Ok guys .. been looking at your fantastic pictures of underground slate mines... but am a bit confused re how they were worked.. can any one just post a description on how lets say Fred dug his hole into mountain... did he dig up hill in lairs and was each openworking a seperate entity then linked with underground inclines to allow ease of transport... not got many slate books but the ones I have dont really shed too much light on how mines were started and developed...
:flowers:

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There are people who are probably better qualified to answer this than me but this is how I understand it.

1. A tunnel is driven in along the strike, with its roof following the hard granite above the slate vein.

2. A roofing shaft is blasted out upwards following the angle of the dip and the overlying granite.

3. The roofing shaft is opened out to the side and downwards forming a chamber.

4. Drive the tunnel onwards a little bit and repeat 2-4.

The system generally works upwards, so once the roofing shaft has been completely opened up into a chamber, an incline needs to be driven downwards and a new floor driven to allow another phase of working upwards to join the chambers above. If the chambers are in line, they would often open out over several floors. Some of the ones in Cwmorthin are open from floor E to 2.

Important point to remember - leave a wide enough pillar between each chamber to support the weight of the mountain above!

Slate splits in two planes - cleavage and pillaring which occur at right angles. By looking for these two properties, along with natural jointing in the rocks the rockmen were able to remove large squarish slabs of rock.

This is roughly how the system works in Blaenau although there were some exceptions such as Rhiwbach.

Sort of guessed a little of that but given the nature of slate and its tenency to crack surely this must have required a very precise knowledge of how to tackle each floor, in that in breaking out a large lump going up hill ... would that not bring more down than oft expected...?

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that's a general comment on mining. The object of the exercise is to remove a hatful of jam without getting the whole cake on your head.

it's not strictly correct that the props 'support the whole mountain'; what they do, and this is a very simplified account of a very complex subject, is support the unsupported area, and balance the out-of-balance stresses, created by the removal of the product.

I've never seen slate mining, but the procedure described sounds essentially similar to other techniques I have seen for removing a product ( such as building stone or hearthstone ) which must be extracted in a given configuration.

If you are mining for a mineral such as, say, tin, which must be crushed and processed to be turned into a material which is then smelted and cast, the parameters are different and you can work in a different manner

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That description is really only valid for Ffestiniog mines, or mines where the angle of the vein supports that method.

In the Corris area mines, where the vein is nearly vertical, the method is very different. This is my understanding:
A shaft is dug between two levels, and a crane erected at the top to allow material to be lowered. A working floor is opened out around the top of the shaft, and gradually worked down. When it reached the bottom of the shaft, a new shaft was dug, and the process repeated. In this way you get huge vertical chambers descending many hundreds of feet, with pulley blocks hung from the ceilings in what now appear to be the most inacessible places!

Chris.

P.S. I stand to be corrected.

So in essence its all down to the plane of the slate. When a good bit of slate is found in an underground mine how would they break it out, just the same as for above ground pits? The reason I ask is that above ground seems to generate vast amounts of waste in the area of removal so my point is did they have to be more methodical in approach and was the process much more difficult in terms of managing an underground pit, management of waste must have been tricky.? In removal was blasting common then splitting from above?
I know these questions are a bit inane to you guys in Wales but I see all these lovely pics and I never remember to ask about them ... hence this post.

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Bear with me - I think a lot of the questions can be answered (for the Ffestiniog area at least) by my old "Candles to Caplamps" which I'll post to the Oakeley mine on here just as soon as I can convert it to pdf - I've got most of it already scanned for another job, but trying to put it together just now, I find I'd only got as far as page 29!

Patience is a virtue, virtue is a grace, Grace is a little girl with dirt upon her face...

Now where did I here that from ?

Cheers

Grahami

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Hi Mate... I find slate working on the surface quite logical to follow.. but underground ... :confused: ...its a great subject and come the day I get to go into one of the mines I want to be in a position to undertsand how they were worked. So any gen for me is good gen! Thanks! 🙂

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Regarding waste, I was alway under the impression that 90 percent of the rock removed is not good enough for splitting for quality slating material, so it has to be dumped.

I was told that re above ground hence my question re underground as that is a huge amount of rock to deal with underground.. just one of those thing you mean to ask but dont.

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I think the extraction ratio for a number of non-metalliferous materials is quite similar - china clay and granite to name but two.

Bear with me - I think a lot of the questions can be answered (for the Ffestiniog area at least) by my old "Candles to Caplamps" which I'll post to the Oakeley mine on here just as soon as I can convert it to pdf - I've got most of it already scanned for another job, but trying to put it together just now, I find I'd only got as far as page 29!

Patience is a virtue, virtue is a grace, Grace is a little girl with dirt upon her face...

Now where did I here that from ?

Cheers

Grahami

Was just about to post that if anyone was lucky enough to have a copy of 'Candles to Caplamps' it is very well described in there....it's just that most people don't have a copy 😞

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Doesnt surprise me that in the least, the amount of spoil is vast.

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To be fair, the extraction ratio for gold is absolutely terrible - a couple of ounces per tonne if I recall correctly?

Turning back to slate, around 10:1 seems to have been an average-ish return, with some better than that and some as low as 20:1 or worse.

I would imagine that the method of extraction (ie blasting) was also responsible for some of the wastage - trials were done to see if slabs could be removed by drilling lines of holes, but I don't think this was very successful. I'll see if I can find a pic somewhere...

In the meantime, here's a pic of Moel Fferna which shows the shot holes (just off the vertical) and the layers in which the chamber was developed downwards:

🔗Vanoord-Photos-Moel-Fferna-Vanoord-Photos-Moel-Fferna-004.jpg[linkphoto]Vanoord-Photos-Moel-Fferna-Vanoord-Photos-Moel-Fferna-004.jpg[/linkphoto][/link]

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At "best" times oakeley had a make of 1:4.

One reason for the prevalence of gunpowder for extraction rather than "high" explosive was that it was more gentle with the rock. The process of extraction of the slabs in the chambers was both manual, and skilled - and also slow! The men had to exploit every visible weakness in the slate, and minimise the use of explosives. This meant that the make was good - but the rate of production of slabs was therefore slow. In later days volume became more important than the make ratio and therefore modern methods are extremely wasteful - but quicker!

Grahami

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To be fair, the extraction ratio for gold is absolutely terrible - a couple of ounces per tonne if I recall correctly?

Well, I did qualify my claim with the words "non metallifereous".

Well, I did qualify my claim with the words "non metallifereous".

Indeed :)

As Graham notes, modern methods are particularly wasteful - although it's an odd juxtaposition that modern untopping work is able to recover slate that couldn't be removed by the original process (ie the walls) and was (effectively) wasted!

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Some smart Alec is now busy working out the ratio for diamond extraction......

Vanoord wrote [quTo be fair, the extraction ratio for gold is absolutely terrible - a couple of ounces per tonne if I recall correctly?
ote]
That would be a very rich gold mine indeed. The figure for Australian mines is now less than 5 grammes per tonne

Going back to slate. Grahami remarked that modern methods are extremely wasteful, that may apply to slate mining but it is now Delabole's Quarry proud boast that nothing is taken to the waste dumps.
Huge blocks weighing 600 tons are sawn from the face and then split into more manageable bocks of about 30 tons and taken to the splitting sheds

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As Graham notes, modern methods are particularly wasteful - although it's an odd juxtaposition that modern untopping work is able to recover slate that couldn't be removed by the original process (ie the walls) and was (effectively) wasted!

Not strictly true - untopping is nothing new, It was seriously proposed by Thomas Jones for the Oakeley Quarries in the 1890's on a very large scale - removing rock deeper and even further to the North than McAlpines have done - it would have meant an open quarry as far down as L floor! He admitted that some form of "mechanical contrivances" would be required.
The foloowing give some idea of the scale of the work proposed:
http://www.aditnow.co.uk/documents/Oakeley-Slate-Mine/Fig061.pdf 
http://www.aditnow.co.uk/documents/Oakeley-Slate-Mine/Fig062.pdf 

Llechwedd actively began untopping around 1899-1900 - despite the repeated tales in the various Quarry Tours guidebooks about the "avaricious landlords" and having to wait till they had expunged their grazing rigfhts etc. etc. in the 1920's. The landlords were all too willing for the quarries to be untopped and slate produced - they were, after all getting the royalties from them! And the royalties were far higher than the surface rent.

Grahami

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