In the Timbuktu region, slaves work on farms or as household servants or shepherds. Deeper in the vast desert of the north, inhabited by Tuaregs and Arabs, the slaves mine salt, a back-breaking task done under the Saharan sun. Salt is the north's main economic product and black slaves deliver the giant grayish slabs by boat or truck to the black Africans, who then take it to markets in the south. Yattara and his companions agreed that Tuaregs were the worst slave-masters in Mali. http://www.usatoday.com/story/news/world/2013/02/14/mali-slavery/1920579/
Sadly, slavery is still a significant issue in many parts of the world including Africa and Asia. Once you add in 'debt slavery', there are believed to be a minimum of 50 million enduring slavery on the face of the earth.