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Identity HelpPossible topaz with cassiterite from Trevaunance mine, Cornwall, UK

19th Jan 2016 14:10 UTCJason Evans

I have been looking over my prized cassiterite specimen which I collected last year and have found a crystal, or a partial crystal of what I suspect is topaz but would like confirmation, it has a diamond shaped cross section and flat cleavage which is very similar to my topaz crystals from Brazil which is very lustrous. It seems to have a slightly pink colour, compared to the greyish white quartz.

19th Jan 2016 15:26 UTCDale Foster Manager

Yes that will be a Topaz, it is quite common at the locality.

Good crystals are rare though.

19th Jan 2016 18:49 UTCJason Evans

Cheers Dale, this was found when you were there, when we, well you found those decent topaz crystals but when i found this one it was the cassietrie i collected it for, i have only just noticed the topaz so I am pleased that at ;least I managed to find some topaz after all!

Hopefully I will have another collecting trip in Cornwall this year, if I can I am going to spend more time at Trevaunance as I found the best specimens here in the short amount of time we were there,

Do you happen to know when Trevaunance mine was closed? I read somewhere that the Polberro consols mines closed in 1941 and I think Trevaunance was one of those mines so maybe I already know the answer.

Also i noticed there is a mine called seal hole mine, the mindat location marker looks very close to the dumps where we were collecting, nearer then the marker for Trevaunance mine, are these markers not that accurate or is it possible that the tips were from Trevaunance and seal hole mine?

20th Jan 2016 07:44 UTCDale Foster Manager

Jason Evans Wrote:

-------------------------------------------------------

Do you happen to know when Trevaunance mine was closed? I read somewhere that the Polberro Consols mines closed in 1941 and I think Trevaunance was one of those mines so maybe I already know the answer. Also i noticed there is a mine called Seal Hole mine, the mindat location marker looks very close to the dumps where we were collecting, nearer then the marker for Trevaunance mine, are these markers not that accurate or is it possible that the tips were from Trevaunance and Seal Hole mine?

Hi Jason,

The Trevaunance Mine is part of what became a group of mine known as Polberro Mines and St Agnes Consols. As with many Cornish Mines, they can be a fun job to sort into any semblance of sense.

As to the marker for Trevaunance - no it isn't that accurate, so I wouldn't rely on it totally. As it is showing currently it is too far to the south. I have edited the OS grid reference to lie as close to the location of Engine Shaft as possible as this lies as near as dammit to the centre of the Trevaunance sett. Regarding the Seal Hole marker, again I wouldn't use it as a definitive location tool. If you look on the St Agnes Consols page, have a good look at the 1870 map extract I have uploaded. This is about as clear as it gets as to where the individual mines of the group are located.

In terms of date of closure, the mines in this group largely finished prior to 1890.

The closure date you refer to relates to an attempt to find the Wheal Kitty lode in depth by accessing through Turnavore Shaft and sinking it to a greater depth to intersect the lode. This working started in 1937 and although they cut the West Kitty lode at 730 feet, they didn't find the Wheal Kitty Lode by the time they had gotten to the 1020 foot level. They did pass through a zone of Cassiterite bearing veinlets at between 900 and 1000 feet. Ironically the earlier re-working of Wheal Kitty discovered a signifcant ore shoot by pursuing a similar series of veinlets, so the possibility exists that there is a potential deeper ore body that is yet to be discovered. The second world war caused financial difficulties for the company undertaking the work and it had to be abandoned, hence the 1941 closure date. Incidentally the West Kitty lode assayed values of up to 400 pounds of tin to the ton, but was too patchy to be economic.

20th Jan 2016 09:08 UTCDale Foster Manager

This is the map I mention above.

20th Jan 2016 19:36 UTCJason Evans

Thanks Dale, very interesting info. I guess it is fair to say that the specimens we found last year have been laying in those tips for over 100 years!

Did mines ever share tips?

21st Jan 2016 08:27 UTCDale Foster Manager

Well as those I showed you where you collected your specimen were last used in the 19th Century, then it has been sitting there for over a century at the very least.

I am not aware of specific tip 'sharing' although with so many small mines forming a larger group with close proximity of shafts in a relatively small area there is possibility of a bit of mixing of waste as tips expanded with use.

Given they all worked various parts of the same group of lodes, unless you can untangle the various shaft names and identify them on the ground you would not be able to draw a greater distinction on the material.

Over time reconciling the old maps to the modern, I have managed to sort out some of the tangle to my own satisfaction.

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