Research on earth’s ancient water cycle may shed new light on how largest gold deposits formed

Most of the gold mined in the Fimiston open pit, pictured here, occurs within ore lodes formed by ancient shears in a rock unit called the Golden Mile Dolerite. (Image by Brian Voon Yee Yap, Wikimedia Commons).

Researchers at Curtin University discovered that water was transported much deeper in the early earth than previously thought, a finding that sheds new light on how continents were originally formed.

In a study published in the journal Earth and Planetary Science Letters, the scientists answer long-standing questions about the early earth’s water cycle and point out that the way water is stored and transported through the planet’s crust influences everything, from where volcanoes and mineral deposits form to where earthquakes occur.

“Although we understand the modern deep-water cycle, we know very little about how it worked when earth was still a very young planet,” lead researcher Michael Hartnady said in a media statement. “Multiple lines of geological evidence show that water was transported to great depths within earth all the way back to 3.5 billion years ago, although it is not well understood how exactly it got there.”

Hartnady and his team used sophisticated modelling to show that primitive high-magnesium volcanic rocks – that erupted onto the ocean floor in the early earth – would have soaked up much more seawater than more modern lavas.

“This water, which is locked into particular crystals within the rock, would have been released as the rocks were buried and began to ‘sweat.’ In modern lavas, this sweating happens at a temperature of about 500 degrees Celsius,” the scientist said.

But the recent results indicate that much of the seawater initially bound within the ancient primitive lavas would have been released at much higher temperatures, greater than 700 degrees Celsius.

According to Hartnady, this means that the water was transported much deeper into the early earth than previously thought and that its release would have caused surrounding rocks to melt, ultimately forming continents.

“Interestingly, the oldest parts of the continents, the cratons, also contain some of the largest gold deposits on earth including the Golden Mile near Kalgoorlie,” the researcher said.

“These gold deposits required huge volumes of water to form, and we still don’t have a good explanation for where this water came from. Our new research may help solve these and other questions, perhaps even those related to the origins of life.”