Major resources of magnesite are included as sedimentary interbeds within Late Proterozoic Skillogalee Dolomite which extends the length of the Geosyncline for 820 km. Magnesite interbeds are best developed from Leigh Creek to the Willouran Ranges, and are exposed over a strike length of over 80 km. Small pits at Copley, Old Myrtle Springs, and Witchelina have supplied 18 000 tonnes of magnesite, and 3 larger quarries at Myrtle Springs produced 30 000 tonnes in 1984-5. Quarries expose between 13 and 60 magnesite interbeds, 0.3 to 1.5 metres thick, within a stratigraphic thickness of 300 to 700 metres. Late Proterozoic Balcanoona Formation within the Gammon Ranges National Park includes a large resource of 20 million tonnes of replacement magnesite.