Mount Isa Mines
Encyclopedia
The Mount Isa copper
, lead
, zinc
and silver
mines near Mount Isa, Queensland
, Australia
are part of the Xstrata
mining company.
, zinc
and silver
was discovered by the miner John Campbell Miles. The company Mount Isa Mines http://www.xstrata.com/operation/mountisa was founded 1924 but full scale production was not reached before 1931. The lead and zinc mining continued with a break between 1943 and 1946. The copper ore was first discovered in 1927 and production grew steadily with a peak between 1957 and 1965.
Urquhart Shale. The Urquhart is 1000 metres thick and is a grey dolomitic
shale
with tuff
aceous horizons. Near the ore horizons the shale is pyritic
. The orebodies are on one limb of a plunging anticline
and are extensively faulted.
The ore occurs as en-echelon bodies parallel to the shale bedding. Orebodies may extend more than one kilometre along strike and three-fourths of a kilometre down dip
. Thickness may reach 50 metres.
The ores are considered to be syn-genetic with the host shale and interbedded volcanic material.
and tetrahedrite
as ore minerals along with common accessories pyrite
, pyrrhotite
, quartz
, carbonates and graphite
. Minor arsenopyrite
, marcasite
, chalcopyrite
, valleriite, proustite
, polybasite
and argentite
also occur.
Original surface oxidized
ore contained cerussite
, anglesite
and pyromorphite
. Silver and zinc were removed from the surface oxidized zone and were deposited as supergene
ore at a depth above the primary ore.
, marcasite, valleriite, chalcostibite, galena and others are reported.
Smelter operations release sulfur dioxide
emissions very close to the city of Mount Isa. The Mount Isa Mines Panel Assessment Study recently spent 4 years investigating the air quality and the effects on community health. The panel found no evidence of adverse effects from the mine. However, the panel did not report on emissions of lead and several other metals associated with sulphur dioxide emissions and which are known to have potentially severe environmental and health effects. Mount Isa Mines is currently the highest atmospheric emitter of sulphur dioxide, lead and several other metals in Australia. Other research has confirmed that there has been widespread contamination of soils with lead, copper and other metals in and around Mount Isa and that these contaminants are derived from both historic and ongoing smelter emissions and fugitive dust from Mount Isa Mines. Queensland Health reported in 2008 that the average blood lead concentration for children (1–4 years old) in Mount Isa was 5 microgram/dL and 11.3% exceeded 10 microgram/dL. In comparison, average blood lead in children from uncontaminated comparable urban areas is around 2 microgram/dL. Recent medical research has documented adverse health effects at blood lead concentrations above 5 microgram/dL and possibly down to as low as 2 microgram/dL.
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
, lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
, zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
and silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
mines near Mount Isa, Queensland
Queensland
Queensland is a state of Australia, occupying the north-eastern section of the mainland continent. It is bordered by the Northern Territory, South Australia and New South Wales to the west, south-west and south respectively. To the east, Queensland is bordered by the Coral Sea and Pacific Ocean...
, Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
are part of the Xstrata
Xstrata
Xstrata plc is a global mining company headquartered in Zug, Switzerland and with its registered office in London, United Kingdom. It is a major producer of coal , copper, nickel, primary vanadium and zinc and the world's largest producer of ferrochrome...
mining company.
History
In 1923 the orebody containing leadLead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
, zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
and silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
was discovered by the miner John Campbell Miles. The company Mount Isa Mines http://www.xstrata.com/operation/mountisa was founded 1924 but full scale production was not reached before 1931. The lead and zinc mining continued with a break between 1943 and 1946. The copper ore was first discovered in 1927 and production grew steadily with a peak between 1957 and 1965.
Orebodies
Mount Isa contains two separate orebodies: a stratigraphically lower lead-zinc-silver ore horizon and an upper copper ore. Both are contained within the Lower ProterozoicProterozoic
The Proterozoic is a geological eon representing a period before the first abundant complex life on Earth. The name Proterozoic comes from the Greek "earlier life"...
Urquhart Shale. The Urquhart is 1000 metres thick and is a grey dolomitic
Dolomite
Dolomite is a carbonate mineral composed of calcium magnesium carbonate CaMg2. The term is also used to describe the sedimentary carbonate rock dolostone....
shale
Shale
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...
with tuff
Tuff
Tuff is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. Tuff is sometimes called tufa, particularly when used as construction material, although tufa also refers to a quite different rock. Rock that contains greater than 50% tuff is considered...
aceous horizons. Near the ore horizons the shale is pyritic
Pyrite
The mineral pyrite, or iron pyrite, is an iron sulfide with the formula FeS2. This mineral's metallic luster and pale-to-normal, brass-yellow hue have earned it the nickname fool's gold because of its resemblance to gold...
. The orebodies are on one limb of a plunging anticline
Anticline
In structural geology, an anticline is a fold that is convex up and has its oldest beds at its core. The term is not to be confused with antiform, which is a purely descriptive term for any fold that is convex up. Therefore if age relationships In structural geology, an anticline is a fold that is...
and are extensively faulted.
The ore occurs as en-echelon bodies parallel to the shale bedding. Orebodies may extend more than one kilometre along strike and three-fourths of a kilometre down dip
Strike and dip
Strike and dip refer to the orientation or attitude of a geologic feature. The strike line of a bed, fault, or other planar feature is a line representing the intersection of that feature with a horizontal plane. On a geologic map, this is represented with a short straight line segment oriented...
. Thickness may reach 50 metres.
The ores are considered to be syn-genetic with the host shale and interbedded volcanic material.
Lead zinc silver ore
The primary ore consists of galena, iron rich sphaleriteSphalerite
Sphalerite is a mineral that is the chief ore of zinc. It consists largely of zinc sulfide in crystalline form but almost always contains variable iron. When iron content is high it is an opaque black variety, marmatite. It is usually found in association with galena, pyrite, and other sulfides...
and tetrahedrite
Tetrahedrite
Tetrahedrite is a copper antimony sulfosalt mineral with formula: 12Sb4S13. It is the antimony endmember of the continuous solid solution series with arsenic bearing tennantite. Pure endmembers of the series are seldom if ever seen in nature. Of the two, the antimony rich phase is more common...
as ore minerals along with common accessories pyrite
Pyrite
The mineral pyrite, or iron pyrite, is an iron sulfide with the formula FeS2. This mineral's metallic luster and pale-to-normal, brass-yellow hue have earned it the nickname fool's gold because of its resemblance to gold...
, pyrrhotite
Pyrrhotite
Pyrrhotite is an unusual iron sulfide mineral with a variable iron content: FeS . The FeS endmember is known as troilite. Pyrrhotite is also called magnetic pyrite because the color is similar to pyrite and it is weakly magnetic...
, quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
, carbonates and graphite
Graphite
The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...
. Minor arsenopyrite
Arsenopyrite
Arsenopyrite is an iron arsenic sulfide . It is a hard metallic, opaque, steel grey to silver white mineral with a relatively high specific gravity of 6.1. When dissolved in nitric acid, it releases elemental sulfur. When arsenopyrite is heated, it becomes magnetic and gives off toxic fumes...
, marcasite
Marcasite
The mineral marcasite, sometimes called white iron pyrite, is iron sulfide with orthorhombic crystal structure. It is physically and crystallographically distinct from pyrite, which is iron sulfide with cubic crystal structure. Both structures do have in common that they contain the disulfide...
, chalcopyrite
Chalcopyrite
Chalcopyrite is a copper iron sulfide mineral that crystallizes in the tetragonal system. It has the chemical composition CuFeS2. It has a brassy to golden yellow color and a hardness of 3.5 to 4 on the Mohs scale. Its streak is diagnostic as green tinged black.On exposure to air, chalcopyrite...
, valleriite, proustite
Proustite
Proustite is a sulfosalt mineral consisting of silver sulfarsenide, Ag3AsS3, known also as light red silver or ruby silver ore, and an important source of the metal. It is closely allied to the corresponding sulfantimonide, pyrargyrite, from which it was distinguished by the chemical analyses of...
, polybasite
Polybasite
Polybasite is a sulfosalt mineral of silver, copper, antimony and arsenic. Its chemical formula is [62S7][Ag9CuS4].It forms black monoclinic crystals which can show dark red internal reflections. It has a Mohs hardness of 2.5 to 3. It is found worldwide and is an ore of silver...
and argentite
Argentite
Argentite was primarily treated as a mineral belonging to the galena group, cubic silver sulfide , occasionally found as uneven cubes and octahedra, but more often as dendritic or earthy masses, with a blackish lead-grey color and metallic lustre. All these forms are structurally not argentite, but...
also occur.
Original surface oxidized
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
ore contained cerussite
Cerussite
Cerussite is a mineral consisting of lead carbonate , and an important ore of lead. The name is from the Latin cerussa, white lead. Cerussa nativa was mentioned by Conrad Gessner in 1565, and in 1832 F. S. Beudant applied the name cruse to the mineral, whilst the present form, cerussite, is due to...
, anglesite
Anglesite
Anglesite is a lead sulfate mineral with the chemical formula PbSO4. It occurs as an oxidation product of primary lead sulfide ore, galena. Anglesite occurs as prismatic orthorhombic crystals and earthy masses, and is isomorphous with barite and celestine. It contains 74% of lead by mass and...
and pyromorphite
Pyromorphite
Pyromorphite is a mineral species composed of lead chlorophosphate: Pb53Cl, sometimes occurring in sufficient abundance to be mined as an ore of lead. Crystals are common, and have the form of a hexagonal prism terminated by the basal planes, sometimes combined with narrow faces of a hexagonal...
. Silver and zinc were removed from the surface oxidized zone and were deposited as supergene
Supergene (geology)
In ore deposit geology, supergene processes or enrichment occur relatively near the surface. Supergene processes include the predominance of meteoric water circulation with concomitant oxidation and chemical weathering. The descending meteoric waters oxidize the primary sulfide ore minerals and...
ore at a depth above the primary ore.
Copper ore
Copper occurs in brecciated "silica-dolomite" rock. Primary minerals are chalcopyrite, pyrrhotite and arsenopyrite. minor amounts of cobaltiteCobaltite
Cobaltite is a sulfosalt mineral composed of cobalt, arsenic and sulfur, CoAsS. It contains up to 10 percent iron and variable amounts of nickel. Structurally it resembles pyrite with one of the sulfur atoms replaced by an arsenic atom....
, marcasite, valleriite, chalcostibite, galena and others are reported.
Production
- 5.4 million tonneTonneThe tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...
s copper ore with 3.3% copper (1986) - 4.6 million tonnes silver-lead-zinc ore wit 154g/t silver 5.4% lead 6,5% zinc (1986)
Smelter operations release sulfur dioxide
Sulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...
emissions very close to the city of Mount Isa. The Mount Isa Mines Panel Assessment Study recently spent 4 years investigating the air quality and the effects on community health. The panel found no evidence of adverse effects from the mine. However, the panel did not report on emissions of lead and several other metals associated with sulphur dioxide emissions and which are known to have potentially severe environmental and health effects. Mount Isa Mines is currently the highest atmospheric emitter of sulphur dioxide, lead and several other metals in Australia. Other research has confirmed that there has been widespread contamination of soils with lead, copper and other metals in and around Mount Isa and that these contaminants are derived from both historic and ongoing smelter emissions and fugitive dust from Mount Isa Mines. Queensland Health reported in 2008 that the average blood lead concentration for children (1–4 years old) in Mount Isa was 5 microgram/dL and 11.3% exceeded 10 microgram/dL. In comparison, average blood lead in children from uncontaminated comparable urban areas is around 2 microgram/dL. Recent medical research has documented adverse health effects at blood lead concentrations above 5 microgram/dL and possibly down to as low as 2 microgram/dL.