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The mineral sands industry operated in the Myall Lakes area on the central
coast of New South Wales, Australia, between 1974 and 1983. This reserve of
heavy minerals was contained in a massive dune of wind-deposited sand, reaching
heights of over 100 in, which stretches for 17 km and is covered in eucalyptus
forest. This was the first time a high dune had been dredged and rehabilitated
on a continuous basis. Some problems arose during operations. For example, the
mined sand slumped back into the dredge pond making it impossible to rebuild the
dune. A technique was developed to dewater the newly restored dune so that it
would remain in a stable condition.
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Bridge Hill Ridge during mining.
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The objective of the rehabilitation program was to re-establish a dry forest
on the mined dune. Rehabilitation was to be carried out continuously behind the
mining operation, commencing as soon as the mined sand (tailings) were
contoured. Topsoil from the next section of the operation was spread on newly
formed tailings so that all the valuable attributes, such as organic matter,
plant nutrients, microorganisms and seeds suffered minimal deterioration.
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Bridge Hill Ridge after mining.
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Other innovative practices included: the collecting of seeds from trees and
shrubs on the mining path to ensure that the same types of plants were used;
the direct planting of seeds of indigenous species; the large-scale raising
of nursery stock of a wide range of species; and, mulching with vegetation
collected on the mining path.
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Temporary plastic mesh fences were erected on the newly planted areas to
protect young growth from wind damage in the first couple of years of
rehabilitation. Dune heights and major dune conformations were re-established,
and a vegetative cover in various stages of progression towards a mature forest
now covers the mined dune.
The mined and rehabilitated area is now part of the Myall Lakes National
Park. Various species of fungi, lichens and ground orchids have returned to the
area, and the system is developing into a dynamic forest ecosystem.
Harsh climatic and on-site conditions at the mine include an average of five
inches precipitation annually, and a day to night temperature variation of 23
degrees Fahrenheit during the growing season. Highs can reach 100 degrees for
days at a time. A natural lack of plentiful topsoil, high saline/sodic; levels,
and low available soil water on the neutralized heap leach pads were additional
site specific constraints. Over a five year period starting in 1995, HMC and
their consultants including Harding Lawson Associates, combined field and
laboratory research to determine the most effective reclamation procedures to
reclaim neutralized heap leach pads under these adverse site conditions. Test
plots evaluated both revegetation techniques and plant species best suited to
the site. Unfortunately, characteristics of the neutralized heap material
necessitated additional effort. A Bench Scale Column Test was performed in the
lab using soil samples and on-site well water to remove residual salts from the
root zone. Test results showed that 5-10 inches of well water leached out the
salts, and that 3-6 inches of top soil significantly reduced the upward
migration of salts. These results provided the technical basis for implementing
the current reclamation program. By 1997, site work had begun and the heap I
each pads were recontoured to ensure slope stability and revegetation. Top soil
was applied, and temporary irrigation was installed early in 1998. The pads were
seeded and mulched as the site awaited the warm growing season temperatures.
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