I'm working on a project at the moment with regard to the Seathwaite, Borrowdale graphite or Wad as they call it locally. I'm particulary interested in the "lump" deposits at Seathwaite (almost 96% pure) and not the metamorphic associated graphite deposits.

I'm trying to pin down the age of the deposit but I'm not convined I have got it right.

I'm assuming the deposit is hydrothermal in origin and associated with the temperature increases during the massive intrusions into the Borrowdale Volcanics.

Taking that into account I'll put my head above the parapit and say the graphite is roughly Middle Ordovician (450-470 Ma), however, I'm not convinced to be honest.

I'm just wondering if anybody can throw any light on the age of these deposits as I think I have all but exhausted the information I can find on the subject.

Open to any suggestions or theories.

Thanks, much appreciated :confused:

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I know this may sound pretty stupid but I take it you had no joy with the BGS? The map I have for the Camborne-Redruth area is pretty detailed.

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Prof. Adam Sedgwick in 1848 suggests early Ordovician (500 m yrs), which seems to have been bolstered by carbon dating in 1981. However all theroies seem highly contentious still!
(ref p142 "Lakeland Mining Heritage" CATMHS 2000)
Ian Tyler has a book on the site (Seathwaite Wad & the mines of the Borrowdale Valley) which is no doubt well worth consulting.

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Hi carnkie, many thanks for the reply, not much luck with the BGS I'm afraid. You have lost me a little reference the Camborne-Redruth area, :confused: .

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Hi Mr C, thanks for the reply, I think we can safely nail it down to the Ordovician, however, which part of the Ordovician is the problem. Strens (1965) suggests the deposits occur as joint coatings and replacements in an intrusive diabase and in surrounding volcanic rocks. Millard and Young (BGS) suggest ages of 382-376 Ma for the dolerite and graphite respectively, using the K-Ar method, however, extensine investigations of a wide variety of Lake District igneous rocks have shown the dates using other isotopic dating methods to be much older than the dates using the K-Ar method.

The elements K and Ar are mobilised very readily during geological processes, thus resetting the isotopic clock.

This would suggest the Seathwaite graphite is much, much older than Middle Devonian.

It is commonly understood that the graphite at Seathwaite is closely associated with the dolerite intrusion (diabase) which cuts andesite within the lower part of the Ordovician Borrowdale Volcanic Group.

Can I then conclude, if the graphite was formed as a result of the dolerite intrusion, it must be Middle Ordovician or even Upper Ordovician.

Is there a link you can supply with regard to p142 of Ian Tyler's book

Once again, thanks, much appreciated. :confused:

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I'm a bit surprised. I mentioned the map for Camborne and Redruth because the BGS issue pretty detailed maps in their 1:50 000 series for specific areas of Britain. I just happen to live in Camborne and have one for this area. It just crossed my mind that one of the area you are interested in would be useful.

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Sorry for the confusion, I thought by you mentioning the map of Camborne and Redruth there may have been some connection with that and the graphite I was talking about.

Many apologies, no offence was meant. The maps at 1:50 000 are excellent as well as the 1:25 000 special sheets etc.

I've studied the maps but it is still a little confusing as to the correct age of the graphite.

Your suggestion was much appreciated, thank you very much, :thumbsup:

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I thought the K-Ar dating was down to Ineson & Mitchell?
The dates given by them, as above, seem to fit in reasonably well with the end phase of the Caledonian and the intrusion of the batholith. The origins of the graphite have long been speculated on but it would seem to make it even more of a unique deposit by dating it alone at some 80-100ma older than the acepted general dates for almost ever other mineral occurrence in the area.

Hi Buckhill, Millard has also carried out work using isotopes.

The existing K-Ar radiometric age of about 375 MA makes no sense as this was determined on "illite" from late vein fills, do you agree on that.

As the graphite is intimately associated with a dioritic intrusion, we can safely suggest the graphite was emplaced during the late Ordovician, probably much later than the emplacement of the BVG and associated intrusions, roughly 450 Ma.

I think a formally determined age for the emplacement of the graphite at Seathwaite is some time away and will remain a contentious issue amongst geologists for years to come.

And then we could go into the formation of that particular deposit of graphite, however, that is another story!

What do you think, do you agree on an age of between 450 and 460Ma?

:thumbsup:

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Just as a matter of interest can anybody tell me when the last "Graphite" Wad mine closed in Cumbria. Was it opened during WW1 and closed after the war?

Cheers.

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Just as a matter of interest can anybody tell me when the last "Graphite" Wad mine closed in Cumbria. Was it opened during WW1 and closed after the war?

Cheers.

This http://www.engineering-timelines.com/scripts/engineeringItem.asp?id=856  source stated that the last mine closed in 1891 and makes no mention of wartime reopening. Though if the where vestigial remains reopening would make sence. 🙂

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Cheers jr48, thought I had read somewhere they had reopened during WW1 for some military reason. I must have been mistaken. Thanks for the link, much appreciated.

:thumbsup:

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Looking again at the possible age of the graphite emplacement just seems to throw up more questions.

There is another diabase intrusion some 3- 4 miles east - Steel Fell - which was also dated as Devonian by Ineson and Mitchell. This intrusion is in BVG rocks somewhat higher in the sequence than at Seathwaite, the volcanics themselves being around the 450Ma age.

Is the diabase intrusion then associated with the pre- Caradoc earth movements, or is it, as suggested by the K- AR dating, later.

The graphite occurrence as given by Strens is, as you say, "joint coatings and replacements in the diabase and surrounding volcanics". The various veins in the mine cut through both the intrusion and the surrounding host rock and graphite is found in the veins in both. So, did the veins post-date the intrusion.. which post-dated the BVG?? .. or is there another answer yet to be found?

Rb-Sr dating of some of the major intrusions have agreed with the K-Ar datings but obviously much more work needs to be done in this area.

Your recent query on the possibility of the mine being re-opened for military use in WW1 made me think of Carrock. That mine was re-opened in 1913 and closed again in 1919 when the price of tungsten dropped. It was also re-opened for a very short time in 1942 by the Ministry of Supply.

Many thanks for that Buckhill, food for thought indeed. I will get back to you on that. I have got the Tungsten Wolfram(ite) mine at Carrock mixed up with the Graphite (Wad) mine at Borrowdale with regard to the re-opening.

Cheers again.

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