求翻译：尼日利亚是西非地区唯一的产煤国，煤炭具有低硫、低灰分、环保、富含沥青等特点，估计资源量约为30亿吨是什么意思？

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Nigeria is the only region of West Africa, the largest coal producer with a low-sulfur coal, low-ash, environmental protection, and rich with features such as asphalt, it is estimated that approximately 3 billion tons of resources

Nigeria is the West Africa area only produces the coal country, the coal has the low sulfur, the low ash, the environmental protection, contains characteristics and so on asphalt, the estimate amount of resources approximately is richly 3,000,000,000 tons

Nigeria is West Africa's only coal, coal with low ash, low sulfur, environmental protection, is rich in features such as asphalt, estimated resources of about 3 billion tons

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