Thunderbox gold project is located in Western Australia. Image courtesy of Saracen Mineral Holdings Limited.
The Thunderbox project achieved first gold in 2016. Image courtesy of Saracen Mineral Holdings Limited.
The project is a part of the Thunderbox operations (TBO). Image courtesy of Saracen Mineral Holdings Limited.

The Thunderbox gold project includes the Thunderbox, Rainbow and Otto Bore gold deposits in Western Australia.

The Thunderbox deposit was discovered in 1999 and is considered to be one of the significant gold deposits discovered within the last 20 years in Australia.

The project was acquired by Saracen Mineral from Norilsk Nickel in 2014. It poured first gold in early 2016, while commercial production was achieved in April 2016.

Thunderbox has an initial open-pit mine life of approximately five years with potential for underground operations. Drilling operations are being undertaken to define a long-term underground mine, extending the project life beyond ten years.

Thunderbox gold project location

The Thunderbox gold project is part of the Thunderbox operations (TBO), which comprises the Thunderbox project, the Kailis project, the Bannockburn project and the Waterloo project.

Thunderbox is situated at the southern end of the Yandal greenstone belt while TBO is located in the Yandal belt and the Agnew-Wiluna belt in the North Eastern Goldfields. The Thunderbox open-pit mine and CIL gold treatment plant are located 45km south of Leinster.

Thunderbox project geology and mineralisation

Thunderbox is a mesothermal lode gold deposit situated in an area where multiple major shear zones meet with the Perseverance Fault. The deposit contains three main mineralised zones, known as A, C, and D.

Mineralisation in the deposit is present in the form of heavily distorted, silicified and carbonate altered albite-quartz porphyry in the hangingwall of the 200m-wide shear zone. The mineralisation is mainly restricted to the intrusive porphyry.

Thunderbox gold project reserves

The Thunderbox deposit is estimated to contain ore reserves of 21.65Mt at 1.5g/t of gold, including 2.9Mt of proved and 18.75Mt of probable reserves as of 30 June 2019. The estimate includes 1.23Moz of contained metal.

Mining at Thunderbox gold project

Mining operations by Saracen at the Thunderbox gold project commenced in July 2015.

Both open pit and underground methods can be employed at the mine. The company is using conventional hydraulic excavator and dump truck fleet.

The project is currently undertaking mining operations at zone C, with the pit expected to be completed by May 2020. The zone is providing a major portion of the feed supplied to the mill. Pre-stripping of zone D commenced ahead of schedule to optimise utilisation of the TBO mining fleet.

The planned diamond drilling campaign was completed at Thunderbox, while the underground development was completed for the upper four levels. Pre-production activities are expected to start in the third quarter of 2020.

The Otto Bore deposit is the focus area of the resource development activities. The company plans to significantly increase production from the project in FY2021.

Processing at Thunderbox project

The ore reserves from the mine undergo treatment at the Thunderbox process plant, a CIL cyanide leach plant with a gravity circuit. The Thunderbox processing facility processed more than 9Mt of ore between 2002 and 2007. It achieved gold recoveries of 93.4% to 96.6% over the initial life of the mine.

The processing plant was kept on care and maintenance since 2007 and has been operating at a nameplate capacity of 2.5Mtpa since May 2016.

The Thunderbox mill employs a conventional crushing, grinding and CIL leaching process for the extraction of gold. It includes a single-stage crusher, a SAG mill and a ball mill along with elution circuits.

Infrastructure at Thunderbox project

Saracen acquired the existing infrastructure including a modern accommodation camp, a gravel airstrip, Goldfields Gas pipeline spur and the CIL ore processing facility. Contract power supply, water supply from borefield and telecommunication services were also part of the acquisition.

The mine site is linked to Leinster via a 2km sealed highway.

Saracen developed a powerhouse with seven gas-fired generators and four dual-fuel units.

Contractors involved

In March 2020, SRG Global was awarded a $70m contract to provide drill and blast services at the mine for five years.

Kalgoorlie Power Systems (KPS) was contracted for rewiring of the powerhouse while BLA Burgess undertook re-installation of the SAG and ball mills.

Maca Interquip was contracted for plant refurbishment while SMS Rental (WA) won a contract for the supply and maintenance of run-of-mine (ROM) loaders.