The development of this mine commenced in 2005, on the site of the earlier Nebo Colliery opened in 1947, in the outcropping Wongawilli seam. The Dendrobium mine was established on land included in the purchase made in 1946, by the Australian Iron & Steel (AI&S) Company, of the Mount Kembla Colliery and the rail line from that mine to Port Kembla. The Nebo colliery was at that time, the first mine in the coal industry to be opened from a greenfield site, as a completely mechanised underground mining operation.
Nebo colliery operated for some 46 years until it was closed as part of a 1993 reorganisation of the BHP Steel Collieries Division, known earlier as the AI&S Collieries group. The remaining lease areas of Nebo, along with the abandoned Mount Kembla and Kemira collieries to the north, were linked to the Wongawilli Colliery, and the mine renamed the Elouera Colliery. Whilst the original administration, workshop, bath and change house and other buildings erected on the Nebo site remained standing, the coal handling plant, decline conveyor, coal rail storage bin and rail trackwork, were removed.
In 2001 feasibility studies and conceptual development plans were prepared to develop the Dendrobium Colliery on the Nebo site and submitted for approval. Following a review of this information by a Commission of Enquiry, the NSW Department of Planning, and the BHP Billiton board of directors, the project was given the go ahead in 2001 .Consent for the mine was granted by the NSW Government in 2002 and modified in 2008, to allow the mine to produce up to a consent limit of 5.2 million tonnes (run of mine) coal per annum.
The new mine was named Dendrobium, after an orchid native to the area, the same name used earlier to define an area of coal to the north west of the new mine site.
The plans and studies noted above included in house capital expenditure evaluations, risk and review assessments and the conduct of Peer and Tollgate Review Team studies. Groups addressed a complete range of issues that included mine ventilation, strata control, inrush of water, mining systems and roof support, personnel and coal haulage transport systems, safety and risk assessment, and environmental issues. Their studies confirmed Mount Kembla as the preferred site to mine the Wongawilli seam, with its preferred inherent seam characteristics, and its ready access to an existing rail line system to deliver the coal to the Port Kembla steelworks coal preparation plant. The coal mined at this site could be blended with the Bulli seam coal from the other company mines, to produce a high-quality coke product, for use at the Port Kembla steelworks and also export to overseas markets.
Site work commenced in 2002, and represented the very first investment made in opening a new mine in the southern coalfield, for more than 20 years. The production of coal from the mine, using the longwall system of mining was planned to commence in 2004. In November 2003, the mine was officially opened by the Premier of New South Wales, Mr. Bob Carr.
The scope of works for development of the mine surface area included the renovation of the existing Nebo colliery surface buildings, to provide the facilities required to support the operation of a modern underground coal mine, while respecting the heritage value of buildings erected in 1947. These works also included the construction of a 150,000 tonnes raw coal stockpile and rail handling facilities in the Kemira Valley, comprising a mine trunk belt conveyor delivering coal from the mine to the Kemira Valley through a portal entry created on the escarpment, 60 metres above the floor of the Kemira Valley. The emerging trunk conveyor delivers the coal through an enclosed coal sizer erected adjacent to the portal to an elevated conveyor support structure, to discharge the coal into a rill tower and thence to the stockpile. A tunnel constructed beneath the stockpile provides the means to load a train of wagons, drawn by a diesel locomotive, passing through the tunnel.
The trunk conveyor roadway was driven 1150m into the escarpment from the portal, with the initial 900m driven as a cross measures inclined drift, on a rising grade of 1:20, before levelling out in the Wongawilli seam, at the established pit bottom area. Extensions to this trunk belt conveyor system are made as part of the ongoing development of the underground workings of the mine.
In 2003 the first shipment by train of coal was loaded from the mine in the Kemira Valley and dispatched by rail to the coal preparation plant in the steelworks. The existing rail haulage system from the Kemira Valley, and the coal preparation plant (CPP), in the steelworks were both upgraded to handle the planned increased tonnage, and the role of the CPP was changed to process only Wongawilli seam coal from the Dendrobium Colliery.
At the pit top, the mine surface area is confined to a relatively narrow strip of land which includes the original surface buildings and working areas, and the Nebo mine portal entry in the outcropping Wongawilli seam. The original site chosen to establish a mine portal for the Dendrobium Colliery and drive a roadway into the outcrop of the Wongawilli seam was found to be overlain by an unstable ground cover, and completely unsuitable as a site for the mine portal. This led to a decision to create the portal at another site by erecting a preformed concrete portal entry, and reinforcing the overlying strata, the portal entry and the immediate in-seam driven roadway.
A short distance in from the portal the roadway was driven on a 1:10 decline, using arched roof supports, from the Wongawilli seam to the floor of the American Creek seam, some 8.0 metres below. The driving of this roadway was continued on in that seam, using arched roof supports for a further 800 metres, before being driven back up into the Wongawilli seam on a 1:10 incline to establish the pit bottom area of the mine. The mining of the in-seam development roadways commenced at the pit bottom, and provided a point of connection underground for the Kemira Valley trunk belt conveyor and stockpile to the mine wide trunk belt conveyor system.
The Development of the Mine
The area available to drive the initial mine entries and development roadways to establish the Area 1 Longwall mining panel was confined to a relatively narrow corridor of Wongawilli seam coal adjacent to pit top area. The area is adjacent to the abandoned Bulli seam workings in the Mount Kembla Colliery above, the Kemira Colliery Bulli and Wongawilli seams workings to the north, and the Nebo and Wongawilli (Elouera) workings and known geological anomalies, to the south.
Above is the mine development plan envisaged at the beginning of the feasibility study. The plan below shows the changes made to that plan later, and again later, as the mine development has proceeded
The roadway driven from the surface mine portal in the Wongawilli and American Creek seams terminated in the area chosen as the pit bottom area of the mine, and the mining of the roadways required for the development of the mine commenced. These developments included the progressive installation of a mine wide trunk belt conveyor system, and its linking to the Kemira Valley trunk belt conveyor and the delivery of all coal mined to the Kemira Valley stockpile.
The development of the mine involved the driving of roadways for the planned longwall mining areas, and the longwall panels in each of those areas. These developments have been carried out to date to the south west, and to the west and north west of the abandoned Nebo and Wongawilli/Elouera colliery workings. Longwall panels 1 and 2 were developed in Area1 of the mine, and the first production of longwall coal commenced in the LW1 panel in April 2005, with the extraction of the LW 2 panel following.
Each of these panels was developed and extracted some 30 metres below the abandoned and partially flooded Mount Kembla colliery workings in the Bulli seam, and adjacent to the abandoned Bulli and Wongawilli seam workings in the Kemira colliery. An Inrush Management Plan was developed and the results of hydrology studies led to the adoption of a water pumping/drainage programme, and ongoing probe drilling from the Wongawilli to the Bulli seam during the development of the longwall gate roads, and the later extraction of the longwall panels. While the roof conditions during the mining of these panels required some special attention, the output from these panels was not adversely effected.
The mine employs approximately 450 people, and in 2006 the annual production from the mine was 2.766 million tonnes and in the fiscal year ending June 2008, 3.48 million tonnes. By December 2008, four longwall panels had been extracted in Areas 1 and 2, the mining of LW5 panel had commenced, and the development roadways for the mining of Area 3A, had been completed. In Area 3B, ten longwall panels were planned, and the development roadways required for the mining of that area were being driven.
In 2002 the No1 Shaft was sunk a short distance from mine pit top area, behind the escarpment and two mine ventilation fans were installed on that shaft. In 2008 the sinking of the No2 shaft, followed by the No3 shaft, commenced some 6.6 km to the north west of the mine pit top, adjacent to the Cordeaux Dam water storage. On completion of that sinking, the two mine fans installed on the No1 shaft were dismantled and installed on the No2 shaft, along with a recently purchased third fan, to create a triple mine ventilation fan installation. These changes enabled the No1 and No 3 Shafts to serve as the downcast shafts, of the mine ventilation system. The changes were completed in 2008 and included the rehabilitation of the surface area surrounding shaft sites. This work included the seeding and planting of vegetation native to the area prior to the sinking of the shaft, and its ongoing maintenance.
The more traditional method of drill and blast adopted in the past to sink shafts was not adopted at this mine. The Blind Boring method was chosen, using a rotating drill rig to complete the sinking, it being later modified to complete the concrete lining of the No1 Shaft. The concrete lining of the shaft walls was carried using a rotating arm attached to the earlier drilling rig suspended in the shaft. Concrete was supplied from the surface and applied to the shaft walls using the ‘’Shotcrete’’ method of application.
This method of sinking first the No1 Shaft was primarily chosen as a result of the proximity of the shaft site to adjacent residential areas. The method of sinking and lining shafts proved to be successful, and was adopted to sink and line both the No2 and No3 Shafts. The sinking and lining operations were carried out by an operator located in a control cabin on the surface, remotely controlling these processes with the support of video cameras. Details of this method of shaft sinking and lining are described in detail by Mr. P. Whittle.
As this mine is operating near residential areas, a Community Consultative Committee (CCC) was established at the commencement of the project. The committee is comprised of residents, and company staff. The role of the Committee is to provide a forum for discussion on the company’s planned development and operations of the mine, and issues arising from those activities, and the expenditure of the financial support provided by the company on agreed community projects. A twenty-four-hour call line is provided and encourages residents to register complaints, and provide feedback related to the mine’s operations.
A Community Enhancement Fund (CEF) has been established within the CCC and is funded by the company from a levy of three cents per tonne of saleable coal produced each year. One example of the expenditure of these funds has been the joint funding of the Memorial Pathway project shown in part below, by the CEF and Wollongong City Council.
Shown below is an example of members of the Community Consultative Committee members in action. In this case an inspection is being made by committee members and mine officials regarding surface land subsidence overlying extracted longwall mining panels, and the work being carried out at another site of the sinking of mine ventilation shafts and installation of mine ventilation fans.
In July 2008, the Dendrobium colliery had completed the extraction of the Longwall (LW) 1 and 2 Panels in Area 1, LW3 in Area 2, LW4 nearing completion and the mining of the LW5 area planned to commence extraction, before the end of the year 2008. The driving of the main gate roadway for the LW5 Panel was at that time proceeding on schedule, as were the roadways required to support the future mining of Areas 3A and 3B (see mine plan above).
Future Mining and Developments
The operation of the mine and its planned development are subject to prior and ongoing approval by the relevant Statutory Authorities. To view information related to the current mining areas and the planned developments of the Dendrobium Colliery, dated December 2016 see https://www.south32.net.