Melbourne: Gold was far more abundant in the oceans three billion years ago—ten times as compared to the modern oceans, a new study has claimed.

Researchers have developed a new technique to estimate how much gold was in oceans billions of years ago. The team led by the University of Tasmania’s ARC Centre of Excellence in Ore Deposits (CODES) created a “time series curve" that shows how gold concentrations in the oceans have varied through time over 3.5 billion years.

The research found that gold was far more abundant in the oceans at certain periods in the past, whereas at other times, gold was virtually absent from the oceans. The time series curve indicates that three billion years ago there was ten times the gold in the ancient oceans compared to the modern oceans—more than 2,000 times the Fort Knox gold reserves in US, researchers said.

“This was a time when the world’s greatest gold ore deposits were formed in South Africa in the Witwatersrand Basin," said Professor Ross Large, from CODES. “Over the next 400 million years, gold remained high in the oceans and many other important deposits formed, including the Golden Mile in Western Australia," said Large.

Large said the concentration of gold in the oceans indirectly relates to gold ore generation in the shallow crust. “This means peak times of gold in the oceans correspond to the best times in Earth history for gold ore formation," said Large. “Firstly, there was far more volcanic activity and gold was carried in micro-particles in the volcanic magmas and volcanic gases from deep in the Earth and erupted on the Earth’s surface," he said.

“Erosion then transported the gold along with other related elements arsenic, nickel, antimony, tellurium and mercury into the oceans. The very ancient oceans were therefore enriched in gold but highly toxic," Large said. Following this period of gold-rich oceans, the time series curve shows that in middle Earth history, during the Proterozoic period, gold was at an all-time low in the oceans.

This helps to solve a great conundrum in Earth Sciences, of why so few gold deposits are present during this billion-year period, researchers said. However, gold returned to the oceans in a third period of Earth’s history starting 550 million years ago. Experimental studies have shown that the solubility of gold, under ocean conditions, is strongly affected by the amount of oxygen dissolved in the seawater.

“When oxygen increased during the explosion of life in the oceans in the Cambrian period, gold also gradually increased and ultimately reached a maximum 525 million years ago," Large said. The research was published in the journal Earth and Planetary Science Letters.

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