Abstract Using a case study from the Mungo Field in the Central North Sea, we investigate the relative impact of acquisition and processing improvements on 4D seismic repeatability. The results show that, while advancements in both have helped to reduce 4D noise, significant noise reduction can be attributed to processing alone. 4D noise can be thought of as any non-production-related amplitudes that are observable on a 4D difference section, and has both random and coherent components. Both are undesirable as they can mask any real 4D signal. A great deal of effort is employed to reduce noise levels by optimizing acquisition and processing between the 3D surveys, which are differenced to highlight the 4D signal. This paper studies the changes introduced by acquisition and processing improvements using the calibrated difference in reflectivity measure.

Abstract Mineral-microbe interaction is a broad, rather poorly understood field of science. Some aspects of mineral-microbe interactions are relatively well understood, e.g. the oxidation of pyrite and the industrial bioleaching of metals. However, other aspects of mineral-microbe interactions are less well understood, e.g. the significance of microbial weathering of silicate minerals. The field encompasses many interactions in addition to those considered in this short collection of papers. For example, the field encompasses bacterial control on biologicallyinduced mineralization of magnetic iron minerals (Bazylinski and Moskowitz, 1997), effects of clay colloids as a physical substrate for growth and adhesion of microbes (Stotzky, 1986) and the orientation of clay platelets surrounding bacteria. The papers presented here are largely restricted to one area of this broad field, that of mineral transformations mediated by microbes. This area is where much of the current research effort is being directed and advances in our understanding of mineral-microbe interactions are being made. We live on (or, more properly, are a part of) a biologically-mediated planet. It is now well known that the actions of biological organisms are largely responsible for the precise balance of gases in the Earth ’s atmosphere that makes life possible. However, there is a tendency for geologists and mineralogists to think within the paradigm of physical and chemical factors only and to neglect biological factors. Whilst this may be justified for processes at very elevated T and/or P it is not likely to be justified for processes at surface or near-surface PT coditions. When describing the weathering of igneous minerals to form either sedimentary rocks or soil, many textbooks list chemical and physical processes as primary factors and biological processes as an additional, relatively minor factor.

Abstract Microorganisms are widespread in all natural environments where, in order to generate energy to form new cell structures, they oxidize and reduce organic and inorganic materials, and form gaseous, liquid and solid metabolic compounds which they excrete into their environment. The energetic and chemical activities of microorganisms are involved in the solubilization or fixing or precipitation of inorganic elements, in the weathering of minerals (silicates, phosphates, carbonates, sulphides, oxides) and in the formation of mineral deposits. Both autotrophic (chemolithotrophic) and heterotrophic (chemo-organotrophic) microorganisms are involved and participate directly (mainly by oxidation-reduction processes) or indirectly (by metabolic products) in the weathering, transformation and evolution of minerals in soils and sediments. Some examples are provided by: (1) the weathering of layer silicates in the rhizosphere of plants (root environment) as influenced by microorganisms (bacteria and mycorrhizal fungi) associated with the roots; (2) the autotrophic bacteria ( Thiobacilli ) which solubilize sulphides by oxidation of Fe and S that depend on the contact between bacteria and mineral and of mineral surface properties and electrochemical parameters; and (3) heterotrophic bacteria ( Bacilli, Clostridia , etc.) which are able, using the available soil organic matter as source of C and energy, to dissolve ferric oxides (hematite, goethite) by reduction of insoluble ferric iron in soluble ferrous iron with rates depending on mineral element substitution in the oxide structure. Such examples illustrate the importance, the interest and the diversity of ‘microorganism–mineral interactions’ and allow us to underline different incidences, applications and perspectives of research and development.

Abstract Mineral dissolution, the primary mechanism of release of inorganic species/nutrients to the Earth’s surface, can be influenced by heterotrophic microbial activity. Heterotrophic (also known as organotrophic) bacteria may affect mineral dissolution directly or indirectly via a number of mechanisms, which can be grouped in two main categories: (1) dissolution from bacterially-formed organic and/or inorganic products; and (2) chelation or uptake by cells, either in suspension or attached to mineral surfaces. In this chapter, the principles of mineral dissolution and of heterotrophic biology in relation to dissolution are discussed. A review of recent evidence of the role of heterotrophic bacteria in mineral dissolution, with particular emphasis on the mechanisms involved, is presented.

Abstract The production of organic acids by fungi has profound implications for metal speciation and biogeochemical cycles. Metal-complexing properties of organic acids, e.g. citric and oxalic acid, assists essential metal and anionic (e.g. phosphate) nutrition of fungi, other microorganisms and plants, and affects metal speciation and mobility in the environment, including transfer between terrestrial and aquatic habitats, biocorrosion and weathering. Metal solubilization processes also have potential for metal recovery from contaminated solid wastes, soils and low-grade ores. Such ‘heterotrophic leaching’ can occur by several mechanisms but organic acids occupy a central position in the overall process supplying both protons and metal-complexing organic acid anions, e.g. citrate. Most simple metal oxalates (except those of alkali metals, Fe(III) and Al) are sparingly soluble and precipitate as crystalline or amorphous solids. Calcium oxalate is the most important oxalate in the environment and is ubiquitously associated with free-living, symbiotic and pathogenic fungi. The main forms are the monohydrate (whewellite) and the dihydrate (weddelite) and their formation affects nutritional heterogeneity in soil, especially that of Ca, P, K and Al, while in semi-arid environments, calcium oxalate formation is important in the development of terrestrial subsurface limestones. The formation of insoluble toxic metal oxalates, e.g. Cu, may ensure fungal survival in the presence of elevated metal concentrations.

Abstract Despite the abundant evidence that rock-encrusting lichens can weather their substrates, it is currently unclear whether rates of lichen-mediated weathering are faster or slower than rates of abiotic weathering of otherwise identical rock surfaces (i.e. are lichens biodestructive or bioprotective?). This question is of considerable academic and commercial importance. Lichens weather rocks by a combination of biophysical and biochemical mechanisms. Fungal hyphae can penetrate into rocks at ≤~0.1 mm y ;1 and sandstones and limestones are especially vulnerable. Biophysical weathering leads to the fragmentation of minerals, exposing grain interiors. These fresh surfaces may be attacked by a variety of compounds including extracellular polysaccharides, lichen acids and oxalic acid. Evidence for the effectiveness of these biochemical agents includes etched and leached mineral grains and reaction products such as oxalate salts, clay minerals and Fe-hydroxides. Few studies have quantified rates of lichen-mediated weathering and fewer still have compared these data with the weathering rate of unencrusted rock surfaces. The conclusion of this work is that lichens enhance the weathering rate of rock surfaces relative to identical but abiotic substrates. As weathered mineral grains and weathering products are bound within the lichen, these materials will not be eroded until the lichen dies after ~10 1 —10 3 y. Thus, despite being active agents of weathering, lichens should stabilize and protect rock surfaces over the short term. Studies of dated surfaces of a variety of rock types colonized by diverse lichen populations are essential before the impact of lichen colonization on rates of rock weathering can be accurately quantified and predicted.

Abstract The ‘Anthropogenic Influences ’ section of this volume on Environmental Mineralogy is concerned with controls on mineral-environment interactions that are in some way influenced by human activity. Mineral-environment interactions include all types of mineral growth and decomposition, with associated chemical and isotopic signatures, and all other chemical reactions such as ion exchange and adsorption. The controls on these interactions are the physical, chemical and biological conditions that exist in the immediate vicinity of the mineral. Many mineral-environment interactions occur naturally in response to natural processes of change, and the significance of an anthropogenic influence may simply be in the rate or the scale of change. Thus, for example, pyrite oxidation resulting in the liberation of protons (pH decrease), has occurred wherever pyritiferous rocks have been exposed to the atmosphere or to oxygenated waters (Keith and Vaughan, chapter 7). But it is often only where humans have opened new conduits in rocks, or have spatially concentrated gangue sulphides in heaps of high-porosity mine waste, that the scale of interactions has become significant to the wider environment. Alternatively, the significance of an anthropogenic influence may be in the combining of substances that would not normally be found together in nature, or it may be in the creation of reactive conditions.

Abstract The aqueous oxidation of metal sulphide minerals in natural rocks, minewastes or mineworkings generates acidic waters, often containing elevated concentrations of toxic metals, and known as acid mine drainage ( AMD )or, more generally, as acid rock drainage ( ARD ). Understanding the mechanisms and rates of oxidation of key sulphide minerals is the essential first stage in understanding the processes giving rise to ARD . In this chapter, our knowledge of the aqueous oxidation of the most important sulphide minerals (pyrite, pyrrhotite, galena, chalcopyrite, sphalerite, marcasite and arsenopyrite) is considered in the context of problems associated with ARD . In certain cases, qualitative or semi-quantitative data concerning oxidation rates are available (for example, in tailings impoundments the sequence from most to least reactive is generally pyrrhotite > galena - sphalerite > pyrite - arsenopyrite > chalcopyrite)and a substantial body of data (some conflicting)exists concerning the products of oxidation. It is acknowledged that surface reaction control is the key to oxidation reaction mechanism. However, as reviewed here, the data and models currently available to describe the oxidation of particular sulphides do not, as yet, yield a consistent picture. Fundamental understanding of oxidation mechanisms remains sketchy, therefore, but the tools are now available to make progress in this field through in situ studies of oxidation processes at atomic resolution.

Abstract Static tests are the most widely used method to assess the net acid-generating potential of rocks at prospective mine sites. The results influence mine plans in which the safe disposal of wastes, such as tailings and waste rocks, is an environmental requirement in most jurisdictions. Static tests are chemical tests that are intended to provide predictions of the extent to which the minerals in representative samples will react to produce acidity, or neutralize acidity, during weathering in potential ARD (acid rock drainage) scenarios. Weathering, however, is not an instantaneous process that affects all minerals equally. Consequently, if static tests are to be interpreted meaningfully, the rates of weathering of the common gangue minerals need to be taken into account. Although the amount of neutralization contributed by an individual mineral during the vigorous reactions in most laboratory static tests is an important measure, it is commonly assumed that this amount of neutralization is directly correlative with that accessible during natural weathering. Static tests by definition exclude mineral-dissolution kinetics, but these vectors are intrinsic to the interpretation and application of the results of static tests. Experimental dissolution rates of silicate and aluminosilicate minerals are rapid relative to normal weathering rates, but most of these minerals react slowly relative to the rapidity at which acid is generated by the oxidation of iron sulphides. Most silicates or aluminosilicates therefore contribute to the attenuation of acidity only after ARD has already been established. For environmental assessments, it is suggested that carbonate contents (calcite and dolomite, but with siderite excluded) provide a more realistic assessment of whether rocks have neutralization potential adequate for the prevention of ARD

Abstract Mynydd Parys in Anglesey is the site of two famous mines which dominated copper production in the early industrial revolution, and is still under investigation for possible future deep mining. It is now a valuable research site for its ore deposits, being an excellent example of the volcanic-associated massive sulphide (‘VMS’) type, its primary and post-mining mineralogy, surface water geochemistry, and related specialized microbiology and problems of acid mine drainage, as well as for its industrial and archaeological record. This chapter discusses the general background to these different geochemical aspects and their specific occurrence and intricate interdependence on Mynydd Parys as well as the problems posed by the management of such a site.

Abstract Granite buildings of Braga show extensive saline contamination, mainly related to anthropogenic activities.G ypsum is the salt associated with the most intense and widespread decay, affecting both internal and external surfaces of buildings. More soluble salts such as thenardite, niter and halite are associated with decay of wall paint. Soluble salts also affect mortars, mostly by the disruption of mortar joints, but, in addition, there is evidence of chemical attack. The zoned distribution of decay indicates that salt concentration is strongly linked to decay.

Abstract High concentrations of toxic substances in the environment may be the result of natural processes (e.g. hydrothermal processes). However, it is mainly human activities, particularly industrial operations and mining, that have scarred the planet with a plethora of contaminated environments. As we are becoming increasingly aware of the potentially permanent damage inflicted upon the Earthâ∈™s surface, and the need to ameliorate this damage, we are also developing a precise scientific understanding of environmental processes, including those that either release or lock up pollution. An essential component of the pollution jigsaw puzzle is the substrate that sustains it; a large part of this substrate is made of minerals. It is thus somewhat surprising that only in the last decade has Environmental Mineralogy been recognized as a research field in its own right.

Abstract Mn oxides are one of the most significant groups of substances which control the distribution of heavy metals in river sediments. This occurs because of their favourable structures, sizes and surface areas. In the Tyne, Tees and Yorkshire Ouse river basins in northeast England, heavy metal-bearing, X-ray amorphous Mn oxides are common (forming upto 15 modal % of heavy metal-bearing grains) though not always abundant phases in river channel and floodplain sediment. Manganese oxides, however, contain significantly more Pb (upto 23 wt.%) than do Fe oxides, and also contain Zn, Cd and Cu (up to 19 wt.%, 0.5 wt.% and 0.8 wt.%, respectively). Within floodplain alluvium, Mn oxides play a major role in controlling the post-depositional redistribution of heavy metals. This is shown by authigenic, Pb-, Zn-, Cd- and Cu-bearing Mn oxides in alluvial profiles at Blagill and Prudhoe in the Tyne basin, and overbank alluvial sediments at Myton-on-Swale and York in the Yorkshire Ouse basin containing multiple horizons of X-ray amorphous Mn-Ba oxides, some of which contain up to 1.0 wt.% Zn. The overbank alluvial sediments at Myton-on-Swale contain the Ba (-Mn) silicate verplanckite [Ba 2 (Mn,Fe,Ti)Si 2 O 6 (OH) 2 . 3H 2 O], although this contains negligible (<0.1 wt.%) amounts of Zn, Pb, Cr, Ni and Co. Manganese oxides play an environmentally significant role in sequestering heavy metals, as shown by contents of upto 39—74% of total sediment-borne Pb, and 10—35% of total Zn, held by Mn oxides in north-east England fluvial sediments. Lower proportions of readily removable Pb and Zn (0.8 — 18% of total Pb, and 3—26% of total Zn) under ambient conditions suggest that the Mn oxides may be long-term sinks for heavy metals in the fluvial environment.

Abstract Expanding layer silicates have been proposed as sorbents for both organic and inorganic contaminants. With specific surfaces that may exceed 800 m2/g and interlayer distances as large as 30Å, montmorillonite in particular possesses a high capacity to sorb large amounts of pollutants with diverse morphologies. The intercalation of hydrolytic polymers of Al, Cr, Cu, Fe, Mn and Ni by smectite has been widely reported and reduces the bioavailability of these metals in both terrestrial and aquatic ecosystems. Hydroxy-Al interlayers possess the greatest order and, when present with other hydrolysed metals in the interlayer, confer a greater order and stability to the coprecipitated intercalate. Organic contaminants may also be effectively sorbed by expandable layer silicates. Cationic organic molecules may be intercalated through simple exchange reactions. Non-polar organic contaminants may be effectively sorbed only by those clays that have been modified to possess an organophilic character.

Abstract In crustal fluids uranium transport and deposition is dominated by redox conditions. The concentrations of dissolved U(IV) species never exceed μg l ;1 levels, whereas the concentration of U(VI) species reaches tens of μg l ;1 depending on pH and ligand concentration(s). As a result, uranium is transported in aqueous fluids of high Eh but deposited when Eh decreases, e.g. in sedimentary environments and engineered barriers that contain sulphide, organic matter, and/or Fe(II)-bearing minerals; bacteria and mineral surfaces are known to catalyse these reduction reactions. Mining activities result in remobilization of uranium as U(VI). In the presence of oxy(hydr)oxides or clay minerals, aqueous uranyl ions are sorbed at intermediate pH. In rivers, uranium transport is dominated by surface-sorbed uranium on colloids and particles. Upon entering the oceans. uranium is deposited in estuarine sediments due to flocculation, or desorbed due to the presence of carbonate ligands in seawater. Uranyl-carbonate complexes can be transported over long distances and thus the uranium residence time in the oceans is greater than that of water. In the presence of appropriate ligands uranium precipitates to form stable minerals and the transport path can be traced by U isotopic ratios of alteration products. The mobility of uranium and its enrichment in the Earth’s crust is magnified by subduction zone processes.

Abstract The remediation of metal-contaminated soils is a growing environmental problem. Current practice often involves either capping contaminated sites or removing contaminated material and storing it elsewhere. However, given that metal phosphates are highly insoluble under a wide range of Eh and pH conditions, it has been suggested that the conversion of metals into metal phosphates may represent a sustainable, in situ , remediation technique for metal-contaminated soils. In this chapter the solubility of metal phosphates and experimental work investigating the potential for metal phosphate formation as a remediation technique are reviewed. It is concluded that current work indicates that metal phosphate formation may well be a viable treatment. However, further field trials and investigations into the solubility of some less well known metal phosphates, particularly in the presence of organic ligands and microorganisms are required.

Abstract The purpose of this introduction is to outline briefly why and how minerals are currently used in various waste disposal and waste management situations, and to introduce three papers on specific aspects of minerals and wastes. A further purpose is to highlight the wider potential of minerals in connection with waste management, by reference to examples from the current and recent literature. Many recent papers on wastes and the geosphere, of relevance to the mineralogist, can be found in Metcalfe and Rochelle, (1999). At the heart of utilization of any type of material, for any purpose, is an appreciation of the interactive characteristics of that material. In the context of minerals and waste disposal, these characteristics include the intrinsic physical properties of minerals themselves (e.g. density), and in addition, the attributes governing the behaviour of a mineral in relation to its environment. Hence, mineral stability is dependent on both the nature of the mineral itself, and the nature of the surrounding environment. For the purpose of this discussion, the term also encompasses many geotechnical properties of minerals or mineral aggregates, suchas plasticity.

Abstract Inorganic ion-exchangers are the preferred media for the treatment of nuclear wastes. Because of this, natural zeolites have received considerable attention as potential highly selective cation exchangers. Reasons for this, based upon the properties of zeolites, are described. This article provides an introduction to the nature and sources of wastes produced by the nuclear industry and reviews the earlier work in the 1950s which investigated the potential of natural zeolites as scavengers of specific radioisotopes from aqueous waste streams. Comprehensive coverage is given to the type and sources of the zeolites used as well as the range of radioisotopes investigated. Examples of industrial plants using natural zeolites to treat various wastes are given. Their future potential as barrier and back-fill or overpack materials is cited. Cases where these materials have been used successfully to clean up after nuclear accidents are documented (including Chernobyl and Three Mile Island) with a discussion of the compatibility of zeolites to ceramic and cementitious waste forms, coupled with their safe disposal. The scavenging of fall-out products from living hosts, including man, is described, together with the influence of zeolite amendments to soils and growth media. Finally work in which zeolites have been studied as sorbents for gaseous emissions from nuclear plant is commented on briefly.

Abstract A programme of 143 simple gas injection experiments was performed on unconfined and initially water-saturated clay pastes at water contents between the plastic and liquid limits. The aim was to investigate the relationships between gas entry pressure, water content and plasticity for a range of clay types, to define the principal mechanisms of gas entry and flow by simple visual observations and to determine the effects of previous gas injection and residual gas content on entry pressure. Gas movement was found to be entirely through pressure-induced pathways, including highly-dilated tension fractures, flattened ellipsoidal cavities and bubbles. By examining entry mechanisms across the range of water contents, it was possible to delineate three zones of behaviour. Gas entry pressures in the region of the plastic limit were surprisingly large, particularly for clay types with high total specific surface and plasticity index. The highest individual entry pressure recorded in the study was 1810 kPa for Wyoming bentonite. There was no evidence in any test that gas actually penetrated, or flowed through, the intergranular porosity of the clay matrix. In all cases, gas made its own volume by pushing back the paste and lifting the free surface of the sample. After gas injection, remnant gas-filled voids and cracks remained within the clay. These were re-opened during repeated injections at pressures which were only a fraction of the entry pressures of the gas-free pastes. Gas entry at high pressures was audible and occasionally violent. The significance of these findings to gas migration modelling and the quantitative prediction of gas fluxes in clay formations is briefly examined.