Sometimes there's more, sometimes there's less, but that's about the average - the gold comes in tiny nuggets, sometimes about as big as a matchhead or fingernail.

There's a lot of work just finding where it is, chasing down quartz reefs amid the waste rock, but once they find it, the miners make the most of it.

The Courier was invited to join the Committee for Ballarat for an underground tour last week at Castlemaine Goldfield's Ballarat mine, heading hundreds of metres beneath the surface to see what goes on in a surprisingly busy subterranean workplace.

Led by our trusty tour guides Brandon and Jack, we don bright red 'visitor' overalls and hard hats with lights, as well as a self-rescue kit, which is a bag of air that'll keep us alive if anything should happen.

It probably won't, they grin - while they've seen pieces of rock "the size of Tasmania" occasionally drop, this is their workplace, and Brandon drives up and down the passages eight or nine times a day.

He's a truck driver, taking ore back to the surface for processing, he explains - with a degree in mine engineering, he's enthusiastic explaining how the systems work.

The numbers spraypainted on the walls increase as we drive a ute further down, at one stage ticking past 600 metres from the 'portal' to the surface - they don't use sea level here.

We watch a 'dogger' rumble up to where we've parked in an antechamber, and Whitey the driver jumps out to let people take photos in the cockpit.

Then we head further down, where a 'jumbo' is drilling support bolts into the rock walls with two ponderous boom arms.

WATCH THE JUMBO AT WORK:

Trucks and utes are always driving up and back, and there's an interesting discussion about who has right-of-way in the cramped tunnels.

It's damp underground - the camera fogs up instantly when we get out of the ute - with deep puddles on the ground.

We're warned not to touch the bright quartz on the walls, as the rock blasting can leave it sharp enough to cut bare skin.

It smells like subway stations anywhere, and there's a dull noise from ventilation systems.

The mine reopened in 2011, before it was taken over by Singapore-listed LionGold in 2012.

To stay sustainable, the aim isn't to mine all the gold at once, instead geologists explore ahead to ensure there's at least a year's worth of gold ahead of them.

One of the geologists, Matt Hernan, said about 50 kilometres of sample cores are drilled each year.

He said the ore bodies were "complex".

"It makes it difficult to estimate, and it means we're always battling with understanding the geology and trying to make decisions," he said.

READ MORE: Check out the last time The Courier visited the mine

"We regularly get surprises on a small scale - I do get surprised by how often we're able to find new reefs, when you explore for something, it starts in the geologist's imagination, then you drill a hole into something in your imagination and you find quartz and gold there.

"I'm genuinely surprised by how frequently we get success."

All that exploration information is turned into 3D maps, which inform where the miners look next.

Crews work in twelve hour shifts, one week on, one week off, alternating between day and night.

They begin before 7am or 7pm, getting suited up before the daily briefing.

Mining manager Darren Watkins said it's always busy above the surface as well.

"My work finishes when the ore gets handed over to the processing guy - there's other people like fitters, maintenance, mobile plants, they do a lot of maintenance work, and there's a team of guys in the workshop 24-7, we do all our own light vehicle maintenance," he said.

"The place never closes."

Having worked in mining for 25 years, Mr Watkins has seen a lot change.

"From a safety point-of-view, the industry's moved ahead significantly in preventing harm day-to-day," he said.

"Technology is certainly improving as well, it's making work safer for us, and more productive as well."

It's not just safety that's improved - according to the mine's environment and community manager Kurtis Noyce, its green credentials were strong enough to woo him from a Landcare background.

"A lot of my friends were stirring me up about going into mining, but I found the company had a very strong environmental perspective," he said.

"They want to do it, they're ahead of the game in sustainability as a business - we're prepared to take a financial hit to improve the quality of life on the surface for people."

BACK TO THE SURFACE:

Heading back through the portal, we emerge blinking into a rainy Ballarat afternoon, and we're quickly shown the vehicle plants and refueling station as we head back to the office.

Looking around the surface site, it's surprisingly heavily wooded, which helps obscure the processing operations from the public - there are houses nearby, though the main worry is when blasting occurs.

To prevent disturbances, it only happens during business hours, and most people would never feel it, Mr Noyce said.

He added he was proud of the mine's focus on local suppliers, including Ballarat-based Gekko, which handles the processing.

"We're quite of the fact that our processing plant is not only built in Australia, it's built in Ballarat," he said.

"Seventy or 80 per cent (of the gold) can be extracted using simple techniques from the gold rush, and we don't use a lot of chemicals or excess energy to extract the gold from the quartz."

The gold rush link is worth noting, as the mine pushes north underneath Sovereign Hill to some historic leads.

The mine's boss, Stephen Jeffers, said people would be surprised at how big the project is.

"From where we are out at Mount Clear, there's a patch of nothing until you get deep enough, but then you get to Elsworth Street, there's a patch underneath the Gold Museum, and at Llanberis Reserve and the skate park, it's pretty intensive around there," he explained.

"We've just finished mining an area directly underneath the Bakery Hill post office."

The focus, he said, is on the future - while there's woes about taxes and future investment, there's "decades" of opportunities for gold mining underneath Ballarat.

READ MORE:

"We're learning more about the ore body and we're getting better at it from a technical sense," he said.

"The one thing we do have is lots of opportunity."

Have you signed up to The Courier's variety of news emails? You can register below and make sure you are up to date with everything that's happening in Ballarat.