Humberside Geologist no 11
published 1994
This field trip was organised by the North Eastern Geological Society, and members of the Hull Geological Society were invited as guests. The leader was John Senior of Durham University.
The lead ore is deposited in the Carboniferous Limestone of the area and was mined during the 19th and early 20th century. The original small workings were bought out by the London Lead Company, who then organised the extensive mines that we see today. The London Lead Company was Quaker inspired and a very good employer by the standards of the day. They built most of present day Nenthead on the profits from the mine, including houses for the workers and the school.
Nenthead is a village near Alston in Cumbria, and coming along the Weardale road, the A689, you descend a hill into the village. Turn left at the first crossroads, then immediately left again, where you will find a place to park. We assembled at about 10.20 and started to equip ourselves. A boiler suit as a coverall, wellington boots, and a helmet were the most important items. A helmet light is advisable, but a hand lamp is adequate. A strong rucksack to carry food, hammer and spare torch is essential. There was a total of 12 in our party including John Senior. Another group was also assembling, from the Open University, due to go down about half an hour after us.
We set off from the car park at 10.30 and walked up the valley of the river Nent. It is about half a mile to the mine. The weather was overcast and there was a cold wind. About half way up the valley are the ruins of the lead smelting works. This had been a large scale operation judging from the size of the works. Lead smelting was not a very healthy occupation and most of the workers would have suffered lead poisoning from the fumes. We arrived at the mine entrance and John and two of the others lit their acetylene lamps. The mine is rather unimpressive, a hole about 1.75 metres high and 1 metre wide with a steel gate across it and a trickle of water running out. Another party had entered before us, clearly a busy day.
When we were all ready we entered. The gate was pivoted in the middle. Therefore with one person holding it horizontal, we crawled under, being careful not to put our knees in the shallow water. The tunnel we now walked down was fairly straight and the water rapidly deepened to about 5cm from the top of our boots. We walked carefully to avoid splashing and to avoid holes in the floor. Most of the way we walked as close to the left side as possible (the high ground) with our right hand on the opposite wall for balance. This part of the mine was driven through shales which dripped water in various places. Apart from iron stains there was no sign of mineralisation. Eventually we reached the end of the water and on to dry land. Now, with wet boots, we had to get over a rockfall. A section of the shale had fallen. We clambered up this slippery pile and then down the other side. At the bottom of the far side was a gap only 0.6 metres high. We had to take our packs off and scramble through on our backs dragging our packs after us. Well, we knew we would get dirty.
We had now reached the limestone and it was dry. We went along the tunnel a little further and emerged into quite a large chamber. Here we stopped for a rest, and John encouraged us to remove excess clothing. We were all pretty warm after our exertions. Looking around the chamber we could see lots of cavities in the walls and ceiling full of sparkling crystals. John advised us not to bother collecting though, because they were much better further on. There were several exits from this chamber, and after a short rest John guided us through the least obvious one.
Further on we passed a drain, a sheer vertical shaft at the side of the path, which impressed us of the need to not wander off. The next large chamber we entered contained a lot of broken rock. The method of mining these large bodies of ore, which had replaced the limestone, was to undermine them, then blast the ceiling and stand on the fallen rock produced to reach higher up. This continued until they reached the top of the ore body, and then they would start to remove the ore. They sorted the ore underground and left as much rock as possible. In places they used the waste rock to build walls to support the ceiling or simply to stop waste heaps sliding. Apparently the men who were employed building dry stone walls for the farmers during the summer were employed in the mines during the winter to do exactly the same job. The walls of this chamber were largely covered with creamy coloured crystals of dolomite. In the cavities were perfect cubic crystals of grey galena surrounded by the dolomite. We spent about half an hour here, hammering the walls and the rocks on the floor. The acetylene lamps gave off a yellower light than the electric torches, which did not make the minerals sparkle so well. Electric light was better for finding specimens.
This chamber also had more than one exit, and we proceeded up a path after our guide. We passed through more chambers and the tunnel varied in size. Often it was lined with darker coloured crystals of ankerite. After a while the path became a little tortuous and we had to bend double due to the low ceiling. In places it was easier to crawl, and we all tested the strength of our helmets. Eventually it opened out and we entered the original mine railway.
The rails are still there and it appears in very good condition. It was pleasant to walk upright again. The railway tunnel was cut into the shale in this part, and John pointed out an excellent example of a fault, which had thrown one side down considerably. Because the shale was liable to collapse, this part of the tunnel was lined with stone in the form of a dry stone arch. Interestingly the stone for the lining was sandstone which we had not seen at all in the mine, so it must have been brought in. The method of construction was also ingenious. As the right side of the tunnel leaned outwards due to the fault, the bottom was narrower than the top, and so part way up steel pins were driven into the shale, a steel rod placed on top and the arch of stone started at that point. On the left side the building stone reached the floor.
Along the railway line we passed many wooden shoots. Ore had been dropped down these from upper levels into waiting trucks. In other parts of the mine we found walls constructed with turf between the stones, This was to make these walls airtight and help to control the flow of ventilation air around the mine. We often commented on noticing gentle breezes, but when it was active the mine would have required a lot of forced ventilation. The railway tunnel often branched and each tunnel we did not take looked just like ours. John commented that the tunnels are so extensive that you can spend several days exploring them. That's without being lost. Eventually we reached the largest chamber of all and stopped to have lunch.
This chamber was cut out of the limestone and had nearly straight sides. It was at least 6 metres high, 4 metres wide and 20 metres long. Strangely it showed few signs of mineralisation. Apparently it had once been used for a celebration banquet, and all the food, lights, musicians and guests had been brought in on the mineral railway. For most of its time it had been the stables. As we sat eating our packed lunches we cooled down and realised that the mine was not as warm as we had thought. We could see our breath in the air. The Open University party arrived as we ate, looked around and then left us in peace.
When we left this chamber, John led us to a blind tunnel, where they had prospected for the zinc ore, sphalerite. The prospect was not successful but the cavities in the walls of this tunnel are lined with beautiful shiny black crystals of Sphalerite which the miners had called "Black Jack". We spent some time here trying to extract good specimens.
After we had finished collecting here, we started the long journey back. In many places along the route we saw chalked arrows indicating the way out. We retraced our steps pretty much the way we had come in, resting not infrequently, and eventually reached the first chamber, where we had removed surplus clothing. We were still quite hot, and few of us felt like putting more clothes on. Next was the scramble through the 0.6 metre gap, made much worse by the weight of rock in our rucksacks. This was followed by the scramble up and down the slippery shale, and then the walk in the water. It was about 16.15 when we came out, we had been underground over 5 hours. When we came out of the mine, the weather was just as overcast but the wind made it feel much colder than in the mine. We put our extra clothing on before walking back to our cars. I was neither as tired or as dirty as I had expected and had thoroughly enjoyed my visit.
copyright Hull Geological Society 2021