Underground Mining

In 2013 KCGM’s Mt Charlotte Underground Mine celebrated 50 years of continuous operation; a major milestone in Australia where most mines are lucky to reach their 21st birthday. One of the first mines in Australia to use mechanised equipment underground, Mt Charlotte currently produces approximately 740,000 tonnes of ore, yielding around 56,500 ounces of gold per year. The close-knit team of about 60 employees dedicated to running the mine exemplifies the company’s core value of Continuous Improvement, finding better and more efficient ways to operate and keep the site productive.

Near Hannan’s First Find

The history of mining at Mt Charlotte stretches back to 1893 when Paddy Hannan, Dan Shea and Thomas Flanagan made their first alluvial gold discoveries nearby. The Mt Charlotte mine lies three kilometres from the Fimiston Open Pit at the northern end of the Golden Mile, but it is not part of the rich reef associated with the Mile. The mine exploits the main Charlotte and Reward ore bodies and the satellite Maritana and Northern bodies.

The site was mined intermittently over the next half century and by 1945 several small-scale operations had reached an average depth of 215 metres. The area remained in the shadow of its enormously rich neighbour until 1954 when geologists defined the large, low grade ore body which was later to become the Mt Charlotte Underground Mine.

Development

Large scale underground mining began in 1963 when GMK took over the lease and employed the modern, mechanised “cut and fill” method. This was achievable only after the then Department of Minerals and Energy allowed diesel engines and machinery to be used underground for the first time in Western Australia.

As access to the underground operations was only possible via the original Reward and Man and Supply Shafts, large machinery such as trucks, bulldozers and loaders had to be dismantled, lowered into the mine and reassembled underground in giant workshops. With the exception of tyre changes, all work on the mine’s vehicle fleet and plant is still done underground today.

In 1964 the underground workings were linked to the “Glory Hole”, a 30 metre deep open pit at the top end of Hannan Street which had been mined in the early 1900s. The Glory Hole was expanded to provide backfill for the mine to ensure the long-term stability of the underground workings. In the early 1980s extensions to the main ore bodies were identified at a depth far beyond the capacity of the Reward Shaft and the then owners, Kalgoorlie Lake View, decided to sink a brand new shaft.

Today the Cassidy Shaft is 1,200 metres deep at its bottom level although active mining currently takes place only to the 2,300 feet level, which is 700 metres deep. Named after Goldfields pioneer prospector Jim Cassidy, its 50 metre steel headframe remains an iconic Kalgoorlie-Boulder landmark.

Sam Pearce Decline

The Sam Pearce Decline linked the Mt Charlotte Underground Mine to the Fimiston Open Pit in December 1997. Named after Sam Pearce – the prospector credited with discovering the Golden Mile – the decline made it feasible to mine lower grade remnant ore from the upper levels of Mt Charlotte and is now the main access to the mine.

In 1999 the Cassidy Shaft ceased the transportation of underground ore, with the last deep ore hoisted in March of that year. The shaft and its friction winder remain in use as a secondary egress for emergencies and for the transportation of personnel and equipment, mainly to check the dewatering pumps at the lower levels.

Production at Mt Charlotte

The method of “remnant mining” at Mt Charlotte, which extracts the lowergrade ore remaining after higher grade ore has been removed, requires smaller blasts which are conducted most weekdays. Most blasts are barely detectable, but those closest to Mt Charlotte can set their clocks by the afternoon blast and, when a larger blast is likely to be felt at the surface, nearby residents are notified by letter drop.

Although mining at Mt Charlotte is now conducted on a much smaller scale than in the past, the ore body, when combined with the Fimiston resource, is still one of the largest accumulations of economically recoverable gold in the world. The mine currently produces around 4,700 ounces of gold every month. After half a century in operation, Mt Charlotte has produced around 5,000,000 ounces of gold.

Hidden Secret

The Underground Mine gained a further two years mine life after the identification of the Hidden Secret ore body about 350 metres east of Mt Charlotte. The resource is currently estimated at 665,000 tonnes at 3.65 grams per tonne and will be mined at depths of between 215 and 440 metres below the surface. Hidden Secret will be the first new resource to be mined by KCGM in the past 15 years. It is expected to produce 76,000 ounces of gold and extend Mt Charlotte’s mine life to 2018.

Download KCGM Hidden Secret Information Sheet