Some of these tenements are potentially in production or have changed hands in mergers and acquisitions over recent years.

Many mining companies will not know if their tenements are deemed invalid and the WA government could not tell Australia's Mining Monthly what it was doing about the situation with any substance.

Legal experts told AMM the Court of Appeal judgment was a watershed moment for WA's mining industry.

Allens partner Jodi Reinmuth said the decision, which related to Forrest's attempt to keep mining companies off his Minderoo pastoral estate, "should be taken seriously".

Sand miner Onslow Resources had hoped to mine up to 2.3 million tonnes of river sand and shingle from a seasonal river on Forrest's Minderoo pastoral Station.

Forrest's lawyers went to the court in 2017 arguing Onslow had made an error when it applied for a mining lease.

The case was won in High Court, however, Onslow then attempted to uphold the validity of its tenement in the WA Court of Appeal.

This appeal has, officially, failed.

On August 23 the Court of Appeal found Onslow failed to submit its annual environmental report in time, and that Onslow failed to abide by requirements of the Mining Act of 1978 by not submitting other reports at the time it applied for a mining lease.

Onslow did not submit a comprehensive mineralisation report or mining operations statement on time. It submitted them some months later, which the WA government had previously accepted as common practice. 

This technicality will have a resounding impact on the entire state's mining sector.

Ashurst partner Catherine Pedler, told AMM while the decision in the Court of Appeal was "unsurprising" it created a threat "to the security of mining tenure already granted".

It is not uncommon for mining companies to submit their application for a mining lease without detailed copies of both reports at the time of the applying.

Companies usually "cure" their applications, at a later date, as Onslow attempted to do.

The Court of Appeal decision found this practice was not acceptable, and that Onslow was never granted its tenement because companies could not "cure" their applications.

"A failure to comply strictly with the Mining Act meant the Registrar - determining the outcome of mining lease applications - did not have jurisdiction to even consider whether to grant the application," Pedler said.

Onslow is therefore left without a valid mining lease. Its mining lease simply vanished overnight the day the judgment was published.

This also means hundreds - potentially thousands - of tenements granted to mining companies in WA have not been legally granted and do not exist.

AMM understands some of these tenements will already be in production.

Senior Counsel Stephen Davies, a barrister at Francis Burt Chambers, said the deeper implications of the decision could have a resounding effect on the WA mining industry.

"The risk arises for an original titleholder where there were defects in those documents at the time of the grant," Davies said.

It may not just impact original titleholders, but also mining leases subsequently acquired by purchase and some other mechanisms.  

The requirement to provide a mineralisation report and a statement of operations was introduced in 2006.

Since then thousands of existing tenements have been acquired by mining companies.

Companies may well have acquired mining leases that were never valid. 

"Of far greater significance to the industry is the question of whether the grant of such a tenement is valid in the hands of a subsequent holder, that is a person who has acquired a tenement, with these problems, from the original grantee," Davies said.

"The security of title for a subsequent holder depends on the effect of the indefeasibility provision in section 116 of the Mining Act."

Indefeasibility - conclusive evidence of ownership - is being tested in a separate case before the WA Supreme Court.

"The extent to which the indefeasibility provision protects subsequent holders is still uncertain," Davies said.

"That question is currently reserved in the Supreme Court of Western Australia in a case that came before Justice Tottle called Wyloo Metals."

It will shed light on the question of ownership of subsequent owners of mining tenements.

Why does this matter? It all comes down to land ownership laws.

Under the old system of land title, still prevalent in the United Kingdom, settlement of the purchase of land can take an extensive period of time because someone selling land needs to prove title (ownership) with reference to the original grant of the land.

That can mean examining the validity of numerous transfers of the land back over multiple generations to get comfort of the ownership.

Australia uses a modern system of land title, which is very different, known as Torrens Title.

Under the Torrens system, every time land is sold, there is, in effect a fresh grant of land by the Crown to the purchaser.

There is no need to backtrack over, potentiall, hundreds of years .

Does this indefeasibility apply to mining leases, subsequently acquired? It remains to be seen.

However, the validity of thousands of mining tenements in the state, could hinge on this question.

Davies' opinion is shared by Reinmuth.

She said mining companies were becoming aware of the importance of strictly complying with the requirements of the Mining Act 1978, however, tenements already granted would be affected.

"It is difficult to say what the fallout will be or how many miners are affected by the decision," Reinmuth noted.

"The Western Australian government recognised that a number of the state's mining leases were potentially invalid because it was not uncommon at the time for miners to submit mineralisation reports after lodgement of a mining lease application."

Enquiries by AMM to find out the exact number of leases went unanswered by the government.

The government introduced an emergency bill to parliament in 2018 to prevent the potentially thousands of mining tenements from being ruled invalid.

However, the government has since put the legislation on ice. The bill has not progressed to the Legislative Council and is unlikely to be passed in the short term.

"The WA government continues to consider options to respond to the High Court decision in Forrest and Forrest in consultation with the WA Solicitor General and the Commonwealth Government," WA Mines and Petroleum minister Bill Johnston told AMM.

A spokesperson from the Department of Mines, Industry Regulation and Safety said it stood by its grant of all mining tenements in WA.

"Given the legal implications arising from the Forrest & Forrest Pty Ltd and Wilson High Court decision, DMIRS is currently progressing legislation to remove any remaining doubt over the validity of granted tenements."

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