Lead is a relatively soft, malleable, blue-grey, heavy metal and is probably the earliest discovered metal that does not occur naturally in its pure state. Galena (PbS) is the principal ore mineral, usually found in association with sphalerite (ZnS). Galena often contains inclusions of silver and is a major source of that metal. The main oxidised ore minerals of lead are cerussite (PbCO3) and anglesite (PbSO4).
Lead is one of the most widely used metals and over 60% of all lead produced is used in lead–acid batteries for the storage of energy. Other uses include lead foil, plumbing, solder, sound proofing, ammunition, addition to glass to block harmful radiation from television and computer screens and as an ultraviolet ray protector in PVC plastics. Lead is toxic in some applications, and environmental and health concerns have reduced its use in paint pigments and anti-knock additives in petrol. Over 50% of the supply is recycled from scrap, particularly lead–acid batteries of which >90% are recycled.
Zinc is a brittle, crystalline, bluish white metal and is principally mined as the primary sulphide sphalerite, usually in association with galena. Sphalerite contains 67% Zn and often includes traces of cadmium, gallium, germanium and indium as simple sulphides in solid solution. The secondary minerals willemite (Zn2SiO4), smithsonite (ZnCO3) and hemimorphite (Zn4Si2O7(OH)2.H2O) also occur as ore. Zinc readily combines with other metals forming alloys - brass (copper and zinc), bronze (copper, tin and zinc) and nickel silver (copper, nickel and zinc).
Zinc is the third most used non-ferrous metal after aluminium and copper. About 50% of production is used for galvanising steel to protect it from rust. Zinc compounds and dusts are used in cosmetics, plastics, rubber, ointments, sun screen creams, soaps, paints, ink, fertilisers and batteries. Around 30% of zinc used in the western world comes from recycling.
In 2013 the annual world mine production of lead was is ~5.4 Mt, and zinc was 13.5 Mt. Australia’s annual mine production was bout 0.69 Mt of lead and 1.35 Mt of zinc. China is the world's biggest producer of lead (56%) and zinc (37%), while Australia is the world’s largest exporter of both lead and zinc.
Discovery in 1883 of the massive Pb–Zn–Ag deposits at Broken Hill, just east of the NSW–SA border, resulted in the establishment of a sea port at Port Pirie, followed by construction of a lead smelter and refinery in 1889. The smelter operated by Pasminco Australia Ltd is now the world’s largest integrated Pb–Zn producer, yielding 250 000 t of lead, 40 000 t of zinc, 4000 t of copper, 450 t of silver, and 600 kg of gold annually. Smelter feed is sourced from the Broken Hill, Elura (New South Wales), Rosebury (Tasmania) and Cannington (Queensland) mines.
Lead-zinc in South Australia
Aerial view of the Pasminco Metals-BHAS smelters at Port Pirie
Australia’s first metal mine was opened in 1841 at Glen Osmond, where lead ore was produced from the Wheal Gawler. However, South Australia’s current annual production (1998) of 3188 t of zinc and 15 t of lead is minor. Although Pb–Zn mineralisation is widespread in a variety of geological environments, a major resource has yet to be developed in the State. Over 180 small deposits have been worked and a further 100 occurrences have been recorded.
Gawler Craton and Stuart Shelf
Known Pb–Zn mineralisation is generally within Palaeoproterozoic Hutchison Group metasediments, particularly serpentine marble, calc-silicate gneiss and banded iron formation (BIF), but total production is small and estimated at ~100 t.
The largest of the workings was the Miltalie Mine (Pb–Ag) which operated intermittently from ~1860 to 1914 with ore grades up to 61.5% Pb and 118.5 g/t Ag. Zinc-rich zones up to 10.8% were also reported. Mineralisation comprised galena, pyrite, pyrrhotite, chalcopyrite and sphalerite as disseminations and massive veins.
Other mines include Atkinson’s Find (Ag–Pb), Cleve (Pb–Zn), Elson (Ag–Pb), Lady Franklin (Pb–Ag), Mangalo (Pb–Ag), Mount Miller (Ag–Pb), Poonana (Pb–Ag–Cu) and Yalpoudnie (Cu–Pb).
Drilling of aeromagnetic targets adjacent to the southern margin of the Gawler Ranges in 1981 resulted in discovery of significant Pb–Zn–Ag mineralisation at the Menninnie Dam and Telephone Dam prospects. Mineralisation is hosted by Hutchison Group serpentine marble, laminated graphitic, ankeritic, dolomitic marble and carbonate-facies BIF, and comprises massive pyrite–sphalerite–galena with minor chalcopyrite and pyrrhotite. The mineralising event may be related to intrusion of Mesoproterozoic rhyolitic dykes. There is an inferred resource of 737 Mt at 3.1% Zn, 2.6% Pb and 27 g/t/Ag for the Menninnie Dam prospect.
Between 1974 and 1986, the Mount Gunson Copper Mine produced, as by-products, ~31 000 t of zinc and 7500 t of lead within a mixed sulphide concentrate derived from 7.5 Mt of Cattlegrid deposit ore. Mineralisation, comprising chalcopyrite, bornite and chalcocite with minor sphalerite and galena, occurs in the upper surface of a palaeo-permafrost brecciated sandstone of the pre-Adelaidean Pandurra Formation.
Minor Pb–Zn occurrences are widespread within Palaeoproterozoic Willyama Supergroup rocks but there has been little production, with the exception of the giant Broken Hill Pb–Zn–Ag deposit located in the southeast of the province in New South Wales.
In South Australia, significant Pb–Zn mineralisation has been found within rocks equivalent to those hosting the Broken Hill deposit. In particular, the albitic metasiltstone, marble and calc-silicate of the ‘Bimba formation’ and underlying calc-silicate suite contain stratiform and stratabound, disseminated, laminated and vein sulphides comprising, pyrite, pyrrhotite, sphalerite, galena, chalcopyrite, arsenopyrite and cobaltite.
Promising exploration prospects include Blue Dam – Meningie Well (Zn–Pb), Hunters Dam (Zn–Pb), Putts Well (Zn–Pb), Ram Dam (Pb–Zn), Telechie (Cu–Zn), Ballara (Zn), McBride’s (Zn) and Benagerie (Au–Cu–Pb–Zn.
Australia’s first metal mine, the Wheal Gawler, is one of the Glen Osmond Mines which also included Mount Osmond, Wheal Watkins, Wheal Augusta, Eagle, Champion and Macfarlane’s. The mines were worked intermittently between 1841 and 1889, producing an estimated 2300 t of ore which yielded 1700 t of lead and 1.5 t of silver. Mineralisation occurred as crosscutting galena veins hosted by shale and siltstone of the Burra Group Saddleworth Formation.
The Mount Malvern Mine, also hosted by Saddleworth Formation slate, produced ~1900 t of ore averaging 55% Pb and 470 g/t Ag around the 1890s.
The Baratta Silver–Lead Field comprises several workings including the Cross Crusader, Eukaby Hill, West Eukaby, Eukaby Extended and Eukaby South. The field was discovered in 1887, and after intermittent activity there has been a small but steady production from the Eukaby Hill workings since 1976. Total production to 1999 is ~440 t of lead, 493 kg of silver and 47 kg of gold. Mineralisation comprises galena, sphalerite, pyrite and chalcopyrite in generally concordant quartz–calcite–siderite veins up to 1.2 m wide hosted by Tapley Hill Formation dolomitic siltstone with interbedded shale and quartzite and Tarcowie Siltstone.
Adelaidean rocks host numerous small Pb–Ag–Zn mines that were worked around the 1890s but have only minor production, including Avondale (Pb–Ag), Commodore (Pb–Ag), Emily (Pb–Ag), Gilead P. Beck (Pb–Ag), Great Gladstone (Pb–Ag), Hahndorf (Pb–Ag), Jubilee (Cu–Pb), Kangarilla (Pb), Mack’s (Pb–Ag), Mount Lofty Park (Pb–Ag–Zn), Mount Roebuck (Pb), Riversedge (Cu–Pb–Ag), Uncle Tom (Pb–Ag), Vranes (Pb), Waukawoodna Creek (Pb–Ag), Wheal Grainger (Pb–Ag) and Winklers (Pb–Ag).
Mississippi Valley-type (MVT) mineralisation from the Cambrian Hawker Group Ajax and Wilkawillina Limestones has been the State’s major source of lead and zinc.
Pasminco Australia Ltd. periodically mine willemite zinc ore from the Ajax Limestone hosted deposits Beltana (Puttapa) and Aroona Mines. The ore is of high grade (40% Zn) and requires only crushing and screening prior to smelting at Port Pirie where it is used as a "sweetener" with other zinc ores at a rate of 10 000 - 15 000 t per annum. Between 1968 and 1994 Beltana produced 313 525 t of zinc ore and about 120 000 t of high grade ore remains. Aroona produced 23 179 t of zinc ore between 1990 and 1999. Mining operations ceased at Aroona in 2000 and the site was rehabilitated. Ore was removed and stockpiled at Beltana of which 27 846 t was sent to Port Pirie in 2001. The last production form Beltana was 12146 tonnes of stock piled material in 2010. Willemite mineralisation is localised in fault zones from metal-rich solutions, and subsequently concentrated by supergene enrichment.
During 2001-2002 Perilya Ltd. have been exploring for zinc mineralisation along the Beltana and Aroona Faults between the Beltana and Aroona deposits. Several prospects have been identified, the most promising being Relience Prospect where ore grade zinc mineralisation, comprising of smithsonite and willemite, has been identified over a distance of 1.3 km. High grade intercepts include 27m at 28% Zn and 11m at 21% Zn. The Moolooloo and Aristotle prospects have also had significant drill intercepts including 17m at 21% Zn and 4m at 27% Zn respectively
The Ediacara Mineral Field was discovered in 1869 and from 1888 to 1913 produced an estimated 24 000 t of ore averaging ~31% Pb and 270 g/t Ag. The main workings were Southern, Greenwood, Morish and Black Eagle (predominantly a copper producer). An inferred resource of 17 Mt at 1.2% Pb and 10 g/t Ag remains. Mineralisation mainly occurs in sandy dolomite near the base of the Ajax Limestone within the Ediacara Basin. A major fault crosses the basin and may have controlled mineralisation.
The Wilkawillina Limestone hosts lead mineralisation at the Wirrealpa and Fountain Head Mines, and zinc mineralisation as scholzite (CaZn2(PO4)22H2O) at Reaphook Hill and willemite at the Third Plain prospect.
Small amounts of lead with minor zinc have also been mined from Cambrian Normanville Group limestone (Wilkawillina Limestone equivalent) on Fleurieu Peninsula at the Rapid Bay (Yattagolinga), Sellicks Hill, Barritt’s, Wheal Coglin, Wheal Mary and Carrickalinga Head mines.
The Cambrian Kanmantoo Trough comprises metamorphosed flysch-like clastic sediments from which >100 000 t of high-grade Pb–Ag–Zn–arsenic sulphide ore were mined, mostly during the last century. Mineralisation is generally confined to the Tapanappa Formation, Talisker Calc-siltstone and Carrickalinga Head Formation. A synsedimentary exhalative origin from a distal volcanic source is the favoured genesis for the mineralisation.
The Talisker Mine, worked between 1862 and 1935, produced ~2200 t of dressed Ag–Pb ore. Mineralisation comprised galena and arsenopyrite with minor sphalerite, pyrite and pyrrhotite, within a fault zone hosted by phyllite and quartzite of the Talisker Calc-siltstone.
Other mines hosted by Talisker Calc-Siltstone include Cambell’s Creek (Ag–Pb–Cu) and the Stockwell–Parlor–Newbold group (Ag–Pb).
The Aclare Mine produced ~14 000 t of ore, averaging 7% Pb, 12% Zn, 680 g/t Ag and 2 g/t Au, between 1859 and 1896. Mineralisation comprises disseminated to massive galena and sphalerite with minor arsenopyrite, pyrite, pyrrhotite and chalcopyrite hosted by Tapanappa Formation meta-chert and quartz–mica schist.
The Wheal Ellen (Commonwealth Mine) produced ~75 000 t of sulphide ore averaging ~10% Pb, 18% Zn, 150 g/t Ag and 4 g/t Au. Mineralisation comprised massive pyrite–sphalerite–galena with minor chalcopyrite, gahnite, tetrahedrite, marcasite, pyrrhotite and arsenopyrite hosted by biotite schist, sericite schist and quartz–garnet–andalusite–biotite–staurolite rocks within a sequence of metagreywacke and quartz–biotite–garnet schist of the Tapanappa Formation.
The Strathalbyn Mine produced ~2000 t of supergene ore, averaging 8% Pb, 12% Zn, 220 g/t Ag and a few grams per tonne of gold, between 1848 and 1858. Some copper carbonate ore was also produced. Mineralisation comprised massive sphalerite and galena hosted by Tapanappa Formation quartz–garnet–mica–gahnite–staurolite–andalusite schist.
The Angas Mine was commissioned in July 2008 producing Zn-Pb-Cu-Ag-Au ore from massive sphalerite and galena hosted by Tapanappa Formation quartz-garnet-mica-gahnite-staurolite-andalusite schist. Annual production was around 6 million tpa at 7% Zn, 2.72% Pb, 0.24%Cu, 1 g/t Ag and 0.48 g/t Au. Zinc concentrate was produced on site while a Pb-Cu- Au- Ag concentrate was sent to Port Pirie smelter for treatment. Due to falling commodity prices the mine closed in September, 2013 and place on care and maintenance.
Scotts Creek Mine (Wheal Margaret) produced ~2000 t of supergene ore, averaging 2 kg/t Ag and 45% Pb, between 1848 and 1889. Mineralisation comprised galena and sphalerite with minor chalcopyrite, pyrrhotite and pyrite hosted by Tapanappa Formation quartz–garnet–mica schist.
The Rhineberg, Mount Rhine and Royal Keyneton Ag–Pb mines, worked ~1890, are hosted by Milendella Limestone of the Carrickalinga Head Formation. Mineralisation comprised mainly galena and iron oxides concentrated along fault zones, with the limestone acting as a chemical trap for mineralised fluids generated by nearby Ordovician granite intrusions.
Kanmantoo Group metasediments also host Pb–Ag–Zn mineralisation on Kangaroo Island. Workings are small and include Western River (1892–1907), Snug Cove (1889) and Perseverance (1889–1907).
Significant exploration prospects include:
- Mount Torrens, located in 1976, contains an inferred resource of 700 000 t at 6.4% Pb, 1.6% Zn and 41 g/t Ag hosted by quartz–calcite–scapolite–garnet rock at the base of the Talisker Calc-siltstone.
- Angas, located in 1992, contains an inferred resource of 1 Mt at 10% Zn, 4% Pb, 60 g/t Ag and 1 g/t Au hosted by quartz–mica–garnet–andalusite–staurolite–gahnite schist of the Tapanappa Formation (Fig. 3).
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