A pre-2,000 Myr old granulite facies metamorphosed evaporite from Caraiba, Brazil?

THE identification of the first occurrence on Earth of sediments of evaporitic origin formed from seawater is obviously important not only for the study of the chemical evolution of ocean water but also in understanding the development of common sedimentary rock assemblages and the stabilisation of cratons. Until recently 1,2 confirmed pre-2,000 Myr old evaporites were unknown and indeed Ronov 3 maintained that they did not exist. Pyroxene granulite facies metamorphosed evaporites are also extremely rare 1,4 and thus a pre-2,000 Myr old example is important. We give here a brief account of the mineralogy of some of the rocks found in the Caraiba mine area of Brazil which suggests that evaporites existed earlier than previously recognised and were associated with dolomitic rocks.