The latest geophysical study, Kimbell et al, interprets the orefield as 5 separate plutons and the zinc mineralisation is concentrated around the flanks of the Tynehead Pluton and in the embayment between that and the Weardale Pluton with a bit more on the SW flank of the Weardale Pluton.
The veins in the main areas of zinc mineralisation are typically characterised by a lack of either baryte or fluorite which are the main gangue minerals of the rest of the orefield. Dunham 1990.
The main fluorite zones are over the roof of the Weardale and Tynehead plutons and to a much lesser extent the Scoredale Pluton
Dunham summarises work on mineralization temperatures for fluorite and they range from 207 degrees down to 110 at the margins and More, Vaughn and Ashworth give sphalerite temp of 100-140 degrees C based on samples from Smallcleugh mine at Nenthead.

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Towards the end of the 1970s, BSC Research Organisation Geologists, building on the pioneering work of Rick Smith, made over 2,000 measurements of homogenisation temperatures on fluorites from the eastern side of the NPO over the Weardale cupola. Most of this work has remained unpublished but a summary of the results from 1,751 measurements was given in the discussion to Steve Creaney's paper on vitrinite reflectance over the Alston Block given to the YGS in 1980. This showed a range from around 90 °C to 200 °C over the entire data set. Most of the higher temperatures were found in association with the main fluorspar orebodies (eg Groverake), which was in fact the main point of the exercise, however, out of interest several measurements were made on fluorite from galena flats. Without exception the flat measurements all gave the lowest temperatures, which from memory were around the 100 °C to 120 °C mark, giving a strong impression that this kind of mineralisation was distal and had occurred as the mineralising solutions cooled to what were probably close to background temperatures at the time. This would fit in with the later work by More, Vaughan and Ashworth and does not suggest, that in terms of temperature, the Nenthead mineralisation was any different.

Perhaps Minegeo could give us a reference to support his statement about there being a higher temperature phase centred on the Burtreeford Disturbance that pre-dates the main fluorite mineralisation.

Dave Greenwood.

Thanks Minegeo, for the ore genesis of Galmoy and Lisheen Mines. I have seen some of the Computer generated stope drawings for the latter mine, and as they seemed to be limited in their depth, I wondered if there was as possibility that their mineralisation might be different from that of Tara, which has such large vertical range.
As far as I am aware, Galmoy is closed and Lisheen has a very limited life, the ore deposits at Palace Green have still to be exploited. If this last statement is correct it could show what is the size of ore-body they have to find before mining companies will even consider deep mining.

John

Mineralization at Lisheen / Galmoy occurs within a tabular zone at the base of the Waulsortian mudbank limestones. Mineralization comprising massive to semi-massive sulphides occurs as matrix to a black matrix hydrothermal dolomite breccia and as replacements of dolomitized micrites. Water depth of sedimentation was at least 200m. At Navan the minealization occurs throughout a thick (~250m) sequence of shallow water ramp transgressional carbonates dominated by oolites, micrites and calcarenites passing up via deepening sediments with increasing argillaceous content into the Waulsortian. At Navan large scale rotational extensional faulting caused substantial erosion scarps and the unroofing of the syn-diagentic mineralization enabling exhalation into conglomeratic debris flows forming above these erosional surfaces.

Interestingly and fundamental to Irish-type mineralization, due to the diachronism of marine transgression in the midlands the Waulsortian mudbanks at Lisheen / Galmoy are the same age as the ramp carbonates at Navan (late Courceyan to early Chadian) with the unroofing event occurring in the early Arundian thus precisely dating the age of mineralization as mineralized clasts are seen in the conglomerates.

You are correct in that Ga;moy closed last year and Lisheen and Navan are anticipated to close in 2019.

Since mining operations commenced in 1977, total production at Navan has amounted to 81.9Mt grading 8.0% Zn and 1.9% Pb. At the end of 2012, the mine’s JORC classified ore reserves (proven and probable) stood at 14.0Mt grading 7.2% Zn and 1.7% Pb, whilst mineral resources (measured, indicated and inferred) were 11.4Mt at 6.3% Zn and 2.0% Pb. So at the end of the day Navan is greater than 100Mt of ore.

Since mining was initiated in 1999 at Lisheen, approximately 20.3Mt grading 11.8% Zn and 2.0% Pb has been mined at Lisheen. The last official Resource and Reserve Statement issued by Lisheen at the end of March 2013 showed remaining reserves amounting to 2.26Mt at 11.56% Zn and 1.67% Pb, with additional resources of 2.55Mt grading 14.21%.

Xstrata Zinc indicated a JORC compliant Inferred Resource estimate for Pallas Green of 30Mt at an average grade of 7% Zn and 1% Pb (based on a 4% zinc equivalent cut-off). This is still at the Feasibility Study stage.

Sopwithfan

One of the fundamental problems of using vitrinite reflectance levels is that they often contradict fluid inclusion, isotopic data and mineral pair temperatures. In Ireland, for example, vitrinite reflectances, greatly exceed mineralization temperatures throughout the orefield and reflect post-mineralization burial metamorphism. In the NPO as mineralization is probably post-burial metamorphic peak they may have better relationships to mineralization but need to be treated with caution especially in the vicinity of late tectonism. In addition in the NPO the effects of the intrusion of the Whin Sill are noted to increase vitrinite reflectances up to ~40m above and below the intrusion (Dunham, 1990; p.50) and metamorphic mineral suites show temperatures as high at 550 degrees C (presence of wollastonite).

I am fully aware of Creaney's work because I acted as the Industrial Supervisor for his PhD together with Mick Jones of the Organic Geochemistry Unit at Newcastle.

But where is the evidence for this statement?

The style of mineralization they have intersected really should be of no surprise. The zinc "core" along the Burtreeford Disturbance shows higher temperatures than the marginal parts of the NPO suggesting a central and thus warmer zone of mineralization which could explain the difference in styles and gross chemistry of the GL and other replacements. They are, of course, all proximally related to the feeder vein systems which may have ultimately been filled by later (cooler) styles of fluorspar dominated mineralization.

Apart from a probable emanative centre at Burtree Pasture, I have never seen any evidence for the Burtreeford Disturbance having had a positive influence on the mineralisation in the NPO. In fact just the reverse since it divides the orefield into two very distinct areas around the Weardale and Tynehead cuplolas and for example completely cut off the mineralisation on Allenheads Old Vein leading the barren area to the west tested by the Goldfields Crosscut.

Dave Greenwood.

The way it appears to me in the broadest terms, the highest mineralisation temperatures are at the emanative centers over the roofs of the granite plutons.
In the case of Tynehead the associated mineral suite includes some copper minerals as well as the fluorite, quartz, lead and iron mineralisation.
Weardale/Allendale we get alot of fluorite along with the lead, iron and associated gangue.
The areas where sphalerite is dominant are between these plutons (or cupolas if you prefer) and here temperatures are slightly lower.
In the outer margins of the orefield mineralisation temperates are lower still and the dominant mineral associated with these areas is baryte.

Lots of variation within this outline and there is much evidence for dissolution, alteration and redeposition of minerals throughout the course of the mineralising event including the former presence of fluorite in some of the cross veins that minco are investigating (Bridges and Wilkinson 2003. Journal of the Russell Soc) but not on anything like the scale that this mineral appears over the plutons.

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Bridges and Wilkinson are by no means the first to have seen this. Wallace (1861 p143-4) says:

In the Nenthead mines, however, fluoride of calcium is rarely met with in considerable quantities. At some former period it must have been plentifully deposited in the veins of this district, since casts of its crystals in quartz are by no means uncommon, even in veins where not the smallest particle of the substance can now be found

He also notes (p 138)

Much change has been produced upon the Great Limestone forming the sides of Scaleburn vein. The decomposition in many places extends to a considerable distance on each side. Extensive mining works have been made in these flats to procure the lead ore deposited in them, but on account of their very hard character much flatted ground remains unworked, the lead ore deposited in them being too small to repay the cost.

which may be exactly what Minco have just "found".

Wallace may have had some mad ideas but he was an acute observer.

Dave Greenwood.

Yes, Wallace still makes very interesting, and relevant, reading even today as far as his observations go and especially regarding areas that are no longer accessible.

I don't think it's quite fair to call his theories mad given the state of knowledge at the time, although they would sound that way if proposed today.

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Perhaps not mad - just misguided and a bit prone to quoting things in Latin. But what about "Mr Electricity" Leithart!

Thanks for the info Minegeo. Judging from your comments on Pallas Green I think we can safely infer that unless you have a proved deposit of around 30Mt then any deep mining is questionable.
Clearly it must also depend on the % metal content and it's potential composition. As you know if even if a high value metal is found, it may be left in the ground, as at Lisheen , simply because it costs so much to alter the flotation cells.
Minco, therefore have quite a lot of discovering to make up this quantity of ore.
It is interesting to note that the Pallas Green proved reserves, are, seven times greater than the total lead ore raised from the NPO(Dunham p281)

ohh lovely, not come across him before, can't imagine why that idea didn't catch on, Alston Moor as a giant battery!!

http://books.google.co.uk/books?id=V3VRAAAAYAAJ&pg=RA1-PA89&lpg=RA1-PA89&dq=Mr+Electricity++Leithart+geology&source=bl&ots=tzGmrC8Dbx&sig=FmZSIIPZ_qu73RBU5FOyCHCSRhU&hl=en&sa=X&ei=1gBDU8H8MaSI7AbcrYGABA&ved=0CDwQ6AEwAQ#v=onepage&q=Mr%20Electricity%20%20Leithart%20geology&f=false 

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Yes - but strangely enough the banded nature of the fluorspar veins must have resulted from repeated changes in the electro-chemical conditions in the hypersaline brines. As with Wallace, Leithart was attempting to explain what he saw in terms of what were to him "modern" ideas. Incidentally he worked with Sopwith under the Dickinsons in their office in Alston that handled the Greenwich Hospital Estates.

Dave Greenwood.

Nice photo of Smallcleugh on the cover of Minco's Annual Report that provides more on the results of their Pennine drilling including some on the Northumberland side of the county boundary. They propose a further 3,000 m of drilling this year. See:

http://www.minco.ie/annualReports/2014%2004%2029%20Minco%20Directors%20Interim%20Report%20and%20Accounts%20 (Final)%20April%2030-14.pdf

and draw your own conclusions.

Dave Greenwood

Intersected grades and widths in table on page 9 are all marginal in terms of economics. Need to get better than these to have a mine.

Success rate of the drill holes does not seem very high, bearing in mind they are operating in a highly mineralised area and if this replacement deposit is going to be large then, presumably you need more hits than they are getting.

For the latest account of Pennine exploration see parts of:

http://www.minco.ie/corporate/MIOMDAMaarch312014F.pdf 

Dave Greenwood.

Thanks for the posting Sopwithfan. Results do not look like a bonanzas find, but it is encouraging that they are continuing to drill.
I am right in assuming that this latest drilling is at Wellhope?

Thanks for the posting Sopwithfan. Results do not look like a bonanzas find, but it is encouraging that they are continuing to drill.
I am right in assuming that this latest drilling is at Wellhope?

Drill rig has been on Gudhamgill vein and Brownley Hill veins recently.

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Speaking from long experience of speculative drilling programmes, they can be remarkably durable beasts with no real relationship to the likely commercial value of the findings.

Look at events at WUM.

Speculative drilling is cheap, in terms if the wider economics of the industry and it necessarily represents the projection of a belief that is held within that industry sector, or it would never happen at all.

There us also no doubt that manipulation of financial events based upon such data is as old as the extractive industries.

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