The Mount Isa copper, lead, zinc and silver mines near Mount Isa, Queensland, Australia are part of the Xstrata mining company. In 1923 the orebody containing lead, zinc and silver was discovered by the miner John Campbell Miles. The company Mount Isa Mines 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. Xstrata purchased Mount Isa Mines for A$2.9 billion in 2003.
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 Proterozoic Urquhart Shale. The Urquhart is 1,000 metres thick and is a grey dolomitic shale with tuffaceous 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.
Lead Zinc Silver Ore:
The primary ore consists of galena, iron rich sphalerite 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.
Copper occurs in brecciated "silica-dolomite" rock. Primary minerals are chalcopyrite, pyrrhotite and arsenopyrite. minor amounts of cobaltite, marcasite, valleriite, chalcostibite, galena and others are reported.
- 6.1 million tonnes copper ore with 3.3% copper
- 4.6 million tonnes silver-lead-zinc ore wit 154g/t silver 5.4% lead 6,5% zinc (1986)