Small scale gemstone mining is carried out in several areas in Tanzania. Gemstones are found in the Usagaran and Ubendian granulite system. Areas of concentrated artisanal workings include:-
(i) Merelani in Kiteto District, Arusha Region - famous for the mining of tanzanite (a blue-violet zoisite).
(ii) Matombo and Mahenge in Morogoro Region, Longido in Arusha and Umba in Tanga Region are famous for ruby and sapphire mining.
(iii) Rukwa Region and Manyara in Arusha Region are known to produce emeralds.
For the purpose of this study, a visit to Merelani Tanzanite Mines was made; the target area being Block D which belongs to Arusha Region Miners Association (AREMA).
An area is normally allocated to interested persons by the Association in return for a 10% fee levied on tanzanite sales.
Once the area has been allocated, a prospecting pit is excavated to depths of 30-50 metres until the graphitic zone has been encountered. It is in this zone that tanzanites are found. To a large extent, the miners at Merelani appear to be employing mechanization that is higher than that employed by the gold diggers (they are semi-mechanized). Machines such as compressors, jack hammers, explosives and accessories could be seen, the main underground extraction method used being room-and-pillar. Pits measure approximately 1.5m × 2m and in the gemstone zone horizontal drifts measure 1.5m × 2m on average and have a length of up to 150 metres as shown in Figure 10 below.
Figure 10: Structure of Gemstone Mining Pits
Explosives are extensively used for fragmenting the rock. For lighting purposes, miners use dry battery torches which have turned out to be very expensive inputs. In such precarious working conditions, no consideration is given to safety gear. The miners do not wear safety boots, glasses, dust muffs or helmets, and are therefore exposed to all possible hazards.
Ventilation is provided by compressed air normally used for drilling purposes. However, this is not sufficient, given the working depths. Miners have to come to the surface time and again to inhale oxygen.
Hoisting is carried out in three very dangerous ways:-
(i) manual (through pulleys mounted on wood);
(ii) manual drum hoists; and
(iii) tractors pulling hoisting rope through pulleys.
During the time of the visit, an accident happened where a tractor pulled the hoisted rope beyond its length, resulting in the destruction of the tripod system to which the pulley was connected. These methods are shown in Figures 11, 12 and 13.
Figure 11: Artisanal Hoisting Mechanism at Merelani Tanzanite Mines
Figure 12: Artisanal Hoisting Mechanism at Merelani Tanzanite Mines
Figure 13: Artisanal Hoisting Mechanism at Merelani Tanzanite Mines
The process of gemstone recovery is extremely simple and only involves screening. If a 'pocket' is found, the lot would be sieved and the oversize consists of tanzanite and gangue (uneconomical material) is discarded.
However, once the material is brought to the surface, scavenging takes place to recover even the smallest tanzanites.
As cited in the mining method, pits have to be excavated to win the gemstones and in so doing the area allocated to mining operations suffers severe degradation caused by hundreds of mine pit excavations. In Block D alone there were 459 pits out of which only 100 of them were active. Inactive pits were not reclaimed by being refilled and it would appear that no priority was being given to this exercise.
Excavated materials are not transported from the area but remain piled up near the mine pits; thereby posing the danger of rocks falling back into the pits. The pits have fragile, and with no protection around them, can endanger the lives of miners. Figures 14 and 15 clearly demonstrate the extent of environmental destruction.
(i) Tanzanite gemstone miners do not use any harmful chemicals to recover the minerals.
(ii) Ventilation is inadequate, and graphitic (carbon) dust pollutes the ambient atmosphere. The subsequent inhalation of carbon dust is a health hazard to miners and could result in the black lung disease.
(iii) Abandoned mine pits are not refilled; this endangers people's lives. Although leaders of the association recognize the need to reclaim the mined out areas,, it appears that this is not the priority at the moment. It is recommended that the Mineral Resources Department, in cooperation with the miners associations should prioritize this implementation exercise.
(iv) Sanitation is poor, as is health in the mining areas. Cases of e.g. diarrhoea, malaria, and dysentery are the order of the day.
Figure 14: A Mound of Stockpiled Rock from Artisanal Mining Activites at merelani
Figure 15: Land Degradation at Merelani Tanzanite Mines: Inactive Mine Pits.