Solid Earth Sciences最新文献

Skarn Cu deposits are one of most important deposit-type in Middle-Lower Yangtze River region, eastern China, but skarn formation process remains unclear. Mineralogical, morphological and in situ geochemical data from the skarn stage of Tongguanshan skarn Cu deposit in Tongling region are systemically investigated, to reveal the timing, physical-chemical conditions, and fluid evolution during the skarn formation. The Tongguanshan garnets can be identified homogeneous and unzoned early generation garnet (GrtI), and oscillating zoned late generation garnet (GrtII) with the Fe-rich core (GrtII-Fe) and Al-rich edge (GrtII-Al). Garnet U–Pb dating results show that the Tongguanshan Cu mineralization was formed in 145.6 ± 4.4 Ma. In situ elemental composition results of the garnet samples indicate that they belong to grossular-andradite solid solution series, and are a magmatic-hydrothermal origin. The distinctly geochemical characteristics (e.g., Sn and U contents, (La/Yb)_N, δEu and Y/Ho values) reveal that the physiochemical conditions from GrtI to GrtII-Fe, and GrtII-Fe to GrtII-Al stages in the Tongguanshan skarn formation were an increase and a decrease of fluid salinity and oxygen fugacity, closed to open and then to closed of fluid environment, and neutral-weakly acidic to acidic and acidic to neutral-weakly acidic of fluid pH, respectively. A comprehensive discriminant analysis indicates a fluid boiling occurred in the GrtI to GrtII-Fe stage of the Tongguanshan skarn Cu deposit, and there is little or no external fluid mixed during the skarn stage.

The Panzijian gold deposit is located in the Jiaobei uplift on the eastern margin of North China Craton. It is a quartz vein-type gold deposit in the southern end of the Qixia-Penglai ore belt. In order to explore the source and properties of ore-forming fluids and materials in the Panzijian gold deposit, explore the ore-forming process and reveal the genesis of the deposit, this work has carried out petrographic observation and temperature measurement of gold-bearing quartz fluid inclusions, laser Raman experiment, gold-bearing quartz H–O isotope study, and gold-bearing pyrite Pb isotope study. The Panjian gold deposit is divided into four metallogenic stages and the metallogenic stage Ⅲ is the main gold mineralization stage. Fluid inclusions show that the ore-forming fluids at the Panzijian gold deposit belong to a CO₂–H₂O–NaCl system with low temperature (172–341 °C), salinity (1.57–10.49 wt% NaCl), and density (0.79–0.96 g/cm³). Gold-bearing Quartz H–O isotopic data (δD = −79.8 to −65.1‰, δ¹⁸O_H2O = 1.33–2.63‰) show that the ore-forming fluid was derived from the mixing of magmatic water and meteoric water. Gold-bearing Pyrite Pb isotopes with crustal signature (²⁰⁶Pb/²⁰⁴Pb = 16.06–16.943, ²⁰⁷Pb/²⁰⁴Pb = 15.337–15.858, ²⁰⁸Pb/²⁰⁴Pb = 37.143–38.081, and ²⁰⁶Pb/²⁰⁷Pb = 1.025–1.105) support that some ore-forming materials were crust-derived. We proposed a metallogenic model for the Panzijian gold deposit: Stress transition of Jiaobei uplift tectonic system inducing asthenospheric upwelling. The lithostatic pressure dropped and fluids were exsolved from the magma. The ore-forming fluid ascended along local faults and the pressure further dropped, resulting in fluid immiscibility and gold deposition along structural traps (e.g., faults).

The increasing importance of rare earth elements (REE) and critical metals in contemporary society has led us to investigate the mineral potential of the Ngaoumbol area, located within Cameroon's Central African Fold Belt (CAFB). In this study, we have conducted a comprehensive analysis that includes petrography, whole rock geochemistry, and mineral chemistry, along with the application of an outlook coefficient known as Koult, with the aim to evaluate the prospectivity of the Ngaoumbol iron formations as a potential source of REE-Y resources. This coefficient is defined as the ratio of the relative abundance of critical Rare Earth Elements to the relative abundance of excess REE. The iron formations in the Ngaoumbol area are fine-to medium-grained foliated rocks with alternating magnetite and actinolite bands and quartz bands, suggesting a sedimentary parentage. These rocks have an average REE-Y content of 1438.43 ppm and a Koult of 0.77, indicating their potential as raw sources for REE. Furthermore, the investigated samples exhibit high average Zr content (7748 ppm), suggesting that the rocks may host potentially economic Zr ore. The Zr-REE-Y mineralization in the Ngaoumbol area is hosted in detrital zircon, monazite and xenotime, probably deriving from the weathering of alkaline/subalkaline rocks surrounding the deposits. Our findings suggest that the Ngaoumbol area has promising REE and Zr resources. However, further exploration and evaluation are necessary to determine the extent and economic viability of these resources.

The Zhuqing vanadium–titanium magnetite is a large deposit recently discovered in the western margin of the Yangtze Block, where the Zhuqing gabbroic intrusion and associated Fe–Ti–V oxide deposits are fund and dated at 1647 ± 39 Ma (MSWD = 0.79) through U–Pb dating of gabbro zircons. The εHf(t) values of zircons are all positive, with an average of 10.7. The average age of the one-stage model age (T_DM) is 1661 Ma, which is very close to the diagenetic and metallogenic age 1647 ± 39 Ma (MSWD = 0.79). These new results indicate that the magma source come directly from the mantle. The contents of Al₂O₃, CaO, and (Na₂O + K₂O) increases with the increase of SiO₂ contents, while, the contents of MgO, TiO₂, and Fe₂O₃ decreases with the increase of SiO₂ contents. Mg^# is relatively stable with the increase of SiO₂ contents. In the primitive mantle-normalized trace element spider diagrams and chondrite-normalized rare earth element patterns, the characteristics of all samples are similar to that of ocean island basalts (OIBs), showing a right inclination curve. Meanwhile the western margin of the Yangtze Block as an essential part of the supercontinent of Colombia, began to extend at 1.7 Ga, lasted to ca. 1.4 Ga, and finally split. These suggest that the Zhuqing gabbroic intrusion and associated Fe–Ti–V oxide deposits with OIB characteristics formed in the Late Paleoproterozoic, which is a response to the breakup of the Colombian supercontinent in the western margin of the Yangtze Block.

A conceptual model has been proposed based on water samples collected from geothermal springs in the Shyok suture zone of North-West Himalayas, Ladakh geothermal province, India by nurturing hydrogeochemistry, mineralogical insights, and stable isotopic (δD, δ¹⁸O) systematics. The reservoir rock is comprised of granitic segment with intrusion of volcano-plutonics and a variety of meta-sedimentaries which becomes more exposed towards western side of the valley in the form of Shyok Ophiolitic melange. Thermal waters, located above 3100 m above msl, with variable genetic classification (Changlung: Na–HCO₃; Panamik: both Na–HCO₃ and mixed type; Pulthang: purely mixed type), have TDS and temperature lying between 587 and 2278 mg/L and 28−78 °C, respectively. High concentration of trace elements (Li, B, As, Cs, Rb, W) in geothermal fluids points to the magmatic origin regarding their enrichment mechanism. Surface manifestation of hydrothermal/evaporitic minerals like thenardite, trona, sylvite, halite, nahcolite, thermonatrite, etc. establishes a signature of high-temperature at shallow level of reservoir and their dissolution kinetics decipher origin of solutes apart from weathering of alkali/alkaline aluminosilicates. Utilizing empirical chemical geothermometry and Si-Enthalpy mixing modelling, the estimated reservoir temperatures exhibit significant variability ranging from 100 to 210 °C and reservoir silica concentration 382 mg/L with average circulation depth of geothermal waters around 1.8 Km and fluid residence time of 2640 years. The Shyok-Nubra springs liberate substantial amount of CO₂-enriched water, with degassing flux of 6.26 × 10⁵ mol of CO₂/year. δD and δ¹⁸O systematics reveal that geothermal springs are recharged by meteoric water, snow-melt and magmatic fluid with cold-water component of 27.1–62.4% mixed with hot fluids. Thermal springs are recharged from a single reservoir source located a shallow level towards North-West of Changlung having large lateral flow of about 25 Km generating Panamik and Pulthang fluids with subsequent dilution. This study highlights the extent and consequences of water–rock interaction across diverse lithologies (granite and mafic volcanics) in the Himalayas, emphasizing its implications over fluid circulation time and subsurface temperature considerations which rationalizes the evolution of geothermal fluids.

More recently Kohat's fold-thrust belt, including the Karak area has emerged as an important hydrocarbon fertile region of the western Himalayan orogenic system. The Eocene and Paleocene strata, including mechanical weak Eocene units representing a shallow decollement have a noticeable contribution to the deformation style and petroleum system of the area. In the present study, surface mapping is integrated with seismic information to elucidate the structural style of the Karak area, the data reveal that there are two different structural entities, separated by Karak Fault Zone. The northern domain portrays salt diapiric structures representing doubly plunging and complexity overturned, and fault bounded folds' geometries. However, in the subsurface below the Eocene sequence, the deformation is characterized by south-directed imbricate thrust system. In contrast, because of the absence of Eocene salt horizon, the southern domain of the Karak area illustrates a brittle style of deformation, mimicking fault propagation folding. In addition, an array of south-verging imbricate system from a regional basal decollement translates rock as old as Permian along the Surghar range frontal thrust. It can be observed that fault geometry and fold styles in the north and south of Karak Fault Zone are entirely different. Restored cross-sections across the area indicate 35% of shortening has been accommodated in the area. Moreover, from the present study it has been concluded that in the purlieu of Karak Fault Zone, possibly occupy auspicious structural traps at top Paleocene Lockhart level.

The Mundeck and Mungo River Formation sandstones located within the Douala sub basin in Cameroon were subjected to both petrographic and geochemical analyses to unveil their geological characterization such as chemical and mineralogical maturity, litho-tectonic setting, climate and weathering intensity of the source area at the time of their formation. Petrographic studies reveals that the sandstones show variable colours ranging from reddish to brownish, pinkish, grey and white with textures ranging from medium to coarse grained. The studied sandstones consist of various types of angular to sub angular, quartz, rock fragments, mica, feldspar. Modal analysis data and plots of detrital modes of the studied sandstones on Qt–F–RF diagrams suggest that they were derived from a plutonic source rock (igneous origin) with little or no contribution from metamorphic sources. Plot of the Qm–F–L diagram of the studied sandstones reveal a quartzose recycled and transitional continental provenance fields. Mineralogical classification of these sandstones from Qt–F–RF triangular diagram classifies them as arkose, lithic arkose and sub-litherarenite. Bivariate plot of Qp/(F + R) vs (Qm + Qp)/(F + R), SiO₂ Vs Al₂O₃ +K₂O + Na₂O coupled with values of Chemical index Alteration (CIA = 70–99) and plagioclase index Alteration (PIA>80) reveal a moderate to high intensity of weathering in the source area under a semi-humid to humid paleoclimatic conditions with high lixiviation of feldspars (PIA>80 %) for the studied sandstones. The mineralogical maturity index (MMI = 3–9) coupled with the new index of compositional variation (ICV_new <1) reveal that the sandstones are sub mature to mature. Geochemical binary plots of La/Sc, Th/Co, Th/Sc couple with plots of DF1vs DF2 and K₂O/Na₂O vs SiO₂ points to an igneous felsic source rock formed in a passive margin for the studied sandstones.

The origin and evolution of tungsten ore, a key metal resource, have long been controversial. In order to reveal the origin of tungsten mineralization related to weakly fractionated I-type granites, we have carried out detailed in situ element analysis on apatite from gabbro-diorite enclaves and their host rocks (biotite granodiorites) in Zhuxiling deposit, Jiangnan orogenic belt. The groups of apatite samples were identified, respectively from gabbro-diorite enclaves (Group A) representing deep early magma, and biotite granodiorites with weak tungsten mineralization stage (Group B) and strong tungsten mineralization stage (Group C). The three-group apatite samples with high F (2.15–4.74 wt.%) and low Cl (<0.19 wt.%) contents, belong to fluoroapatite, and have LREE enrichment, negative Eu anomalies (Eu/Eu∗ = 0.27–0.52), and low Sr/Y ratios (mainly <1). The Sr content difference between the apatite studied and host rocks, and the gradual increase of Sr contents from Group A to Group B to Group C, indicate that high tungsten content magma mixing is the dominant cause of mineralization in the Zhuxiling region. The studied apatite samples with different internal zonal textures, suggest that more significant oscillatory growth zone is associated with higher tungsten content, more complex internal compositions, and longer crystallization times. Apatite trace elements (e.g., Sr, Y, Eu/Eu∗, REE) characteristics indicate that the Zhuxiling mineralized intrusions mainly experienced shallow feldspar crystalline differentiation. The F- and Li-rich, high evolution degree, and moderate oxygen fugacity of magma may contribute to tungsten mineralization in the Zhuxiling region.

Metal dissolution, complexation, and speciation are the key processes that facilitate metal mobilization and transport in fluids. Niobium (Nb), a kind of critical metal, has traditionally been regarded as a fluid-immobile element; however, it sometimes shows apparent hydrothermal mobility and even mineralization. Studying the solubility and complexation of Nb in fluids is thus crucial for understanding its dissolution, transport, enrichment, and mineralization. In this paper, we reviewed the geological observations on Nb mobility related to magmatic-hydrothermal and metamorphic fluid activities, especially compiled and reprocessed the published data on Nb solubility and related thermodynamic calculation to discuss the complexation and speciation of Nb in fluids. Previous solubility experiments demonstrate that Nb has much higher solubility in F-bearing solutions than in other solutions (Cl⁻, ClO₄⁻, CO₃²⁻, HCO₃⁻, OH⁻, SO₄²⁻, etc.), the maximum of which is up to ∼3 wt% in a 2 mol/kg HF solution. It is revealed that Nb solubility is related to the solution's composition, pH, ionic strength, oxygen fugacity, temperature, and pressure. High solubility could be found in neutral and weakly-basic solutions at near ambient temperature and pressure or in F-bearing fluids at high-temperature and high-pressure conditions. Modeling calculations show that Nb could be soluble and stable in fluids as the mononuclear or polynuclear complexes, such as fluoride complexes, hydroxide complexes, chloride complexes, and hexametalate ions, etc. Thereinto, Nb–OH–F complexes should play a dominant role in Nb hydrothermal mobility and be enriched in medium–high temperature, acidic, and F-bearing fluids. Experiments and modeling calculation have also inferred the existence of the species (e.g., $\text{Nb}{\left(\text{OH}\right)}_{4+y}{F}^{y-}$, $\text{Nb}{\left(\text{OH}\right)}_{3+y}{F}_2^{y-}$, and $\text{Nb}{\left(\text{OH}\right)}_{2+y}{F}_3^{y-}$), in which the F coordination number is no more than 3. Considering that it could have higher F contents than the experimental solutions (F < 4 wt%), we believe that natural mineralized F-rich fluids would facilitate the formation of the species with higher F coordination numbers due to the positive relationship between the F coordination number in the species and F content in fluids