Researchers say the discovery in rocks from the beach at Millport on the Isle of Cumbrae has raised the possibility of bigger finds elsewhere.
This is because gold deposits are normally found in “veins” deep in the Earth’s crust, which are produced by water flowing at high temperature.
The study by researchers at Aberdeen University adds to a growing awareness that concentrations of gold can be present in red sandstone or other common sedimentary rock.
Some studies have been carried out in England where gold has also been found in red sandstone, but not to the consistency discovered in the Millport rocks.
Professor John Parnell from the School of Geosciences said: “In undertaking this research I was initially interested in analysing little structures found within common red sandstone rocks which we took from the beach at Millport, which to the naked eye appear as tiny black spots.
“By analysing the structures using a high-powered microscope, we discovered that they contain concentrations of gold, which is unusual because gold normally tends to be concentrated by hot waters rising up through cracks in the Earth.
“In this case the gold has been formed and concentrated in a completely different environment, which raises the possibility of similar structures appearing within red sandstone elsewhere but on a much bigger scale.”
“While there is certainly no prospect of a modern-day gold rush in Millport, this analysis is helping us to understand unusual circumstances where gold can be formed, which in the future may even lead to discoveries that are commercially viable.”
The study has been published in the Journal of the Geological Society.