Prospect Awards review: Gwalia gold mine grows old gracefully

The Gwalia site

The Gwalia mine in Western Australia, winner of the Atlas Copco Hard Rock Mine of the Year at the 2017 Prosepect Awards, is a gold operation that keeps on giving.

Since Gwalia was established in 1897 by Herbert Hoover, who later became the 31st President of the United States, the mine has produced 4 million ounces of gold.

The foundations have this year been set by owner, St Barbara, for Gwalia to add significant ounces to this already impressive achievement.

Gwalia, the cornerstone of the Leonora operations with reserves of 1.9 million ounces of gold at 7.9 grams a tonne, has re-emerged as one of Australia’s standout producers of the precious metal over the past decade.

The journey to this strong position started in 2008 when first gold was poured from the mine after two years of redevelopment. The 100,000-ounce milestone at the upgraded operation was reached a year later.

Gwalia is now preparing for its next era almost a decade later, with St Barbara approving funding for a $100 million extension project in March this year.

The mine’s main decline, called the Hoover Decline, was developed to 1600 metres below surface in 2016 to allow for production from a range of ore sources.

The latest extension project, which will take two-and-a-half years to complete, aims to expand the operations to at least 2000 metres below surface, guaranteeing future production at the mine until 2024.

Gwalia’s expansion involves two main components: a ventilation upgrade and a paste aggregate fill (PAF).

The additional ventilation will come through raise bore intake and exhaust ventilation shafts, as well as associated power and cooling infrastructure needed to mine between 1800 and 2000 metres below surface.

The PAF involves mixing paste from surface with waste rock crushed underground for stope fill.

By disposing waste underground, truck and ventilation resources are able to focus on ore production, increasing efficiency and production. It also enables faster stope filling and reduces stope cycle times.

St Barbara expects the project will generate a higher financial return and increase the potential for further extensions. Managing director and chief executive officer, Bob Vassie, said the extension project’s approval launched a new phase in the Gwalia mine’s history.

“Gwalia started in 1896 and it just keeps going,” Vassie said. “The project will ensure Gwalia can continue delivering strong, high margin gold production until at least 2024, with the foundation laid for further extensions to the mine life beyond this, as well as potential for increased production.”

In January, St Barbara’s board approved a $6 million investment for project readiness and early works, including engineering, hiring project staff, contracting vendors and beginning underground works. These activities now form part of the overall $100 million budget for the extension.

If major resources are identified deeper than 2000 metres, the feasibility study indicates that additional infrastructure could extend ventilation to enable mining at 2200 metres.

Gwalia’s processing plant is a conventional CIP circuit with capacity of 1.2 million tonnes per year of hard rock, or up to 1.8 million tonnes per year when softer material is blended.

The mine’s other infrastructure includes a gas-fired power station, a paste fill plant and a refrigeration plant to cool the underground environment.

A central part of the mine ventilation system is a 5.5-metre ventilation shaft, which at 800 metres long is the largest raise bored shaft ever drilled in Australia.

Gwalia’s accommodation village was significantly upgraded in 2008 to incorporate energy efficient and environmentally-friendly initiatives. The camp received a certificate of merit in the 2009 Golden Gecko Awards for environmental excellence.

This article also appears in the November edition of Australian Mining.