Coal and kohl are homophones. Coal is sometimes used when the writer actually means kohl, but I have never come across a ‘kohl mine’ or a ‘kohl fire’.

Coal

• a black or brown rock consisting largely of carbonised vegetation
• one or more lumps of coal
• a piece of red-hot, glowing coal or other material
• to provide with a supply of coal
• to extract coal

Kohl

• a powder or substance used to darken the area around the eyes
• to darken with kohl
• an abbreviation of kohlrabi (a type of cabbage)