The company said a gravity survey had revealed the structure just 5km north of the previously mined one-million-ounce Trident underground mine and HGO mill.

RNC said the new structure was thought to runr sub-parallel to the major regional Zuleika, Speedway and Boulder Lefroy shears, which controlled the bulk of the gold mineralisation between the Golden Mile (60Moz) and Norseman (6Moz) mining centres.

The company wants to fast track exploration in this new area as part of its expanded exploration focus on the 1800sq.km HGO land package.

CEO Paul Andre Huet called the development "exciting".

"Although early stage, our interpretation of the potential size of this new structure is an exciting development for our HGO-focused exploration activities," he said.

"With the Morgan Stanley royalty recently renegotiated in December, it now makes sense to explore these and many other areas across the Higginsville tenement package which holds strong potential for new discoveries."

RNC also announced it had received regulatory approval to start the second phase of Baloo mining. The company expects to start production there by mid-year and extend to January 2021.

Considering that both Baloo stage one and two pits were initially expected to be completed by mid-2020, the extension of Baloo out to early 2021 was a testament to the quality of the openpit opportunities at Higginsville, Huet said.

"We expect the extended Baloo life to provide the additional production and mining flexibility that comes from operating two openpits over the course of this year."

As part of the HGO openpit "production pipeline", it is expected that both stages of Baloo will be mined in conjunction with a series of additional openpits beginning with Fairplay North and Pioneer (mining at the former has already begun), the company said.

RNC shares closed 12.2% higher at C46c, capitalising it at $279 million.