Miner Northern Star Resources strikes gold under Kalgoorlie Super Pit

It has been described as the “first glimpse” of a new world-class gold system beneath the famous Kalgoorlie Super Pit.

Despite more than a century of mining on the historic Golden Mile, exploration has been limited outside of the rich deposits that have produced more than 21 million ounces since the Super Pit began production in 1989.

Underground access portals on the west wall were developed last year to provide new drill pads for testing to the northwest of the existing pit.

The work represented the first major underground mining activity on the Golden Mile in more than 30 years.

The investment by Perth-based gold mining company Northern Star Resources is starting to pay off after it said it had hit rock bottom.

In the company’s annual reserves and resources statement to the ASX this week, Northern Star said drilling had increased underground resources by 20% to 5 million ounces.

Northern Star Resources Chief Operating Officer Simon Jessop inspects the entrance to the new underground portal inside the Super Pit in May last year. (ABC Goldfields: Jarrod Lucas)

Northern Star chief executive Stuart Tonkin said the portals had been developed to a length of 1.5km and drilling only started last November.

“It really didn’t take that long to drill and we’re obviously continuing to drill now,” he said.

“But we’ve already added a million ounces of suspected material.”

He said there were 5 million ounces of Sonny’s underground resources.

“So again it shows us the thin end of the wedge,” he said.

Deepest works 1.4 km underground

More than 3,500 km of tunnels and shafts have been created under the Super Pit – equivalent to driving from Perth to Sydney – in a century of mining in the area.

The deepest historic workings extend to about 1400 m below the surface.

But the drilling reached gold mineralization as deep as 2 km below the surface.

Northern Star has made no secret of its ambitions to eventually restart underground mining and is taking delivery of 39 new haul trucks as part of a $250 million fleet overhaul.

A man wearing high visibility workwear and safety glasses at a mining site.
Northern Star Resources Managing Director Stuart Tonkin inspects the Fimiston plant.(ABC Goldfields: Jarrod Lucas)

“We’re really only looking at one quadrant right now,” Tonkin said.

He said the company would put more drills on the south as well as on the east side under the plant.

Life of mine beyond 2035

Current reserves at the Super Pit and nearby Mt Charlotte mine stand at 11.9 million ounces.

There are 27 million ounces of resources that require further geological work to prove they are reserves under the JORC code.

The significance of the latest underground drilling results is that they are outside the current mine plan, which will drive further Super Pit cuts through at least 2035.

Mining machinery in a gold mine.
Drilling from the underground portal has already defined one million ounces of new gold resources. (ABC Goldfields: Jarrod Lucas)

“That’s currently not in the plan, so it’s important that we step in and do that work over the next couple of years to define that and start to figure out the scale and the magnitude and how that can fit into the mine plan,” Mr Tonkin said. said.

He said he was not surprised by the latest discovery.

“We really believe we have several decades ahead of us,” Tonkin said.

“There’s no geological reason why it ends deep.”

The drilling results were released as Northern Star prepared to announce the results of a feasibility study into a potential expansion of the Fiston plant in the coming months.

The Fimiston processing plant is one of Australia’s largest and was commissioned in 1989.

It has since undergone two expansions and processes more than 13 million tonnes of ore per year from the Super Pit and Mount Charlotte.

Mr Tonkin said expanding to 23 million tonnes a year was among the options being considered.

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