What is this airstrip in Mali?
This seems to be the "Assedreme airport and seismic camp", according to Openstreetmap. Aviation Africa has a picture.

This is most likely a now disused airstrip for a base camp for seismic oil and gas exploration. Seismic exploration is a technique for searching for oil and gas deposits by measuring the reflection of artificial seismic waves (simple introduction at oilandgaslawyerblog.com).

The airstrip seems to have been built in 1985, expanded in 2008, and then abandoned. This fits pretty well with an article describing exploration in Mali, which states that lots of seismic exploration was carried out in Mali in the 70's and 80's, with renewed interest in the 2000's.

As J Walters pointed out in a comment Algerian exploration company ENAGEO mentions using this airstrip for its operations in a presentation from 2009.