Unique diamond find an Australian first

The research team confirmed the presence of metamorphic diamonds in rocks along the Clarke River Fault, west of Paluma in north Queensland, in a new paper published in the Science Advances Journal.

But before any would-be prospectors head out to find their own shiny rock, JCU Economic Geology Senior Lecturer Dr Ioan Sanislav warns the diamonds are invisible to the naked eye.

“Don’t go to Paluma and start looking for them. Even for us, it was very difficult to find them,” he said.

“We had to analyse many, many thin sections of rock, and to prove the diamonds were there, it took about a year-and-a-half.”

Metamorphic diamonds are formed in subduction zones when two land masses collide, causing the edge of one tectonic plate to descend below another and sink deep within the Earth’s interior.

The process of metamorphism, which takes millions of years, generates a massive increase in pressure and temperature as rocks, once at the Earth’s surface, descend down to the earth’s mantle before coming back up in the form of metamorphic rocks containing the tiny diamonds.

These diamonds differ from the more commonly recognised diamonds initially formed in the earth’s mantle, which are mined across the world for use in jewellery, such as engagement rings.

Dr Sanislav said the team made use of a special Raman microscope to identify the diamonds, shooting a laser beam onto a rock sample which can then be used to determine the presence of minerals contained in a rock.

“The light then gets scattered and each mineral has a characteristic response, which gets back to the detector,” he said.

Dr Sanislav said until confirmation of the find near Paluma, there were only six other locations in the world where metamorphic diamonds were known to exist, ranging in size from microscopic right down to nanoscopic.

“In some places, there are metamorphic diamonds which you can’t even see with a microscope. You just see a reading in the rock which indicates they are in there,” he said.

Dr Sanislav said he was drawn to investigate the presence of metamorphic diamonds in the Clarke River Fault due to the work of a former Honours student, who found evidence suggesting the rocks there had potentially experienced high-pressure metamorphism.

“This discovery will influence our understanding of the tectonic models and how the eastern coast of Australia formed,” he said.

“We now need to follow through and see how extensive these deposits of metamorphic diamonds are and where else we can find them.”

The research team involved Dr Sanislav, JCU PhD student Alexander Edgar, JCU Associate Dean of Research Professor Paul Dirks and University of Adelaide Associate Professor Dr Carl Spandler.