SYDNEY (AFP) - An Australian mining firm was convicted on Friday of desecrating a sacred outback Aboriginal site in a landmark ruling protecting the beliefs of the beleaguered minority in the country.

OM (Manganese) Limited, an Australian subsidiary of Singapore-based OM Holdings Limited, was fined A$150,000 (S$172,031) for damaging the spiritual significance of an Aboriginal rock site at Bootu Creek, north of remote Tennant Creek in the Northern Territory.

OM Manganese had previously been convicted of physically damaging the site when an overhanging rock feature known as the Horse's Head collapsed due to nearby blasting activities in 2011, destroying the area known in English as "Two Women Sitting Down".

But Darwin magistrate Sue Oliver on Friday ruled it had also amounted to desecration.

"The defendant did not consider damage to the site as a vague and remote possibility," Ms Oliver said, describing the company's failure to do so as "wilful blindness".

"The defendant company made decisions that involved the sacred site that favoured business and profit over the (cultural protection) obligations they had."

Ms Oliver imposed the fine for what the local Kunapa people said amounted to destruction of the site, forever disrupting their relationship with the land and its mythology or "dreaming".

"It will always remain a sacred site to us, but it has been ruined and we don't know what to do," said Kunapa representative Gina Smith of the site which had been "there for thousands of years as part of our culture and our story".

"It's been significantly changed, which makes it much harder for Aboriginal people to recognise the dreaming," she added.

"We're not likely to use it any more."

According to the Kunapa dreaming, a marsupial rat and a bandicoot fought over bush tucker, or native food, at the Bootu Creek site and their blood spilled over the rocks, turning them the rich red of manganese ore.

The Aboriginal Areas Protection Authority, the statutory body responsible for overseeing sacred sites in the Northern Territory which brought the case against OM Manganese, welcomed the "historic" ruling.

"When a sacred site is desecrated or damaged it tears the social fabric of the affected community, as the harmony of those people is inherently linked to that sacred site," said AAPA chief Ben Scambary.

OM Holdings said it had contested the desecration charge on the basis that the damage was unintentional, but it accepted Oliver's ruling.

"The company never intended to harm, damage or disrespect the sacred site. We sincerely regret the damage and the hurt caused and I unreservedly apologise to the site's custodians and traditional owners," OM CEO Peter Toth said in a statement to the Australian stock exchange.

Aborigines, the most disadvantaged Australians, are believed to have numbered around one million at the time of British settlement in 1788. There are now just 470,000 out of a total population of 23 million.