Hello,
I'm far from am expert but I will offer the following since I recently happened to be poking about in topics related to African weapons.
The decoration resembles that on a knife in my collection from the Tabwa (also called Batabwa, Taabwa,Rungu ) tribe. The Tabwa people live in small autonomous villages scattered within a territory that extends from the southeast of the Democratic Republic of the Congo to the northeast of Zambia, along Lake Tanganyika.
The Tabwa are well known for their carving. Their western neighbors, the Luba, influenced the incorporation of prestige objects into Tabwa life. The face represents ancestor worship. Among Tawba, the village chief or sorcerer alone were allowed to possess prestige items of ancestor worship. Eastern Tanzanian neighbors influenced the Tabwa with geometric designs. These two influences may account for the presence of
both ancestor and geometric features in my knife and your axe.
Beautiful item!
Best Regards,
Dave A