When Harold Lasseter set off on his fateful trek almost 80 years ago, he could scarcely have imagined that his tale would become a source of endless fascination for prospectors and conspiracy theorists alike. As the story goes, Lasseter claimed to have discovered a miles-long quart reef filled with gold in a remote part of the central Australian desert. He spent the rest of his life trying to prove the reef’s existence to his many sceptics, only to die years late while attempting to relocate it.

Melbourne-based filmmaker Luke Walker first heard of Lasseter’s Reef from a  friend while living in London. It quickly became an obsession for the director, and his latest documentary, Lasseter’s Bones, is the culmination of several years’ work on the topic.

“I was fascinated by the idea that there could be a reef of gold that big, just lost in the middle of Australia,” laughs Walker.

After exhausting every publicly available record on Lasseter’s life, Walker managed to track down his son Bob and, after much deliberation, decided to call him. Bob Lasseter had spent much of his 85 years trying in vain to find his father’s reef, heading into the desert almost every year in the hope of vindicating his father.

Though hesitant at first, Bob soon formed a friendship with Walker, providing a turning point in the making of the documentary. “At first he was quite wary, because he gets hundreds of people ringing him up… and most of them are crazy!” Walker recalls. “He realised after twenty minutes of talking to me that I’d spent a lot of time researching this.”

That’s when Bob invited Walker to accompany him on his next trip out to the desert. “There was simply no way I could turn down that offer,” says Walker.

After finally completing Lasseter’s Bones, Walker is convinced there is at least an element of truth to the story. The unresolved questions surrounding Lasseter’s death and the random Elvis-like sightings of the man himself only add to the legend.

In the end, his search became about much more than the lost treasure. “Originally it was about gold,” Walker admits. “That was what drew me to the story, and that’s what draws everyone to it.

“But then it becomes about truth, getting through this fog and trying to clear it away to see what really happened. I was trying to understand why people get so obsessed with this story.

“I came to the conclusion that it’s largely because it’s an unfulfilled narrative. It’s just so irresistible. You cannot bear the idea that the story didn’t finish properly… and people feel a need to complete it in some way. Lasseter can’t just die in the desert for no reason.

“The film is a tapestry of all the things I encountered along the journey. I hope it presents the full spectrum of every argument to do with Lasseter and what he did or didn’t find, so that audiences can make up their own minds. That’s what a good documentary should do.”

Lasseter’s Bones is screening exclusively at Cinema Nova from 31 October.