Australian gold producer Northern Star Resources has awarded a $73.4m (A$101m) contract to GR Engineering Services for the Thunderbox expansion project in Western Australia (WA).

The contract includes the design, engineering, procurement, construction and commissioning of the 6Mtpa expansion project.

Estimated to cost $132.4m (A$180m), the expansion project involves the installation of a new 18MW mill and classification circuit, according to miningweekly.com.

It also includes the installation of new leach tanks, elution and gold room upgrades, a new tailing thickener and tailings pumping.

GR Engineering plans to commence work on the expansion project immediately.

The Thunderbox operations currently have a 3Mtpa processing capacity and are located in the highly prospective Yandal Belt and the Agnew-Wiluna Belt in WA.

Previously owned by Saracen Mineral, these operations include the Thunderbox, Kailis, Bannockburn and Waterloo Projects. Saracen Mineral was later merged with Northern Star.

GR Engineering managing director Geoff Jones said: “We have worked with the Northern Star team over many years and see this award as a strong endorsement of our proven EPC delivery capability.”

Northern Star processing general manager Simon Tyrrell said: “The Thunderbox expansion increases the operation’s hard rock processing capacity to 6Mtpa from the current 3Mtpa, and decreases processing costs as outlined in the 2021 Investor Day Presentation.”

GR Engineering was previously contracted to carry out various projects for the Thunderbox operations, including EPC work on the Thunderbox paste plant work.

Northern Star recently signed a $294.78m deal to divest its Kundana gold assets in WA to Evolution Mining.

The assets being sold include a 100% stake in Kundana operations, a 100% interest in tenements comprising the Carbine project, a 51% stake in East Kundana joint venture (EKJV) and 75% interest in the West Kundana joint venture (WKJV).