Silver (Ag) is a silver-white, lustrous, precious metal that conducts heat and electricity better than any other metal and, with the exception of gold, is the most malleable and ductile. It readily tarnishes on exposure to air, forming a corrosion resistant coating of silver sulphide. The purity of silver is expressed as its fineness (e.g. sterling silver is 925 fine or 925 parts silver and 75 parts copper).
Silver is found in the pure state as native silver but is more commonly combined with other elements, and half the world’s silver production is obtained as a by-product in the processing of lead, copper and zinc ores, particularly the lead sulphide galena. Gold deposits invariably contain silver as an alloy with gold and, where the silver content exceeds 20%, the alloy is known as electrum.
Photography is the largest end use of silver using the silver halide salts (silver bromide, silver chloride and silver iodide) which darken on exposure to light and are used in emulsions for photographic paper, plates and film. Silver is also widely used in jewellery, tableware and coinage, and is often alloyed with small amounts of other metals, such as copper, to make it harder and more durable. Other industrial uses include electronics, batteries, braising alloys, mirrors, medicinal compounds and dental amalgams.
The world’s major silver producers are Mexico (21%), China (15%), Peru (13%) and Australia, along with Russia, is ranked fourth and produced 1 700 t of silver in 2013 which represents about 6.5% of the world production of an estimated 26 000 t. South Australia’s annual production is about 144 000 kg (2013) principally from the Olympic Dam and Prominent Hill Mines.
South Australian deposits
Silver production in South Australia commenced in 1841 as a by-product of smelting lead ore from Australia’s first metal mine at Glen Osmond, an eastern suburb of Adelaide. In 2001, the State produced 27 502 kg of silver solely from the world-class Olympic Dam Cu–U–Au–Ag mine.
The Pasminco Ltd smelter at Port Pirie is the world’s largest integrated Pb–Zn producer and third largest silver producer, yielding 450 t of silver annually using feed sourced from the Broken Hill, Elura (NSW), Rosebury (Tas.) and Cannington (Qld) Mines.
Gawler Craton and Stuart Shelf
Silver is produced as a co-product at the Olympic Dam Mine, which has reserves of 629 Mt of ore containing 11 Mt of copper, 0.36 Mt of uranium, 459 t of gold and 2113 t of silver. Mining commenced in 1988 and and it’s annual production capacity is about 10 Mt of ore containing 200 000 t of copper, 4 000 t of U3 O8, 2 488 kg of gold and 26 400 kg of silver. The silver occurs mainly within copper sulphides, particularly bornite (Cu5FeS4) and chalcocite (Cu2S), and variable amounts are found with gold; minor amounts of native silver and argentite (Ag2S) are also present.
Silver is produced as a co-product at the Prominent Hill-Malu (Cu-Au-Ag) Mine which ha reserves of 59 Mt at 0.8% Cu, 0.6 g/t Au and 2.7 g/t Ag. The adjacent Prominent Hill-Ankata (Cu-Au-Ag) Mine has reserves of 7.5 Mt at 2% Cu, 0.4 g/t Au and 2.9 g/t Ag. In 2013 the mines produced 19 000 kg of silver in a mixed concentrate.
The Carrapateena Prospect was discovered in June 2005, it contains silver as a co-product and subsequent feasibility studies have shown that the IOCG prospect has a total indicated and inferred resource of 800 Mt at 0.8% Cu, 0.3 g/t Au, 3.3 g/t Ag and 155 ppm U. The Khamsin IOCG deposit has a resource of 202 Mt at 1.7 g/t Ag, 0.1 g/t Au, 0.6% Cu, and 101 g/t U3O8.
The Tunkillia deposit south of Tarcoola has a resource of 15.6 Mt at 5.5 g/t Ag (and 1.6 g/t Au).
There are several Ag–Pb mines on Eyre Peninsula, generally within Palaeoproterozoic Hutchison Group metasediments, but total silver production is small and amounts to only a few kilograms. 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. 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).
Epithermal silver-(lead) mineralisation associated with the Gawler Range Volcanics has been identified at the Paris deposit, and in several adjacent prospects in the northern Eyre Peninsula in host Hutchison Group metasediment. Resource at Paris has been determined at 5.9 Mt at 110 g/t Ag for 622,000 kg contained silver. The nearby Menninnie Dam (Pb-Zn-Ag) skarn deposit has a resource of 5.2 Mt at 28 g/t Ag.
The Moonta and Wallaroo copper deposits produced ~5000 kg of silver as a by-product of copper production. A total of 9.6 Mt of ore containing 3.7% Cu, 0.56 g/t Ag and 0.4 g/t Au were mined, mainly from underground workings, between 1860 and 1923.
Between 1941 and 1986, the Mount Gunson Mine produced ~65 t of silver metal as a by-product in the mixed sulphide concentrate comprising mainly copper (chalcopyrite, bornite and chalcocite) with lesser zinc (sphalerite) and lead (galena) from the Main Open Cut, East Lagoon, West Lagoon and Cattlegrid deposits. Mineralisation is located in the upper surface of a palaeopermafrost brecciated sandstone of the pre-Adelaidean Pandurra Formation. Silver resource at the MG-14 Cu-Co-Ag deposit is 1.5 Mt at 17 g/t Ag, and for the Windabout Cu-Co-Ag deposit 19 Mt at 10 g/t Ag.
Silver is generally associated with the numerous Pb–Zn, copper and gold occurrences, and exploration prospects within the Palaeoproterozoic Willyama Supergroup. The ‘Bimba formation’ and underlying calc-silicate suite in particular contain sulphide mineralisation which includes pyrite, pyrrhotite, sphalerite, galena, chalcopyrite, arsenopyrite and cobaltite.
The Olary Silver Mine was worked ~1888 where a siliceous haematite–magnetite ‘blow’, within quartzo-feldspathic gneiss, contained copper carbonate and pyrite. Surface samples assayed up to 105 g/t Ag with a trace of gold, but there was no recorded production.
Silver was produced as a by-product from virtually all of the numerous lead and Pb–Zn mines worked in the late 1800s, most of which are detailed in the lead and zinc commodity reviews.
Australia’s first metal mine, the Wheal Gawler, one of the Glen Osmond Mines, produced an estimated 2300 t of ore that yielded 1700 t of lead and 1.5 t of silver between 1841 and 1889. Mineralisation occurred as crosscutting galena veins hosted by shale and siltstone of the Burra Group Saddleworth Formation.
The Bird in Hand Gold Mine, with past production of ~290 kg of gold, has a resource of 557,000 tonne at 5.5 g/t Ag (and 13 g/t Au).
The Mount Malvern Mine, also hosted by Saddleworth Formation slate, produced ~890 kg of silver from 1900 t of ore, averaging 55% Pb and 470 g/t Ag, between 1890 and 1918. Mineralisation is contained within fault-controlled barite veins up to 6 m wide and extending for ~150 m, with patches of galena, pyrite, chalcopyrite and quartz.
The Almanda Mine was first prospected for copper in 1850 before becoming a silver producer between 1868 and 1887. About 300 kg of silver were produced at an average grade of 1560 g/t from two open cuts, an adit and shafts to 38 m depth within Burra Group Woolshed Flat Shale. Mineralisation, comprising tetrahedrite, galena, chalcopyrite, sphalerite, arsenopyrite and native bismuth, occurs as sub-parallel veins within a fault-controlled ore zone 1–2 m wide and extending for ~850 m.
The Baratta Silver–Lead Field comprises numerous workings including the Cross Crusader, Eukaby Hill, West Eukaby, Eukaby Extended, Eukaby South, Silver King, Silver Queen, Silver Monarch and Silver Prince. The field was discovered in 1887 and, after intermittent activity, there has been a small but steady production since 1976. Total production to 1999 was ~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.
Neoproterozoic Adelaidean rocks host numerous small Ag–Pb–Zn mines that were worked around the 1890s but have minor production, including Avondale (Ag–Pb), Commodore (Ag–Pb), Emily (Ag–Pb), Gilead P. Beck (Ag–Pb), Great Gladstone (Ag–Pb), Hahndorf (Ag–Pb), Mack’s (Ag–Pb), Mount Lofty Park (Ag–Pb–Zn), Uncle Tom (Ag–Pb), Wheal Grainger (Ag–Pb), Winklers (Ag–Pb), Cherry Gardens (Ag–Pb), Eagle (Ag–Pb) and Riversedge (Ag–Pb–Cu).
Cambrian limestone hosts Mississippi Valley-type Pb–Zn mineralisation, often with associated silver, the most significant deposit being the Ediacara Mineral Field hosted by Ajax Limestone. The field was discovered in 1869 and produced ~7440 t of lead and 6.5 t of silver from ~24 000 t of ore between 1888 and 1913. The main workings were Southern, Greenwood and Morish. An inferred resource of 17 Mt of 1.2% Pb and 10 g/t Ag remains.
The Cambrian Wilkawillina Limestone hosts Ag–Pb mineralisation at the Wirrealpa and Fountain Head Mines in the Flinders Ranges; the equivalent Normanville Group limestone hosts Ag–Pb mineralisation at the Rapid Bay (Yattagolinga), Sellicks Hill, Barritt’s, Wheal Coglin and Wheal Mary mines on Fleurieu Peninsula.
Silver was produced as a by-product from virtually all of the lead and Pb–Zn mines worked in the late 1800s. Mineralisation is generally confined to the Talisker Calc-siltstone, and Tapanappa and Carrickalinga Head Formations of the Kanmantoo Group. The main producing Ag–Pb mines were:
Tapanappa Formation — Aclare (~9500 kg Ag, 1859–96), Wheal Ellen (~11 000 kg Ag, 1857–1911), Strathalbyn (~440 kg Ag, 1848–58) and Scotts Creek (~4000 kg Ag, 1848–89). Angas (2 Mtonne Zn-Pb-(Ag-Au-Cu) ore treated from 2009-2013 for recovery of 44,000 kg silver.
Talisker Calc-siltstone — Talisker (~2200 t of dressed Ag–Pb ore, 1862–1935).
Carrickalinga Head Formation — Rhineberg, Mount Rhine and Royal Keyneton were worked ~1890.
Kanmantoo Group metasediments also host Ag–Pb–Zn mineralisation on Kangaroo Island. Workings are small and include Western River (1892–1907), Snug Cove (1889) and Perseverance (1889–1907). The mine reopened in 2011 and in 2013-14 produced 132, 854 oz Ag, 17 184 t Cu and 5962 oz Au as a concentrate.
The Kanmantoo Mine produced ~5000 kg of silver as a by-product in copper concentrate, from 4.05 Mt of copper ore (average grade 0.89% Cu) mined from a large open cut within Tapanappa Formation between 1970 and 1977.
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