Miners in the blood diamond mines are usually the poor people who are forced to be slaves by gangs. If you lived by the mines or in the area around you would already be working in the mines due to the slavery. Some miners are kids that are 5 years old. Miners in Africa's mines start their work at early ages.
If you were a slave and you didn't want to mine the people or person would either kill you, kill your family, or chop your and sometimes even your families limbs off. The gangs just do this so they can have all the diamonds and be rich.