The Siluro‐Devonian, volcano‐sedimentary rift basin sequence at Breadalbane, NSW, has undergone three phases of deformation, with biotite grade metamorphism occurring during the first two events. A peak metamorphic temperature of 425 ± 30°C is indicated by calcite‐dolomite geothermometry, and a pressure of 4.0 ±0.5 kbar is estimated from the Si content of white mica. These P/T estimates give a geothermal gradient of 30°C/km, consistent with the inferred tectonic environment in the Lachlan Fold Belt during the Devonian.