The McArthur River zinc-lead mine located in the Northern Territory of Australia has been operational since 1995.
Owned and operated by McArthur River Mining (MRM), a wholly-owned subsidiary of Glencore, the open-pit mine produced 271.2 thousand tonnes (Kt) of zinc and 55.3Kt of zinc in 2019.
The McArthur River zinc-lead deposit was originally known as ‘Here’s Your Chance’ deposit which was discovered in 1955.
Although the first feasibility studies were started in 1977, MIM Holdings, the previous owner of the mine, completed a full feasibility study and formed the MRM joint venture with Japanese consortium ANT Minerals comprising Nippon, Mitsui, and Marubeni to develop the deposit in 1992.
MRM commenced production with the commissioning of an underground mine and processing plant in 1995.
Xstrata (now Glencore) acquired MIM in July 2003 followed by the acquisition of ANT Minerals’ share in MRM to wholly own the operation in September 2005.
The mine transitioned to open-pit operations in 2006 to increase the mine life from the initial 15 years by a further 17 years to 2027, while in 2013, an expansion approval was received to increase the ore production capacity to 5 million tonnes per annum (Mtpa) and to extend the mine life until 2037.
Project location and geology
The McArthur River lead-zinc mine encompasses five adjoining mineral leases located in the McArthur River Station Pastoral Lease, near the Gulf of Carpentaria, 65km south-west of Borroloola, in the Northern Territory of Australia. The project lies approximately 970km south-east of Darwin by road.
The McArthur River deposit is situated within the McArthur Basin of the NW-SE trending Carpentaria Zinc Belt which is mainly composed of unmetamorphosed sedimentary and volcanic rocks.
The south-west, north and south-east successions of the McArthur Basin is overlain by Palaeozoic and younger sedimentary sequences of the Georgina, Arafura and Carpentaria basins
Mineralisation and reserves
The zinc-lead and silver mineralisation at the McArthur River mine primarily occurs in an ultrafine bedded parallel sphalerite and galena rich bands.
The mineralised bands are hosted within dolomitic, carbonaceous, and pyritic siltstones as well as in graded beds and chaotic debris flow breccias.
The mineralised zone covers approximately 2km2 with an approximate thickness of 55m containing eight discrete ore zones.
The proven and probable ore reserves at the McArthur River mine were estimated to be 177 million tonnes (Mt) grading 8.3% zinc, 3.9% lead, and 53g/t silver, as of December 2019.
The measured and indicated resources were estimated to be 163Mt grading 9.8% zinc, 4.4% lead and 45g/t silver.
Mining operations at Mc Arthur River Mine
The McArthur River mine uses conventional open-pit mining methods of drilling, blasting, loading and haulage. The ore excavation plan involves six stages of which the first three target the shallowest ore bodies.
The target ore is exposed by blasting the overburden, while the ore excavation is carried out in horizontal benches.
The mining fleet includes excavators with a load capacity of up to 550 tonnes (t) and 175-220t haul trucks.
The overburden from the mine is primarily stored at the North Overburden Emplacement Facility, while the mined ore is separated on-site before being trucked to the processing plant.
Ore is trucked from the open pit to the processing plant where it goes through three stages of crushing and screening, pre-concentration via heavy media separation followed by flotation, oxidative leaching and dewatering.
The run-of-mine (ROM) ore undergoes three-stage crushing in a primary jaw crusher, followed by secondary and tertiary cone crushers to reduce the ore size to a minimum of 9mm. The low-grade ore is upgraded to process feed grade in a heavy medium plant, while the high-grade ore is transferred for grinding.
The high-grade ore undergoes two-stage grinding in a semi-autogenous grinding (SAG) mill and a ball mill, before passing through hydrocyclones to produce a fine ground slurry material of 80% less than 45 microns.
The slurry is introduced into a flotation circuit to separate zinc and lead-bearing minerals, and produce a froth concentrate. The concentrate is pumped through a pre-cycloning stage to produce a fine material which undergoes conditioning and passes through a six-stage cleaner circuit to produce a final zinc-lead bulk concentrate.
The concentrate is thickened and filtered through Larox pressure filters, and stored for transport.
Concentrate transportation and shipping
The concentrate output is trucked to a loading facility at Bing Bong, approximately 120km north of the mine.
It is stored in a 90,000t concentrate storage shed at the Bing Bong port before being loaded on to the MV Aburri bulk carrier barge.
The MV Aburri bulk carrier barge is operated by Carpentaria Shipping Services (CSS) under a joint venture with Indigenous Business Australia, P&O Maritime Services and the Mawurli and Wirriwangkuma Aboriginal Association (MAWA).
The Aburri barge measures 79.95m by 18.5m with a draft of 3.5m, and has a 3,200t carrying capacity.
The mine operates as a fly-in/fly-out (FIFO) site via a single sealed runway 2,500m-long and 23m-wide.
The power supply requirement is met through a 54MW gas-fired power plant which is owned and operated by EDL, while the potable water supply is drawn from nearby bore fields and treated on site.
The project also involves an accommodation village for approximately 530 employees.
Fluor was contracted by MIM for the engineering, procurement and construction management (EPCM) services for the McArthur River mine, and Bing Bong port and ship-loading facilities.