Petrographic, stratigraphic, and structural evidence is presented for the sedimentary origin of one of the oldest known stratiform barite deposits. The setting of the barites within the Fig Tree Group of the Swaziland Supergroup (> 3.2 b.y.) is outlined in terms of a new facies concept. The barite was deposited on a narrow submarine ridge zone. This "Proto-Inyoka Zone" separated a "graywacke facies" from a "shallow-water facies" within the Fig Tree basin.