The Mount Isa copper mines complex in Queensland, Australia comprise two underground mines including the country’s deepest underground copper mine at an operating depth of more than 1,900m. Glencore is the current owner and operator of the Mount Isa mines.
The Anglo-Swiss company acquired the Mount Isa operations from Xstrata Copper in 2013 and has since undertaken various upgrades and additional explorations at the property.
In September 2020, Glencore signed an agreement with the Government of Queensland for the continued operation of the Mount Isa copper smelting plant and the Townsville Copper Refinery beyond 2022.
The Mount Isa property was discovered in 1923 by prospector John Campbell Miles and Mount Isa Mines was established in January 1924. The company focused on zinc-lead-silver production in its early years with copper undertaken briefly to contribute to the nation’s World War II effort.
The Mount Isa mines complex also houses a separate mining and processing stream for zinc, lead, and, silver.
Glencore produced 64.4 thousand tonnes (kt) of copper metal and 22.8kt of copper concentrates during the first half of 2020 from its Australian operations that also include Ernest Henry in Queensland and Cobar in New South Wales.
Project location Image courtesy of Mount Isa Mines. and geology
The Enterprise and the X41 underground mines that form part of Mount Isa copper mining operations are located near the mining city of Mount Isa in northern Queensland, Australia. The Mount Isa mining lease covers approximately 32,000ha and includes the zinc mining operations at the George Fisher underground mine.
The Mount Isa deposits are hosted by the Urquhart Shale Formation of the Mount Isa Group which is a weak metamorphic sequence of mid-Proterozoic carbonate siltstones, mudstones and shales, with sandstone and conglomerate towards the base of the shale.
Mineralisation and reserves
Mineralisation at the X41 and Enterprise underground are characterised by massive to disseminated chalcopyrite mostly hosted in breccia within silica dolomite altered pyritic dolomitic siltstone.
The proven and probable copper reserves at the X41 underground mine were estimated to be 3.8Mt and 10.9Mt grading more than 1.67% copper, as of December 2019.
The Enterprise mine was estimated to hold 8.3Mt of proven and 4.9Mt of probable ore reserves containing 2.23% and 1.95% copper respectively.
Mining and processing operations at Mount Isa
The X41 and Enterprise underground mines constitute Mount Isa as Australia’s largest underground mine network development, as well as one of the country’s biggest copper producers with a processing capacity of 6.5 million tonnes per annum.
The extracted ore undergoes crushing at the underground mines before being hoisted to the surface where it undergoes grinding in a SAG mill and three ball mills to produce a fine copper mineral dust.
The fine ore material is then passed through the froth flotation circuit of an on-site copper concentrator facility to separate the mineral content from waste rock and sulphides.
The copper concentrate powder is fed into the ISASMELT furnace of the nearby smelter and heated to 1185 degrees Celsius to further draw out additional sulphide impurities and produce a molten copper concentrate which is then allowed to settle in two holding furnaces.
The heavy copper concentrate is collected at the bottom while the slag from the top is collected to be processed again to extract up to 6% more copper.
The heavy copper concentrate undergoes further refining in two furnaces where it is heated to approximately 1250 degrees Celsius to produce a 99.7% pure, molten copper. The molten copper is poured into a cast and set into 350kg copper anode slabs which are transported in trains to the Townsville Copper Refinery. The slabs undergo further refining to produce the final 99.995 % pure copper cathode which is exported Glencore's Townsville Port facility.
Townsville copper refinery
The Townsville copper refinery that utilises Glencore's proprietary IsaKIDD process has a capacity to produce up to 300,000 tonnes (t) of 99.995% pure copper cathode a year.
The copper anodes from the Mount Isa copper smelter are submerged in an acidic copper sulphate solution and a low voltage electric charge is fed through the tanks which cause the copper anode to dissolve into the copper sulphate solution over a period of seven days.
The positively charged copper gets deposited on the stainless-steel mother plates as 99.995% pure, premium ISA brand copper cathodes while the remaining impurities fall to the bottom of the tank.
The copper cathodes from the mother plates are then stripped, washed, sampled and bundled for sale. The impurities or slimes from the electrolytic refining contain a range of valuable minerals including gold and silver and are exported globally for further refining.
Fluor was engaged for the engineering, procurement, and construction management (EPCM) services for the copper smelter upgrade to increase production to 250,000 tonnes per annum (tpa).
Glencore Technology worked with Scott Automation and Robotics for the detailed design and fabrication for the Cathode Plate Robotic Handling and Welding System at the Townsville Copper Refinery which was put into operation in January 2020.