Drill Core Samples Research Articles

Evidence of widespread wildfires in coal seams from the Middle Jurassic of Northwest China and its impact on paleoclimate

Today wildfire is an important disturbance in many continental ecosystems, and it is assumed that with ongoing climate changes the frequencies and impacts of wildfires will increase in many regions. One way to obtain information about the potential long term influences of wildfires on ecosystems and the climate system itself is to study palaeo-wildfires. A total of 140 Jurassic samples, including 122 coal samples and 18 rock samples from roof and floor of coal seams, were collected from 4 coalfields in Northwestern China. The samples were analyzed by macropetrography, microscopy, scanning electron microscopy, gas chromatography, and gas chromatography–mass spectrometry to study the evidences of wildfires and their impact on the paleoclimate. High contents of pyrogenic inertinites (charcoal), natural char and natural coke particles observed in the samples which indicate that widespread wildfire events occurred in the early Middle Jurassic in all over Northwestern China. Additionally, high-molecular-weight polycyclic aromatic hydrocarbons were detected in the coal samples. These aromatic compounds were formed under high temperature and provide further evidence of wildfires. According to a carbon emission model for modern forest fires, the total carbon and gas emissions from wildfires in peat swamps of the Middle Jurassic in Northwest China were calculated by the data from 21,575 coal samples of number of 1567 drill core samples. The total carbon released from peat-swamp forest wildfires was at least 1207 Gt, corresponding to emissions of CO2, CO and CH4 of 1926 Gt, 163 Gt, and 8.8 Gt, respectively. The huge amount of CO2 released by forest fires in the peat swamp systems of the Middle Jurassic in Northwestern China alone was equivalent to 64.20% of the total CO2 in the atmosphere at present (3000Gt). The large amounts of greenhouse gases released by wildfires must have led to long-term changes in the atmospheric composition and have caused global warming, which could have the reason of affected the paleoclimate.

Lead Isotopes in Exploration for Basement-Hosted Structurally Controlled Unconformity-Related Uranium Deposits: Kiggavik Project (Nunavut, Canada)

Pb-isotopes have been proposed as pathfinders for sandstone-hosted unconformity-related U deposits, with isotope ratios providing information on mineralization timing and element remobilization and migration. Pb-isotopes proximal to mineralization display radiogenic signatures, often with ‘excess Pb’ suggestive of derivation from greater U concentrations than are currently present. The U deposits in the Kiggavik project area (west of Baker Lake, NU, Canada) are basement-hosted, contain several generations of pitchblende mineralization, display a strong structural control, and are located in fault-related fracture systems and foliation-parallel veinlets. Drill core samples were analysed by Inductively-Coupled Plasma-Mass Spectrometer (ICP-MS) for Pb isotopes following multi-acid total-digestion, reverse Aqua Regia partial-digestion, and weak-acid-leach attacks, to evaluate the utility of the respective dissolution methods in Pb-isotope pathfinder geochemistry. Partial-digestion results are similar to weak-acid-leach results, indicating that interpretation of Pb-isotope signatures can be carried out from partial-digestion data if weak-acid-leach data are unavailable. Application of this pathfinder method at Kiggavik shows that Pb-isotope ratios display systematic trends useful for exploration vectoring. Uranium-content-adjusted 206Pb/204Pb ratios and 206Pb/204Pb ‘excess-lead’ data highlight anomalous isotopic values. 207Pb/206Pb ratios display downhole trends complementary to location of mineralization. Three-dimensional (3D) distributions of Pb-isotope data at the Contact U prospect show systematic trends and form halos around the mineralization. Isotopic footprints are limited to <50 m from the mineralization outline, reflecting host-rock and structural control, but indicate areas with elevated potential for U mineralization and provide vectoring information within basement lithologies.

Textural Quantification and Classification of Drill Cores for Geometallurgy: Moving Toward 3D with X-ray Microcomputed Tomography (\xb5CT)

Texture is one of the critical parameters that affect the process behavior of ore minerals. Traditionally, texture has been described qualitatively, but recent works have shown the possibility to quantify mineral textures with the help of computer vision and digital image analysis. Most of these studies utilized 2D computer vision to evaluate mineral textures, which is limited by stereological error. On the other hand, the rapid development of X-ray microcomputed tomography (µCT) has opened up new possibilities for 3D texture analysis of ore samples. This study extends some of the 2D texture analysis methods, such as association indicator matrix (AIM) and local binary pattern (LBP) into 3D to get quantitative textural descriptors of drill core samples. The sensitivity of the methods to textural differences between drill cores is evaluated by classifying the drill cores into three textural classes using methods of machine learning classification, such as support vector machines and random forest. The study suggested that both AIM and LBP textural descriptors could be used for drill core classification with overall classification accuracy of 84–88%.

Preferred orientation distribution of shock-induced planar microstructures in quartz and feldspar.

Shocked quartz and feldspar grains commonly exhibit planar microstructures, such as planar fractures, planar deformation features, and possibly microtwins, which are considered to have formed by shock metamorphism. Their orientation and frequency are typically reported to be randomly distributed across a sample. The goal of this study is to investigate whether such microstructures are completely random within a given sample, or whether their orientation might also retain information on the direction of the local shock wave propagation. For this work, we selected samples of shatter cones, which were cut normal to the striated surface and the striation direction, from three impact structures (Keurusselkä, Finland, and Charlevoix and Manicouagan, Canada). These samples show different stages of pre‐impact tectonic deformation. Additionally, we investigated several shocked granite samples, selected at different depths along the drill core recovered during the joint IODP‐ICDP Chicxulub Expedition 364 (Mexico). In this case, thin sections were cut along two orthogonal directions, one parallel and one normal to the drill core axis. All the results refer to optical microscopy and universal‐stage analyses performed on petrographic thin sections. Our results show that such shock‐related microstructures do have a preferred orientation, but also that relating their orientation with the possible shock wave propagation is quite challenging and potentially impossible. This is largely due to the lack of dedicated experiments to provide a key to interpret the observed preferred orientation and to the lack of information on postimpact orientation modifications, especially in the case of the drill core samples.

The Mesoarchaean Dominion Group and the onset of intracontinental volcanism on the Kaapvaal craton – Geological, geochemical and temporal constraints

The ca. 3.07 Ga volcanic rocks of the Dominion Group, South Africa, represent the oldest example of intracontinental, rift-related volcanism on the Archaean Kaapvaal craton. The volcanic assemblage comprises a >2 km-thick succession of mafic-intermediate lavas interlayered with felsic lavas and pyroclastic rocks. Textural and geological features indicate emplacement in a subaerial environment probably in an incipient intracontinental rift. We report SHRIMP UPb zircon ages, elemental and Nd-isotope bulk-rock analyses of drill core samples and interpret their petrogenesis in the context of a Mesoarchaean continental setting. The UPb zircon ages of four felsic samples from different stratigraphic levels yielded the same dates, resulting in a pooled 207Pb/206Pb age of 3074 ± 5 Ma. Primitive mantle-normalised incompatible trace element concentrations show enriched patterns with fractionated rare earth elements over high field-strength elements and negative anomalies of Nb and Ta relative to La.Initial εNd values for mafic and felsic rocks from −1.0 to −0.2 indicate melting of sources comprising time-integrated incompatible element-enriched mantle. The combined trace element and SmNd isotopic data suggest that the enrichment of incompatible elements and the low εNd values in the most primitive basalt samples (Mg# of 65–67) can be explained with contamination of asthenosphere-derived melts with crustal material or melting of an incompatible element-enriched upper mantle. The chemical compositions of the Dominion Group and Pongola Supergroup represent a significant petrogenetic departure from earlier Archaean (>3.6–3.1 Ga) magmatism as recorded in the Kaapvaal craton, which was dominated by komatiite-basalt volcanism and tonalite-trondhjemite-granodiorite intrusions. This change reflects the transition from a “greenstone belt type” tectonic setting to a failed intracontinental rift setting shortly after stabilisation of the Kaapvaal craton.

A novel technique for asphalt pavement interlayer contact condition diagnosis

Asphalt pavement is a multi-layer continuous structure with an interlayer bonding condition that can greatly influence its bearing capacity and must be monitored over the whole service length. Hence, proper maintenance and rehabilitation measures are taken and better feedback can be made for the design. Nevertheless, asphalt pavement interlayer bonding condition plays a hidden role and is difficult to quantify unless applying damage discovery techniques like drilling core process. The original structure is destroyed by the damage detection approaches, the results also suffer from low coverage rate and high dispersion, therefore, actual engineering demands are not satisfied. Here, some recent methods are briefly presented based on asphalt pavement interlayer bonding condition non-destructive diagnosis and their restrictions are discussed. Moreover, a new technique is provided with the merits of utilizing only mechanical simulation and overall superficial distresses condition evaluation index with high accuracy. This simulation procedure adopts bridging principles to build a connection between asphalt pavement superficial distresses and asphalt pavement micro mechanic parameters. It uses a structure behavior equation capable of identifying four typical deterioration modes and has specific physical meaning parameters to predict asphalt pavement overall superficial distresses. The established model allows the asphalt pavement interlayer bonding acting as a hypothetical input variable. The known input variables include easily obtainable design parameters of the asphalt pavement structure, historical superficial distresses, surface deflection, traffic load, and environmental factors, however, the output is the predicted asphalt pavement overall superficial distresses condition. The asphalt pavement interlayer bonding condition is defined by contrasting the theoretical asphalt pavement overall superficial distresses conditions between its complete bonding condition and discontinuous bonding condition to a certain degree. Examples in parts of the Jingha highway show that great discrepancies exist between theoretical asphalt pavement overall superficial distress in the condition of complete interlayer bonding and actual asphalt pavement overall superficial distress. The actual asphalt pavement sections in overall superficial conditions are deteriorated much faster than normal ones. By setting the asphalt pavement interlayer bonding continuations as 75% and 90% for K315–K316 section and K316–K317 section, respectively, the revised and predicted overall superficial distresses of the theoretical asphalt pavement are consistent with the real ones. The hypothetical values are then chosen as the diagnosed quantitative asphalt pavement interlayer bonding continuations and are proven to be correct through drilling core sample results. The analyses in other sections show that middle traffic volume asphalt pavement structure is quite weak when its interlayer bonding continuation is 70%, and under this value, its bearing capacity is almost equivalent to the situation when its interlayer bonding continuation is 0%; when its interlayer bonding continuation is 85% or more, its bearing capacity is almost equivalent to the situation where its interlayer bonding continuation is 100%. This proposed non-destructive diagnosis method for asphalt pavement interlayer bonding condition is effective and shows good application prospects in road engineering.

Drill-Core Mineral Abundance Estimation Using Hyperspectral and High-Resolution Mineralogical Data

Due to the extensive drilling performed every year in exploration campaigns for the discovery and evaluation of ore deposits, drill-core mapping is becoming an essential step. While valuable mineralogical information is extracted during core logging by on-site geologists, the process is time consuming and dependent on the observer and individual background. Hyperspectral short-wave infrared (SWIR) data is used in the mining industry as a tool to complement traditional logging techniques and to provide a rapid and non-invasive analytical method for mineralogical characterization. Additionally, Scanning Electron Microscopy-based image analyses using a Mineral Liberation Analyser (SEM-MLA) provide exhaustive high-resolution mineralogical maps, but can only be performed on small areas of the drill-cores. We propose to use machine learning algorithms to combine the two data types and upscale the quantitative SEM-MLA mineralogical data to drill-core scale. This way, quasi-quantitative maps over entire drill-core samples are obtained. Our upscaling approach increases result transparency and reproducibility by employing physical-based data acquisition (hyperspectral imaging) combined with mathematical models (machine learning). The procedure is tested on 5 drill-core samples with varying training data using random forests, support vector machines and neural network regression models. The obtained mineral abundance maps are further used for the extraction of mineralogical parameters such as mineral association.

Incremental Growth of Layered Mafic-Ultramafic Intrusions Through Melt Replenishment Into a Crystal Mush Zone Traced by Fe-Hf Isotope Systematics

Layered mafic-ultramafic intrusions are among the largest igneous bodies on Earth, and represent aggregations of large volumes of mantle- and some crustal-derived melts. Melts are emplaced over time-intervals of less than one million years, predominantly through multiple pulses of injections into pre-existing melt-crystal slurries. The dynamic interaction of physical processes, including density-driven separation and mixing of different components, within a solidifying magma chamber leads to such extreme chemical diversity between cumulate rock units, that no unified model currently explains all aspects of the genesis of these intrusions. Here we present whole-rock stable Fe isotope data (expressed in ‰ variations as 57Fe relative to IRMM-014) for samples of drill core taken from the stratified paleo-magma chamber of the Upper Zone of the late-Archean Windimurra Igneous Complex, Western Australia. Variations from near chondritic (57Fe ~ +0 ‰) to heavy (57Fe~ +0.2 ‰) values show a co-variation with initial radiogenic Hf isotope data that is unique to the Windimurra Upper Zone. The systematic isotopic variations from the roof to the base of the Upper Zone are best explained by an intricate sequence of events that included fractional crystallisation and physical mixing. We propose that melt freshly sourced from the mantle was injected into and inflated a pre-existing crystal-melt mush comprising the upper Middle Zone. Re-establishment of crystal layering after replenishment introduced a chemical stratification with the formation of what became the Upper Zone and a crystal-interstitial melt ratio decreasing from roof to base. Basal, vanadiferous magnetitite horizons crystallised through enhanced fO2 during liquid replenishment. Variable degrees of perturbation and chaotic stirring of crystals with imperfect mixing of new and old components was followed by rapid crystal settling and subsequent cumulate stratification. Such melt rejuvenation, proposed here to be the cause for a newly established Upper Zone, leaves no unique petrologic fingerprint but can explain not only the observed coupled Fe-Hf isotope systematics but also mineral disequilibria and cryptic layering in layered intrusions.

Pore structure characteristics and fractal dimension analysis of low rank coal in the Lower Indus Basin, SE Pakistan

The significance of pore structure and fractal characteristics is important for understanding untapped Coalbed Methane (CBM) exploration. In this study, these features of low rank coal in the lower Indus Basin, SE Pakistan, were evaluated using drill core samples from several locations. The pore size distribution and fractal dimension on adsorption (AdDs) and desorption (DeDs) values were systematically analyzed by scanning electron microscopy (SEM), low pressure adsorption N2, and CO2 methods for better evaluation of CBM and its pores geometrical mechanism. Coal petrographic properties, were investigated for macerals composition revealed a huminite domination. SEM analysis of various pore structures, showed first-developed pores present in the larger pores and thermogenic gas pores. CO2 density functional theory revealed micropore particle size peaks in three adsorption phases on incremental pore volume (0.47–0.64 nm,0.64–0.83 nm, 0.83–11.11 nm), where gas molecules distort bonding with increasing pore size and define the micropore surface complexities. The mesopore size distribution analysis of differential and incremental pore areas indicated a transition zone at 22.8 nm, suggesting major micro-mesopores within smaller size particles. Nonhomogeneous particle sizes caused a dynamic range of peak trends due to different kinds of porespheres are interconnected with macrosphere, which can trap accessible and inaccessible gas molecules in the different pores structures. Fractal dimension analysis demonstrated that Ds values linear correlation showed a good fit for the AdDs value was 0.98–0.99, and 0.96 to 0.99 for the DeDs value. This finding showed that average obtained surface complexity of AdDs was 2.35, and the DeDs was 2.44 with notably more complicated pore roughness and high semifusinite content, possibly resulting in the higher DeDs value because larger pore spheres consist of microspheres.

Increasing the accuracy of estimated porosity and saturation for gas hydrate reservoir by integrating geostatistical inversion and lithofacies constraints

Abstract Porosity, saturation, thickness of gas hydrate-bearing layers and their spatial distributions are key factors for production tests. The gas hydrate-bearing layers ranging from a few to tens of meters thickness are confirmed by Logging While Drilling (LWD) data and core samples at Sites W11 and SC-03, in the Shenhu area, South China Sea. Gas hydrate-bearing layers of two wells (about 200 m) show that not all layers exhibit good lateral continuity. Several thin layers (~4 m) with low gas hydrate saturations (15–20% of the pore space) or non-gas hydrate are laterally discontinuous. The interbedding of gas hydrate-bearing and non-hydrate layers with different saturations, thickness and random distribution cause the heterogeneities in the reservoir. The gas hydrate saturation and distribution inverted from deterministic and traditional geostatistical inversion have high uncertainties due to the limitations of the empirical relationship and probability density functions (PDFs). A better understanding of spatial distribution and saturation for each gas hydrate layer is useful to build a realistic net hydrate pay and resource estimation. In this study, we first divide gas hydrate saturations, porosity, acoustic impedance into low and high values based on the estimated LWD results, which is call as lithofacies. Then, we propose to create multivariate PDFs by lithofacies constraints. The acoustic impedance, saturation, thickness, porosity of gas hydrate-bearing layers and non-gas hydrate layers are inverted by displaying geostatistical inversion with lithofacies constraint. We found the spatial variations and heterogeneous distributions with a thickness ranging from 4 to 35 m and the laminated gas hydrate layers with saturations ranging from 10% to 40% are clearly shown from seismic data, which are useful for the horizontal well development method of a hydrate production test.

Study of Shale Gas Release from Freshly Drilled Core Samples Using a Real-Time Canister Monitoring Technique: Release Kinetics, Influencing Factors, and Upscaling

Gas release from organic-rich shale rock plays a significant role in the migration and production of hydrocarbons in the shale reservoir. Despite recent progress in gas adsorption/desorption experi...

Integrated geological and geophysical studies for delineation of laterite covered chromiferous ultramafic bodies around Bhuban, southwestern part of Sukinda ultramafic complex, Odisha

Chromite and Platinum Group of Elements (PGE) mineralization in the Eastern Indian Shield region is found in the ultramafic rocks distributed in the Baula-Nuasahi and Sukinda massifs intrusive into the Iron Ore Group (IOG) of rocks. In addition to this, recent geological studies have also reported the occurrences of chromiferous ultramafic bodies within the granulite tracts of Eastern Ghat Group around Asurabandha and Maulabhanja areas in the southwestern part of Sukinda Massif. In the present study, detailed gravity and magnetic surveys (1510 stations) were conducted over a laterite covered area of ~0.16 km2 at Bhuban-Asurabandha to locate the anomalous zones/sources, the geometry of the chromite bearing host rocks and its depth continuity in the subsurface. Four distinct coincident positive gravity anomalies (up to ~0.18 to 0.36 mGal) and residual magnetic anomalies (~−200 to 350 nT) with the NE-SW strike indicate the presence of high density mafic/ultramafic bodies under the laterite cover. The results of 3-D Euler deconvolution and two-dimensional compact gravity inversion models in this region further suggest the presence of high-density material (~3100–3600 kg/m3) at a depth of 20–40 m in the subsurface. Exploratory drill hole data in the area confirms the subsurface occurrence of thin chromiferous serpentinite as lensoidal and sandwiched bodies within the granulite rocks of Eastern Ghat Group. Petrological studies of the drill core samples reveal the occurrences of disseminated and thin banded chromite within the serpentinites which is identical to the Sukinda ultramafics in terms of its mineralogy and alteration. On the other hand, the surrounding mafic granulite rocks contain occasional magnetite and sulfides within the granulite rocks. Hence, the chromiferous ultramafic bodies within the granulite rocks can be considered as the tectonically detached portions of the Sukinda ultramafic rocks during the regional thrusting.

Groundwater flow system analysis in the regolith of Dodowa on the Accra Plains, Ghana

Study Region: Accra Plains. Study Focus: We conducted a field geology mapping, a well inventory exercise, used ERT, drilled boreholes at 8 locations (15–60 m depth), took drill core samples which we subjected to dilute acid leaching experiments, installed piezometers and equipped them with pressure transducers, analyzed tidal signals in high frequency groundwater hydrographs, carried out pumping tests, and, finally, took 49 groundwater samples. New Insights: Our results indicated a diverse groundwater system. On the one hand, groundwater was found at shallow depths in the saprolite of the Togo Structural Unit (TSU), which, in unweathered state, is composed of phyllites, schists, and quartzites. This system was shallow and predominantly unconfined, as revealed by tidal analysis. In addition, transmissivities of TSU saprolite, all in the order of < 6e-5 m2/s, reduced with depth, which indicated either the lack of a stratiform fractured layer or the presence of such layer beyond drilled depths. On the other hand, groundwater was found in fractures of the gneisses of the Dahomeyan Structural Unit (DSU). This system was potentially deeper, but DSU transmissivities were significantly lower than those of TSU saprolite. Hydrochemically, groundwater was mainly characterized by infiltration of waste-water, evidenced by elevated ion concentrations, including nitrate. Due to the thinly weathered basement, groundwater system development in the area is local and restricted to the Dodowa area.

Digital Drill Core Models: Structure-from-Motion as a Tool for the Characterisation, Orientation, and Digital Archiving of Drill Core Samples

Structure-from-motion (SfM) photogrammetry enables the cost-effective digital characterisation of seismic- to sub-decimetre-scale geoscientific samples. The technique is commonly used for the characterisation of outcrops, fracture mapping, and increasingly so for the quantification of deformation during geotechnical stress tests. We here apply SfM photogrammetry using off-the-shelf components and software, to generate 25 digital drill core models of drill cores. The selected samples originate from the Longyearbyen CO2 Lab project’s borehole DH4, covering the lowermost cap rock and uppermost reservoir sequences proposed for CO2 sequestration onshore Svalbard. We have come up with a procedure that enables the determination of bulk volumes and densities with precisions and accuracies similar to those of such conventional methods as the immersion in fluid method. We use 3D printed replicas to qualitatively assure the volumes, and show that, with a mean deviation (based on eight samples) of 0.059% compared to proven geotechnical methods, the photogrammetric output is found to be equivalent. We furthermore splice together broken and fragmented core pieces to reconstruct larger core intervals. We unwrap these to generate and characterise 2D orthographic projections of the core edge using analytical workflows developed for the structure-sedimentological characterisation of virtual outcrop models. Drill core orthoprojections can be treated as directly correlatable to optical borehole-wall imagery data, enabling a direct and cost-effective elucidation of in situ drill core orientation and depth, as long as any form of borehole imagery is available. Digital drill core models are thus complementary to existing physical and photographic sample archives, and we foresee that the presented workflow can be adopted for the digitisation and digital storage of other types of geological samples, including degradable and dangerous ice and sediment cores and samples.

Brittleness Evaluation in Shale Gas Reservoirs and Its Influence on Fracability

The brittleness index (BI) is a key parameter used to identify the desirable fracturing intervals of shale gas reservoirs. Its correlation with fracability is still controversial. There have been a variety of methods proposed that can estimate BI. The brittleness evaluation method based on stress-strain curves according to the energy-balanced law is the most suitable and reliable in this study. Triaxial compression test, optical microscopy and scanning electron microscopy (SEM) observation, and X-ray diffraction analysis (XRD) were performed on nine drill core samples from well SY3 located in the peripheral regions of Sichuan Basin, China. These tests further evaluated several commonly used methods (brittleness indices based on rock elastic parameters, rock mineral compositions) and determined the relationship between brittleness, rock elastic parameters, and the content of minerals. The results obtained indicate that for sedimentary rocks, a higher Young’s modulus reduces the brittleness of rock, and Poisson’s ratio weakly correlates with brittleness. Excessive amounts of quartz or carbonate minerals can increase the cohesiveness of rock, leading to poor brittleness. Furthermore, the most suitable fracturing layers possess a high brittleness index and low minimum horizontal stress.

Geochemistry, geochronology and petrogenesis of Maya Block granitoids and dykes from the Chicxulub Impact Crater, Gulf of México: Implications for the assembly of Pangea

The Late Paleozoic tectono–magmatic history and basement of the Maya block are poorly understood due to the lack of exposures of coeval magmatic rocks in the region. Recently, IODP–ICDP Expedition 364 recovered drill core samples at borehole M0077A from the peak ring of the Chicxulub impact crater, offshore of the Yucatán peninsula in the Gulf of México, have been studied comprehensively. In the lowermost ~600 m of the drill core, impact–deformed granitoids, and minor felsite and dolerite dykes are intercalated with impact melts and breccias. Zircon U-Pb dating of granitoids yielded ages of around 326 ± 5 Ma, representing the first recovery of Late Paleozoic magmatic rocks from the Maya block, which could be genetically related to the convergence of Laurentia and Gondwana. The granitoids show the features of high K2O/Na2O, LaN/YbN and Sr/Y ratios, but very low Yb and Y contents, indicating an adakitic affinity. They are also characterized by slightly positive ԑNd(326Ma) of 0.17–0.68, intermediate initial 87Sr/86Sr(326Ma) of 0.7036–0.7047 and two–stage Nd model age (TDM2) of 1027–1069 Ma, which may indicate a less evolved crustal source. Thus, the adakitic granitoids were probably generated by partial melting of thickened crust, with source components similar to Neoproterozoic metagabbro in the Carolina block (Pan–African Orogeny materials) along Peri–Gondwana. Felsite dykes are shoshonitic with typical continental arc features that are sourced from a metasomatic mantle wedge by slab–fluids. Dolerite dykes display OIB–type features such as positive Nb and Ta anomalies and low ThNpm/NbNpm. In our interpretation, the Chicxulub adakitic granitoids of this study are formed by crustal anatexis due to asthenospheric upwelling resulting from slab breakoff. Through comparing sources and processes of Late Paleozoic magmatism along the Peri–Gondwanan realm, a tearing slab breakoff model may explain the discontinuous magmatism that appears to have occurred during the convergence of Laurentia and Gondwana.

Deep-penetrating geochemistry for concealed sandstone-type uranium deposits: A case study of Hadatu uranium deposit in the Erenhot Basin, North China

Traditional geochemical exploration methods are not effective for locating concealed sandstone-type uranium deposits occurring at depths of hundreds of meters in sedimentary basins. In order to identify and trace the geochemical anomalous sources from the deposits in overburden regions, systematical luminescence intensity analyses have been carried out on mineral particles from both near-surface late Quaternary sediments and drill-core samples from the Hadatu sandstone-type uranium deposit in the Erenhot Basin. Luminescence intensity analyses yielded much older optically stimulated luminescence (OSL) ages for quartz minerals in late Quaternary sediments than their true depositional ages. In the same sedimentary layer, the apparent quartz OSL ages around the medium-grade borehole are particularly higher than those of the low-grade borehole. Therefore, the anomalies and the variations of these quartz OSL ages in late Quaternary sediments were ultimately controlled by concealed sandstone-type uranium deposits beneath. In contrast, the feldspar infrared stimulated luminescence (IRSL) signals of drill-core samples show no co-variations with deposits grade and sampling depth. Given the oversaturated luminescence signals on minerals from drill-core samples, they have no potential to unravel concealed sandstone-type uranium deposits. The strongly positive correlation between quartz OSL ages and previously published near-surface Rn anomalies in sediments confirms that the combination of OSL and areal Rn measurements is a cost-effective prospection approach for concealed sandstone-type uranium deposits.

INSIDER UC2: the BR3 biological shield preliminary results and future work

Aiming at economical optimization, the characterisation of the biological shield of the Belgian Reactor 3 is one of the three use cases intended to validate the integrated characterization methodology developed within the INSIDER project. Pre-existing data were used to define the sampling design strategy. The additional sampling and analysis program consisted of total gamma measurements at the inner surface of the biological shield (secondary data) and gamma spectrometry measurements on drill core samples (primary data). The newly acquired data is supplemented with the historical available data. The full data set currently consists of a total of 283 secondary and 379 primary data points. Preliminary calculations already provide a clear-cut representation of the three different end-stage classes: unconditional clearance, conditional clearance and radioactive waste. On the short term, the current model will be further refined and completed with proper risk evaluation. On the longer term, we envisage a global uncertainty calculation and sensitivity analysis of the entire process.

Enhancing industrial X-ray tomography by data-centric statistical methods

AbstractX-ray tomography has applications in various industrial fields such as sawmill industry, oil and gas industry, as well as chemical, biomedical, and geotechnical engineering. In this article, we study Bayesian methods for the X-ray tomography reconstruction. In Bayesian methods, the inverse problem of tomographic reconstruction is solved with the help of a statistical prior distribution which encodes the possible internal structures by assigning probabilities for smoothness and edge distribution of the object. We compare Gaussian random field priors, that favor smoothness, to non-Gaussian total variation (TV), Besov, and Cauchy priors which promote sharp edges and high- and low-contrast areas in the object. We also present computational schemes for solving the resulting high-dimensional Bayesian inverse problem with 100,000–1,000,000 unknowns. We study the applicability of a no-U-turn variant of Hamiltonian Monte Carlo (HMC) methods and of a more classical adaptive Metropolis-within-Gibbs (MwG) algorithm to enable full uncertainty quantification of the reconstructions. We use maximum a posteriori (MAP) estimates with limited-memory BFGS (Broyden–Fletcher–Goldfarb–Shanno) optimization algorithm. As the first industrial application, we consider sawmill industry X-ray log tomography. The logs have knots, rotten parts, and even possibly metallic pieces, making them good examples for non-Gaussian priors. Secondly, we study drill-core rock sample tomography, an example from oil and gas industry. In that case, we compare the priors without uncertainty quantification. We show that Cauchy priors produce smaller number of artefacts than other choices, especially with sparse high-noise measurements, and choosing HMC enables systematic uncertainty quantification, provided that the posterior is not pathologically multimodal or heavy-tailed.

A Multivariate Geochemical Investigation of Borehole Samples for Gold Deposits Exploration

The aim of this paper is to carry out a geochemical multivariate analysis on Qolqola gold deposit which is located in Kordestan province of Iran. The analysis and interpretation of geochemical data was carried out based on the results of 543 drilling core samples analyzed for Cu, Pb, W, Mo, Ag, As, Bi, Hg and Au. The purpose of this paper is to use probability plot modeling method for anomaly separation and data classification. For this purpose, three sub-population from Au probability plot modeling was recognized and the thresholds obtained and labeled with the codes 0, 1, and 2 after modeling (code 0: Au 870 ppb as anomaly range). The rearranged data set was used to evaluate discriminant function method. The results were introduced Ag, Hg, Sb, W and Pb as variables related to the mineralization event. The stepwise method was reduced the important variables as Au, Ag, As, W and Bi. Base on the exploration information from the study area, variables such as Ag, As, Sb, Hg, W, Pb were considered as variables were affected by Au mineralization event.