Underground miners in outback Western Australia have unearthed rare gold specimens which geologists are calling a "once-in-a-lifetime discovery".

These gold-covered rocks weigh in at 90kg and 60kg respectively. ( ABC Goldfields-Esperance: Jarrod Lucas )

Workers at the Beta Hunt mine near the small town of Kambalda, 630 kilometres east of Perth, have brought more than $15 million worth of gold specimens to the surface in just four days.

The gold-encrusted rocks were found about 500 metres below the surface in an area just three metres wide and three metres high.

The largest specimen weighs in at 90 kilograms and took three men to lift it onto the back of a ute.

The quartz rock is covered in an estimated 2,300 ounces of gold worth about $3.8 million at today's gold price.

Another 60kg specimen is estimated to contain 1,600 ounces, or about $2.6 million in gold.

Acting general manager Trevor Steinhauser, senior geologist Zaf Thanos and geologist Lachlan Kenna holding gold specimens ranging from 13kg to 18kg. ( ABC Goldfields-Esperance: Jarrod Lucas )

Senior geologist Zaf Thanos said in most mines around the world it is only possible to see gold through a magnifying glass.

"You might go your whole life and you'll never see anything like it. It's definitely a once-in-a-lifetime discovery," he said.

"As a geologist, like I said, you get excited by a pinhead speck. But to see something on this scale is just phenomenal.

"This sort of bonanza zone is incredibly unique."

The rich cluster of high-grade gold has so far produced more than 9,000 ounces.

More than 9,000 ounces, or $15 million worth of gold, has been recovered in a four-day period. ( ABC Goldfields-Esperance: Jarrod Lucas )

'I've never seen anything like this': miner

Kambalda miner Henry Dole is credited with the discovery, describing it as hitting the "mother lode".

Mr Dole had drilled holes into the wall of the mine and planted explosives which were fired once he was safely on the surface.

A close-up look of the gold, which is hosted in quartz. ( ABC Goldfields-Esperance: Jarrod Lucas )

When he came back to the same area for his next shift, Mr Dole thought it was business as usual.

"Everything was covered in dust, and as I watered the dirt down there was just gold everywhere, as far as you could see," he said.

"I've been an airleg miner for 16 years. Never in my life have I ever seen anything like this.

"There was chunks of gold in the face, on the ground, truly unique I reckon.

"I nearly fell over looking at it … we were picking it up for hours."

Security tightened but temptation remains

Beta Hunt mine workers were checking vehicle wash bays and gutters after gold fell off the back of trucks. ( ABC Goldfields-Esperance: Jarrod Lucas )

A handful of gold rocks could be worth several thousand dollars, so security has been beefed up in the days since the find.

Armed guards have been transporting the gold to a secure vault.

These tiny fragments were found in the gutter and handed in by a worker cleaning his vehicle in the wash bay. ( ABC Goldfields-Esperance: Jarrod Lucas )

Workers are under constant video surveillance and the area of the mine where the gold was found has been fenced off and padlocked.

The irony is that Beta Hunt has been mined for nickel, which is a key ingredient in stainless steel, since the 1970s, and gold has always played second fiddle.

There are stories among the workforce dating back to the early days of the mine which suggest similar bonanza finds may have been made in the past but were not considered significant at the time because of low gold prices.

There are also tales that workers in those days would bury bags of gold rocks in the event the commodity came back stronger.

A haul truck at the entrance to the underground portal at the Beta Hunt mine. ( ABC Goldfields-Esperance: Jarrod Lucas )

Large specimens to be auctioned off to collectors

The mine's Canadian owners, RNC Minerals, are planning an auction for the large specimens.

RNC Minerals president Mark Selby is calling the find a "world-class discovery". ( Supplied: RNC Minerals )

RNC president Mark Selby said collectors in north America and around the world are known to pay up to a 50 per cent premium on the gold metal value for rare specimens.

"Given the rarity of the rock, and the physical beauty and presentation of the gold that's there, it's a very spectacular stone in multiple ways so we'll see whether 20, 30 or even 50 per cent premiums apply here," he said.

"We're really looking forward to auctioning the key stones off over the coming weeks.

"There's a pretty select group of collectors who this would appeal to.

"When you look at nuggets, which are a solid piece of gold, the biggest are around 2,000 ounces, so this is right up there in terms of the largest specimens we've ever seen."

Even this fly has gold fever. ( ABC Goldfields-Esperance: Jarrod Lucas )

Rich find will not stop sale of Beta Hunt

An interesting sub-plot to the discovery is the fact Beta Hunt's future had been in doubt.

The Toronto-based company was battling to keep it open and put Beta Hunt on the market several months ago.

A truck driver clocks off after a long shift at the Beta Hunt mine. ( ABC Goldfields-Esperance: Jarrod Lucas )

The sale process is now in the final stages, but Mr Selby said the "world-class discovery" does not make RNC think twice about selling up.

"When we started the sale process it wasn't because we don't like the asset. We always believed that it had the potential to become a multi-hundred-thousand ounce mine, we just weren't able to raise capital required to do the exploration drilling," Mr Selby said.

"We believe that a different set of management should be running the asset with the right amount of capital to take it forward."

Geologist Lachlan Kenna, air-leg miner Henry Dole, mine foreman Warren Edwards and senior geologist Zaf Thanos with the biggest specimens found at Beta Hunt. ( ABC Goldfields-Esperance: Jarrod Lucas )

Are the miners just scratching the surface?

The question now is whether there is more bonanza gold waiting to be found at Beta Hunt.

In the eyes of Mr Dole, there is no doubt and he hopes it is just the beginning of a revival for the Kambalda community, which has been hit by multiple mine closures in recent years.

"It's no secret we were looking down the barrel for a while, but with this, it's picked everyone's morale up," he said.

"It's good for the town, the mine life, all of that.

"I truly believe there's something bigger and better down there.

"I reckon we're just on the fringe of it … and if we get deeper I reckon we'll find more."