Showing papers in "Elements in 2012"
TL;DR: The rare earth elements (REEs) are all around us, not only in nature but in our everyday lives as discussed by the authors, and they are used in many applications, such as tracing the provenance of magmas and sediments, studying body structures with magnetic resonance imaging.
Abstract: The rare earth elements (REEs) are all around us, not only in nature but in our everyday lives. They are in every car, computer, smartphone, energy-efficient fluorescent lamp, and color TV, as well as in lasers, lenses, ceramics, and more. Scientific applications of these elements range from tracing the provenance of magmas and sediments to studying body structures with magnetic resonance imaging. The realization that we need rare earths for so many applications, but that their supply is effectively restricted to several mining districts in China, has brought these elements to the headlines and created a critical-metals agenda. Here we introduce the REE family: their properties, minerals, practical uses, and deposits. Potential sources of these elements are diverse and abundant if we can overcome the technical challenges of rare earth mining and extraction in an environmentally and socially responsible way.
447 citations
TL;DR: Although rare earth elements have been thought by many to be immobile in hydrothermal fluids, we have known since the first attempts to separate them in the early nineteenth century that they are soluble in aqueous solutions as mentioned in this paper.
Abstract: Although the rare earth elements have been thought by many to be immobile in hydrothermal fluids, we have known since the first attempts to separate them in the early nineteenth century that they are soluble in aqueous solutions. Driven by a need to isolate individual REEs for industrial applications, and more recently to explore for them, we have started to develop an understanding of their solubility and speciation in hydrothermal fluids. This knowledge is allowing us to understand the processes that promote their transport in the Earth's crust, their concentration, and their fractionation.
353 citations
TL;DR: The European Commission recently designated tantalum and niobium as critical materials or “strategic resources, and field relationships, mineral chemistry, and experimental constraints indicate that these elements are concentrated dominantly by magmatic processes as discussed by the authors.
Abstract: Rare-element granitic pegmatites are well recognized for the diversity and concentrations of metal ores that they host. The supply of some of these elements is of concern, and the European Commission recently designated metals such as tantalum and niobium as “critical materials” or “strategic resources.” Field relationships, mineral chemistry, and experimental constraints indicate that these elements are concentrated dominantly by magmatic processes. The granitic melts involved in these processes are very unusual because they contain high concentrations of fluxing compounds, which play a key role at both the primary magmatic and metasomatic stages. In particular, the latter may involve highly fluxed melts rather than aqueous fluids.
226 citations
TL;DR: Pegmatites accentuate the trace-element signatures of their origins, and through that signature pegmatites can commonly be attributed to origins from granites whose source characteristics are known and distinctive as mentioned in this paper.
Abstract: Pegmatites accentuate the trace-element signatures of their
sources, and through that signature pegmatites can commonly be
ascribed to origins from granites whose source characteristics
are known and distinctive. Interactions with host rocks that
might modify the compositions of pegmatites are limited by the
rapid cooling and low heat content of pegmatite-forming magmas.
Though the plutons from which most pegmatites arise may have
extended histories of magma accumulation and contamination by
host lithologies, the trace-element signatures of most
pegmatites clearly align with those of the S-type (sedimentary
source, post-collisional tectonic environment) and A-type
granites (anorogenic environment, lower continental crust +
mantle source). Pegmatites are not prevalent among the I-type
(igneous source) granites, and the distinction between the
granites that spawn pegmatites and those that do not appears to
stem from the presence or absence, respectively, of fluxing
components of B, P, and F at the source.
211 citations
TL;DR: Li et al. as mentioned in this paper showed that not only hypogene but also secondary processes create economic rare earth elements (REEs) in China, which is a world-class phenomenon.
Abstract: As a source of strategic commodities for high technologies, the deposits of rare earth elements (REEs) in China are a world-class phenomenon. The combination of the world's largest accumulation of REEs in the Bayan Obo deposit and the low cost of mining the extremely valuable heavy REEs from residual deposits makes China almost a monopoly producer. Research on a range of Chinese deposits shows that not only hypogene but also secondary processes create economic REE deposits. These deposits have characteristic REE distribution patterns, which range from primary light REE enrichment in carbonatites from the Himalayan Mianning–Dechang orogenic belt and in metamorphosed carbonatite and polyphase mineralization at Bayan Obo, through unusual flat REE patterns in carbonatites from the Qinling orogenic belt, to strong secondary heavy REE enrichment in residual clays from southern China.
201 citations
TL;DR: In this article, the authors compare the geochemical and mineralogical characteristics of rare earth elements (REEs) mineralization in carbonatites, peralkaline feldspathoid rocks, and granites, and find that the differences in the extent of postmagmatic reworking of primary REE minerals by hydrothermal fluids reflect different sources and evolutionary pathways of their parental magmas.
Abstract: Deposits of rare earth elements (REEs) in igneous rocks have played an instrumental role in meeting the growing industrial demand for these elements since the 1960s. Among the many different igneous rocks containing appreciable concentrations of REEs, carbonatites and peralkaline silicate rocks are the most important sources of these elements, both historically and for meeting the anticipated growth in REE demand. The contrasting geochemical and mineralogical characteristics of REE mineralization in carbonatites, peralkaline feldspathoid rocks, and peralkaline granites reflect different sources and evolutionary pathways of their parental magmas, as well as differences in the extent of postmagmatic reworking of primary REE minerals by hydrothermal fluids.
190 citations
TL;DR: The long-term growth of numerous industries will depend on the ability to secure stable and diverse sources of rare earths as mentioned in this paper, and this sector is increasingly considered as strategic and critical to a wide range of technologies.
Abstract: The long-term growth of numerous industries will depend on the ability to secure stable and diverse sources of rare earths. Recent years have seen unprecedented volatility in this sector, with the rare earths being increasingly considered as strategic and critical to a wide range of technologies. During the next few years, demand for some of the rare earths is expected to exceed supply. Chinese export-quota policies have had a severe impact on the market. Worldwide exploration efforts are now leading to the deployment of a rare earth supply chain based outside China.
184 citations
TL;DR: In this paper, numerical simulations of the dispersion process and vertical profiles of radionuclides in soils are used to describe the contamination of soils, and the most highly contaminated areas are to the northwest of the plant and in the Naka-dori region of Fukushima Prefecture; this contamination was mainly the result of wet deposition.
Abstract: Radionuclides, such as 134Cs, 137Cs, and 131I, were released during the Fukushima Daiichi nuclear power plant accident in March 2011. Their distribution was monitored by airborne surveys and soil sampling. The most highly contaminated areas are to the northwest of the plant and in the Naka-dori region of Fukushima Prefecture; this contamination was mainly the result of wet deposition on March 15. Radionuclides were also released on March 21, and they were dispersed up to 200 km south of the plant. The Cs/I ratios are different for these two events, probably because of differences in the initial ratios in the airborne plumes and the amount of wet deposition. Numerical simulations of the dispersion process and vertical profiles of radionuclides in soils are used to describe the contamination of soils.
143 citations
TL;DR: A review of the active areas of research on clay-microbe interactions can be found in this article, where the authors provide perspectives for future work and discuss the role of microbes in clay mineral transformations.
Abstract: Clay minerals are ubiquitous in soils, sediments, and sedimentary rocks, and they play important roles in environmental processes. Microbes are also abundant in these geological media, and they interact with clays via a variety of mechanisms, such as reduction and oxidation of structural iron and mineral dissolution and precipitation through the production of siderophores and organic acids. These interactions greatly accelerate clay mineral reaction rates. While it is certain that microbes play important roles in clay mineral transformations, quantitative assessment of these roles is limited. This paper reviews some active areas of research on clay–microbe interactions and provides perspectives for future work.
126 citations
TL;DR: A dating campaign is urgently needed if we are to fully understand the role of impacts in Earth history as discussed by the authors, but only a few terrestrial impact events are accurately and precisely dated, which makes it difficult to evaluate whether they are related in time to mass extinctions.
Abstract: Hypervelocity impacts of asteroids and comets have played a key role in the evolution of the Solar System and planet Earth. Geochronology, the science that investigates the ages of rocks, has become a preponderant tool for dating impact events and for assessing whether they are related in time to mass extinctions on Earth. Impact events are instantaneous compared to other geological processes and, in theory, represent easy targets for multitechnique geochronology. Yet, only a few terrestrial impact events are accurately and precisely dated. A dating campaign is urgently needed if we are to fully understand the role of impacts in Earth history.
114 citations
TL;DR: The occurrences of rare earth elements (REEs) in North America are abundant and diverse in mineralogy and geology as mentioned in this paper, with emphasis on the heavy rare earth element (REE) spectrum.
Abstract: The occurrences of rare earth elements (REEs) in North America are abundant and diverse in mineralogy and geology. The Mountain Pass carbonatite in California historically has been a major world source for the light REEs. Monazite sands have also been mined on a moderate level in the southeastern United States. Fluids released from the mining of uraninite at Elliot Lake, Ontario, were intermittently a source for yttrium. Peralkaline igneous rocks in several areas of North America are currently under exploration for the entire REE spectrum, with emphasis on the heavy REEs. Although many REE occurrences contain a substantial tonnage of REEs, amenability to mineral processing and extraction of the REEs must be definitively established in each case.
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TL;DR: A recent model combining aspects of both concepts invokes the formation of a flux-enriched boundary layer of silicate liquid in advance of a crystallization front as discussed by the authors, which can explain the internal chemical and textural features of pegmatites.
Abstract: Virtually every conceivable model to explain the internal evolution of granitic pegmatites had been proposed by the 1920s. Two of these hypotheses have prevailed: (1) the fractional crystallization of flux-bearing granitic melt inward from the margins of the pegmatite body to the center, and (2) the buoyant separation of an aqueous fluid from the silicate melt and its effects on the redistribution of components. A recent model combining aspects of both concepts invokes the formation of a flux-enriched boundary layer of silicate liquid in advance of a crystallization front. Though most of the internal chemical and textural features of pegmatites can now be reconciled, the puzzle of pegmatites is far from solved.
TL;DR: In this article, five models have been used to estimate the oceanic dispersion of 137C from the Fukushima Daiichi nuclear power plant during March and April 2011, following the accident on March 11, 2011.
Abstract: Five models have been used to estimate the oceanic dispersion of 137Cs from the Fukushima Daiichi nuclear power plant during March and April 2011, following the accident on March 11, 2011. The total discharged activity of 137Cs is estimated to be 2 to 15 petabequerels. A weak southward current along the Fukushima coast was responsible for the initial transport direction, while mesoscale eddy-like structures and surface-current systems contributed to dispersion in areas beyond the continental shelf. Most of the discrepancies among the models in April are caused by differences in how the mesoscale current structures off the Ibaraki coast are represented.
TL;DR: In this article, the basic principles of shock compression are introduced to understand the formation and geological significance of shock-metamorphic effects in minerals and special emphasis is placed on the formation of high-pressure phases such as stishovite and diamond as well as on the decomposition of carbonates.
Abstract: The hypervelocity impact of extraterrestrial objects causes unequivocal changes in the target due to extreme deformation rates, pressures up to hundreds of gigapascals, and postshock temperatures that may even vaporize silicates. This article introduces the basic principles of shock compression, as required to understand the formation and geological significance of shock-metamorphic effects in minerals. Special emphasis is placed on the formation of high-pressure phases such as stishovite and diamond as well as on the decomposition of carbonates.
TL;DR: The distal ejecta layers consist primarily of millimeter-scale glassy bodies (impact spherules) that form from melt and vapor-condensate droplets.
Abstract: During the formation of large impact structures, layers of melted and crushed rock (ejecta) are deposited over large areas of the Earth9s surface. Ejecta thrown farther than 2.5 crater diameters are called distal ejecta. At distances greater than ~10 crater diameters, the distal ejecta layers consist primarily of millimeter-scale glassy bodies (impact spherules) that form from melt and vapor-condensate droplets. At least 28 distal ejecta layers have been identified. Distal ejecta layers can be used to place constraints on cratering models, help fill gaps in the cratering record, and provide direct correlation between impacts and other terrestrial events.
TL;DR: In this paper, the authors trace the evolution of radioactivity release to the atmosphere and subsequent dispersion as simulated by models, and compare these to actual measurements, highlighting four main release periods.
Abstract: On March 11, 2011, an earthquake and tsunami hit the northeast coast of Japan and damaged the Fukushima Daiichi nuclear power plant, leading to the release of radioactive material into the atmosphere. We trace the evolution of radioactivity release to the atmosphere and subsequent dispersion as simulated by models, and we compare these to actual measurements. Four main release periods are highlighted. The first event had limited consequences to the north of the power plant along the coast; the second had no impact on Japanese territory because the plumes travelled toward the Pacific Ocean; the third was responsible for significant and long-term impact, especially northwest of the plant; and the last had consequences of lesser impact on the Tokyo area.
TL;DR: Pegmatites are sources of gem-quality crystals of beryl, tourmaline, topaz, spodumene, and spessartine as mentioned in this paper, which are found in Brazil, Madagascar, Russia, and the United States.
Abstract: Pegmatites are sources of gem-quality crystals of beryl, tourmaline, topaz, spodumene, and spessartine. Historic localities are found in Brazil, Madagascar, Russia, and the United States, but important deposits have recently been discovered in Africa and Asia. Most high-quality gem minerals occur in miarolitic cavities found near the centers of pegmatite bodies or in reaction zones between pegmatites and ultramafic host rocks. The most important gem-bearing granitic pegmatites formed at shallow levels in the continental crust during the latest stages of collisional plate tectonic events. Single, spectacular miarolitic cavities in some pegmatites have produced tons of gem crystals valued in excess of $50 million.
TL;DR: Granitic pegmatites have been a focal point of research by petrologists and mineralogists for over a century as mentioned in this paper, mainly motivated by exploration for the economic commodities they provide.
Abstract: Granitic pegmatites have been a focal point of research by petrologists and mineralogists for over a century. Mineralogical interest stems from the diversity of rare minerals that some pegmatites contain. Petrologic efforts are aimed at resolving the processes or agents that produce the complex textures and spatial heterogeneity that distinguish pegmatites from granites. Much of the scientific study of pegmatites has been motivated by exploration for the economic commodities they provide. Pegmatites yield quartz, feldspars, and micas for industrial uses; strategic rare metals for electronic, aerospace, and energy applications; and many of the world's finest gem and mineral specimens.
TL;DR: In this paper, the authors deal with terrestrial impact structures and the role of impacts in environmental change throughout the geologic record and reveal the possible role of impact in environmental changes throughout the world.
Abstract: Geochemical analysis is an essential tool for the confirmation and study of impact structures and the characterization of the various rock types involved (target rocks, impact breccias, melt rocks, etc.). Concentrations and interelement ratios of the platinum-group elements, as well as the osmium and chromium isotope systems, allow quantification of extraterrestrial components and the identification of impactor types in impact deposits. In addition, chemolithostratigraphy can reveal the possible role of impacts in environmental change throughout the geologic record. This article deals predominantly with terrestrial impact structures.
TL;DR: In this article, the microbe-mineral interactions in tailings were investigated to mitigate the environmental impacts of mining activities, and the results showed that microbe activities greatly enhance sulfide oxidation and result in the release of heavy metals and the precipitation of iron (oxy)hydroxides and sulfates.
Abstract: Mining activities have created great wealth, but they have also produced colossal quantities of tailings. An important source of heavy metal contamination, sulfide tailings are usually disposed of in open-air impoundments and thus are exposed to microbial oxidation. Microbial activities greatly enhance sulfide oxidation and result in the release of heavy metals and the precipitation of iron (oxy)hydroxides and sulfates. These secondary minerals in turn influence the mobility of dissolved metals and play important roles in the natural attenuation of heavy metals. Elucidating the microbe–mineral interactions in tailings will help us mitigate the environmental impacts of mining activities.
TL;DR: Impact cratering is an important and unique geologic process as discussed by the authors, and the high speeds, forces and temperatures involved are quite unlike conventional endogenic processes, and the environmental consequences can be catastrophic.
Abstract: Impact cratering is an important and unique geologic process. The high speeds, forces and temperatures involved are quite unlike conventional endogenic processes, and the environmental consequences can be catastrophic. Kilometre-scale craters are excavated and collapse in minutes, in some cases distributing debris around the globe and exhuming deeply buried strata. In the process, rocks are deformed, broken, heated and transformed in unique ways. Elevated temperatures in the crust may persist for millennia, and important chemical reactions are promoted by the extreme environment of the impact plume. Released gases may cause long-term perturbations to the climate, and impact-related phosphorus reduction may have played a role in the origin of life on Earth.
TL;DR: The potential and limitations of bioremediation for these two toxic metals and highlights the importance of biologically mediated transformation, immobilization, and mineralization of toxic metals during the course of remediation as discussed by the authors.
Abstract: Anthropogenic sources of the toxic metals chromium and uranium have contaminated the ecosystem and become major public and political concerns. Biomineralization, a process by which microorganisms transform aqueous metal ions into amorphous or crystalline precipitates, is regarded as a promising and cost-effective strategy for remediating chromium and uranium contamination. This review describes the potential and limitations of bioremediation for these two toxic metals and highlights the importance of biologically mediated transformation, immobilization, and mineralization of toxic metals during the course of remediation. It also provides nonspecialists with an introduction to several of the main approaches to remediation and acknowledges some questions about this technology that remain to be answered.
TL;DR: Studies integrating metal geochemistry with human health impacts reveal the complicated layering of environment, exposure, uptake, and human health in cities, and they call for more effort towards the integration of Earth and health science data.
Abstract: Cities are typically evaluated by metrics involving transportation, energy, and economics, but increasingly, environmental quality and human health are becoming important indicators of safe and habitable cities. Population density and industrialization history have resulted in urban contaminant legacies that can impact the health of urban populations. Integrating environmental assessment with human exposure and health studies is in its infancy, but combined geospatial and geotemporal studies have the capacity to explain and predict the health of urban environments. Studies integrating metal geochemistry with human health impacts reveal the complicated layering of environment, exposure, uptake, and human health in cities, and they call for more effort towards the integration of Earth and health science data.
TL;DR: In this article, the authors show that the dissolution, precipitation, and transformation of minerals are either directly controlled by microorganisms or induced by biochemical reactions that usually take place outside the cell.
Abstract: Minerals and microbes have coevolved throughout much of Earth history. They interact at the microscopic scale, but their effects are manifested macroscopically. Minerals support microbial growth by providing essential nutrients, and microbial activity alters mineral solubility and the oxidation state of certain constituent elements. Microbially mediated dissolution, precipitation, and transformation of minerals are either directly controlled by microorganisms or induced by biochemical reactions that usually take place outside the cell. All these reactions alter metal mobility, leading to the release or sequestration of heavy metals and radionuclides. These processes therefore have implications for ore formation and the bioremediation of contaminated sites.
TL;DR: Granitic pegmatites are mined for feldspar, quartz, mica, lithium aluminosilicate minerals, and kaolin this paper, and they contain nearly 100% of minable rock.
Abstract: Granitic pegmatites are mined for feldspar, quartz, mica, lithium aluminosilicate minerals, and kaolin. These industrial minerals have a myriad of uses, some as mundane as glasses, porcelains, and bulk fillers, and others that are critical to the most advanced electronic devices. The chemical fractionation that produces pegmatites refines these industrial minerals to a purity that is not achieved in other geologic environments. The high chemical purity of their constituents and the fact that they contain nearly 100% of minable rock make large granitic pegmatites some of the most valuable sources of industrial minerals.
TL;DR: The environmental effects of impact events differ with respect to time (seconds to decades) and spatial (local to global) scales as mentioned in this paper, and short-term localized damage is produced by thermal radiation, blast-wave propagation in the atmosphere, crater excavation, earthquakes, and tsunami.
Abstract: The environmental effects of impact events differ with respect to time (seconds to decades) and spatial (local to global) scales. Short-term localized damage is produced by thermal radiation, blast-wave propagation in the atmosphere, crater excavation, earthquakes, and tsunami. Global and long-term effects are related to the ejection of dust and climate-active gases (carbon dioxide, sulfur oxides, water vapor, methane) into the atmosphere. At the end of the Cretaceous, the impact of a >10 km diameter asteroid led to a major mass extinction. Modern civilization is vulnerable to even relatively small impacts, which may occur in the near future, that is, tens to hundreds of years.
TL;DR: The past is frequently a hidden source of environmental problems with the potential to affect the health of current and future urban residents as discussed by the authors, even though progress has changed human habits and positively influenced the quality of city life.
Abstract: Modern cities are affected by multiple sources of contamination and pollution, the effects of which overlap in space and time. Toxic metal contamination, organic pollution, smog, acid rain, and greenhouse gas accumulation are the most widespread legacies of an often uncontrolled growth that has deeply changed the geochemical character of the urban environment over the last four millennia. Even though progress has changed human habits and positively influenced the quality of city life, the past is frequently a hidden source of environmental problems with the potential to affect the health of current and future urban residents.
TL;DR: Intuitively, mineral dissolution and mineral precipitation must provide a benefit for the organism, that is, they must supply the cell with the energy and materials needed to maintain cell structure and function.
Abstract: Conceptually, minerals represent challenging “substrates” (sources of nutrients and/or energy) for prokaryotes because they can transfer only soluble compounds into or out of their cells. Yet, prokaryotes are able to use a wide array of minerals as sources of energy, trace nutrients, electron acceptors and, remarkably, for positioning themselves using the Earth’s magnetic field. Mineral dissolution exposes microorganisms to a wide range of soluble and potentially toxic metals. Conversely, microbial mineralformation processes can entrap cells, producing microfossils. Intuitively, mineral dissolution and mineral precipitation must provide a benefit for the organism, that is, they must supply the cell with the energy and materials needed to maintain cell structure and function.
TL;DR: The major nuclear accident at the Fukushima Daiichi nuclear power plant more than one year ago was the result of a combination of four interrelated factors: site selection, external hazard assessment and site preparation, the utility's approach to risk management, and fundamental reactor design as mentioned in this paper.
Abstract: The major nuclear accident at the Fukushima Daiichi nuclear power plant more than one year ago was the result of a combination of four inter-related factors: site selection, external hazard assessment and site preparation, the utility's approach to risk management, and fundamental reactor design. The reactor accident was initiated by a magnitude 9 earthquake, followed by an even more damaging tsunami. An insufficient tsunami defense-in-depth strategy led to significant core damage in three units and radioactive release to the environment. This paper provides a summary of the sequence of events that led to the accident and current efforts to contain and manage the released radioactivity.
TL;DR: A major mass extinction at the Cretaceous-Paleogene boundary has been confidently related to an impact event (Chicxulub, Mexico) and it is now universally accepted that the impact of planetesimals, asteroids, and comets has been a fundamental process throughout the Solar System as mentioned in this paper.
Abstract: It is now universally accepted that the impact of planetesimals, asteroids, and comets has been a fundamental process throughout the Solar System. Catastrophic impact events have been instrumental in developing the early history of the planets and have caused environmental disasters throughout Earth history. A major mass extinction at the Cretaceous–Paleogene boundary has been confidently related to an impact event (Chicxulub, Mexico). While the study of impact cratering is a multidisciplinary field, mineralogical and geochemical investigations have been central since the beginning, focusing on the nature of impact-generated rocks and of the extraterrestrial projectiles as well as their interaction with geological materials. Chemical and isotopic techniques have allowed the dating of impact events and the identification of traces of meteoritic projectiles in impact-formed rocks on Earth and the Moon.