Mineral Formation Processes Research Articles

The growth of nacre in the abalone shell

The process of mineral formation following periods of growth interruption (growth bands) is described. Flat pearl implantation as well as a new trepanning method are used to observe the transitory phases of calcium carbonate which nucleate and grow during this process. An initial random nucleation of the aragonite polymorph is observed followed by a transition towards spherulitic growth. During this transition the animal forms the structure of the shell through both mechanical and chemical actions. About 6 weeks after implantation a steady-state growth of aragonite tiles begins after shorter and more irregular tiles cover the outer surface of the spherulites. The growth rate of aragonitic spherulite during this transition period was calculated to be approximately 0.5 μm per day. An organic scaffolding is observed during the steady-state growth of tiled aragonite. Observations of mineral growth following the deposition of these membranes confirm the presence of mineral bridges originating from subsurface tiles and extending through the organic matrix, confirming the growth model proposed by Schäffer et al. [Schäffer TE, Ionescu-Zanetti C, Proksch R, Fritz M, Walters, DA, Almqvist N, et al. Does abalone nacre form by heteroepitaxial nucleation or by growth through mineral bridges? Chem Mater 1997;9:1731–40]. Field emission scanning electron microscopy of fractured deproteinated nacre shows the presence of mineral bridges existing between individual layers of tiles. Transmission electron microscopy provides further evidence of mineral bridges.

Ion implantation modified stainless steel as a substrate for hydroxyapatite deposition. Part II. Biomimetic layer growth and characterization

The interest in stainless steel as a material widely used in medicine and dentistry has stimulated extensive studies on improving its bone-bonding properties. AISI 316 stainless steel is modified by a sequential ion implantation of Ca and P ions (the basic ions of hydroxyapatite), and by Ca and P implantation and subsequent thermal treatment in air (600( composite function)C, 1 h). This paper investigates the ability of the as-modified surfaces to induce hydroxyapatite deposition by using a biomimetic approach, i.e. immersion in a supersaturated aqueous solution resembling the human blood plasma (the so-called simulated body fluid). We describe our experimental procedure and results, and discuss the physico-chemical properties of the deposed hydroxyapatite on the modified stainless steel surfaces. It is shown that the implantation of a selected combination of ions followed by the applied methodology of the sample soaking in the simulated body fluid yield the growth of hydroxyapatite layers with composition and structure resembling those of the bone apatite. The grown layers are found suitable for studying the process of mineral formation in nature (biomineralization).

Thermodynamic description of equilibria in mixed fluids (H2O-nonpolar gas) in a wide range of temperatures (25–700°C) and pressures (1–5000 bar)

A new method is proposed for calculating equilibria in mixed multicomponent systems H2O-nonpolar gas at high temperatures and pressures. The method is based on calculation of electrostatic interactions between a solute component and surrounding molecules of a solvent (H2O). The SUPCRT98 database and the Helgeson-Kirkham-Flowers equation of state for components of an aqueous solution were used for computer realization of the method. The thermodynamic properties of solute gases at elevated temperatures and pressures are calculated by the Redlich-Kwong equation. The dielectric properties of a mixed solvent are determined using the modified Kirkwood equation. The proposed method was approved in description of the available set of experimental data on constants of H2O and NaCl dissociation, as well as data on solubility of both covalent and ionic crystals [SiO2, AgCl, Ag2SO4, Ca(OH)2, CaCO3] in mixed solvents H2O-nonpolar component [1,4-dioxane (C4H4O2), Ar, CO2]. The calculation and experimental data agree in a wide range of PTx conditions (temperatures up to 500°C, pressures up to 5000 bar, and mole fractions (x) of a nonpolar component in fluid up to 0.3). The proposed approach can be used for assessing the Born parameters of solute components. The calculation algorithm developed allows us not only to consider separate reactions but also to study equilibria in hydrothermal systems as a whole. Hence, the proposed approach can be used for constructing thermodynamic models of evolution of fluids rich in volatile components and vital to natural processes of mineral formation.

REE controls in ultramafic hosted MOR hydrothermal systems: An experimental study at elevated temperature and pressure

A hydrothermal experiment involving peridotite and a coexisting aqueous fluid was conducted to assess the role of dissolved Cl − and redox on REE mobility at 400°C, 500 bars. Data show that the onset of reducing conditions enhances the stability of soluble Eu +2 species. Moreover, Eu +2 forms strong aqueous complexes with dissolved Cl − at virtually all redox conditions. Thus, high Cl − concentrations and reducing conditions can combine to reinforce Eu mobility. Except for La, trivalent REE are not greatly affected by fluid speciation under the chemical and physical condition considered, suggesting control by secondary mineral-fluid partitioning. LREE enrichment and positive Eu anomalies observed in fluids from the experiment are remarkably similar to patterns of REE mobility in vent fluids issuing from basalt- and peridotite-hosted hydrothermal systems. This suggests that the chondrite normalized REE patterns are influenced greatly by fluid speciation effects and secondary mineral formation processes. Accordingly, caution must be exercised when using REE in hydrothermal vent fluids to infer REE sources in subseafloor reaction zones from which the fluids are derived. Although vent fluid patterns having LREE enrichment and positive Eu anomalies are typically interpreted to suggest plagioclase recrystallization reactions, this need not always be the case.

Fossilization of Haversian bone in aquatic environments

The process of fossilization is still in many respects poorly understood. Changing chemical conditions in the fossilizing bone allows us to distinguish successive stages of bone diagenesis. As long as organic compounds are present in the bone, the first stage, the early diagenesis, is not completed. However, the early diagenesis itself can be subdivided into three stages. Initially the organic compounds, mainly collagen, allow intensive microbial activity on the bone and this microbial decay characterizes the first stage by high decay rates and strongly reducing conditions. After about one year, the microbial activity ceases and the second stage begins, which lasts much longer and is characterized by chemical gelatinisation of collagen in the bone. Finally imbibition of the gelatinised collagen produces cracks across cement lines of secondary osteons and opens additional pathways for diffusion. In this last stage of the early diagenesis, collagen is replaced by apatite and other minerals. After this replacement, late diagenesis begins. The redox milieu in the fossilizing bone is now controlled by the environment, but the high phosphate content of the apatite still buffers the pH to high values. During late diagenesis, pH-dependent precipitation is the most important mineral formation process. To cite this article : H.-U. Pfretzschner, C. R. Palevol 3 (2004).

Studies of Thermophilic Microorganisms at the Institute of Microbiology, Russian Academy of Sciences

The thermophily studies at the Institute of Microbiology (INMI), Russian Academy of Sciences, were started more than six decades back, at the end of the 1930s and in the early 1940s. The first experiments to study the metabolic diversity of thermophiles and their physiology, biochemistry, and enzymology were conducted at the institute by A.A. Imshenetskii and his coworkers L.I. Solntseva, S.Z. Brotskaya, and L.A. Kuzyurina. The obtained experimental evidence relating to cellulolytic, amylolytic, and proteolytic thermophiles and their enzymes was generalized in Imshenetskii’s monograph Microbiological Processes at High Temperatures [1]. This book also compared thermophilic and mesophilic processes and discussed the origin of thermophiles. In 1950, the contemporary view of thermophily was presented in E.N. Mishustin’s monograph Thermophilic Organisms in Nature and Practice [2], which dealt not only with general and specific properties of thermophilic organisms but also considered their habitats and possible applications. Unlike metabolic diversity, the phylogeny of thermophiles did not figure prominently in any of these monographs, and the experiments and conclusions regarding adaptation of mesophilic species to high temperatures should be regarded as a tribute to the ideology prevailing at the time. Dealing with thermophiles in natural environments, the book focused on soil and anthropogenic biotopes (compost, silage, and selfheating substrates) and on the gastrointestinal tract of higher organisms. The pioneering paper on the microbiology of volcanic habitats was published by S.I. Kuznetsov and was based on his studies of Kamchatka hot springs [3]. The conclusions of this paper outlined all major lines of investigations of thermophilic prokaryotes in their natural habitats that a few decades later were being conducted at the Institute of Microbiology. In the work of Kuznetsov, hyperthermophilic prokaryotes growing at temperatures over 90°e were found and thermophilic microorganisms were shown to be functional in the reductive and oxidative parts of the sulfur cycle and to be involved in mineral formation processes in hot springs.

Metal distribution during diagenesis in the contaminated sediments of Dulas Bay, Anglesey, N. Wales, UK

The Tessier sequential extraction procedure was applied to discrete layers from 9 sediment cores from Dulas Bay, Anglesey. Results provide data on the chemical association of heavy metals (Fe, Mn, Cu, Zn, Cd, and As with major) sedimentary phases, and provide information on changes in metal partitioning associated with the changing physico-chemical conditions encountered during burial. Extremely high concentrations of heavy metals were recorded (e.g. Zn 3000 μg g −1, Cu 2000 μg g −1) and resulting depth profiles clearly indicate the differential behaviour of metals during diagenesis where, with increasing depth, Fe, Mn and Cu become increasingly associated with sulphide phases. Substantial changes in porewater concentrations indicate zones of preferential mobilisation due to sharp alterations in physicochemical conditions. All metals are involved in processes of post depositional diagenetic cycling driven by organic matter degradation and O 2 utilisation in thermodynamically favoured sequence, Fe and Mn oxide and oxyhydroxide dissolution act as controlling variables leading to zones of solid phase metal enrichment. Phase equilibria have been calculated to elucidate observed solid phase partitioning at the redox boundary and processes of subsurface sulphide mineral formation.

Geochemical modeling of bacterially induced mineralization of schwertmannite and jarosite in sulfuric acid spring water

Mineralogy and geochemistry of a sulfuric acid spring water with a pH of 3.37 to 2.89 were investigated to verify the formation processes of iron minerals and the effects of bacteria on their formation. To estimate the solubility of schwertmannite, experimental dissolution in 10.0 mM H2SO4 was conducted and this solubility data was used for geochemical modeling. Experimental incubation of the spring water containing bacteria was also performed and compared with a simulated abiotic system to evaluate the role of bacteria in the mineral formation. The spring water seeps through cracks of hydrothermally altered andesitic rocks containing pyrite, and precipitates schwertmannite and jarosite. Schwertmannite appears as a film-like thin layer floating on the water surface and composed of aggregates of spherical particles with diameters of 1 to 5 μ m. Jarosite is produced as a precipitate on submerged rock surfaces. The precipitate contains well crystallized jarosite spheres 5 to 10 μ m in diameter. Some ellipsoidal to rod shaped bacteria covered or decorated by poorly ordered iron minerals are also present in close association with the schwertmannite spheres. Results of the experimental incubation demonstrate that the oxidation rates of Fe2+ are 5.3 × 103 to 7.2 × 103 times greater than those of the simulated abiotic system, suggesting that the formation of the iron minerals is promoted by bacterial oxidation of Fe2+. The dissolution experiment indicates that the solubility product of the schwertmannite having an average chemical composition of Fe8O8(OH)5.9(SO4)1.05 is approximately log K s = 7.06 ± 0.09. Using this data, geochemical modeling reveals that the spring water is supersaturated with respect to schwertmannite and also goethite and jarosite, but undersaturated with respect to ferrihydrite. Additionally, it is confirmed that the bulk solution chemistry deviates slightly into the stability field of goethite rather than jarosite. This suggests that the aquatic environments in contact with the rock surfaces may be more acidic and/or enriched in SO2−4 relative to the bulk solution, which may eventually lead to the formation of jarosite instead of goethite.

Geochemical evolution of a Devonian diaspore–crandallite–svanbergite-bearing weathering profile in the Middle Timan, Russia

A diaspore–crandallite–svanbergite-bearing occurrence in the Timan folded area of Russia is underlain by Riphean dolomite that bears dispersed francolite and pyrite. The Devonian weathering profile reaches a thickness of 27 m. It contains francolite, crandallite, svanbergite, diaspore and berthierine. Sericite, goethite and kaolinite are less common. There is no distinct boundary between bauxite and phosphate zones. Crandallite and svanbergite often appear together with diaspore so that the P 2O 5 content in the bauxite zone reaches 10%. The Al 2O 3 content increases upwards through the section from ∼7 to ∼55%. The content of Sr varies from 0.02 to 5.2%. Factor analysis ( R-mode principal components) and other statistical methods have been used to identify mineral and element associations and processes of mineral formation. Trace elements tend to associate with diaspore (Th, Pb, Y, Zr), svanbergite (Ba), phosphates (U), berthierine (Cr, V, Ni, Co) and sericite (Rb); accessory minerals are hosts for Ti, Cr, V and Zr. Francolite was inherited from the underlying rock during dissolution of dolomite and accumulated in the lowest part of the weathering profile. Diaspore, goethite, crandallite and svanbergite were formed during dolomite leaching and weathering of phosphate and dispersed aluminosilicates. Mg, Ca and Sr derive from the dolomite, and the source of Fe and S was oxidized pyrite. Berthierine and kaolinite are diagenetic minerals. An epigenetic supply of alkali elements (K and Rb) was responsible for sericite formation.

By-product materials in cement clinker manufacturing

The use of Cl- and SO 3-containing by-products from chemical industries for manufacturing Portland cement clinker using a wet process was examined. The chemical and mineralogical compositions of the by-products and raw materials were determined. Homogeneous raw mixes containing different concentrations of by-products (5–30%) were prepared and the influence of the by-products on all steps of burning the mixes in a kiln to form a cement clinker was investigated. It was shown that introducing Cl- and SO 3-containing by-products to the raw mixes significantly changes all the cement clinker producing stages and changes the chemical and mineralogical compositions at all intermediate stages and in the finished products, forming new minerals containing Cl and SO 3 [CaO X (SiO 2) y CaCl 2] or [CaO x (SiO 2) y CaSO 4] and increasing the amount of well-known intermediate minerals. The presence of the chlorides and sulfates in the cement clinker burning processes removes alkali from the raw mixes, turning them to volatile forms, accelerating the raw mineral decomposition processes and accelerating the formation processes of cement minerals (C 2S, C 12A 7, C 4AF) and formation of chloride and sulfate cycles in the kiln, forming clinker liquids and decreasing the formation and growth of the main cement minerals (C 3A, C 3S). The cement clinker contains some quantity of minerals with Cl or SO 3. Their presence in the final product decreases cement quality by reducing the amount of active CaO (C) and reducing the active CaO/SiO 2 ratio.

Effects of Growth Factor Presence on Mineralization of Porous Poly(Lactide-Co-Glycolide) Scaffolds In Vitro

AbstractBasic design requirements of scaffolds for bone tissue engineering applications include biocompatibility, temporally controlled degradability, osteoconductivity, mechanical integrity, and mass transport capabilities. A recent study has attempted to meet design criteria via the growth of a carbonated apatite (bone-like) mineral on the inner pore surfaces of a highly porous 85:15 poly(lactide-co-glycolide) scaffold using a biomimetic process. It has also been recently demonstrated that the mineralization strategy can be combined with sustained growth factor delivery to induce vascular tissue ingrowth. The present study examines the effect of protein presence on the mineralization process by measuring the amount of protein incorporated into the scaffold during the process of mineral formation. Surprisingly, vascular endothelial growth factor incorporates more readily into control scaffolds than into scaffolds subjected to mineralization treatment. This finding suggests that there is little incorporation of protein into the growing mineral film, and offers insight into the mechanism for sustained drug delivery from the mineralized scaffolds.

The double helix meets the crystal lattice; the power and pitfalls of nucleic acid approaches for biomineralogical investigations

The inability to culture the majority of microorganisms from natural habitats has been well documented. In response to this constraint, the development and application of culture-independent methods for studying microbial communities have been a focus of microbial ecology for the past several years. Molecular approaches, in particular, offer great potential to investigate the role of microorganisms in areas as diverse as biogeochemistry, pollutant remediation, and disease causation. The purpose of this review is to give a brief critique of nucleic acid-based techniques currently used in microbial ecology, to serve as a reference for those wishing to employ such techniques, and to examine the applicability of these techniques toward studying the biogeochemical roles of bacteria, especially as related to metal cycling and biomineralization. Although published reports on the application of molecular techniques to biogeochemical and biomineralogical problems are scarce, this review aims to familiarize biogeochemists and biomineralogists with the strengths and weaknesses of these approaches. Advances have been made in describing the diversity of uncultured microbial communities, detecting/identifying specific cells and functional genes in environmental samples, detecting in situ activities of specific microorganisms, and determining some of the factors controlling gene expression in in vitro studies. However, the current methods provide limited quantitative information about natural processes. Acknowledging these limitations can assist the development of methods to answer basic questions concerning the in situ distribution and activities of microorganisms. Studies relating these in situ measurements of microbial activity and distribution to the physical and chemical microenvironment will ultimately permit a better understanding of the importance of microorganisms in mineral formation and dissolution processes.

Genetic diversity of the biofilm covering Montacuta ferruginosa (Mollusca, bivalvia) as evaluated by denaturing gradient gel electrophoresis analysis and cloning of PCR-amplified gene fragments coding for 16S rRNA.

The shell of the bivalve Montacuta ferruginosa, a symbiont living in the burrow of an echinoid, is covered with a rust-colored biofilm. This biofilm includes different morphotypes of bacteria that are encrusted with a mineral rich in ferric ion and phosphate. The aim of this research was to determine the genetic diversity and phylogenetic affiliation of the biofilm bacteria. Also, the possible roles of the microorganisms in the processes of mineral deposition within the biofilm, as well as their impact on the biology of the bivalve, were assessed by phenotypic inference. The genetic diversity was determined by denaturing gradient gel electrophoresis (DGGE) analysis of short (193-bp) 16S ribosomal DNA PCR products obtained with primers specific for the domain Bacteria. This analysis revealed a diverse consortium; 11 to 25 sequence types were detected depending on the method of DNA extraction used. Individual biofilms analyzed by using the same DNA extraction protocol did not produce identical DGGE profiles. However, different biofilms shared common bands, suggesting that similar bacteria can be found in different biofilms. The phylogenetic affiliations of the sequence types were determined by cloning and sequencing the 16S rRNA genes. Close relatives of the genera Pseudoalteromonas, Colwellia, and Oceanospirillum (members of the gamma-Proteobacteria lineage), as well as Flexibacter maritimus (a member of the Cytophaga-Flavobacter-Bacteroides lineage), were found in the biofilms. We inferred from the results that some of the biofilm bacteria could play a role in the mineral formation processes.

Mineral formation in micaceous Mediterranean Red soils of Sierra Nevada, Granada, Spain

We investigated the processes of mineral formation in three Alfisol profiles of Sierra Nevada (southern Spain), with special emphasis on the little‐studied process of mica inheritance, particularly as regards its quantitative aspects. X‐ray diffraction, conventional and high resolution transmission electron microscopy, selected‐area electron diffraction, and geochemical analysis of the soil solution were used, and the granulometric fractions gravel, coarse sand, fine sand, silt and clay were studied, as was unaltered parent rock. Most interesting was inheritance of dioctahedral mica (illites) with small crystallochemical changes. The transition of mica from parent rock to clay was characterized by small crystallochemical changes affecting their structural formulae, reduction of the 2M1 polytype content, decrease in crystallite size, increase in crystal defects, and other changes in particle morphology. We propose the term ‘pedocrystallochemical evolution’ for the transition. The changes reverse the processes that take place in micas when rocks are formed by sedimentation, diagenesis and metamorphism. The kaolinite in the soils is a result of neoformation, and acts as the equilibrium phase within the chemical system. Reddening seems to have been caused by both inheritance and neoformation of iron oxides (haematite + goethite).

Mineral Precipitation by Epilithic Biofilms in the Speed River, Ontario, Canada

Epilithic microbial communities, ubiquitously found in biofilms on submerged granite, limestone, and sandstone, as well as on the concrete support pillars of bridges, were examined in the Speed River, Ontario, Canada. Transmission electron microscopy showed that attached bacteria (on all substrata) were highly mineralized, ranging from Fe-rich capsular material to fine-grained (<1 mum) authigenic (primary) mineral precipitates. The authigenic grains exhibited a wide range of morphologies, from amorphous gel-like phases to crystalline structures. Energy-dispersive X-ray spectroscopy indicated that the most abundant mineral associated with epilithic bacteria was a complex (Fe, Al) silicate of variable composition. The gel-like phases were similar in composition to a chamositic clay, whereas the crystalline structures were more siliceous and had compositions between those of glauconite and kaolinite. The consistent formation of (Fe, Al) silicates by all bacterial populations, regardless of substratum lithology, implies that biomineralization was a surface process associated with the anionic nature of the cell wall. The adsorption of dissolved constituents from the aqueous environment contributed significantly to the mineral formation process. In this regard, it appears that epilithic microbial biofilms dominate the reactivity of the rock-water interface and may determine the type of minerals formed, which will ultimately become part of the riverbed sediment. Because rivers typically contain high concentrations of dissolved iron, silicon, and aluminum, these findings provide a unique insight into biogeochemical activities that are potentially widespread in natural waters.

The Effect of Gallium Nitrate on Healing of Vitamin D– and Phosphate–Deficient Rickets in the Immature Rat

The effect of gallium on rapid in vivo mineralization was studied in a rachitic rat model in which rickets were induced in immature rats then reversed ("healed") with repletion of vitamin D and phosphate. Gallium was administered to selected groups of animals before and during the healing phase. In nonrachitic animals and rachitic animals before healing, the mineral content of diaphyseal and metaphyseal bone was increased, and the crystal size was decreased in those animals that received gallium compared with those that did not. Mineralization of the undermineralized osteoid appeared histologically normal by 72 hours in all animals. However, animals that received gallium both before and during the healing phase had less well-mineralized bones at 18 hours, and by 72 hours, they had lesser increases in osteocalcin and mineral content, which was associated with smaller crystal sizes, than did any animal that did not receive gallium at any time. Prior to the healing phase, the ratio of gallium to hydroxyproline in the metaphyses of rachitic animals was similar to that in nonrachitic animals. Likewise, this ratio did not change in the animals receiving gallium both before and during the healing phase. The ratio of gallium to calcium was higher in rachitic animals compared with controls, and this ratio lowered significantly by the end of the healing phase. Results may be explained in part by direct effect of gallium on the physical process of mineral formation during the rapid healing phase as well as by effects of gallium on osteoblasts and osteoclasts during the induction of rickets.

Formation of Secondary Uranium Minerals in the Koongarra Deposit, Australia

ABSTRACTSecondary uranium minerals from the Koongarra deposit, Northern Territory of Australia, were examined in order to understand the formation and alteration processes of the uranium minerals and their relevance to the migration behavior of uranium, lead, calcium and rare earth elements in the weathered zone. In most of the secondary ore zone, the only stable uranium mineral was saléeite (Mg(UO2)2(PO4)2·10H20), occurring as euhedral platy crystals up to 1 mm in length in veins and at surfaces. Apatite (Ca5(PO4)3F), an accessory mineral of the host rock, has saléeite reaction rims, suggesting formation at the expense of apatite. Ca-uranyl phosphates, such as autunite (Ca(UO2)2(PO4)2·10H2O), were not identified, and Ca-rich uranyl silicates are also absent in the primary ore zone. Pb-bearing uranyl phosphates were found only in the graphite layer cross-cutting the secondary ore zone. In the graphite layer, the local low oxidation condition and high hydrocarbonate content of ground water have affected the formation of uranium minerals and the migration behavior of uranium.

Participation of a cyanobacterial S layer in fine-grain mineral formation.

Cyanobacteria belonging to the Synechococcus group are ubiquitous inhabitants of diverse marine and freshwater environments. Through interactions with the soluble constituents of their aqueous habitats, they inevitably affect the chemistry of the waters they inhabit. Synechococcus strain GL24 was isolated from Fayetteville Green Lake, New York, where it has a demonstrated role in the formation of calcitic minerals. In order to understand the detailed interactions which lead to mineral formation by this organism, we have undertaken detailed ultrastructural studies of its cell surface and the initial events in mineral growth using a variety of electron microscopic and computer image enhancement techniques. Synechococcus strain GL24 has a hexagonally symmetrical S layer as its outermost cell surface component. The constituent protein(s) of this structure appears as a double band by sodium dodecyl sulfate-polyacrylamide gel electrophoresis with M(r)s of 104,000 and 109,000. We demonstrate that the S layer acts as a template for fine-grain gypsum and calcite formation by providing discrete, regularly arranged nucleation sites for the critical initial events in the mineralization process. To our knowledge, this is the first time that a bacterial S layer has been shown to have a role in mineral formation in a natural environment, and this report provides conclusive evidence for the specific involvement of bacterial surfaces in natural mineral formation processes.

Sur lʼâge et la genèse de certains gîtes metallifères dans lʼAtlas tunisien (dʼaprès les études isotopes du Pb)

The radioisotopic studies carried out on mineralizations from the Tunisian Atlas allow to additionally elucidate the debatable question concerning their age and genesis. The data obtained for the isotopic composition of Pb fall between the curves of growing of "orogen" and "Upper Cretaceous" which indicates a crustal source of the metals. Besides the data obtained, they also indicate that the mineral-formation process occurred polychronously. These conclusions are in accordance with the phenomena caused by the conversion of the plates of the lithosphere at the boundaries of the Tunisian Atlas. During the thickening and reprocessing of the Earth's crust an additional supply of radiogenic lead into "Upper Cretaceous" was realized. Large masses of Triassic evaporitic sediments were mobilized during the multifold periods of tectonic activity. The Triassic diapirism favoured the generation, mobilization and draining of hydrothermal solutions which enriched in metals at the expense of their leaching by the adjacent rocks or by preceding mineralizations. The mineralization started first in the East Tunisian structural metallogenic zone along the N-S tectonic lineament. lt evolved from the end of Lower Cretaceous until Miocene tending to rejuvination from the central towards the external parts of the Tunisian Atlas.

Early diagenesis of sulfur in the sediments of lakes that receive acid mine drainage

Fifteen final-cut strip mine lakes, located throughout the Western Interior, Eastern Interior, and Appalachian Coal Basins in the U.S.A., were selected to represent a wide variety of values for the variables lake-water pH, alkalinity, SO 4 and Fe concentrations, sediment organic matter content, overburden lithology, and lake age. Lake-water, porewater and sediment samples were collected for geochemical analysis. Sequential digestion of sediment samples was used to determine the amount of the inorganic S phases (elemental S, metal monosulfide, metal disulfide, and total) present in the sediment. Authigenic inorganic reduced S minerals were found in the sediments of all 15 lakes that receive acid mine drainage from groundwater input. Authigenic FeS 2 was the largest fraction in most of the lake sediments, but elemental S was larger in some. The amount of C-bonded S, determined by difference, ranged widely but was nearly always less abundant than the inorganic phases. Correlations of the nature and amount of authigenic reduced S minerals to the SO 4 and Fe concentrations in porewater, the organic matter content of the lake sediments, and lake age were tested. The formation of SO 4-reduction end products was not limited by Fe or SO 4 availability. The amounts of reduced S in the sediments correlated with the amount of organic matter in the sediment, indicating that the authigenic mineral formation process is organic-matter limited in these Fe- and SO 4-rich environments. Lake age, which represents a complex function of the diminishing acid-mine-drainage load derived from weathered spoil piles and the generation of alkalinity by biogeochemical reactions in the lake sediments, was a good predictor of the amounts of reduced S mineral in the sediment regardless of geological setting.