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Artisanal and small-scale gemstone miners are the workers with the highest health risk exposure in Tanzania. Gemstone mining at Merelani tanzanite mines which has gone to depths of 100 m or more in narrow straight and inclined shafts, underground artisanal miners work under a very harsh environment. Tanzanite deposits are located within sheared zones, lying along a deep-seated Lelatema fault zones. Rocks along these zones which are mainly graphitic and or/gypsum-bearing gneisses surrounded by limestone are soft, fractured and strongly weathered. Poor mining techniques, lack of geological background, chronic shortage of capital, and the lack of awareness on environmental pollution in the shafts have led to health and safety problems. In deep mines such as Merelani tanzanite mine, where the rocks are graphitic (C-rich), existence of poisonous gases is common. Dust exposure during drilling, blasting and shovelling indicates high average levels of overall respirable dust 15.5 mg/m3 whereby respirable quartz and graphite are 2.4 mg/m3 and 1.5mg/m3, respectively. The total amount of dust is 28.4 mg/m3. Supply of air (oxygen) to such depths by using small compressors is unreliable and inadequate, since they sometimes fail or deliberately are switched off. Further, lack of adequate ventilation for eliminating the toxic gases after blasting results in particles hazardous to the miners. Exposure to dust mixed with graphite; quartz and micas particles are harmful and may cause lung cancers or development of chronic silicosis. The workers and mine owners are supposed to adhere to mining rules, regulations and code of practice. Mines must be properly ventilated and back filling is necessary in mined out pits. Most of artisanal gemstone mining in Tanzania is sub-standard which results in fatal accidents. It is recommended that proper mining methods should be adhered to following the code of practice issued by the Ministry of Energy and Minerals. Tanzania Journal of Science Vol. 31 (1) 2005: pp. 1-12

Environmental risks for gemstone miners with reference to Merelani tanzanite mining area, Northeastern Tanzania