The British Gypsum Brightling mine, near the Robertsbridge wallboard plant in East Sussex, has been in operation since the early 1960s. In the 1970s and 1980s it supplied up to 0.8Mt/yr of gypsum to the Robertsbridge wallboard plant, first via an aerial ropeway system and then a 4.7km-long conveyor, which was installed in 1989.
In the early 1990s the arrival of flue gas desulphurisation gypsum (FGD or DSG), rendered much of the mine's gypsum less desirable for use in wallboard. The mine now predominantly produces 'cement rock', gypsum for the cement industry and operates at only around ~10% of its historical capacity.
The Mine Manager at British Gypsum's Brightling mine is David Partridge. Along with Production Manager David Dunk, he took Global Gypsum on a tour of the Brightling workings, which have been operational for nearly 50 years.
Global Gypsum: "Can you provide an overview of the British Gypsum Brightling mine?"
David Partridge: "The Brightling Mine is a drill-and-blast operation and was first open in 1963. It worked alongside the nearby Mountfield mine until that site was closed in 1998. Brightling mine is accessed by Land Rover via a 420m-long drift at a 1:8 decline from the surface. The mining depth varies from around 100m to 350m at its lowest point. We are currently operating at around 300m below the surface."
"The current workings that have been mined cover a 6.5km2 area and the consent for our current operations covers a total footprint of 26km2."
GG: "How much gypsum does the mine produce and who are its main customers?"
DP: "Peak production was in the 1980s and was close to 1Mt/yr. We had somewhere in the region of 120-130 employees on full shifts. We are only running a day-shift operation of 17 employees at the moment, who work a split shift on Monday and Friday and a full day-shift Tuesday to Thursday."
"We have actually been producing the lowest tonnages that the mine has ever had over the past two to three years. In 2011 we produced around 75,000t with the majority for the cement industry. The cement industry uses our gypsum as a retarder. Without gypsum, cement would set far too quickly."
"The chemical breakdown of the material that we supply to the cement industry is 35-60% gypsum, 25-40% anhydrite, >30% sulphate, <15% clay and <20% CaCO3, with 95% to pass under 63mm rock size. Around 10% of our product goes to Robertsbridge for use in our wallboard.
GG: "How is the material extracted?"
DP: "There are actually five British gypsum mines, three of which are drill-and-blast and two of which use continuous mining machines. Brightling is a drill-and-blast operation that adopts a 'room-and-pillar' mining method using two twin-boom drill rigs supplied by the former British company Torque Tension, which also supplied bespoke charging machines for charging the faces."
"We mark up the face according to our plans, get the headings and directions and drill the pattern. Upon completion of the pattern, the drill-holes are then charged using ANFO (ammonium nitrate / fuel oil) explosives intitiated by a primer cartridge with electric delay detonators. After the blast, during which the mine is evacuated, the blasters make sure that everything is safe from an explosives point of view and then the scaling team will start to make the place safe with one of our two Canadian scalers, supplied by Teledyne and BTI. The GHH-made scoops, an LHD 7.4 and an LHD 7.2, each with a 8t loading capacity, are used to transfer the material from the face to the primary crusher."
"The primary crusher is a Stamler rotating breaker-bar crusher, which takes material down to <250mm. From there the material goes out from the working area via a series of six conveyors and two further MMD crushers, which reduces the material to <63mm. There is around 3km of out-bound conveyors in total in the mine."
"The material heads to the 800t bunker. That forms our reserve stock at the mine. On demand we can transfer that material from here to the distribution point at Robertsbridge."
"All of that material exits the mine via the S3A drive house, which transfers the material from underground to the main S4 overground enclosed conveyor. This conveyor is 4.7km long and takes the gypsum to the Robertsbridge plant. There the cement rock is discharged into a distribution point in the form of a bunker, which has a capacity of 180t. From there it is discharged into lorries for delivery to our outside customers. The mill rock is put onto a stacker-conveyor, which goes into the Robertsbridge plant via the reception building and homogeniser."
GG: "So the long conveyor comes under the command of the mine. What is its history?"
David Dunk: "The Continental Conveyor-supplied conveyor replaced an earlier aerial ropeway system in 1989 and was installed by Fairport Engineering. At that point we were ramping up to produce 1Mt/yr of gypsum for the plant but could only put out 0.8Mt/yr with that system, even when running 24/7."
"In the early 1990s a change in legislation meant that flue-gas desulphurisation (FGD) gypsum became readily available. By the mid 1990s FGD had largely replaced Brightling gypsum in plasterboard manufacture. At the moment we run it at around 120-140t/hr and transfer around 1650t/week."
"Brightling is a very important site strategically and British Gypsum understands that it is very important to keep the skills that we have here for changes in the market in future. At the moment there is a lot of FGD because we are burning a lot of coal. That is the situation at the moment but it can change. We want to be in the best possible shape when there is a resurgence in demand for natural gypsum."
GG: "How has the mine developed over its lifespan?
DP: "Looking over the long term perspective, the method that we have always used at the mine is a room and pillar mining technique, which lends itself to around 70% recovery of material. We have property protection pillars and various bore-holes that not only prove the geology ahead of us but also detect any water issues that there may be in the area. Fortunately there is no evidence of any significant reason for concern in that regard in this area. While we have some property protection pillars, we don't actually pass underneath any village or town."
"In the mine we actually have four seams in the mine, numbered one, two, three and four. Numbers two and three are actually economically unviable but one seam and four seam are suitable. One seam is what was mined at the start of the life of the mine and it has been extensively mined over the years. Superimposed below that is four seam, which is where we are mining at the moment."
"The ceiling height is 4.2m where we are mining at the moment, but there are areas where the roof is around 2.4m. Our roof horizon is in anhydrite, our floor horizon is in Portland sandstone. The pillars are 14.75m centres East to West and as they go deeper, we make them longer according to geotechnical design. Currently they are in the region of 12m by 7.75m and they are 'rectangle,' as far as it is possible to work at exact right-angles down there. The current area that we are working in gives us a nominal 66% recovery of material."
"We typically have 24 rooms and pillars across 330m in each mining area, like South 1, South 2, etc on the map (See below). You can see that there are barrier pillars between the different areas. South 3 is where we are working at the moment. That area is not flat, it actually goes down a dip as we work further from the main entrance because the gypsum seam is on an anticline. At our current rate, South 3 will still be mined in six or seven years time."
GG: "The mined workings cover a vast area. Would it be fair to say that you don't know how far the gypsum goes?"
DP: "I wouldn't like to speculate beyond saying that we are in the process of applying for a permit to mine this site for another 25 years."
GG: "Does the mine have any unusual features?"
DP: "The original exploration in this area was not concerned with gypsum but with coal and oil. They found the gypsum almost by accident. Because of that we are actually a flame safety-lamp mine because there is oil shale between one seam and four seam, which obviously contains an oil content."
"When we drive between one seam and four seam we have to take extra care because in places that oil is exposed. In one seam there is potential for methane. We obviously have monitoring and ventilation systems in place to monitor and mediate that risk. Those measures have been in place since the mid 1960s when it was discovered that there was a methane risk here."
GG: "Can you describe the plant's health and safety strategy?"
DP: Our vision is to be the safest and best rock supplier as defined by our company and our customers within Saint-Gobain's policies and procedures," says David Partridge. "Along with the Robertsbridge plant we are one of the few Saint-Gobain operations to have dual 'Millionaire' status, which signifies over a million man-hours without a lost time incident (LTI). One of the things that we are most proud of here at Brightling mine is that we are now 14 years and eight months lost time injury free - a phenomenal achievement. There are a lot of background activities that go towards that including safety inductions and training and the fact that the guys look after each other. The fact that we are a group of just 17 does help."
"Something else that we have to consider is that we are very far away from the nearest mine rescue centre at Rawdon, around 4.5hr away by road. As a result of that we are trying to make alternative preparations so that if we have a major incident here we can be well prepared while Mine Rescue is deployed. We have made a lot of progress with local emergency services and indeed East Surrey Fire and Rescue Service are very active with us.
Recently Urban Search and Rescue (USAR) and Hazardous Area Response Team (HART) got involved too. These services have been very enthusiastic because the mine provides a unique environment for them to carry out their own exercises. In case of a very serious incident we have developed a plan whereby Mine Rescue can deploy a full team down to us by helicopter, which will significantly reduce their travel time."
"Typically we carry out joint drills where we simulate, for instance, a fire on one of our surface buildings. We have also run exercises on an alternative way of getting people out of the mine via a 198m-long ventilation shaft. We will repeat that test, known as a line rescue, in the next two weeks with some new equipment for testing and training purposes."
"We also have dedicated safe-havens underground, which British Gypsum has invested in at all of its mines. These are self-contained units that every one of our employees has been trained to deploy single-handedly, and we have continuous training on that."
"We have a 17-strong workforce at the moment, six of them are craft, seven are production and we have four staff. We have two members of staff who are volunteer mine-rescue trained, the section leader Paul Dunk and shot-firing blaster Ron Haffenden. Should there be an emergency, they can be designated as our guides in the mine. In addition 11 employees are First-Aid trained, which again illustrates the responsibility and the level of interest that we take with regards to safety in the mine. The number of First-Aiders will soon increase because we currently have more staff being trained."
GG: "Thank you for your time."
