Bottom sediments from 78 sites in the Skagerrak-Kattegat area have been used to determine the semi-quantitative distribution of clay minerals, and to interpret sediment provenance and the transport pathways. The sediment reflects incorporation of four sources, affected both by earlier glacial processes and on-going marine mixing. The southern North Sea, characterized by dioctaheadral illite, kaolinite and smectite, is the dominating source. The central North Sea provides a limited, but significant, source for chlorite. The sediment from the Swedish west coast has an unweathered character, containing trioctaheadral illite, vermiculite, illite-vermiculite mixed-layer minerals and chlorite. The contribution from the southern Kattegat (southern Sweden and Denmark) is dominated by kaolinite and smectite. Correlation between clay content and the contents of smectite, kaolinite and chlorite in the Skagerrak indicate that the clay mineral distribution is influenced by sorting. This grain-size dependency must be considered when interpreting sources.

Dissolution of feldspar and mica and precipitation of kaolinite require a through flow of meteoric water to remove cations such as Na+ and K+ and silica. Compaction driven pore-water flow is in most cases too slow to be significant in terms of transport of solids. The very low solubility of A1 suggests that precipitation of new authigenic clay minerals requires unstable Al-bearing precursor minerals. Chlorite may form diagenetically from smectite and from kaolinite when a source of Fe and Mg is present. In the North Sea Basin, the main phase of illite precipitation reducing the quality of Jurassic reservoirs occurs at depths close to 4 km (130-140°C) but the amount of illite depends on the presence of both kaolinite and K-feldspar. Clay mineral reactions in shales and sandstones are very important factors determining mechanical and chemical compaction and are thus critical for realistic basin modelling.

Cationic binuclear oxo- and carboxylate bridged Fe(III) complexes of N-alkyl-N,Nbis(2-pyridylmethyl)amines are introduced into the interlayer region of smectites by cation exchange reactions. The reaction can be divided into three steps. After a predominant loading of external surfaces, cation exchange sites at internal surfaces react, accompanied by considerable stmctaral expansion. Both reaction stages belong to the steep section of the exchange isotherms. At a certain loading, which depends on the complex substituents and the layer charge of the smectite, the isotherms become flat. With bulky shaped complex cations and highly charged smectites, exchange is not quantitative; vermiculite-type minerals show a very small complex uptake. For this behaviour, both thermodynamic and kinetic reasons must be considered. From these results the number of cation exchange positions at external surfaces of smectite crystals may be estimated.

The evaluation of clays as barriers to fluid movement can be improved by geochemical methods that provide ways to examine the reactivity and weathering of minerals in soils and sediments. X-ray radiography, X-ray powder diffraction, and stable isotope geochemistry provide new data from field locations in the Mississippi River Delta of Louisiana indicating that the clays are not effective barriers to the vertical migration of fluids in the shallow subsurface. Systematic changes in the mineral assemblages, the soil structure and the δD and δ18O values of time clay fractions can best be explained by an alteration sequence produced as the originally smectiterich clay mineral assemblage was kaolinized by percolating groundwater.

More than 50 samples from a Barents Sea borehole near the Mjolnir Structure (an extraterrestrial impact feature) were used to investigate changes in the clay assemblage associated with the submarine impact. Seismic evidence, the presence of shocked quartz and a prominent Ir anomaly restricted the potential impact affected zone to a 10 m interval, straddling the Jurassic/Cretaceous boundary.

Increased abundance (up to 30 wt%) of a smectite, a randomly interstratified smectite-illite with 85% smectite layers, forms the basis for a two-layer oceanic impact clay model that differs from published terrestrial cases. The smectite is assumed to represent seawater-altered impact glass from the ejecta blanket material that was mixed with resuspended shelf sediments by the collision generated waves. The smectite-rich interval is almost 5 m thick. It is overlain by a coarser unit (~2 m thick) containing abundant smectite, shocked quartz grains, and anomalous Ix contents at its base. The smectite-rich interval may have originated as a density/turbidity current, generated by the impact and the collapse and erosion of the crater rim. Seawater alteration of volcanic glass and changes in the tectonic regime of the provenance area, or changing oceanic current circulation patterns could produce similar variations in the clay mineral assemblage. The most compelling evidence for the possible impact derivation of this clay assemblage is the direct association with the Mjolnir Impact Structure and associated mineralogical and geochemical anomalies.

According to multivariate analysis, the following were established (a) kaolinite crystallinity index (KCI) values determined by XRD are highly correlated to one another and seemingly influenced by kaolin impurities; (b) kaolin minerals are concentrated mainly in the fractions <4 µm; (c) the kaolin surface area as determined by the BET (nitrogen adsorption) method is more markedly affected by kaolin impurities than by kaolin minerals themselves; (d) BET surfaces increase when kaolinite crystallinity decreases; (e) brightness is inversely correlated with kaolin impurities; (f) the more ordered the kaolinite and the greater the proportion in the <4 µm fraction of the kaolin, the greater the brightness; and (g) KCI values are particle size-distribution dependent for sedimentary-residual kaolins. The correlations obtained were better when kaolins were selected according to their origin because the kaolin minerals and their impurities, particle size-distribution and texture were more alike. The industrial properties of kaolin can not be predicted from other basic properties such as mineralogy, KCI, etc., because they are intricately related to one another.

Fifteen Swedish and Finnish soil samples from spodic B horizons containing imogolite-type materials were equilibrated with dilute NaCl and HC1 at 8°C. For the NaCl extracts, apparent equilibrium with respect to an AI(OH)3 phase was reached in one to two weeks. Equilibrium with respect to an imogolite-type phase was slower, especially at large soil:solution ratios. The results show that log *Ks (gibbsite), i.e. the logarithm of the solubility constant for reactive AI(OH)3 at 8°C was ~9.40 (8.29 at 25°C) while log *Ks (imogolite) was variable; for the soil studied in most detail it was 7.66 (6.64 at 25°C) As well-ordered gibbsite rarely forms in spodic B horizons, it is suggested that Al(OH)3 and poorly-ordered allophanic materials may be slowly converted to less soluble and less reactive imogolite-type materials.

Iron(II)-containing minerals are potential inorganic nitrate reductants in soils and sediments. Specifically, synthetic green rust (Fe4IIFeIII2(OH)12SO4.yH2O, GR) reduces nitrate to ammonium. The reaction of GR with two different nitrate salts, NaNO3 and Ba(NO3)2, has been compared. The reaction stoichiometry and the reaction order with respect to Fe(II) in GR does not change in the examined temperature range (15-50°C) irrespective of the nitrate salt used. Activation energies of 83.9±7.6 kJ mol-1 and 90.5±6.9 kJ mol-1 have been determined for the reaction of GR with NaNO3 and Ba(NO3)2, respectively. However, for the latter reaction the rate of reaction is increased 40 times. Based on X-ray and M6ssbauer investigations, this acceleration of the reaction rates is attributed to the forced exchange of sulphate with nitrate in GR interlayers caused by precipitation of BaSO4 outside the GR particles, a reaction which does not occur in the presence of NaNO3. This difference in anion exchange behaviour is confirmed by anion exchange experiments with the redox-inactive GR-analogue, pyroaurite. A reaction model initiated by nitrate electrostatically bound at positively charged sites of GR is proposed.

The Athabasca oil sands deposit in Alberta contains ~5 x 109 m3 of bitumen accessible by surface mining. During bitumen separation from the mined ore, ultra-fine (<300 nm) aluminosilicate clays only a few layers thick (U/F) are mobilized and become dispersed in the process water. In this water containing dissolved salts from natural deposits, U/F are capable of forming thixotropic gels. The consequence of this is the production of large volumes of mature fine tailings (MFT) with a high water holding capacity. For mine planning purposes, the objective of predicting and possibly mitigating MFT formation requires an understanding of the colloidal behaviour of U/F particles in salt solutions. In this work, photon correlation spectroscopy and the deuterium NMR method are used to provide an insight into the U/F floc formation process. These results are correlated with conventional analysis of settling data.

Mineralogical and geotechnical investigations on the possible use of compacted bentonite as a buffer material in nuclear waste repositories are reported. The swelling capacity is highly dependent on the density of the compacted bentonite. Swelling pressures >30 MPa were measured for dry densities of ~2.0 g/cm3. Added iron or magnetite powder up to 20 wt% had no influence on the swelling capacity. Compacted mixtures of 20 wt% ground set cement and bentonite showed higher swelling pressures but lower swelling strain capability than compacted bentonite alone. Steam lowered the swelling pressure of compacted bentonite to ~60% of the original value. The influence was, however, reversible by ultrasonic treatment. The thermal conductivity of saturated compacted bentonite at a density of 2.0-2.1 g/cm3 is ~1.35-1.45 W/m°K The volumetric heat capacity ranges from 3.1 x 106 to 3.4 x 106 j/m3°C The saturated hydraulic conductivity of the compacted bentonite is <10-12 m/s. The apparent diffusion coefficients for various ions in compacted bentonite for water contents in the range of 20 to 25 wt% are: K+: 5 x 10-11, Cs+: 6 x 10-12, Sr2+: 3 x 10-11, UO22+: <10-13, Th4+: <10-13, Fe2+: 4 x 10-11, Fe3+: 4 x 10-11, Cl-: 1 x 10-10 and I- : 1 x 10-10 m2/s. The 'breakthrough time' for an apparent diffusion coefficient of 10-11 m2/s in compacted bentonite 1 m thick was estimated to be ~3000 years. The mineralogical longevity was investigated on natural K-bentonites from Kinnekulle, Sweden, and Montana, USA. Although these materials have undergone considerable changes during diagenesis and contain various amounts of mixed-layer illite-smectite, they still have a substantial swelling and adsorption capacity. The investigations demonstrate that although the properties of bentonite are negatively influenced to a certain extent by heat, hot steam, iron and cement, compacted bentonite is still the best choice to act as a buffer material in a nuclear waste repository.

The claystones and mudstones investigated are London Clay, Fullers Earth, Oxford Clay and Kimmeridge Clay. The thermal conductivities were measured using a divided bar apparatus and the values measured perpendicular to layering ranged from 0.68 to 0.97 W/mK. Comparative measurements of thermal conductivities were carried out by the needle probe method and Middleton's method. Deviations of up to 50% were obtained between the needle probe and the divided bar method. The thermal conductivities estimated from the geometric mean model based on mineralogy and water content ranged from 0.87 to 2.01 W/mK, considerably higher than the measured values. A correlation was found between the grain size distributions of the samples and the measured thermal conductivities. This textural effect on the thermal conductivity is assumed to be the main reason for the low measured values and the lack of correlation between the measured and the calculated values.

Experimental illitization of smectite has been simulated by means of hydrous pyrolysis, using a smectite-rich starting material from a Lower Tertiary claystone from the Oseberg field, North Sea. The <2 µm fraction was subjected to hydrous pyrolysis using KCL solutions at concentrations of 1.0 and 0.01 N, temperatures from 180-350°C and reaction times from 24-72 h. The conversion of smectite into illite has been identified by XRD analysis of the pyrolysed products. It was clearly demonslrated that the K+ concentration ([K+]) and temperature are the major factors controlling the rate and extent of illitization. The distributions of activation energies around 33 kcal/mol and frequency factors in the range of 10+8 to 10+9 S-1 have been calculated by applying a parallel reaction model. However, geological modelling and comparison with buried smectite clays indicates that both 1.0 n and 0.01 N KCL are too high in K+ content compared to the pore-water. The results suggest that dilute KCL solution close to pore-water should be used in hydrous pyrolysis to obtain proper kinetic models.

Mineralogical trends have been investigated on a detailed scale in two Westphalian fluvial sandstone sequences in contact with either a coal seam or shales. The evolution in an authigenic clay mineral assemblage can be related to changes in the pH of the pore-water. Firstly, kaolinite formed early in diagenesis, mainly as a result of K-feldspar dissolution and alteration. This process, which took place under acidic conditions, consumed protons. Subsequently the pH of the pore-water increased and after compaction, illitization of kaolinite occurred under near neutral conditions. Deep burial is marked by dickite formation, which again reflects acidic conditions. Distribution of clay minerals is related to meteoric water flux through the sediments and the release of organic acids and CO2 from coalification of organic matter in the underlying strata.

In the North Sea Tertiary section, wellbore instability problems are frequently reported in Palaeocene-Early Oligocene smectite-rich mudrocks. Analysis of the mechanical properties of these Tertiary mudrocks is generally hampered by the lack of suitable core material. This study represents an attempt to study the geomechanical behaviour of mudrocks by triaxial tests of side-wall cores obtained from the borehole wall. The tests performed include measuring the changes in pore pressure during shearing and undrained shear strength in specimens initially consolidated to in situ effective stress levels. The coefficients of permeability (kf), estimated from the consolidation time behaviour range from 2.6 x 10-11 to 2.4 x 10-12 m/s. The tested cores behaved like slightly overconsolidated to normally consolidated materials with an initial near constant volume (elastic behaviour) for low deviatoric load followed by an increasingly contractant behaviour approaching failure. Compared with results from onshore analogues, the strength properties of the investigated mudrocks appear to be related to their content of expandable clay minerals. A wellbore stability chart to forecast adequate drilling fluid pressures for future wells has been developed by the use of linear (Mohr-Coulomb) failure criteria based on the peak strength data. It is demonstrated that side-walt cores can provide satisfactory test materials for rock mechanical analysis, and their use may serve to improve our knowledge of the rock mechanical behaviour of typically troublesome mudrocks for which no conventional cores are available.