic metamorphic sedimentary rocks around the study area, which prompted precipitation of fluorapatite together with Au-Sb bearing pyrite and arsenopyrite in the Mazhala Au-Sb deposit. This study puts an emphasis on the contribution of metamorphic water as the dominant ore-forming fluid origin in the Mazhala Au-Sb deposit. In contrast, the close spatial and temporal association of the Cuonadong Sn polymetallic mineralization with the Miocene leucogranite intrusion-induced hydrothermal activity in the Cuonadong dome demonstrates that their genetic links, as was also evidenced by C-H-O-S-Pb isotope data that point to a dominant contritution of Miocene leucogranite to ore-forming fluid and materials for the Cuonadong Sn polymetallic ore deposits. As such, from a perspective of ore-forming model in South Tibet it be seen that during the main collision stage to late collision stage ore-forming fluid and materials were mainly derived from metamorphic water, whereas during the crustal extension stage, ore-forming fluid and materials were dominantly sourced from magmatic water.

Study of rotating gravastars

In this work, we have discussed about a rotating gravastar model and some physical aspects in the presence of an anisotropic fluid source in the framework of General Relativity. We have considered two cases: one is gravastar’s interior fluid rigidly (or slowly) rotates, and the other is gravastar’s interior fluid non-rigidly rotates. We have considered a gravastar with three regions: interior region, thin shell region, and exterior region. We have written the field equations for a spherically symmetric object in which interior fluid rigidly (or slowly) rotates with angular velocity ([Formula: see text]). Next, we have solved the field equations in three regions of a gravastar. To compute the analytical solution within the shell region, we have used the approximation [Formula: see text]. Some physical quantities, like the proper length of the thin shell, energy, and entropy within the shell, have been obtained and discussed graphically. We have evaluated the surface energy density and the surface pressure analytically through the junction conditions between the surfaces of the interior and exterior regions. Next, we have discussed the equation of state parameter of the surface layer, the mass of the thin shell, and the total mass of the gravastar analytically and graphically. Also, we have discussed the stable region of such type gravastar. Again, we constructed the field equations for a spherically symmetric object in which interior fluid rotates non-rigidly. Next, we have discussed these field equations for a gravastar with three regions. Also, we have obtained some physical quantities like the proper length of the thin shell region, energy, entropy, density and angular velocity within the shell region for such type of gravastar. The stability has been discussed through the surface redshift within the shell region, and we get our model stable and physically valid.