< Terug naar vorige pagina


Mineralogical and geochemical characterization of Mo-rich black shales inthe Grand Duchy of Luxembourg

Tijdschriftbijdrage - Tijdschriftartikel

“Schistes carton”, Jurassic black shale rocks occurring in the south-western part of the Grand Duchy of Luxembourg, were investigated, based on a combined mineralogical and geochemical approach. The major aimof this study was to understand the lateral and vertical variation in mineralogy, and the distribution of major andtrace elements within the different black shale lithologies, as well as in the overlying soils. The mobility of tracemetal(loids) in the black shale and in the soil developed upon the black shale was also addressed. The “Schistescarton” bedrock consists mainly of illite and kaolinite, quartz, calcite and pyrite. Framboidal pyrite is found inthe clay matrix, while stratiform pyrite lenses are found in calcitic beds or in lag deposits. At a depth of 4.25 m,pyrite is altered to goethite and gypsum. The acidity generated by pyrite oxidation is neutralized by calcitedissolution, resulting in neutral to slightly alkaline pH conditions. The “Shistes Carton” bedrock is characterizedby variable concentrations of Ca, S, Cd, Mo and Zn. Compared to the surrounding matrix, the (stratiform) pyritesfound in the “Schistes carton” express an enrichment with As, Cd, Pb and Zn, while the lag deposit containedhigh concentrations of As, Cd, Mn, Zn, and P. Mo concentrations in the bedrock and the soils up to 74 mg/kgwere found, which is comparable with Mo concentrations in soils developed on black shales at other locations inthe World. Most trace elements are not leached from the shales under the prevailing pH conditions (7–7.5),except Mo, which leaches in concentrations up to 85 μg/l. This study highlights the importance of small andlarge-scale variations in bedrock composition and its influence on soil geochemistry, which should be taken into account during the development of national and regional guidelines and regulations on soil quality.
Tijdschrift: Journal of Geochemical Exploration
ISSN: 0375-6742
Issue: 206
Volume: 206
Aantal pagina's: 18
Jaar van publicatie:2019
Trefwoorden:Geowetenschappen en technologie