Mansfield is located near the alpine resort of Mt Buller, approximately 21/2 hours from Melbourne, passing through the towns of Yarra Glen, Yea and Bonnie Doon along the way. Geology of the Mansfield region is quite diverse. Leaving Melbourne and travelling through Yea, marine sediments of the Melbourne Trough are evident in the road cuttings. Near Yea is a National Heritage Site for the Baragwanathia Plant Fossil, which occurs in a road cutting just outside of Yea. In the hills between Yea and Bonnie Doon lies the Strathbogie Granite, a large coarse-grained granite batholith. Crystals of smokey quartz, topaz and tourmaline can be found in the creeks here. Taking the track to Tallangalook from Bonnie Doon, old gold workings are evident in the creek and around Tallangalook, once a rich gold mining area. Further up the mountain from Tallangalook is the Crystal King Quartz Crystal Mine. Huge quartz crystals were mined here during the 1950’s. One of the shafts was recently reopened, however, no further crystals were recovered and the mine is kept in maintenance state. The shafts were dug into several large pegmatite pipes, which hosted the quartz crystals.
Closer to Mansfield, along the Ford Inlet Road, are the Old State Phosphate Mine Workings. Many shallow trenches and pits are left and samples of phosphorite and phosphate minerals can be collected. Turquoise, wavellite and variscite can be found, however the specimens are very small.
Mansfield lies within the Mansfield Basin, a sequence of terrigenous sediments that are called “Red Beds”, due to the rusty red coloring from the iron left in them. Red Beds contain huge deposits of uranium in overseas countries and drilling around Mansfield has located traces of uranium minerals. The small size of the Mansfield Basin and lack of coarser sediments means no economic deposits of uranium occur here.
Travelling into the Tolmie Ranges, north of Mansfield, rocktypes change to a sequence of volcanics, consisting of rhyolites and quartz porphyry. Approaching Whitfield, rocktypes again change as we enter the Edi-Cheshunt Slate Belt. The Edi-Cheshunt Slate Belt is a group of Ordovician-Silurian marine sediments, including black slates that host widespread turquoise mineralisation. Turquoise occurs as thin veins parallel to the cleavage in the black slates. Most of the turquoise veins are soft and friable but occasional hard patches do occur. There are many old turquoise diggings in the hills around Cheshunt but often it pays to follow the strike of the black slates until the characteristic blue-green stains are found, marking turquoise veins in the slate.
Further into the alpine region around Mansfield lie the Cambrian Greenstones of the Howqua Hills and the gold bearing Mt Easton Slate Belt between Woods Point and Walhalla.
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Turquoise from Whitfield
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Smokey Quartz Crystal in Pegmatite Matrix, Crystal King Mine
