Stable isotopic compositions of early Archaean sulphate deposits of probable evaporitic and volcanogenic origins

SIGNIFICANT Archaean bedded sulphate deposits have been described only from the Pilbara Block (Western Australia) 1,2 , the Barberton Mountainland (South Africa) 3–6 and southern India 7 . These are all barite deposits, but there is petrographic evidence suggesting replacement of original evaporitic gypsum in the North Pole (Pilbara) and Barberton deposits. This contrasts with the apparent volcanogenic deposition of barite in the relatively sulphide-rich Big Stubby prospect (Pilbara). This letter summarises the petrographic evidence, concentrating on recent data from North Pole, and reports stable isotopic results for barite and associated sulphides which provide corroborative evidence for the environments of formation of these deposits. Some implications concerning the early hydrosphere, atmosphere and biosphere are outlined.