Speaking at Diggers & Dealers 2014, St Ives exploration manager Julian Woodcock said it was certainly the most significant discovery in the long history of the mine.

Gold Fields, which has four WA gold mines, has already pledged to spend $US50 million on exploration in Australia this year.

“I can also disclose that we’ve just had approval for another $5 million at St Ives,” Woodcock said.

The focus of that will be the Invincible discovery.

Invincible, which sits on a salt lake, was discovered during a four-hole program in the first quarter of 2012.

The results prompted further drilling and 41 holes were completed to the end of 2012 to delineate a maiden resource.

Resources now sit at 1.3 million ounces at 4.5 grams per tonne gold, comprising around 950,000 ounces of open pit resources and 383,000oz of underground resources.

Gold Fields also recently announced a modest maiden open pit reserve of 496,000oz and is hoping to report a maiden underground reserve this year.

Drilling a salt lake is not without its challenges with lake-based track mounted rigs initially used, before the company built 15km of causeway for permanent access.

Studies have shown the ore can be trucked to the St Ives mill 8km away and an open pit, to be mined in eight stages, would generate robust returns.

Woodcock said he’d received word yesterday morning that the mining proposal Invincible had been approved.

Gold Fields is targeting first production from the pit later this year.

In the meantime, the company believes the resource will continue to grow.

“There is significant potential to increase the resource in the open pit,” Woodcock said.

There is also strong underground potential with little drilling below 400m depth.

A single deep drillhole last year returned 26m at 8.5gpt gold.

And more exciting for the company is that Invincible sits on a newly defined trend dubbed Speedway.

Gold mineralisation has also been intersected at Invincible South, 400m from Invincible, and Gold Fields is targeting a maiden resource this year.

“The magnitude and potential of the Speedway trend continues to deliver,” Woodcock said.

“This could be a game-changer for St Ives.”