Erosion of the Australian Alps between the last five to ten million years has formed many mineral sands deposits. The eroded minerals were carried down rivers to the sea where they settled and formed deposits.
The grains of sand that make up the Fingerboards mineral sands deposit in Glenaladale were originally crystals which grew when magma cooled to form the igneous rocks of the Victorian high country.
This igneous (parent) rock contained small amounts of heavy mineral, along with quartz and feldspar. As hard minerals, the heavy mineral and quartz are very resistant to weathering. Over millions of years the igneous rock slowly eroded and weathered until all that was left were the hard, resilient grains of sand. These grains of sand were then carried to the coast by the Mitchell River during floods and heavy rainfall.
When all this was taking place about 2-5 million years ago, the coastline was much further inland than it is today. The grains of sand were carried to the west of the river mouth by the ocean current, then washed onto the shore by waves. As each wave retreated to the ocean, the heavy grains of sand (the heavy mineral) were left behind, and the lighter grains of sand (the quartz) were washed out to sea.
This repetitive concentrating wave action over millions of years – a slow gravity separation process – formed the economic concentration of heavy minerals at Glenaladale.
During the past 2.6 million years, sea levels dropped. As a result, the deposit became stranded well away from the coastline that we know today.