Mount Isa - Mining and Fossils

Thursday, Aug 27, 2009 at 00:00



Mount Isa is the site of the largest underground mine in Australia and one of the largest in the world. It is also one of the few mines in the world where the four minerals; lead, silver, zinc and copper are mined.

The lead-silver-zinc and copper ore bodies are mined separately. The position, extent and quality of the minerals have already been established by exploration drilling.

The lead-silver-zinc deposits extend from the surface to about one kilometre below. Some of the copper deposits are 1800 metres below the surface, but are of such a high grade that it is still economical to mine them.

Processing procedures vary according to the mineral being mined and the mine from which it has been taken.

From data at the Outback in Isa Visitor Centre.

Gold prospector John Campbell Miles with his horse “Hard Times” discovered one of the world's richest deposits of copper, silver and zinc during his 1923 expedition into the Northern Territory. While camping on the banks of the Leichhardt River, Miles found yellow-black rocks nearby that reminded him of the ore found in the Broken Hill mine where he had once worked. A sample sent away to the assayer in Cloncurry confirmed that these rocks were mineral rich.

Mount Isa is also fairly unique in having the town right alongside the copper and lead smelters with no buffering. The original town, Mineside, was moved from where the mine now is to the present nearby location.

Mount Isa is a well serviced town, being the major centre of the region.Mount Isa Mines employs about 2,400 people as direct employees and contractors.

The chimney of the lead smelter is the most dominant feature of the Mount Isa mines. The current lead stack was built in 1977 and 1978, replacing the former lead stack. It is 270 metres high, with a base diameter of 22 metres tapering to 12.4 metres at the top. 17,400 tonne of concrete were used.

Outback at Isa

The Outback at Isa Visitor Centre has a number of different displays including mining and geology, World War II history, and a tour of an underground mine (created for display purposes only). It is also home to the Riversleigh Fossil Centre and displays of fossils and mock ups of the creatures uncovered at Riversleigh.

Colourful and sparkling ores and crystals are on display in the mining museum area. Lead, copper, silver and zinc are mined; silver and zinc are often found in conjunction with lead.

War history

During World War II an underground hospital was constructed, although fortunately this was never needed. In 1942, Mount Isa became a depot for 8,000 American soldiers driving convoys of supplies and equipment to military bases in the Northern Territory. There was racial tension between black and white American soldiers. Wartime memorabilia is also on display at Outback at Isa.

Hard Times display mine

This display mine has been constructed 22 metres below the park around the Outback in Isa Visitor Centre. Physical safety and health measures in underground mining have improved dramatically in recent years, and with modern mining equipment, the size of tunnels has greatly increased. Remote machinery is now used in high risk areas. Temperatures can reach up to 60º when two or three kilometres underground.

We took the underground mine tour, where mining techniques from the 1960s are demonstrated, and explanations given by the tour guide of how mining is different now. Overalls, boots and hard hats provided must be worn, and a heavy battery for the headlamp is carried on a belt.

After being taken down underground in the Alimak Cage, a railcar takes the visitors around to each display point. The tour gives a realistic and hands on experience which lasts the whole afternoon, including afternoon tea in the Crib Room.

Riversleigh Fossil Centre

Within the Outback at Isa Visitor Centre, the Riversleigh Fossil Centre has displays of how the fossils found at Riversleigh may have looked when alive in their environment. There are also cabinets showing fossils that have been recovered from the Riversleigh site.

We were lucky to be there at a time when Dr John Scanlon was working in the laboratory with the utmost patience recovering many bones fragments and working what animals these came from. He has a personal interest in snake fossils.

In the laboratory, limestone is dissolved slowly in acid, leaving the fossil bone fragments to be recovered from the slurry. Sources may be just a few animals or parts thereof, or maybe a rich fossil area such as the feeding grounds of a crocodile, a bat cave with fragments deposited, or a sinkhole where animals have become trapped.

Most of the fossils identified are direct ancestors of present day mammals, proving that Australia has been a distinct continent for over 25 million years.

Lake Moondarra

Fifteen kilometres North of Mount Isa, the Leichhardt River has been dammed to form Lake Moondarra, which provides water for the town and the mine. Although a large dam, it is not very deep due to the terrain. Suitable for recreational boating, there are tow boat ramps. 75,000 Barramundi fingerlings are released into the lake each March for recreational fishermen, although different reports show different numbers of fingerlings and times of year for the release.

Mount Isa Lookout

This vantage point gives a good vista of the mine and smelters plus views all around.

Read more detail about this trip and see all the photos in our 2009 Travelogues

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