The mine, which produced about 50,000 ounces of gold each year, will go into care and maintenance by November.
Drilling by contractor HMR began two weeks ago and Mr Thomas joins workmates at the rock face 700 metres underground, drilling 20 metres every shift.
In tunnels lit by helmet torches and LED work lights, they leave the samples for geologists to test for gold.
Mr Thomas was here when the mine started in 1996, then a different sight to the grey, dusty surfaces surrounding him today.
"You could see the gold in the walls," he said.
"There's a chance you could see a bit of gold in the ore [today], but it's minute."
With operations winding down, many of Henty's 130 employees are thinking of their future beyond the mine.
For some, its downscaling is the end of a 19-year era, and many have worked there since its beginning.
It's reached 19 years without death or significant injury.
Relief shift boss Marcus Rigby credits Henty with putting enough food on the table for him to start a family with his wife, Lydia, at Port Sorell.
He's been able to have two children, Emerald, 2, and Dustin, 14 months.
Deep underground and 135 metres below sea level, he said the mine had been a strong influence in his life.
"It's just a shame it's ending," he said.
"In a perfect world I'd love for it to keep going."
When he joined in 2006, he had recovered from face and leg injuries in a tyre explosion at a West Australian mine.
Now he ensures Henty keeps trucking ore out to schedule.
He's learnt at the mine "not to be too cocky, shut your mouth and learn from the guys around you".
"The one thing about Henty, there was a wide knowledge base among the guys," Mr Rigby said.
"It's good to be part of something that's gone on. It's good to see something succeed."
Improved gold prices and mining of higher-grade ore this year will let Henty end its cycle on a better note than expected.
Gold is trading at $1500 an ounce, $100 more than forecast in the mine's 2015 financial year plan.
The windfalls will make it $22 million more in cash than forecast this financial year.
According to mine general manager Scott Jones, employees were concerned a year ago owner Unity Mining may not afford to pay their entitlements when downsizing Henty.
"That was one of the major concerns when I got here the workforce had," he said.
Henty made a loss last financial year.
Mr Jones said it could use increased revenue to cover the expenses.
Mr Rigby said there was a different mood around the mine now.
"When you see cash flow, that's good in any sense."
Mr Jones said Henty's financial plan involved maximising cash flow, minimising development, mining only current reserves and paying out entitlements.
Twenty workers have taken redundancies this year, reducing its workforce from 150. By the end of July it will reduce to 88 workers.
The mine will halve its production that month.
When it enters care and maintenance four months later, about 18 employees will remain.
Mr Thomas keeps his eyes on the drill in his pocket of Henty's maze of dark, warm tunnels. He's one worker in a $5 million gold exploration program.
The three-stage drilling program if completed will allow Diversified Minerals, 100 per cent owned by PYBAR Mining Services, earn a joint venture stake of up to 50 per cent in Henty.
Control of the Henty gold mine will remain with Unity.
Mr Thomas is drilling around known ore bodies in the mine, and Henty is optimistic his team will strike more gold.
"As [Henty's] progressed south, they've continued to find more ore," Mr Jones said.
Geologists have confirmed an alteration zone of the type often containing gold continues south beyond known ore bodies.
Unity Mining expects early drilling results in July.
Mr Jones said Henty needed at least 600,000 tonnes of ore reserves discovered to justify reopening mining.
At 19 years, the mine lasted longer than anyone expected. The West Coast operation started with a four-year mine plan.
It has a history of nearing closure before more ore is found.
Unity Mining acquired Henty when it had been going for 13 years and was expected to close within six months.
The company has told the ASX Henty remained "a strategic and highly prospective mineral asset with a significant mineral resource endowment".
Mr Jones said there was a need to keep workers' minds on their job, especially when they were thinking about their futures.
Mr Rigby is resigned to its pending closure and is focusing on his role rather than planning his next job.
As a relief mine shift boss he's used to his plans falling apart at first touch with reality.
After Mr Rigby leaves, the drillers will stay behind on night and day shifts.