Geochemical Characterisation of Soils in the Impact Zone of the Zhitikara Chrysotile Asbestos Quarry (Kostanay Region, Kazakhstan)

Soils developing in ultramafic (serpentinite) provinces are naturally enriched in Mg, Ni and Cr, which makes it difficult to separate the natural geochemical background from technogenic contamination near chrysotile asbestos mining operations. This problem is examined for the agricultural soils in the impact zone of the Zhitikara chrysotile asbestos quarry (Kostanay Region, Kazakhstan), one of the largest such operations in the world. The elemental composition of the soils was characterised by portable X-ray fluorescence, verified against ICP-OES, and complemented by X-ray diffraction. When contamination was assessed against the global crustal background (upper continental crust), nickel and chromium appeared enriched; however, relative to the local geochemical background, these elements fall within the natural lithogenic range, showing that global crustal values generate false-positive contamination signals in ultramafic terrains. Magnesium was the only element enriched above the local background and the only one that decreased systematically with distance from the quarry, identifying it as the most sensitive tracer of aerogenic serpentinite dust among the elements measured. The discordance between total and acid-soluble chromium is consistent with chromium being hosted mainly in a refractory chromite phase, so that total chromium contents overestimate the environmentally relevant fraction. The study demonstrates the pitfall of applying global crustal backgrounds in ultramafic provinces and supports a locally referenced, differentiated approach to soil-contamination assessment in such settings.