Search Results (12)

Unconformities are of significant interest to petroleum geologists because of their crucial roles in influencing reservoir quality and controlling oil and gas migration. This study investigates the impact of unconformities on a reservoir within a prolific oil–gas-bearing zone between the Middle Permian and Lower Triassic strata in the northwestern Junggar Basin, utilizing thin sections, well logging data, seismic profiles, and geochemical analyses. The results reveal a well-developed three-layer unconformity structure characterized by a thick weathered clay layer, which acts as an effective caprock for hydrocarbons. The diagenetic evolution of the Lower Wuerhe Formation in the northwestern Junggar Basin consists of an initial stage of compaction followed by a subsequent stage of dissolution and cementation. Four key factors, including low argillaceous content in sandstone and conglomerate, diagenetic compaction, zeolite dissolution and cementation, and clay mineral infill, have played a crucial role in influencing the reservoir characteristics of the Lower Wuerhe Formation. In addition, the development of unconformities promotes atmospheric freshwater leaching, which enhances the dissolution of the underlying reservoir while developing an extensive network of strike-slip faults that improve connectivity within hydrocarbon reservoirs. This process facilitates both vertical and lateral migration of hydrocarbons along hard rock layers, which allows the unconformity to breach into the overlying conglomerate reservoirs. The results of this study suggest that the reservoir in proximity to the unconformity surface often exhibits high porosity and rich hydrocarbon content, offering valuable insights for future oil and gas exploration and development. Full article

A mineralogical mapping (terrain analysis) based on micro-mounts has been performed in the Archipelago of the Canary Islands, Spain. The rare elements Be, F, Li, Nb, Ta, Zr, Hf, and rare earth elements (REE) were investigated on the largest island of the Canary Islands Archipelago, Tenerife, Spain. This study forms a contribution to the metallogenetic evolution of the offshore area of the NW African Rare Mineral Province. The finds made at Tenerife were correlated by means of minero-stratigraphy with the adjacent islands La Gomera, Gran Canaria and Fuerteventura, where typical critical element host rocks, e.g., carbonatites, are exposed. At Tenerife, these hidden rock types are only indicated by a wealth of 128 compositional first-order marker minerals hosting Be, F, Zr, Nb, Ta, Zr, Hf, Li, Cs, Sn, W, Ti and REE plus Y and another 106 structural second-order marker minerals describing the geodynamic and morpho-structural evolution of Tenerife (Mn, Fe, Pb, U, Th, As, Sb, V, S, B, Cu, Zn, Mo, Au). Based upon the quantitative micro-mineralogical mapping of lithoclasts and mineralogical xenoliths (foid-bearing monzodiorite/gabbro, (nepheline) syenite, phonolite trachyte) in volcanic and volcaniclastic rocks, hidden intrusive/subvolcanic bodies can be delineated that are associated with contact-metasomatic, zeolitic and argillic alteration zones, as well as potential ore zones. Two potential types of deposits are determined. These are pegmatite-syenites with minor carbonatites bound to a series of agpaitic intrusive rocks that are genetically interlocked with rift zones and associated with a hotspot along a passive continental margin. Towards the east, the carbonatite/alkali magmatite ratio reverses at Fuerteventura in favor of carbonatites, while at Gran Canaria and La Gomera, shallow hypogene/supergene mineral associations interpreted as a marginal facies to Tenerife occur and a new REE discovery in APS minerals has been made. There are seven mineralizing processes different from each other and representative of a peculiar metallogenic process (given in brackets): Protostage 1 (rifting), stages 2a to 2d (differentiation of syenite–pegmatite), stages 3 to 4b (contact-metasomatic/hydrothermal mineralization), stages 5a to 5b (hydrothermal remobilization and zeolitization), stage 6 (shallow hypogene-supergene transition and kaolinization), and stage 7 (auto-hydrothermal-topomineralic mineralization). The prerequisites to successfully take this holistic approach in economic geology are a low maturity of the landscapes in the target area, a Cenozoic age of endogenous and exogenous processes amenable to sedimentological, geomorphological, volcano-tectonic and quantitative mineralogical investigations. The volcanic island’s mineralogical mapping is not primarily designed as a proper pre-well-site study on the Isle of Tenerife, but considered a reference study area for minero-stratigraphic inter-island correlation (land–land) and land–sea when investigating the seabed and seamounts around volcanic archipelagos along the passive margin, as exemplified by the NW African Craton and its metallogenic province. This unconventional exploration technique should also be tested for hotspot- and rift-related volcanic islands elsewhere on the globe for mineral commodities different from the ones under study. Full article

Direct disposal of dual-purpose canisters (DPC) has been proposed to streamline the disposal of spent nuclear fuel. However, there are scenarios where direct disposal of DPCs may result in temperatures in excess of the specified upper temperature limits for some engineered barrier system (EBS) materials, which may cause alteration within EBS materials dependent on local conditions such as host rock composition, chemistry of the saturating groundwaters, and interactions between barrier materials themselves. Here we report the results of hydrothermal experiments reacting EBS materials—bentonite buffer and steel—with an analogue crystalline host rock and groundwater at 250 °C. Experiment series explored the effect of reaction time on the final products and the effects of the mineral and fluid reactants on different steel types. Post-mortem X-ray diffraction, electron microprobe, and scanning electron microscopy analyses showed characteristic alteration of both bentonite and steel, including the formation of secondary zeolite and calcium silicate hydrate minerals within the bentonite matrix and the formation of iron-bearing clays and metal oxides at the steel surfaces. Swelling clays in the bentonite matrix were not quantitatively altered to non-swelling clay species by the hydrothermal conditions. The combined results of the solution chemistry over time and post-mortem mineralogy suggest that EBS alteration is more sensitive to initial groundwater chemistry than the presence of host rock, where limited potassium concentration in the solution prohibits conversion of the smectite minerals in the bentonite matrix to non-swelling clay species. Full article

Arsenic is a potentially toxic element (PTE) that is widely present in groundwater, with concentrations often exceeding the WHO drinking water guideline value (10.0 μg/L), entailing a prominent risk to human health due to long-term exposure. We investigated its origin in groundwater in a study area located north of Rome (Italy) in a volcanic-sedimentary aquifer. Some possible mineralogical sources and main mechanisms governing As mobilization from a representative volcanic tuff have been investigated via laboratory experiments, such as selective sequential extraction and dissolution tests mimicking different release conditions. Arsenic in groundwater ranges from 0.2 to 50.6 μg/L. It does not exhibit a defined spatial distribution, and it shows positive correlations with other PTEs typical of a volcanic environment, such as F, U, and V. Various potential As-bearing phases, such as zeolites, iron oxyhydroxides, calcite, and pyrite are present in the tuff samples. Arsenic in the rocks shows concentrations in the range of 17–41 mg/kg and is mostly associated with a minor fraction of the rock constituted by FeOOH, in particular, low crystalline, containing up to 70% of total As. Secondary fractions include specifically adsorbed As, As-coprecipitated or bound to calcite and linked to sulfides. Results show that As in groundwater mainly originates from water-rock interaction processes. The release of As into groundwater most likely occurs through desorption phenomena in the presence of specific exchangers and, although locally, via the reductive dissolution of Fe oxy-hydroxides. Full article

The Hatrurim Basin, Israel, is located on the western border of the Dead Sea Transform. This is one of the localities of a unique pyrometamorphic complex whose genesis remains problematic. This paper deals with zeolite-bearing rock that is known in the Hatrurim Basin only. The strata subjected to zeolitization is called the “olive unit” and consists of anorthite–pyroxene (diopside–esseneite) hornfels. Zeolitization occurred in an alkaline environment provided by the interaction of meteoric water with Portland-cement-like rocks of the Hatrurim Complex. The resulting zeolite-bearing rocks contain 20–30% zeolitic material. The main zeolitic minerals are calcic: thomsonite-Ca ± Sr, phillipsite-Ca, gismondine-Ca, and clinoptilolite-Ca. The remainder is calcite, diopsidic pyroxene, garnets (either Ti-andradite and/or hydrogrossular), and less frequently, fluorapatite, opal, and others. Their major mineralogical and chemical compositions resemble carbonated zeolite-blended Portland mortar. Rocks show different values of porosity. Their mechanical characteristics are much better for samples with porosity values below 24%. The related parameters are like those of blended concretes. The minimal age of zeolitization is 5 Ka. The natural zeolite-bearing rocks are resistant to weathering in the Levant desert climate. Full article

Clinoptilolite is a precious zeolite mineral that has the most comprehensive physicochemical properties among all the zeolite group minerals. Due to these unique properties, clinoptilolite has a wide range of applications in many different industries. In Poland, the clinoptilolite occurs only as an accompanying mineral in the sedimentary rocks nearby Rzeszów. In Europe, the abundant clinoptilolite-bearing deposits are located in Slovakia and Ukraine, where clinoptilolite mineralization occurs in the volcanic tuffs. Due to clinoptilolite’s rare performance, it is extremely crucial to manage its deposits in a complementary manner. In this paper, the mineralogical and structural characterization of the clinoptilolite powders obtained by mineral processing of the clinoptilolite-rich tuffs from Slovakia and Ukraine deposits were discussed. The scope of research covered determination of the mineral composition of the tuffs, structural analysis of the clinoptilolite crystals, as well as textural and physical properties of the powders obtained by mineral processing of the tuffs. In addition, this paper includes the comparative study of the most significant zeolite deposits in the world and investigated clinoptilolite-rich tuffs. A wide spectrum of methods was used: X-ray powder diffraction (XRD), thermal analysis (DSC, TG), X-ray fluorescence (XRF), optical microscopy, Scanning Electron Microscopy (SEM-EDS), the laser diffraction technique, and low-temperature nitrogen adsorption/desorption. The test results indicated that the major component of the tuffs is clinoptilolite, which crystallized in the form of very fine-crystalline thin plates. The clinoptilolite mineralization in the Ukrainian and Slovakian tuffs exhibited a strong resemblance to the clinoptilolite crystals in Yemeni and Turkish tuffs. With respect to the mineral composition, the investigated tuffs showed excellent conformity with the Miocene white tuffs from Romania. The Ukrainian and Slovakian tuffs do not reveal the presence of the clay minerals, which is quite common for naturally occurring zeolite-rich rocks in various deposits in the world. The textural features together with mineral composition of the investigated samples incline that they are potentially suitable raw materials for the sorbent of petroleum compounds. Moreover, the obtained results can be useful indicators with respect to the crushing and compaction susceptibility of the Ukrainian and Slovakian clinoptilolite-rich tuffs. Full article

Six zeolite-bearing rocks, often used as building materials, were analyzed by thermodilatometry, together with a rock not bearing zeolites and a plaster covering a containing wall made of zeolite-bearing dimension stones, up to 250 °C. The main results obtained were the following: (i) the zeolite-bearing rocks exhibited very small, if any, positive variation of ΔL/L_o (%) up to about 100 °C, whereas they more or less shrank in the temperature range 100–250 °C (final values ranging from −0.21 to −0.92%); (ii) the rock not bearing zeolites regularly expanded through the whole temperature range, attaining a final value of 0.19%; (iii) the plaster showed a thermodilatometric behavior strongly affected by its water content. Obtained results were interpreted based on plain thermal expansion, shrinkage by dehydration, cation migration and thermal collapse of the zeolitic structure. The decay of the zeolite-bearing building materials was essentially related to: (i) the large differences recorded in the thermodilatometric behavior of the various rocks and the plaster; (ii) the different minerogenetic processes that resulted in the deposition of the various zeolite-bearing rocks. Full article

In the last 15 years, zeolite-like mayenite, Ca₁₂Al₁₄O₃₃, has attracted significant attention in material science for its variety of potential applications and for its simple composition. Hydrogen plays a key role in processes of electride material synthesis from pristine mayenite: {Ca₁₂Al₁₄O₃₂}²⁺(O²) → {Ca₁₂Al₁₄O₃₂}²⁺(e⁻)₂. A presence of molecular hydrogen in synthetic mayenite was not confirmed by the direct methods. Spectroscopy investigations of mayenite group mineral fluorkyuygenite, with empirical formula (Ca_12.09Na_0.03)_∑12.12(Al_13.67Si_0.12Fe³⁺_0.07Ti⁴⁺_0.01)_∑12.87O_31.96 [F_2.02Cl_0.02(H₂O)_3.22(H₂S)_0.15□_0.59]_∑6.00, show the presence of an unusual band at 4038 cm⁻¹, registered for the first time and related to molecular hydrogen, apart from usual bands responding to vibrations of mayenite framework. The band at 4038 cm⁻¹ corresponding to stretching vibrations of H₂ is at lower frequencies in comparison with positions of analogous bands of gaseous H₂ (4156 cm⁻¹) and H₂ adsorbed at active cation sites of zeolites (4050–4100 cm⁻¹). This points out relatively strong linking of molecular hydrogen with the fluorkyuygenite framework. An appearance of H₂ in the fluorkyuyginite with ideal formula Ca₁₂Al₁₄O₃₂[(H₂O)₄F₂], which formed after fluormayenite, Ca₁₂Al₁₄O₃₂[□₄F₂], is connected with its genesis. Fluorkyuygenite was detected in gehlenite fragments within brecciaed pyrometamorphic rock (Hatrurim Basin, Negev Desert, Israel), which contains reduced mineral assemblage of the Fe-P-C system (native iron, schreibersite, barringerite, murashkoite, and cohenite). The origin of phosphide-bearing associations is connected with the effect of highly reduced gases on earlier formed pyrometamorphic rocks. Full article

The morphology, chemical, and mineralogical composition of subsurface filamentous fabrics (SFF) from the Deccan Volcanic Province (DVP) were investigated to determine the origin of these spectacular aggregates. SFF occur in a wide variety of morphologies ranging from pseudo-stalactites to irregular fabrics and are classified as SFF_Ir (irregular) or SFF_Ma (matted). The SFF samples exhibit a thread-like (or filament-like) center from which mineral precipitation starts to form the final macroscopic morphologies. Detailed investigations revealed organic material (fungal chitin) in the innermost filamentous core, which may have acted as an initial nucleus for the mineralization processes. The morphometric characteristics of certain filamentous fabrics are very similar to those of microbial filaments and the fabrics formed from them but are clearly distinct from similar types of non-biological precipitates (fibrous minerals, speleothems, and “chemical gardens”). These features indicate that the filamentous cores might be products of microbial communities that were active in the basaltic cavities. The SFF cross-sections display similar concentric layers of the mineral succession and reach thicknesses of several centimeters with spectacular lengths up to 100 cm and constant diameters. The typical mineralization sequence points to temporal variation in the chemical composition of the mineralizing fluids from Fe(Mg)-rich (Fe-oxides/-hydroxides, Fe-rich sheet silicates such as celadonite and di-/tri-smectite) to Ca-dominated (Ca-rich zeolites) and finally pure SiO₂ (opal-CT, chalcedony, and macro-crystalline quartz). Assuming biological activity at least during the early mineralization processes, circumneutral pH conditions and maximum temperatures of 100–120 °C were supposed. The formation of filamentous cores including Fe-bearing phyllosilicates probably occurred near the surface after cooling of the lava, where the elements necessary for mineral formation (i.e., Si, Mg, Al, Fe) were released during alteration of the volcanic host rocks by percolating fluids. Full article

Natural zeolite occurrences have been recognized in several Cenozoic pyroclastic deposits in central Sardinia. This study concerns the mineralogical and geochemical characterization of the zeolitized tuffites in the Asuni area (Oristano province) and aims to complement information regarding the zeolitization processes developed in the nearby Allai deposits. Optical and scanning electron microscopy, X-ray powder diffraction, qualitative vs. quantitative microanalyses and bulk-rock geochemistry were performed. Analytical results allow defining the mineral distribution, textural relationships and geochemical features of the zeolite-bearing rocks. The most abundant secondary minerals are Ca-Na mordenites. Contrarily to the most common worldwide clinoptilolite + mordenite paragenesis, mordenite is dominant and occurs in different morphologies, rarely coexisting with clinoptilolite in the studied volcanic tuffites. Glauconite and dioctahedral smectite complete the authigenic assemblages. The primary volcanic components mostly include plagioclase, quartz and glass shards, roughly retaining their original appearance. The tuffites range in composition from dacite to rhyolite. The collected dataset shows that zeolitization is most abundant in coarser-grained deposits and points to a genetic process that mainly involves an open hydrothermal environment governed by aqueous fluids with significant marine component, in post eruption conditions. Full article

The present work reports on new mineralogical and whole-rock geochemical data from the Breivikbotn silicocarbonatite (Seiland igneous province, North Norway), allowing conclusions to be drawn concerning its origin and the role of late fluid alteration. The rock shows a rare mineral association: calcite + pyroxene + amphibole + zeolite group minerals + garnet + titanite, with apatite, allanite, magnetite and zircon as minor and accessory minerals, and it is classified as silicocarbonatite. Calcite, titanite and pyroxene (Di_36–46 Acm_22–37 Hd_14–21) are primarily magmatic minerals. Amphibole of mainly hastingsitic composition has formed after pyroxene at a late-magmatic stage. Zeolite group minerals (natrolite, gonnardite, Sr-rich thomsonite-(Ca)) were formed during hydrothermal alteration of primary nepheline by fluids/solutions with high Si-Al-Ca activities. Poikilitic garnet (Ti-bearing andradite) has inclusions of all primary minerals, amphibole and zeolites, and presumably crystallized metasomatically during a late metamorphic event (Caledonian orogeny). Whole-rock chemical compositions of the silicocarbonatite differs from the global average of calciocarbonatites by elevated silica, aluminium, sodium and iron, but show comparable contents of trace elements (REE, Sr, Ba). Trace element distributions and abundances indicate within-plate tectonic setting of the carbonatite. The spatial proximity of carbonatite and alkaline ultramafic rock (melteigite), the presence of “primary nepheline” in carbonatite together with the trace element distributions indicate that the carbonatite was derived by crystal fractionation of a parental carbonated foidite magma. The main prerequisites for the extensive formation of zeolite group minerals in silicocarbonatite are revealed. Full article

Epithermally altered volcanic rocks in Greece host amethyst-bearing veins in association with various silicates, carbonates, oxides and sulfides. Host rocks are Oligocene to Pleistocene calc-alkaline to shoshonitic lavas and pyroclastics of intermediate to acidic composition. The veins are integral parts of high to intermediate sulfidation epithermal mineralized centers in northern Greece (e.g., Kassiteres–Sapes, Kirki, Kornofolia/Soufli, Lesvos Island) and on Milos Island. Colloform–crustiform banding with alternations of amethyst, chalcedony and/or carbonates is a common characteristic of the studied amethyst-bearing veins. Hydrothermal alteration around the quartz veins includes sericitic, K-feldspar (adularia), propylitic and zeolitic types. Precipitation of amethyst took place from near-neutral to alkaline fluids, as indicated by the presence of various amounts of gangue adularia, calcite, zeolites, chlorite and smectite. Fluid inclusion data suggest that the studied amethyst was formed by hydrothermal fluids with relatively low temperatures (~200–250 °C) and low to moderate salinity (1–8 wt % NaCl equiv). A fluid cooling gradually from the external to the inner parts of the veins, possibly with subsequent boiling in an open system, is considered for the amethysts of Silver Hill in Sapes and Kassiteres. Amethysts from Kornofolia, Megala Therma, Kalogries and Chondro Vouno were formed by mixing of moderately saline hydrothermal fluids with low-salinity fluids at relatively lower temperatures indicating the presence of dilution processes and probably boiling in an open system. Stable isotope data point to mixing between magmatic and marine (and/or meteoric) waters and are consistent with the oxidizing conditions required for amethyst formation. Full article