Published in September 2007 Australian Longwall Magazine

In the heart of Queensland's Bowen Basin, south-west of Mackay, the complex encompasses two underground operations, Oaky Creek No.1 and Oaky North, which both produce high quality coking coal from the German Creek seam.

When Swiss mining giant, Xstrata purchased the coal complex from MIM Holdings in 2003, they invested time and money in the two underground operations and began winding down the two open cut operations, which were closed last year.

Oaky No.1 was developed from the highwall of a worked-out opencut pit and began producing in 1990. The larger scale Oaky North was developed in 1995 and boasts thicker seams, wider longwall blocks and more powerful mining equipment.

In 2006 a second longwall was installed at Oaky No.1 using recycled equipment from the Xstrata-owned Cumnock mine in the New South Wales Hunter Valley.

Xstrata Coal's General Manager for the Emerald region, Dave Stone told Oaky Creek has four complete longwall equipment sets.

"The plan is to maximise ROM output in line with the preparation plants capacity and optimise rail and port entitlements to allow the use of three operating longwalls at any one time within the two existing undergrounds," he said.

The company is also making considerable effort to explore around the infrastructure, looking for other viable underground and opencut deposits.

Apart from the obvious advantage of an increased production profile, Stone says being a multi-longwall operation also allows for sharing ideas and swapping equipment and skills.

Oaky No. 1

The oldest of the two undergrounds, Oaky No.1 has been a consistently high achiever, with year to date production at 2.4 million tonnes as of August 1, and a forecast 5.2Mt for the 2008 financial year.

With proven reserves of 37.7Mt ROM coal, Oaky No.1 is forecast to remain a high capacity longwall operation until 2016.

For the past 20 months, the mine has been operating two longwall units, but from 2008 and onward, Stone says there will be only one longwall face with two development headings.

"Hence overall annual production for this colliery is expected to decrease, but still reach around 5.3 million tonnes per annum," he said.

Oaky No.1 mines the German Creek seam at an average height of 2.3m, using a 1150kW Eikhoff SL300 DERDS shearer, 174 DBT 2-leg chock shields and a DBT armoured face conveyor.

Also working the face is a DBT 300kW beam stage loader and 400kW coal crusher.

The second face uses an Eickhoff SL300 DERDS shearer, 127 Joy 2-leg chock shields, Inbye AFC, Joy 150kW BSL and 150kW coal crusher. The coal clearance conveyor to surface has a capacity of 3200 tonnes per hour.

The two longwall faces vary from 300m to 200m and panel lengths are between 1345m to 4648m.

"Depending on the mining conditions and equipment availability, the DBT longwall produces between 20 and 25,000 ROM tonnes daily. The weekly production time is between 80 and 90 hours a week with monthly tonnages from 520 to 570,000 ROM," Stone said.

"The second longwall supplements this production by 50 to 60,000 per week."

Longwall maintenance regimes at Oaky No.1 include a planned belt down day every Tuesday for 12 hours and planned maintenance on the remaining weekdays for three hours.

The development panels also have a belt down day on Tuesday for 12 hours, planned maintenance on Monday, Wednesday and Friday for three hours, and on Thursday for 12 hours.

Using one Joy 12CM12D continuous miner, 5 Joy 15SC-32 shuttle cars, one ARO 4000 and one ARO 5500 series fixed rig bolters, development is expected to advance an average of 28m daily and 854m monthly for the remainder of 2007.

Like Oaky North, Stone says the main challenge at Oaky No.1 is dealing with gas issues, which have the potential to delay development, particularly in the eastern area of the mine where the virgin gas content increases up to 10 cubic metres per tonne.

Stone said management are working towards moving from mostly underground in-seam (UIS) drainage to surface to in-seam (SIS) drilling - the preferred method at Oaky North.

Looking forward, Stone is confident Oaky No.1 will continue to be a reliable longwall performer for the next decade and an integral part of the Oaky Creek Complex.

Oaky North

Located east of the Oaky No.1 infrastructure, Oaky North began coal production in February 1999, using state-of-the-art, high capacity DBT longwall equipment which broke production records.

In its second full year of production, Oaky North produced 5.1Mt ROM coal, taking out the title of top longwall producer in the country for the 2001 fiscal year. Still boasting 170Mt of proven coal reserves, Oaky North should continue producing up to and beyond September 2027.

At the end of July 2007, Oaky North had produced 2.7Mt, well on its way to a projected 5.3Mt for the full year. The longwall is churning up the 2.45-3.6m coal seam at a daily rate of 20,000-30,000t using 2m wide Joy supports and an Eickoff shearer. This new longwall kit was installed in April.

The gear includes 127 Joy hydraulic powered supports that span the longwall cutting face from maingate to tailgate.

"These shields have an operating range of 2.1 metres to 3.6 metres with a setting load of 810 tonnes and a yield load of 1180 tonnes," Stone said.

The Eickhoff SL750 DERDS shearer works alongside the 855kW DBT AFC, 300kW BSL and coal crusher. The maingate conveyor is rated at 6500tph.

The mine recently began using Longwall Visual Analysis' software to record longwall shield pressure and shearer position, and plot the information in 3D form.

"This has assisted in identifying cyclic loading trends, the interaction of shields to differing roof conditions, and has helped with maintenance by identifying when the shields are not performing," Stone said.

Working at a depth of cover from 70-200m, the mine's biggest challenge is successfully navigating through the steep monocline (major seam roll) that crosses all of the southern longwall blocks.

"Through these regions flight plans have to be produced to assist in the retreat horizon control," Stone said.

"Another feature of the monocline is the extensive associated jointing and shearing ... through this structured zone consolidation work has been undertaken to minimise slabbing and roof failure across the longwall face."

There are also several faults across the western longwall blocks that will not be mined due to their size and subsequent business risk.

In terms of coal seam gas management, Oaky North has focused on SIS drainage to minimise underground drilling and associated production delays.

According to Stone, SIS drainage provides the key benefits of increased drainage time, isolation from development and longwall underground workings, broader technology options for drainage, and early warning of drainage bottlenecks.

In 2006, Oaky North had drill holes over 2800m, making them some of the longest SIS holes in coal in the world to date.

The management plan has also turned the gas into an energy resource rather than a waste product - with some of the gas produced from Oaky North's and Oaky No.1's SIS program fed to an on-site 12MW gas turbine power station for electricity production.

"Oaky North will continue to consistently produce throughout 2007 and expand its production profile over the next two to three years," Stone said.

To read about new longwall equipment ordered for Oaky North, click here..