Mining Methods Vary Widely - Mining and the Environment: From Ore to Metal - page 235

dumps. Spent heap leach ore from gold operations is usually strongly alkaline; mixing
waste types can help compensate for acidic waste rock (MMSD 2002). In terms of cata-
strophic failures, the history of heap and dump leaching is, in comparison to tailings
dams, very good. There have been no signii cant leach heap or dump slope failures
and no failure-related fatalities. Spent heaps are also more stable and easier to reclaim
than old tailings deposits, if for no other reason than their self-draining characteristics.
Thus, simply reducing reliance on conventional tailings disposal is of itself a move
towards more sustainable development (Leduc et al. 2004).

4. Economy - The obvious points here are that heap leach technology allows more ore to

be processed since a lower cut off grade results, allowing a longer life or a larger opera-
tion, or both. It is also less capital intensive and thus less sensitive to commodity price
l uctuations and generally a lower risk investment. Beyond these obvious answers lie
some other important considerations. Heap leach technology shifts the balance of invest-
ments, de-emphasizing capital in favour of operating expenses. Payments for operations
are something that the communities can generally share in to a greater extent than ini-
tial capitalization. Heap leaching also increases employment beyond the process circuit.

5. Traditional and non-market activities - By expanding employment in areas with transfer-

able skills, a more sustainable workforce results. While the tools and techniques used at
a modern mine are not directly applicable to traditional activities, certainly they have
more in common in the case of heap leaching then mill operations and maintenance.

6. Institutional arrangements and governance - The types of problems inherent to a heap

leach project tend to be more manageable at a local level. The typical threat from a
leach heap is excessive leakage from the leach pad during its operating life. At closure,
heaps are usually self-draining and thus the potential for post-closure leakage is sig-
nii cantly reduced.

7. Synthesis and continuous learning - Heap leaching has the potential for reducing all types

of impacts, improving economic benei ts in the local community and reducing economic
risk. It also leaves a more secure site after operations and thus reduces long-term environ-
mental liability. At the same time, it uses technologies that are both more locally available
and have more applications outside mining. Since the projects are less capital intensive
and typically subject to expansions or revisions in the leach pad and stacking operations
annually or bi-annually, project reevaluation is a deeply engrained part of the heap leach
culture. Expanding this to include the local community should be an easy step.

CASE 5.6
Heap Leaching Applied to Barrick Gold's Pierina Mine in Peru

Barrick's Pierina Mine in Peru uses heap leaching to
extract gold. Pierina was expected to produce more than
800,000 ounces of gold at a total cash cost of less than
$ 50 per ounce in 1999, making it the world's lowest-cost
major gold mine. The ore is stacked in a lined contain-
ment area behind a retention dam as depicted right.
A leach solution is applied to the top of the ore and
allowed to percolate through the heap. As the solution
migrates through the ore, it leaches the gold and silver
from the rock and holds it in a solution. The gold-bearing

solution is collected at the base of the leach pad
in the pore space within the heap. The pregnant
solution is pumped to the gold recovery plant
where suspended solids are removed and the
solution is then treated in a conventional Merrill-
Crowe precious metal circuit. The same valley-fi ll
system was successfully used at Barrick's Mercur
Mine in Utah. (Article and photo borrowed from
METSOC 2006)