Switzerland's Barbier-Mueller museum said Saturday it will return to Tanzania a tribal mask which it acquired 25 years ago without knowing it had been stolen from the African nation. The Makonde mask, which was worn at male initiation rites by the animist ethnic group, was taken by burglars from the National Museum of Tanzania at Dar Es Salaam in 1984 and bought by the Swiss museum the following year. An official “mask-giving” ceremony will take place in Paris Monday between representatives of the Geneva-based Barbier-Mueller museum and the Tanzanian museum, under the guidance of the International Council of Museums. The Barbier-Mueller said in a statement that in 1990, a professor at an Italian university told it that the Makonde mask in its collection could have come from the Tanzanian museum and it informed the council.