Search Results (25)

Red sandstones of the Cambrian age are globally distributed and represent an important sedimentation phase during this critical time interval. Their sedimentology and geochemistry can provide key information about the sedimentation style, paleoclimatic conditions, and weathering trends during the Cambrian. In the Salt Range of Pakistan, the Khewra Sandstone constitutes the Lower Cambrian strata and consists of red–maroon sandstones with minor siltstone and shale in the basal part. Cross-bedding, graded bedding, ripple marks, parallel laminations, load casts, ball and pillows, desiccation cracks, and bioturbation are the common sedimentary features of the formation. The sandstones are fine to medium to coarse-grained with subangular to subrounded morphology and display an overall coarsening upward trend. Petrographic analysis indicates that the sandstones are sub-arkose and sub-lithic arenites, and dolomite and calcite are common cementing materials. X-ray Diffraction (XRD) analysis indicates that the main minerals in the formation are quartz, feldspars, kaolinite, illite, mica, hematite, dolomite, and calcite. Geochemical analysis indicates that SiO₂ is the major component at a range of 53.3 to 88% (averaging 70.4%), Al₂O₃ ranges from 3.1 to 19.2% (averaging 9.2%), CaO ranges from 0.4 to 25.3% (averaging 7.4%), K₂O ranges from 1.2 to 7.4% (averaging 4.8%), MgO ranges from 0.2 to 7.4% (averaging 3.5%), and Na₂O ranges from 0.1 to 0.9% (averaging 0.4%), respectively. The results of the combined proxies indicate that the sedimentation occurred in fluvial–deltaic settings under overall arid to semi-arid paleoclimatic conditions with poor to moderate chemical weathering. The Khewra Sandstone represents the red Cambrian sandstones on the NW Indian Plate margin of Gondwana and can be correlated with contemporaneous red sandstones in the USA, Europe, Africa, Iran, and Turkey (Türkiye). Full article

A set of samples from the Monte Castelo kaolin deposits (Burela, NW Spain), corresponding to igneous acidic rocks affected by chemical weathering with variable intensity have been investigated in order to establish the mineralogical and chemical changes with weathering, and the micro- and nano-scale textures developed. For the study, XRD, FESEM, HRTEM and chemical analyses have been used. The more intense the weathering, the more the dissolution of aluminosilicates (albite, K feldspars and K micas) and the crystallization of kaolinite is favored. Kaolinite grows, forming booklets and generating a fine-grained matrix and, along the cleavages of muscovite, forming mica–kaolinite intergrowths. Bidimensional crystallographic continuity between mica and kaolinite has been observed and no intermediate phases have been identified as a consequence of the high W/R ratio. Kaolin mainly contains kaolinite with high crystallinity; however, when there are quartz impurities, they interfere with the ‘optimal’ reflections for the calculation of the Hinckley index. In this case, the use of the AGFI index almost eliminates the effect that the relative intensities of the quartz and feldspar impurities may have on those of kaolinite. With weathering, there is a progressive decrease in the contents of most chemical elements, except Al, TiO₂, HREEs, Ta, Hf, Th, U, V, Cr, S, Zr, Mo and Sn. Full article

This article examines the clay mineralogy of twelve representative soils developed from gypsum-rich parent materials on several geomorphic positions. These soils were classified as Haploxerept, plus one profile as Humixerept and another as Xerorthent. The clay mineralogy, determined by X-ray diffraction, showed quite a similar clay composition in all profiles, with mica, chlorite, and smectite, from most to less abundant. Mica and chlorite are deemed inherited, while smectite—appearing in minor proportions—could result from both transformation and/or neoformation, because the leaching of bases by free drainage does not favor the transformation of mica to smectite. Therefore, the differences in clay mineralogy appeared to be lithogenic rather than pedogenic. These compositional data are an advance in the basic knowledge of the studied soils. Full article

Previous studies on the Ke’eryin pegmatite-type lithium ore field in the Songpan–Ganzi Orogenic Belt have explored the characteristics of the parent rock but have not precisely determined its magma source area. This uncertainty limits our understanding of the regularity of lithium ore formation in this region. In this study, to address the issue of the precise source area of the parent rock of lithium mineralization, a detailed analysis of the Li isotope composition of the ore-forming parent rock (Ke’eryin two-mica monzogranite) and its potential source rocks (Triassic Xikang Group metamorphic rocks) was conducted. The δ⁷Li values of the Ke’eryin two-mica monzogranite, Xikang Group metasandstone, and Xikang Group mica schist are −3.3–−0.7‰ (average: −1.43‰), +0.1–+6.9‰ (average: +3.83‰), and −9.1–0‰ (average: −5.00‰), respectively. The Li isotopic composition of the Ke’eryin two-mica monzogranite is notably different from the metasandstone and aligns more closely with the mica schist, suggesting that the mica schist is its primary source rock. The heavy Li isotopic composition of the two-mica monzogranite compared to the mica schist may have resulted from the separation of the peritectic garnet into the residual phase during the biotite dehydration melting process. Moreover, the low-temperature weathering of the source rocks may have been the main factor leading to the lighter lithium isotope composition of the Xikang Group mica schist compared to the metasandstone. Further analysis suggests that continental crust weathering and crustal folding and thickening play crucial roles in the enrichment of lithium during multi-cycle orogenies. Full article

Weathered granite contains a high concentration of feldspar, quartz, and kaolin. However, while it becomes rich in clay due to strong physical weathering, the granite minerals that are not fully weathered are still very hard, which makes the grinding process more difficult and limits its use. This study proposes a multi-step process involving grinding, desliming, and flotation to address this issue. The study determines the appropriate grinding time and power index for the original ore, as well as the optimal desliming method using a hydrocyclone. To remove iron-containing impurities like mica, a combination of NaOL/BHA/A CO collectors is used for the reverse rough flotation of quartz. Additionally, a combination of DDA/SDS collectors is employed to separate quartz and feldspar through flotation, resulting in a quartz product with a silicon dioxide content of 99.51%. The objective of efficiently recycling feldspar, quartz, and kaolin from weathered granite is accomplished. Additionally, the inclusion of intermediate mineral components as by-products of feldspar and raw materials for aerated bricks is introduced, resulting in the complete utilization of all components. This innovative approach ensures a clean and environmentally friendly process, eliminating the need for solid waste disposal. Full article

Mica schist weathered soil possesses a number of poor engineering characteristics, which make it difficult to use as a subgrade material for resource utilization. Therefore, in this study, a new type of curing agent, CFSD (cement–fly ash–slag–desulfurized gypsum), is proposed for this soil. The effects of different curing agent dosages, age of preservation, and confining pressure on the stress–strain curves were analyzed via the uniaxial compression test and triaxial compression test, while the micromorphological characteristics of cured soil were analyzed via X-ray diffraction analysis and the SEM test combined with Image J software. In this paper, we also establish a microscopic mechanism model to determine how curing agents increase the strength of mica schists. The results reveal that the compressive strength of solidified soil increases rapidly within 28 days; the CFSD dosage of 4% at 7 d increased by 103.23% by 28 d. After 28 d, the trend of compressive strength growth was flat. The CFSD dosage of 4% at 7 d increased by 128.34% by 90 d; with the increase in the dosage, the curve transformed from flat to steep. These results suggest that the CFSD dosage is positively correlated with the damage strain and damage bias stress of solidified soil. The curves for the strain softening type with a 4% dosage as the initial effective confining pressure increased from 50 kPa to 300 kPa; the failure stress and failure strain increased by 202.09% and 90.85%, respectively. With the increase in curing agent dosage and maintenance age, the pore size of 2~5 μm, >5 μm interval decreased from 56.46% to 27.92%, the porosity decreased from 12.51% to 4.6%, and the hydrate produced by the curing agent cemented and filled up the pore space between the loose particles of the soil body. Thus, the large pore space became microporous, and the pore structure densification was greatly improved. Full article

With proven reserves of 9.836 × 10¹⁰ m³, the largest known natural gas reservoir among terrigenous basement rocks has been discovered within the granitoids of the northern Qaidam Basin. Due to their high heterogeneity, the genesis of basement reservoirs remains unknown. Herein, the structure of the weathering crust in granitoids and their potential controlling factors on the reservoir development mechanism are discussed using a multidisciplinary approach based on data from cores, thin sections, scanning electron microscopy (SEM), conventional and imaging logs, and physical property and major elements analyses. Moreover, the classification standard of the weathering crust structure is established. The dissolution belt holding diverse reservoir spaces accounts for more than 50% of the total porosity, while the disintegration belt is the main context for the development of cleavage fractures and crack fractures. The original pores exist mainly among the crystal grains of quartz and mica, while the secondary pores and fractures were generated by the alteration of aluminosilicate minerals as well as biotite or hornblende. The quality of these reservoirs is controlled by their mineral composition, tectonic uplift, faulting, and paleogeomorphology. The femic granitoid is the main reservoir-forming lithology in the case of dissolution, while the felsic granitoid is more likely to develop cracks. The formation of the disintegration belt is significantly linked to the presence of faulting. These belts were mostly induced by tectonic deformation along the Altyn fault belt from the late Oligocene to the early Miocene. The diversity in paleogeomorphology influences the extent of the weathering. The exhumation in the Altyn terrane from the late Jurassic to the Cenozoic corresponds to the weathering and hypergene leaching period of the weathering crust within granitoids. Three types of reservoirs are present in the rocks: fractured-porous (Type Ⅰ); porous (Type Ⅱ); and fractured (Type Ⅲ). The fractured-porous and fractured reservoirs were developed mainly in the granitic gneiss and granite, while the porous reservoir was formed in granitic diorite and granitic gneiss. The reservoirs that developed in the weathering crust of granitoids are dominated by Type Ⅰ and Type Ⅱ. The highest quality reservoir, which is the fractured-porous type, developed mainly in the dissolution belt of the weathering crust, and has a porosity ranging from 1.56% to 8.48% and a permeability ranging from 0.03 mD to 14.48 mD. The mechanisms of the development of weathering crust reservoirs provide further information for the hydrocarbon exploration of basement rocks worldwide. Full article

The influence of large rivers on the Subei littoral plain area requires more research than the results that have been available up to now. Thus, specific diagnostic indices of detrital mica are successfully applied for the first time to identify the detritus of the Yangtze River and the ancient Yellow River and to analyze their influence on the coast in the Subei littoral plain area. Based on field investigation and sample collection, detrital mica minerals within the 0.063–0.125 mm grain size fraction were selected and identified. Their content/ratio differentiations and possible origins were analyzed. Moreover, specific diagnostic indices were evaluated for detritus identification considering these two large rivers in addition to their provenance influences on the Subei littoral plain area. The results indicate that the detrital mica contents in the Yangtze River Estuary differed from those in the ancient Yellow River Estuary. The mass percentage in the former (average value of 32.2%) was much higher than that in the latter (average value of 13.1%). The former contained abundant weathered mica, with a particle percentage of approximately 50.6%, while the latter contained abundant biotite (with a particle percentage of approximately 40.9%). Differences, including but not limited to those above, could be attributed to basic geological, climatic and hydrodynamic conditions. In particular, the mica indices were clearly distinguished between these two river estuaries. These indices constitute specific diagnostic indices for differentiating river detritus and quantitative contribution analysis of detritus provenance in the Subei littoral plain area. Finally, the changes and quantitative contributions of four diagnostic indices demonstrated that in the Subei littoral plain area, northward from the Yangtze River Estuary to sample site SBY11 located in Yangkou town, Rudong County, detrital micas were mainly affected by the Yangtze River, and southward from the ancient Yellow River Estuary to sample site SBY12 located in Bengcha town, Rudong County, detrital micas were largely affected by the ancient Yellow River. The main mixing area should be located between these two towns. This study provides both a good example and an efficient approach to the application of detrital mica in detritus identification, mixed zone determination, sediment provenance analysis and transport tracing. Full article

The assessment of the micromorphological characteristics of soils is a powerful tool for studying the transformation of soils under the influence of various weathering mechanisms (physical, biogenic). The central part of Yakutia is characterized by a large area of agricultural lands, some of which has become fallow land and is subject to cryogenic processes, fires and anthropogenic impact. Under the conditions of climate change, the fallow soils of Yakutia can be re-involved in the agricultural complex. To study their state, a method of micromorphological investigation of thin soil sections is proposed. Thin sections of soils were analyzed using a polarizing microscope Leica DM750P. As a result of the work, zonal, fallow, pyrogenic and agricultural soils of the central part of Yakutia were analyzed. The soils were found to be in a degraded state. Zonal soils were characterized by the presence of quartz grains, feldspar, and undecomposed plant tissue, as well as biogenically transformed humus. Fallow soils were characterized by a thick organo-mineral (A) horizon, quartz grains, feldspar, and silty-clay plasma. Pyrogenic soils have differences from natural and fallow soils; as a result of fires and active illuviation of organo-mineral substances. The Anthrosol soils were characterized by a large number of aggregates of various sizes. In their composition there were various minerals, such as quartz, feldspar and mica. The signs of soil cryogenesis were noted only in the underlying horizons (B), while the upper horizon (A) had no signs of cryogenic transformation. Full article

After subjecting Zamora building stones to accelerated ageing tests, colour changes were studied, namely: (a) freezing/thawing and thermal shock (gelifraction and thermoclasty), and (b) combination of freezing/thawing plus thermal shock and salt crystallisation (sulphates or phosphates) (gelifraction, thermoclasty and haloclasty). Zamora building stones are silicified conglomerates (silcretes) from the Cretaceous that show marked colour changes due to the remobilisation of iron oxyhydroxides. In this work, four varieties were: white stone; ochreous stone; white and red stone; and purple stone Their micromorphological characterization (skeleton, weathering plasma and porosity/cutan) is formed of grains and fragments of quartz and quartzite as well as by accesory minerals muscovite and feldspar (more or less altered), and some opaque. Quartz, feldspar and illite/mica were part of the skeleton; kaolinite, iron oxyhydroxides, and CT opal were part of the weathering plasma or cutans; their porosity were 11.7–8.7%. Their chromatic data have been statistically analysed (MANOVA-Biplot). They showed higher variations in ΔE*, ΔL*, Δa* and Δb*on combined freezing/thawing plus thermal shock and sulphates crystallisation leading to rapid alteration of the building stones. Chromatic differences between the other two artificial ageing tests were less evident and were not detected in all samples. The global effect of ageing on the Zamora building stones darkened them and reduced their yellowing. The ochreous stone suffered the least variation and the purple stone the most. This study of the colour by statistical analyse may be of interest for the evaluation and monitoring of stone decay, which is an inexpensive, simple, easy and non-destructive technique. Full article

Drilling has been conducted to investigate the petrogeochemistry of the Late Pleistocene Guxiangtun Formation and Holocene Wenquanhe Formation in Northeast China. Both Guxiangtun and Wenquanhe Formations are fluvial facies, which are composed mainly of quartz and feldspar, with minor mica and clay minerals. To understand the provenance and tectonic setting of these sediments, geochemical analyses of fifteen selected samples from the drill core have been carried out. Compared to the composition of the upper continental crust (UCC), the sediments exhibit higher SiO₂, similar TiO₂ and K₂O, and lower Fe₂O₃, MgO, MnO, CaO, and Na₂O contents. The bivariant plot of Th/Sc versus Zr/Sc ratios indicates the contribution from recycled sedimentary provenance for our studied sediments; furthermore, the low to medium degree of weathering of these sediments is commonly indicated by the chemical index of alteration (CIA) of 52. The discriminant function diagram using major elements shows a mixed provenance of the sediments, including quartzose sedimentary and felsic igneous rocks. According to the Fe₂O₃+MgO vs. K₂O/Na₂O plot and Th–Sc–Zr/10 diagram, the sediments under the investigation fall mostly within the active continent margin field. Full article

To further explore the uranium-bearing prospects of the Zhiluo Formation, the petrography, major elements, trace elements and rare earth elements of Zhiluo sandstone samples collected from four boreholes were analyzed in this research to determine the provenance, tectonic setting and paleoweathering of the formation. The results of the analysis reveal that the Zhiluo Formation sandstone comprises primarily feldspar sandstone, with quartz, feldspar, and mica as the main mineral components. The rare earth elements are mainly characterized by enrichment in light rare earth elements and loss of heavy rare earth elements. The ratio of light to heavy rare earth elements (LREEs/HREEs) is 5.55–7.79, with an average of 6.33. The value of (La/Yb)_CN is 12.96–22.33, with an average value of 17.41, indicating obvious fractionation of LREEs and HREEs. The chemical index of alteration (CIA) value of this sandstone is 56.30–63.04, with an average of 59.75, which indicates that the parent rock experienced weak chemical weathering in a dry climate. The discrimination diagrams of the source area and parent rock show that the source area of the Zhiluo sandstones had a mixed intermediate-felsic composition, and that the main parent rocks were andesite and granite. The tectonic setting discrimination diagram indicates that the tectonic setting of the source area was the passive margin. Thus, the provenance of the sandstone of the Zhiluo Formation is proposed to be the volcanic-sedimentary rock series developed on the northern margin of the Ordos Basin. Full article

Fluorine (F) enrichment originating from natural sources is difficult to remove using chemical washing methods due to the large chemical-resistant residual fraction. This study evaluates the feasibility of using a froth-flotation separation method to remediate soil with a high F concentration caused by mica weathering, and it investigates the optimal conditions for this process, including pH of the slurry, collector dosage, and sample mechanical preparation strategy. The established optimum conditions are pH 3.5, 300 mg/kg collector dosage (tallow amine acetate), which can effectively separate quartz and mica, and a sieving-and-milling strategy that involves discarding particles of size < 0.05 mm, milling those in the range of 0.5–2.0 mm (until < approx. 0.3 mm), and mixing particles with sizes in the range of 0.05–0.5 mm. The target contamination level of 400 mg/kg for the test soil was not met after the first flotation separation process. However, after milling the residue of the first process and subjecting it to a second flotation separation process, the required contamination level was achieved. Consequently, the proposed froth-flotation separation process can be used as a successful alternative technique to remediate F-enriched soils from natural origin that have highly chemical-resistant forms. Full article

The Nakdong River delta, located in southeastern Korea, preserves thick and wide sediments, which are suitable for the high-resolution study of the evolution of depositional environments in the lower delta plain area. This study traces the Holocene evolution of the Nakdong River delta using deep drill core (ND-3; 46.60 m thick) sediments from the present delta plain. Sedimentary units of the sediments were classified based on grain size compositions and sedimentary structures: (A) alluvial zone, (B) estuarine zone, (C) shallow marine, (D) prodelta, (E) delta front, and (F) delta plain. The weathered sediment, paleosol, was observed at 43.16 m below the surface. There is an unconformity (43.10 m) to separate a Pleistocene sediment layer in the lowermost part differentiating from a Holocene sediment layer in the upper part of the core. The shallow marine sedimentary unit (32.20~23.50 m), in which grain size decreases upward is overlain by the prodelta unit (23.50~15.10 m), which consists of fine-grained sediments and relatively homogeneous sedimentary facies. The boundary between the delta front unit (15.10~8.00 m) and the delta plain unit (8.00~0.00 m) appears to lie at 8.0 m, and the variation in grain size is different; coarsening upward in the delta front unit and fining upward in the delta front unit, respectively. These sediments are characterized by a lot of sand–mud couplets and mica flakes aligned along with cross-stratification, which may be deposited in relatively high-energy environments. Until 13 cal ka BP, the sea level was 70 m below the present level and the drilling site might be located onshore. At 10 cal ka BP, the sea level was located 50 m below the present level and the drilling site might be moved to an estuarine environment. From 8 to 6 cal ka BP, a transgression phase occurred as a result of coastline invasion by the rapid rise of the sea level. Thus, the drilling site was drowned in a shallow marine environment. After 6 cal ka BP, the sea level reached the present level, and, since then, progradation might begin to form, primarily by more sediment input. After this period, the progradation phase continues as the sediments have advanced and the delta grows. Full article

Rapid advancement of drone technology enables small unmanned aircraft systems (sUAS) for quantitative applications in public and private sectors. The drone-mounted 5-band MicaSense RedEdge cameras, for example, have been popularly adopted in the agroindustry for assessment of crop healthiness. The camera extracts surface reflectance by referring to a pre-calibrated reflectance panel (CRP). This study tests the performance of a Matrace100/RedEdge-M camera in extracting surface reflectance orthoimages. Exploring multiple flights and field experiments, an at-sensor radiometric correction model was developed that integrated the default CRP and a Downwelling Light Sensor (DLS). Results at three vegetated sites reveal that the current CRP-only RedEdge-M correction procedure works fine except the NIR band, and the performance is less stable on cloudy days affected by sun diurnal, weather, and ground variations. The proposed radiometric correction model effectively reduces these local impacts to the extracted surface reflectance. Results also reveal that the Normalized Difference Vegetation Index (NDVI) from the RedEdge orthoimage is prone to overestimation and saturation in vegetated fields. Taking advantage of the camera’s red edge band centered at 717 nm, this study proposes a red edge NDVI (ReNDVI). The non-vegetation can be easily excluded with ReNDVI < 0.1. For vegetation, the ReNDVI provides reasonable values in a wider histogram than NDVI. It could be better applied to assess vegetation healthiness across the site. Full article