Kalbar Conversations Column

The Story of Zircon (Part 1)

   Wednesday 18th November, 2020

Earlier this year we explained how the Glenaladale mineral sands deposit formed and how the heavy minerals - zircon, rutile, leucoxene and monazite – concentrated by wave and wind action along an ancient coastline.

In the next few Kalbar Conversations columns we will provide some information about each of the heavy minerals. The first heavy mineral of focus is zircon – the major component of the Fingerboards project deposit.

What exactly is zircon?

Zircon deposits take millions of years to form. The mineral zircon is found in trace quantities in many igneous and metamorphic rocks, though it may not be noticed because of its very small particle size. Zircon occurs in higher concentrations in pegmatites and carbonatites. Due to its hardness and durability, zircon does not weather easily, hence why it’s found in sedimentary deposits and is a common constituent of most sands. Grains of zircon are usually less than a millimetre in size.

Zircon is also referred to as zirconium silicate – the chemical composition is ZrSiO4. It is a co-product from the mining and processing of ancient heavy mineral sands deposits. Although Australia is the major source of the world’s zircon through mineral sands mining (35 percent of the world’s zircon), it is also found in Southern Africa, Southeast Asia, China, East and West Africa, Ukraine and North and South America. Zircon content varies between deposits. The Fingerboards project zircon content in ground is 1.2 percent.

When zircon is modified chemically, there are two common derivatives – zirconium the element, and zirconia the oxide.

The element zirconium – Zr in the periodic table - is the 20th most abundant element in the earth’s crust, and takes the form of a silvery grey metal.

Zirconia is processed zircon which has been melted at very high temperatures (typically above 2,600oC in an electric arc furnace) to form zirconium oxide – ZrO2.

Zircon is no different to other rocks and minerals in that it is a naturally occurring radioactive material (NORM) as small amounts of radio nuclei became “locked” in the zircon crystal structure when the earth was formed billions of years ago. Natural radiation from zircon is extremely low and similar to that of other naturally occurring sources such as granite.

In our next story we will talk about the uses of zircon and its importance in our daily lives and modern world.

Matt Golovanoff - Geologist