In the far north-west of Tasmania there is a strip of shore that has been returned as Aboriginal land. This is Preminghana, a wild and beautiful place. Just to the north lies Cape Grim, once the site of a notorious massacre, now better known for the purity of its air, reputedly the cleanest in the world. Wind farms adorn a nearby promontory. The turbines can be seen carving circles slowly in the air. It is a weird conjunction of the pre-European and the post-carbon. For hidden on the shore at Preminghana is the finest expression of Aboriginal art in Tasmania.

Under a heaped dune, by a small creek, lies a complex of remarkable carvings. A matrix of geometric motifs – concentric circles, drifting trellises, rows of dots, crosses, parallel lines – has been chiselled into slabs of fallen sandstone along a buried cliff face. Certain rock formations are so covered with engravings that they resemble monumental abstract sculpture. Elsewhere, tracks of a bird – thought to be the extinct Tasmanian emu – have been discovered carved into the rock. Tools of hard quartzite and basalt have also been found, perhaps the Aboriginal sculptors’ chisels.

Giants of Australian archaeology were once intensely interested in the site. Fred McCarthy, author of Stone Implements of Australia, said it was as important to the human story as the temples of Abu Simbel, then saved from the rising waters of the Aswan Dam by hundreds of millions of dollars. McCarthy was hoping for funds at Preminghana. His hopes were not realised. All that can now be seen of this great work of hunter-gatherer art is a pair of circles floating in a single block of protruding stone. The rest lies buried. It is a strange story.

Workers removing a panel with a cross cut saw in 1962. Tasmanian Museum and Art Gallery

Peter Sims tells the tale. He is an octogenarian former industrial chemist with hawk-like eyes who has devoted much of his life to rock art and is now finishing a work on Preminghana. At his home in a rainforested dell outside Devonport, and later in his personal archive at the Queen Victoria Museum in Launceston, Peter pulls out the old photographs and faded documents, and puts the pieces together.

A schoolteacher and amateur archaeologist made the rediscovery in 1933, after the petroglyphs were blown free of sand at Mount Cameron West, as it was then known. Archibald Meston was taken to the site by shepherds from the nearby Van Diemen’s Land Company (a pastoral concern with a bloody past in the island’s notorious Black War of the 1820s). Meston immediately recognised the petroglyphs’ significance and prepared a paper for the Royal Society of Tasmania.

This elicited the attention of a stonemason, Leo Luckman, who documented the site and removed a fallen carving in several pieces to his local museum in Launceston. Then, in 1962, the island’s leading museum, the Tasmanian Museum and Art Gallery (TMAG) arrived on the scene. Workers took a crosscut saw – generally used for logging operations – and cut off one of the finest panels, hefting the slab back to Hobart. At the time this caused real dismay in the Australian archaeological community and was deplored as official vandalism by John Mulvaney, ‘the father of Australian archaeology’, at the Australian Institute of Aboriginal Studies in Canberra.

Rhys Jones, a young Welsh archaeologist freshly out of Cambridge and soon to be a gilded name, was dispatched to the Tasmanian backwater. Together with Fred McCarthy, he did a major excavation in 1969, making fibreglass casts of the motifs. They carbon-dated material and found the carvings were at least as old as the Hagia Sophia and probably far older. Rhys Jones judged the site was abandoned to windblown sand, then soil, around 850 years ago, until cattle caused erosion.

There was talk of building a dome and seawall to protect the ancient art from the abrasive sands and waves of the Southern Ocean. Eventually, in lieu of funds, concerned locals, with a nod from the Institute of Aboriginal Studies, decided to rebury the petroglyphs in the late '70s. The ground was seeded with marram grass and has now changed beyond recognition. In 1995 the Liberal state government of Ray Groom returned Preminghana to the Aboriginal Land Council of Tasmania. The carvings have not been sighted since.

Peter Sims is quietly incredulous as he relays this tale. At the time when the petroglyphs were reburied, Sims and others believed that in 20 years' time there would be an "enlightened community" to protect and promote them.

A photograph of one of the carvings taken in 1971. Peter Sims

"Well, it’s not 20 years, it’s 50 years," he says. "My lifetime will pass and nothing will change. It should somehow be resurrected. TMAG holds the key.’'

Located down near the Hobart docks, TMAG is not to be confused with the city’s other museum, David Walsh's fizzing, contemporary Museum of Old and New Art (MONA). In comparison, TMAG can seem traditional, even sedate.

Yet inside the museum can be found a willing exploration of Tasmania’s complex past. There are two galleries dedicated to the island’s Indigenous people.

According to a written statement provided by the Museum’s communications manager, Andrée Hurburgh, the petroglyph was taken off display in 2005 ‘'at the request of the Tasmanian Aboriginal community’'. Later, from annual reports it emerged that in 2011-2012, TMAG had commenced formal discussions with the custodians of the site ‘'regarding the return of the petroglyph'’. The status of those discussions is unclear.

Graeme Gardner, head of the Aboriginal Land Council of Tasmania, says there has been ‘'no discussion with TMAG for years'’.

Aboriginal activist and lawyer Michael Mansell is more forthright: "They’re not going to give up anything willingly. They think that they are the keepers of mankind’s history. They think that they are the only ones who can be trusted. But the carvings were stolen – sawn off and taken away in a truck. If that’s not desecration, I don’t know what is."

"White people say Aborigines were illiterate," Mansell says. "We weren’t illiterate. If you carve out the camping grounds, the walking tracks, the totems to honour as you go through, the birds and the trees you cannot cut down, you might not be writing it down in English, but you are writing down messages, you are writing a roadmap to the territory. Then this lot come in and carve it up."

Fred McCarthy examines carvings of emu feet during the 1969 excavation. Rhys Jones (right) and Nick Peterson are seated.  Jack Thwaites Collection, Tasmanian Archives

Director of TMAG Janet Carding, in written answers to questions, confirms the museum accepts the Tasmanian Aboriginal community has "a claim on the Preminghana material" and adds it is open to restarting formal discussions ‘'when requested'’. She also says the museum is exploring with the Land Council their viewing the material held in storage.

Informed of this, Michael Mansell says, ‘'This is progress. We will sit down and talk with them now about a timetable. We will hold an Aboriginal community meeting to determine exactly how the missing petroglyph should be repatriated to the place of origin, the place from which it was cut.’'

Paul Taçon is a leading authority on rock art, the co-author of an assessment of best practice for the Getty Conservation Institute, entitled Rock Art: A Cultural Treasure At Risk (2015). Originally from Ontario, and a recipient of the Rhys Jones Medal (the highest honour in Australian archaeology), he has had exposure to similar issues in Canada, Australia and many parts of the world. From his office at Griffiths University, Professor Taçon says the Aboriginal Land Council of Tasmania has a claim to the missing piece and it should be returned to them. In his view, proper resources – funds, technical advice, a place to care for the sawn-off petroglyph – should also be made available once it is returned.

Beyond repatriation, it is unclear, however, what the fate of the Preminghana carvings could be. To uncover them once more for viewing would be fraught with hazards. Vandalism has occurred at other rock art sites in Tasmania, most recently three years ago, when red and yellow ochre hand stencils thousands of years old were defaced in the Tasmanian Central Highlands, scratched at with rock.

To build a protective structure against erosion would also run to several millions of dollars. And then there is the matter of climate change and receding shorelines. ''The petroglyphs could be carefully uncovered,'’ Paul Taçon suggests, ''and a 3D laser scan undertaken. 3D models could be made and an exact replica created, if the Tasmanian Aboriginal Land Council wanted one. The petroglyphs could then be reburied, if that is what the Aboriginal community would like.’'

He draws a parallel to the great Chauvet cave paintings in France where a replica now ensured that a timeless work of the human imagination was not damaged, and yet tourists still had ‘'a realistic experience'’ of the site.

Graeme Gardner says that leaving aside questions of money, ‘'which we don’t have'', these were all options that could be considered if the Tasmanian Aboriginal community felt it was able to decide. The first step remains the missing piece. His personal preference is that it be restored exactly as it was beside the bracing waters of the Southern Ocean, but there must be community consultation. ‘'And we don’t need to see it to know that it’s there,’' he adds. ‘'We just have to have the right to make the decision. That is the key.’'