Quantitative Evaluation Of Minerals Research Articles

Factors Controlling Differences in Morphology and Fractal Characteristics of Organic Pores of Longmaxi Shale in Southern Sichuan Basin, China

Shale gas is a prospective cleaner energy resource and the exploration and development of shale gas has made breakthroughs in many countries. Structure deformation is one of the main controlling factors of shale gas accumulation and enrichment in complex tectonic areas in southern China. In order to estimate the shale gas capacity of structurally deformed shale reservoirs, it is necessary to understand the systematic evolution of organic pores in the process of structural deformation. In particular, as the main storage space of high-over-mature marine shale reservoirs, the organic matter pore system directly affects the occurrence and migration of shale gas; however, there is a lack of systematic research on the fractal characteristics and deformation mechanism of organic pores under the background of different tectonic stresses. Therefore, to clarify the above issues, modular automated processing system (MAPS) scanning, low-pressure gas adsorption, quantitative evaluation of minerals by scanning (QEMSCAN), and focused ion beam scanning electron microscopy (FIB-SEM) were performed and interpreted with fractal and morphology analyses to investigate the deformation mechanisms and structure of organic pores from different tectonic units in Silurian Longmaxi shale. Results showed that in stress concentration areas such as around veins or high-angle fractures, the organic pore length-width ratio and the fractal dimension are higher, indicating that the pore is more obviously modified by stress. Under different tectonic backgrounds, the shale reservoir in Weiyuan suffered severe denudation and stronger tectonic compression during burial, which means that the organic pores are dominated by long strip pores and slit-shaped pores with high fractal dimension, while the pressure coefficient in Luzhou is high and the structural compression is weak, resulting in suborbicular pores and ink bottle pores with low fractal dimension. The porosity and permeability of different forms of organic pores are also obviously different; the connectivity of honeycomb pores with the smallest fractal dimension is the worst, that of suborbicular organic pores is medium, and that of long strip organic pores with the highest fractal dimension is the best. This study provides more mechanism discussion and case analysis for the microscopic heterogeneity of organic pores in shale reservoirs and also provides a new analysis perspective for the mechanism of shale gas productivity differences in different stress–strain environments.

Sedimentary dynamics and depositional model for mud accumulation in deep lake basins: A case study in the Upper Triassic Chang-7 Member, Ordos Basin, northern China

Shales in deep lake basins have become the main focus of continental shale oil and gas exploration. In order to highlight the sedimentary dynamics of mud deposition in deep lake basins, a combination of core observation, thin section examination, X-ray diffraction, and QEMSCAN (quantitative evaluation of minerals by scanning electron microscopy) was used to analyze the depositional characteristics of mudrocks in the Chang-7 Member from the Yanchang Formation (Upper Triassic) in Ordos Basin, and to establish a depositional model for mud accumulation in deep lake basins. This study recognizes four mudrock lithofacies in the Chang-7 Member: (1) the laminated silt-bearing mudstone, which generally develops a binary composition of “silt–clay” or a ternary composition of “silt–clay–organic matter”; (2) the graded mudstone, mainly composed of dark gray and gray-black mudstone sandwiched by silt-bearing mudstone; (3) the massive mudstone, internally showing a uniform distribution of quartz, clay, and carbonate minerals, with also a small amount of organic detritus; and (4) the laminated shale, which is generally composed of clay laminae, and organic laminae of the former two. Sediment supply, topographic slope, and flood intensity combine to control the evolution of gravity flows and the transport and deposition of the mudrock in the Chang-7 Member. The influence of orogeny provides terrain gradient, water depth, abundant sediments at source areas, and triggering mechanism for the formation of gravity flows. Floods triggered by wetting events provide the impetus for sediment transport. Mud deposition in the Chang-7 Member was mainly related to the transport and sedimentation of mud by hyperpycnal flows and rapid sedimentation by buoyant plume flocculation. A comprehensive evolutionary model for shale accumulation in the deep lake basin is established by integrating various triggering mechanisms and mud transport sedimentary processes.

How to Quantify Heavy Mineral Fertility From Point‐Counting Data

AbstractHeavy minerals (HM) are widely used in provenance studies, for example, for reconstructing source areas and quantifying sediment budgets. Source rock mineral fertility influences the composition and concentration of HM in sediments. The resulting bias is of particular interest when interpreting single‐grain data such as detrital age distributions. However, the quantification of fertility is complex and there are no robust data for most HM, which prevents the routine implementation of fertility in many studies. In this study, we test whether mineral fertility can be assessed by quantifying mineral concentrations in detrital samples through point counting and quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN). The challenge is to transform the resulting area percentage into mass percentage, which is a prerequisite for comparing those data with grain size or geochemical data. We suggest overcoming this problem by recording grain‐size and shape metrics of minerals using image analysis, and applying several transformation steps. We test our method by (a) using a series of detrital grain mixtures of known density and mass, and (b) applying it to a natural sediment from the European Alps. Our results agree with existing methods developed for apatite and zircon, that is, the quantification of fertility through geochemistry (with P2O5 and Zr concentrations as proxies for apatite and zircon) and the separation of pure apatite and zircon concentrates using additional separation steps. The advantage of our method is its applicability to all HM (not only apatite and zircon) and the redundancy of additional separation steps, which might create bias.

Determination of the Thickness and Fracture Toughness of Shale Interfacial Transition Zone Near Various Micromineral Aggregates Using Nano-Scratch Tests

Summary Heterogeneously distributed micromineral aggregates (MMAs) are common in shale reservoirs. The interfaces between these MMAs and the surrounding minerals significantly affect fracture propagation behaviors during shale oil exploitation. In this paper, the concept of interfacial transition zone (ITZ) between the MMAs (e.g., striped barite, pyrite, calcite, apatite blocks, and bedding plane) and the surrounding mineral in shale is introduced. Due to the small thickness of the ITZ, its thickness and mechanical properties are very difficult to determine by traditional standard methods. To address this issue, this paper proposes a method combining nano-scratch tests, scanning electron microscopy (SEM), and quantitative evaluation of minerals by SEM (QEMSCAN) techniques to investigate the thickness and fracture toughness of the ITZ near typical MMAs. The results show that the thickness of the ITZ determined by the transverse force FT and scratch depth (-d2) varies from 3.2 μm to 17.3 μm. In addition, the fracture toughness of both MMAs and ITZs is characterized by high heterogeneity ranging from 0.1 MPa·m0.5 to 2.1 MPa·m0.5. Moreover, a formula evaluating the fracture toughness of the ITZ is proposed taking into account the type and content of minerals in the ITZ. A strong linear relationship is observed between the thickness of the ITZ and the average fracture toughness ratio. In addition, a relationship is established between the fracture toughness of the ITZ and MMAs, and an evaluation equation is derived. This study is helpful for understanding the characteristics (i.e., mainly thickness and fracture toughness) of the ITZ within shales.

The Effect of HPGR and Conventional Crushing on the Extent of Micro-Cracks, Milling Energy Requirements and the Degree of Liberation: A Case Study of UG2 Platinum Ore

Comparative high pressure grinding rolls (HPGR) and cone crusher pilot-scale tests were conducted using Upper Group 2 (UG2) platinum-bearing ore in order to determine the impact of micro-cracks in HPGR products toward energy requirements in ball mills and the degree of liberation. The ball mill was fed with HPGR and cone crusher products of similar particle size distributions (PSDs). Qualitative analysis of the degree of micro-cracking on the HPGR and cone crusher products performed using scanning electron microscope (SEM) and image analysis software showed that an HPGR product had more micro-cracks than the equivalent cone crusher product. Milling energy requirements were evaluated using size-specific energy consumption indices calculated based on three grind sizes of 300 µm, 150 µm and 75 µm. The effect of residual micro-cracks in the products of HPGR and cone crusher on the milling size-specific energy requirement is inconclusive. The kinetic parameter k in the cumulative rate kinetic model for ball milling cone crusher products and for ball milling HPGR products were similar. Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMSCAN) was used to determine the degree of liberation of various mineral phases in the mill products. At a coarser grind size (P80 of 300 µm), the sulfides in the mill products pre-crushed using the cone crusher have consistently poorer liberation than in the equivalent HPGR pre-crushed sample. However, at a finer grind size (P80 of 75 µm), the sulfides in the mill products pre-crushed using the cone crusher and using an HPGR showed similar liberation.

Characteristics and Geological Significance of Organic Matter Veins in Shale Reservoir: A Case Study of the Silurian Longmaxi Formation in Luzhou Area, Sichuan Basin

Organic matter serves as the hydrocarbon-generating parent material for shale reservoirs, in which organic pores are also important reservoir spaces. Different types of organic matter have wide differences in hydrocarbon generation and pore-forming ability. Based on the occurrence state of organic matter, in the over-mature Marine shale organic matter mainly includes in situ and migrated organic matter. It has been extensively studied on in situ organic matter and organic matter migrating into inorganic pores, while there are few reports of organic matter migrating into microfractures. In this study, the over-mature Marine shale reservoir in the first sub-member of the Silurian Longmaxi Formation in the Luzhou area of the Sichuan Basin is taken as an example. Core observation, optical microscope, high-precision large-view scanning (MAPS, modular automated processing system) and mineral analysis scanning (QEMSCAN, quantitative evaluation of minerals by scanning electron microscopy) were conducted to observe the morphological characteristics of organic matter veins, and then analyze the genesis and pore-forming characteristics of such organic matter. The results show that: ① Organic matter veins (OM veins) are soluble organic matter with fractures as an effective channel, and OM veins in the study section is easy to form under the condition of micro-fractures in the shale sweet segment after organic matter generating oil and before gas generation ② Organic matter in the OM veins are less efficient in pore-forming, with sparse pores and smaller pore sizes. The occurrence of fractures varies greatly, including horizontal fractures, oblique fractures and high-angle fractures, which are mostly developed in the Long111 and Long112 layers. ③ The development of OM veins can indicate better reservoir conditions, that is, the layers have strong hydrocarbon generation intensity (strong pore-forming ability of organic matter) and high brittle mineral content (strong reservoir compressibility). The new findings in this paper reveal that OM veins are instructive for the determination of geological–engineering sweet spots in the Longmaxi Formation in the Sichuan Basin, and also provide guidance for future research on occurrence form and geological significance of different types of organic matter.

Localized host-rock porosity near sealed fractures at 7 km depth: Geochemical evidence of deep-seated porosity controls

In Cretaceous Bashijiqike Formation sandstone from 6.5 to 7 km depth in the Kelasu tectonic zone, Kuqa depression thin section observation, quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN), nano CT scanning and digital core reconstruction reveals localized host-rock porosity near sealed fractures. Primary interparticle pores are the main type, followed by some secondary (dissolved) pores at the edge of grains, interparticle secondary pores, intercrystalline pores and microfractures. Dolomite and calcite are the common fracture-filling minerals, while a few fractures are filled with gypsum and quartz. The phases that exist in fractures are progressively more common farther from the fracture. Thus there is a sort of halo around the fracture that is depleted in the phases that exist in the fracture. Although the types of pores are the same, the farther from the fracture, the tighter the rock, the lower the porosity and average pore size, and the weaker the inter-pore connectivity with local preservation of interparticle pores. We propose a mechanism for how this pore structure arises. This study enhances the understanding of the physical properties and pore-fracture interaction of deep tight reservoirs, and contributes to further accurate evaluation of reservoirs.

Automated mineralogy using optical microscopy in a geometallurgical context: A comparative study on Dumont nickel project ores, Amos, Quebec

The Dumont Nickel Project is a low-grade, large-tonnage, ultramafic-hosted, disseminated nickel mine development project located in the Abitibi region of Quebec. The nickel mineralization is a result of the serpentinization of a dunite protolith that contained magmatic nickel sulfides (pentlandite ((Ni, Fe)9S8), heazlewoodite (Ni3S2)) with concurrent generation of nickel–iron alloy (awaruite (Ni2.5Fe)) considered as metallurgically recoverable Ni in the resource.The challenge in developing Dumont-type deposits lies in the mapping of recoverable Ni-phases through a geometallurgical approach. To quantify recoverable Ni, it is desirable to develop an affordable and cost-effective mineralogical quantification method for recoverable minerals to assess the economic value of mineralization.This study proposes an innovative way to quantify relevant mineralogy for future mining operations at the Dumont Nickel project using automated optical microscopy based on image analysis and quantification. To reach this goal, four samples that represent the geometallurgical domains of the deposit were characterized by automated optical microscopy and these results were compared to existing mineralogical quantification data for the same samples acquired by Quantitative Evaluation of Minerals by SCANning electron microscope (QEMSCAN®). The mineral abundance results obtained with the two techniques were compared with a focus on Ni deportment within opaque minerals. This comparative study has proven the effectiveness of automated optical microscopy for mineralogical quantification purposes as applied to the Dumont Nickel Project samples studied.

Copper concentrate dual-band joint classification using reflectance hyperspectral images in the VIS-NIR and SWIR bands.

A study on the classification of copper concentrates relevant to the copper refining industry is performed by means of reflectance hyperspectral images in the visible and near infrared (VIS-NIR) bands (400-1000nm) and in the short-wave infrared (SWIR) (900-1700nm) band. A total of 82 copper concentrate samples were press compacted into 13-mm-diameter pellets, and their mineralogical composition was characterized via quantitative evaluation of minerals and scanning electron microscopy. The most representative minerals contained in these pellets are bornite, chalcopyrite, covelline, enargite, and pyrite. Three databases (VIS-NIR, SWIR, and VIS-NIR-SWIR) containing a collection of average reflectance spectra computed from 9×9p i x e l neighborhoods in each pellet hyperspectral image are compiled to train the classification models. The classification models tested in this work are a linear discriminant classifier and two non-linear classifiers, a quadratic discriminant classifier, and a fine K-nearest neighbor classifier (FKNNC). The results obtained show that the joint use of VIS-NIR and SWIR bands allows for the accurate classification of similar copper concentrates that contain only minor differences in their mineralogical composition. Specifically, among the three tested classification models, the FKNNC performs the best in terms of overall classification accuracy, achieving 93.4% accuracy in the test set when only VIS-NIR data are used to construct the classification model, up to 80.5% using only SWIR data, and up to 97.6% using both VIS-NIR and SWIR bands together.

Tectonic Factors Restricting Differences among Layers in Microstructure of Ultradeep Clastic Rock Reservoir: A Case Study on Cretaceous Bashijiqike Formation in Kuqa Depression

Abstract The Cretaceous Bashijiqike Formation in the Kelasu structural belt of Kuqa Depression is an ultradeep reservoir with burial depth of more than 6 km. Due to the influence of strong thrust nappe from the South Tianshan in the north, the burial depth gradually deepened from north to south in the Kelasu tectonic belt. With the increase of the burial depth, the influence of tectonic compression relatively weakens, and the formation mechanism that affects the microstructure of ultradeep clastic reservoir is changed. Comprehensive analysis of thin section and quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN), scanning electron microscope (SEM), and micro-CT scanning are used to investigate the characteristics of the Cretaceous Bashijiqike Formation at the depth of 8000 m (TVD) in various stress sections. The result shows that, for the ultradeep reservoir with burial depth up to 8000 m, its reservoir characteristics and interlayer differences are not completely restricted by the neutral surface effect. (1) The porosity and permeability of various stress sections are different, and the reservoir physical properties of the tensile section are higher than that in the compressive section. (2) The pore types, pore radius, and pore throat connectivity of various stress sections are different, and the development of pores and throats in the tensile section is better than that in the compressive section. (3) As an ultradeep clastic rock reservoir, the vertical fracture development characteristics of Well Bozi9 at the depth of 8000 m differ from that in Kela-Keshen area at the depth of 6000 m in the model of strain neutral surface. The interlayer difference in the microstructure of ultradeep clastic rock reservoir is clarified, which has a positive effect to evaluate and predict the distribution of favorable deep reservoir.

3D Multiclass Digital Core Models via microCT, SEM-EDS and Deep Learning

We describe an integrated methodology for constructing a 3D multiclass model of a rock sample, based on X-ray microtomography (microCT) and quantitative evaluation of minerals (QEMSCAN) by automated SEM-EDS (Scanning Electron Microscopy, Energy Dispersive Spectroscopy). We focus on building an automated operator-independent workflow, allowing to distinguish between voxels featuring substantially different physical properties, such as void, quartz, denser and less dense clay aggregates. The workflow is demonstrated using a set of five ⌀8 mm Berea sandstone miniplugs. For each miniplug, a ~40003voxel microCT image is acquired. Next, each miniplug is cut into smaller pieces, and the 45 resulting polished surfaces are subjected to the QEMSCAN analysis, producing ~40002pixel mineral maps. Each mineral map is automatically spatially registered with the corresponding microCT image using an in-house surface-based algorithm. Further, the ground truth images for the supervised multiclass segmentation are constructed from the mineral maps. We compare 3D and 2D convolutional neural network (CNN) architectures with the baseline Naïve Bayes classifier, which is roughly equivalent to the approaches commonly used in practice today. We find that supervised CNN-based segmentation is fairly stable, despite microCT image quality non-uniformness and achieves higher quality scores compared to feature based and baseline approaches.

Calculation of oil saturation in clay-rich shale reservoirs: A case study of Qing 1 Member of Cretaceous Qingshankou Formation in Gulong Sag, Songliao Basin, NE China

The targeted reservoir, which is referred as the first member of Cretaceous Qingshankou Formation in Gulong Sag, Songliao Basin, NE China, is characterized by the enrichment of clay and lamellation fractures. Aiming at the technical challenge of determining oil saturation of such reservoir, nano-pores were accurately described and located through focused ion beam scanning electron microscopy and quantitative evaluation of minerals by scanning electron microscopy based on Simandoux model, to construct a 4D digital core frame. Electrical parameters of the shale reservoir were determined by finite element simulation, and the oil saturation calculation method suitable for shale was proposed. Comparison between the results from this method with that from real core test and 2D nuclear magnetic log shows that the absolute errors meet the requirements of the current reserve specification in China for clay-rich shale reservoir. Comparison analysis of multiple wells shows that the oil saturation values calculated by this method of several points vertically in single wells and multiple wells on the plane are in agreement with the test results of core samples and the regional deposition pattern, proving the accuracy and applicability of the method model.

Depositional controls on diagenetic evolution of the Lower Cretaceous Wealden Sandstones (Wessex Basin, southeast England)

Depositional processes hold crucial controls on the diagenetic processes, events and evolution in sedimentary basins. Using the example of non-marine, Lower Cretaceous Wealden Sandstones from Wessex Basin in southeast England, this study reveals the depositional controls on diagenetic evolution in a sedimentary basin. Seventy-four surface samples, from 6 field locations across the Wessex Basin in Dorset and Isle of Wight were subjected to laboratory analyses such as optical petrography, scanning electron microscopy and Quantitative Evaluation of Minerals by Scanning Electron Microscopy analysis. The degree of compaction in the Wessex Basin sandstones includes moderate packing with most grains in a mix of point and long contact, with rare grains displaying concave-convex or non-grain contact and a loose packing dominated by non-grain contacts, with minor point and long contacts. The authigenic mineral phases identified in the sandstones are quartz, kaolinite, calcite and halite in decreasing abundance. The dissolution of felspars observed in the Wessex Basin sandstones possibly provided the main source of silica for the quartz overgrowths, with silica sources adjacent to the site of cementation. The small amount of quartz overgrowths may have formed during shallow burial. The partial dissolution of quartz observed in the Wessex Basin sandstones is considered likely to be the result of flushing of organic-compound rich waters derived from shale interbeds, under low temperature conditions (c. 25–50 °C). The precipitation of authigenic minerals within the Wessex Basin had a limited impact on the porosity and permeability of sandstones. Detrital mineralogy appears to be the main depositional control on diagenesis and may also explain the low abundance of authigenic kaolinite in the Wessex Basin. Similarly, the shallow burial depth of the sandstones is considered to be the main factor inhibiting more pervasive quartz cementation within the basin.

High-Resolution Pore Space Imaging, Mineralogical Characterization, and Sealing Capacity Estimates of Confining Units at a Geologic Carbon Storage Demonstration: The Illinois Basin–Decatur Project, USA

At the Illinois Basin–Decatur Project, a large-scale CO2 capture and geologic storage demonstration project in the saline Mount Simon Sandstone in central Illinois, three overlying and laterally continuous shale formations (the Eau Claire, Maquoketa, and New Albany) are considered confining units overlying the sandstone reservoir. The Mount Simon reservoir contains internal mudstone baffles that will influence CO2 migration pathways and future interaction with seals. Understanding the sealing properties of rock units deemed seals or confining units is vital to commercialization of geologic carbon storage. For this article, nanoscale-resolution focused ion beam scanning electron microscopy (SEM), mercury injection capillary pressure (MICP), X-ray diffraction (XRD) spectroscopy, and quantitative evaluation of minerals by SEM were used to characterize the controls on the sealing integrity of these seals and reservoir confining units. Results show that porosity and pore size generally decrease with depth, except in the carbonate-rich Maquoketa Shale. The Maquoketa contains the highest pore volume owing to abundant dolomite in the mineral matrix compared with the other mudstone and shale intervals, which are clay rich. The shallowest seal sample, the organic-rich New Albany Shale, contains the highest frequency of the smallest pore throat size and is most comparable, with respect to pore sizes and entry pressures, to the deepest black shale and primary Mount Simon reservoir seal, the Eau Claire. Point-specific MICP threshold pressure results, theoretical calculations based on a range of permeabilities, and column height calculations indicate that the internal Mount Simon mudstone and Eau Claire Shale are effective seals of CO2 in the Mount Simon reservoir.

Microstratigraphy and palaeoenvironmental implications of a Late Quaternary high‐altitude lacustrine record in the subtropical Andes

AbstractHigh‐mountain lake records in semiarid foreland settings, such as the central Andes of North‐western Argentina, are highly restricted and often deprived of well‐preserved microstratigraphic information to analyze palaeoenvironmental changes and their causes, particularly for periods prior to the Last Glacial Maximum. Laguna La Salada Grande (23°S/65°W, 4063 metres above sea‐level) is a closed shallow lake located at Cordillera Oriental, North‐western Argentina with a unique depositional record, including geomorphic and stratigraphic evidence of palaeoenvironmental changes since the Late Pleistocene. In order to understand the depositional dynamics of this mountain lacustrine system at different timescales, limnogeological multiproxy analyses together with a radiocarbon and 210Pb‐based chronology were applied on massive and laminated sediments from La Salada Grande. Laminated deposits were further analyzed using novel sub‐centimetric mineralogical, textural and geochemical automated methods (including a combination of micro‐X‐ray fluorescence and quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN®). Thick laminated microfacies at the beginning of the sequence record a deep and organic matter productive palaeolake prior to ca 34 ka (1 ka = 1000 years before 1950), that changed into a highly fluctuating shallower‐palaeolake with frequent detrital influxes after ca 34 ka. Microstratigraphy of the coarser‐grained detrital laminae between 31 ka and 25 ka reveals irregular and probably sub‐centennial high‐energy discharge events, pointing to convective atmospheric activity as the main trigger. After ca 21 ka the lake evolved to deeper water‐level conditions resulting in fine‐grained deposits with limited delivery of coarse‐grained sediments, followed by an abrupt lake level drop and incision. The multi‐millennial palaeoenvironmental reconstruction of La Salada Grande, and its correlation with other palaeoclimate records, shows a close link between the lacustrine depositional processes and palaeoclimate changes associated with the South American summer monsoon dynamics. This multifocal research in such an understudied environment provides key knowledge about lacustrine functioning and discharge events−climate interactions of mountain lakes of semi‐arid climates.

Research on Micro-Pore Structure and 3D Visual Characterization of Inter-Salt Shale Based on X-CT Imaging Digital Core Technology

Pore structure is the key factor affecting reservoir accumulation and enrichment behavior. Due to the complex mineral components and pore structure of shale oil reservoirs and strong heterogeneity, it is necessary to explore the micro-pore structure characteristics of inter-salt shale. In this study, in order to qualitatively and quantitatively analyze the pore structure of inter-salt shale reservoirs, as well as evaluate the mineral composition and its spatial distribution characteristics, three shale samples from the 10th cyclothem of the Eq3 (Eq34–10 cyclothem) inter-salt shale were selected to acquire 2D and 3D grayscale images by modular automated processing system (MAPS) and X-ray micro-computed tomography (Micro-CT), respectively. The color map of the inlaid characteristics of mineral aggregates was established by Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMSCAN), and different mineral types in the grayscale image were determined. After that, the digital core technology was used to reconstruct the core in 3D, and the maximum sphere method was used to extract the pore network model, so as to realize the quantification of micron pore throats and the 3D visualization of inter-shale samples. Meanwhile, in order to compare the fractal characteristics of the pores of the samples, the two-dimensional and three-dimensional fractal dimensions of the three cores were calculated by combining the digital core technique with fractal theory. The study yielded several notable results: the pore structure of inter-salt shale reservoirs is complex and multi-scale, and the CT scanning digital core technology can effectively realize 3D visualization of rock microstructure without damage. The pore types of rock samples are mainly intergranular pores, interparticle pores, and dissolved pores, and the minerals are mainly dolomite, calcite, and glauberite. The micron pore throat radius of the rock sample is 0.5–13.9 μm, the distribution of coordination number is mainly in the range of 1–4, and the shape of the pore throat is mainly triangular and square. The pore space of inter-salt shale has suitable fractal characteristics, and the three-dimensional fractal dimension of the three cores is in the range of 2.41–2.49. In sum, this work used digital core technology to study the microscopic pore structure of inter-salt shale oil, establishing a basis for further understanding of the seepage characteristics and exploration and development of shale oil.

Exploring deep carbonate reservoir samples: Anisotropy and correlation of static and dynamic Young’s moduli

In total, 14 limestone samples, drilled in the vertical and horizontal directions from a depth >3 km, are analyzed to understand the correlation between static (operating at in-situ strain levels) and dynamic (at a sound wave strain level) Young’s moduli, [Formula: see text] and [Formula: see text], and also to investigate their directional dependence. Young’s moduli are measured simultaneously under a confining pressure of 30 MPa to a differential axial stress of 50 MPa using a triaxial frame with linear variable differential transformers: two axial and one radial calibrated with a standard aluminum slug. Static and dynamic moduli decrease with increasing porosity whereas the static moduli are typically less than the dynamic moduli. The static measurements exhibit significant hysteresis indicating a nonlinear (irreversible) regime, whereas the dynamic moduli, measured with low-strain amplitude, indicate a linear (reversible) regime. The static Poisson’s ratio increases with porosity, but the dynamic ratio remains unchanged over the whole range of porosity, which seems to not be sensitive enough to the heterogeneity in the pore structure. The induced microfractures, naturally developed under tensile stress after these deep samples were brought to the surface, are imaged in computer microtomography (micro-CT) scan experiments. The mineralogical composition is determined as higher than 95% calcite CaCO3and mapped out using quantitative evaluation of minerals by scanning electron microscopy. Elastic anisotropy is observed with increasing porosity, where the ratio [Formula: see text]/[Formula: see text] increases for the vertical but decreases for the horizontal samples. Likewise, a permeability anisotropy also is observed as porosity increases, where the ratio of the vertical to horizontal permeability [Formula: see text]/[Formula: see text] is higher than one, indicating a preferred vertical structure for fluid flow. Two linear correlations between [Formula: see text] and [Formula: see text] are developed for the studied calcite samples, and for samples composed of up to 30% dolomite CaMg(CO3)2reported in the literature.

Redistribution of Minor and Trace Elements During Roasting of Cu-Rich Complex Concentrate in Inert Atmosphere

Abstract A Cu-rich polymetallic complex concentrate produced at the Garpenberg Mines of Boliden Mineral AB, Sweden is investigated. Roasting at 700 °C in N2 leads to extensive liquid formation. The calcine obtained after cooling down to the room temperature is found to be severely sintered, entrapping numerous melt nuggets. This work focuses on analyzing redistribution of the minor (Ag) and trace elements consequent to the roasting treatment. Advanced micro-analytical techniques such as quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN), laser-ablation inductively coupled plasma-mass spectrometry (ICP-MS) and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) are used in conjunction for detailed characterization of the initial concentrate and the roasted calcine, especially the melt nuggets (which symbolizes the phases which were molten at 700 °C). The minor element—Ag is primarily in the silver-antimonide and tetrahedrite mineral phases in the initial concentrate. Ag separates out of tetrahedrite when the later interacts with galena to form a liquid phase. Furthermore, Mn, Cd, Tl and Hg are the relevant trace elements in the Garpenberg concentrate. Sphalerite is the major host of Mn, Cd and Hg. Tl is mainly in galena. Consequent to liquid formations at 700 °C, the trace elements redistribute and tend to segregate in low-melting phase-fractions. Statistical methods such as correlation matrices and clustering analysis are used effectively in evaluating the data from laser-ablation ICP-MS measurements on sulphide samples. Graphical Abstract

The Passa Três Granite Intrusion-Related/Hosted Neoproterozoic Gold Deposit (Paraná State, Brazil): Mineralogical, Geochemical, Fluid Inclusion and Sulphur Isotope Constraints

The Passa Três granite is a 5 km2 intrusion in southern Brazil with an NNE–SSW-elongated shape, hosting gold-bearing quartz veins with fluorite, carbonates, sulphides (pyrite, chalcopyrite, aikinite, molybdenite) and native gold. Orebodies are hosted by the pluton roof zone, which is marked by various textures indicating magmatic–hydrothermal transition processes. Mineralisation formed between 613 and 608 Ma in extensional pull-apart structures controlled by two conjugated N–S and E–W fault systems. We report results from petrography, quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN), scanning electron microscopy (SEM), electron probe microanalyses (EPMA), X-ray fluorescence (XRF), trace element analyses of pyrite by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), sulphur isotope (δ34S) analyses, and fluid inclusion microthermometry. Hydrothermal alteration is dominantly developed as phengite–quartz–carbonate and sericite–carbonate–chlorite assemblages along mineralised structures. Fluid inclusion study indicates mineralising fluids with H2O-CO2-NaCl composition, low to moderate salinity (0.2–12.84 wt % NaCl eq.), and temperatures from 400 to 150 °C. The sulphur isotopic composition of pyrite (−0.1 to 1.1‰) suggests magmatic origin. These data, in conjunction with structurally controlled mineralisation enriched in Au-Bi minerals shortly post-dating the granite emplacement, appoint towards similarities between the Passa Três deposit and intrusion-related gold systems. The specific location of the mineralisation in the core (and in the roof zone, regarding its vertical position) of the Passa Três granitic intrusion defines it as “granite-hosted” thus, it is representative of a specific model that can be used for exploration of other intrusion-related/hosted gold deposits near the studied area or in other locations.

Petrophysics applied in mineralizations, hydrothermal alterations and lithology mapping: A case study from the Zn–Pb (Cu–Ag) epithermal deposit of Santa Maria, Brazil

ABSTRACTThe epithermal Zn–Pb (Cu–Ag) deposit of Santa Maria represents a distal magmatic‐hydrothermal system, whose mineralizations are controlled by fault systems located in the sedimentary units of the upper Camaquã Basin, above the tectonic units of the Sul‐Riograndense Shield. The hydrothermal alteration zones contain illite, chlorite and pyrite, besides galena, sphalerite, chalcopyrite and bornite. To improve the knowledge of this mineral system, this work investigated the petrophysical footprints of samples representing the predominant lithology, altered rocks and hydrothermal mineralization. The core samples of the predominant lithology, altered rocks and hydrothermal deposit mineralizations were used to determine the following petrophysical properties, density, magnetic susceptibility, primary wave velocity, resistivity, conductivity and chargeability. Moreover, the quantitative evaluation of minerals by scanning electron microscopy coupled with an automated image analysis system allowed us to map lithological and alteration processes. The results indicate density as the most effective physical property to map lithology, hydrothermal alteration and the Zn–Pb (Cu–Au) mineralization. Furthermore, all studied physical properties have moderate effectiveness in the alteration zones of known geological and geophysical anomalies in the Santa Maria deposit. Chargeability could be used, especially when sulphides are disseminated, but additional geological factors complicate its interpretation. The mineralogical and petrophysical diversity of the Santa Maria deposit provided vital data for geological–geophysical interpretations while allowing the creation of a key exploration plan to investigate the Zn–Pb (Cu–Au) mineralization. Finally, petrophysics should be used in prospection to help understand complex geological processes, their overlapping subpopulations and to accelerate mineral research while reducing the use of technical and financial resources and expenditure on ineffective geophysical methodologies.