The Blue Circle Southern Cement works at New Berrima is a dominant feature of the picture-postcard NSW Southern Highlands. The plant was put in exactly this spot because of the availability of all the raw materials used for making cement – including coal.
Some 7km from the cement works, beyond the hamlet of Medway, the road peters out at the entrance to one of the state’s oldest coal mines, located in spectacular country.
The Berrima mine was originally set up in the 1920s to supply the cement works, with assistance from BHP Steel’s predecessor, Australian Iron and Steel.
The Wongawilli seam is accessed by a rail drive and conveyor system that crosses a bridge over the swirling Wingecarribee River in a gorge below and then dives into a small opening in the opposite cliff face.
Horses were used underground until 1968, and it is still possible to see where they were spelled on the surface at weekends and where blacksmithing was carried out. Some of the older workers remember these times still.
In 1994 Centennial, as part of its ASX listing, acquired Berrima along with Ivanhoe and Charbon mines from Blue Circle Southern Cement.
This was the first of several acquisitions that have made Centennial Coal a major force in the NSW coal industry. The acquisition of the former Powercoal mines in August 2002 means that Centennial is now the largest underground operator in NSW.
Berrima, with a single customer, has always had to tailor production to what that customer requires. Output per year can vary from as low as 140,000t to the anticipated 220,000tpa this year; all of it transported by road to the cement works.
However, with the cement works undergoing a $74m upgrade, Berrima’s future looks assured; and there is even some potential to supply small tonnages to another Blue Circle Southern Cement works at Maldon in the same area.
With an inferred reserve of 50Mt, the mine has a good long-term life, even at higher output. In addition, there are further potential reserves on leases between Medway and the town of Sutton Forest.
Nevertheless, the mine must ensure it remains a low cost producer. Every five years Blue Circle Cement goes out to the marketplace and Berrima has to be competitive.
Being such a small operation, the mine at one time in the 1980s looked at expansion into export markets, with talk of lifting production to 1.5Mtpa and installation of a rail loop. This is no longer on the drawing board.
However, with just 25 employees – mostly with the mine until retirement – mine manager Michael Cunnion is proud of the capacity to produce up to 250,000tpa of coal if required, working a limited week of single 8.75 hour shifts for just four days a week.
While the Wongawilli seam being mined ranges in thickness from 6m to 10m, Berrima takes only the bottom 2.1-2.2m to provide the exact coal specification required by the cement works. A shale marker band provides a good guide to the extraction height to be mined. The top part of the seam is interbedded with clays and shales.
High ROM ash content of around 27-31% is required in the cement making process, so no processing other than crushing is required prior to trucking.
Mining is carried out using the bord and pillar method with secondary extraction using three Voest-Alpine breaker line supports.
Two Joy 12CM11 continuous miners are in use, one for development and the other for secondary extraction, coupled with Joy shuttle cars.
The second of the miners was acquired last year but the other is much older, and consideration is being given to replacing it with a newer model.
Relocation of the pillar extraction system to the north west 1 panel is underway and, at the same time, development has commenced in 403 panel, which is 3.5km north east of pit bottom and will be the mine’s subsequent pillar extraction panel.
North west 1 panel has 170,000t of recoverable reserves based on an estimated 80% extraction ratio and will be mined over the next 12 months.
The mine is in the fortunate position of having no known history of methane gas, a fact confirmed by recent in-seam drilling and testing.
Cunnion describes the roof conditions as “benign” especially compared with other operations mining the same seam. The bolting regime is generally just two bolts every two metres, with additional support where necessary to comply with the mine’s strata control management plan.
However, there is “nuisance” water during development because the coal seam dips from above the Wingecarribee River at around 2º to well below the riverbed at 150m from surface.
The coal seam itself acts as an aquifer, so that water continuously drips out of the roof, particularly from roof bolt locations.
As a consequence, workers on the continuous miners and shuttle cars tend to wear oilskins. Sitting on a shuttle car under a solid drip can be drenching – not to mention cold. The ambient temperature throughout the mine varies very little in winter or summer, and can best be described as cool. The temperature at pit bottom in winter can drop to freezing point and even at the innermost working faces the temperatures remain cool.
Geologically, the only inconvenience is caused by igneous intrusions, mainly dykes that are generally handled easily by the continuous miner. There is no major faulting. However, a recently intercepted fault had a throw of 150cm, which in a 10m seam is, relatively speaking, insignificant.
The coal produced is shuttled by two contractor trucks to the cement works daily at the rate of 800-1000t a day. However, a stockpile is kept at another disused mine 2km away that is capable of handling up to 100,000t of coal if required.
With truck movement of coal, the mine has been at pains to ensure a good relationship with the residents of the hamlet of Medway. If a surge in truck movements is planned, the locals are consulted first.
As well, mine water is supplied to the houses for sewage and septic uses, something that has been a boon during the recent drought.
FOOTNOTE: The bridge for the rail entry to the mine crossing the Wingecarribee River is now steel. It was once timber but deteriorated after a series of small fires. Rumour has it that miners flicking out their cigarette butts just before the man-rider entered the mine entrance caused these fires.