Converting the mine to longwall mining has long been on the cards, but only when Enex Resources became the majority owner in 1999 was the possibility reassessed. The option became even more attractive when the Macquarie Coal joint venture (in which Enex holds an 80% interest) made the decision to place its Teralba mine near
Newcastle on care and maintenance, making available 135 Joy series 3 shields (vintage circa mid 1980s) and a Joy AFC. Because the working range of the Teralba shields closely matched the projected range for the seam at United, this meant longwall mining could be implemented for much lower capital expenditure.
United has been mining by bord and pillar methods since 1992 using Joy 12CM12D continuous miners with Joy 15SC shuttle cars. "Cut and flit" mining was introduced two years later incorporating a mobile roofbolter.
As a bord and pillar mine, United’s production has typically been between 1Mt - 2 Mt ROM. This is expected to increase to around 2.7 Mt ROM per annum with an operating longwall.
The main seam at United is the 3m-3.5m thick Woodlands Hill seam, dipping to the south west at 1:20. Minimal faulting is expected in the area to be mined by the longwall and good marker bands are expected to help with horizon control.
The mine plan for the longwall delineates seven blocks lying in the same orientation as the previous bord and pillar operations. The first panel will be three kilometres in length, with the face 200m in width and a working seam height of 2.7m-3.3m. Block lengths shorten somewhat towards the end of the mining area. Longer-term further exploration is expected to delineate other mineable resources to the north-west of the lease.
Since the last pillar was extracted in December, the mine has been focused on the development of the first longwall block, scheduled to be completed at the end of February. The mine traditionally used cut and flit in its multi-heading layout but has now decided to adopt a conventional development approach.
Longwall superintendent, Phil McNamara said cut and flit was good in a multi-heading layout but better performance was expected in two heading development with drill rigs mounted on the continuous miners. The mine’s Joy 12CM12s are being converted to conventional gateroad machines.
Budgeted development rates are 21 metres per shift with one development unit and two continuous miners.
The Teralba supports are meanwhile undergoing a complete overhaul and retrofit at Joy’s Mt Thorley workshop. The structures have undergone crack testing and weld repairs along with some modifications. The hydraulic cylinders have been fully overhauled and in some cases replaced. A new relay bar has been fitted with a base lift unit. The entire control system has been replaced with new hydraulics valves, hoses and Joy’s RS20 control system with shearer initiation.
“To ensure quality control, Joy built an overhaul prototype which enabled the mine to check aspects such as hosing and ergonomics. All the subsequent supports to be overhauled will confirm with the prototype standards,” McNamara said.
The shearer is a Joy 4LS5, assembled from some used and new components. It is equipped with Joy’s JNA electrics and horizon control system. Cutter drums have an installed power of 375 kw (continuous).
The Hydra shearer drums have a diameter of 1950mm, and are being supplied by Joy via Southern Engineering Services (SES), which will also supply the hydraulic pump station. DBT will supply a mono-rail system for maingate services handling.
McNamara said the main challenge to mining is expected to be gas management - United had a minor spontaneous combustion (sponcom) incident last year. Various measures are being implemented to reduce the impacts of gas levels expected and the risk of sponcom.
The existing conveyor system is currently undergoing a major upgrade with all major components being replaced over weekends. New soft start drive components supplied by conveyor company Nepean are being installed.
McNamara said a group of employees has been selected from the existing mine personnel of 150 for training on longwall equipment prior to the installation. Similarly, a group of people have been selected to use the newly upgraded development machines, in a new system to be introduced this year.
He added that there is a sense of excitement and expectation among the work-force about the decision to longwall mine and the ability to make a success of the new venture.
