TEM and FESEM characterization of asbestiform and non-asbestiform actinolite fibers in hydrothermally altered dolerites (France)     

Didier Lahondère  Florence Cagnard  Guillaume Wille  Jéromine Duron  Maxime Misseri 《Environmental Earth Sciences》2018,77(10):385

This paper provides new mineralogical and morphological characterizations of calcic amphiboles from hydrothermally altered dolerites from France to discuss their potential to contain naturally occurring asbestos (NOA) and to release elongated mineral particles corresponding to asbestos fibers, or asbestos-like fibers, into the air. The calcic amphiboles were characterized using electron microprobe analysis, scanning and transmission electron microscopy. The results underline that fibrous occurrences of actinolite and ferro-actinolite regularly occur in hydrothermally altered dolerites, both in the groundmass and in quartz veins. In the groundmass, actinolitic amphiboles crystallize at the expense of magmatic clinopyroxenes and are rarely fibrous. Conversely, actinolite and ferro-actinolite fibers from quartz veins are potentially asbestiform to clearly asbestiform. The identification of quartz veins in hydrothermally altered dolerites is, therefore, an important parameter which should draw attention to the possible presence of asbestiform actinolite fibers. The mineralogical characterization of such veins as well as the estimation of their thickness and density is an important point to consider during studies involving NOA issues. Moreover, the degree of weathering of the dolerites, which directly affects the ability of non-asbestiform actinolite crystals to dissociate into very thin fibers, regarded as cleavage fragments instead of as asbestos, is also a key parameter to consider. Hydrothermally altered dolerites are common rocks likely to be exploited by the quarrying industry to produce aggregates or to be affected by construction works. Due to the abundance of actinolite fibers that they may contain locally, these rocks become priority targets to be monitored in terms of geological characterization and airborne fiber emission to ensure the protection of populations and workers.  相似文献   

Mineralogy and geochemistry of Neoproterozoic siliceous manganese formations from Ntui–Betamba (Cameroon Pan-African Fold Belt): implications for mineral exploration     

Ngnotue Timoleon  Ganno Sylvestre  Gus Djibril Kouankap Nono  Nzenti Jean Paul 《International Journal of Earth Sciences》2015,104(5):1123-1138

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Depositional age and tectonic environment of the Gouap banded iron formations from the Nyong group,SW Cameroon:Insights from isotopic,geochemical and geochronological studies of drillcore samples     

Landry Soh Tamehe  Chongtao Wei  Sylvestre Ganno  Carlos Alberto Rosiere  Jean Paul Nzenti  Chesther Gatse Ebotehouna  Guanwen Lu 《地学前缘(英文版)》2021,12(2):549-572

The discovery of the Gouap banded iron formations(BIFs)-hosted iron mineralization in the northwestern of the Nyong Group(Ntem Complex)in southwestern Cameroon provides unique insights into the geology of this region.In this contribution,we firstly report detailed study of geochemistry,isotopic and geochronology of well preserved samples of the Gouap BIFs collected from diamond drillcores.The Gouap BIFs consist mainly of amphibole BIFs and amphibole-pyrite BIFs characterized by dominant Fe₂O₃+SiO₂contents and variable contents of CaO,MgO and SO₃,consistent with the presence of amphibole,chlorite,epidote and pyrite,formed during amphibolite facies metamorphism and overprinted hydrothermal event.The amphibole–pyrite BIFs are typically enriched in trace and rare earth elements(REE)compared to the amphibole BIFs,suggesting the influence of detrital materials as well as secondary hydrothermal alteration.The Post Archean Australian Shale(PAAS)-normalized REE–Y profiles of the Gouap BIFs display positive La,Eu anomalies,weak negative Ce anomalies,indicating a mixture of low-temperature hydrothermal fluids and relatively oxic conditions probably under relative shallow seawater.We present here the first isotopic data of BIFs within the Ntem Complex.Theδ³⁰Si_NBS28values of the quartz from the Gouap BIFs vary from-1.5‰to-0.3‰and from-0.8‰to-0.9‰for the amphibole BIFs and amphibole–pyrite BIFs,respectively.The quartz hasδ¹⁸OV-SMOW values of 6.8‰–9.5‰(amphibole BIFs)and 9.2‰–10.6‰(amphibole–pyrite BIFs).The magnetite from the Gouap BIFs showsδ¹⁸O values ranging from-3.5‰to-1.8‰and from-3‰to-1.7‰for the amphibole BIFs and amphibole–pyrite BIFs,respectively.Moreover,the pyrite grains in the amphibole–pyrite BIFs displayδ34S values of 1.1‰–1.8‰.All isotopic data of the Gouap BIFs confirm that they might have precipitated from low-temperature hydrothermal fluids with detrital input distant from the volcanic activity.According to their geochemical and isotopic characteristics,we propose that the Gouap BIFs belong to the Superior type.In situ U–Pb zircon dating of BIFs was conducted to assess the BIF depositional age based on strong evidence of zircon in thin section.The Gouap BIFs were probably deposited at 2422±50 Ma in a region where sediments extended from continental shelf to deep-water environments along craton margins like the Caue Formation of the Minas Supergroup,Brazil.The studied BIFs have experienced regional hydrothermal activity and metamorphism at 2089±8.3 Ma during the Eburnean–Transamazonian orogeny.These findings suggest a physical continuity between the protocratonic masses of both Sao Francisco and Congo continents in the Rhyacian Period.  相似文献   

Aquifer parameter estimation using tide-induced water-table fluctuations in the Biscayne Aquifer,Miami-Dade County,Florida (USA)     

Rogers  Martina  Sukop  Michael C.  Obeysekera  Jayantha  George  Florence 《Hydrogeology Journal》2023,31(4):1031-1049

The Biscayne Aquifer (Florida, USA) is a coastal, shallow, unconfined, and heterogeneous aquifer with high water tables, composed of less-permeable sand to highly permeable karstic limestone. These properties make the Biscayne Aquifer one of the world’s most productive groundwater resources. The aquifer’s high yield and non-Darcian flow cause challenges for estimating aquifer parameters, which are essential for understanding groundwater processes and managing and protecting the groundwater resources. Water-table fluctuations in the Biscayne Aquifer are associated with astronomical tidal forces and gate operations on canal water-control structures. Analysis of observed groundwater level fluctuations can provide an understanding of the connectivity between the aquifer, Biscayne Bay, and the water level in the canals. Further, groundwater level fluctuations can be used for aquifer parameter estimation. In this research, observed ocean water levels measured at tidal stations and groundwater levels are fitted to Jacob’s analytical solution, where the amplitude of the groundwater head fluctuation decreases exponentially, and the time lag increases with distance from the shore. Observed groundwater levels were obtained from monitoring wells along the Miami-Dade shore and the barrier island of Miami Beach. Results indicate that Jacob’s solution is effective for aquifer parameter estimation in Miami Beach, where monitoring wells are closer to the shore. Estimated hydraulic conductivity appears to increase by four orders of magnitude to approximately 1 m s^–1 as the distance from shore increases. Constructing monitoring wells closer to the shore in Miami-Dade County and elsewhere would permit improved aquifer parameter estimation and support enhanced groundwater modeling efforts.

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Response of antioxidant systems to copper in the gills of the clam Ruditapes decussatus   总被引：1，自引：0，他引：1  

Geret F  Serafim A  Barreira L  Bebianno MJ 《Marine environmental research》2002,54(3-5):413-417

Copper (Cu) is an essential element for biological systems, however, when present in excess, is toxic. Metallothioneins can play an important role in Cu homeostasis and detoxification. Moreover, Cu can catalyse the production of toxic hydroxyl radicals that cause lipid peroxidation but defence systems in the cells can limit the oxidative damage. The present study was performed to investigate the effect of three Cu concentrations (0.5, 2.5 and 25 microg l(-1)) on the response of antioxidant enzyme activities (superoxide dismutase (SOD), catalase (CAT), selenium-dependent glutathion peroxidase and total glutathion peroxidase), total proteins, metallothioneins (MT), malondialdehyde (MDA) concentrations in the gills of the clam, Ruditapes decussatus. The activity of antioxidant enzymes and total proteins, MT and MDA concentrations were measured in the gills of the clams after 1, 3, 7, 14, 21 and 28 days of Cu exposure. Results indicate that Cu only induces an imbalance in the oxygen metabolism during the first week of Cu exposure due to a decrease in mitochondrial SOD and CAT, selenium-dependent and total glutathion peroxidase activities. Cu also causes lipid peroxidation, measured by the MDA formation, that was Cu dependent. In the gills of clams exposed to 25 microg Cu/l, the excess of Cu triggers the induction of MT synthesis after 3 days of exposure.  相似文献   

A complete hydro-climate model chain to investigate the influence of sea surface temperature on recent hydroclimatic variability in subtropical South America (Laguna Mar Chiquita,Argentina)     

Magali Troin  Mathieu Vrac  Myriam Khodri  Daniel Caya  Christine Vallet-Coulomb  Eduardo Piovano  Florence Sylvestre 《Climate Dynamics》2016,46(5-6):1783-1798

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Geochemical Fingerprint and Iron Ore Potential of the Siliceous Itabirite from Palaeoproterozoic Nyong Series,Zambi Area,Southwestern Cameroon          下载免费PDF全文

Sylvestre Ganno  Cyriel Moudioh  Adjija Nzina Nchare  Gus Djibril Kouankap Nono  Jean Paul Nzenti 《Resource Geology》2016,66(1):71-80

The study area forms part of an emerging iron ore province of southern Cameroon. Geochemistry analyses reveal that the siliceous itabirite has a very simple chemical composition, with Fe₂O₃ and SiO₂ representing more than 96 wt.% of the average composition; suggesting chemical precipitates of silica and iron. Low Al₂O₃ and TiO₂ concentrations and a weak positive correlation between them point to a minor detrital component in the precipitated marine sediments. The Si/Al ratio (average 52.7) indicates the hydrothermal origin of the studied itabirite. The Al–Si discrimination diagram supports this interpretation through the plot of all data in the hydrothermal field. The studied samples have low iron content (about 39.32% Fe), high gangue content (40.97% SiO₂ and 1.3 % Al₂O₃) and low concentration of the deleterious elements (0.16 % P and < 0.01% S). The main gangue mineral is silica which can be efficiently removed from iron ores during preparation of raw materials for the blast furnace process. According to commercial standards for crude iron ores, it may be concluded that the Zambi iron ores are a low‐grade magnetic ore that can be profitably exploited for the production of iron for steel production.  相似文献   

Influence of chronic exposure to silver and mercury in the field on the bioaccumulation potential of the bivalve Macoma balthica     

Florence Boisson  Mark G.J. Hartl  Scott W. Fowler  Claude Amiard-Triquet   《Marine environmental research》1998,45(4-5)

In order to assess the adaptation to metals previously observed in the bioindicator organism, Macoma balthica, subjected to chronic contamination by silver and mercury in the French Loire estuary, the bioaccumulation potential of individual organisms originating from the contaminated Loire estuary and a relatively uncontaminated control estuary (Somme) was evaluated using both radiotracers and stable isotopes of Ag (80 μg Ag litre⁻¹) and Hg (100 μg Hg litre⁻¹). Clams from the contaminated estuary were more sensitive to Ag (LT₅₀ = 9d) than those originating from the Somme estuary (LT₅₀ > 15d), even though the former bioaccumulated Ag to a significantly lower degree. This is attributed to a consequence of the chronic stress induced by Ag while clams were living in their natural environment. Therefore, past history of trace metal contamination should be considered when evaluating the susceptibility of M. balthica to heavy metal exposure. Lower uptake rates obtained for Hg (during the initial uptake phase only) and for Ag in clams from the polluted estuary suggest the presence of an adaptive trait for survival in contaminated areas. However, the lower degree of bioconcentration observed for Ag was not sufficiently low to reduce the sensitivity of the organisms to Ag and allow them to resist the toxic stress. Clams that survived Ag or Hg exposure at LT₅₀ did not protect themselves against metal toxicity by accumulating a significantly lesser amount of these metals than clams which did not survive metal stress. The results suggest that the bioaccumulation potential of each individual was not a factor which can explain the survival ability of M. balthica exposed to chronic Ag and Hg contamination in estuaries. In this case, cellular, biochemical and genetic levels of adaptation are presumed to be of greater importance.  相似文献   

The suitability of annual tree growth rings as environmental archives: Evidence from Sr,Nd, Pb and Ca isotopes in spruce growth rings from the Strengbach watershed     

Peter Stille  Anne-Désirée Schmitt  François Labolle  Marie-Claire Pierret  Sophie Gangloff  Florian Cobert  Eric Lucot  Florence Guéguen  Laure Brioschi  Marc Steinmann  François Chabaux 《Comptes Rendus Geoscience》2012,344(5):297-311

The combination of the Sr, Nd and Pb isotope systems, recognized as tracers of sources, with the Ca isotope system, known to reveal biology-related fractionations, allowed us to test the reliability of spruce (Picea abies) growth rings as environmental archives through time (from 1916 to 1983) in a forest ecosystem affected by acid atmospheric deposition. Sr and Pb isotopes have already been applied in former tree-ring studies, whereas the suitability of Nd and Ca isotope systems is checked in the present article. Our Sr and Nd isotope data indicate an evolution in the cation origin with a geogenic origin for the oldest rings and an atmospheric origin for the youngest rings. Ca isotopes show, for their part, an isotopic homogeneity which could be linked to the very low weathering flux of Ca. Since this flux is weak the spruces’ root systems have pumped the Ca mainly from the organic matter-rich top-soil over the past century. In contrast, the annual growth rings studied are not reliable and suitable archives of past Pb pollution.  相似文献   

Global,regional and local scale factors determining glaciation extent in Eastern Siberia over the last 140,000 years     

Gerhard Krinner  Bernhard Diekmann  Florence Colleoni  Georg Stauch 《Quaternary Science Reviews》2011,30(7-8):821-831

The aim of this work is to evaluate the effect of variations of greenhouse gas concentrations, orbital parameters, sea-surface conditions, vegetation and dust deposition on the extent of East Siberian mountain glaciations during the late Quaternary. An atmosphere-only general circulation model is used in a series of 16 sensitivity tests at high spatial resolution over the region of interest to systematically evaluate the relative importance of these different forcing parameters. No attempt was made to reproduce in detail the history of late Quaternary mountain glaciations in East Siberia, because, given (a) the temporal and spatial scarcity of available evidence of mountain glaciations in this region and (b) the large uncertainties concerning the boundary conditions to be prescribed in this model, such an exercise must necessarily remain incomplete and partially inconclusive. The results of this study suggest that moisture delivery from the Atlantic is an important factor determining mountain glacier mass balance in Eastern Siberia and is very sensitive to the geometry of the West Eurasian ice sheet. This means that variable moisture blocking by the West Eurasian ice sheet during the Weichselian is the most important single factor explaining the opposite history of glacier and ice sheet extent in West and East Eurasia during the Weichselian. This work confirms earlier results showing that the large 140 kyr BP West Eurasian ice sheet caused regional-scale cooling extending towards Eastern Eurasia. Nevertheless, the simulated response of the regional summer temperature (and thus glacier extent because of the strong dependency of glacier mass balance of summer melt rates) is to a very large extent directly determined by insolation. For the Early Weichselian, this leads to a clear maximum of local glacier extent at 70 kyr BP, which is in line with the variations of top-of-the-atmosphere insolation on orbital time scales, but to some degree at odds with geological evidence which suggests larger glacier extent at 115 and 90 kyr BP than at 70 kyr BP. Through snow feedbacks, the effects of changes in the prescribed vegetation distribution and dust deposition rate are also substantial. In summary, it appears that the broad features of late Quaternary glaciation history in Eastern Eurasia can be understood in terms of known forcings.  相似文献