Why is there a mineral sands deposit at Glenaladale?
The grains of sand that make up the Glenaladale mineral sands deposit started their life many millions of years ago and have been on quite a journey. Long before becoming sand, the minerals began as 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. The heavy mineral and quartz are hard minerals that are very resistant to weathering, and over millions of years this parent 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 between two to five million years ago, the coastline was much further inland than it is today - in fact, sea levels were approximately 100 metres above their current level - somewhere near Iguana Creek.
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.
The Glenaladale deposit is classified as a Placer deposit – a natural concentration of heavy minerals caused by gravity on moving particles. The heavy minerals of interest at Glenaladale are rutile, ilmenite, zircon and monazite. They are known as heavy minerals because their relative density is quite high – in the order of 4 to 5.5 grams per cubic centimetre. Comparably, regular beach sand, which is mostly made up of quartz, has a relative density of 2.65 grams per cubic centimetre.
In future editions of Kalbar Conversations we will talk more about how these heavy minerals will be mined and processed, and what is driving the growing global demand for these heavy minerals.