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Artisanal gold mining in Tanzania is currently concentrated in the following areas:-
(i) The Lake Victoria Goldfield;
(ii) The Mara/Musoma Goldfield;
(iii) The Iramba Sekenke Goldfield;
(iv) The Mpanda Minerals field; and
(v) The Lupa Goldfield.
However, new or reactivated gold mines have recently emerged in areas such as Manyoni and Nzuguni near Dodoma and Mbinga in the Southern Highlands.
A great deal of time and funds would be required to cover in adequate detail all the above-mentioned areas. Therefore, this study limits itself to parts of the Lake Victoria Goldfield mainly; Nzega, Kahama, Ushirombo, Nyakagwe, Nyarugusu and Mugusu areas2. In the Mara/Musoma Goldfield, the mines visited were at Nyabigena, near Tarime.
2As per the Terms Of Reference (TOR).
Most of the small scale mining activities share common visible similarities with respect to mining and gold recovery methods either from alluvial, eluvial or reef gold deposits which are referred to as primary ores (reef gold deposits) and secondary ores (alluvial and eluvial gold deposits).
Miners prefer to work on secondary ore deposits because they contain free gold which can easily be recovered. Experienced miners work on reefs due to the fact that they can be worked perennially (hence eliminating the need to move from prospect to prospect during the heavy rainy seasons). However, miners working in primary deposits encounter bottlenecks due to hardness of the ore which does not easily yield to mining and processing tools currently being employed.
After the potential gold area has been 'discovered' by 'bush' prospectors, something that occurs mostly misadvertently than by design, the first task is to get to the ore body. This is done by sinking prospecting pits which approximately measure 1.5 metres by 2.0 metres (or even less). These pits later on develop into a shaft which serves as man-way and for the hoisting of ore, waste and supplies.
The waste material is not transported away but is piled up around the mine shaft opening. The shaft develops to depths of between 15 metres and 100 metres in some cases. Deeper shafts were observed in Nyabigena mines, Mugusu and Nyarugusu. At Ushirombo, mines are found only at shallow depths due to a high water table which cannot be drained efficiently.
Mine support is achieved through the use of timber which is usually obtained from the surrounding forests. At Nyabigena, where the rock is able to withstand the mining operations, timbering is not used. In Ushirombo mine, timbering is used extensively due to poor rock competence and the presence of underground water.
Tools used for rock excavation are very simple and include picks, shovels, hammers, wedges, and sharpened steel rods. These tools were employed in all the artisanal mining areas visited. In areas such as Nyabigena, one miner had his own compressor, generator, water pump, drilling accessories and employed explosives for underground rock breaking. However, most artisanal miners use hand tools as shown in Figure 1.
The hoisting of materials from an underground mine to the surface is done by simple timber fabrications whereby two V-like timber posts are erected on both sides of the shaft. A timber log on which sisal or tree-bark rope is wound is placed in between the two poles. The log is then turned manually to elevate or descend the rope which is fitted to a leather sack for hoisting ore and waste or to a 25-50 litre bucket for mine drainage. The most common hoisting arrangement is illustrated in Figure 2.
It was generally observed that ventilation was poor, which raises an issue of concern as the depth of the mines would demand proper and adequate ventilation. However, a single shaft is used in most of these mining activities; which means that natural ventilation does not occur easily. In most cases, the air supply is improved when a heading connects two mine shafts thereby creating a natural draught.
Lighting for the underground mine is generally done using torches powered by dry batteries (two 1.5 volts batteries connected in series). This is a normal practice at Nyabigena, Nyarugusu and Mugusu. At Isungangwanda and Lusu in Nzega, the miners use small kerosene lanterns called 'koroboi'3. However, this method produces a lot of soot in the underground mines. The more advanced artisanal miners have their own power generating sets.
3A 'koroboi' consists of a small can which has a cover and into which paraffin is fed. The top cover is pierced at the centre to allow for the entry of a thin cloth dipped into the paraffin (serving to draw the paraffin up). With the tin cover in place, the end of the cloth that protrudes outside the cover is lit providing light to the miners.
Safety gears are almost non-existent in these mines. As this is a precarious occupation, one would expect miners to use boots, helmets, dust muffs, safety glasses, and have first aid kits. However, it was merely in 2% of the areas visited that miners paid some attention to the safety aspects.
Flooding in the mines is a common phenomenon. Many underground mines are abandoned not because of ore depletion, but due to excessive water inflow. This has been a major production bottleneck which most miners have failed to contend with. Those with pumps charge exorbitant fees to miners requiring such services.
Figure 1: Artisanal Miners' Simple
Hand Tools
Figure 2: Illustration of a Commonly
Used Hoisting
Arrangement
The recovery of gold from mined out ore showed striking similarities in the various mining areas visited. The basic ore-processing steps (in descending order) were primary crushing, screening, secondary crushing, grinding and repeated screening, pulping in a pan ('karai") amalgamation with Mercury, amalgam heating, and finally recovering the gold (as shown in Figure 3).
Figure 3: Gold Recovery Process
The above processes can be modified depending on the properties of the ore.
The subject of environmental impacts emanating from activities of small scale miners in gold and other minerals is currently receiving increasing awareness. On the other hand increasing serious pollution problems are being posed by the growing number of small scale mining entrepreneurship. It is worthwhile to note that these activities have grown for a number of reasons which include:-
(i) the shedding of labour force from formal but inefficient mines and processing plants;
(ii) growing poverty causing families to search for alternative income and
(iii) the new "gold rush" phenomenon associated with new discoveries.
The environmental behaviour of these small miners is closely linked to the conditions of poverty which gave rise to them. These miners are generally poorly educated with no formal, or technical training. With the exception of a few miners coming from formal mines, they have little access to technology and lack the credit to buy it. Many of them should be considered as squatters on gold bearing "land" or they rent it from local claim holders or "land owners" to whom they are obliged to sell their gold under a "production-sharing scheme". In the process, huge mounds of materials are moved from the earth when digging mining pits.
The nature of such small-scale mining poses a number of policy challenges to the Government. First, it is an extremely inefficient way to produce minerals and in the long-term limited source of revenue as the miners reach both technological and financial limitations to enable them to continue mining. Also, such activities lead to the exhaustion of the high quality ores and inhibit more efficient forms of investment.
A typical artisanal gold mine as was seen during the survey is poorly conceived without much emphasis due to the lack of knowledge on rock stability or rock supports. It is estimated that at least 5% of the fatality rate per annum is possible through such workings, while injury rates are much higher. In some artisanal underground mines, drilling (with jack hammers) is done without water. Once the ore is brought to the surface, it is crushed and grounded. In both cases, this may cause acute respiratory problems due to the inhalation of silica-containing dust. Such a case is as shown in Figure 4.
Figure 4: Crushing and Grounding of
Ore Using the Jack
Hammer
The digging of thousands of mining pits by the artisanal miners is bound to be the single most disturbing problem; particularly because the miners are normally on the move to " more lucrative" areas in a nomadic fashion, with no regard whatsoever to the pits left behind. Table 3 shows the number of mine pits in the area visited. There is no evidence showing that any efforts are geared towards reclaiming the mined-out pits.
Table 3: Estimated Number of Mine Pits
|
Name of Location |
Total Number of Pits |
Active Pits |
Status of Inactive Pits |
|
Merelani Tanzanite Mine, (Gemstones) |
459 |
100 |
Not refilled |
|
Nyabigena Mining Cooperative Society, (Gold) |
199 |
140 |
Not refilled |
|
Isungangwanda and Lusu, (Gold) |
510 |
10 |
Not refilled |
|
Ushirombo, Kahama, (Gold) |
40 |
40 | |
|
Bulyanhulu, (Gold) |
500 |
200 |
Not refilled |
|
Mugusu, (Gold) |
700 |
300 |
Not refilled |
In the gold recovery process, tremendous amounts of Mercury are used to amalgamate the gold; this is caused by the erroneous belief that the more Mercury used, the greater the rate of gold extraction. A lot of ore is treated in the rivers and Mercury finds its way into the water and finally into the ecosystem affecting the food chain. This was found to be rampant at Ushirombo, Bulyanhulu, Nyarugusu and Mugusu.
As shown in Table 4, 739.5, 564.3 and 170.5 kilogrammes of Mercury were sold around the Lake Zone in 1991, 1992 and between January-June 1993 respectively.
Table 5 shows atomic absorption spectrophotometric analytical results from river and well water samples collected; these results reveal the presence of high Mercury concentrations. The lowest (0.106 microgram per litre), and the highest (2.306 micrograms per litre) which are considered to be very high values particularly as the maximum permissible is 0.005 microgram per litre (i.e considering that these are values refer to effluents discharging straight into receiving waters). On the other hand, the usage rate has been estimated at one kg. of Mercury for one kg. of gold produced (Madini officials, Mwanza). Figure 5 shows an amalgam in which gold is contained.
Figure 5: Gold-Containing Amalgam
Figure 6: Children Near a Stream
Active in Gold Panning
Table 4: Quantity of Mercury Sold per Annum Within the Lake Zone (in Kgs)
|
Year |
Amount (in kgs) |
|
1991 |
739.5 |
|
1992 |
564.3 |
|
1993 |
170.5 |
|
TOTAL |
1,474.3 |
Source: Mwanza Zonal Mines Office.
Table 5: Results of Analysis of Mercury in Water
|
Sample |
Mercury Concentration (Microgram/Litre) |
|
1. Ushirombo: Drinking water |
0.105 |
|
2. Ushirombo: Gold washing area |
0.977 |
|
3. Bulyanhulu: Gold washing area |
0.347 |
|
4. Bulyanhulu: Drinking water |
0.135 |
|
5. Bulyanhulu: Gold washing water |
0.179 |
|
6. Nyarugusu: Gold washing water |
0.649 |
|
7. Mugusu: Upstream Mugusu river gold washing area |
0.117 |
|
8. Mugusu: Downstream Mugusu river (1) |
0.574 |
|
9. Mugusu: Area with the highest number of gold washers at Mugusu river |
2.306 |
|
10. Mugusu: Downstream Mugusu river (2) |
1.205 |
Analysis by: Government Chemist.
It is important to note that all rivers around the Lake Zone lead to Lake Victoria which is essentially the life line not only for Tanzania but also for Kenya, Uganda and all other countries along the River Nile drawing water from Lake Victoria. This is the magnitude of the problem or rather, its source.
A study of small-scale alluvial gold mining in the Madeira River Basin in Brazil (Malm et. al. 1990) shows high concentration levels of Mercury in fish as far as 19, 780 kms. downstream from the main gold mining areas and very high values of Mercury in hair samples obtained from the local Indian population and local gold miners.
In the Tanzanian case, Lake Victoria is surrounded by artisanal mines located only a few kilometres away; therefore, one cannot rule out the possibility of Mercury pollution in the Lake itself - and subsequently River Nile. The seriousness of the problem therefore, is reinforced by the complexities of the food chain and the fact that affected fish can be eaten hundreds of kilometres downstream (far from the actual mining areas). Figure 6 shows two children holding fish near a stream active in gold panning that makes use of Mercury. The Mercury concentration in the water here was analysed; it was 0.649 microgram per litre.
Heating the amalgam to drive off Mercury also presents a health hazard; Mercury fumes are inhaled and particularly by those who decide to do this exercise at home - inside closed rooms.
Artisanal mining is increasingly becoming a fact of life in Tanzania as employment in the formal industrial sector continues to decrease. This is a fact that has to be recognized. Trying to limit or abolish artisanal mining activities without providing alternative sources of income is likely to meet with stiff resistance. Artisanal miners, are, in all likelihood, here to stay.
Environmental problems are not only restricted to the mining and processing of ore; informal villages spring up which have little or no basic sanitary facilities and which often bring problems with regard to law and order. The shift from farming to speculative digging has reduced food production which threatens famines in some areas. The greater availability of money has created pockets of inflation and put pressure on the price of essential goods, thus serving to further impoverish those who do not participate in mining.
In all the areas visited, severe environmental side effects required urgent attention. Where large numbers of artisans work, the common practice is to clear the bush by burning and thus establish both the mine site and villages, thus destroying the flora and driving out wildlife. With most of the ground covered with dug out pits created by artisanal mining activities, agriculture becomes virtually impossible or costly to carry out.
Silting is a common phenomenon in artisanal mining areas. This happens when miners wash their ores in the river to recover gold. The result has been the raising of river bed levels and, in some cases, this has been manifested in the drying up of streams, rivers and dams. Since this is a slow process, it becomes difficult for the miners to notice the differences in river bed levels each subsequent season. The combined effect of silting due to floods and silting caused by artisanal mining activities is bound to speed up the degradation of drainage patterns. In areas such as Bulyanhulu, Nyarugusu and Mugusu the effects of silting can clearly be observed already and as shown in Figures 7 and 8 (taken at Mugusu and Bulyanhulu respectively).
Figure 7: Effects of Silting in the
Mugusu Area
Figure 8: Effects of Silting in the
Bulyanhulu
Area
Gold production in the whole of Tanzania, currently stands at about 3.5 tons per annum, and is produced by the informal industry (mainly through artisanal mining activities).
The artisanal miners use crude gold extraction methods which include the haphazard digging of thousands of mine pits and the recovery of gold using Mercury. Some of the Mercury finds its way into streams and rivers and hence continuously pollutes them.
Due to the poor organizational structure of the artisanal miners, it has become increasingly difficult for Officers in the Mines Department to regulate artisanal mining activities.
Neither the Minerals Resources Department, nor artisanal mining communities has any concrete plans designed to carry out land reclamation measures or to control the chemical pollution of streams and rivers.
Health and sanitation in the area is extremely poor.
As shown in Figure 9, artisanal mining operations affect the environment in ways that raise concern. Lateritic soils contaminated with Mercury causes silting in rivers and results in the subsequent raising of the river bed. During floods (in the rainy season) part of the contaminated material may be transported into Lake Victoria thus polluting it.
It is recommended that the extensive and intensive use of Mercury for recovering gold should either be technologically controlled or discontinued altogether if efforts to control its use do not succeed.
It is recommended that the Mineral Resources Department designs and implements plans to reclaim all mined out and abandoned mine pits.
Figure 9: Artisanal Mining Versus
Environmental
Hazards
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