We studied the heavy mineral fraction, separated from mining- and smelter-affected topsoils, from both a humid subtropical area (Mufulira, Zambian Copperbelt) and a hot semi-arid area (Tsumeb, Namibia). High concentrations of metal(loid)s were detected in the studied soils: up to 1450mgAskg(-1), 8980mgCukg(-1), 4640mgPbkg(-1), 2620mgZnkg(-1). A combination of X-ray diffraction analysis (XRD), scanning electron microscopy (SEM/EDS), and electron probe microanalysis (EPMA) helped to identify the phases forming individual metal(loid)-bearing particles. Whereas spherical particles originate from the smelting and flue gas cleaning processes, angular particles have either geogenic origins or they are windblown from the mining operations and mine waste disposal sites. Sulphides from ores and mine tailings often exhibit weathering rims in contrast to smelter-derived high-temperature sulphides (chalcocite [Cu2S], digenite [Cu9S5], covellite [CuS], non-stoichiometric quenched Cu-Fe-S phases). Soils from humid subtropical areas exhibit higher available concentrations of metal(loids), and higher frequencies of weathering features (especially for copper-bearing oxides such as delafossite [Cu(1+)Fe(3+)O2]) are observed. In contrast, metal(loid)s are efficiently retained in semi-arid soils, where a high proportion of non-weathered smelter slag particles and low-solubility Ca-Cu-Pb arsenates occur. Our results indicate that compared to semi-arid areas (where inorganic contaminants were rather immobile in soils despite their high concentrations) a higher potential risk exists for agriculture in mine- and smelter-affected humid subtropical areas (where metal(loid) contaminants can be highly available for the uptake by crops).

BRGM Avenue Claude Guillemin 45082 Orléans Cedex 2 France

Czech Geological Survey Geologická 6 152 00 Praha 5 Czech Republic

Department of Geology Faculty of Science Palacký University in Olomouc 17 listopadu 12 771 46 Olomouc Czech Republic

Department of Geology Faculty of Science University of Namibia Private Bag 13301 Windhoek Namibia

Department of Soil Science and Soil Protection Faculty of Agrobiology Food and Natural Resources Czech University of Life Sciences Prague Kamýcká 129 165 21 Praha 6 Czech Republic

Institute of Geochemistry Mineralogy and Mineral Resources Faculty of Science Charles University Prague Albertov 6 128 43 Praha 2 Czech Republic

University of Zambia School of Mines P O Box 32 379 Lusaka Zambia

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Contaminant Binding and Bioaccessibility in the Dust From the Ni-Cu Mining/Smelting District of Selebi-Phikwe (Botswana)