Mount Isa Mines operates two separate mining and processing streams, copper and zinc-lead-silver. Mount Isa Mines' zinc operations include an underground zinc-lead mine ? George Fisher from which 3.1 million tonnes of ore is mined per annum, and two open pit zinc-lead mines ?Black Star and Handlebar Hill; a concentrator with 6.5 million tonnes throughput per annum capacity; and a lead smelter.
The Handlebar Hill open pit mine is being developed and from the second half of 2008 should provide 1.75 million tonnes per year for the next three years.
Xstrata Zinc is expanding the Mount Isa zinc concentrator from 6.5 to 8 million tonnes of throughput per annum.
Xstrata employs more than 3200 employees and 1100 contractors at Mount Isa.
Mount Isa, Queensland, Australia, is a thriving outback city approximately 1000 km west of Townsville, 2000 km northwest of Brisbane, and 1600 km east of Darwin and Alice Springs. Mount Isa Mines is based here and has massive mining and mining support operations along with other major mining companies operating in the region.
Mount Isa is vast. It covers 41,000 square kilometers and is located among the ochre-red Selwyn Ranges on the banks of the Leichhardt River. The Lawn Hill Gorge in Boodjamulla National Park and the world-heritage listed Riversleigh Fossil Fields are nearby. Deep in dinosaur fossil country, the rocky terrain is harsh but beautiful, a rugged 'Mars-like' landscape with stark striking colours.
The population is 23,500 and is a significant administrative centre for the region. Although situated in an arid area, the artificial Lake Moondarra to the north provides both drinking water and an area for watersports. The city hosts Australia's largest rodeo annually and is in the center of some of Australia's biggest cattle stations.
Copper orebodies were formed within the Urquhart Shale Formation, in a sequence of alternating pyrite-rich dolomitic siltstone and shale beds up to 1000 metres thick.
The zinc-lead-silver orebodies extend from the surface to about one kilometre below the surface. Individual orebodies range in widths up to 35 metres and may persist for hundreds of metres in length.
The large 1100 copper orebody extends from 400 metres to 1000 metres below the surface. It is three kilometres long and one of the largest and richest copper orebodies in the world.
The main copper mineral is chalcopyrite. Closer to the surface, weathering and ground water leaching has changed the chalcopyrite to secondary copper minerals such as chalcocite. This weathering has also affected some of the near-surface lead orebodies, forming cerussite, a secondary lead carbonate mineral.
A significant increase in known copper resources has led to a planned 40% expansion in copper production by 2006. Resources sufficient to support a 400,000 tpa rate for up to 20 years from Mount Isa and Ernest Henry was announced in 2002.
Mount Isa operations are carried out in two production streams. Copper operations consist of the X41 (1100 and 1900 orebodies) and Enterprise (3000 and 3500 orebodies) underground mines along with a copper concentrater and smelter. Zinc, lead and silver operations consist of the Hilton and George Fisher (formerly Hilton North) underground mines and the Black Star open pit mine.
Underground operations are accessed via surface shafts, two equipped with ore hoists, and a decline, which is shared with the Isa Lead mine. Both the interconnected X-41 and Enterprise mines contain massive orebodies, which are extracted using long-hole open stoping with delayed backfill. Operations are mechanised with a complement of rubber-tired trucks and loaders, electro-hydraulic drilling rigs, raise boring rigs and ancillary vehicles.
The main ore hoisting shaft for the Mount Isa copper operations is the 710-m deep U-62 shaft from surface. The R-62 shaft, located near U-62 is an ore hoisting and service shaft for personnel and supplies to the copper mine. R-62 is also the main ore hoisting facility for the Isa Lead mine, and is also used to feed copper ore to the lead concentrator when required. The internal M-62 shaft is used for hoisting ore from the deep Enterprise zone to the crushing and conveying system at the base of the U-62 shaft. A decline from surface, also shared with the Isa Lead mine, can be used for movement of personnel, materials and equipment into the Enterprise area.
A variety of mining methods have been used at Isa during the course of its operation. Sub-level open stoping (''SLOS'') is the method currently used in both the X-41 and Enterprise areas of the mine. SLOS is designed to extract massive blocks of ore in vertical slices throughout the orebodies. Stope sizes in the large 1100 ore body (X-41 area) are mined in blocks of 40 metres by 40 metres, and up to 300 metres high. Drilling sublevels for the blocks are developed at every 40 metres of elevation. Stope sizes in the 3000 orebody (Enterprise area) are as small as 25 metres by 25 metres, and up to 100 metres high. Drilling sublevels for mining the 3000 orebody are spaced approximately 25 metres apart. Blast-hole drilling is carried out using mechanised drill rigs. The broken ore is collected at the bottom of the stope and is extracted at drawpoints by load-haul-dump (''LHD'') mining equipment.
Smelter capacity increased to more than 250,000 tonnes of copper anode per year to accommodate all mine production from Ernest Henry mine as well as Mount Isa.
The Hilton concentrator recovers three products shipped to Mount Isa as slurry. It uses SAG milling, tower-mill regrinding and flotation with company-designed column cells and Jameson cells. The plant reached rated output shortly after commissioning but switched to treating copper converter slag from Mount Isa in the mid 1990s when the mining rate was cut and ore was trucked to the Mount Isa lead-zinc concentrator.
Copper anode from the Mount Isa smelter is sent by rail to be refined at Xstrata's Townsville copper refinery to produce 99.995% pure London Metal Exchange (LME) grade A copper cathode.