Mining Methods Vary Widely - Mining and the Environment: From Ore to Metal - page 236

TABLE 5.3
Seven Questions to Sustainability (from MMSD North America) - In 1999 the International Institute for Environment and Development was commissioned
by the World Business Council for Sustainable Development to undertake the Mining, Minerals and Sustainable Development (MMSD) project. MMSD North America was then formed
as a partnership of the International Institute for Sustainable Development and the Mining Life-Cycle Center at Mackay School of Mines, which produced The Seven Questions to
Sustainability: How to Access the Contribution of Mining and Minerals Activities

Engagement Are engagement processes in place and working effectively?

People Will people's well-being be maintained or improved?

Environment Is the integrity of the environment assured over the long term?

Economy Is the economic viability of the project or operation assured, and will the economy of the community

and beyond be better off as a result?

Traditional and Non-market Activities Are traditional and non-market activities in the community and surrounding area accounted for in a way

that is acceptable to the local people?

Institutional Arrangements and Governance Are rules, incentives, programmes and capacities in place to address project or operational consequences?

Synthesis and Continuous Learning Does a full synthesis show that the net result will be positive or negative in the long term, and will there

be periodic reassessments?

The above arguments perhaps over-state the virtues of heap leaching while understating
the potential problems. Heap leaching does have a signii cant role in the processing of oxi-
dized low grade gold and copper ores, but is unlikely to i nd further applications.

Closure
Rehabilitation of spent ore from heap leaching operations is relatively straightforward.
Rinsing is the i rst step as it utilizes the same application and containment facilities used
for leaching. Generally, up to eight pore volume displacements (Hutchison and Ellison
1992) will remove all but the smallest trace of reagents. Oxidizing agents such as hypochlo-
rite, peroxide or specially bred strains of reagent destroying bacteria may be added to the
rinse solution to reduce the required volume of rinse water. Intermittent rinsing is more
effective than continuous rinsing.
Following rinsing, the piping and other surface installations are removed as are the liners
from solution ponds and drains. The surface is then re-graded to construct a landform suited
to the required land use. Consideration of drainage from the heap is required, given that
the pad is usually retained, preventing downward drainage beneath the heap. This results in
seepages from the base of the heap, unless measures are implemented to collect and discharge
this drainage water. Generally, drains and ponds are back-i lled using the same materials
removed in their original construction, with further i lling using spent ore, if appropriate.
The heap is usually graded to produce a rounded, natural-looking proi le. Following appli-
cation of a layer of topsoil, if available, the entire surface can then be re-vegetated.

Dump Leaching

Dump leaching refers to leaching that takes place on an unlined surface. The term 'dump
leaching' derives from the practice of leaching materials that were initially deposited as
waste rock; however, it is now also applied to run-of-mine, low-grade sulphide or mixed