ECOSYSTEMSOFTHEFUTURE
Transforming mining pits into sustainable habitats
DR CLINT MCCULLOUGH
PRINCIPAL ENVIRONMENTAL SCIENTIST, GOLDER ASSOCIATES
PRINCIPAL/SENIOR RESEARCH FELLOW,
MINE WATER AND ENVIRONMENT RESEARCH CENTRE
As anyone who has flown from Perth to Kalgoorlie, or into
the Pilbara, would have seen through their aircraft window –
mine pit lakes dot the Western Australia landscape. Indeed,
one estimate places their number at more than 1,800.
Given that open cut operations have only been in Western
Australia for some 50 years, with another century of mining
at higher rates and of lower grades ahead, we can expect
an increase in the size and number of mine pit lakes in the
next 50 years.
Mining is an extractive industry. When mining is
completed, more often than not, it leaves a void behind.
When open cut mining has been used, the voids can fill with
water from groundwater and/or surface flows to leave a pit
lake. Such pit lakes are often quite substantial size; hundreds
of metres to kilometers wide, and hundreds of metres deep.
Pit lakes result from mining of commodities ranging from
gold and coal (historically significant and, in the case of
coal, often vast wide lakes) to iron (more significant through
mining development over the next few decades) and future
mining opportunities such as uranium.
Pit lake water quality is determined by a variety of factors
including the geology, regional and local groundwater
regime, climate, geometry of the void, and the manner of pit
closure. Depending on these factors, lake water quality can
alter over the long durations that the pit lake will be part of
the closure landscape. In dry and arid environments lake
salinity may often increase over time, as it does in natural
WA lake systems which are often saline/hyper-saline. Of
greater challenge is Acid and Metalliferous Drainage (AMD)
that can significantly degrade mine water for millennia if
not managed well. Pit lakes represent new environments
that were not present prior to mining; a change from
terrestrial to aquatic-based habitats for plants and animals
in particular. These changes can present challenges to the
industry, especially at closure. Equally, pit lakes may also
often represent great opportunities.
As this pit lake in the South-West of WA shows, spectacular water colour can be caused
by poor water quality when pit lakes are acidified by acid and metalliferous drainage
MINESITE 2012
105