Environmental Risks for Gemstone Miners with Reference to Merelani Tanzanite Mining Area, Northeastern Tanzania

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 deepseated Lelatema fault zones. Rocks along these zones which are mainly graphitic and or/gypsumbearing 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/m whereby respirable quartz and graphite are 2.4 mg/m and 1.5mg/m, respectively. The total amount of dust is 28.4 mg/m. 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 substandard 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. INTRODUCTION Although small-scale mining in developing countries provides employment and source of income, health hazards and risks are very high. These mines are labour intensive, with low-level mechanisation, and the sub sector employs men, women and children. In Merelani tanzanite mine, there are more than 3000 underground miners mostly young boys working in shifts down to 100 meters. The aerial coverage for individual tunnels are about 1.5-2 m and no other machinery is used except old compressors, pneumatic drills, air blowers, generators, jackhammers, hosepipes and explosives. After drilling and blasting, the rocks are removed with hands and loaded into sacks that are carried to the surface through buckets pulled up by simple pulleys. Miners do not use any kind of personal protective equipment or gear. The main objective of this study was to monitor health hazards and risk including effects of toxic gases and dust exposure during work processes at Merelani mine that are typical for small-scale mining in developing countries. The findings also present brief statistics of accidents from 1996-2002. Malisa & Kinabo Environmental risks for gemstone miners ... 2 GENERAL GEOLOGY The Proterozoic (1900-700 Ma) lithostratigraphic units within the Mozambique Belt of Tanzania stretch in a N-S direction east of the Tanzanian Craton and are known to host most of the coloured gemstones (Fig.1). This paper concentrates on the Merelani tanzanite mining area lying near the contact between the volcanic and the high-grade metamorphic rocks of the Mozambique Belt. Figure 1: Sketch map showing gemstone mineralization in the Mozambique belt of Tanzania. 1) Longido, 2) Manyara, 3) Babati, 4) Merelani, 5) Lelatema, 6) Tiriri, 7) Landanai, 8) Umba, 9) Mvuha, 10) Magogoni, 11) Namaputa, 12) Nabunju, 13) Sumbawanga, 14) Mpwapwa, 15) Kilosa and 16) Loliondo (After Malisa and Muhongo 1990). Tanz. J. Sci. Vol 31(1) 2005 3 The supracrustal rocks in the Merelani area are very similar to the rocks found elsewhere in the Mozambique Belt, consisting of psammitic, pelitic and psammo-pelitic gneisses, crystalline limestones, and to a lesser extent granite pegmatites and quartz veins. After the main phase of the Pan African tectonothemal event, these rocks have in some areas suffered alteration as reflected in their chemical and mineralogical composition as a result of the hydrothermal processes. The mineralization lies within the hydrothermally altered zone along the Lelatema fault zone with a northerly plunging regional scale fold structure. High quality blue zoisite (tanzanite) occurs in boudinaged quartz veins within the graphiterich hydrothermally altered gneisses. However, honeyyellow coloured with other colours may also be found outside the boudinaged structures. Inhalation of graphitic dust and silica particulates is the main problem miners face during extraction of the gems from the host rocks. Detailed studies on the geology of Merelani area is discussed by Malisa (1987) while the paragenesis of tanzanite, its crystallographic structure, mode of occurrence, the tectonic setting are described by Malisa and Koljonen (1986), Sundberg et al. (1988), Malisa and Muhongo (1990), respectively. METHODOLOGY Three one cubic meter glass containers opened on one side were used to collect dust in three selected mineshafts. The total dust collection was carried out during four consecutive days in the selected mine shafts. Sampling started before the miners entered the shafts and lasted until when they reappeared at the mine entrance after eight hours. The quartz content of the respirable dust samples was analysed by classical wet chemical method and graphite (C) with a Leco analyser (Carbon Determinator C12) in the chemical laboratories of the Geological Survey of Finland (GSF) in Espoo. The values obtained in the four sample containers were averaged for the silica and carbon. GEMSTONE MINING IN MERELANI Mining History The date of the first discovery of tanzanite is not exactly known. However, two prospectors, Mr. Manuel de Souza and Mr. Daudi Mayaya, have laid claim to the discovery at the Merelani area Saria (1973). It is without doubt that the Masai who live and graze cattle there showed the area to them. Private prospectors and local miners continued to mine from the time of discovery until 1971 when the government of Tanzania took over the administration of all mines. In 1971-1972, the Merelani mines operated under Tanzanian Gemstone Industries Ltd. (TGI), a subsidiary of the National Development Corporation (NDC). In 1972, the newly formed State Mining Corporation (STAMICO) took over the mines. Mining was done on small scale until recently when the government split the area into blocks of which block B and D were given to small-scale miners and Block A and C to large mining companies (Fig. 2). Large mining area which was been mined by the State Mining Company was given to a South African Company (AFGEM) who fenced it (see Fig. 3A) while the some artisanal miners have small plots around the fence (see Fig. 3B). Malisa & Kinabo Environmental risks for gemstone miners ... 4 Figure 2: Tanzanite claims in the Merelani mining area, NE Tanzania (After Malisa 1987). Tanz. J. Sci. Vol 31(1) 2005