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.