OVERVIEW OF THE IMPACT OF MINING ON THE ... - IIED pubs

The MRC cannot be held responsible for any conclusions made or actions taken by the client
based on data presented in this report.
In addition, it is important to note that the time and budget constraints limited the ability of the Project Team to
provide a complete picture of every aspect of mining-related impacts on the water resources of the three river
basins considered. In particular, very little information was available for mining-related activities in the Angola,
Malawi, Tanzania and Mozambique sectors of the Zambezi basin. Nevertheless, in the professional opinion of
the Project Team members, sufficient information could be compiled and synthesized to provide an overview
that would meet the requirements set out in the Terms of Reference for this research topic.
1.3.4 Estimation of impacts
The impact of a particular mining or minerals processing operation on the biophysical environment can take the
form of either or both chemical and physical impacts. Chemical impacts include changes in acidity or alkalinity
levels, and the release of arsenic, mercury and other heavy metals, and the release of cyanide from gold mining
operations. These impacts are mainly the result of treatment of ore. Additional impacts occur as the result of
washoff of chemicals deposited onto the catchment surface from dusts, vapours and gases emitted from mining
operations. Typical physical impacts on the biophysical environment include: salinization, siltation (increased
levels of suspended and deposited solids), changed patterns of water use, the excavation of large pits, the
diversion of rivers and streams from their original courses, and deforestation / de-vegetation of sites.
The different types of typical chemical and physical impacts associated with different mining and mineral
processing operations are shown in Table 1.1 and Table 1.2, respectively. These descriptions provide an
overview of the specific types of impacts that are normally associated with the mining or processing of specific
minerals. In several cases, it is difficult to determine the specific impact exerted by a mining operation, because
the impact(s) will also depend on the degree of management control exerted during mining. The criteria used to
segment impacts into “high”, “medium” or “low” categories are given in Table 1.3 for each mining type.
Chemical impacts relate mostly to waste rock and low-grade ore dumps, which are present at all sites, and to
chemical treatment, with associated tailings dams, which are present at many mining sites. A wide variety of
chemical impacts are possible and these can include acid mine drainage, the less common alkaline mine
drainage, the release of highly toxic metals (most notably arsenic, antimony and mercury), the release of heavy
metals, such as nickel, copper, cobalt, lead and zinc, and the release of cyanide from gold mining operations.
Physical impacts on water resources include the use of water for a variety of mining operations, siltation of
water courses by contribution to suspended solids loads, salinization by contribution to dissolved solids loads,
the creation of large pits (that act as rain water traps), diversions of watercourses and sometimes associated
extensive deforestation or de-vegetation of mine sites with concomitant erosion problems. The area affected
can be segmented into three typical classes or groups, namely: the mine environs only (typically consisting only
of the mine property), the local area (one or more properties that are adjacent to the mine property), or more
widespread (regional).
On the basis of these impacts, mining and mineral processing operations could be classified into high impact,
medium impact and low impact, as shown in Table 1.3. These descriptors were then used in descriptions of the
scale and variety of impacts linked to mining activities in each of the sub-catchments.
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