CGS Foreign Development Cooperation - Zambia

Assessment of the impacts of mining for copper-cobalt ores on the environment in the Copperbelt province, Zambia

The impacts of mining and mineral processing of copper and cobalt ores on the environment and health of the local population in the NW part of the Copperbelt province in Zambia were assessed during 2004–2006. To determine the extent of industrial pollution, the environmental geochemical mapping of stream sediments, soils and agricultural products was carried out in the area north of Kitwe, which is heavily affected by mining and processing of copper and cobalt ores in some parts. The first stage of mapping was carried out by a team of specialists from the Czech Geological Survey, Geological Survey of Zambia and Zambian University, School of Mines in the year 2002.

The aim of the project was to analyse the degree of contamination of stream sediments, soils and agricultural plants with toxic metals in a selected model area, to determine the effect of mining on the environment and to elaborate a long-term monitoring scheme of stream sediments and soils contamination. To achieve the aim of the project, geochemical  evaluation of essential types of materials deposited in spoil piles, in tailing impoundments and slag heaps, and the study of mechanisms of mobilization of toxic metals from the deposited anthropogenic materials were also carried out.

Two underground-mined ore deposits (Mufulira and Chambishi) and the Mufulira smelter and refi nery lie in the area of a model environmental geochemical study (scale 1:50,000; the total area of 429 km2). Large spoil banks, abandoned and active tailing impoundments and slag deposits occupy an area exceeding hundreds of hectares in the vicinity of the mines.

The area was covered by a semiregular network of the soil sampling (partly completed with the sampling of agricultural products) and stream sediments samples collected in the irregular network. It was found that the main sources of the contamination in the studied area are: (1) mining waters and seepage through the tailing dams, (2) wash-out of the finegrained material from spoil banks, and, (3) airborne particles from beaches of tailing impoundments, crushers and from the Mufulira smelter.

Washed-out finegrained material from spoil heaps sampled at the bottom of heaps contain up to 4 ppm As, 40 ppm Co, and 3200 ppm Cu. Heavy metals in airborne particles are bound mostly to the very fine sulphide fraction (pyrite, chalcopyrite, covelline, chalcocite and carrollite) found in washed-out materials from spoil-banks, in dust from slag deposits, and from smelter, as well as in the uppermost layers of soils close to mining and processing “hot spots”. A strong anthropogenic contamination by Co, Cu, Cr, Hg, Mo, and Se was detected in the stream sediments of the Musakashi, Chambeshi, and Mwambashi rivers that drain the Chambishi tailing ponds area.

To differentiate geological source, i.e. primary geochemical regional background of metals in soils and anthropogenic contamination, higher concentrations of metals in the surface layer of soil than in deeper soil horizon were considered to represent anthropogenic contamination caused mainly by airborne dust particles.

It was established that the degree of industrial contamination may be best expressed using the Coeffi cient of Industrial Pollution (CIP) which is a sum of the concentrations of selected metals in topsoil at the individual sampling point, divided by the median values of the same metals in topsoil of the whole region. In the Mufulira area, increased amounts of heavy metals were recorded in almost all collected agricultural products. Very high contents of Co (up to 78 ppm) and Cu (up to 372 ppm in dry matter- were found in cassava leaves closely to the Chambishi tailing impoundments.

The project documented that the results obtained from the geochemical mapping of stream sediments, soils and vegetation can be used to characterize an extent of contamination even in areas with multiple geological and anthropogenic sources of heavy metals. The results presented in the form of maps of CIP values can be used in allocating suitable land-use zones in town planning.

Public education in schools and training of Zambian experts formed an integral part of the project.