Lead Fact Sheet

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Introduction

Lead (Pb) is one of the oldest metals known to humans. Its widespread occurrence, relatively simple extraction and combination of desirable properties have made it useful to humans since at least 5000 BC. In deposits mined today, lead is usually found in ore which also contains zinc, silver and commonly copper and is extracted as a co-product of these metals. More than half of the lead consumed today comes from recycling, rather than mining.

Lead's malleability and ease of smelting accounted for its early use in pipes and lead sheeting for construction purposes. Most lead today is used in batteries for motor vehicles and in communications.

The effect of lead mining on the environment has been markedly reduced over the past 20 years as has the use of toxic lead compounds. Lead in petrol is being progressively reduced in many countries and lead compounds in paints have been replaced with non-toxic titanium compounds.

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Occurrence

The main lead mineral is galena (PbS), which contains 86.6% lead. Cerussite (PbCO3) and anglesite (PbSO4) commonly occur in the near-surface weathered or oxidised zone of a lead orebody. Deposits containing lead form from hot (hydrothermal) fluids generated within the earth which may be trapped below the surface in cracks where galena and other minerals may precipitate to make vein deposits. If limestones are present, the fluids may fill cavities to form rich but patchy deposits. Some fluids may reach the ocean floor in areas of underwater volcanic activity to form 'volcanogenic' deposits. Some are forming today under the ocean off Papua New Guinea and Canada. Other fluids may escape to the surface into small shallow lakes or seas through cracks or faults, and, if conditions are right, lead-zinc-silver deposits may build up.

For thousands of millions of years, deposits have been forming in this manner and may eventually be exposed at the surface following weathering and erosion. Some are completely eroded away and may be recycled by natural processes into new deposits. Partially eroded deposits exposed at the surface were relatively easily discovered by the early miners with examples being Broken Hill discovered in 1883 and Mt Isa discovered in 1923. These deposits formed the basis of Australia's lead-mining industry.

Exposed deposits are becoming harder to find in Australia so exploration companies are looking beneath the surface for the deposits of the future. This is a more costly and difficult way to find orebodies but a series of successes have occurred since the late 1970s. Such discoveries include the Scuddles mine (140 metres deep) and Admiral Bay deposit (1.5km deep) in Western Australia, the Cannington deposit (10 metres deep) in north Queensland, the Hellyer mine in Tasmania (90 metres deep), and the Wilga deposit in Victoria (50 metres deep).

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Australian Resources and Deposits

Lead was the first metal mined in Australia at Glen Osmond in South Australia in 1841. In 1876, lead-silver ore was discovered and mined at Thackaringa, near Broken Hill in New South Wales, but the mines closed in 1877. Silver mines flourished nearby at Silverton, Umberumberka, the Pinnacles and Purnamoota. In 1883 Charles Rasp found some dark, heavy rocks at Broken Hill which he thought may contain tin. Subsequent assays (analyses) proved that he had located rich oxidised (weathered) silver and lead ore that led to lead mining becoming a major industry in Australia. More than 100 years later, ore is still being mined from the Broken Hill deposit and it has been the largest producer of lead-zinc-silver in Australia.

The rich lodes at Mt Isa were not discovered until 1923 and were developed despite the remote location and harsh environment. The nearby, rich Hilton deposit was discovered in the late 1940s but not developed until the mid-1980s. Production at Mt Isa continues and it has been the second biggest lead producer in Australia. In the Mt Isa region, there are large mines at the George Fisher, Cannington and Century deposits, while the Dugald River and Lady Loretta deposits are yet to be mined. In the Northern Territory, the large McArthur River lead-zinc-silver deposit is a major producer.

Lead ore also is produced at Rosebery and Hellyer in Tasmania; Elura in New South Wales; Browns in the Northern Territory; and Pillara, Goongewa, Scuddles and Gossan Hill in Western Australia.

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Australia in the World

Australia ranks first in the world in economic lead resources because of the development of the large, world-class zinc-lead-silver deposits at McArthur River, Cannington and Century. This position is further supported by resources in the many other deposits of various sizes in Australia.

Australia also leads the world in mine production of lead and is the world's largest exporter of lead, with the bulk of Australian production exported as lead bullion to the United Kingdom and some to South Korea. Of the rest, lead in ores and concentrates goes mainly to Japan for further processing, while refined lead is sent to Taiwan, South Korea, Indonesia, India and Malaysia. Australia is also at the forefront of technological development in lead mining and processing.

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Mining and Processing

Almost all of Australia's lead-zinc mines are underground operations and are highly mechanised. Ore is drilled and blasted in large volumes, transferred to underground rock crushers by large loaders and trucks before being hoisted to the surface in skips or driven directly to the surface by truck via a spiral access tunnel (decline).

At the surface, the ore is subjected to additional crushing and fine grinding. A flotation process separates the lead and other valuable sulphide minerals from the waste rock particles (tailings) to form a concentrate. The flotation process was developed in Australia in the early days of mining at Broken Hill. Further Australian innovation has resulted in the improved Jameson flotation cell, which is installed in many mines around Australia.

Ground ore, water and special chemicals are mixed together and constantly agitated in banks of flotation cells. Air is blown through the mixture in each cell and the fine lead sulphide particles stick to the bubbles, which rise to form a froth on the surface of the flotation cell. The tailings sink and are removed from the bottom of the cell. The froth is skimmed off and the resulting lead sulphide concentrate is dried. During this process, the ore, which may contain only 5% lead, is upgraded to a concentrate with about 50% lead. At Broken Hill, concentrate grades average about 70% lead, mainly because the relatively coarse grain of the ore allows excellent recovery of lead sulphides.

The concentrate is sintered (partly melted) to combine the fine particles into lumps and to remove some sulphur as sulphur dioxide. The sintered product is then smelted in a blast furnace to produce impure lead metal (97% Pb). The lead metal is cooled in stages but kept molten to cause trace copper and impurities to separate as a dross (impurities) surface layer. At each cooling stage the dross layer is removed to be recycled to the blast furnace or further processed. The remaining molten crude lead is either passed direct to the refining stage or cast into lead bullion ingots for later refining.

Refining (purifying) the crude lead or bullion involves remelting then blowing the molten lead with air to form a slag (impurities) layer containing antimony, arsenic and some lead. Silver, and any trace gold or copper, is removed and the refined lead (more than 99.9% Pb) is cast into ingots (blocks) for use in the manufacturing industry.

Concentrates from various Australian mines are smelted and refined at Port Pirie, South Australia, which is Australia's sole producer of primary refined lead. Mount Isa Mines Ltd smelts most of its lead concentrate to lead bullion at Mt Isa before shipping it to the United Kingdom for refining. Lead bullion also is produced at Cockle Creek in Newcastle and is sent to Port Pirie for refining. More than 60% of Australia's lead concentrates are processed domestically.

Recycling has long been a feature of the lead industry, with about half the lead consumed in Australia now coming from this source. Secondary lead refineries in Melbourne and Sydney recycle lead scrap, mainly from lead-acid batteries.

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Uses

Lead pipes, water tanks and weights for fishing nets were used in ancient Egypt, and the hanging gardens of Babylon were floored with soldered sheets of lead. The old Roman baths at Bath in England were lined with lead and fed by lead pipes from hot mineral springs. The ancient Phoenicians also mined and smelted lead in Cyprus, Sardinia and Spain. The Japanese added lead to bronze to increase fluidity. In medieval times, lead was widely used for construction and many buildings in Europe still have the lead roofs constructed in the 15th and 16th centuries. Later, lead alloys were used for printing and continue to be used today.

Currently, lead ranks after aluminium, copper and zinc in terms of usage with the largest application being in batteries for transport vehicles and communications. Less important uses include cable sheathing, solder, casting alloys, chemical compounds, ammunition, in ceramics and in glass for TV and computer screens for radiation protection. Its use as a petrol additive has declined significantly with the gradual introduction of lead-free petrol worldwide. New uses for lead could be in large storage batteries used for load-levelling of electrical power and in electric vehicles.

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Suggestions for Further Reading

  • Blainey, G.L. 1993 The Rush that never ended: A history of Australian Mining, 4th edition, Melbourne University Press, Melbourne.
  • Australia's Identified Mineral Resources 2007, Geoscience Australia, Canberra.
  • Hughes, F.E. (Ed) 1990) Geology of the Mineral Deposits of Australia and Papua New Guinea, Australasian Institute of Mining and Metallurgy, Monograph 14.
  • Roarty, M.J. 1989 Lead, In Australian Mineral Industry Annual Review for 1987, A Paine (Ed), Australian Government Publishing Service, Canberra,pp 152-163.
  • Woodcock, J.T. and Hamilton, J.K. (Eds) (1993). Australian Mining and Metallurgy: The Sir Maurice Mawby Memorial Volume, Australasian Institute of Mining and Metallurgy, Monograph 19.
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