Solving the mystery of how 900-year-old African coins ended up in remote Australia could not only recast the history of foreign contact Down Under, but shed light on Aboriginal rock art.

How the ancient Kilwa coins, believed to date from about 1100, came to be discovered on the Wessels Islands off the Northern Territory in 1944 has long posed questions about foreign visits to far off Australian shores.

Australian Ian McIntosh, a professor of anthropology at Indiana University-Purdue University in the United States, said rock art found on the islands -- which includes one image which appears to show a type of European sailing vessel -- could hold some clues.

"A big part of the next stage will be documenting, dating and interpreting (the art), together with indigenous peoples," McIntosh told AFP from his home in Indiana.

The Kilwa coins were discovered lying in the sand by Royal Australian Air Force radar operator Maurie Isenberg during World War II when he was stationed on the island as the Pacific conflict raged.

He found nine coins in all, five African copper pieces and four Dutch coins of European origin which are not nearly as old.

Isenberg initially tried to sell the coins but was unsuccessful. He put them away for decades and it wasn't until 1979 that he sent them to a museum for identification, along with a map showing where he had found them.

McIntosh said there were several theories on the coins, including that they were washed ashore after a shipwreck.

European sailors are known to have sailed the coast of Australia in the 1600s, but it wasn't until captain James Cook landed in Sydney's Botany Bay in 1770 that the British laid claim to the country.

The coins -- believed to have originated in the medieval sultanate of Kilwa, an area which is now in Tanzania -- have led to speculation that parts of northern Australia were visited by other mariners from as far away as the Middle East and Africa.

As McIntosh wrote in a recent paper for the journal "Australian Folklore", in terms of the chain of events in the discovery, "the argument for the involvement of Kilwa traders and also the Portuguese is quite compelling".

He notes the sea route from Kilwa in east Africa to Oman and then onto India, Malaysia and Australia's close neighbour Indonesia was well established by the 1500s and probably for many hundreds of years before that.

McIntosh said a number of his team felt the coins had simply been washed ashore but admitted "we're still toying with a whole bunch of ideas here".

The academic says one explanation could be that a known Indonesian, a shipwreck survivor who lived his life on the Wessels Islands, could have brought the coins to the area. The coins, he speculates, may have represented this man's "worldly wealth".

McIntosh said an expedition he led in July to the site where the coins were discovered, which involved an intensive search in the harsh terrain, had not uncovered any further coins.

"Over the past couple of years we've developed a whole series of hypotheses to explain how those coins might have got from East Africa to northern Australia," he said.

"The whole point of this initial site survey was to try and get enough evidence to push us in particular directions."

What the researchers did uncover was the Aboriginal rock art and some potential evidence of shipwrecks -- a not unlikely proposition given the dangerous reefs off the islands -- in the form of a six-foot piece of timber from a boat.

McIntosh said the scientists would work with indigenous people to look at the art and see whether it matches any known ship types, adding that there were multiple stories of interaction in the past with "different people -- black and white from somewhere else, not Aboriginal".

For now the mystery remains.

"These coins probably remained in circulation for a couple of hundred years but only in the vicinity of East Africa, beyond that they didn't have value," McIntosh said, adding that other coins of this type had only been found in Zimbabwe and Oman.

"Nowhere else in the world have they been found, except for northern Australia," said McIntosh. "Very unusual. That's had everybody puzzled."