A record I found some years ago in a remaindered record shop in East London.
"The Dark City Sisters were a group of session singers who came together to record an album and in the process popularized an innovative new style of singing. Rather than singing a common four-part harmony, the Sisters used five parts, which created a richer tone. Sometimes known as "vocal jive," this technique was subsumed under the umbrella term "mbaqanga," meaning, literally, dumpling, and figuratively, a homegrown style. ~ Leon Jackson, All Music Guide"
It puzzles me though that there are only three ladies featured on the front cover of this sleeve? No other information found on the interweb sadly though see they have a couple of compilations available on CD on Sterns and World Curcuit records.