Mineralogical Variations Research Articles

Amendments of waste ochre from former coal mines can potentially be used to increase soil carbon persistence

There is an increasingly urgent need to remove CO2 from the atmosphere. Increasing C storage in soils has been discussed as a possible method of achieving this. Regardless of whether increasing soil C would result in reduced atmospheric C or not, increasing the amount of organic carbon (OC) stored as organic matter in soils is widely regarded as leading to agronomic benefits such as increased water retention and resistance to erosion. Fe oxides adsorb OC in soil, protecting it from degradation. In this study we investigated the use of waste ochre (Fe oxy-hydroxide) that precipitates from the drainage of former coal mines as a soil amendment to increase C storage in soils via reduced C lability. In preliminary batch experiments, ochres reduced the release of OC from soils into solution. In plant growth experiments with wheat (var. Skyfall, RAGT) 5 wt% amendments of ochre to soils significantly reduced the concentration of hot water extractable OC by approximately 16% and OC lost from the soils in leachate by approximately 43%. Above ground plant biomass was significantly reduced by approximately 50% in the amended soils. There was no evidence for increased uptake of potentially toxic elements in the plants from the ochre-amended soils compared to the study controls but Olsen P extractable phosphate was decreased by the ochre amendments. In subsequent experiments with agronomically realistic additions of KH2PO4 there was no difference in plant biomass between the study controls and the ochre-treated soils suggesting that reduced plant growth was due to reduced P availability; C lability was still significantly reduced. Furthermore, the ochre amendments helped retain th added phosphate in the soil. These results indicate that Fe oxide amendments to soil may be a viable way of changing soil chemistry in order to increase the amount of OC retained in soils. Further experiments investigating the impacts of the ochre amendments on greenhouse gas emissions and soil biology are required followed by field trials where the impact of more variable soil moisture and temperature effects can be assessed and crops grown to harvest. A full Life Cycle Analysis could then be performed. Given the relatively limited quantities of former coal mine ochres available in the UK and the carbon footprint of transporting materials prior to adding them to soils, similar experiments to those reported here, taking into account chemical and mineralogical variations, are warranted to determine the global stock pile of Fe-rich wastes that could potentially be used to reduce C lability in soils.

BIOTITA-XISTO DA SUÍTE INTRUSIVA TRACUATEUA DO NORDESTE DO PARÁ E SEU POTENCIAL AGROMINERAL

The main purpose of this work is the chemical and mineralogical characterization of a biotite-shist from northern Brazil, in order to evaluate its potential as an alternative rock of potassium fertilizer. For the characterization, one composite sample of about 40 Kg was crushed and classified into four subsamples with the following grain sizes: (-4000 +1000), (-1000 +300), (-300 +53) and (-53) μm. All four subsamples were submitted to the following analyses: X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier Transform Infrared Spectrometry (FTIR) and optical microscopy (OM) for textural analysis. The biotite-shist is mainly composed by albite, quartz and biotite, besides small amounts of chlorite and traces of K-feldspar and clinopyroxene. No significant mineralogical variation was observed among the studied granulometric fractions. Mean K2O contents are 2,61%, above the minimum of 1% required by the Normative Instruction of the Ministry of Agriculture of Brazil. Although further studies are still needed, the biotite-shist studied may have good potential when compared to other rocks already used in Brazil, e.g., other biotite schists from Central Brazil, as agromineral or soil remineralizer. Keywords: Biotite-schist, potassium fertilizer, soil remineralizer, agromineral.

Petrogenesis and in situ U-Pb zircon dates of a suite of granitoid in the northern part of the Central Indian tectonic Zone: Implications for prolonged arc magmatism during the formation of the Columbia supercontinent

The timing and petrogenesis of magmatic rocks in the Central Indian Tectonic zone (CITZ) have paramount importance in understanding the (a) growth of the Indian shield and (b) formation and disintegration of the Columbia and Rodinia supercontinents. In this study, the petrology, geochemistry and U-Pb in-situ zircon dating of a suite of porphyritic granitoids from the Makrohar Granulite Belt (MKGB) of the CITZ are presented. The studied rock suite develops megacrystic K-feldspar and plagioclase phenocrysts, embedded in medium to fine-grained matrix of biotite ± amphibole + quartz + K-feldspar + plagioclase + ilmenite ± garnet with widely variable phenocryst to matrix ratio. The bulk compositions of the studied rocks overlap with the compositions of the I-type granitoid, emplaced in a continental arc setting. The in-situ U-Pb zircon age fixes the timing of magmatism at 1750 Ma. Systematic geochemical trends combined with the variation in modal mineralogy suggest crystal fractionation to be the dominant process during the evolution of this arc magma. Phase equilibrium modeling in Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2-O2 system under various physicochemical conditions suggests that both post-emplacement fractionation of a felsic magma and combined fractionation-crustal assimilation of a mafic magma at shallow depths (≤5 kbar) can produce the chemical variation observed in the studied arc granites. Petrography and field evidences negate substantial granite formation from combined fractionation and crustal assimilation of arc basalt in the studied area. Plagioclase and K-feldspar occur as early crystallising phases. Variation of the modeled melt compositions simulates the variations of the major element compositions in the studied granitoid suite. The ca. 1750 Ma old arc magmatism in the MKGB is also reported from the Mahakoshal Supracrustal Belt (MSB). This feature is consistent with the view that both MKGB and MSB, now separated by the Son Narmada South Fault formed a coherent block till 1750 Ma. In combination with the published information, the present study demonstrates southward progression of the arc front in the Indian shield from ca. 1900 Ma to ca. 1600 Ma during growth of the Columbia supercontinent.

Seasonal Variations of Mineralogical and Chemical Composition of Particulate Matter in a Large Boreal River and Its Tributaries

Despite the importance of river suspended matter (RSM) for carbon, nutrient, and trace metal transfer from the land to the ocean, the mineralogical control on major and trace element speciation in the RSM remains poorly constrained. To gain a better understanding of environmental and seasonal factors controlling the mineral and chemical composition of riverine suspended load, we studied, over several hydrological seasons, including winter baseflow, the RSM of a large boreal river in Western Siberia (Ob in its middle course) and its two small tributaries. The concentration of RSM increased from 2–18 mg/L in winter to 15–105 mg L−1 during the spring flood. Among the dominant mineral phases of the RSM in the Ob River, quartz (20–40%), albite (4–18%), smectite (2–14%), and chlorite (6–16%) increased their relative proportions with an increase in discharge in the order “winter ≤ summer < spring flood”; illite (5–15%) was not affected by seasons or discharge, whereas the abundance of calcite (0–30%) decreased with discharge, from winter to summer and spring. Seasonal variation of elemental composition of the Ob River’s RSM allowed distinguishing three main groups of elements. Sodium, K, Si, Al, trivalent, and tetravalent hydrolysates increased their concentrations in the RSM with an increase in discharge, reflecting enhanced contribution of lithogenic material during high flow, whereas the concentration of alkaline-earth metals (Ca, Sr, Ba), P, Mn, and As decreased with discharge, reflecting accumulation of these elements in the suspended matter under ice. At the same time, a number of nutrients and trace elements demonstrated progressive accumulation in the RSM during winter (Ca, P, Cu, Zn, Mo, As, Cd, Sb). Micronutrients (V, Co), Fe, and Cr exhibited a minimum during summer, which could reflect both the uptake of these elements by the biota during baseflow (micronutrients) and their enhanced export during winter and spring compared to summer (Fe). The RSM of small tributaries demonstrated quite a different pattern compared to the Ob River main stem. Maximal concentration of suspended matter was observed at low discharges during the winter. During this period, the RSM was dominated by amorphous Fe hydroxides. Overall, the obtained results confirm the overwhelming impact of peatlands on element export in suspended form in small rivers of Western Siberia, and strong seasonal variations of both mineralogy and chemistry of the RSM in the Ob River main stem. Elemental yields (watershed-normalized export), assessed for the first time for the middle course of the Ob River and tributaries, were shifted towards the more important role of particulate vs. dissolved export for a number of trace elements, compared to that of the small and medium-sized rivers of Western Siberia, draining the taiga forest and peatlands of the boreal zone. The contrasting pattern of RSM chemical composition across the year demonstrated the importance of seasonal approach for sampling river suspended matter and calls a need for addressing strongly understudied RSM sources during winter baseflow, under ice.

Laser Induced Breakdown Spectroscopy (LIBS) for whole rock geochemistry

To meet the ever-increasing global demand for metals, new mineral deposits need to be discovered. However, as the exploration frontier progressively moves towards deeper buried prospective areas, sampling is becoming costlier and deposit discovery rates are in decline. New technologies and analytical procedures able to deliver fast, reliable, and cheaper samples, analysis, and data, compared to current procedures are therefore, crucial in decreasing the risk of exploration targeting and can represent a step change in mineral exploration. In this study we demonstrate how to emulate laboratory whole-rock geochemical data for major elements (Al, Ca, Fe, K, Mg, Na, Si, and Ti) by averaging LIBS spot analyses performed over single, 1-mm spaced transects, that imitate downhole trajectories, along ~1-meter length drill core intervals for chemically, texturally, and mineralogically diverse rocks. Data was collected using a benchtop prototype LIBS instrument that could be reconfigured to fit within a ≥ 75 mm diameter drill hole. The prototype comprises a customised 8 ns pulsed 532 nm Nd:YAG laser with maximum pulse energy of 40 mJ at 5 Hz; two high-resolution spectrometers that together cover a spectral range from 190 to 830 nm, hence allowing all elements to be analysed; a motorised stage; and optics. Estimated LIBS geochemistry shows strong correlations with laboratory whole rock geochemistry for the selected major elements, particularly for Si, Al, and Na, and to a lesser extent K, although the LIBS estimation can breakdown for elements found in low concentrations (e.g., 0.06 wt%). Factors including the variability in mineralogy and element deportment, or roughness of the analysed surface can result in under- or over-estimation in LIBS whole rock geochemistry. In addition, for more efficient data collection processes, investigations of the optimal number of LIBs spot analysis showed that optimal ~30 to ~560 spot analyses per meter are required to emulate whole rock geochemistry (e.g., 1 % error and 95 % confidence). The strongest influence on the optimal number of LIBS analysis required for estimation of whole rock geochemistry is the range of element concentration and to a lesser extent the number of minerals that host an element as well as grain size. The results of this study show promise in development of strategies for rapid whole rock geochemical analysis down a drill hole.

A 13 million-year record of Li isotope compositions in island carbonates: Constraints on bulk inorganic carbonate as a global seawater Li isotope archive

Lithium isotope (δ7Li) variations in marine carbonate sediments and rocks have been widely used to reconstruct global seawater Li isotope compositions and then trace the paleo-weathering processes. However, there are still debates on whether ancient carbonates can faithfully document original seawater δ7Li signals, as δ7Li values of shallow-water carbonates are tightly related to carbonate mineralogy and diagenetic alteration. In this study, we present high-resolution δ7Li, trace element and carbonate mineralogy data of shallow-water carbonate deposits from two shallow drillcores (Jiuzhang A and B) and a deep drillcore (XK-1) in the South China Sea. We compare these new δ7Li data to the ca. 13 Myr history of seawater δ7Li evolution from the middle Miocene to Pleistocene, in order to better constrain the effects of carbonate mineralogy and early diagenesis on δ7Li values of bulk inorganic carbonates. We observe that the δ7Li values of primary carbonate deposits in Jiuzhang A, B and the uppermost XK-1 drillcores (24.6% ± 1.6%, n = 37, 1σ) are significantly lower than modern seawater δ7Li values (Δ7Liprimary-seawater = ∼–6.0%). In contrast, marine diagenetic carbonates in the XK-1 drillcore exhibit δ7Li values of 28.7% ± 0.7% (n = 54, 1σ), approaching coeval seawater values (Δ7Limarine diagenetic-seawater = ∼–2.0%) and much higher than those of primary carbonate deposits. Meteoric diagenetic carbonates in the XK-1 drillcore show δ7Li values of 22.4% ± 1.6% (n = 46, 1σ), close to that of primary carbonate deposits in Jiuzhang A, B and the uppermost XK-1 drillcores, but significantly lower than coeval seawater δ7Li values (Δ7Limeteoric diagenetic-seawater = –5.0% to –9‰ for modern and Miocene seawater). Such δ7Li variations in shallow-water carbonates are attributed to variations in carbonate mineralogy (i.e., aragonite, high-Mg calcite and low-Mg calcite) and diagenetic regimes (fluid- or sediment-buffered conditions of marine and meteoric diagenesis). By comparing δ7Li data from the South China Sea to those from the Bahamas, we suggest strongly fluid-buffered conditions for Li isotopes during marine diagenesis, resulting in δ7Li values of marine limestones and dolostones approaching ambient seawater δ7Li signals. In contrast, meteoric diagenetic carbonates, likely marked by sediment-buffered conditions, may inherit the original δ7Li signals of primary carbonate deposits. Hence, full considerations of the carbonate mineralogy and diagenesis facilitate a better use of bulk inorganic carbonate-archived δ7Li to reconstruct paleo-weathering evolution in deep time lacking the skeletal fossil records.

Evolution of Alkaline Mine Drainage and Unique Biodiversity on Soil-Free Mine Substrates, Southern New Zealand

Relatively impermeable soil-free substrates (clay-rich outcrops and sediments) exposed at eight abandoned placer gold mines generate alkaline mine drainage through evaporation and minor interaction between water and rock in a semi-arid rain shadow climate. Original mine sluicing a century ago created drainage channels over the land surface that still control the flow of ephemeral surface waters, with localised construction of erosional outwash pans. Ephemeral surface waters and associated evaporitic salts are dominated by halite derived from marine aerosols in rain, yielding circumneutral pH and electrical conductivity (EC) values locally exceeding 50 mS/cm. Weakly altered schist basement rocks and Miocene mudstone exposed at the surface contain abundant calcite, and surface waters are supersaturated with respect to Ca-carbonate minerals with a pH of ≈ 8 and an EC of ≈ 1 mS/cm. Water interaction with albite increases the dissolved Na/Cl molar ratio to > 1, and evaporative formation of Na-carbonate precipitates can raise the pH to > 10. Pyrite oxidation does not offset the alkaline pH in any of these processes, although dissolved sulfate can rise to high levels (> 2000 mg/L; EC ≈ 5 mS/cm), forming evaporative sulfate minerals. Ephemeral waters drain down outcrops and the relatively impermeable erosional pans, leaving salt encrustations with variable mineralogy and associated waters with pH and EC values that are partially controlled by rates of dissolution and reprecipitation of the minerals in the salts. The saline alkaline chemistry of the pans excludes most vegetation and has allowed development of salt-tolerant ecosystems with rare endemic halophytic plants. Maintenance of soil-free halophytic surfaces has potential applications in dryland mine sites around the world, especially as climate change enhances and extends aridity.

Assessing the spatial variability of the ~3 μm OH/H2O absorption feature in CM2 carbonaceous chondrites

AbstractH2O and OH are readily detected in hydrated minerals in CM chondrites via reflectance spectroscopy due to their characteristic vibration absorptions at infrared wavelengths. Previous spectroscopic work on bulk powdered CM chondrites has shown that spectral parameters, like the wavelength position of the “3 μm absorption feature,” vary systematically with the extent to which the samples have been aqueously altered. However, it is yet unclear how these spectral features may vary across an intact meteorite chip when measured at spatial scales smaller than that of the individual components of the meteorite. Here, we explore the spatial variability of this spectral feature and others on intact CM2 chips which, unlike powders, retain their petrologic and textural characteristics. We also model the modal mineralogy of the bulk meteorite powders and correlate this with key spectral features, demonstrating that microscope Fourier transform infrared spectroscopic mapping provides a powerful, rapid, and non‐destructive technique for assessing compositional diversity and variations in water–rock interactions in chondritic planetary materials. In all CM2 chondrites studied here, we find that variations in the position, shape, and strength of the 3 μm absorption feature reveal a single chondrite can exhibit as much spectral variation as the entire suite of CM2 chondrites. The observed variations in the position and shape of the 3 μm feature within individual CM2 chondrite chips suggest a range of alteration products (e.g., Mg‐rich to Fe‐rich phyllosilicates) are present and record sub‐mm scale variations in the amount and/or chemistry of the altering fluids. The samples having experienced the most progressive aqueous alteration show the least amount of variability in features like the 3 μm absorption band minimum position, whereas the least altered samples exhibit the most variability. We also find that the bulk spectral signatures in the least altered samples appear to be biased toward the spectral signatures of clasts versus matrix. By extension, asteroid reflectance spectra exhibiting 3 μm absorption features consistent with those measured here may be interpreted in a similar framework in which the spectrum of what may appear to be the least altered asteroids represents an average that belies the true diversity of mineralogy and chemistry of the body.

Southwestern Australia Acid-Saline Mineralogy: Observations From Reflectance Spectroscopy

Acid-saline sediments in shallow-lake environments in southwestern Australia host complex mineralogical suites representing long-term weathering and modern extreme acid-saline chemistry. It is not known whether large-scale reflectance spectroscopy datasets from watersheds across the Yilgarn Craton show regional mineralogical variability. This study assesses over 2500 spectra from datasets of shallow subsurface sediments by using automatic minima detections for spectral features of interest. Integrating microscopic and spectral observations show that proportionally similar mineral assemblages exist in a variety of recognizable textures. Spectral results indicate that iron oxide and phyllosilicates are the most detected mineral types, alongside less common alunite, jarosite, and gypsum. The difference in detection abundance by percentage for mineral groups, particularly iron oxides, accounts for the largest regional variation observed in spectra. Spectral feature characteristics show significant regional variation for iron oxide, alunite, and hydrated mineral absorptions. The spectral observations align with previous mineralogical observations of these landscapes and the expected weathering evolution for granitoids, where Al-phyllosilicates and iron oxides are most prevalent. Observations of these mineral suites enhance understanding of regional differences and similarities in chemical precipitates and products of water–rock interaction in extreme acid-saline environments and have implications for studying sediments and rocks on Mars.

Chemical and mineralogical variability of sediment in a Quaternary aquifer from Huaihe River Basin, China: Implications for groundwater arsenic source and its mobilization

Arsenic (As) is a conspicuous contaminant, and exposure to this element through contaminated drinking groundwater poses a significant challenge to public health. Geogenic groundwater arsenic is associated with sedimentary setting. This work concentrates on the investigation of lithology, elemental abundance and mineralogical compositions about the arsenic profile and its effect to the groundwater from Huaihe River Basin, China. There are 90 sediment samples from the borehole at the field monitoring sites were collected and analyzed. The results reveal that sedimentary concentrations of As, Fe, Mn, S, Al, N, organic carbon and mineralogical compositions vary across the Quaternary aquifer. Arsenic abundance of sediments is 10.63 ± 0.56 mg/kg, and peak As concentrations occur between 59.0 m and 64.8 m in fine particle sediments. The specific higher As concentrations in sedimentary aquifer are concordant with arsenic-rich groundwater around the investigated borehole. Fe, Mn, and Al depth profiles follow similar tendency to those of As. Sedimentary As concentrations are significantly correlated to Fe, Al, and Mn concentrations, but are not correlated to organic carbon and S concentrations. Arsenic probably exists in the form of non-crystalline colloids, and Fe, Al minerals are potential host minerals for arsenic. Under alkaline conditions, groundwater arsenic is released and enriched within the Quaternary aquifer by reductive dissolution of As-hosting Fe and Al minerals.

Petrography and Clay Mineral Variations Across the Cretaceous/Paleogene (K/Pg) Boundary, Sulaimani, Kurdistan Region, Iraq

The Cretaceous/Paleogene (K/Pg) boundary marks the global extinction of many life forms, this boundary around Sulaimani city coincides with the boundary between Tanjero and Kolosh formations. These two units are flysch deposits of the Zagros Foreland Basin. This study focuses on petrography and clay mineralogy variations between these two units. Petrographic study, X-Ray Diffraction analysis, and Scanning Electron Microscope analysis were conducted on samples from different lithologies. The petrographic study of fine-grain lithologies shows that they are mainly wackestone without variation across the boundary. Sandstone petrography shows variation in framework components by increasing quartz, feldspar, and igneous fragments while argillaceous, carbonates, chert, and chalcedony fragments are decreased from Tanjero to Kolosh formations. Obtained results from XRD and SEM show that the clay mineral assemblage is dominated by corrensite (regularly interstratified chlorite/smectite) with discrete chlorite, smectite and traces of illite. The existence of these clay assemblage suggests that corrensite is the diagenetic product of smectite as it is an intermediate stage of smectite chloritization. Enrichment of precursor smectite and high content of unstable grains in sandstones across the K/Pg boundary is the result of low-intensity weathering in arid and seasonal climates of the source area. The smaller size of detrital smectite than other clay minerals is behind its enrichment in the deep marine basin for both Tanjero and Kolosh formations. Sandstone enrichment with sedimentary fragments in both formations related to uplifted sedimentary terrain in its hinterland, while variation across the boundary indicates gradual uplift of Zagros ophiolite zone in the early Paleogene.

Temperature as a likely driver shaping global patterns in mineralogical composition in bryozoans: implications for marine calcifiers under global change

The Southern Ocean is showing one of the most rapid responses to human‐induced global change, thus acting as a sentinel of the effects on marine species and ecosystems. Ocean warming and acidification are already impacting benthic species with carbonate skeletons, but the magnitude of these changes to species and ecosystems remains largely unknown. Here we provide the largest carbonate mineralogical dataset to date for Southern Ocean bryozoans, which are diverse, abundant and important as carbonate producers, thus making them excellent for monitoring the effects of ocean warming and acidification. To improve our understanding of how bryozoans might respond to ocean warming and acidification, we assess latitudinal and seafloor temperature patterns of skeletal mineralogy using bryozoan species occurrences together with temperature data for the first time. Our findings, combining new mineralogical data with published data from warmer regions, show that the proportions of high‐Mg calcite and bimineralic species increase significantly towards lower latitudes and with increasing seawater temperature. These patterns are consistent with the hypothesis that seawater temperature is likely a significant driver of variations in bryozoan mineralogy at a global scale.

Portland cement clinkers turned into garnets by spark plasma sintering

The feasibility of sintering Portland cement clinker powders by Spark Plasma Sintering (SPS) has been studied. Different SPSed compacts have been successfully obtained by this technique. The compacts have been characterized by means of X-Ray Diffraction, InfraRed spectroscopy, Scanning Electron Microscopy, Raman Microscopy and Vickers hardness. It is worth noting the finding that slight mineralogical variations in the starting compositions may induce dramatic changes, both in the final mineralogical composition and in the morphology, which can affect the properties of the SPSed compacts. Thus, we find that SPS allows artificial garnets to be obtained in the laboratory by applying pressures as low as 50 MPa, while they are materials that would require much higher pressures in natural environments (2–10 GPa). According to the Selsing model, it has been calculated that the material itself acts as a pressure amplifier at the micrometric level by a factor of 40–200 times. A new model describing the formation of garnets considering the emergence of two transitory eutectic liquids has been explained to justify this phenomenon. This result opens the door to looking for compositions for specific applications with high added value in the field (i.e. high hardness), mainly in the manufacturing of high-pressure (GPa) phases by applying relatively low pressures (MPa).

The flotation behaviour of liberated Platinum Group minerals in Platreef ore under reduced reagent conditions

In spite of numerous studies on PGM behaviour in flotation, there remains much discrepancy regarding PGM speciation and its impact on floatability, as PGMs are routinely considered as an entire group for recovery prediction and trouble-shooting investigations. The understanding of preferential floatability of PGM species under a given flotation regime is important in predicting and addressing mineralogical variability in processing plants, to ensure efficiency in PGM upgrading and recovery. In this contribution, the effect of reduced collector and frother dosages on floatability of individual liberated PGM species was studied in Platreef ore from South Africa, which contains a large variety of different types of PGM species.Reagent tests were performed, with the aim to facilitate a more competitive environment for PGM flotation, by decreasing the collector and frother dosages with respect to a baseline test. Automated mineralogical analysis was performed on the feed, rougher concentrates and tails of the reduced reagent and baseline tests to ascertain how PGM species respond to reducing collector and frother dosages by virtue of the concentrate streams and tails they report to. PtS showed preferential upgrading compared to PdBiTe, PtPdS, PtBiTe, and PtAs, in the reduced reagent test. PdBiTe overall performs better than PtBiTe. PtAs consistently performs the worst in both baseline and reduced reagent tests and is therefore deemed a poorly floatable mineral irrespective of the reagent conditions used. PtPdS, PtAs and PtS floatability seem to be sensitive to grain size with coarse PGM preferentially recovered, over finer grains, in first concentrates.These results can aid in predictive studies for flotation of Platreef ores with variable PGM assemblages, and consequent tailoring of reagent conditions to improve flotation efficiency.

Origin of Lower Cretaceous quartzose arenites in northern India and the Indus Basins of Pakistan—The result of provenance composition, weathering or diagenesis?

AbstractLower Cretaceous (Aptian‐Albian) sandstones of the Ghaggar‐Hakra Formation in the Barmer Basin of northwest Rajasthan, India, have a complex depositional history which is confusing given they are quartzose arenites. The heavy mineral grains are very well‐rounded, and the assemblage is dominated by zircon and rutile grains suggesting that the sediments have been recycled multiple times, whilst the presence of staurolite indicates a metapelite provenance component. Petrographical analysis suggests that extreme diagenesis cannot account for the quartzose arenite composition, despite Early Cretaceous soil formation and at least two periods of subsequent telogenetic modification. An alternative explanation to extreme chemical weathering in the provenance area is that the Ghaggar‐Hakra sandstones are multi‐cycle sediments derived, at least in part, from the quartzose arenites of the Cambrian Jodhpur Group. This analysis suggests that variations in detrital mineralogy across the Western India Rift System and Indus Basins are the result of transcontinental fluvial transport systems sourcing sediment from specific basement highs (Nagar Parker High, Devikot High, Deodar Ridge and Aravalli Mountain Range) mixed with varying proportions of sediment derived from sandstones of the Jodhpur Group. Consequently, we suggest that Cretaceous fluvial systems were controlled by the local palaeogeographies within the failed rifts of the Barmer and Cambay Basins and that both basins formed barriers to sediment transport from the Aravalli Mountain Range across the northwest Indian plate and into surrounding basins.

Experimental Study on the Impact of Clay Distribution and Mineralogy on NMR T2 and Internal Gradient: Insights From Well-Controlled Physical Samples

Summary Nuclear magnetic resonance (NMR) is a reliable tool for petrophysical evaluation and the characterization of pore structures. Compared to conventional carbonate reservoirs, sandstone reservoirs contain higher amounts of ferromagnetic and paramagnetic ions (such as iron, nickel, or manganese) usually found in microporous clay aggregates. The interpretation of petrophysical data in sandstone formations can be complicated by variations in clay mineralogy and distribution patterns (laminated, structural, and dispersed). Nevertheless, the impact of clay distribution patterns on NMR signals is not well understood. This study aims to investigate the impact of clay mineralogy and distribution patterns on the T2 relaxation times and internal gradient (i.e., inhomogeneity in the magnetic field). Glass beads were mixed with three different clay minerals characterized by no iron content (kaolinite) to higher iron content (illite and nontronite). The bead-clay mixtures were prepared at a fixed clay content but with variable clay distribution patterns to examine the impact of clay distribution alone. NMR T2 measurements at several echo times were performed on the pure glass beads and the mixtures to evaluate how clay mineralogy and distribution patterns affect the T2 and the internal gradient of the host glass beads. At a given clay distribution pattern, a more significant decrease in T2 relaxation times and a larger increase in the internal gradient of glass beads were observed when adding clays with higher iron content. This is explained by the higher surface relaxivity, and magnetic susceptibility caused when introducing clay with higher iron content. Such an impact can complicate the characterization of NMR-derived pore sizes as similar pore size distribution (PSD) can have very different T2 distribution and the logarithmic mean of T2 relaxation time distribution (T2LM) values. Micro-computed tomography (µCT) images were acquired to compute the PSD to compare it with ones obtained from the NMR measurements. The PSD for the three clay minerals showed almost the same distribution using µCT; however, they showed totally different T2 relaxation times distributions. That is due to the significant impact of the internal gradient causing a distortion in the magnetic field. Thus, careful consideration must be taken before converting the NMR data into PSD. The introduction of iron-free kaolinite resulted in a negligible impact on the internal gradient of glass beads regardless of the clay distribution pattern. On the other hand, the addition of dispersed iron-rich clays (illite and nontronite) results in up to two orders of magnitude increase in internal gradients, compared to mixtures with laminated and structural clays (at the same clay mineralogy and content). Moreover, dispersed clay mixtures display larger changes in T2LM and porosity as a function of increasing echo time. The results from this study suggest that changes in T2LM and the logarithmic mean of the effective internal gradient distribution geff,LM, compared to the clean host sand, can provide insight into iron-rich clay distribution. Larger changes in any given clay content and mineralogy would suggest a more dominant dispersed clay distribution while negligible changes would suggest a laminated distribution.

Variation in Iron Ore Sinter Mineralogy with Changes in Basicity

The target basicity of iron ore sinter is set by blast furnace slag composition requirements, and therefore varies with the proportion of acid burden such as lump iron ore and pellets. Increasing the lump proportion of the burden will increase the target sinter basicity. The mineralogy of sinter produced with a range of basicity between 1.0 and 3.0 was analysed using optical point counting under reflected light microscopy. Sinter from BlueScope Steel’s industrial sinter strand was analysed over a 30-year period, during which time a wide range of iron ore fines blends were utilised and several significant process modifications made. These data were compared with the mineralogy of sinters produced in a pilot-scale sinter pot, a laboratory-scale milli-pot, and small-scale sinter analogues. The mineralogy of the sinters from all scales followed a predictable trend with basicity, generally following the diagram proposed by Bagnall. At a basicity of 1.0, high temperatures were required to produce sinter with adequate strength, resulting in bonding phases dominated by magnetite and glass. Increasing basicity to 2.0 decreased the required sintering temperature and changed the mineralogy to a majority of hematite and SFCA. Further increases in basicity to 3.0 further decreased the required sintering temperature and increased the SFCA and dicalcium silicate content.

A submarine hydrothermal origin of banded iron formations from Archean Kiriburu-Meghahatuburu iron ore deposit, Singhbhum Craton, eastern India

The high-grade (>62 wt% Fe) iron ores of Kiriburu-Meghahatuburu deposit (KMID) of the Singhbhum-Orissa region, eastern India are mainly hosted by banded hematite Jasper (BHJ) and shale. These BIFs belong to oxide facies (hematite ± martite) iron formations without sulfidic/carbonitic signatures. These BIFs have low concentrations of Al2O3 (0.86 wt%), TiO2 (0.13 wt%) and trace HFSE [(high field strength elements such as Zr (13 ppm), Hf (0.30 ppm), Ta (5 ppm), Pb (7 ppm) and Th (0.45 ppm)], reflecting minor amounts of clastic contamination. The SiO2-Zr/TiO2 ratios and the binary plots between certain trace elements, e.g., Hf-Zr and Zr-Y indicate clastic contamination derived from various sources. The weak positive chondrite normalized Eu anomaly (average 1.13) in BHJ, associated with low V (7 ppm) and Ni (17 ppm) contents are analogous to the Superior-type BIFs worldwide, and are consistent with deposition in a submarine hydrothermal environmental setting under low oxygenated environment. Positive Eu anomalies and the Y/Ho vs Eu/Sm relationships indicate mixing of seawater with a small amount of high-temperature hydrothermal fluids (<0.1 %). Based on the field studies, ore mineralogical and geochemical signatures, a “polygenic-supergene- hydrothermal” model has been proposed for the genesis of Kiriburu-Meghahatuburu BIFs that can be used in understanding the mineralogical variations in the iron ores and their genetic aspects at KMID which has implications for exploration.

Calibrated petrophysical model for elevated organic matter intervals and mineralogical variability in the Agrio Formation, Neuquén Basin, Argentina

Organic carbon-bearing mudstone units of variable lithologies exhibit complex internal heterogeneities in total organic carbon (TOC) enrichment and mineralogy related to stratigraphic and geographic variability. Elevated organic matter-bearing intervals within unconventional reservoirs are commonly contained within these thick (100's of meters), low TOC mudstone units, but poorly delineated. The Cretaceous Agrio Formation is a mixed siliciclastic-carbonate mudstone, known source rock unit, and an emerging unconventional play in the hydrocarbon-rich Neuquén Basin of Argentina with internal and geographic heterogeneity. Source rock intervals within the formation have been identified from a detailed outcrop study; however, the variability of hydrocarbon source rock quality and mineralogy of the unconventional reservoir target intervals in the subsurface is relatively unconstrained. A published petrophysical model for a bimodal clay-silica system was modified to predict intervals of elevated organic matter and ternary clay-silica-carbonate mineralogical compositional trends for distinguishing mudstone complexity in the Agrio Formation. This study uniquely distinguishes carbonate-rich from silica-rich mudstone log response across the paleodepositional profile of the system. The calibrated petrophysical model utilized cuttings programmed pyrolysis and mineralogical XRD data applied to wireline well logs from the southern Mendoza and central Neuquén provinces. Predicted logs were used to correlate elevated organic matter distribution, mineralogical composition, and assess stratigraphic and geographic heterogeneity. Thirteen log-derived elevated organic matter-bearing intervals (wireline TOC >1.25 wt%) were identified using the modified petrophysical model, expanding on the previously interpreted five outcrop source intervals in the Agrio Formation. Organic richness thickness and abundance increases in the northern Neuquén to southern Mendoza province within the study area. The new petrophysical workflow can be applied to improve unconventional target decisions for hydrocarbon exploration efficiency in mudstones worldwide.

Mineralogy, fabric and deformation domains in D″ across the southwestern border of the African LLSVP

SUMMARYRecent advances in seismic anisotropy studies that jointly use reflections and shear wave splitting have proven to place tight constraints on the plausible anisotropic and deformation scenarios in the D″ region. We apply this novel methodology to a large area of the D″ region beneath the South Atlantic, in proximity to and within the African large low seismic velocity province (LLSVP). This area of the mantle is characterized by a transition from fast to slow seismic velocity anomalies and it is thought to be the location of deep-seated plumes responsible for hotspot volcanism. Attempting to probe mantle composition and deformation along the LLSVP borders may provide key information on mantle dynamics. By analysing seismic phases sampling this region, we detect a D″ discontinuity over a large area beneath the South Atlantic, with inferred depth ranges ∼170 to ∼240 km above the core–mantle boundary. We find evidence for a D″ reflector within the area of the LLSVP. Shear wave splitting observations suggest that anisotropy is present in this region of the mantle, in agreement with previous studies that partially sampled this region. We model the observations considering lattice- and shape-preferred orientation of materials expected in the D″ region. A regional variation of mineralogy, phase transition boundaries, and deformation direction is required to explain the data. We infer two distinct domains of mineralogy and deformation: aligned post-perovskite outside the LLSVP and aligned bridgmanite within the LLSVP. The scenario depicted by this study agrees well with the current hypotheses for the composition of the LLSVP and with the prevalence of vertical deformation directions expected to occur along the LLSVPs borders.