Lava outcrops in the UK

[martinb]

I was wandering around Derbyshire - Alport to be exact - whilst 'escorting' Duke of Edinburgh students - and came across what I think is a lava outcrop.

I'll post some pics when I've downloaded them, but the rock was full of air bubbles - pumice like - and there were a couple of areas where the 'oozing' of lava was noticable.

In the same location were shallow caves and possible resurgence like features.

Interesting - anyone know of more?

Martin

 

[SamT]

The only one I know of (which doesn't mean there aren't others)  is in cave dale in castleton.

about 3/4 of the way up on the LHS.

IIRC you can even see the hexagonal formation like you get at giants causeway.

 

[paul]

Mosey Mere on the edge of Winster exists due to impermeable lava deposits beneath. See this link which refers to it.

 

[Cave_Troll]

there's some in creesbrook dale as well

 

[Roger W]

Aren't the 'toadstone' layers around Matlock Bath volcanic in origin?

I remember my attention being drawn to it years ago in candle-lit tours of the mines/caves on the Heights of Abraham.

Googling for 'toadstone' brings up loads of rubbish, but    http://www.lindahall.org/events_exhib/exhibit/exhibits/vulcan/toadstone.shtml  and http://www.lindahall.org/events_exhib/exhibit/exhibits/vulcan/42_large.shtml seem to be relevant.

 

[Turner]

found one in tiddsa the other week...

53?16'1.80"N  1?46'8.76"W

darkish patch on can be seen on GE

 

[NOZ]

Some on the Monsal trail as well. The information boards even give you some information about them.

 

[T pot 2]

Hi
There's one at Whormill / Millersdale, one at Carlton lees and another at Waterswallows Buxton where the old Tarmac roadstone plant used to be

T pot

 

[zippy]

Hi!

My understanding (and I'm sure someone will corect me if I'm not quite right) is that Masson Hill is the remains of Matlock's ancient (sub oceanic) volcano - and hence the lead deposits in the various rake veins.  There are two main layers of lava - the Matlock Upper lava, and the Matlock lower, with limestone layers inbetween.

Toadstone is often referred to as "decomposed basalt".  My understanding is that it is more akin to volcanic ash - therefore chemically similar, but physically a bit stickier!  It is certainly possible to see evidence of the lavas in some of the mines in the area.  I can think of some places where you definitely descend through limestones, through lava, and pop out in limestone again!

Other volcanic areas include Windmill nr. Great Hucklow.  The mineshaft at High Rake was driven through a significant (400ft?) basalt plug, to no avail.  If they'd dug a short distance to the East, they might have been more successful, as the basalt thins to nearer 80ft!

There are some good publications on the geology in the area by Trevor Ford, of course, some of which are certainly available in pdmhs bulletins.  http://www.pdmhs.com/BulletinIndex.asp  I know there's on on the Stanton syncline & area - not sure if it extends as far as the Alport mining field.

Z!

 

[owd git]

Yep, my understanding too. I believe the same lava flows are evident in the Castleton area too.
Also ,whilst hardly an outcrop, deep (ish) in Masson many occurrences of the same flows may be followed as ceiling, wall or floor

 

[Pitlamp]

If you want to identify the Cavedale basalt outcrop (which Sam rightly drew your attention to) go up through the gate just before the spring (which incidentally rises on top of the basalt because it's an "aquiclude" - a sort of damp proof course in the limestone - and which also explains why some parts of Peak Cavern have very few stals apart from areas with faulting). Just on the left of the spring is a knobbly dark coloured exposure with several holes drilled into it. I think these were from studies of paleomagnetism many years ago - but they make it easy to find the actual lava if you're not sure what you're looking for.

 

[gus horsley]

My understanding (and I'm sure someone will corect me if I'm not quite right) is that Masson Hill is the remains of Matlock's ancient (sub oceanic) volcano - and hence the lead deposits in the various rake veins. 

I'd be interested if anyone can shed any light as to how these undersea volcano and lead rakes (if they are contemporaneous to each other) are connected as they would constitute a very unusual deposit, or is it that the lava flows have influenced later lead deposition?

 

[RobinGriffiths]

Someone once told me, very roughly and generally, that negatively charged clay particles in muddy basins attract positive metal ions and such metals are sparsely dissipated when the rock is deposited as a mudstone. The ions are then mobilised by hydrothermal processes and deposited where the physical and chemical conditions are right, concentrating the metal compared to the source mudstone. Presumably such deposition conditions occur in faulted limestone. In the Pennines I assume the two underlying granite blocks were responsible for hydrothermal activity, maybe the lavas were associated with such activity in the Peak?


Robin

 

[gus horsley]

The same process of concentration and mobilisation of metals in sediments is thought to have occurred in the Southwest in the Plymouth Bay Basin, which is probably Late Permian in age, the lead/zinc then being deposited in crosscourses a considerable distance away.  These are post-granitisation, which occurred in Late Carboniferous/Early Permian.

I also thought the Pennine ore deposits were derived from granites which would post-date the volcanics if the latter were interbedded with limestones.  Perhaps the lavas influence mineral deposition structurally by restricting the upward flow of hydrothermal gases and fluids and channelling them into pre-existing faults and joints.

 

[martinr]

Some info here

extract: One of the major industries in the Peak District has been the extraction of metal bearing minerals but how did they get there in the first place?
The mineral deposits are mainly hydrothermal, occurring in veins of varying thickness in the rocks. Mineralisation is exclusive to the Limestone area which suggests that it was could be related to the vulcanism that the region experienced during Carboniferous times rather than a later event. So, at one time, a large mass of granite, deeply buried and not yet discovered, was postulated to explain the Peak District mineral field. However, The Peak District metalliferous minerals are mesothermic in origin i.e. created at moderate depths, pressure and temperature as the mineralogy is galena and sphalerite. In the Castleton area, the unique Blue-John (a form of fluorite) and barytes exist, together with some galena. This sort of mineralogy suggests an epithermic origin i.e. closer to the surface.
After much research and debate, it is now generally accepted that the source of the circulating groundwater was the deep water basins surrounding the limestone shelf areas. It is thought for example, that hydrothermal solutions picked up minerals from the basin clays to the north. These hydrothermal solutions then penetrated the limestones, through joints and faults where minerals such as galena and sphalerite were deposited in fissures along the edge of the St George?s Land shelf.