Primary Clay Minerals Research Articles

Late Cretaceous erosion and chemical weathering record in the offshore Cape Basin: Source-to-sink system from Hf[sbnd]Nd isotopes and clay mineralogy

Source-to-sink research has often used sediment fluxes as a fundamental parameter when seeking to understand the perturbations caused by tectonics or climate. This parameter is often interpreted only in terms of erosion rates, dismissing the component exerted by chemical weathering. In this study, we characterize sediments from the Deep Surface Drilling Program core 361 (DSDP 361) located in the Cape basin to show the evolution of both, physical erosion and silicate chemical weathering, during the late Cretaceous (100.5–66 Ma) in the source-to-sink system consisting of the South African plateau and the Cape Basin. Transmission Electron Microscopy (TEM) images and trace element analyses indicate that detrital clays predominate within the site and thus reflect variations in surface continental processes. Clay mineralogy shows a predominance of detrital smectite (60–98%) throughout the section. However, an increase in primary clay minerals, in particular illite (20%), indicates a relative enhancement in physical erosion, while an increase in palygorskite (10%) indicates regional climate aridification during the Campanian–Danian interval (ca. 77–62 Ma). Concomitant to this enhancement, we observe both, more radiogenic Hf isotopic compositions and less radiogenic Nd isotopic compositions in the clay fractions (< 2 μm). These variations can be respectively associated to an increase in silicate chemical weathering and the incorporation of unradiogenic material, likely related to the orogenic belts present on the western-south margin of Southern Africa. The regional aridification and the global climate cooling trend observed on δ18O benthic foraminifera records do not appear as suitable mechanisms for the increase in physical erosion and silicate chemical weathering observed. Our results, together with the reported increase in sedimentation rates and the reported tectonic uplift between 80 and 70 Ma, suggest that it is tectonic activity and not climate the main driver in the enhancement of denudation processes. Furthermore, our data suggests that such uplift episode could have impacted the regional climate by causing a rain-shadow effect, with an inland aridification suggested by the increase in palygorskite proportions. The increase in silicate chemical weathering suggested by our new dataset begins in the Campanian (ca. 77 Ma), later than the onset of the global climatic cooling trend that occurs from the Turonian onward. If enhanced weathering of the South African Plateau may not have triggered the recorded climatic cooling, it may still have contributed to maintain cooler conditions in the Campanian-Danian interval.

Clay minerals and provenancial implications of surface sediments in the Dongping Lake, North China

Clay minerals have great potentials in pinpointing sediment provenance for large depositional systems. However, source identification using clay minerals for small floodplain lakes is not well known. Situated in the North China Plain, the Dongping Lake receives sediments from both the Yellow River and the Dawen River, thereby representing an ideal site for testing the utility of this method. Here we use clay minerals in conjunction with the Bayesian end-member modeling analysis (BEMMA) to quantify the riverine contribution to modern sediments in the Dongping Lake. Results showed that modern sediments of the Dongping Lake are characterized by four primary clay minerals: illite, smectite, kaolinite, and chlorite, with average contents of 60.53%, 11.37%, 12.70%, and 15.40%, respectively. Clay minerals in modern sediments of the Dongping Lake are mainly delivered by the Yellow River, accounting for approximately 58.99–72.33%; whereas those originating from the Dawen River only account for 27.67–41.01%. It is also found that clay mineral from these rivers have a marked spatial variability. For example, source materials from the Yellow River are widely distributed across the lake, while those from the Dawen River only occur at the estuary of the river and slightly spread out in all directions under the action of water flow.

Clay mineralogy and provenance modeling of the Paleoproterozoic Kaladgi shales, Dharwar Craton, Southern India: Implications on paleoweathering and source rock compositions

Proterozoic clastic sediments reveal vast information regarding provenance, depositional conditions, and environmental evolutions. Peninsular India comprising Archean cratons, also have numerous intracratonic Proterozoic sedimentary basins along their margins. The Archean Dharwar craton in southern India has many Proterozoic successions, namely Cuddapah, Kurnool towards the East, and Kaladgi, Badami, and Bhima towards the northern margin. The Paleoproterozoic Kaladgi Basin (∼1.85 Ga) consists of siliciclastic sedimentary rocks with stromatolitic carbonate formations. XRD analysis of shale layers of the Lower Lokapur and Upper Simikere Subgroups have been carried out to understand the primary clay mineral assemblages, weathering history, and provenance. The Lower and Upper shale layers of Lokapur and Simikere Subgroups show a dominance of montmorillonite and kaolinite, respectively. The geochemical affinities and the clay mineral assemblages indicate a more mafic source to the lower shales (Manoli and Hebbal Formations) and increased felsic contribution to the upper shales (Govindakoppa and Daddanhatti Formations). Illite is ubiquitous in all the shales of the Kaladgi Supergroup possibly representing the diagenetic transformation of montmorillonite and kaolinite to illite. Geochemical modeling of provenance has been carried out using (Eu/Eu*)N, (La/Yb)N, (Gd/Yb)N, and (La/Sm)N of all the plausible source rocks and the average compositions of lower and upper shales. The modeling results suggest that the lower shales are derived from a source of mafic rocks – 45 %, K-rich granite – 35 %, and TTG – 20 %. While the upper shales are derived from source characterized by K-rich granites – 61 % and intermediate volcanic rocks – 39 %. These results signify the classical unroofing of TTG-greenstone belts exposing K-rich granites with the progression of sedimentation. Further, a good correlation between K-enrichment (a measure of % difference between CIA and pre-metasomatic CIA) and ƩLREE is attributed to the abundance of kaolinites that fractionate more LREE.

Climatic and weathering conditions in southern high latitudes during the Turonian-Santonian interval: New insights from IODP Site U1512 (Bight Basin, Southern Australia)

A detailed study, based on a coupled mineralogical and geochemical approach, was done on IODP Site U1512 sediments (Bight Basin, Southern Australia). The mineral assemblages of the clay size fraction (<2 μm), obtained by X-ray diffraction, have been compared to inorganic (major and trace elements) geochemical signals, obtained from both whole rock and clay size fraction, and Sr/Nd isotopes, obtained from clay size fraction to determine climatic and weathering conditions during the Turonian to Santonian interval (∼94–84 Ma, Late Cretaceous) in the southern high latitude band. This study reveals that the mineral assemblages of clay fraction consist of R0-type illite/smectite mixed-layers (considered as smectites), illites, and kaolinites associated with opal-CT and clinoptilolites. Electron microscopy observations have demonstrated a negligible impact of burial diagenesis on clay assemblages while authigenesis contributions of clay minerals are limited and associated with minor volcanic contributions. Clay assemblages would be thus dominantly primary in origin. Based on Sr and Nd isotopic values, clay minerals are interpreted as the resulting from the weathering of rocks and pedogenic blankets of Eastern Australian Highlands and from the remobilization of older sediments from nearby uplifted basins. The chemical compositions of both whole rock and clay size fraction show a relative stability during the studied interval with two exceptions: during the Middle/Late Turonian times for Si, P and Ba and at the Turonian-Coniacian boundary for Ti, K and Zr, associated respectively to an increase of biogenic fraction and to an enhanced input of terrigenous material. The clay assemblages, dominated by smectites, show weak variations along the borehole reflecting stable climatic conditions during the 10-Myr Turonian-Santonian interval. The dominance of smectites, coupled to the absence of chlorite and the low proportions of illite, which are both considered as primary clay minerals, indicates a dominant warm/temperate and sub-humid climate during the studied interval. However, changes in weathering conditions occurred during the Turonian-Santonian interval in southern high latitude. The Early Turonian, characterized by high Chemical Index of Alteration values (>75), is followed by an interval of lower chemical weathering with enhanced biogenic silica during the Middle/Late Turonian. The slight increase of kaolinites, recorded during Coniacian and coeval with increase of Ti/Al and Zr/Al ratios, probably reflects an increase in coarser terrigenous inputs associated with a sea-level fall.

Persistent Provenance of South Asian Monsoon‐Induced Silicate Weathering Over the Past 27 Million Years

AbstractThe development of the South Asian monsoon (SAM) and Himalaya‐Tibetan Plateau uplift were closely intertwined with some studies suggesting that uplift initiated the monsoon whereas others link tectonics with monsoon‐controlled exhumation. Silicate weathering controls atmospheric CO2 on geological timescales resulting in a large potential for monsoon strength and the Himalayan orogeny to influence global climate but detailed records of SAM‐induced weathering on million year (Myr) timescales are lacking. Here, we present radiogenic Sr, Nd, and Pb isotope compositions of clay minerals produced by silicate weathering and transported to the central Bay of Bengal. The radiogenic isotope data exhibit a relatively small range and demonstrate a remarkably consistent mixture of sources dominated by Himalayan rocks and the Indo‐Burman ranges, which consist of sediments derived from the Himalayas. This suggests that the spatial pattern of regional weathering, which today is highest in the regions of strongest monsoon rains, has persisted in a similar form for the last 27 Myrs. A pronounced increase in primary clay mineral abundance (from 9% to 22%) coincident with global cooling 13.9 Myrs ago points to a shift in the weathering regime given that the clay provenance did not change dramatically. Relatively weaker chemical weathering intensity during the mid and late Miocene cooling suggests increased aridity and changes in the large scale atmospheric circulation in the SAM domain. The establishment of the dry winter monsoon season during the mid and late Miocene may have caused this shift in the weathering regime and can reconcile much of the contrasting evidence for SAM initiation.

Evaluation of Shale Source Rocks and Clay Mineral Diagenesis in the Permian Basin, USA: Inferences on Basin Thermal Maturity and Source Rock Potential

The use of mineral diagenetic indices and organic matter maturity is useful for reconstructing the evolution of sedimentary basins and critical assessments for potential source rocks for petroleum exploration. In this study, the relationship of clay mineral diagenesis and organic matter thermal indices (Rock-Eval Tmax) and calculated vitrinite reflectance (%Ro) were used to constrain the maximum burial depths and temperatures of three distinct intervals within the northern Permian Basin, USA. X-ray diffraction of clay fractions (&lt;2 µm) consists of illite, chlorite, and illite-smectite intermediates. Primary clay mineral diagenetic changes progressively increase in ordering from R0 to R1 I-S between 2359.5 and 2485.9 m and the appearance of chlorite at 2338.7 m. Rock-Eval pyrolysis data show 0 to 14 wt% TOC, HI values of 40 to 520 mgHC/g TOC, and S2 values of 0 to 62 mg HC/g, with primarily type II kerogen with calculated %Ro within the early to peak oil maturation window. Evaluation of the potential for oil generation is relatively good throughout the Tonya 401 and JP Chilton wells. Organic maturation indices (Tmax, %Ro) and peak burial temperatures correlate well with clay mineral diagenesis (R0–R1 I-S), indicating that maximum burial depths and temperatures were between 2.5 and 4 km and &lt;100 °C and 140 °C, respectively. Additionally, the use of clay mineral-derived temperatures provides insight into discrepancies between several calculated %Ro equations and thus should be further investigated for use in the Permian Basin. Accordingly, these findings show that clay mineral diagenesis, combined with other paleothermal proxies, can considerably improve the understanding of the complex burial history of the Permian Basin in the context of the evolution of the southern margin of Laurentia.

Phanerozoic Quartz Arenite Formation and Sequence-Analytical Patterns: Indirectly Relating to Major Impacting and Super Plume Volcanism, Jordan, Arabian Plate

This paper deals with indirect effects of major impacting throughout the Early Paleozoic resp. with those of super plume activity during the Early Cretaceous, both applied to the siliciclastic series of Jordan deposited on the Arabian Platform, Arabian Plate. Its focus is mainly directed on gases released by both processes (CO2, SO2, NOx, HCl, HF) and the relating acids, challenged by experiments and microscopic analysis of grain mounts and thin sections that reveal chemical instability of quartz and ultrastable heavy minerals (i.e. tourmaline) under high acidity (pH °C - 90°C). According to Lopatin’s Time/Temperatur-Index the Lower Cambrian reached the onset of hydrocarbon generation (liquid window) during the Lower Early Cretaceous. Unstable heavy minerals (apatite, garnet, hornblende, epidote, zoisite/clinozoisite) are generally absent in quartz arenites while in arkosic sandstones of marine environment carbonate cement and primary clay minerals (illite) provide conservation. As known since the eighties, the K/T-event’s indirect effects had global influence on Earth’s surface sediments and atmospheric chemistry by wildfires, hot whirl storms, acidic “sturz rain”, dust, soot, darkness, loss of photosynthesis, toxic metals, gases and relating acids. All of them are here concerned and applied to major impacting throughout the Early Paleozoic using the impact data of Price (2001); while superplume volcanism during Cretaceous led to the opening of the South Atlantic accompanied by the cyclic outflow of the Para?a/Etendeka Flood Basalts and relating gases in a gigantic scale (137 - 127 Ma). Assuming that the gases cause similar global effects on Earth’s surface sediments, an according result may be expected in form of quartz arenites and their sequence-analytical patterns (cyclic SBs, MFSs).*

Mineral replacement in long-term flooded porous carbonate rocks

This study reports mineralogical and physical property changes linked to geo-chemical alterations processes during three ultra-long-term tri-axial tests on outcrop-chalk from Liège (Belgium). The test core plugs were flooded with MgCl2-brines for approximately one and a half, two and three years, mimicking effective reservoir stresses (9.5–12.5 MPa) and temperature (130 °C) of important hydrocarbon deposits at the Norwegian Continental Shelf. The flooded cores were studied using electron microscopy, whole-rock and stable isotope geochemical analyses, and ion chromatography of the effluent water.All tests show altered textures and mineralogy at the flow-inlet side of the approximately 7 cm long cores. With longer duration of flooding, these alterations moved further into the cores, and for the three-year-test, the entire core was altered. When studied at nano-scale, the newly formed crystals were found to be magnesite containing minor calcium impurities, together with clay-minerals. On the outlet side of the alteration-fronts in the two shorter tests, the mineralogy still mainly consists of calcite and primary clay-minerals, together with newly formed magnesite and secondary clay-minerals. Dolomite or low- and high-Mg-calcite are not observed. The textures of larger micro-fossils are often preserved, but the mineralogy of their shells is altered.A sharp, only 4 mm narrow transition zone at the border of the alteration front towards the less altered area for the two shorter tests, shows the highest porosity in the cores. This pattern resembles what is observed in single-crystal experiments, where the alterations are driven by phase dissolution and subsequent precipitation, the progression of high porosity zones and the state of equilibrium at the boundary between the primary and new mineral phase. This is also in line with observations in nature and models for transport driven mineral replacement in porous media, where differences in dissolution and precipitation rates may cause high porosity transitions zones.During the experiments, all cores underwent severe overall compaction between 10.1% and 18.2%. However, in the two- and three-year long test-cores, the permeability, and calculated porosity, started to increase after a primary phase of reduction. As magnesite precipitates at the expense of calcite, the density increase, but the solid volume decrease. As the bulk volume is constant, porosity and permeability are increased. The changes in ion-concentration of effluents, monitored throughout the experiments, balance the changes in mineralogy, compaction and permeability within the cores. Compositional variations of the injection fluid effectively control the amount of chemical reaction in chalk. This allows for control and predicting changes in geo-mechanical parameters induced by mineralogical replacement, which has significant impact on reservoir conditions.

Origin and Sources of Minerals and Their Impact on the Hydrocarbon Reservoir Quality of the PaleogeneLulehe Formation in the Eboliang Area, Northern Qaidam Basin, China

The Lulehe sandstone in the Eboliang area is a major target for hydrocarbon exploration in the northern Qaidam Basin. Based on an integrated analysis including thin section analysis, scanning electron microscopy, X-ray diffraction, cathodoluminescence investigation, backscattered electron images, carbon and oxygen stable isotope analysis and fluid inclusion analysis, the diagenetic processes mainly include compaction, cementation by carbonate and quartz, formation of authigenic clay minerals (i.e., chlorite, kaolinite, illite-smectite and illite) and dissolution of unstable materials. Compaction is the main factor for the deterioration of reservoir quality; in addition, calcite cement and clay minerals are present, including kaolinite, pore-filling chlorite, illite-smectite and illite, which also account for reservoir quality reduction. Integration of petrographic studies and isotope geochemistry reveals the carbonate cements might have originated from mixed sources of bioclast- and organic-derived CO2 during burial. The quartz cement probably formed by feldspar dissolution, illitization of smectite and kaolinite, as well as pressure solution of quartz grains. Smectite, commonly derived from alteration of volcanic rock fragments, may have been the primary clay mineral precursor of chlorite. In addition, authigenic kaolinite is closely associated with feldspar dissolution, suggesting that alteration of detrital feldspar grains was the most probable source for authigenic kaolinite. With the increase in temperature and consumption of organic acids, the ratio of K+/H+ increases and the stability field of kaolinite is greatly reduced, thereby transforming kaolinite into mixed layer illite/smectite and illite. Within the study area, porosity increases with chlorite content up to approximately 3% volume and then decreases slightly, indicating that chlorite coatings are beneficial at an optimum volume of 3%. A benefit of the dissolution of unstable minerals and feldspar grains is the occurrence of secondary porosity, which may enhance porosity to some extent. However, the solutes cannot be transported over a large scale in the deep burial environment, and simultaneous precipitation of byproducts of feldspar dissolution such as authigenic kaolinite and quartz cement will occur in situ or in adjacent pores, resulting in heterogeneity of the reservoirs.

Geotechnical and Minerology Properties of Marine Clay at the Northeast of Penang Island

A series of subsurface investigation including in-situ and laboratory tests has been carefully planned and executed for a proposed residential and commercial development over soft marine clay at Tg Tokong, Penang Island. This paper presents the approach taken in determining and developing fundamental geotechnical engineering design parameters of the soft clay. The subsurface investigation was carried out in two phases to suit the overall development implementation plan namely subsurface investigation done near-shore with about 70 nos of boreholes, 50 nos of cone penetration tests (CPT) and 100 nos of Mackintosh probes and those that were carried out off-shore with 72 Nos of boreholes. The samples extracted from the field work were subjected to grain size analyses, Atterberg limits, oedometer test and consolidated undrained compression. Subsequently, correlations were established between physical soil properties with undrained shear strength from field vane and laboratory tests. The subsurface investigation has suggested that the soft marine clay at the northeast of Penang island comprises of a very soft upper marine clay layer overlying a stiffer lower marine clay. An intermediate stiff clay is sandwiched between these two marine clay layers. The soft clay was also subjected to x-ray diffraction to observe the minerology make up. The primary clay mineral was kaolinite/chlorite followed by smectite. The clay is anticipated to pose minimum effect onto the swelling and compression behaviour.

Clay mineralogical characteristics at the Permian–Triassic Shangsi section and their paleoenvironmental and/or paleoclimatic significance

High–resolution clay mineralogical investigations were conducted on the Permian–Triassic (P–Tr) carbonate– and siliceous rocks from the Shangsi section, South China. The clay mineralogy is dominated by illite and illite/smectite mixed–layers (I/S) throughout the sampled section with subordinate chlorite and vermiculite emerging from bed 24 (approaching the End–Permian mass extinction horizon–EPME) onwards. Positive correlations of clay fraction with mainly land–derived TiO2 and magnetic susceptibility (MS) indicate a primary continental origin of the clay minerals. Rock–Eval pyrolysis analysis, palynomorph coloration, scanning electron microscope (SEM) and Transmission Electron Microscope (TEM) observations, all suggest that the rocks experienced thermal diagenesis which mainly promotes illitization processes of smectite clay minerals while discrete clay minerals are merely affected. Despite this diagenetic effect, clay minerals still carry valuable paleoenvironmental and paleoclimatic information in the Shangsi section. The overall illitic composition of the clay minerals and nearly absence of kaolinite suggest a general semi–arid condition during the P–Tr interval. Appearance of chlorite from bed 24 onwards suggests further aridification compared to the Late Permian. Occurrence of vermiculite from beds 24–28 in association with abundant volcanogenic materials, most negative δ13Ccarb values as well as enhanced soil–derived moretane abundance, suggests catastrophic soil erosion and likely soil acidification during the P–Tr transition in the source area(s) in relation with the active volcanism in that time. Further, decrease of chemical weathering and increase of physical weathering are indicated by increased input of primary clay minerals such as chlorite, a better illite crystallinity and increase of Al2O3/TiO2 ratios. A climate cooling period corresponding to the Clarkina changxingensis–Clarkina deflecta conodont zone to the lower Clarkina zhangi conodont zone is indicated by higher abundance of illite, lower terrigenous TiO2, MS and Al2O3/TiO2 in comparison with the overlying uppermost Permian strata.

Mineralogy and geotechnical properties of Singapore marine clay at Changi

An engineering geological study was undertaken to determine the geotechnical properties and mineralogy of Singapore marine clay at Changi in the Republic of Singapore. This soft soil is a quartenary deposit that lies within submarine valleys cut in an old alluvium formation. The marine clay comprises a soft upper marine clay layer overlying a stiffer lower marine clay layer. An intermediate stiff clay layer is sandwiched between these two marine clay layers; it is believed to be the dessicated crust of the lower marine clay layer. In the present study, morphological and mineralogical observations of Singapore clay were taken by scanning electron microscopy, X-ray diffraction and photographic identification. The geotechnical investigation included physical, compression, permeability and field vane shear tests. The upper marine clay was found to be soft with undrained shear strength values ranging from 10 to 30kPa, while the lower marine clay was found to have undrained shear strength values from 30 to 60kPa. The sensitivity of the marine clay at Changi varied from 3 to 8 and is described as highly sensitive marine clay. The upper clay layer had a coefficient of consolidation of 0.47–0.6m2/year due to the vertical flow (cv) and a coefficient of consolidation of 2–3m2/year due to the horizontal flow (ch). The lower marine clay had a cv of 0.8–1.5m2/year and a ch of 3–5m2/year, while the intermediate stiff clay had a cv of 1–4.5m2/year and a ch of 5–10m2/year. The primary clay mineral was kaolinite, followed by smectite and mica. With this high kaolinite content, the activity of the Singapore marine clay was found to be low at approximately 0.5–1.3 and classified as inactive to active clay. With reference to the intrinsic state line, natural Singapore clay (upper, intermediate and lower layers) has been classified as structured clay and is in a meta-stable state. The compression behaviour can be modelled by the Intrinsic State Line and the destructuring framework. The predicted and the measured compression curves were comparable for various depths. The successful modelling of compression curves will be useful for settlement calculations and for further research on the development of a constitutive model for Singapore marine clay.

Alunite characterization in the upper Eocene clay deposits of Central Tunisia: an implication to its genesis

Alunite mineral was recently identified at the upper Eocene clay deposits associated with laminated primary gypsum and iron oxide in Central Tunisia, particularly at El Gnater site. The alunite characterization has been performed by several analytical techniques [atomic absorption spectroscopy (AAS), X- ray diffraction (XRD), scanning electron microscope (SEM), thermogravimetric analysis (TGA) and differential thermal analysis (DTA)]. The mean features of their chemical composition are its deficiency of Al, water excess content, small replacement of K by Na and absence of impurities such as Fe. The X-ray diffraction pattern reveals the purity of the alunite samples. The SEM micromorphological study shows a compact facies which is made up by homogeneous pseudocubic microcrystals having approximately the same diameters of 1 μm. Thermal behaviour of El Gnater alunite closely matches published literature which shows two major endothermic peaks at 528 and 744 °C with total weight loss 17.27 and 29.09 %, respectively. The former corresponds to the dehydroxylation processes and the latter corresponds to sulphate decomposition reaction. The association of studied alunite with laminated primary gypsum, hematite and clay minerals implies its late diagenetic origin in reduced conditions and in evaporitic environment. However, jarosite was produced by oxidation of pyrite which was very abundant in the claystone host.

Oxygen permeation properties of HDPE-layered silicate nanocomposites

The current manuscript describes the effects of two different processing conditions on the barrier properties of HDPE/MMT nanocomposites. It is well known that the exfoliation degree of the primary clay mineral determines the gas permeation properties of the final composite. The tortuosity effect caused by the dispersed nanolayers improve the gas barrier properties in some cases while in other cases the interfacial regions or the free volume variations may overcome the tortuosity impact reducing the barrier effectiveness. In the present work, twenty MMT-HDPE nanocomposites were obtained using two types of commercial clay, two compatibilizers, and two different processing methods. The exfoliation and agglomeration of the nanocomposites were investigated by WAXD and TEM. Their gas permeability was measured as a function of the filler loading and was correlated to their impermeable inorganic volume fraction. The oxygen permeability of the nanocomposites decreased as much as 40 % when compared to the pure HDPE.

Effect of Lime on the Compaction and Strength Behaviour of Red Earth treated with Mine tailings

Mine tailings is an industrial by-product obtained from mining industry. The effective disposal of mine tailings(MT) is a great challenge to both civil engineers and mining engineers. On the other hand red earth(RE) is a non expansive soil which is having kaolinite as primary clay mineral and it is a natural soil available in vast areas of India, and also in Karnataka. In the present investigation an attempt has been made to improve the engineering properties of red earth by using mine tailings. The mine tailings properties were studied and treated with red earth soil in the presence of optimum lime content. Unconfined compressive strength tests were conducted to evaluate the engineering properties of the soil samples. The increase in strength due to long term pozzolanic reaction of the calcium oxide present in mine tailings with red earth resuling in the flocculation of particles. This encourages the effective utilization of Mine tailings for Geotechnical applications. Keywords - Mine tailings, Maximum dry density, Optimum moisture content, Pozzolanic reaction, Strength

Physical properties of surface outcrop cataclastic fault rocks, Alpine Fault, New Zealand

We present a unified analysis of physical properties of cataclastic fault rocks collected from surface exposures of the central Alpine Fault at Gaunt Creek and Waikukupa River, New Zealand. Friction experiments on fault gouge and intact samples of cataclasite were conducted at 30–33 MPa effective normal stress (σn′) using a double‐direct shear configuration and controlled pore fluid pressure in a true triaxial pressure vessel. Samples from a scarp outcrop on the southwest bank of Gaunt Creek display (1) an increase in fault normal permeability (k = 7.45 × 10−20 m2 to k = 1.15 × 10−16 m2), (2) a transition from frictionally weak (μ = 0.44) fault gouge to frictionally strong (μ = 0.50–0.55) cataclasite, (3) a change in friction rate dependence (a‐b) from solely velocity strengthening, to velocity strengthening and weakening, and (4) an increase in the rate of frictional healing with increasing distance from the footwall fluvioglacial gravels contact. At Gaunt Creek, alteration of the primary clay minerals chlorite and illite/muscovite to smectite, kaolinite, and goethite accompanies an increase in friction coefficient (μ = 0.31 to μ = 0.44) and fault‐perpendicular permeability (k = 3.10 × 10−20 m2 to k = 7.45 × 10−20 m2). Comminution of frictionally strong (μ = 0.51–0.57) cataclasites forms weaker (μ = 0.31–0.50) foliated cataclasites and fault gouges with behaviors associated with aseismic creep at low strain rates. Combined with published evidence of large magnitude (Mw ∼ 8) surface ruptures on the Alpine Fault, petrological observations indicate that shear failure involved frictional sliding within previously formed, velocity‐strengthening fault gouge.

DNA adsorption on synthetic and natural allophanes

The adsorption of DNA on natural and synthetic samples of allophane, which is a primary clay mineral of andosols, was investigated with respect to the DNA concentration, pH, ionic strength in the sample solution, and competition between DNA molecules and phosphate ions for adsorption to understand the behavior of extracellular DNA molecules in andosols. The relationships between DNA adsorption and the final concentrations were significantly fitted to a simple linear Langmuir equation. DNA adsorption decreased considerably with increasing suspension pH in the range between 3 and 9. The adsorption was less affected by the ionic strength of the suspension from 0.1 to 0.5 mol L − 1 . Under the same experimental conditions, DNA adsorption on allophanes was relatively higher than that on montmorillonite and silica but relatively lower than that on gibbsite and goethite. DNA adsorption on allophanes decreased on the addition of phosphate, indicating that there was a competition between DNA molecules and phosphate ions for adsorption on the minerals. These results suggested that DNA adsorption on allophanes occurred via two mechanisms: direct bonding of the phosphate group at the end of the DNA molecule to the OH groups of the Al-oxide layer on allophane, and the association of DNA molecules with the surface of negatively charged allophane via a bridging of inorganic cations. ► DNA adsorption by allophanes decreased considerably with increasing suspension pH. ► The adsorption was less affected by ionic strength of suspension (0.1 – 0.5 mol L –1 ). ► DNA adsorption on allophanes was higher than silica but lower than gibbsite and goethite. ► There was a competition between DNA molecules and phosphate ions for adsorption.

Rare earth and trace element geochemistry of termite mounds in central and northeastern Namibia: Mechanisms for micro-nutrient accumulation

Rare earth element (REE) and trace element concentrations of ten termite mounds and adjacent topsoil from central and northeastern Namibia were used to investigate the processes underlying the alteration of soil chemical and physical properties by termites ( Macrotermes spp.). Accumulation of micro-nutrients in the mounds was of particular interest because of the ecological implications of the enhanced availability of these scarce elements. The absolute concentrations of REE and trace elements, including nine micro-nutrients (B, Fe, Mn, Ni, Cu, Zn, Se, Mo and Cd), were greater in termite mounds compared to topsoil, suggesting a possible external supply of enriched materials or accumulation of in situ weathering products of the underlying bedrock. Similarities between the chondrite normalized REE patterns of the samples and those of the average upper continental crust (UCC) and Post-Archaean Average Australian Shale compositions indicated that the mounds and topsoil at each site originated from the same host bedrock. Coherent behavior between two incompatible elements (Th and La) in both topsoil and mound samples suggested that the two sets of samples were exposed to two different weathering processes. The relatively low Zr/Sc ratios, fine particle sizes and the persistence of positive Eu anomalies of the mounds relative to UCC were interpreted as reflecting (1) a lack of grain sorting effects and (2) active transport of materials rich in primary clay minerals and trace elements from the deeper regolith to the surface by termites. Lower permeability of mound materials may also prevent leaching of primary minerals and trace elements. Titanium and Zr enrichment in most mound samples (8 samples) was attributed to the decomposition of biotite by Macrotermes with the concomitant release of Ti and Zr into the mounds, suggesting the termites' ability to transform soil minerals and enhance chemical weathering. This was further corroborated by a substantial increase in Th/U ratios in most mounds relative to topsoil. Because of the oxidizing conditions of the mounds, Ti and Zr are likely to be adsorbed onto Fe-oxides. Positive Ce anomalies relative to UCC and the high pH values in the mounds indicate calcrete aggradation or mound aeration as a result of burrowing activities of the termites and evaporation from mounds. The impacts of the changes in environmental conditions and the termite activities on the mound geochemistry are highlighted by heavy REE (HREE) as well as Fe and Mn retentions in the mounds. Heavy REE and light REE (LREE) are likely to coprecipitate with carbonate complexes and Fe- and Mn-oxyhydroxides, and in the process, scavenge a series of micro-nutrients such as Zn, Cu, Cd and Co. A substantial enrichment of Se in mounds, despite the oxidizing conditions of the mounds, could be attributed to active transport of Se-enriched materials from deep soil horizons. The study demonstrated the suitability of REE and trace element geochemistry for assessing the influence of Macrotermes on the physico-chemical properties of semi-arid soils.

Modelling iron–clay interactions in deep geological disposal conditions

In the context of deep geological disposal of high level radioactive wastes, the interactions between iron and clay-rich materials may lead to adverse transformations of clay minerals with a potential loss of confining properties such as swelling and capacity to exchange cations. Such transformations have been experimentally observed at temperatures starting at ca. 80 °C, where smectites contained in a mixture of bentonite and iron powder are transformed into iron-rich serpentine-type minerals. The reaction-transport code CRUNCH is used to investigate the iron–clay interactions at 50 °C over a period of 10,000 years, which are the conditions considered here to represent the mean temperature value and the expected timescale for the corrosion stage. The aim is to predict the nature and quantity of corrosion product, calculate the chemistry of water (essentially the pH) and the mineralogical transformation in the system containing the canister, an optional engineered barrier (bentonite) and the host-rock (argillite). The results of the calculations show that at the interface with the canister, where steel corrosion occurs, the iron is partly immobilized by the precipitation of iron oxides (essentially magnetite) and small amounts of siderite. The pH stabilizes at high values, between 10 and 11, at this location. In the bentonite or the argillite in contact with the container, the primary clay minerals are destabilized and iron-rich serpentine-like minerals precipitate as observed in the experiments (cronstedtite and berthierine). These minerals show low cation exchange and swelling capacities. The results also show that the interactions between iron and clay may lead to significant porosity changes in the system. A reduction of the porosity is predicted at the surface of the steel canister, due to the precipitation of iron oxides. Porosity increase is predicted in the clay material due to the dissolution of the primary clay minerals. The effect of these porosity changes have yet to be observed experimentally and assessed with regard to the confinement capability of the repository near field, especially by considering the mechanical aspects in the case with and without the engineered barrier.

Modelling The Alteration of Son-68 Glass with Nearfield Materials

ABSTRACTThe model tested in this paper couples glass dissolution rate and geochemistry in the surrounding environment, thus leading to the comprehensive description of the interactions between the glass and the minerals and their transformations. Leaching of glass is simulated at 90°C and S/V=80 cm-1 in pure water or with iron from the canister and overpack or with argillite. The glass dissolution is described with an affinity law with respect to a nontronite-like phase, which saturation state depends on Si, Al, Fe, Na and Ca activities. The simulations results allow to reproduce both the decrease of the initial alteration rate and the so-called residual regime while the composition of the alteration layers are explained in terms of precipitated phases. In presence of metallic iron, the corrosion does not affect much glass dissolution rate if silica sorption is neglected. On the contrary, in presence of argillite, the alteration is enhanced by the dissolution of primary clay minerals and the precipitation of feldspar, K-zeolite and clay minerals.