Gold Mining in Siberia as a Source of Mercury Contamination of the Environment
369
background underground waters. Hence, concentration of suspended mercury
forms and enrichment of suspended matter with the metal are better indicators
of water reservoir contamination than the content of dissolved mercury.
5.5
Bottom Sediments
One of the most dangerous effects caused by mining of gold placer deposits is a
significant increase in turbidity of natural water streams, resulting in silting of
riverbeds and deterioration of feeding base of fisheries as well as a steady
mercury contamination of bottom sediments of industrial water reservoirs.
During emergency discharges of waste waters from such reservoirs or flood
erosion of dams and dikes, a potential danger of mercury contamination of
natural water streams is created.
Mercury concentrations in bottom sediments in background waters Siberia
range within narrow intervals from 0.01 to 0.18 mg/kg (Anoshin et al. 1995
Laperdina et al. 1995, 1996; Roslyakov and Kirillova 1995). Hence, the background
water streams of the studied areas fall in the category of unpolluted.
As the results of the studies carried out in the gold mining areas of the Chita
Oblast (Laperdina et al. 1995, 1996; Tupyakov et al. 1995), Buryatia (Taisayev
1991) and the Krasnoyarsk Krai (Roslyakov and Kirillova 1995) have shown that
the mercury content in bottom sediments of technogenic water streams and
reservoirs ranges widely from 0.01 to 54.2 mg/kg (Table 1). The most intensive
mercury contamination of bottom sediments is observed in the area of the
Lyubov mine. High concentrations of mercury (0.43-54.2 mg/kg) were found in
silts of the former tailings dump of the gold-extracting plant. The elevated
mercury content (0.42-1.29 mg/kg) was found in bottom sediments of the river
Khangaruk, subjected to a vigorous influence of the tailings dump of the GEP.
The former dredge pit, located in the bed area of this river, is also characterized
by a high mercury content (2:83 mg/kg).
The study of bottom sediments of techno genic mercury flux formed by the
tailings dump of the GEP (Buryatia) has shown that dam break of the tailings
dump has resulted in the formation of highly contrasted and extended (more
than 12 km) lithochemical mercury (1-5 mg/kg) and gold (0.5-4.0 mg/kg) flux
due to mechanical migration. Accumulation of technogenic materials, silting of
boulder and cobble bed, formation of technogenic dune ranges and bars took
place over the first 3 km along the river bed. Further, transportation of
technogenic materials prevails and silting of boulder and cobble bed are
observed at some places. In the period of low water, the floodplain of the
river and, in some places, of the river bed are covered with a crust of technogenic
silt.
Similar steady, contrast and extended (about 17 km) mercury dispersion flux
(0.04-3.0 mg/kg) is registered in the Krasnoyarsk Krai in the Bogunay river,
eroding mine heaps. Gold mining was stopped 50 years ago but the contrast of
technogenic mercury flux is still retained. Mercury content in bottom sediment
of the river, 7 km upstream from the mine, varies between 0.03 and 0.18 mg/kg,
369
background underground waters. Hence, concentration of suspended mercury
forms and enrichment of suspended matter with the metal are better indicators
of water reservoir contamination than the content of dissolved mercury.
5.5
Bottom Sediments
One of the most dangerous effects caused by mining of gold placer deposits is a
significant increase in turbidity of natural water streams, resulting in silting of
riverbeds and deterioration of feeding base of fisheries as well as a steady
mercury contamination of bottom sediments of industrial water reservoirs.
During emergency discharges of waste waters from such reservoirs or flood
erosion of dams and dikes, a potential danger of mercury contamination of
natural water streams is created.
Mercury concentrations in bottom sediments in background waters Siberia
range within narrow intervals from 0.01 to 0.18 mg/kg (Anoshin et al. 1995
Laperdina et al. 1995, 1996; Roslyakov and Kirillova 1995). Hence, the background
water streams of the studied areas fall in the category of unpolluted.
As the results of the studies carried out in the gold mining areas of the Chita
Oblast (Laperdina et al. 1995, 1996; Tupyakov et al. 1995), Buryatia (Taisayev
1991) and the Krasnoyarsk Krai (Roslyakov and Kirillova 1995) have shown that
the mercury content in bottom sediments of technogenic water streams and
reservoirs ranges widely from 0.01 to 54.2 mg/kg (Table 1). The most intensive
mercury contamination of bottom sediments is observed in the area of the
Lyubov mine. High concentrations of mercury (0.43-54.2 mg/kg) were found in
silts of the former tailings dump of the gold-extracting plant. The elevated
mercury content (0.42-1.29 mg/kg) was found in bottom sediments of the river
Khangaruk, subjected to a vigorous influence of the tailings dump of the GEP.
The former dredge pit, located in the bed area of this river, is also characterized
by a high mercury content (2:83 mg/kg).
The study of bottom sediments of techno genic mercury flux formed by the
tailings dump of the GEP (Buryatia) has shown that dam break of the tailings
dump has resulted in the formation of highly contrasted and extended (more
than 12 km) lithochemical mercury (1-5 mg/kg) and gold (0.5-4.0 mg/kg) flux
due to mechanical migration. Accumulation of technogenic materials, silting of
boulder and cobble bed, formation of technogenic dune ranges and bars took
place over the first 3 km along the river bed. Further, transportation of
technogenic materials prevails and silting of boulder and cobble bed are
observed at some places. In the period of low water, the floodplain of the
river and, in some places, of the river bed are covered with a crust of technogenic
silt.
Similar steady, contrast and extended (about 17 km) mercury dispersion flux
(0.04-3.0 mg/kg) is registered in the Krasnoyarsk Krai in the Bogunay river,
eroding mine heaps. Gold mining was stopped 50 years ago but the contrast of
technogenic mercury flux is still retained. Mercury content in bottom sediment
of the river, 7 km upstream from the mine, varies between 0.03 and 0.18 mg/kg,