Limestone Layers Research Articles

Assessment of the Hydrogeochemical Characteristics of Groundwater Resources at some Wadis in the East of El Minia Governorate, Eastern Desert, Egypt

AbstractThe El Minia governorate lies within the Nile Valley, surrounded by calcareous plateaus to the east and west. The present study focuses on the hydrogeochemistry of the Eocene limestone aquifer at some wadis in the east El Minia governorate, Eastern Desert, Egypt. Hydrogeologically, two main aquifers are encountered in the study area, namely the Maghagha marly limestone and the Samalut chalky limestone aquifers. The Maghagha aquifer is composed of alternating layers of marly limestone and shale with thicknesses ranging from 3.49 m to 177.05 m and a groundwater depth ranging from 8.5 m to 59.27 m which reflects low groundwater potentiality. The groundwater salinity representing this aquifer ranges from 603.5 mg/L to 978.5 mg/L, reflecting fresh water type. Samalut aquifer is made up of chalky, cavernous and fractured limestone with thickness ranging from 30 m to 205 m and groundwater depth ranging from 9 m to 86.77 m, which indicates good groundwater potential. The groundwater salinity of the concerned aquifer ranges from 349.7 mg/L to 2043.9 mg/L, reflecting fresh to possibly brackish water types. Groundwater in the study area is of meteoric water origin; recent recharge is mainly controlled through the presence of fractures and their densities. The majority of groundwater samples in the study area are suitable for drinking and irrigation purposes.

Origin of large-scale variegated reef limestones in the southern South China Sea: Implications for Miocene regional and global geological evolution

Marine sediments featuring special colors have always played an important role in disclosing regional or global environmental transitions and geological evolution. A deep well (Nanke-1), drilled on Meiji Atoll in 2017, penetrated Cenozoic reef strata in the central Nansha Block (also referred to as Dangerous Grounds) in the southern South China Sea (SCS) and revealed two pronounced variegated (containing colors of white, reddish and red brown) reef limestone layers in the Miocene. Similar large-scale variegated reef limestones have not been found in other reef drilling cores to date, so its coloration origin, formation mechanism and geological implications are unclear. Here, synthesized mineralogical, petrographic, and geochemical analyses demonstrated that the presence of trace amounts of amorphous microsized hematite with varying crystallinity imparted reddish or red brown colors to reef limestones. Hematite formed during meteoric water-induced karstification after the carbonate platform was exposed subaerially. Long-term exposures were mainly controlled by regional tectonic uplifts closely associated with the subduction of the proto-SCS, the seafloor spreading of the Southwest Sub-basin and the collision between blocks (i.e., the Sabah collision and the Palawan collision). The different tectonic settings have led to the different developments of carbonate platforms in the northern and southern SCS during most of the Early and Middle Miocene, but the major expansion of the high-latitude Antarctic ice sheets and the resultant significant drop in global sea level may have contributed to wide exposure of carbonate platforms both in the northern and southern SCS in the late Middle Miocene. Our studies demonstrated that the occurrences of variegated reef limestones in isolated oceanic reef carbonate platforms have great potential in indicating subaerial exposure, regional tectonic uplift or sea level fall.

Near-surface resistivity imaging using resistivity Tomography in some most impacted areas due to the 2018 Earthquake in North Lombok Island

The Lombok earthquake in July 2018 caused considerable damage to public facilities and residential areas. Most of the houses in the north of the island of Lombok were damaged by the 6.9 magnitude earthquake. We want to know what parameters cause houses and buildings in North Lombok not to experience a severe liquefaction process. We used near-surface tomographic resistivity imaging to characterize the subsurface of North Lombok to map the subsurface of the most affected areas in North Lombok. The geological condition of northern Lombok is the most vulnerable area to liquefaction due to volcanic loose sand layers, shallow groundwater, and thick deposits. However, almost all subsurface images from resistivity tomography from North Lombok show limestone layers at shallow depths, which may play an important role as a protective layer from liquefaction phenomena in this area.

Geomorphological evolution of the calcareous coastal cliffs in North Iberia (Asturias and Cantabria regions)

This paper presents an analysis of the main morphologies observed in the coastal cliffs of northern Spain (Asturias and Cantabria regions). The objective of this contribution is to establish a hypothesis on the origin and evolution of this rocky coast, as well as to present a detailed inventory, to characterise quantitatively and qualitatively singular morphologies and to highlight the geological heritage of this protected coast. The evolution process starts with the formation of an ancient coastal planation surface characterised by a flat morphology caused by regional mainly uplift and to relative sea level falls. Afterwards, wave erosion processes would have started eroding the cliff foot and simultaneously, karst activity produced some exokarst morphologies (sinkholes, karren, etc.) through stratification and fracturing network, while the underground drainage systems produced some caves and chasms. In the following step, corresponding to the last glaciation from the paleoclimatic point of view, sea level fall together with a deepening of the fluvial network caused the preservation of the existing caves and chasms and the generation of new ones at a lower level. On the other hand, dissolution processes on limestones created sinkholes in those areas characterised by alternating layers of limestones and marls, generating collapses. When the sea level reached the maximum height during the Holocene a new erosion cycle of the coastal cliffs began. As a consequence, new landforms and processes were produced, like bays, caves fillings, and intrusion of new sediments in small confined estuaries. In these areas, other types of morphologies associated with the last sea level rise can be observed, such as closed beaches, uncommon closed estuaries developed inside a sinkhole, blowholes produced by mixed wave action and widening of prevailing vertical pipes inside the limestones (including the second largest in the world), total or partial sedimentary filling of small confined estuaries, as well as a tombolo deposit. It is important to point out, that some sites described are included in the Spanish Inventory of Sites of Geological Interest (IELIG). Due to the evolution model here proposed, a portion of the coastal sector described are included in the Global Geosites Project.

Application of the Concrete Stressmeter for Augered Cast-in-Place (ACIP) Deep Foundation Testing

The conventional method of computing forces from strain gage data during deep foundation load testing relies on knowing the cross-sectional area and Young’s Modulus of the pile’s concrete or grout. Errors in estimating these parameters directly affect the computed force distribution of the foundation element being tested. Since the standard formulas were derived for concrete with coarse aggregates, the problem of estimating Young’s Modulus for augered-cast-in-place (ACIP) piles or other piles constructed with grout is compounded by the lack of mathematical relationships for converting grout strength into modulus of elasticity. Concrete Stressmeters (CSMs) are instruments designed to overcome these difficulties and directly measure unidirectional stress in cementitious materials. The instrument design creates a load cell out of the in-place cementitious material itself, with the same elastic properties as the surrounding material. This study discusses the installation and data analysis of two ACIP bi-directional static load test (BDSLT) piles instrumented with CSMs, to validate the use of these instruments as an alternative to strain gages. The first test pile had a nominal diameter of 610 mm and a length of 26 m; the second test pile had a diameter of 760 mm diameter and a length of 35 m. Both piles were installed in Dade County, Florida, in alternating layers of sand and limestone. CSMs installed using the self-filling method yielded excellent comparison to force values derived from strain gages. An error analysis indicated a potential order of magnitude improvement in the accuracy of computed forces using the stressmeters as opposed to the strain gages, due to minimal reliance on an estimated Young’s Modulus. The two case histories yielded comparable and reasonable force distributions with considerably less effort and fewer assumptions. The paper aims to stimulate the discussion and development of reliable alternatives to traditional strain-gage based analyses.

Delaminated Fracturing and its Controls on Hydrocarbon Accumulation in Carbonate Reservoirs of Weak Deformation Regions: A Case Study of the Yuanba Ultra-Deep Gas Field in Sichuan Basin, China

Since the discovery of the Yuanba gas reservoir, there has been no unified conclusion of hydrocarbon accumulation. The Feixianguan Formation micrite and argillaceous limestone are controversial as the direct cap rock. This research analyzed the integrity of the limestone layer from delaminated fracturing to judge whether it can be as the caprock and then discuss the mechanism of accumulation. Delaminated fracturing and its controls on hydrocarbon accumulation were studied using seismic data, well logging data, rock mechanic measurements, and petroleum geological data. Mudstones from the Upper Permian Wujiaping Formation serve as the source rock. Changxing Formation dolomite from the Upper Permian is the reservoir rock. The caprock is marlites from the Lower Triassic Feixianguan Formation. The Changxing Formation had middle-high dip angle fractures formed by integrating pore fluid pressures and the tectonic stresses in the Late Triassic Indosinian Movements. The Feixianguan Formation had horizontal stylolites and fewer fractures, which kept the Feixianguan Formation marlites good caprocks. The adjacent Feixianguan and Changxing formations have their fracture system known as delaminated fractures. As a result, the Upper Permian Changxing Formation dolomite has good reservoir properties, while the Lower Triassic Feixianguan Formation limestone or marlites have good capping performance. These delaminated fractures are formed because of different lithologies and thicknesses in the carbonate rock series. It is the key factor in controlling the formation of Yuanba Gas Field with weak deformation. Delaminated fracturing suggests a significant exploration potential in carbonate strata with weak deformation, particularly in ultra-deep areas.

Lower Ludfordian (Upper Silurian) slope deposits in the Lyagadin section (Ilych River, the Northern Urals)

Research subject. Upper Silurian (Lower Ludfordian) slope deposits of the Lyagadin section (Ilych River, Northern Urals).Materials and methods.The composition and structure of 40 rock samples collected across the section during fieldworks in 2019 were studied. Thin sections were examined under a polarising microscope. Eight samples were investigated by silicate analysis, and clay minerals from 2 samples were determined by X-ray diffraction analysis of oriented samples.Results. The Lyagadin section with a visible thickness of 70 m is represented by an uneven alteration of clayey-siliceouscalcareous schists, micro-grained limestones with burrows, micro-fine-grained layered limestones, fine lime sandstones, coarse- and medium-grained lime sandstones, lime conglogravelites and lime conglobreccias. Clayey-siliceous-calcareous schists and micro-grained limestones with burrows characterise the background periplatform clayey-carbonate deposits. The part of micro-fine-grained layered limestones (their horizontally layered varieties) are bottom current sediments. Gravity flow deposits are represented by clastic rock assemblage. The most characteristic of them is the assemblage composed of lime conglogravelites with an erosional bottom, which pass into gradational-layered lime sandstones, first coarse- and medium-grained, and further the into their fine-grained varieties. They are covered, in turn, with micro- fine-grained limestones with cross or convolute stratifications. That association is interpreted as calciturbidites. Calcidebrites are characterised by lime conglobreccias. The deposits of grainy flows (?) are represented by the layers of lime sandstones not revealing the characteristic features of the Bouma sequence.Conclusion. The reconstructed background sedimentation on the continental slope during Early Ludfordian was characterised by the accumulation of hemi-pelagic clay deposits together with a certain amount of microscopic quartz, orthoclase and organic matter. Periodically appearing thin layers of micro-grained limestones with burrows correspond to the periods of increased supply of carbonate material, which could be attributed to “marine snow”. The irregular nature of the distribution of gravity flow deposits in the Lyagadin section suggests that the studied slope deposits are, most likely, the formation of the outer apron of slope bottom, rather than calciclastic fans.

Effective co-treatment of synthetic acid mine drainage and domestic sewage using multi-unit passive treatment system supplemented with silage fermentation broth as carbon source

A multi-unit passive treatment system was constructed for co-treatment of synthetic acid mine drainage (AMD) and domestic sewage supplemented with silage fermentation broth as carbon source. AMD and domestic sewage mixing pretreatment (unit 1) improved influent quality with pH increase, metals removal and nutrients supplement. The generated metal-rich sludge in unit 1 retained the metals (69.95% of Fe, 97.36% of Cu, 96.53% of Cd, 72.52% of Zn, and 8.59% of Mn) of influent prior to entering subsequent bioreactors. Silage fermentation broth performed well to promote bacterial sulfate reduction in sulfate reducing bioreactor system (unit 2). Residual metals (Mn) and organic/nutrient pollutants were further polished in surface-flow aerobic wetland (unit 3), where relatively high pH (7.4–8.6), aerobic condition, potential Mn-oxidizing bacteria, limestone layer and low concentrations of Fe(II) (0.04–3.5 mg/L) favored the efficient removal of Mn. After 210-day continuous flow-through experiment, this passive treatment system demonstrated the efficient performance, increasing pH from 2.5 to 8.0 with removal of metals (99%), sulfate and organic/nutrient pollutants. Diverse sulfate reducing bacteria including complete organic oxidizers (e.g. Desulfobacter) and incomplete organic oxidizers (e.g. Desulfovibrio) promoted sulfate reduction and organic/nutrient pollutants removal. Ammonia oxidizing bacteria (e.g. Nitrosomonas) and nitrite oxidizing bacteria (e.g. unidentified_Nitrospiraceae) were the potential nitrifiers for ammonia removal. Collaboration of anaerobic denitrifiers (e.g. Denitratisoma) and potential heterotrophic nitrifying and aerobic denitrifiers (HN-AD) achieved effective nitrate removal. This multi-unit treatment system with domestic sewage and silage fermentation broth as stimulation substrates provided an attractive option for AMD treatment.

Torrent rainfall-induced large-scale karst limestone slope collapse at Khanh waterfall, Hoa Binh Province, Vietnam

In recent years, many landslides have occurred in Vietnam, particularly in the Northern mountainous region during the rainy season from May to October. On the morning of October 12, 2017, the Khanh waterfall landslide in Khanh Village, Hoa Binh Province, Northern Vietnam occurred. The landslide killed eighteen people and destroyed five houses. Topographical and geological surveys were conducted around the area to determine its causes. The rainfall data and flow discharge were also analyzed. The results showed that this collapse was different from some previous ones collapsed due to the erosion at the toe of the slope. Khanh waterfall landslide occurred due to the increasing amount of water in cracks and caves in the limestone layer in the slope. The collapse process was simulated based on Coulomb mixture theory. The numerical simulation results show similarities with the actual collapse process. The results provide indicators for assessing the risk of such limestone waterfall landslides in the future.

Application of geophysical and hydrogeological analyses to predict water and hydrocarbon entry to the T5 Tunnel, west Iran

The Garmsiri Project, including the 4.5 km long T5 Tunnel, is under construction in western Iran. The T5 Tunnel passes through the NW–SE-trending Emam Hasan Anticline (EHA), perpendicular to the fold axis. The fold is mainly composed of marlstone and argillaceous limestone layers of Cretaceous to Miocene age, incorporating the Pabdeh–Gurpi Formation, karst limestone of the Asmari Formation, and marlstone and gypsum of the Gachsaran Formation. There was a risk of water entry into the tunnel as it was constructed below the regional groundwater table elevation. In addition, the entry of hydrocarbons, in either liquid or vapour phase, into the tunnel was possible owing to the presence of numerous active bitumen mines in the vicinity of the anticline. To predict the risk of water or hydrocarbon entry geological and hydrogeological analyses together with the audio magnetotelluric (AMT) method were applied. Based on the field work, resistivity and geological cross-sections were provided along the tunnel path. Several boreholes were drilled along the tunnel route and water-table elevation, rock quality designation (RQD) and permeability values were measured. To determine a broad range of features related to the anticline, 55 AMT stations were positioned along the tunnel route. Dimensionality analysis confirmed 2D dimensionality of the AMT transfer functions, which allowed us to apply the 2D bimodal inversion using a non-linear conjugate gradient algorithm. Integration of the geological and hydrogeological data with the resistivity model resulted in a more detailed geological section along the tunnel, including water-table elevation and identification of highly conductive zones in which bitumen migrated. It was predicted that water entry would be observed through the Asmari Formation and also that elevated H 2 S concentrations would be encountered during drilling in the anomalous conductive zones. Monitoring results and field observations gained during the tunnel construction were compared with the predictions.

3-D numerical constraints for the Triassic mafic igneous system of Antalya (SW Turkey): Magma generation associated with southern Neotethyan slow seafloor spreading

A ~ 400 m thick Middle-Late Triassic volcano-sedimentary succession crops out in a relatively narrow corridor ~75 km long and ~ 25 km wide close to Antalya Gulf, SW Turkey. The volcanic and subvolcanic rocks represent the majority of the succession and are associated with epiclastic breccia, turbiditic sediments as well as chert and limestone layers. The igneous rocks are alkali basalts, with incompatible element content matching the classical HiMU-OIB types. These are considered as the precursors of a rift system that would have later evolved into a mature Neotethyan oceanic system, with emplacement of massive tholeiitic basalt sequences, not recorded in the investigated area.Clinopyroxene-melt thermobarometric constraints indicate the presence of two main magma chambers, one equilibrated at ~7–10 km depth and ~ 1070 °C and the other at ~15–21 km depth and ~ 1300 °C. Based on these estimates, a 3-D finite element modelling has been applied, simulating the presence of ellipsoidal magma chambers at different depths and with variable sizes, applying different boundary loading conditions. The scenario that best fits the distribution of the volcanic rocks assumes the contemporaneous presence of two magma reservoirs. One is shallow, with a size of ~17 × 1.5 × 1.5 km, and the second is deeper, with a size of ~37 × 3 × 3 km. Numerical simulations show maximum 6 m opening and dilation through horizontal plane at the surface during the Permian/Triassic intracontinental rift phases. Morphological constraints of this rift zone, with the presence of massive lava eruptions also as pillow facies, have been simulated with the existence of a slowly opening rift system. In order to produce the voluminous magma batches in the Antalya region, pure extensional tectonic regimes seem insufficient, and the presence of a transtensional regime must have accompanied the tectonic forces during the Triassic intracontinental rifting stage.

Identification of aquifer zone in the southern part of Sukoharjo Regency using VES method as a means of irrigation of agricultural land

Sukoharjo is one of the regencies in Indonesia that is famous for its agricultural land. Sukoharjo itself has 12 sub districts spread evenly throughout. In recent years, there have been many conflicts of irrigation water shortages for agricultural land. Therefore, research was conducted on the aquifer zone of the southern district of Sukoharjo. The research was conducted by Vertical Electrical Sounding method to determine the structure of soil in order to improve the efficiency of deep groundwater drilling for irrigation. The study used Schlumberger’s configuration with a target zone of deep aquifers for agricultural irrigation. The length of the track used is 275-300 meters. As a result of the study, it is suspected that the aquifer zone in southern Sukoharjo Regency has a depth of about 11.54-83.93 meters below the subsurface. The soil structure in south of Sukoharjo is dominated by sandy clay layers, limestone layers, and sedimentary layers.

Walkaway Vertical Seismic Profiling (WVSP) Modeling and Imaging Study along FaultedCoal Seams over a High Velocity Limestone Model: A Synthetic Study

The problem of collecting reflection data from the layers below a high velocity layer (HVL) and imaging those layers accurately is solved using walkaway vertical seismic profiling (WVSP) technique. The procedure is shown on a dataset from a model of highly faulted, thin-bedded coal layers separated by a high velocity layer of limestone. By locating the receivers above, in, and below the HVL, the reflections are expected to be recorded locally in situ in the borehole below the HVL before they travel back to the surface as in the case of surface seismic. The imaging results obtained from the model (or synthetic) WVSP data lead to the conclusion that promising results may be obtained via the acquisition of field WVSP data such that the layers below the HVL are well-imaged. Analysis of the test results showed that the layers below the HVL can be imaged accurately and robustly when the receivers are situated below the HVL only, while the strong images below the HVL tend to fade away and lose their strength when the receivers are moved above the HVL. However, both these cases of the receiver location geometry are needed to obtain images that are vertically and horizontally stable. When a full instrumentation of the borehole is provided, good images as far as 500 m away from the VSP borehole are obtained from the layers with various dips and faults that are nearly 800 m in depth from the surface. Two cases of velocities (4000 m/s and 5000 m/s) are tested for the high velocity limestone layer. Both cases showed good images below the HVL. Unfortunately, some pulled-up effects are seen in the images right below the HVL where the layers that are immediately below the HVL are imaged above their correct locations, the pulled-up effects are corrected in the deeper sections below the HVL however. Comparison of a depth converted corridor stack from the zero offset VSP data and the depth migrated image show good agreement.

Walkaway Vertical Seismic Profiling (WVSP) Modeling and Imaging Study along FaultedCoal Seams over a High Velocity Limestone Model: A Synthetic Study

The problem of collecting reflection data from the layers below a high velocity layer (HVL) and imaging those layers accurately is solved using walkaway vertical seismic profiling (WVSP) technique. The procedure is shown on a dataset from a model of highly faulted, thin-bedded coal layers separated by a high velocity layer of limestone. By locating the receivers above, in, and below the HVL, the reflections are expected to be recorded locally in situ in the borehole below the HVL before they travel back to the surface as in the case of surface seismic. The imaging results obtained from the model (or synthetic) WVSP data lead to the conclusion that promising results may be obtained via the acquisition of field WVSP data such that the layers below the HVL are well-imaged. Analysis of the test results showed that the layers below the HVL can be imaged accurately and robustly when the receivers are situated below the HVL only, while the strong images below the HVL tend to fade away and lose their strength when the receivers are moved above the HVL. However, both these cases of the receiver location geometry are needed to obtain images that are vertically and horizontally stable. When a full instrumentation of the borehole is provided, good images as far as 500 m away from the VSP borehole are obtained from the layers with various dips and faults that are nearly 800 m in depth from the surface. Two cases of velocities (4000 m/s and 5000 m/s) are tested for the high velocity limestone layer. Both cases showed good images below the HVL. Unfortunately, some pulled-up effects are seen in the images right below the HVL where the layers that are immediately below the HVL are imaged above their correct locations, the pulled-up effects are corrected in the deeper sections below the HVL however. Comparison of a depth converted corridor stack from the zero offset VSP data and the depth migrated image show good agreement.

INFLUENCE OF SWELLING ON SHEAR STRENGTH OF SHALE-LIMESTONE INTERFACE

Rock slope stability is almost controlled by the behaviour of the interface between rock layers. The presence of shale layers between limestone layers complicates this behaviour. As the shale layer undergoes swelling with moisture, it causes the shear interface properties to change with a specific behaviour different from the dry state. The behaviour will depend on the shale’s degree of saturation, swelling percentage, and stress level over shale. An experimental program was carried out to determine the shear interface behaviour parameters of shale-limestone during swelling phenomena to guide stability checks. The interface cohesion and friction angle results are reported along the swelling process and compared with the dry state condition. These results help engineers assign adequate and accurate values for joint shear and normal stiffness in jointed rock slopes, including swelling layers.

Evaluating an Unconventional Shale Completion with Repeat Crosswell Tomography

Evaluation of hydraulic fracturing relies on indirect inference from measurements that are distorted by distance and noise of various kinds, so reservoir monitoring technology that places the measurement as close to the completion as possible is important. Crosswell tomography is just such a technology, placing source and sensor in the plane of the feature to be analysed, and is an excellent technology for making in situ estimates of subsurface properties in simple geologic settings when source-receiver separation is small and when noise levels are low. Since these conditions are not typical in-field scale surveys of unconventional shales, this study overcomes these deficits by incorporating vertically transverse isotropy in raytracing and applying a strong source effort to increase signal-to-noise. The survey used Schlumberger’s Ztrac source and multicomponent geophones to both generate and record compressional and shear wave energy, matching baseline and repeat surveys within a few days of hydraulic fracturing to detect subtle timelapse changes prior to flowback and fluid diffusion. The result is a unique characterization of fracture creation due to hydraulic fracturing, highlighting an out of zone response and subsequent impact on the bounding limestone layers.

A new 1.32 Ga Tianshui mafic sill in the Liaodong area and its relations to the Yanliao large igneous province in the northern North China Craton

A new 1.32 Ga Tianshui mafic sill was identified in the Liaodong area, which enlarges the scale of the Yanliao large igneous province (LIP, extending >600 km) in the North China Craton. It intrudes concordantly into limestone layers and is overlain by Neoproterozoic strata. SIMS baddeleyite Pb-Pb dating on two coarse-grained gabbros yields weighted mean 207Pb/206Pb ages of 1324 ± 2 Ma (n = 20, MSDW = 1.5) and 1326 ± 5 Ma (n = 9, MSDW = 1.3), similar to those of mafic sills in the Yanliao LIP. The Tianshui mafic sill shows a similar E-MORB geochemical character as the mafic sills in the Yanliao LIP, including tholeiitic composition, enriched light rare earth elements (La/YbN = 2.45–3.77), and large ion lithophile elements, but depleted high field strength elements, positive baddeleyite εHft values of 3.59–10.96, with a peak of 6.07, and negative whole-rock εNdt values of −1.8 to −0.6, with an average of −1.3, indicative of an enriched mantle source. The host limestone layers are 800 m thick and possibly contemporaneous with the Mesoproterozoic Gaoyuzhuang Formation of the Liaoxi area. The 1.32 Ga Yanliao mafic sills underwent extensive crystallization differentiation controlled by olivine, clinopyroxene, and plagioclase. They were generated at a high primary temperature of ∼1550 °C and crystallized at ∼1140 °C at 0.24 kbar, which could be related to the mantle plume magmatism.

An integrated feasibility study using passive geophysical methods for the investigation of the Gerolekas bauxite deposits site, Greece

ABSTRACTThe scope of this research is to delineate an optimized strategy for the implementation of cost‐effective and environmentally friendly passive geophysical methods in a challenging environment, in this case the Gerolekas bauxite mines, Greece. In this region, bauxite deposits have been detected and are being exploited at the interfaces between limestone layers in the autochthonous zone of Parnassus–Giona. The area under investigation, Gerolekas, is an allochthonous overthrust zone that overlays a part of the autochthonous geological structure. Currently, there is no information about the possible continuation of the bauxite deposits under Gerolekas below a certain depth. In this study, an integrated multi‐parameter approach using gravity, magnetotelluric and passive seismic methodologies is evaluated through a feasibility study incorporating realistic synthetic data. The specific strategy involves building a lithological model of the area by exploiting more than 4000 boreholes and incorporating data from in situ geological observations and official geological mapping. The 3D lithological model is then converted to equivalent geophysical models, based on in situ measurements, both on the surface and inside the mining galleries, as well as on data from previous studies in the literature, which together serve as the basis for the inversion procedures. The feasibility study is applied, simulating two different extreme realistic scenarios, by adding synthetic boreholes to the real ones, setting the optimum parameterization to control any possible scenario to be resolved, and evaluating the contribution of a priori information, to create starting models. Finally, a multi‐parameter analysis is formulated and applied to all inverted models to create a litho‐constrained unified geophysical model, providing an unbiased, integrated, statistically driven model of the area and generating updated geophysical models that are significantly improved.

Experimental study on the adoption of flushing technique in successive alkalinity-producing systems with a focus on influence radius of orifice

As a successive alkalinity-producing system pond for purifying mine drainage is operated, sediment accumulates in the limestone layer of the pond, and as the amount of accumulated sediment increases, the water permeability and treatment efficiency of the pond decrease. Hence, a flushing system is required, comprising of a network of perforated pipes installed in the limestone layers, to periodically discharge sediment and mine drainage to the outside. The performance of a flushing system depends on four distinct characteristics of the system: the characteristics of the limestone layer, the sediment, the flow, and the flushing device. However, existing studies have evaluated the performance of the entire system without considering these conditions. In this study, a new experimental method for designing a flushing system is proposed. This method is based on an experiment to evaluate the influence radius of orifice, which is the radius of the spherical volume around an orifice that can suck sludge by flushing. The results showed that the flow rate of water through the orifice in the glass bead layer matched well with the Blake–Kozeny formula, and that the greater the diameter of the orifice is, the greater the influence radius of orifice. The influence radius of orifice according to the diameter and spacing of the orifice was evaluated, which provides a key criterion for designing a flushing system.

Geochemistry of upper Palaeozoic ‘thin-layer’ limestones in the southern North China Craton: implications for closure of the northeastern Palaeotethys Ocean

AbstractDuring the late Palaeozoic Era, a series of related marine strata dominated by multi-layer limestones were deposited in the southern North China Craton. In order to gain new insights into the systematic geochemistry of the carbonate succession of the representative formation (Taiyuan Formation), we examined 59 limestone samples collected from the Huaibei Coal Basin (HCB), with a view towards quantitatively determining the major and trace elements and stable isotope compositions. The data obtained can provide essential evidence for reconstruction of the depositional palaeo-environment and tectonic setting of the Taiyuan Formation. Both X-ray diffraction analyses and palaeoredox proxies (e.g. V/Cr, V/(V + Ni) and authigenic U) indicated that the limestone layers were deposited in an oxic–dysoxic zone, with calcite as the main component. Moreover, palaeomagnetic evidence provided support for the conclusion that these limestones were laid down within an epicontinental sea depositional environment under a warm or hot palaeoclimate during the transition between late Carboniferous and early Permian time. Additionally, evidence obtained from our analyses of trace and rare earth elements revealed that the tectonic setting of the Taiyuan Formation (L1–L5) in the HCB transited from an open ocean to a passive continental margin, thereby indicating that this transformation stemmed from the subduction closure of the northeastern Palaeotethys Ocean. The findings of this study would be of interest to those working on the upper Palaeozoic marine strata in the southern North China Craton.