Environmental contamination caused by uranium mining is becoming a worldwide issue due to its negative impact on the environment. The aim of this study is to evaluate the contamination levels of riparian forest stands and their interaction with pollutants on the example of two localities with long and short-term uranium mining closure. Notably high Cu content, which exceeded the lower range of the toxicity limit in 50–75% of the cases, was detected in the leaves. Increased U content also represents a potential risk. As both of the elements have a negative effect particularly on the root system, it can be assumed that the soil-stabilizing and water erosion-reducing functions of the stands may be reduced. Extremely high U content (51.8 mg/kg DA) in the leaves of Aesculus hippocastanum L. indicates its potential for phytoremediation. Significantly higher U content determined at the locality with the long-term closure of mining was probably caused by the instauration of the shallow hydrogeological circulation after mine inundation. Strong correlation between U and Pb suggests identical trend of their uptake and accumulation by plants. A significant dependence of the level of contamination on the distance from its source was not demonstrated. Therefore, the management of mining areas should focus on the protection of riparian forest, which can through its stabilizing and erosion-reducing functions and through suitable species composition effectively prevent spreading of contamination.
Vulkano-plutonicka asociace alkalických hornin a karbonatitů
Mushugai Khuduk (jižni Mongolsko) je prostoupena řadou žilných
intruzi. Clanek popisuje nový nalez intermedialnich lamprofyrů
(SiO2 53 hmot. %). Mineralogicke složeni studovaných žil
odpovida augitickým minetam, ktere přechazeji do převladajicich
kersantitů. Lamprofyry obsahuji hojne xenokrysty a leukokratni
ocellarni inkluze. Lamprofyry vystupuji v prostorove asociaci s
apatitem bohatými žilnými horninami (nelsonity), ktere vykazuji
texturni doklady miseni mezi silikatovou a karbonatitovou
taveninou. Přitomnost vapenato-alkalických lamprofyrů spolecně
s nelsonity a karbonatity ukazuje na důležitou interakci
metasomatizovaneho (flogopit-klinopyroxen-apatit)
litosferickeho a na CO2 bohateho astenosferickeho plastě při
genezi riftove vulkano-plutonicke asociace Mushugai Khuduk.
Abstract Heavy rare earth elements (HREE) are dominantly mined from the weathering crusts of granites in South China. Although weathering processes occur globally, no economic HREE resources of this type have yet been found outside China. Here, we report the occurrence of unidentified REE minerals in the granites from South Chinese deposits. They contain high levels of both HREE and light REE, but are strongly depleted in Ce, implying high oxidation state. These REE minerals show higher initial Nd isotope than primary REE-rich minerals ( ɛ Nd( t )=0.9±0.8 versus −11.5±0.5). The mineralized weathering crusts inherited REE signature of the granites, but show more Ce depletion and more overall concentration of the REE. We propose, therefore, that highly oxidized, REE-rich fluids, derived from external, isotopically depleted sources, metasomatized the granites, which resulted in Ce depletion as Ce 4+ and enrichment of the remaining REE, especially the HREE, contributing to formation of a globally important REE resource.
Volcanic-plutonic alkaline complexes from Lugiin Gol, Mushgai Khudag and Bayan Khoshuu, southern Mongolia (244, 139 and 131 Ma, respectively) occur within grabens in E-W lineaments. They are represented by syenitic rock-types (silica undersaturated to slightly silica oversaturated) potassic rocks and are associated to stockworks of carbonatitic veins, dykes and so on. Geochemical characteristics and isotope systematics point to a veined mantle source particularly enriched in LILE and LREE. The carbonatitic veins show high contents of Ba, Sr, Th and REE and are suitable as potential ore deposits.
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