Showing papers on "Silicate minerals published in 2015"

Silicon in Soils and Plants

Abstract: The crust of the earth is largely composed of silicon that is found primarily as silicate minerals, secondary alumino silicates and various forms of silicon dioxide. However, the abundance of silicon in soils is not an indication that sufficient supplies of soluble silicon are available for plant uptake. In this chapter, the outcomes of many years of research conducted on silicon are consolidated to understand the state of knowledge for silicon fertilization guidelines in crop production. Monosilicic acid (H4SiO4) is the form of silicon used by plants, which is found both in liquid and adsorbed phases of silicon in soils. The concentration of the H4SiO4 in the soil solution is influenced by the soil pH and the amounts of clay, minerals, organic matter and Fe/Al oxides/hydroxides, which are collectively related to the geologic age of the soil. Fertilization can rapidly increase the concentration of H4SiO4 in the soil solution; therefore, fertilization has become a common practice in areas with intensive cropping systems, particularly for those soils that are inherently low in soluble silicon. The establishment of procedures to estimate the plant-available silicon and the critical soil silicon levels and the method (5-day Na2CO3-NH4NO3 extraction) to analyze the soluble silicon fraction in solid fertilizers were among the advances in research on silicon in agriculture in recent years. These measurements were the key components required for the development and implementation of effective silicon fertilizer management in crop production. However, many aspects of the role of silicon in soil science remain understudied, and these aspects should be the focus of future research.

How large are departures from lithostatic pressure? Constraints from host–inclusion elasticity

Abstract: Minerals trapped as inclusions within other host minerals will develop non-lithostatic pressures during both prograde and retrograde metamorphism because of the differences between the thermoelastic properties of the host and inclusion phases. There is only a single possible path in P–T space, the entrapment isomeke, along which no residual pressure would be developed in a host–inclusion system; non-lithostatic pressures are developed in inclusions as a result of the external pressure and temperature deviating from the isomeke that passes through the entrapment conditions. With modern equation of state and elasticity data for minerals now available, it is possible to perform precise calculations of the isomekes for mineral pairs. These show that isomeke lines are not straight lines in P–T space at metamorphic conditions. We show that silicate inclusions in silicate hosts tend to have flat isomekes, with small values of , because of the small range of thermal expansion coefficients of silicate minerals. As a consequence, the general behaviour under decompression is for soft silicate inclusions in stiffer hosts to develop excess pressures, whereas a stiff silicate inclusion in a softer matrix will experience lower pressures than lithostatic pressure. The opposite effects occur for compression after entrapment on the prograde path. The excess pressures in inclusions, including allowance for mutual elastic relaxation of the host and inclusion, are most easily calculated by using the isomeke as a basis. Analysis of the simplest possible model of a host–inclusion system indicates that deviations from lithostatic pressure in excess of 1 GPa can be readily produced in quartz inclusions within garnet in metamorphic rocks. For softer host minerals such as feldspar, the pressure deviations are smaller, because of greater elastic relaxation of the host. The maximum pressure deviation from lithostatic pressure in the host phase around the inclusion is one-third of the pressure deviation in the inclusion. Routines for performing these calculations have been added to the EosFit7c software package.

First direct evidence of sedimentary carbonate recycling in subduction-related xenoliths

Abstract: Carbon in rocks and its rate of exchange with the exosphere is the least understood part of the carbon cycle. The amount of carbonate subducted as sediments and ocean crust is poorly known, but essential to mass balance the cycle. We describe carbonatite melt pockets in mantle peridotite xenoliths from Dalihu (northern China), which provide firsthand evidence for the recycling of carbonate sediments within the subduction system. These pockets retain the low trace element contents and δ18OSMOW = 21.1 ± 0.3 of argillaceous carbonate sediments, representing wholesale melting of carbonates instead of filtered recycling of carbon by redox freezing and melting. They also contain microscopic diamonds, partly transformed to graphite, indicating that depths >120 km were reached, as well as a bizarre mixture of carbides and metal alloys indicative of extremely reducing conditions. Subducted carbonates form diapirs that move rapidly upwards through the mantle wedge, reacting with peridotite, assimilating silicate minerals and releasing CO2, thus promoting their rapid emplacement. The assimilation process produces very local disequilibrium and divergent redox conditions that result in carbides and metal alloys, which help to interpret other occurrences of rock exhumed from ultra-deep conditions.

Rapid removal of atmospheric CO2 by urban soils

Abstract: The measured calcium carbonate content of soils to a depth of 100 mm at a large urban development site has increased over 18 months at a rate that corresponds to the sequestration of 85 t of CO2/ha (8.5 kg of CO2 m–2) annually. This is a consequence of rapid weathering of calcium silicate and hydroxide minerals derived from the demolition of concrete structures, which releases Ca that combines with CO2 ultimately derived from the atmosphere, precipitating as calcite. Stable isotope data confirm an atmospheric origin for carbonate carbon, and 14C dating indicates the predominance of modern carbon in the pedogenic calcite. Trial pits show that carbonation extends to depths of ≥1 m. Work at other sites shows that the occurrence of pedogenic carbonates is widespread in artificially created urban soils containing Ca and Mg silicate minerals. Appropriate management of fewer than 12000 ha of urban land to maximize calcite precipitation has the potential to remove 1 million t of CO2 from the atmosphere annually. The maximal global potential is estimated to be approximately 700–1200 Mt of CO2 per year (representing 2.0–3.7% of total emissions from fossil fuel combustion) based on current rates of production of industry-derived Ca- and Mg-bearing materials.

The time scale of the silicate weathering negative feedback on atmospheric CO2

Abstract: The ultimate fate of CO2 added to the ocean-atmosphere system is chemical reaction with silicate minerals and burial as marine carbonates. The time scale of this silicate weathering negative feedback on atmospheric pCO2 will determine the duration of perturbations to the carbon cycle, be they geological release events or the current anthropogenic perturbation. However, there has been little previous work on quantifying the time scale of the silicate weathering feedback, with the primary estimate of 300–400 kyr being traceable to an early box model study by Sundquist (1991). Here we employ a representation of terrestrial rock weathering in conjunction with the “GENIE” (Grid ENabled Integrated Earth system) model to elucidate the different time scales of atmospheric CO2 regulation while including the main climate feedbacks on CO2 uptake by the ocean. In this coupled model, the main dependencies of weathering—runoff, temperature, and biological productivity—were driven from an energy-moisture balance atmosphere model and parameterized plant productivity. Long-term projections (1 Myr) were conducted for idealized scenarios of 1000 and 5000 PgC fossil fuel emissions and their sensitivity to different model parameters was tested. By fitting model output to a series of exponentials we determined the e-folding time scale for atmospheric CO2 drawdown by silicate weathering to be ∼240 kyr (range 170–380 kyr), significantly less than existing quantifications. Although the time scales for reequilibration of global surface temperature and surface ocean pH are similar to that for CO2, a much greater proportion of the peak temperature anomaly persists on this longest time scale; ∼21% compared to ∼10% for CO2.

On discrimination between carbonate and silicate inputs to Himalayan rivers

Abstract: We review new and published analyses of river waters, bedloads and their constituent minerals from the Dhauli Ganga and Alaknanda, headwaters of the Ganges in Garhwal, and the Marsyandi in Nepal and their tributaries. These data are used to discriminate between the inputs of major cations and Sr from silicate and carbonate sources. Methods of estimating the proportion of the carbonate and silicate inputs to river waters using mixing arrays in Sr-Ca-Mg-Na-K-87Sr/86Sr space are shown to suffer from systematic correlations between the magnitude of the precipitation of secondary calcite and the fraction of the silicate component. This results in factor-of-two overestimates of the fractions of silicate-derived Ca, Mg and Sr. To correct for this the magnitude of secondary calcite precipitated and relative fractions of silicate and carbonate-derived cations are instead calculated by modeling the displacement of water compositions from the compositions of the carbonate and silicate components of the bedload in subsets of Sr-Ca-Mg-Na-K-87Sr/86Sr space. The compositions of the carbonate and silicate end-members in the bedload are determined by sequential leaching. The results of this modeling are compared with modeling of the modal mineral inputs to waters where mineral compositions are derived from electron-microprobe analyses of the minerals in the bedload. In the upper Marsyandi catchment, which drains low-grade Tethyan Sedimentary Series formations, a set of mainstem samples collected over a two-year period define tight correlations in Sr-Ca-Mg-Na-K-87Sr/86Sr space. Modeling of the magnitude of secondary carbonate precipitation and fractions of silicate-derived Ca, Mg and Sr in Sr-Ca-Mg-87Sr/86Sr space gives self-consistent results that are compatible with both the calculations of mineral modes and published Mg-isotopic compositions, if the ratio of chlorite to biotite weathering is high or if there is another silicate source of Mg. These calculations imply that between 12 and 31 percent of the Sr and 44 and 72 percent of the Mg is derived from silicate minerals where the range reflects the seasonal change in the ratio of silicate-derived to carbonate-derived cations. Modeling in Sr-Ca-Na and/or K space is inconsistent with the Sr-isotopic and Mg-isotopic constraints and we conclude that in this catchment dissolution of Na and K are incongruent relative to Sr-Ca-Mg. Potassium is preferentially retained in micas whereas the controls on Na are unclear. Modeling of the catchments underlain by High Himalayan Crystalline and Lesser Himalayan Series in Garhwal is complicated by the presence of dolomite as well as calcite in the carbonate and the results imply that dolomite dissolves faster in the acetic acid leaches than in nature. Up to 60 percent of the Sr in the catchment on High Himalayan Crystalline Series and 20 to 30 percent of Sr in the catchments on Lesser Himalayan Series are estimated to be derived from silicates. However it should be noted that the element budgets are not all self-consistent and the use of bedrock-element ratios to model the sources of chemical inputs to river waters remains subject to uncertainties.

Accelerated Carbonation of Ca- and Mg-Bearing Minerals and Industrial Wastes Using CO2

Abstract: This chapter introduces the concept of carbon mineralization that involves the conversion of CO 2 into solid inorganic carbonates. It starts by presenting an overall scheme of CO 2 reactions with alkaline-rich materials such as minerals and industrial wastes containing calcium and magnesium. The engineered weathering of silicate minerals including olivine ((Mg,Fe) 2 SiO 4 ), serpentine ((Mg,Fe) 3 (OH) 4 (Si 3 O 5 )) and wollastonite (CaSiO 3 ) are discussed as one of the most safe and permanent carbon storage solutions. The method of using CO 2 to treat industrial wastes such as fly ash, cement kiln dust, stainless steel slag and red mud is also presented in detail. The carbonated materials can be readily landfilled without the concern of contaminant leaching, or utilized in various applications such as in construction. Environmental implications and potential benefits of CO 2 utilization via various carbon mineralization schemes are summarized.

Microfluidic Leaching of Soil Minerals: Release of K+ from K Feldspar.

Abstract: The rate of K+ leaching from soil minerals such as K-feldspar is believed to be too slow to provide agronomic benefit. Currently, theories and methods available to interpret kinetics of mineral processes in soil fail to consider its microfluidic nature. In this study, we measure the leaching rate of K+ ions from a K-feldspar-bearing rock (syenite) in a microfluidic environment, and demonstrate that at the spatial and temporal scales experienced by crop roots, K+ is available at a faster rate than that measured with conventional apparatuses. We present a device to investigate kinetics of mineral leaching at an unprecedented simultaneous resolution of space (~101-102 μm), time (~101-102 min) and fluid volume (~100-101 mL). Results obtained from such a device challenge the notion that silicate minerals cannot be used as alternative fertilizers for tropical soils.

Isolation and the interaction between a mineral-weathering Rhizobium tropici Q34 and silicate minerals

Abstract: The purposes of this study were to isolate and evaluate the interaction between mineral-weathering bacteria and silicate minerals (feldspar and biotite). A mineral-weathering bacterium was isolated from weathered rocks and identified as Rhizobium tropici Q34 based on 16S rRNA gene sequence analysis. Si and K concentrations were increased by 1.3- to 4.0-fold and 1.1- to 1.7-fold in the live bacterium-inoculated cultures compared with the controls respectively. Significant increases in the productions of tartaric and succinic acids and extracellular polysaccharides by strain Q34 were observed in cultures with minerals. Furthermore, significantly more tartaric acid and polysaccharide productions by strain Q34 were obtained in the presence of feldspar, while better growth and more citric acid production of strain Q34 were observed in the presence of biotite. Mineral dissolution experiments showed that the organic acids and polysaccharides produced by strain Q34 were also capable of promoting the release of Si and K from the minerals. The results showed that the growth and metabolite production of strain Q34 were enhanced in the presence of the minerals and different mineral exerted distinct impacts on the growth and metabolite production. The bio-weathering process is probably a synergistic action of organic acids and extracellular polysaccharides produced by the bacterium.

Metal and fluid sources in a potential world‑class gold deposit: El‑Sid mine, Egypt

Abstract: Lode gold mineralization at the El-Sid mine area is associated with the ca. 600 Ma Fawakhir granite intrusion, which cuts the ~737 Ma ophiolite nappes in the Central Eastern Desert of Egypt. The mineralized quartz veins are hosted by ~E- and NE-trending fault/fracture sets cutting the western boundary of the intrusion and sheared ophiolites. The results of electron microprobe analyses of gold-associated hydrothermal sulfide and silicate minerals suggest that Au was mobilized alongside Ni, Co, Cr and As from the adjacent ophiolitic serpentinite. After granite emplacement, hydrothermal fluids interacted with the sheared serpentinite, leaching metals and re-depositing them in the faults/fractures and adjacent wall rock in a cyclic process. Low-salinity aqueous-carbonic fluids with significant quantities of volatile species (CO2, CH4, and N2 ± H2S) leached and transported Au from deep to shallow crustal levels. Carbon dioxide had a buffering effect on the Au-bearing hydrothermal solution, maintaining its pH within a narrow near-neutral range, where elevated gold concentration was transported by complexation with reduced magmatic sulfur in a reducing environment. Gold deposition along fault/fracture conduits in the Fawakhir granite and adjacent serpentinite resulted from interplay of pressure drop, fluctuations in oxygen and sulfur fugacities, and exsolution of the volatile phases. Infiltration of meteoric water may have contributed to the formation of the late stage gold-sulfide mineralization that formed at shallower levels during terrane uplift. Sulfidation of the Fe-rich magmatic minerals was, on the other hand, the overriding process in the wall rock as evidenced by abundant disseminated sulfides with gold inclusions. Considering the structural control by regional shear zones (fluid conduits) and the voluminous granitic and ophiolitic rocks (metal sources), a high tonnage gold deposit amenable to open pit mining at the El-Sid mine area is very likely.

Identification of Magnetite in Lunar Regolith Breccia 60016: Evidence for Oxidized Conditions at the Lunar Surface

Abstract: Lunar regolith breccias are temporal archives of magmatic and impact bombardment processes on the Moon. Apollo 16 sample 60016 is an ancient™ feldspathic regolith breccia that was converted from a soil to a rock at ~3.8 Ga. The breccia contains a small (70 -— 50 �m) rock fragment composed dominantly of an Fe-oxide phase with disseminated domains of troilite. Fragments of plagioclase (An95-97), pyroxene (En74-75, Fs21-22,Wo3-4) and olivine (Fo66-67) are distributed in and adjacent to the Fe-oxide. The silicate minerals have lunar compositions that are similar to anorthosites. Mineral chemistry, synchrotron X-ray Absorption Near Edge Spectroscopy (XANES) and X-ray Diffraction (XRD) studies demonstrate that the oxide phase is magnetite with an estimated Fe3+/Fe ratio of ~0.45. The presence of magnetite in 60016 indicates that oxygen fugacity during formation was equilibrated at, or above, the Fe-magnetite or wustite-magnetite oxygen buffer. This discovery provides direct evidence for oxidised conditions on the Moon. Thermodynamic modelling shows that magnetite could have been formed from oxidisation-driven mineral replacement of Fe-metal or desulphurisation from Fe-sulphides (troilite) at low temperatures (<570 �C) in equilibrium with H2O steam/liquid or CO2 gas. Oxidising conditions may have arisen from vapour transport during degassing of a magmatic source region, or from a hybrid endogenic-exogenic process when gases were released during an impacting asteroid or comet impact.

CONSONORM_LG: New Normative Minerals and Alteration Indexes for Low-Grade Metamorphic Rocks

Abstract: The CONSONORM\_LG method provides a standardized solution for approximating metamorphic parageneses, as well as indexes for estimating chemical and mineralogical changes caused by hydrothermal alteration. CONSONORM\_LG is designed for rocks dominated by silicates, Fe-Ti oxides, and/or carbonates, and it approximates the main parageneses of greenschist and lower amphibolite-grade metamorphic rocks for three sets of temperature and pressure conditions (350°C and 2.5 kbars, 450°C and 2.5 kbars, 575°C and 2 kbars). For each model, the norm calculates the main paragenesis using an ACFMNK tetrahedron, a convenient way of representing a large number of silicate assemblages. In addition to silicate minerals, CONSONORM_LG calculates Fe-Ti oxides and other accessory minerals from minor elements, as well as sulfides from analyzed S or from analyzed metals, and carbonates from analyzed CO2 or from normative CO2 estimated from loss on ignition (LOI). CONSONORM_LG also calculates several alteration indexes to estimate Fe-Mg (e.g., chloritization), Ca (e.g., propylitic alteration), Na and K acid alterations (e.g., sericitization, phyllic alterations), and Al gain (e.g., argillization). Carbonatation indexes are also calculated using the amount of normative minerals formed by this type of alteration, i.e., carbonates, chlorite, and muscovite. The normative calculation is validated using published whole-rock analyses and petrographic descriptions. Alteration indexes are validated using several natural samples of alteration halos around base metal and gold deposits.

Spectroscopic Characterization and Quantitative Estimation of Natural Weathering of Silicates in Sediments of Dikrong River, India

Abstract: The sediments samples were collected from the Dikrong River at various sites to assess the weathering nature and mineral characterization. The Fourier Transform Infrared (FTIR) and X-ray fluorescence (XRF) spectroscopic techniques have been used to characterization of minerals in the sediment samples. The plagioclase index of alteration (PIA), chemical index of alteration (CIA) and index of compositional variation (ICV) are investigated for evaluating the weathering nature in the sediment. The obtained results show the presence of quartz, feldspar in different structure and kaolinite as major minerals. Carbonates and organic carbon are found as minor minerals. The correlations of SiO2 with major elements are authenticated the presence of bulk quartz grains and primary depositional environment. The presence of metamorphosed pyrophanite (MnTiO3) in the adjoined areas is reported. The presence of infrared absorption peaks in between 1611 - 1622 cm?1 in this study is indicative to the weathered metamorphic origin of the silicate minerals. The index of compositional variation indicates the presence of less clay minerals and more rock forming minerals such as plagioclase and alkali-feldspar. The obtained results exhibit the area belongs to the intermediate silicate weathering.

Radiation damage from long-term alpha particle bombardment of silicates – a microfocus XRD and Fe K-edge XANES study

Abstract: A detailed understanding of the response of mineral phases to the radiation fields experienced in a geological disposal facility (GDF) is currently poorly constrained. Prolongued ion irradiation has the potential to affect both the physical integrity and oxidation state of materials and therefore may alter a structure's ability to react with radionuclides. Radiohalos (spheres of radiation damage in minerals surrounding radioactive (α-emitting) inclusions) provide useful analogues for studying long term α-particle damage accumulation. In this study, silicate minerals adjacent to Th- and U-rich monazite and zircon were probed for redox changes and long/short range disorder using microfocus X-ray absorption spectroscopy (XAS) and high resolution X-ray diffraction (XRD) at Beamline I18, Diamond Light Source. Fe3+→ Fe2+ reduction has been demonstrated in an amphibole sample containing structural OH− groups – a trend not observed in anhydrous phases such as garnet. Coincident with the findings of Pattrick et al. (2013), the radiolytic breakdown of OH− groups is postulated to liberate Fe3+ reducing electrons. Across all samples, high point defect densities and minor lattice aberrations are apparent adjacent to the radioactive inclusion, demonstrated by micro-XRD.

Method and system of activation of mineral silicate minerals

Abstract: A method for activation of magnesium silicate minerals by conversion to magnesium hydroxide for sequestration of carbon dioxide (CO 2 ) is provided. The method includes heating a dry solid-solid mixture of an alkaline earth Silicate-based material with an alkali metal compound at a temperature below 300 C to form a solid product predominantly comprising a mixture of magnesium hydroxide and alkali metal silicate, wherein the Silicate-based material comprises a naturally occurring Olivine, Serpentine mineral and alkali metal silicate. The method includes a subsequent dissolution of the solid product in aqueous solution to form an alkaline aqueous liquid slurry, comprising solid and aqueous phase products and the reaction of the solid phase thus formed with Carbon Dioxide (CO 2 ), producing a metal Carbonate. The method provides a process that has shown significant cost and energy efficiencies for producing magnesium hydroxide and CO 2 sequestration via mineral carbonation.

Geochemical Characteristics and Salt-Forming Analysis of Jurassic Strata in the Qiangtang Basin

Abstract: The gypsum-bearing strata and high-salinity spring have been found widely in the Jurassic strata of the Qiangtang basin in recent years,suggesting apotential for salt mineralization in the areaThis study performed a comprehensive geochemical analysis in the Jurassic sediments in the Yanshiping area of the Qiangtang basin,combined with the sedimentary environments analysis,to reveal sea level fluctuations of Tethys Ocean,paleoclimate changes and potential of potassium deposit formation in the areaIn order to obtain a clear indication of paleo-proxies and using the sediments with gypsum,carbonate and detrital material,we employed the water and acetic acid to distinguish the elements from water-soluble salts,carbonates and the silicate minerals in the bulk sedimentsThe results show that,1the Fe/Mn ratios and CaCO3 content in the bulk samples indicate that Buqu and Suowa formations display high sea level with low Fe/Mn and high carbonate content due to the transgression of the Tethys Ocean;however,the Quemocuo and Xiali formations were in the regression stage with high Fe/Mn and low carbonate content2 The chemical weathering proxies based on the oxides content in the silicate minerals,eg,the ratio of Na2O/Al2O3,and Na2O/K2 O in the acid-insoluble fraction and chemical index of alternation(CIA),exhibit the much more arid paleoclimate with weak chemical weathering in the source areas periods of Buqu and Xiali formations,while the relatively less arid climate with strong chemical weathering in periods of Quemocuo and Suowa formations3 The K+and Na+contents in water soluble salts,which are sensitive proxies of salt formation,show the much higher concentrations in the Xiali Formation and low concentrations in other formationsSummarized by provenance,tectonics,paleoclimate,and palegeographical conditions,the results indicate the Xiali Formation has the great potential of potassium deposits in the Qiangtang basinBecause Tethys Ocean retreating from the east to the west of the Qiangtang basin in Jurassic and Yanshiping locates in the eastern margin of the basin,there is no potassium deposits formation but some gypsum outcrop in this areaThe further work of potassium deposits exploration should focus on the Xiali Formation in the central and western part of the Qiangtang basin