Sequential Mineral Research Articles

Mineral precipitation sequence from multi-stage fluids released by eclogite during high-pressure metamorphism

Abstract Arc magmas above subduction zones hold abundant fluid-mobile elements attributed to fluids released from the dehydrating subducted oceanic crust. However, the quantity of trace elements in the fluids and their evolution with the metamorphic processes during subduction and exhumation are still unclear. The precipitation sequence of vein minerals preserves the nature of multi-stage high-pressure (HP) metamorphic fluids and the fingerprint of mass exchange in deep subduction zones. In this contribution, we conducted detailed petrological studies and phase equilibria modeling on a unique HP omphacite-rich vein and its host eclogite from the Chinese southwestern Tianshan. The host eclogite consists mainly of garnet, omphacite, epidote, glaucophane, phengite, quartz, and rutile. Garnet in the eclogite records prograde subduction and early exhumation characterized by decompression heating at P-T conditions of ~2.4–2.6 GPa and 460–540 °C. The embedded omphacite-rich vein has similar mineral assemblage to the host eclogite. Garnet grains in this vein are predominantly distributed along or intersect the vein wall, which record similar eclogite-facies metamorphic conditions to that of the host eclogite. Omphacite is dominant in the vein, while epidote and glaucophane occur interstitially. Phase equilibria modeling reveals a sequential growth of garnet-dominated, omphacite-dominated, and epidote-dominated assemblages from fluids originating from the breakdown of different hydrous minerals. These lines of evidence suggest that the formation of multi-stage HP fluids are a continuous long-term process with a spontaneously short-distance transport and sequential mineral precipitation. Calculated fluid compositions demonstrate that the fluids released by lawsonite breakdown during exhumation have great potential to modify the trace element systematics of arc magmas. Our findings reveal the nature and evolution of multi-stage HP metamorphic fluids from internal sources during subduction and exhumation of oceanic crust, providing valuable insights into the chemical compositions of arc magmas.

The dual roles of dissimilatory iron reduction in the carbon cycle: The "iron mesh" effect can increase inorganic carbon sequestration.

Dissimilatory iron reduction (DIR) can drive the release of organic carbon (OC) as carbon dioxide (CO2 ) by mediating electron transfer between organic compounds and microbes. However, DIR is also crucial for carbon sequestration, which can affect inorganic-carbon redistribution via iron abiotic-phase transformation. The formation conditions of modern carbonate-bearing iron minerals (ICFe ) and their potential as a CO2 sink are still unclear. A natural environment with modern ICFe , such as karst lake sediment, could be a good analog to explore the regulation of microbial iron reduction and sequential mineral formation. We find that high porosity is conducive to electron transport and dissimilatory iron-reducing bacteria activity, which can increase the iron reduction rate. The iron-rich environment with high calcium and OC can form a large sediment pore structure to support rapid DIR, which is conducive to the formation and growth of ICFe . Our results further demonstrate that the minimum DIR threshold suitable for ICFe formation is 6.65 μmol g-1 dw day-1 . DIR is the dominant pathway (average 66.93%) of organic anaerobic mineralization, and the abiotic-phase transformation of Fe2+ reduces CO2 emissions by ~41.79%. Our findings indicate that as part of the carbon cycle, DIR not only drives mineralization reactions but also traps carbon, increasing the stability of carbon sinks. Considering the wide geographic distribution of DIR and ICFe , our findings suggest that the "iron mesh" effect may become an increasingly important vector of carbon sequestration.

Multiple metal sources of coupled Cu-Sn deposits: Insights from the Tongshanling polymetallic deposit in the Nanling Range, South China

Formation of hydrothermal Cu and Sn deposits is thought to be related to magmas of differing oxygen fugacities, so the existence of mixed Cu-Sn hydrothermal ores poses a challenge to our understanding of the controls on their genesis. The Tongshanling polymetallic deposit in western Nanling Range (South China) is exceptional for its multiple mineralization types, which include skarn Cu-Pb-Zn and quartz-vein Sn-W-Pb-Zn mineralization, providing an excellent opportunity to reveal the genesis of coupled Cu-Sn deposits. An integrated study was carried out from petrological, mineralogical, geochronological, isotopic, and geochemical perspectives to determine the genesis of the Tongshanling polymetallic deposit and obtain a better understanding of coupled Cu-Sn mineralization processes. The granodiorite in the Tongshanling ore field is classified as oxidized I-type granitoids and emplaced at ∼ 167 Ma based on zircon U-Pb dating, and it is derived from partial melting of amphibolite-facies crustal rocks. In sharp contrast, the quartz porphyry and granite porphyry in the Tongshanling ore field were emplaced at ∼ 171 Ma and ∼ 162 Ma, respectively, both of which are highly evolved, reductive, and volatile-enriched A-type partial melts produced by remelting of granulite-facies crustal rocks. The close spatial relationship between the granodiorite and the skarn orebody is due to a ∼ 167 Ma skarn Cu-Pb-Zn mineralization event. In comparison, cassiterites from the quartz-vein ores define a later ore-forming event at ∼ 162 Ma, consistent with the intrusive age of the granite porphyry. Together with the crosscutting relationship of the quartz vein and skarn mineralization-related rocks (e.g., granodiorite, skarn, and sulfide ores), a ∼ 162 Ma Sn-W polymetallic mineralization event in the Tongshanling deposit may have been associated with a concealed, highly evolved granitic magmatism. Oxygen fugacity of the I-type granodiorite (median ΔFMQ = −1.47) is higher than those of the A-type quartz porphyry and granite porphyry (median ΔFMQ = −1.65 and −2.66, respectively), which may have been a key factor leading to multiple mineralization in the Tongshanling ore field. The chemical compositions of cassiterites indicate that the ore-forming fluid of the quartz-vein stage was reductive, volatile-enriched, and of magmatic origin. In addition, its temperature was lower than that commonly associated with greisen or pegmatite mineralization. These observations suggest that the Cu-Sn metallogeny of the Tongshanling polymetallic deposit was spatially-coupled rather than temporally-coupled, and that the genesis of this deposit can be explained with a two-stage metallogenic model. A comparative study of worldwide Cu-Sn deposits indicates that, in most cases, the Cu and Sn metals do not come from a single source, and that Cu-Sn deposits are a product of spatial coupling, i.e., sequential mineralization events within a single ore field.

Engineered bone tissues using biomineralized gelatin methacryloyl/sodium alginate hydrogels

At present, the treatment of bone defect is one of the most concerned problems in biomedical fields. Despite the wide variety of scaffolds, there is a challenge to select materials that can mimic the structural integrity and biocompatibility of natural bone. In our study, gelatin methacryloyl (GelMA) and sodium alginate (Alg) were used to prepare three-dimensional (3D) GelMA/Alg hybrid hydrogel, which can simulate the structure and biological function of natural extracellular matrix due to their high water content and porous structure. The interconnected and homogeneous pores of the scaffold facilitate the transport of nutrients during the bone regeneration. Then hydroxyapatite (HA) coated GelMA/Alg (GelMA/Alg-HA) hydrogel was obtained by sequential mineralization. The mineralized hydrogel was obtained by immersing hydrogel alternately in a solution of calcium and phosphorus at 37 °C. The hydrogel was modified with a coating of HA under a mild condition. The calcium crosslinked Alg could provide nucleation sites for HA crystals. And the sequential mineralization will improve the physical properties and osteoinductivity of the hydrogels by introducing HA, which is similar to the mineral component of natural bone. Analytical results confirmed that the HA particles were uniformly distributed in the surface of the hydrogels and the mineral contents were about 40% after three cycles. The compressive strength was improved from 22.43 ± 6.39 to 131.03 ± 9.26 kPa. In addition, MC3T3-E1 cell co-culture experiments shown that the mineralized GelMA/Alg-HA hybrid hydrogel possess good biocompatibility, which is conducive to the growth of new bone tissue and bone repair.

Digital image processing (DIP) application on the evaluation of iron-rich heavy mineral concentrates produced from river sand using a sequential mineral processing approach

Digital image processing (DIP) application on the evaluation of iron-rich heavy mineral concentrates produced from river sand using a sequential mineral processing approach

Mineralized paper scaffolds for bone tissue engineering.

Mineralized polymer scaffolds have proven to be effective biomaterials for inducing osteoinductivity in bone tissue engineering. Sequential mineralization is a promising technique for depositing minerals in three-dimensional (3D) scaffolds. Paper, which is made of cellulose fibers, can be used as a tissue scaffold due to its highly porous structure and flexibility, as well as its excellent ability to wick fluids and support the growth of bone cells. In this study, paper-based, mineralized scaffolds were fabricated using sequential mineralization. We conducted experiments with two groups of scaffolds based on different incubation times in the mineralization solutions (30 min and 24 h). Ten cycles of mineralization were performed for each group. We found that the mineral content increased as the cycle number increased and that the 24-h group scaffolds consistently had more mineralization than did the 30-min group scaffolds when measured at the same cycle number. A quantitative reverse transcription-polymerase chain reaction was performed for two osteogenic differentiation markers of the preosteoblasts that were grown on the mineralized paper scaffolds. The gene expression results for bone-specific markers revealed that the mineralized scaffolds were osteoinductive. Subcutaneous implantation of the scaffolds in rats demonstrated favorable biocompatibility, high vascularization, and non-immunogenicity in vivo. The overall results suggest that the sequentially mineralized paper scaffolds are promising materials for use in bone tissue engineering.

Mineralized Hydrogels Induce Bone Regeneration in Critical Size Cranial Defects.

Sequential mineralization enables the integration of minerals within the 3D structure of hydrogels. Hydrolyzed collagen-based hydrogels are sequentially mineralized over 10 cycles. One cycle is defined as an incubation period in calcium chloride dihydrate followed by incubation in sodium phosphate dibasic dihydrate. Separate cycles are completed at 30-minute and 24-hour intervals. For the gels mineralized for 30min and 24 h, the compressive moduli increases from 4.25 to 87.57kPa and from 4.25 to 125.47kPa, respectively, as the cycle number increases from 0 to 10. As indicated by X-ray diffraction (XRD) and Fourier transform infrared analysis (FTIR) analyses, the minerals in the scaffolds are mainly hydroxyapatite. In vitro experiments, which measure mechanical properties, porous structure, mineral content, and gene expression are performed to evaluate the physical properties and osteoinductivity of the scaffolds. Real time-quantitative polymerase chain reaction (RT-qPCR) demonstrates 4-10 fold increase in the expression of BMP-7 and osteocalcin. The in vivo subcutaneous implantation demonstrates that the scaffolds are biocompatible and 90% biodegradable. The critical size cranial defects in vivo exhibit nearly complete bone regeneration. Cycle 10 hydrogels mineralized for 24 h have a volume of 59.86 mm3 and a density of 1946.45 HU. These results demonstrate the suitability of sequentially mineralized hydrogel scaffolds for bone repair and regeneration.

Sequential carbonate mineralization of desalination brine for CO2 emission reduction

Desalination brine is a potential source for CO2 mineralization aimed at reducing CO2 emissions, because the concentration of Ca and Mg in brine is almost twice that of ordinary seawater. However, the previously achieved conversion ratio of CO2 to carbonate minerals is too low for commercial application, as Ca and Mg compete and interfere with each other during precipitation. In this study, we tested the separate and sequential mineralization of Ca and Mg in brine, enhancing the CO2 conversion ratio to 57% from 12%. We also tested the use of 15% CO2 gas (the typical concentration of actual combustion gas), and it was observed that 69% of injected CO2 was precipitated as Ca and Mg carbonate minerals and 99% of Ca and 69% of Mg in the initial brine were precipitated. In addition, the volume of NaOH solution required was reduced by 76%. This revised method is more material- and reagent-efficient which would likely have lower operation costs; moreover, as no further additives are required, environmental impact of brine release is also likely to be reduced. The findings of this study can help address environmental problems caused by large seawater desalination plants and thermal power plants.

Sequential mineral transformation during underground coal gasification with the presence of coal partings

Underground coal gasification (UCG) can be adopted to convert unminable coal resources into synthesis gas for use in the production of electricity, fuels, and chemicals. UCG is a promising technology with many health, safety, and environmental advantages over conventional mining techniques. It is of great scientific significance to study the mineral transformation and identify the typical minerals in certain process conditions, because it may help to ensure the stable operation of the gasification processes and improve the utilization efficiency of coal seams. The presence of coal partings has an important impact on mineral transformation. In this paper, the UCG process has been subdivided into pyrolysis, reduction, and oxidation stages, and the progressive coal conversion products were prepared. Ulanqab lignite was used as the test coal. The minerals in the coal transformation products were identified by X-ray diffraction (XRD) and scanning electron microscopy coupled with an energy-dispersive spectrometer (SEM-EDS). The thermodynamic equilibrium simulation software, FactSage 7.2, was used to calculate the relevant phase diagram to assist in understanding the mineral transformations. The experimental results indicate that the different iron-bearing minerals occur in raw coal and non-coal partings which are nontronite (Na0.3Fe2Si4O10(OH)2.4H2O) and glauconite (K (Fe, Al)2(Si, Al)4O10(OH)2) respectively. Pyrrhotite is the main iron-bearing mineral in the pyrolysis products. In the reduction stage, the relative content of Al2O3 is increased due to the presence of non-coal partings, which reacts with FeO to produce hercynite (FeAl2O4) at a temperature above 1100 °C. When the temperature increases to 1300 °C, hercynite is converted to the thermodynamically-stable cordierite (Fe2Al4Si5O18). In the oxidation stage, mullite (Al6Si2O13) is produced when the oxidation temperature reaching 1300 °C, which could be used to reflect the underground reaction conditions in the coal seam. The phase diagram of (SiO2)6.2Al2O3-CaO-Fe2O3 proves that mullite and anorthite (CaAl2Si2O8) are the dominant minerals when the mole fraction of (SiO2)6.2Al2O3 is above 0.7. In addition, the ash melting point rises with an increase of Si and Al content in the presence of non-coal partings.

Automatic salt dome detection in seismic data by combination of attribute analysis on CRS images and IGU map delineation

Accurate detection of geo-structures in automatic geological interpretation of seismic data is a challenging task especially in complex media. Solution to this problem goes through integration of advanced seismic pattern recognition methods, image analysis and image classification strategies, applied on seismic image obtained by appropriate seismic imaging method. Accuracy of these approaches mostly depends on the quality of seismic attributes used for subsequent image analysis, seismic data classification and seismic pattern recognition. In this study, we initially analyze the effect of using the common reflection surface (CRS) method on obtaining appropriate data for attribute analysis, in comparison with the conventional NMO/DMO/Stack imaging method. Subsequently, we introduce an automatic salt dome detection method from seismic image based on the intrinsic geological unit (IGU) concept used in sequential mineral exploration. The IGU consists of areas with indexes or critical genetic factors (CGF) related to the target of exploration which is defined itself by several critical recognition criteria (CRC). The CRCs defined as the value of attributes and seismic patterns selected by the interpreter for salt detection. These CRCs were extracted from a large informative database build only for salt dome detection from various seismic data and different geological setting. The CRCs were weighted by the interpreter according to the percentage of success in using selected CRCs for salt identification. Afterwards, probability value of pixels to be considered as salt was calculated by defining a linear relationship between CRCs. Then, matrix of characteristics was defined for CRCs followed by a matrix that shows CRCs score. The final score for each pixel will define the area of the IGU, or salt dome in seismic image, if they were above a predefined threshold. The presented strategy was applied on a field data example from Kazakhstan containing a huge salt dome. The proposed strategy could detect the salt boundary in a fully automatic manner with some befits, such as defining internal reflections and less human interaction. Application of the proposed method on the CRS result showed that it could be considered as an alternative to the other present automatic salt dome detection and classification approaches. However, the presented method still requires of using advanced method in scoring and building matrix of characteristics, especially for salt area detection in seismic image.

Discount rate selection for long-term sequential mineral projects

AbstractMineral projects depict various specific features that differentiate them from alternative investments in other industries. Among these features, one can specify unique characteristics of mineral deposits such as scarcity, geological setting and structure, resource/reserve uncertainty and depletability. Resource uncertainty results in the sequential nature of operations (exploration, development and production stages). Other specific features of mineral projects include long investment - and production periods, high capital intensity, varying production conditions, unpredictability and high volatility of mineral prices, etc. Specific features of mineral projects are sources of exceptionally high risks. To ensure the payback of high capital costs these significant risks must be addressed in the economic evaluation of a mineral project. In the discounted cash flow analysis, DCF, which is the most commonly used in evaluations of such ventures, all project uncertainties are reflected in a level of the discount rate used for the actualization of future cash flow values. The riskier project has a higher discount rate. Apart from being extremely high risk, mineral projects are both sequential and long-term - the first feature means that the extent of a project risk decreases dramatically over time, and second - that care should be taken when evaluating these projects because cash flows arising in later years of the project lifetime have little value. The paper delivers a proposal to apply the time-varying discount rate to the economic evaluation of a mineral project. The first part introduces a commonly accepted approach to evaluating discount rates along with conceptions of adjusting them to risks of individual projects. In the following sections, the article presents the current practice in the setting of discount rates for mineral projects and then a proposed modification of this approach by introducing the time-varying discount rate. In the end, a verification of the proposed suggestion based on a copper project example has been delivered.

Sequential mineral transformation from kaolinite to Fe-illite in two Brazilian mangrove soils

Mangrove soils have peculiar chemical and physical conditions generated by the variable water salinity, cyclic tidal changes and intense biological activity that produce complex clay suites. In this study, the crystal-chemical characteristics of clay minerals from two mangrove soils were investigated in detail to further our understanding of the processes taking place. The two Brazilian mangroves are from zones of contrasting climatic type and continental sediment character: (1) tropical wet climate area receiving highly weathered sediments (Bragança, Pará State) and (2) mild semiarid climate area supplied with a mixture of highly and moderately weathered sediments (Acaraú, Ceará State). The investigation of the 2–0.2μm and <0.2μm size fractions of the soils using XRD, Mössbauer spectroscopy, chemical analysis of individual mineral grains (TEM-EDS) and bulk samples (XRF) showed mineral assemblages composed by endmember and mixed-layer clay minerals. Three to four mineral phases were detected by XRD in each sample such as kaolinite-smectite minerals (K-S), illite-smectite (I-S) and Fe-rich illite, suggesting a progressive transformation via mixed-layering from detrital kaolinite (unstable in mangrove soil conditions) to K-S and I-S minerals rich in smectite, and then to Fe-rich illite. The chemical characterization corroborates this gradual transformation: there is an enrichment in K, Fe and Mg at the expense of Al in all samples. A solid-state reaction explains the sequential transformation, where crystal-chemical changes take place without complete disruption of the lattice. There is evidence of octahedral Fe reduction during the illitization stage, showing the influence of a reducing environment, from decaying organic matter and bacterial activity, on the clay minerals. The increase in layer charge is balanced by K and NH4 ions, abundant in the interstitial water. Superior Fe-rich illite contents in Acaraú mangrove, compared to Bragança mangrove, are explained by high inputs of 2:1 clays from sediment source areas inland. The above clay mineral reactions shed light on the role of clays and the interaction between minerals and biotic components in mangrove soils. In addition, these reactions may influence the cycle of major elements in coastal ecosystem surrounding mangroves.

Speciation and fractionation of phosphorus in biosolids-amended soils: effects of water treatment residual nanoparticles

Phosphorus (P) speciation and fractionation are useful tools for assessing P mobility and potential transfer to water bodies. The current study aims to evaluate drinking water treatment residual nanoparticles (nWTRs) effects on P species in biosolids-amended soils using sequential chemical fractionation and mineral equilibrium model. Three different soil types were selected (El-Bostan, Kafr El-Dawar, Borg Al-Arab), amended with biosolids (3%), and different rates of nWTRs were applied. The P fractionation results revealed that addition of nWTRs to biosolids-amended El-Bostan soil increased the immobile aluminum phosphates from 27.30 to 88.90, 92.20, and 94.93% at 0.10, 0.20, and 0.30% application rate, respectively. Similar trend was noticed in Kafr El-Dawar soil. In Borg Al-Arab soil, nWTRs significantly (p < 0.05) increased aluminum phosphate to only 71.73% at the highest application rate (0.30%) due to its high content of calcium carbonate (35.70%). Similarly, phosphorous speciation analysis revealed that application of nWTRs significantly increased the proportions of immobile phosphate form (P sorbed to Al hydroxide) and amorphous sodium aluminum phosphate. Thus, water degradation via eutrophication can be minimized by applying nWTRs to biosolids-amended soils.

Triggering the Mechanical Release of Mineralized Pickering Emulsion-Based Capsules.

Taking advantage of the benefit of Pickering-based emulsions and sol-gel chemistry, we synthesized mineralized Pickering emulsion-based capsules constituted of a dodecane core and a siliceous shell. To trigger the oily core mechanical release, we first made use of the one-step polycondensation synthesis path, reaching limited shell thickness from 43 to 115 nm with a resistance against the application of an external pressure from 0.5 to 6 MPa. When addressing a sequential mineralization route, we were able to reach both better shell homogeneity and higher values of shell thickness from 85 to 135 nm associated with a shell breaking pressure varying from 1.2 to 10 MPa. In this last configuration, the shell homogeneity and thickness are acting cooperatively toward enhancing the shell mechanical toughness and the associated effective breaking pressure of the dodecane@SiO2 core-shell particles.

MnNCKFMASH Phase Relations in Cordierite–Orthopyroxene Migmatitic Gneisses, Southern India: Implications for Low-pressure Crustal Melting under Granulite-facies

Abstract Cordierite-orthopyroxene migmatitic gneisses exposed in Achankovil unit of the Kerala Khondalite Belt, southern India show evidences of melting, melt extraction and in-situ crystallization of melt under granulite-facies conditions. The sequential mineral assemblages garnet + biotite + orthopyroxene + plagioclase + quartz (± melt) in the mesosomes and garnet + biotite + orthopyroxene + cordierite + plagioclase + K-feldspar + quartz + melt in the melanosomes makes the Achankovil cordierite-orthopyroxene migmatitic gneisses a good example of anatectic rocks, where substantial melt fractions remained in-situ during decompression and cooling. Therefore, the rocks provide an opportunity to investigate deep crustal processes and record of rheological (thermal and mechanical) reequilibration prevailed during the final stages of orogeny. The significance of cordierite formation and its possible relationship with melt formation are investigated applying theoretical calculations in the MnO–Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O (MnNCKFMASH) system. Results of numerical modelling of the mineral assemblages in pressure–temperature–composition (P–T–X) pseudosections using Perple_X infer that the sequence of reactions involving formation of cordierite-orthopyroxene-melt assemblage is consistent with an isothermal decompression (with a pressure drop of &amp;gt;1.5 kbars) at high temperatures (&amp;gt;800 °C), forming leucosomes. Biotite dehydration melting reactions, occurring above 4.5 kbars constrain prograde arm of the P–T trajectory and is interpreted as a product of crustal thickening, which was followed by rapid decompression. The final stage of exhumation is characterized by rehydration of cordierites in the melanosome by melt-solid interactions at exceptionally low-pressure (~3.2 kbars) conditions. The high-temperature isothermal decompression inferred from the mineral reactions and P–T–X pseudosections constitute a clockwise P–T path for the exhumation of the lower crust. This clockwise P–T path is consistent with the common tectonic model accepted for the genesis of granulite-facies migmatites during crustal thickening and later unroofing, accompanied with arc-continent collision. Our conclusions indicate low–P metamorphism and anatexis can be traced to convergent setting, where melt buoyancy considerably decreases density of the lithosphere and modifies rheology leading to rapid exhumation of the lower crust. Therefore, the crustal evolution in the Kerala Khondalite Belt is correlated with two stage processes: (i) thickening of the crust in relation to a continental-arc setting, followed by (ii) exhumation along a high-temperature stable geotherm with sufficient pressure release associated with syn- to post-convergence transpression and transtension.

Fast Decolorization of Azo-Dye Congo Red with Zerovalent Iron Nanoparticles and Sequential Mineralization with a Fenton Reaction

Abstract Azo-dye compounds are widely used in the textile industry and are mostly discharged in industrial wastewater. In this study, we performed a chemical reduction of azo-dye Congo red (CR) using laboratory-synthesized nanoscale zerovalent iron (NZVI) particles to examine the effects of temperature and pH on decolorization kinetics and decomposition products. Decolorization of CR with NZVI undergoes a much faster reaction than that with microscale ZVI (MZVI). Decolorization behaviors of CR with NZVI follow pseudo–first-order kinetics. An increase in the dose of NZVI enhanced the decolorization rate of CR. Reaction rate constants did not decrease significantly with an increase in pH for CR. It was also found that the reaction rate increased slightly with an increase in temperature. Activated energy needed for the removal of CR with NZVI is smaller than that using MZVI (4.8 and 13.9 kJ/mol, respectively), suggesting an insignificant effect of temperature on the decolorization reaction. Intermediate anal...

Dynamics of formation and secretion of heterococcoliths by Coccolithus pelagicus ssp. braarudii

The formation and secretion of heterococcoliths by the non-motile life phase of the coccolithophore Coccolithus pelagicus was investigated using electron microscopy and time-lapse bright field imaging. Coccolithogenesis in C. pelagicus exhibited sequential mineralization of single coccoliths in Golgi-derived and nuclear-associated vesicles, a pattern similar to the formation of heterococcoliths in Emiliania huxleyi. Our TEM data show that only on maturation does the single coccolith vesicle migrate away from the nucleus before secretion. A reticular body, distinct from the Golgi body, was also clearly visible at the distal surface of the developing coccolith vesicle, suggesting this is a common structural feature in placolith cells that mineralize and secrete coccoliths one at a time. Time-lapse imaging revealed that the coccolith secretion process is rapid, taking 60–190 seconds, and involves considerable contractile activity to eject and position the coccolith on the surface of the cell. An intact flagellar root apparatus was discovered at the anterior pole of this non-motile cell from which polarized secretion of coccoliths occurs, which may indicate a novel role for such cytoskeletal structures. Freeze-fracture preparations revealed columnar deposits and adhesions linking the scales and coccolith baseplates to the cell, across the periplasmic space providing points of attachment for cellular movement. Rotatory movements of the cell relative to external coccoliths were exhibited by all actively calcifying cells. These movements enable the cell, while exhibiting morphologically polarized secretion, to locate and secrete a mature coccolith in a spatially well-defined manner. Finally, the time-lapse imaging approach described here provides an opportunity to quantify the regulation of coccolith production in single cells with high temporal resolution allowing responses of calcification to rapidly fluctuating environmental conditions such as light–dark transitions to be examined in detail, which has not been possible with bulk calcification studies.

High-resolution records of past and modern Pb exposure: Laser-ablation ICPMS profiles from tooth enamel

We present compositional and isotopic profiles of past and modern tooth enamel aimed at reconstructing in-vivo Pb exposure at high spatial and time resolution. Focus is on dental enamel because of its sequential mineralization preserving time-series information, and due to its resistance to post-mortem diagenetic alteration. Examples include medieval Pb–Ag miners from SW Germany (Black Forest), the port of ancient Rome (Isola Sacra) for an assessment of the ‘Pb poisoning hypothesis’, and a modern Pb–Zn smelter village in NE NSW. (Sub-)ppb levels of U, LREEs, Y in soil-buried enamel resembling modern enamel are utilized as indicators for the preservation of pristine in-vivo concentrations. This facilitates the identification of in-vivo inter-tooth and particularly intra-tooth Pb concentration variations, which range from below 0.1 up to 150 ppm, and exceed three orders of magnitude even for the same individual. Of particular interest is the identification of sharp Pb peaks recorded in enamel, whose existence may prove more potentially damaging to health than lower average Pb concentrations. Their identification may also improve existing blood-Pb and tooth-Pb calibrations for modern Pb exposure reconstruction. By analyzing several teeth of an individual together with detailed tooth histology (e.g. relative to the neo-natal line), detailed life time trajectories can be established together with—as will be shown—isotopic proxies of mobility (Sr, O).

Partizansky base-metal skarn deposit, Dal’negorsk ore district, Russia: Stages of ore formation, mineral assemblages, and typomorphism of fahlore

As indicated by mineralogical, geochemical, and structural-textural data, the base-metal skarn ore at the Partizansky deposit was formed during two stages (base-metal skarn and silver-sulfosalt), which were separated by intrusion of basaltic dikes. The bulk of the base-metal ore was deposited at the first stage, which comprises four sequential mineral assemblages: skarn-silicate, quartz-arsenopyrite, productive galena-sphalerite, and pyrrhotite-pyrite-chalcopyrite. The mineralization of the second stage was mainly confined to the upper margins of orebodies and pertains to the sulfosalt-galena-chalcopyrite assemblage, which was super-imposed on minerals of the first stage. The vertical mineralogical-geochemical zoning of the deposit is telescopic (related to the formation of the late silver-sulfosalt mineralization) and facies (typical of the early skarn and base-metal assemblages). The zoning of the skarn-silicate assemblage is expressed in the metasomatic replacement of skarn by quartz and calcite in the uppermost zone of skarn bodies and is emphasized by variation of the mineral composition throughout the skarn column, for instance, by the distinct updip enrichment of hedenbergite in manganese. The vertical zoning of the productive assemblage is emphasized by variations in the ratio of sphalerite to galena (the Pb/Zn ratio in the ore increases upward from 0.1 to 1), changes in mineral assemblages, and compositional variation of major ore-forming and minor minerals. In particular, galena from the deep levels is extremely enriched in Bi and Ag, while that from the upper levels is almost completely devoid of isomorphic admixtures. Fahlore displays updip enrichment in Sb, Ag, and Fe and corresponding depletion in Cu and Zn. The vertical chemical variations in fahlore are caused by the specific geological setting of ore deposition, the composition of the ore-forming solutions, and the physicochemical conditions of their transportation and ore deposition.

Numerical simulations of pyrite oxidation and acid mine drainage in unsaturated waste rock piles

Numerical simulations of layered, sulphide-bearing unsaturated waste rock piles are presented to illustrate the effect of coupled processes on the generation of acid mine drainage (AMD). The conceptual 2D systems were simulated using the HYDRUS model for flow and the POLYMIN model for reactive transport. The simulations generated low-pH AMD which was buffered by sequential mineral dissolution and precipitation. Sulphide oxidation rates throughout the pile varied by about two orders of magnitude (0.004–0.4 kg m − 3 year − 1 ) due to small changes in moisture content and grain size. In the fine-grained layers, the high reactive surface area induced high oxidation rates, even though capillary forces kept the local moisture content relatively high. In waste rock piles with horizontal layers, most of the acidity discharged through vertical preferential flow channels while with inclined fine grained layers, capillary diversion channeled the AMD to the outer slope boundary, keeping the pile interior relatively dry. The simulation approach will be useful for helping evaluate design strategies for controlling AMD from waste rock.