Steam and soft coking coal
Mt Owen is located in the Upper Hunter Valley of New South Wales, 20km north of the township of Singleton. Comprising one of the deepest coal open pits in Australia, the mine is wholly owned by the Swiss-based minerals producer and commodity trader, Xstrata, with Thiess Contractors as the mine operator. Following expansions carried out during 2001 and 2002, the mine has a capacity of 7.7Mt/y of thermal and semi-soft coking coal. Actual production in 2005 was 5.95Mt, compared with 5.84Mt in 2004 and 4.79Mt in 2003.
This increase reflects the amalgamation of the company’s adjoining Ravensworth and Glendell coal properties into an expanded Mt Owen complex, a process that began in 2003. At the end of 2004, Xstrata received regulatory permission to upgrade the complex’s infrastructure so as to increase its capacity from 9Mt/yr to 15Mt/yr of export coal, access all of the reserves on the property and extend the project’s life by ten years. As part of this, Ravensworth East has already been re-engineered as an export-coal producer, with an expansion now scheduled for the coal-processing facilities at Mt Owen.
GEOLOGY AND RESERVES
Mount Owen is mined by opencut methods. It is characterised by the presence of up to nine mineable seams that can reach dip angles of 45° close to faults. The majority of coal to be mined dips at 10° or more. Seams range in thickness from 500mm to 10m, with thicker seams found where the strata are folded.
Original marketable reserves were 85Mt within a 240Mt in-situ resource. The amalgamation of the adjoining properties has increased the resource, such that in mid-2005 marketable proven and probable reserves stood at 110Mt, with the overall resource estimated at 440Mt.
Thiess Contractors operates Mount Owen as a shovel-and-truck open pit, relying on hydraulic excavators for both overburden stripping and coal production. The dipping structure of the deposit means that the pit is laid out with benches spaced at 5m vertical intervals.
The company has four Liebherr R996 backhoe excavators and three R994s on site, the R996s being fitted with 33m³-capacity buckets. Thiess has recently augmented its overburden fleet of Caterpillar 793B and 793C, 218t-capacity trucks, with six Liebherr T-262 electric-drive haulers, while using Cat 789Bs for coal haulage. The R996s can accurately four-pass load the haulers through the use of real-time data transmitted from sensors mounted on the truck bodies to an Advanced Systems Integration monitoring unit on the shovel. Their typical handling capability in overburden is around 1,800m³/h, the average output of 4.8Mt/y of run-of-mine coal requiring the removal of some 22Mm³ of overburden and interburden.
Thiess Contractors also took responsibility for the design, construction and commissioning of the coal preparation plant, guaranteeing a maximum cost of AU$114.6m for this aspect of the project. The actual cost was well within this limit. The plant was designed on a modular basis to produce 3.6Mt/yr of saleable coal containing 9–14% ash and achieving an average yield of 77.5%. Following upgrades, the plant currently has a capacity of 7.7Mt/y of saleable coal.
A number of technical innovations have been incorporated into the design of the mine, including the use of a 700t-capacity dual-chamber hopper in the run-of-mine dump station (to give the maximum capacity at minimum height), and low-speed Abon coal sizing technology rather than traditional rotary breaker technology. The benefit of this is to minimise the creation of fine coal during crushing, while removing the need for a separate screening operation.
A 2,000t-capacity surge bin feeds the twin-module washing plant, which uses dense medium cyclones and spirals to produce semi-soft coking, low-ash thermal and mid-ash thermal coal products. 1,000t/h of feed gives 740t/h of products, with rejects being handled through a fully automated bin into haulers for disposal in the waste dumps.
A unique cantilevered stacker supplies dewatered coal products to a 300,000t stockpile. From this, coal is loaded into unit trains at a rate of 4,000t/h using a specially designed, automated batch weighing system that gives an accuracy of 0.05% per wagon. A 7km rail spur line connects the mine with the main Freight Corp line west of Camberwell to transport products to the port of Newcastle.
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