The machines companies use to mine the ore create polutive gases. There is likely a better answer and this one should not be taken seriously but it is an idea that spawns from your question and it can be researched and proven.
Well there are many causes of pollution but I will just name a few. First of all, cars and factories cause pollution. Also, littering can cause pollution.
The industrialization of society, the introduction of motorized vehicles, and the explosion of the population, are factors contributing toward the growing air pollution problem.