Bulletin of the Geological Society of Finland (Jun 1994)
Alteration of podzolized tills by acid load near Ni-Cu smelters at Monchegorsk, Kola Peninsula, Russia
Abstract
Mineralogy and geochemistry of podzolized tills was studied in the area of dieback forest near the Ni-Cu smelters at Monchegorsk, and less extensively forest damage near by Apatity and Kirovsk in the Russian Kola Peninsula. The abundances of main elements (Si, Al, Fe, Mg, Ca, K, Na) in the <64 μm fraction were determined by the hot aqua regia digestion method and inductively coupled plasma spectrometry. The clay mineralogy of the silt plus clay fraction was examined by X-ray diffraction after selective extraction and heating treatments. At all study sites, trioctahedral mica and chlorite were totally weathered from the silt and clay fraction (<64 μm) of the eluvial layer, leaving behind interstratified mica-vermiculite-smectite clays. In general, the mixed-layer clay of the eluvial layer had low levels of hydroxy interlayering. Illuviated layers were characterized by hydroxy interlayered vermiculite-chlorite. The abundance of chlorite and mica was greater, and the degree of interlayering lower, in parent tills than in the overlying illuviated layers. Regardless of differences in bedrock and till geochemistry, the weathering sequence throughout the podzolized till profile was coherent at most of the sampling sites. Exceptionally, in a few profiles sampled at the totally destroyed forest site, the swelling mixed-layer clay of the eluvial layer displayed a neochloritized structure. On the basis of XRD patterns and geochemistry of the samples, it was inferred that a short-term decomposition of plagioclase had promoted, via inputs of Al-hydroxides, the transformation of mica-vermiculite-smectite to a poorly crystalline interstratification of chlorite-aluminous montmorillonite. The accelerated weathering occurring occasionally in exposed places was probably activated by the strongly acidic load in the vicinity of the smelters and the city of Monchegorsk.
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