South Crofty Mine Underground 9: To the South Crofty Miners it was more than a job. They took frequent wage cuts and worked longer hours to keep the mine working. It was a way of life to them and the living life blood of Cornwall.
This page is the first showing the method of ore production from South Crofty Mine. This was known as “Stoping”, the empty area once cleared of ore are known as “Stopes”. These first images on this page show a mining method called “Shrink Stoping”.
Nick Le Boutillier has written some information about this technique for this page.
South Crofty Mine Underground 9.1 – Mickey Roberts (R) and Merv Randlesome (L) Shrink Stoping in South Crofty.
Shrinkage stoping, more correctly, overhand shrinkage stoping is a mining method that was used extensively at South Crofty. Particularly with the advent of compressed air drills in the 20th Century. It is a technique ideally suited for steep-dipping narrow lodes in structurally competent host rocks, such as found at South Crofty.
Short raises within a pre-determined panel, bounded by level to level raises, were joined laterally to form an inter level. Box-hole (Cousin Jack) chutes were built into the raises to transfer broken ore (dirt) out of the stope. The bounding raises were panelled with timber, progressively upwards, to hold in the broken dirt and to maintain a ladderway into the stope from above or below. The miners, working from the inter drilled into the roof (back), firing the lode in lifts.
South Crofty Mine Underground 9.2 – Shrink Stoping was not often employed at the mine. However on some of the smaller veins this was a more efficient method of mining.
After each blast the miners would stand on the broken rock of the previous day to reach the back and drill over the next lift. Because broken rock takes up some extra 30-40% volume, the swell had to be drawn off. This was done via the chutes, to shrink the broken rock back to allow access. The retention of broken rock in the stope added continuous support to the stope wall. This also formed a stable platform for the miners to work from. Shrink stoping was/is a very efficient technique. It allowed the miners to follow a lode very exactly, maximizing ore recovery, while taking a minimum of waste rock.
South Crofty Mine Underground 9.3 – In such a confined area there is no where to hide from the noise and dust.
Lodes are often visualised as planar features. However in reality they flex and undulate along strike as well as down and up dip. A good crew is able to follow the lode contacts very closely and minimise dilution. The only real disadvantage of the technique is that relatively little ore is produced daily. Only the swell tonnage is taken until the stope is complete. At this point the whole stope panel can be drawn out and sent to the crusher.
South Crofty Mine Underground 9.4 – As the miners were always moving upwards. The makeshift wooden platform they are standing on would be above the previous days blast.
Later development at South Crofty moved away from boxholes and inters, to draw points driven from a parallel (waste) drive. Although this required much extra development, it removed the need for timber chutes and allowed the use of rocker shovels and Cavo’s to fill the loco trains more quickly and efficiently. Also this allowed better access.
South Crofty Mine Underground 9.5 – The heat and vapour was too much to bear in such a small area.
South Crofty Mine Underground 9.6 -The final image on this page is of Mick and Merv in the small shrink stope disappearing into the vapour.
This rest of this page continues the set of images showing the main method of ore production from South Crofty Mine. This was known as,”Longhole Stoping”, once again Dr Nick Le Boutillier has written some information on this method.
South Crofty Mine Underground 9.7 – A Longhole Stoping Machine at work, the open stope is behind the drill.
Longhole stoping was developed at South Crofty from the 1970’s as a method of rapid extraction. Sublevels were mined from the panel bounding raises (usually two between main levels). Mapping of the lode in these sublevels and raises was the basis for the development of blast rings, every metre along the sublevels. These blast rings were plans for radiating rings of holes to capture as much of the lode as possible and were designed to take out the entire panel in two major lifts.
South Crofty Mine Underground 9.8 – Bernie Harradine using the drilling machine to bore holes in the roof of the passage. The drills used a huge amount of water in an effort to reduce the dust in the air.
Starting from a raise on the lower sublevel, rings would be drilled away from the raise and were often fired in groups of up to five although sometimes singly. The rings would break (utilising the open spaces of the raise and lower main level) and the broken rock fall towards the draw points. Extraction of the broken rock could be undertaken immediately and no dirt had to be retained to allow access.
South Crofty Mine Underground 9.9 – Another image of the same machine at work.
South Crofty Mine Underground 9.10 – This final image of the drill in use shows the huge amount of water it needed.
The miner, working his longhole drill rig was able to work safely within the sublevel (with access via the second raise). This was far enough from the open stope to keep his workplace safe and stable. In this way panels work fired in a sequential manner, and once the lower lift was complete. The miner would then move to the upper sublevel and repeated the exercise.
South Crofty Mine Underground 9.11 – Almost like something out of a Dr Who episode. This miner controlling his drill, standing amid a tangle of air and water pipes.
Longhole stoping allowed rapid, continuous supply of ore on a daily basis. Panels could be worked far more quickly than by shrink stoping. It was also ideally suited to larger (wider) lodes, up to ten metres, or more, across. These would have been much less stable in a shrink stope environment.
South Crofty Mine Underground 9.12 – Another image of the same miner. Sadly I do not have his name.
The disadvantages of the technique were that it was incapable of flexibility – patterns from ring to ring were only able to vary by around 20cm. So if a lode was rolling or flexing, the pattern could not follow the lode exactly like a shrink stopper could, meaning invariably that some waste was taken while some ore was left behind. This meant ore dilution had to be taken into account.
South Crofty Mine Underground 9.13 – This and the following images on this page show South Crofty Miners Paul Curtis (R), Nigel Mitchell (L). They were preparing a long hole drilling machine for use.
Also the blasting of large rings in unsupported stopes often shook the stope walls so badly that they could partially collapse – leading to further dilution. After some significant dilution events, a process of bolting the the stope walls prior to firing was introduced. However this added significant cash and time costs and had varying success.
South Crofty Mine Underground 9.14 – The control mechanism for the drill is closest to the camera. These machines were monsters and had to be secured firmly in position.
Longhole stoping was by far the most common mining method at South Crofty in the 1990’s. This delivered a high tonnage on a daily basis. Also shrink stoping was employed on a number of lodes. This had the advantage of providing high quality, high-grade, dirt in smaller volumes.
South Crofty Mine Underground 9.15 – The drill is ready for use, Paul Curtis (L), Nigel Mitchell (R).
South Crofty Mine Underground 9.16 – The drill is drilling in the floor with the open stope only a few feet away from the miners.
South Crofty Mine Underground 9.17 – Here, Paul Curtis is attaching another drill rod.
South Crofty Mine Underground 9.18 – Once again the drill is up and running, the exhaust can be seen clearly.
South Crofty Mine Underground 9.19 – I have no location for these images, but it seemed very strange drilling so close to the open stope.
South Crofty Mine Underground 9.20 – The drill was securely fixed into position using acro props and bars.
South Crofty Mine Underground 9.21 – I cannot remember what I was climbing on to get this elevated view. It shows how close the drill is to the edge of the open stope. Once blasted the area they are standing would not have existed, and the rock would have been removed for processing.
South Crofty Mine Underground 9.22 – Nigel Mitchell and another miner watch as Paul Curtis tightens up the securing bars.
Cornish Mine Images Underground 9.23 – The final image of this set shows Nigel Mitchell and Paul Curtis still trying to stabilise the drill mounting.
Another day and another Long Hole Drill site. The miner in the final set of images on this page is Geoff Tonkin. The negatives were very dense and were very difficult to print, the results were worth the effort.
Cornish Mine Images Underground 9.24 – The first image of Geoff Tonkin at work with his Longhole Drilling rig.
Cornish Mine Images Underground 9.25 – This looks like the drilling was on a sublevel, the location is unknown. In the background just visible are the control pipes for another drill rig.
Cornish Mine Images Underground 9.26 – The noise of these drills in such a confined area was deafening.
Cornish Mine Images Underground 9.27 – This is without doubt this is my favourite photograph on the page.
Cornish Mine Images Underground 9.28 – A well lit image of a South Crofty Miner at work.
Cornish Mine Images Underground 9.29 – It was always difficult to keep the camera free of moisture. In this image the lens had started to steam up.
South Crofty Mine Underground 10