Three resources Europeans wanted from Africa.

This question depends on when those Europeans arrived in Africa. Early in Africa's discovery, Europeans wanted slaves from Africa. These slaves were especially valuable in the New World and this created a triangular trade that allowed for the economic expansion of the New World and Europe but effectively drained Africa of its human resources.
Gold made South Africa especially valuable and was one of the key reasons that Britain came to covet the territory and minimize Dutch presence there. Diamonds would also be found in South Africa. The discovery of gold in the 1880s came at a time when Europeans were colonizing large portions of Africa. The idea was not to transplant a large number of Europeans there but rather to harvest the natural resources in the region. The riches of the region did not go to the Africans but instead to the colonizing Europeans.  
Finally, African ivory would prove to be quite valuable. This ivory could be used to make trinkets to trade to other groups or sell as home furnishings. The ivory trade led to market hunting that depleted the wildlife of the region. Even today poachers continue to attack the endangered animals of Africa.