Mount Isa Copper Mine, Queensland, Australia

Mount Isa Mines (Xstrata 100%) operates two separate mining and processing streams, copper and zinc-lead-silver. Mount Isa Mines' copper operations include two underground copper mines – Enterprise and X41, from which 6.5 million tonnes of ore is mined per annum; a concentrator with 7 million tonnes per annum capacity; and a copper smelter.

The Enterprise mine is the most recently developed copper ore source at Mount Isa and is Australia's deepest mine, with an internal shaft which reaches a depth of 1,900m.

Copper production at Mt Isa, Queensland, is derived from separate orebodies from those that form the basis for lead and zinc mining, with the copper operations being regarded as stand-alone operations. Since acquiring MIM, Xstrata Copper has undertaken several steps to improve performance, and is now expanding its smelter capacity at Mt Isa to 300,000t/y.

GEOLOGY AND RESERVES

Brecciated siliceous and dolomitic rock masses within the Urquhart Shale (see Mount Isa lead mine profile) contain several orebodies that comprise complex veins and irregular segregations with chalcopyrite, pyrite and pyrrhotite, and grading 3% to 4% copper.

Production currently comes from the 1,100 and adjacent 1,900 orebodies at the south end of the property and the deeper 3,000 and 3,500 orebodies below the lead mine in the north.

As of mid-2005, Xstrata reported resource figures as:

X41 mine (1,100 and 1,900 orebodies): 35Mt proven ore grading 2.2% Cu with measured resources of 61Mt at 2.3% copper.

Enterprise mine (3,000 and 3,500 orebodies): 33Mt at 3.6% Cu proven, with measured resources of 57Mt grading 3.5% copper. The resource potentially available for open-pit mining contains 98Mt of indicated ore grading 1.4% copper.

MINING

Prospector John Campbell Miles discovered silver-lead ore at Mount Isa in 1923. Mining began the following year and Mount Isa Mines was formed. During Mount Isa Mines' early years the company focused on zinc-lead-silver production with only a brief period of copper production during World War II. Parallel production of zinc-lead-silver and copper did not begin until 1953.

The years from 1969 to 1974 saw more expansion at Mount Isa Mines. Development of copper orebodies and improvements at the company's Townsville refinery boosted copper production dramatically. The next surge of development came in the late 1990s when close to A$1bn was invested in various projects, including two new mines and an expansion of the copper smelter and Townsville refinery. Xstrata acquired Mount Isa Mines in June 2003 through its MIM Holdings Limited acquisition.

During the late 1980s, MIM started to develop the orebodies located between levels 21 and 36. A ramp was driven down from the U62 loading station and an ABB-Kiruna electric truck hoisting system fitted. Production started in 1993. In 1996, MIM launched the A$370m Enterprise Mine project designed to raise deep copper output to 3.5Mt/y.

The 713m-deep internal M62 shaft opened in 2000, with refrigeration and paste backfill plants completed in 2001. Meanwhile the 1100 operation became the X41 Mine. In June 2004, Xstrata approved development of the Northern 3,500 orebody to maintain rated capacity by supplying 5.3Mt ore grading 4.5% Cu over 11 years, starting in late 2006. This should enable the Enterprise mine to achieve its rated concentrator throughput of 3.5Mt/y.

Recent expansion of the MT Isa copper smelter will result in annual production increasing to as much as 300,000t.

ORE PROCESSING

The copper concentrator was rebuilt in 1973, with rod and ball milling and three-stage flotation, to supply the roaster and conventional blister copper smelter on site. In 1981, Mount Isa commenced anode casting as well. In 1988–89, two 6.4MW AG/SAG grinding mills replaced the rod and ball mills at a cost of A$35m.

With the development of Ernest Henry, MIM modified the pre-flotation, column flotation and slag-cleaning circuits to increase the plant's throughput. The flotation capacity was increased again in FY2003 with the addition of the latest-design Jameson cells. Smelter investments have included the copper IsaSmelt plant in 1994 and an expansion in 1998–99.

During 2004, Xstrata decided to add 40,000t/y of copper output by slag treatment and related developments, and also approved a 2,500t/y copper-leaching plant to treat smelter electrostatic-precipitator dust.

MIM established Copper Refineries Pty Ltd near Townsville in 1956 and started treating blister copper in 1959. Capacity has kept pace with the smelter at 260,000t/y, and was raised to 280,000t/y by mid-2006.

PRODUCTION

Currently 6.5 million tonnes of ore is mined per annum from the two underground copper mines Enterprise and X41. In 2005 the figure was 5.6Mt.

A new leaching project will recover 2,500t of copper per annum from the copper smelter's electrostatic precipitator dust. Additionally, Xstrata Copper is expanding the Mount Isa copper smelter from 240,000t to 300,000t per annum.