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At a Glance
The McArthur River zinc-lead-silver mine lies 900 kilometres south-east of Darwin, in the north-eastern part of the Northern Territory. McArthur River is one of the world's largest zinc deposits. Owned by a joint venture between MIM (75%) and ANT Minerals, a consortium of leading Japanese companies (25%), it was brought into production in 1995, 40 years after its discovery. The mixed lead-zinc concentrate from the mine is transported by road to a port facility at Bing Bong where it is barged to waiting ships for despatch to smelters. Local Aboriginal people have a 31% interest in the barging joint venture. Contained zinc production was 3% below the previous year's record, however the years result was good given difficult weather conditions and the 6% reduction in milled zinc head grade that was partly offset by the operational performance.
MIM has commenced a feasibility study into producing zinc metal on site at McArthur River using the company's Albion Process technology. The process, now being pilot tested in Brisbane, comprises ultra fine grinding and atmospheric leaching followed by electrowinning, and eliminates smelting. The project would include expanding operations at McArthur River to produce up to 4.8 million tonnes of ore and 450 000 tonnes of zinc metal a year and would significantly reduce unit costs of production. The project has the potential to put MIM and the Northern Territory in the forefront of the world zinc industry. It would also bring many benefits to the local community, the Northern Territory and Australia.
MIM values the input of local people and the general public to the project. Consultation with local people and traditional owners is an important part of both the feasibility study and EIS process. Information on the project is available from the McArthur River Mine Community Development Officer in Borroloola or the mine General Manager and Community Relations Superintendent at the minesite. People outside the local area can discuss the project with MIM and ask questions by contacting the Project Team below.
Environmental Impact Statement MIM has commenced preparation of an Environmental Impact Statement (EIS) for the project Download [Acrobat - 46Kb]. A Notice of Intent was submitted to the Northern Territory Government in January 2003 and is available below. The Draft EIS Guidelines are available at www.lpe.nt.gov.au/enviro/EIAREG/McArthur/.
MIM's Albion Process pilot plant in Brisbane.  History Traces of silver, lead and copper are reported to have been discovered on McArthur River Station as far back as the mid 1880s. Mount Isa Mines Limited first became interested in the area in 1948, and by 1955 the "Reward" lead deposit on the western side of the Carpentaria Highway was discovered. That same year the HYC "Discovery Outcrop" was also discovered. HYC stands for "Here's Your Chance". Legend has it that Mount Isa's chief geologist, remarked to a colleague at McArthur River that he had never named a prospect. "Here's your chance," came the reply. And so the discovery was named. Exploratory drilling commenced in 1956, but with a slump in metal prices in 1957 and 1958, activity was suspended until 1959. To that time, the main focus was on the "reward" deposit which showed good grades of lead but insufficient quantities of ore. It was not until drilling commenced on the HYC deposit in 1959 that the significance of the find was recognised. By the early 1960s an intensive drilling program had defined the McArthur River HYC deposit as one of considerable magnitude. Further delineation continued until the mid 1960s, by which time its size, composition and metallurgical complexity were identified. In 1966, a permanent camp was built and a shaft was sunk to provide bulk samples for metallurgical testing. The tests confirmed the extent of the separation difficulties and the project was stalled in search of a viable process to treat the ore. Whilst separation was possible, metal recoveries and processing costs achieved at the time could not support the extensive capital cost required in a location devoid of infrastructure. In 1974, a major review of McArthur River HYC deposit commenced, resulting in a feasibility study which was conducted from 1977 to 1979. The study required the development of an exploration adit and the construction of a 50 tonnes per day pilot plant and accompanying infrastructure at the mine site. From the small underground mine, ore representative of the whole deposit was extracted for pilot testing. This feasibility study was based on a concept which entailed extracting the whole deposit from a high tonnage, low head grade, open pit operation. Other key features of this proposal were the establishment of substantial infrastructure including a major town for 2,000 people from which a mine workforce of 920 would be drawn, diverting the McArthur River by way of a seven kilometre channel and the construction of a deep water port facility and associated infrastructure on Centre Island, capable of servicing sea-going vessels. These features contributed to the extremely high capital costs and in 1979 it was announced that the project was not economically viable and development was again deferred. The project was reactivated in 1989. MIM took a new approach to the development, taking account of the company's improved milling technology, advances in smelting and changes in market conditions and political and industrial relations climates. Some of the significant changes included the fact that a single high grade mixed zinc-lead concentrate could be produced at high zinc recoveries rather than producing separate zinc and lead concentrates, and changing the scale of the project from a large open pit mine to a smaller underground operation to selectively mine the higher grade zones. In addition, the concentrate storage and loadout facility at Bing Bong operates exclusively as a bulk carrier loading facility. This achieved a significant reduction in capital from the previous proposal of constructing a highly underutilised, deep water port to accommodate sea-going vessels, which also required a network of roads, bridges and causeways to provide access from the mainland to the island port location. A pre-feasibility study was conducted from 1989 to 1991. The results of this study encouraged Mount Isa Mines Limited to seek joint venture partners for a full feasibility study, and by March 1992 a joint venture had been formed with a group of prestigious Japanese companies to complete that study. In November 1992 the joint venturers advised their intention to proceed with the development of the McArthur River mine. Underground development at the mine site commenced in September 1993 with preliminary surface construction having started earlier in the 1993 dry season. The McArthur River concentrator commenced treatment of ore in mid-May 1995, with the first load of concentrate transported to Bing Bong on 6 June 1995. Australian Prime Minister Mr Paul Keating officially opened the mine in September 1995. The installation of a tower mill has significantly increased throughput and recovery. The McArthur River district is situated within a belt of sedimentary rocks of Middle Proterozoic age. Similar rocks host the significant orebodies of Mount Isa, Hilton, Lady Loretta, Dugald River and the Century deposit. The "Here's Your Chance" (HYC) zinc-lead-silver deposit at McArthur River occurs in the HYC Pyritic Shale Member, a package of interbedded pyritic siltstone, sedimentary breccia and tuff. The HYC deposit consists of seven orebodies, stacked one on top of the other, each separated by dolomitic siltstones and sedimentary breccias. Thin tuff bands are also common throughout the sequence which has an average thickness of 55 metres. Mining selectively extracts the higher grade No. 2 orebody which will be followed by a blend of No. 3 and No. 4 orebodies which are between 100 and 500 metres below the surface. Compared with the other orebodies, No. 2 orebody is zinc rich with a high zinc to lead ratio and it is also low in iron. Access to the ore is provided by two declines. The main decline is used for personnel and equipment, whilst the other is equipped with a conveyor to transport ore to the surface. The access decline portal has been established at Barney Hill, the closest flood free area to the deposit. The access decline has a gradient of 1 in 7, a cross-section of 5.5 by 5.5 metres and runs 1.3 kilometres from the portal to the HYC orebody. It then branches out into a double decline system, with declines following the No. 2 and No. 4 orebodies at an average gradient of 1 in 8. The conveyor decline runs in a straight line from a portal at Barney Hill to the underground crusher station. Room and pillar mining is the primary extraction technique. Rooms of ore are extracted leaving pillars to support the roof. This mining technique is performed using a standard drill, blast, muck and ground support cycle. Underground drilling rigs known as Jumbos, drill holes into the face of the drive. The holes are then charged with explosives and fired.
The centralised location of the crusher results in a truck tramming distance of less than 800 metres in most cases. Ore is fed to the crusher via a tipple and ore storage bin arrangement. The crushed product is then fed onto the conveyor and travels up the conveyor decline to the surface stockpile. As much of the orebody and infrastructure development as possible is mined through No. 2 and No. 4 orebodies. This strategy allows for the collection of data that is used to develop improved geological interpretations of orebody grade and structures. All room and pillar production comes initially from No. 2 orebody. A series of orebody access drives approximately 60 metres apart and measuring 5 metres by 5 metres are mined across the orebody to allow trucking access to the production panels. Smaller production drives, mined to the height of the orebody, are developed between the access drives. The updip walls of these drives are selectively split to maximise ore recovery, while still maintaining overall orebody stability to allow for future No. 4 orebody mining. As No. 2 orebody is gradually exhausted, mining focus will shift to Long Hole Open Stoping. In this scenario, drill drives are developed on the No. 4 Orebody level and blast holes are drilled down to breakthrough into the underlying No. 2 Orebody development. The ore is then blasted and mucked using the No. 2 Orebody level as the extraction horizon. This mining method provides additional efficiencies over and above the existing room and pillar mining. Remote-controlled loaders will be used to recover broken ore. Stope heights will reach 30 metres in many instances. Bench mining, a bulk mining method, has been implemented by MRM. It is a non-entry, low cost method. At MRM access development will be completed in the 4 orebody to allow production blasthole ring drilling to proceed. Ore will be mined from this level down to the 2 orebody in mining blocks up to 25m high, 30m wide and up to 50m long. The ore material will be loaded into haul trucks with diesel powered load haul dump machines at the base of the mining blocks, from the existing 2 ore body development. This development has already been used to extract the 2 ore body by the previous room and pillar entry mining method. The advent of this method has been the result of significant advances in the understanding of the metallurgical treatment route for the orebodies above the 2 orebody. These can now be treated profitably. Although one of the world's largest zinc deposits, the metallurgy at McArthur River Mine is complicated by the fine-grained ore presenting technical processing challenges. MIM technology and advances in the Imperial Smelting Process enabled the mine to proceed. The concentrator has the capacity to treat 150 tonnes of ore per hour, producing 350,000 tonnes of concentrate per annum.
These feeders deposit ore onto the reclaim conveyor which feeds the SAG mill. The SAG mill grinds the ore down to a size suitable for flotation. Flotation is a process used to separate lead and zinc minerals from the ore. Reagents are added which cause these minerals to attach themselves to bubbles which move through the agitated slurry. The resulting froth is collected as the concentrate. Flotation is carried out using 16 cubic metre mechanical flotation cells. Flotation air at 25 kilopascals is supplied via a blower, which delivers between 70 and 90 cubic metres per minute. Rougher flotation recovers over 90% of the zinc to the rougher concentrate which grades approximately 30% zinc.
Five stages of cleaner flotation are used to upgrade the concentrate to between 42 to 46% zinc. The rougher tailing and the first cleaner tailing report to the final tailings. Concentrate is thickened to a dense slurry using two 25 metre diameter high rate thickeners. The process water removed from the concentrate is recovered and reused in grinding and flotation. Two 423 metre concentrate stock tanks are used to store the concentrate prior to the filtration stage. Filtering is carried out using two 132 square metre Larox pressure filters, which use cycles of air pressing and blowing to dewater the concentrate to 12% moisture, at which it can be transported. The concentrate is discharged onto conveyors which remove the dry concentrate to the storage shed, to await transport to the concentrate storage and loadout facility at Bing Bong. Tailings which are rejected from flotation are thickened in a 20 metre diameter high rate thickener. Water is recovered form the thickener overflow for use in the process. The thickened tailings are pumped through a four kilometre pipeline to the tailings pond, which uses a central discharge method to store tailings material. An area of 380 hectares is available for storage of tailings and water. Water is recovered from the tailings area and returned for use in the concentrator via a tailings return water pipeline.
MIM Holdings is committed to conducting business responsibly and in a manner designed to protect employees, the community's health and the environment. MIM Holdings developed an Environmental Policy and Standards in 1997 for all sites to follow to ensure minimal impact of our operations on the surrounding environment. The design, development and operation of our facilities is managed with a view to reducing the impact of our operations; ensuring efficient use of energy, water and other resources; minimising waste generation and disposal; and where waste must be disposed of, doing so responsibly. A high standard of environmental protection across all sites is maintained through site-specific Environmental Management Systems (EMS). A key requirement of the EMS is the ongoing development of comprehensive Compliance Registers for all sites, which is an internal audit of sites' compliance with our environmental commitments. McArthur River Mine (MRM) environment monitoring programmes cover areas such as hazardous substances, waste rock management, rehabilitation, water and tailings management. The programmes at the minesite include sampling from; Potable water is tested regularly and subjected to bacteriological analysis. The levels of heavy metals contained in dust are monitored via dust fallout collectors placed in the surrounding area, and samples of soil and river sediments are also analysed. Weather sensors located on Barney Hill monitor the meteorologic conditions around MRM. A gauging station operates in Barney Creek to monitor the stream height during the wet season. Data received, in conjunction with data from a power and water authority station located on the McArthur River, provides further information on the nature of wet season flows and the volumes of water involved. After examining a number of options for the transportation of MRM (lead/zinc) concentrate to export vessels, a decision was made to truck the concentrate to the Northern Territory coast and then barge it from the Bing Bong port facility to an export vessel anchored offshore. This reduced the potential environmental impact to the coastline surrounding Bing Bong port and lowered overall costs. A channel provides year-round access for the bulk carrier, Aburri, through the shallow waters of the Gulf of Carpentaria. The Bing Bong port facility and channel consists of the turnaround or "swing basin" that allows the Aburri to easily navigate a passage through the channel. The storage and loadout facilities at Bing Bong port have been designed to prevent the loss of concentrate into the environment. All conveyors transferring MRM lead-zinc concentrate, including those on the bulk carrier, are fully enclosed and include sophisticated control and monitoring systems. The cargo hold onboard the Aburri is also fully enclosed. If a problem with the cargo handling equipment occurs, the computerised system automatically shuts down its operation. As added protection the Aburri consists of a double hull that has a number of different compartments. An emergency remote controlled spill recovery system is permanently available onboard the Aburri should a spill occur while concentrate is being loaded onto the bulk carrier. The concentrate storage facility at Bing Bong has been constructed to withstand the impacts of cyclones and flooding. The monitoring programme specific for Bing Bong involves the analysis of seawater, sediments, seagrass, and biots on a regular basis. Recycled water comprises 88% of the water utilised by McArthur River Mining. MRM provided financial support to the Northern Territory University to assist with the research into marine environments of northern Australian. This research included a study into developing a greater understanding of the way in which the traditional land owners of MRM the Yanyuwa "Saltwater People" manage and relate to the dugong and sea turtle, which are of traditional significance to the local community. Other MRM research projects aimed at expanding knowledge about the Gulf of Carpentaria marine environment and the impact the MRM operation has on the Bing Bong swing basin have been conducted in conjunction with the CSIRO Division of Fisheries and the Northern Territory University. MIM took the view that as a business enterprise, it wished to involve local Aboriginal people on a commercial basis in the operations at MRM. MIM made its views on commercial involvement clear to local people. Leaders of the four main language groups in the region, the Yanyuwa, Mara, Gurdanji and the Garrawa, formed the Mawurli and Wirriwangkuma Aboriginal Association (MAWA). MAWA (31%) formed a joint venture, Carpentaria Shipping Services Pty Ltd, which is currently represented by P&O Maritime Services Pty Ltd (50%) and the Aboriginal and Torres Strait Islander Commercial Development Corporation (CDC) (19%).
In addition to this commercial involvement, Aboriginal groups also benefit from opportunities provided by MRM for training and employment. The McArthur River mine won the 2000 Recognition Award for Community Relations in Resource Development. An initiative of the Northern Territory Government, the award recognised McArthur River's achievements in implementing a sustainable education and training programme at Borroloola which provides residents with the opportunity to gain long term and meaningful employment in the mining industry. MRM has its own Accredited Training Programme which is registered nationally and offers Mining Services Traineeships to local aboriginal people. MIM's Indigenous employment and community initiatives are outlined in a case study featured in the Commonwealth Department of Industry, Resources and Tourism's Working in Partnership Programme. There are a number of Aboriginal sites of significance in the vicinity of the McArthur River mine site and the transport corridor to seagoing vessels moored in the Gulf of Carpentaria. McArthur River Mining works in cooperation with the Aboriginal custodians of the various sites of significance to ensure that those sacred sites are not disturbed in the area associated with the McArthur River project.
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