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Identity HelpOdd Weardale paragenisis

18th May 2010 20:40 UTCPhilip Mostmans Expert

Recently I acquired a specimen labeled Weardale with the following suit of minerals:

Fluorite, Quartz, Galena and Sphalerite.

Now the odd thing is I have seen specimens from Weardale showing sphalerite, which isn't all that common in the dale I believe (with the Barium-zinc zone being on the outer edge of the orefield).

In this specimen however the Galena & Sphalerite do not only occur together, but the sphalerite seems to be secondary and has crystallized directly onto the galena, in turn overgrown with double terminated quartz xls. Also the sphalerite is directly associated to the fluorite crystals and quartz. The fluorite itself is not twinned and has a pale purple/pinkish colour. The matrix is a solid fluorite/quartz matrix with interchanging bands of purple & green fluorite.

I can't imagine this paragenisis occurring at a lot of the Weardale mines and I have never seen it before. Any ideas, suggestions, wild guesses,...

Cheers!

Philip

18th May 2010 22:45 UTCHarjo Neutkens Manager

Salut Philip,

I don't know, it sounds more like something from Nenthead.

Although I did see a lot of massive Sphalerite around Cambokeels and I've had a Smithsonite specimen from the Rogerley analysed so zinc is quite present in Weardale.

But, I'm not an expert, merely a casual passer by in this case ;-)

Cheers

Harjo

19th May 2010 04:39 UTCPaul Brandes 🌟 Manager

Phillip,

I'm not sure if it will help, but a good read on the geology of the Weardale District and the Rogerley Mine can be found HERE. What you describe sounds a bit like an MVT deposit, but I don't know the Weardale District enough to make an educated guess....

19th May 2010 10:40 UTCPhilip Mostmans Expert

@ Paul: I've got some books on the geology of the pennines orefield, so no problems there. The pennine orefield is indeed classified as an MVT deposit, however I haven't seen much specimens around where galena & sphalerite occurs toghether with the fluorite in such abundance.

@ Harjo: Based on the paragenisis of sphalerite/Galena I would certaintly suspect a more Nenthead origin, however when the fluorite comes in play its more unlikely (Well I haven't seen any such fluorites from the Nenthead area:-)).

Zinc indeed is present in Weardale but so far my experience is that I've only seen it in small amounts (again, correct me if I'm wrong)

So far my research into mindat and some books show Frazers/ Groverake, Blackdene & Cambokeels (both worked Slitt vein) as possible locations for zinc to appear in sufficient quantity. But then again mines like Burtree Pasture also produced some zinc ore and looking at the fluos from that locality might make it a possible match too.

Again I feel like I haven't seen enough stuff to make educated guesses, which is more than the current shot in the dark.

Cheers!

Philip

19th May 2010 18:11 UTCPhilip Mostmans Expert

Forgot to mention I bought the specimen from Rob Lavinsky and it seems he put a photograph of it on mindat:

http://www.mindat.org/photo-118148.html

Also I checked fluorescence and although it shows the typical weardale purple/blue fluorescence it is not as vibrant as other pieces from the area I have.

cheers!

Philip

19th May 2010 18:37 UTCMark Wrigley Expert

Hi Phillip

I would say it was definitely from Weardale - having seen the pictures, and the habit is not too dissimilar to specimens from Frasers Hush - but these were a lot more recent than 100 years.

Sphalerite was found down the road at Boltsburn and up the road in the Allenheads mines.

Alas -Nothing definite to offer,

Cheers

Mark W

19th May 2010 20:26 UTCJesse Fisher Expert

I saw that specimen on Rob's auction. Pretty sure it is Boltsburn, but a close-up photo would help. Allenheads is also a possibility but Boltsburn was much more prolific for specimens.

19th May 2010 20:30 UTCJesse Fisher Expert

Philip,

Are you sure the black stuff is sphalerite and not oxidized siderite?

19th May 2010 21:02 UTCPhilip Mostmans Expert

Jesse,

some quick and dirty closeups with my flash and macro lens, all the features I mentioned in the first post should be illustrated:

http://farm4.static.flickr.com/3326/4621923349_86d42fe5c5_b.jpg

http://farm4.static.flickr.com/3363/4621921623_e057e90423_b.jpg

http://farm5.static.flickr.com/4033/4622526212_d9d19874f3_b.jpg

http://farm4.static.flickr.com/3301/4621917653_c301c0b873_b.jpg

http://farm4.static.flickr.com/3352/4621915425_778d4d210f_b.jpg

Rob listed it as specular hematite, which it is most definately not. Pretty sure its sphalerite though.

Why would you say its fro Boltsburn

19th May 2010 22:52 UTCIan Jones Expert

Assume that it does fluoresce?:)

My guess would be Boltsburn or Allenheads. if I had to choose, I'd go for Boltsburn, but only on weight of numbers.

20th May 2010 00:28 UTCMark Wrigley Expert

Not the specimen I was trying to find - this a quartz over fluorite with the sphalerite intergrown on the surface.

Collected by me - in 1994 at the processing plant, from Frazers Hush

20th May 2010 07:12 UTCPhilip Mostmans Expert

@ Ian: Yes it does fluoresce, but in my opionion it is a lot weaker than other fluos from the 'neighbourhood'.

The coherent factor in all the mines listed above is the Red vein, which is worked to some extend by all three (allthough named differently).

Allenheads mine: Haven't seen a lot of material from this mine and the ones I have seen are very different

Both Boltsburn & Frazers make a strong case. Assuming the age of the specimen is a correct estimate, Boltsburn would a likely candidate, allthough I have seen similar banding of Quartz/sphalerite/fluorite in Frazers specimens ( there is one pic from Helen on mindat, which the habit closely resembles)

Apparently Sphalerite was abundant at some places in Blackdene as well, however I can't visually reference it to any specimens. Can this be excluded from the list?

Cheers!

Philip

20th May 2010 18:58 UTCIan Jones Expert

Hi Phillip

Agree with the Red Vein scenario. Does seem likely.(tu)

Don't pretend to be a expert on Alllenheads, but do have a couple from Arthur Scobell's collection. They are very similar to Boltsburn.

Hope you can track it down

ian

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