This paper presents the results of a lysimeter experiment in which a forest soil has been artificially spiked with rock fragments from natural copper (Cu) and cobalt (Co)-hills from Tenke-Fungurume (Democratic Republic of Congo). The Cu and Co contents of the percolating water have been analysed at repeated intervals and the impact of rock on the soil properties was evaluated at the end of the experiment. Five rocks were sampled in one copper hill. In natural conditions, these rock fragments located on the top of the hill are mixed to surface soil horizon along the slope through colluvial processes. The Cu and Co contents in rocks range respectively between 470 mg/kg (siliceous rock) and 140,000 mg/kg (shale) and between 450 mg/kg (dolostone) and 5300 mg/kg (shale). Rock fragments were mixed with two horizons (hemi-organic A with 2.7% total organic carbon (TOC), and mineral B with 0.3% TOC) of an acid (pH water < 4.5) acrisol under forest. The mixture was placed in 1 L lysimeters and left in Lubumbashi ex situ conditions during the rainy season. Percolating water was collected for six periods after and the Cu and Co contents have been analysed. At the end of the experiment, soil from the lysimeter was removed for pH, TOC, available nutrients and trace elements, CaCl 2-extractable Cu and Co analysis. The results show great differences between Cu and Co releases in the percolating solutions according to the nature of the rocks. The quantities released were correlated to the concentrations originally present in the unweathered rocks. Differences were also found between the A and B horizons, which indicate that the physicochemical properties of the soil influence reaction with the rocks. The differences between both horizons are mainly organic carbon content, cationic exchange capacity and nutrient content, which were higher in the A horizon. However, the pH of the A horizon was acidic compared with the B horizon. Significant correlations were found between extractable Cu and Co with concentrations of their leaching solution. Because of this, soluble Cu and Co extracted by CaCl 2 can be regarded as vertical transfer risk prediction tools of Cu and Co in the soil. ecosystems of some copper hills to evaluate Cu and Co mobility in soil-plant systems (

Our study aimed at deepen our understanding of relationships between soil properties and vegetation distribution in metalliferous ecosystems of Tenke-Fungurume in the Democratic Republic of Congo. The first question concerned the differences and similarities between soils of the main vegetation units and four variation factors of soil properties were summarized by multivariate analysis. They were all linked to lithology and significantly contributed to explain the distribution of vegetation units. Our result suggest that the variation of soil properties which is observed within the various vegetation units (rocky steppe savanna, sward, and steppe savannas on slope or on Dembo) should partially be attributed to differences of geochemical composition of rocks between sites but the main source of variability is to be found inside each hill. The soil contamination in Cu and Co originates from rock weathering and besides site effect and topographic distribution of the rocks, the variability of soil properties within one vegetation unit may be due to variability of soil parent material and not only to erosion. The second question dealt with the changes of soil properties at small distances. Metric variation was studied from transects between adjacent vegetation units. Our results showed that the abrupt changes of vegetation units which were clearly identified on the field were all truly explained by the variations of one or more properties linked to lithology. The key point being the Cu bioavailability.