Improving Management at Mine Site Pit Lakes

CIM Vancouver 2002
John Crusius, Roger Pieters, Albert Leung, Phil Whittle, Tom F. Pedersen, Greg Lawrence,
Abstract Scientists at Lorax Environmental and UBC
are conducting a three year research program,
funded by NSERC and industry, to determine
the processes controlling pit lake chemistry
and to further validate a coupled
physical-geochemical model. This model will
provide scientifically-defensible predictions of
pit lake water quality over time. The field work
is being carried out on the Main Zone and
Waterline pit lakes at the site of the
now-closed Equity Silver mine near Houston,
BC. The Main Zone pit currently has hydroxide
sludges, a by-product of ARD treatment, being
discharged to surface waters, while the
Waterline pit has no discharges. Initial results
reveal that both pit lakes were well stratified
from June through August. The Main Zone pit
was well oxygenated to the bottom, due to the
sinking of O2-rich sludge. By contrast, the
Waterline pit was anoxic below 10 m due to
the absence of a source of O2 to deep waters.
Initial results reveal elevated concentrations of
Zn, Cu and Cd in the surface waters of both
pits. The physical and biogeochemical
controls of metal concentrations in surface
and deep waters will be discussed to further
our understanding of the controls in a wide
variety of pit lakes.
Keywords: Model, metal, Water quality, ARD, anoxia, pit lake, Sludge, Geochemistry
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