Rob’s and Liz’s Rocky Trips Pt 1

Rob’s and Liz’s Rocky Road Trips Pt. 1

Daylesford Slate Belt/Volcanics

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Daylesford is a 11/2 hour trip from Melbourne and is mostly known for its mineral springs and spa baths. Our purpose for visiting Daylesford was to examine and collect some rock and mineral specimens from the region. Daylesford is situated in the central western Victorian slate belt, which hosts the famous Ballarat and Bendigo goldfields. The slate belt is Ordovician in age and consists of black slates, mudstones, siltstones and quartzite meta-sediments. Tertiary volcanic scoria cones and basalt flows locally intrude and cover the meta-sediments.

There are many old gold diggings in the Daylesford region and the mine dumps are good collecting localities for slates and quartzite’s. The slates and quartzite’s are often veined by quartz and it is these hydrothermal solutions that mineralise the rocks with gold and other minerals. Good sulphide mineral specimens, such as arsenopyrite and pyrite, can be collected on some of the mine dumps.

The volcanic scoria cones represent a completely different type of geological activity. Eruptions at various points have resulted in the formation of scoria cones and basaltic lava flows over the Ordovician sediments. Mt. Franklin, near Daylesford, is a well preserved cone with a central hollow surrounded by walls of scoria. There is a breach in one side where lava once flowed. The central hollow is now a shady campground.

The scoria rock is very light weight from the abundant gas bubbles (vesicles) that fill it. The vesicles are occasionally filled with mineral crystals of olivine, pyroxene and feldspar, some of which can be 4cm or more in size. Scoria is quarried at many locations in Victoria and is a popular garden rock in Melbourne gardens.

Daylesford provides an interesting geological outing that is a diversion from the usual tourist activities in the town.