364
T.G. Laperdina et al.
5
Mercury Contents in the Environmental Compartments
of Background Areas and Zones Impacted
by Gold-Mining Activities
5.1
Rocks and Minerals
The Clarke of mercury in the crust, according to different data, ranges from 0.03
to 0.08 mg/kg, in rocks of various compound from 0.00021 to 0.40 mg/kg
(Saukov 1975; Ozerova 1986; Ovchinnikov 1990). Mercury is an effective
geochemical indicator of gold-bearing deposits and for some of them the second
significant admixture (after silver) in native gold in both occurrence and
concentration (0.1-5.0 g/kg; Stepanov and Moiseyenko 1993). Mercury haloes
border ore bodies all along their length, increasing in thickness and contrast
from lower to upper levels. Haloes are much thicker than gold ore bodies and
extensive in the supra-ore part. Mercury concentrations in the haloes of nearsurface and more subsurface deposits may reach 10-20 mg/kg, more common by
0.1-0.3 mg/kg (Roslyakov and Kirillova 1995). Therefore, industrial mining of ore
gold deposits is, as a rule, accompanied by an admixture of mercury emission
from bedrocks, gold-bearing ore and its reprocessing products and redistribution of emitted mercury between the environmental compartments, which leads
to an increase in mercury concentration level in comparison with the natural
background content (Table 1).
For placer gold deposits, the data on mercury haloes are inadequate to
establish clear geochemical peculiarities. For some placers in Buryatia, however,
the elevated mercury content (1.6-112 mg/kg) was also registered in hypergenic
gold (Karmanov 1985).
In Siberia in the areas of traditional gold mining, a huge amount (millions of
tons) of rocks and bedrocks heaps, concentration tailings with elevated mercury
contents, have been accumulated at present. Problems of mercury emission from
rocks of heaps and tailings due to physicochemical, chemical and microbiological processes, which take place during oxidation of rocks, their destruction,
secondary mineral formation, rainfall drainage and also intensity and dynamics
of migration processes in the atmosphere, soils, surface water streams and
underground waters remain unstudied. The almost universal presence of
permafrost and a seasonal frozen state make it difficult to transfer rules
established for areas with warmer climate to Siberia, which is characterized by
diversity of climate and landscape conditions. The results of the studies carried
out in Zabaikalye (Laperdina et al. 1995, 1996), Yakutia (Omelchenko 1985) and
Gorny Altai (Anoshin et al. 1995) have shown that decreased mercury contents in
frozen rocks of gold ore deposit pits (Yakutia) due to active cryogenic processes,
as well as the enrichment of oxidized metasomatically altered rocks with mercury
are observed in the mining areas.
The increase in mercury content on the average by two to three times in
oxidized rocks (0.013-0.033 mg/kg) in comparison with original rocks (0.005-
T.G. Laperdina et al.
5
Mercury Contents in the Environmental Compartments
of Background Areas and Zones Impacted
by Gold-Mining Activities
5.1
Rocks and Minerals
The Clarke of mercury in the crust, according to different data, ranges from 0.03
to 0.08 mg/kg, in rocks of various compound from 0.00021 to 0.40 mg/kg
(Saukov 1975; Ozerova 1986; Ovchinnikov 1990). Mercury is an effective
geochemical indicator of gold-bearing deposits and for some of them the second
significant admixture (after silver) in native gold in both occurrence and
concentration (0.1-5.0 g/kg; Stepanov and Moiseyenko 1993). Mercury haloes
border ore bodies all along their length, increasing in thickness and contrast
from lower to upper levels. Haloes are much thicker than gold ore bodies and
extensive in the supra-ore part. Mercury concentrations in the haloes of nearsurface and more subsurface deposits may reach 10-20 mg/kg, more common by
0.1-0.3 mg/kg (Roslyakov and Kirillova 1995). Therefore, industrial mining of ore
gold deposits is, as a rule, accompanied by an admixture of mercury emission
from bedrocks, gold-bearing ore and its reprocessing products and redistribution of emitted mercury between the environmental compartments, which leads
to an increase in mercury concentration level in comparison with the natural
background content (Table 1).
For placer gold deposits, the data on mercury haloes are inadequate to
establish clear geochemical peculiarities. For some placers in Buryatia, however,
the elevated mercury content (1.6-112 mg/kg) was also registered in hypergenic
gold (Karmanov 1985).
In Siberia in the areas of traditional gold mining, a huge amount (millions of
tons) of rocks and bedrocks heaps, concentration tailings with elevated mercury
contents, have been accumulated at present. Problems of mercury emission from
rocks of heaps and tailings due to physicochemical, chemical and microbiological processes, which take place during oxidation of rocks, their destruction,
secondary mineral formation, rainfall drainage and also intensity and dynamics
of migration processes in the atmosphere, soils, surface water streams and
underground waters remain unstudied. The almost universal presence of
permafrost and a seasonal frozen state make it difficult to transfer rules
established for areas with warmer climate to Siberia, which is characterized by
diversity of climate and landscape conditions. The results of the studies carried
out in Zabaikalye (Laperdina et al. 1995, 1996), Yakutia (Omelchenko 1985) and
Gorny Altai (Anoshin et al. 1995) have shown that decreased mercury contents in
frozen rocks of gold ore deposit pits (Yakutia) due to active cryogenic processes,
as well as the enrichment of oxidized metasomatically altered rocks with mercury
are observed in the mining areas.
The increase in mercury content on the average by two to three times in
oxidized rocks (0.013-0.033 mg/kg) in comparison with original rocks (0.005-