In 1923 the prospector John Campbell Miles discovered an outcrop of oxidised silver-lead ore in the area now called Mount Isa. Lead is an metal that is particularly useful because it resists many types of corrosion, and can be used for soundproofing and as protection against atomic radiation. The lead from Mount Isa and from Australia’s biggest lead and zinc mines at Broken Hill now make up most of Australia’s production of these important products. By the early 1990s Australia was the world’s largest exporter of lead. In the 1920s Mount Isa was a very isolated place until the railway from Townsville opened and the Mount Isa Mines Company (which controlled the mining in the area) built a town where the people working in the mines could live. In later years big deposits of copper were also discovered, and over the years huge underground mines that employed thousands of people were built.