Geological Survey of Denmark and Greenland Bulletin
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Nr. 7, Review of Survey activities 2004, pp. 77-80 |
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77
Small-scale mining is the main source of income for about
100 million people in Asia, Africa and South America.
However, the processing of raw materials during this mining
activity results in the release of large amounts of mercury to
the environment, creating serious environmental problems.
100 million people in Asia, Africa and South America.
However, the processing of raw materials during this mining
activity results in the release of large amounts of mercury to
the environment, creating serious environmental problems.
Small-scale mining, or artisanal mining, is exploitation
using only shovels, picks and hammers, carried out by indi-
viduals or small groups. A wide variety of commodities are
exploited in this way, ranging from gold, diamonds, precious
stones, tin, coal, dimension stones and slate. Small-scale mi-
ning is often carried out by labourers with virtually no
knowledge of safety procedures. Tunnel cave-ins leading to
loss of life are common, and the widespread use of mercury
in gold extraction causes many long-term health problems for
the miners. It is estimated that about 650 tonnes of mercury
are annually released during small-scale mining to the envir-
onment, and this figure is likely to increase in the future.
viduals or small groups. A wide variety of commodities are
exploited in this way, ranging from gold, diamonds, precious
stones, tin, coal, dimension stones and slate. Small-scale mi-
ning is often carried out by labourers with virtually no
knowledge of safety procedures. Tunnel cave-ins leading to
loss of life are common, and the widespread use of mercury
in gold extraction causes many long-term health problems for
the miners. It is estimated that about 650 tonnes of mercury
are annually released during small-scale mining to the envir-
onment, and this figure is likely to increase in the future.
Mercury is highly toxic and its use causes health problems
not only for the miners, but also to the entire population in
areas where small-scale mining takes place. Some miners are
aware of the dangers of using mercury, but have no know-
ledge of recycling procedures. Several international organisa-
tions, such as the World Bank, UNIDO (United Nations
Industrial Development Organisation), ILO (International
Labour Organisation) and UNDP (United Nations Develop-
ment Programme), have launched programmes to examine
the problems associated with small-scale mining. Progress so
far has been slow, and much more international awareness of
the global mercury pollution of the environment from small-
scale mining is required. The Geological Survey of Denmark
and Greenland (GEUS) has worked as consultant to the
World Bank on projects involving small-scale mining in
Kyrgyzstan, Mongolia and Laos, and has also undertaken
programmes concerning small-scale mining in LesothOFor
UNDP and in Tanzania for the Danish International
Development Agency (DANIDA). This paper reports on
some of the initiatives carried out in Kyrgyzstan and Mon-
golia, to secure and sustain the small-scale mining industry in
these regions.
areas where small-scale mining takes place. Some miners are
aware of the dangers of using mercury, but have no know-
ledge of recycling procedures. Several international organisa-
tions, such as the World Bank, UNIDO (United Nations
Industrial Development Organisation), ILO (International
Labour Organisation) and UNDP (United Nations Develop-
ment Programme), have launched programmes to examine
the problems associated with small-scale mining. Progress so
far has been slow, and much more international awareness of
the global mercury pollution of the environment from small-
scale mining is required. The Geological Survey of Denmark
and Greenland (GEUS) has worked as consultant to the
World Bank on projects involving small-scale mining in
Kyrgyzstan, Mongolia and Laos, and has also undertaken
programmes concerning small-scale mining in LesothOFor
UNDP and in Tanzania for the Danish International
Development Agency (DANIDA). This paper reports on
some of the initiatives carried out in Kyrgyzstan and Mon-
golia, to secure and sustain the small-scale mining industry in
these regions.
A historical view
Small-scale mining has been carried out since ancient times.
Many know the legend of Jason and the Golden Fleece which
may, in fact, be the first record of small-scale mining in the
history of mankind. Herdsmen traditionally placed a ram's
fleece in a river at springtime, which trapped gold particles
tumbling down the river during the spring floods. After a
month or so the fleece would be burned, or dried and shaken,
to collect the gold grains. This ancient technique is still used
by herdsmen in Kyrgyzstan to recover gold from streams.
Many know the legend of Jason and the Golden Fleece which
may, in fact, be the first record of small-scale mining in the
history of mankind. Herdsmen traditionally placed a ram's
fleece in a river at springtime, which trapped gold particles
tumbling down the river during the spring floods. After a
month or so the fleece would be burned, or dried and shaken,
to collect the gold grains. This ancient technique is still used
by herdsmen in Kyrgyzstan to recover gold from streams.
Small-scale mining hazards and opportunities in
Kyrgyzstan and Mongolia
Kyrgyzstan and Mongolia
Peter W.U. Appel
Geological Survey of Denmark and Greenland Bulletin
7, 7780 (2005) © GEUS, 2005
Fig. 1. Sluice for recovering placer gold in a stream in Kyrgyzstan.
The method of using a fleece has, however, largely been
replaced by more efficient techniques. Gold has a high spe-
cific gravity of 19 g/cm
cific gravity of 19 g/cm
3
, that makes gold easy to concentrate
by mechanical means. The traditional gold pan, known from
the gold rush in Alaska in the late 1800s, is still one of the
most efficient and widespread ways of recovering gold on a
small scale. In a gold pan, light minerals such as quartz and
feldspar are removed, and the heavy minerals, including
grains of gold, are left in the pan. The larger gold grains can
be hand-picked from the heavy minerals in the pan, but the
fine-grained gold (gold dust) that can account for up to 60%
of the gold may be lost. This is, of course, not very efficient,
and the most widely used method to increase the recovery of
gold is by amalgamation using mercury (see below).
the gold rush in Alaska in the late 1800s, is still one of the
most efficient and widespread ways of recovering gold on a
small scale. In a gold pan, light minerals such as quartz and
feldspar are removed, and the heavy minerals, including
grains of gold, are left in the pan. The larger gold grains can
be hand-picked from the heavy minerals in the pan, but the
fine-grained gold (gold dust) that can account for up to 60%
of the gold may be lost. This is, of course, not very efficient,
and the most widely used method to increase the recovery of
gold is by amalgamation using mercury (see below).
Small-scale gold mining
Small-scale mining for gold may be carried out
in situ
on
gold-bearing hard rock, or in gold placer deposits forming
riverbeds and riverbanks. Where tunnels are dug into the
unconsolidated placer sediments, cave-ins are common and
make working conditions very dangerous. The gravel that is
extracted is sieved and the heavy minerals are then concen-
trated in a sluice (Fig. 1). River water flowing through the
sluice removes the light minerals, and large gold grains can
then be hand-picked and the residue concentrated in a gold
pan. This concentrate may again be hand-picked for visible
gold grains, or treated with mercury (amalgamation).
gold-bearing hard rock, or in gold placer deposits forming
riverbeds and riverbanks. Where tunnels are dug into the
unconsolidated placer sediments, cave-ins are common and
make working conditions very dangerous. The gravel that is
extracted is sieved and the heavy minerals are then concen-
trated in a sluice (Fig. 1). River water flowing through the
sluice removes the light minerals, and large gold grains can
then be hand-picked and the residue concentrated in a gold
pan. This concentrate may again be hand-picked for visible
gold grains, or treated with mercury (amalgamation).
Hard rock mining is commonly focussed on gold-bearing
quartz veins. Vertical shafts may be sunk down several tens of
metres, and a network of tunnels up to hundreds of metres
long branching out from the shaft are used tOFollow the gold-
bearing veins and excavate the ore. However, even here insuf-
ficient support of roofs and walls may result in frequent
metres, and a network of tunnels up to hundreds of metres
long branching out from the shaft are used tOFollow the gold-
bearing veins and excavate the ore. However, even here insuf-
ficient support of roofs and walls may result in frequent
cave-ins and loss of life. The mined ore is crushed and ground
by hand or in small mills. The fine material is then washed in
a gold pan, hand-picked, and the residue often treated with
mercury.
by hand or in small mills. The fine material is then washed in
a gold pan, hand-picked, and the residue often treated with
mercury.
Amalgamation
During amalgamation mercury is added to a mineral con-
centrate (Fig. 2). Gold dissolves in the mercury, forming an
amalgam. The amalgam is then placed in an iron cup and
heated over an open fire, which evaporates the mercury, and
leaves behind the gold.
centrate (Fig. 2). Gold dissolves in the mercury, forming an
amalgam. The amalgam is then placed in an iron cup and
heated over an open fire, which evaporates the mercury, and
leaves behind the gold.
Amalgamation is a very efficient process for recovering
fine-grained gold, but has the disadvantage that large
amounts of mercury are released into the environment dur-
ing the process. In Mongolia alone several tonnes of mercury
are released to the environment every year, and the amount
released globally reaches many hundreds of tonnes.
amounts of mercury are released into the environment dur-
ing the process. In Mongolia alone several tonnes of mercury
are released to the environment every year, and the amount
released globally reaches many hundreds of tonnes.
Health problems
Mercury that evaporates during amalgamation condenses on
cooling, and often finds its way into local streams and rivers
as metallic mercury. Metallic mercury may be converted by
bacterial action into the even more toxic methylated mercury.
Both forms of mercury readily enter the food chain, and ulti-
mately can lead to severe health problems for human beings.
cooling, and often finds its way into local streams and rivers
as metallic mercury. Metallic mercury may be converted by
bacterial action into the even more toxic methylated mercury.
Both forms of mercury readily enter the food chain, and ulti-
mately can lead to severe health problems for human beings.
Even small amounts of mercury affect the nervous system
in human beings and cause tremors, while larger amounts can
lead to erithism, a mental illness that leaves its victims irri-
tated and very short-tempered. Further stages in mercury
poisoning give rise to inflammation in the gingiva, tunnel
vision and permanent brain damage. Mercury poisoning is
particularly dangerous for pregnant women, as the foetus
concentrates mercury selectively relative to the mother by a
factor of up to ten. Thus, while a mother may have only slight
symptoms of mercury poisoning, the baby may be born with
permanent brain damage.
lead to erithism, a mental illness that leaves its victims irri-
tated and very short-tempered. Further stages in mercury
poisoning give rise to inflammation in the gingiva, tunnel
vision and permanent brain damage. Mercury poisoning is
particularly dangerous for pregnant women, as the foetus
concentrates mercury selectively relative to the mother by a
factor of up to ten. Thus, while a mother may have only slight
symptoms of mercury poisoning, the baby may be born with
permanent brain damage.
Mercury levels of a population may be easily tested by
analysing hair, blood or urine samples.
Recycling of mercury and alternative
methods
methods
Extracting gold by amalgamation has been used for centuries
and on most continents. There are thus very large parts of the
World which have become polluted, and consequently very
many people that suffer from serious mercury poisoning. In
South America various measures for recycling mercury have
been experimented with, and alternative measures for
extracting gold have been developed.
and on most continents. There are thus very large parts of the
World which have become polluted, and consequently very
many people that suffer from serious mercury poisoning. In
South America various measures for recycling mercury have
been experimented with, and alternative measures for
extracting gold have been developed.
78
Fig. 2. Amalgamation in Tanzania. Note the shiny spots of metallic mer-
cury in the pan.
The most efficient, least expensive and most robust appa-
ratus invented to recycle mercury is the so-called retort. This
consists of segments of plumbing tubes joined together. The
amalgam is placed in the retort cup on an open fire (Fig. 3).
The evaporating mercury escapes into the long thin tube that
is cooled by a piece of wet cloth, and condenses back into
mercury that is collected in a small glass filled with water. The
condensed mercury can then be re-used. Using retorts can
reduce the release of mercury to the environment by more
than 95%, and the method has been promoted by different
organisations, including UNIDO and the World Bank.
During World Bank missions in Kyrgyzstan and Mongolia,
the author held classes demonstrating how to use the retort
(Fig. 4), and distributed retorts to small-scale miners in
Mongolia. If mass-produced the cost of the retort is only 5 to
consists of segments of plumbing tubes joined together. The
amalgam is placed in the retort cup on an open fire (Fig. 3).
The evaporating mercury escapes into the long thin tube that
is cooled by a piece of wet cloth, and condenses back into
mercury that is collected in a small glass filled with water. The
condensed mercury can then be re-used. Using retorts can
reduce the release of mercury to the environment by more
than 95%, and the method has been promoted by different
organisations, including UNIDO and the World Bank.
During World Bank missions in Kyrgyzstan and Mongolia,
the author held classes demonstrating how to use the retort
(Fig. 4), and distributed retorts to small-scale miners in
Mongolia. If mass-produced the cost of the retort is only 5 to
10 Euros, which should allow funding organisations to hand
them out to small-scale miners.
them out to small-scale miners.
Teaching small-scale miners to use retorts is a major
advance, but local regulations can prevent its implementa-
tion. During a World Bank mission in Kyrgyzstan in 2003,
the author suggested that training courses for miners in the
use of retorts should be established. The use of mercury is,
however, forbidden by law in Kyrgyzstan, and although mer-
cury is actually used, teaching small-scale miners how to use
retorts is forbidden. The Mongolian government has a more
relaxed attitude. Use of mercury in Mongolia is alsOForbid-
den, but teaching about the advantages of using retorts is not.
tion. During a World Bank mission in Kyrgyzstan in 2003,
the author suggested that training courses for miners in the
use of retorts should be established. The use of mercury is,
however, forbidden by law in Kyrgyzstan, and although mer-
cury is actually used, teaching small-scale miners how to use
retorts is forbidden. The Mongolian government has a more
relaxed attitude. Use of mercury in Mongolia is alsOForbid-
den, but teaching about the advantages of using retorts is not.
There are also alternative methods of extracting gold from
heavy mineral concentrates from placer deposits. A very sim-
ple method, called acid treatment, is used in Kyrgyzstan. The
heavy mineral concentrate is dried and treated with a hand
magnet that removes all magnetic minerals, leaving only gold
and metal sulphides. Concentrated nitric acid is then added
and the mixture is heated (Fig. 5); the acid dissolves the sul-
phides such that only gold is left. Unfortunately, when nitric
acid dissolves the sulphides brown fumes of very toxic nitro-
gen oxides are given off. However, as long as the process is
carried out in the open air and away from houses, the toxic
gases pose little risk to people. The nitrogen oxides are very
unstable and disintegrate rapidly into nitrogen and oxygen.
ple method, called acid treatment, is used in Kyrgyzstan. The
heavy mineral concentrate is dried and treated with a hand
magnet that removes all magnetic minerals, leaving only gold
and metal sulphides. Concentrated nitric acid is then added
and the mixture is heated (Fig. 5); the acid dissolves the sul-
phides such that only gold is left. Unfortunately, when nitric
acid dissolves the sulphides brown fumes of very toxic nitro-
gen oxides are given off. However, as long as the process is
carried out in the open air and away from houses, the toxic
gases pose little risk to people. The nitrogen oxides are very
unstable and disintegrate rapidly into nitrogen and oxygen.
Sources of mercury
Mercury is a fairly rare metal, which only occurs in commer-
cial quantities in a few places on Earth. It has been mined for
centuries in Spain, Algeria, China and Kyrgyzstan. However,
due to the globally declining demand for mercury, many
cial quantities in a few places on Earth. It has been mined for
centuries in Spain, Algeria, China and Kyrgyzstan. However,
due to the globally declining demand for mercury, many
79
Fig. 3. Retort; the amalgam is placed in the cup that is heated over an
open fire. Evaporated mercury is condensed in the pipe and can be col-
lected for recycling. Match for scale.
Fig. 4. Teaching small-scale miners in Mongolia to use retorts.
Fig. 5. Acid treatment. Boiling the gold concentrate with concentrated
nitric acid. The process releases very toxic brown fumes of nitrogen
oxides.
80
mercury mines have either been closed down or production
has decreased.
has decreased.
Nevertheless, there are apparently almost limitless supplies
of cheap mercury available, as mercury has for more than a
century been used as a catalyst in the production of chlorine
and alkali metals in Europe and North America. Production
methods that use mercury as a catalyst have recently been
prohibited by the European Union, and European factories
have developed less toxic methods. Although the ban on the
use of mercury for production purposes does not come into
full effect until 2020, many factories have already converted
to new techniques. This has created a situation where approxi-
mately 50 000 tonnes of mercury in Europe are surplus to
requirements. Such large quantities pose a major problem for
the factories that hold the mercury, and they are actively see-
king for ways of disposal.
century been used as a catalyst in the production of chlorine
and alkali metals in Europe and North America. Production
methods that use mercury as a catalyst have recently been
prohibited by the European Union, and European factories
have developed less toxic methods. Although the ban on the
use of mercury for production purposes does not come into
full effect until 2020, many factories have already converted
to new techniques. This has created a situation where approxi-
mately 50 000 tonnes of mercury in Europe are surplus to
requirements. Such large quantities pose a major problem for
the factories that hold the mercury, and they are actively see-
king for ways of disposal.
The current status of mercury trade within Europe and
the trade with mercury between Europe and the rest of the
World is described by Maxon (2004) in a report for the
World is described by Maxon (2004) in a report for the
European Commission. The mercury trade within the
European Union (EU) is illustrated in Fig. 6 which shows
that export of mercury from the EU is mainly to Third World
countries in Latin America, the Caribbean, South Asia and
the Pacific. It is evident that Dutch, English and Spanish
companies in particular are helping European factories to dis-
pose of their mercury stocks.
European Union (EU) is illustrated in Fig. 6 which shows
that export of mercury from the EU is mainly to Third World
countries in Latin America, the Caribbean, South Asia and
the Pacific. It is evident that Dutch, English and Spanish
companies in particular are helping European factories to dis-
pose of their mercury stocks.
What can be done to help small-scale
miners?
miners?
The most efficient way to reduce the health and environ-
mental problems for miners is to teach them either to recycle
mercury by using retorts, or to use alternative methods. With
that purpose in mind, short teaching and training pro-
grammes for small-scale miners in Bornuur township in
Mongolia have been carried out showing how to use retorts
(Fig. 4). This town is especially appropriate as a target for
teaching, since a recent survey has shown that the population
in Bornuur has high contents of mercury in urine samples
and that the mercury stems from the use of amalgamation by
small-scale miners (Tumenbayar 2003). Building on these
experiences, further projects are now being considered,
including teaching and training medical doctors to diagnose
symptoms of mercury poisoning. Included in these pro-
grammes would also be the establishment of local informa-
tion centres where small-scale miners and others can seek
information on mercury problems.
mental problems for miners is to teach them either to recycle
mercury by using retorts, or to use alternative methods. With
that purpose in mind, short teaching and training pro-
grammes for small-scale miners in Bornuur township in
Mongolia have been carried out showing how to use retorts
(Fig. 4). This town is especially appropriate as a target for
teaching, since a recent survey has shown that the population
in Bornuur has high contents of mercury in urine samples
and that the mercury stems from the use of amalgamation by
small-scale miners (Tumenbayar 2003). Building on these
experiences, further projects are now being considered,
including teaching and training medical doctors to diagnose
symptoms of mercury poisoning. Included in these pro-
grammes would also be the establishment of local informa-
tion centres where small-scale miners and others can seek
information on mercury problems.
The global threat for the environment and health posed by
the use of mercury can be reduced considerably and at little
cost by teaching and training of miners, and handing out
retorts that cost only a few Euros.
cost by teaching and training of miners, and handing out
retorts that cost only a few Euros.
References
Maxon, P. 2004: Mercury flows in Europe and the World: The impact of
decommissioned chlor-alkali plants. Brussels: European Commission.
Directorate General for Environment, 104 pp.
Directorate General for Environment, 104 pp.
Tumenbayar, B. 2003: Action research on mercury pollution in Boroo
area, Mongolia. Ulaan Baatar, Mongolia: Japan International Coope-
ration Agency, Mongolia Office, 75 pp.
ration Agency, Mongolia Office, 75 pp.
Author's address
Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark.
E-mail:
pa@geus.dk
Fig. 6. Mercury trade in the European Union (metric tonnes) in 2000.
Red arrows
indicate export to mainly Third World countries from the
UK, Spain, the Netherlands and Germany.
