9 The Coastal Sandstones - Sapphire Coast

The Montreal GoldfieldsOne interesting Tertiary sandstone area worth a visit is the Montreal Goldfields 5 kmnorth of Bermagui (see http://www.montrealgoldfield.org.au/getting_here.html )Montreal Goldfield, Wallaga LakeAlluvial gold was first found in the nearby region (Dignams Creek) in 1860. The mainsource was vein deposits of gold in the high slopes and crest of Mt Dromedary.These were worked in tunnel and sluicing operations in three main mines over theperiod 1878-1920. Whilst rainforest has reclaimed the highly disturbed crest of themountain the impact of the mining can still be clearly seen.Erosion of the igneous intrusion washed gold into the creek systems and alluvial goldwas found in a number of locations including Dignams Creek. Over 1880 to 1883 asignificant alluvial gold site (Montreal Goldfield) was opened up in the coastal areanorth of Bermagui.The gold is found in an old river bed under a thick aggraded barrier of Tertiarysandstone, probably dating from the same time as the Bermagui sandstone (about30 million years ago). The sandstone includes a considerable amount of quartzduricrust. This was a silica rich crust precipitated in the Paleocene – Eocenerainforest soil profiles during the region’s period of warm humid climate and heavyrainfall (1.5 metres pa). At nearby sites the finer grained component in thesandstone has been eroded out leaving the blocks of quartz duricrust accumulated inheaps. The best example is in the cutting on the Wallaga Lake Road near theBermagui-Cobargo intersection just north of Bermagui.Bermagui-Cobargo Road intersectionThe cap sits on a highly eroded profile of Ordovician sandstone.