Chapter 1

Mineralization in England and Wales:

an introduction

R.E. Bevins

From: Bevins, R.E., Young, B., Mason, J.S., Manning, D.A.C. and Symes, R.F. (2010), Mineralization of England and Wales, Geological Conservation Review Series, No. 36, Joint Nature Conservation Committee, Peterborough, 598 pages, illustrations, A4 hardback, ISBN 978 1 86107 566 6 For more information see: http://www.jncc.gov.uk/page-3298

Background

3

BACKGROUND

The geological record in Great Britain reflectssome 2900 million years of Earth history. A complex evolution through that time-period sawrock sequences developing in a wide range oftectonic settings, from the accumulation of thicksedimentary successions in extensional basins,sometimes associated with magmatism typicallyin the form of tholeiitic basaltic lava-flows andhigh-level intrusions, through subduction ofthese sequences as the Earth’s plates came intocontact, again associated with magmatism butthis time with a calc-alkaline character, leadingthrough to metamorphism in orogenic beltslinked to major plate-collisional events. Thecomplexity of the geology of Great Britain isillustrated in the geological map presented asFigure 1.1.

This volume relates to mineralization inEngland and Wales, and is a companion volumeto that relating to mineralization in Scotland.

A consequence of this lengthy and complexevolution is the presence in Great Britain of awide variety of mineralization styles, many ofwhich provided deposits of economic importance, exploited over many centuries.There is evidence for extraction of copper asearly as Bronze-Age times, for example at theGreat Orme Copper Mines GCR site in NorthWales, and at the Cwmystwyth Mine GCR site in the Central Wales Orefield. Also, there isabundant testimony to the activities of theRomans; Julius Caesar reported tin productionin South-west England in the 1st century BC,and the Romans were known to have workedlead in Derbyshire, Yorkshire, the Mendips andWales. The unique deposit at the SeathwaiteGraphite Mine GCR site has evidence of theextraction of graphite as far back as Elizabethantimes. When active, a number of the deposits inEngland and Wales were important on the worldscale, for example the extraction of tin and copper in South-west England; whilst in its heyday, following discovery of the ‘Great Lode’in 1768, the copper deposit at the ParysMountain GCR site on Anglesey became thelargest copper working in the world. Some sitesbear testimony to former mining techniques,such as the ‘hushes’ at the Pike Law Mines GCRsite. Other deposits, such as the Westphalianironstones of South Wales, were crucial in the industrialization of Britain.

A small number of mineral deposits are still ofeconomic or sub-economic importance today,such as the deposits of potassium salts, halite,anhydrite and gypsum of northern England thatformed in the Zechstein and Bakevellia seas inLate Permian times, and developments of gypsum and celestine that occur in Late Triassicdeposits of the Mercia Mudstone Group, and arerepresented by those at the Gipsy Lane BrickPit and Ben Knowle GCR sites respectively.Some deposits remain on the fringe of economicviability, their exploitation being dictated by theworld price for metals. A rise in tin prices in the1960s saw a number of mines operating inSouth-west England, including Geevor, SouthCrofty, Pendarves, Mount Wellington and WhealJane. However, fortunes changed and the last ofthese to close was South Crofty in 1998. Thecomplex base-metal volcanogenic massive sulphide deposit at the Parys Mountain GCRsite continues to be reviewed, with the latestactivity being the sinking of the Morris Shaft to adepth of 300 m by Anglesey Mining plc in theperiod 1985 to 1990, although exploratorydrilling has continued subsequently. In early2008, talks opened between Anglesey Mining plcand Western Metals, with a view to transfer of ownership. However, the decline in world zincprices since 2007 has meant that those talks havenow fallen through.

The legacy of this long history of mineralextraction is a large number of old mine siteswhich have, over the centuries, been the sourceof numerous mineral specimens, the more aesthetic of which reside in the world’s majormuseum mineral collections. Certain localitiesare renowned by mineral collectors the worldover, for example the Roughtongill Mine GCRsite in the English Lake District for the very fine specimens of supergene lead and copper minerals; the Florence Mine GCR site, else-where in Cumbria, for spectacular ‘kidney ore’hematite specimens; and the Treak Cliff GCRsite in Derbyshire, famous for the uniquedeposits of ‘Blue John’ fluorite. However, it isnot only for their aesthetic value that some localities are renowned. Some sites are famousfor the sheer diversity of the minerals present,for example the Penberthy Croft Mine GCR sitein South-west England, which has producedover 90 confirmed mineral species. Some sites contain mineral species which are extremelyrare on a world-wide basis, such as the Meldon

Mineralization in England and Wales: an introduction

4

Figure 1.1 Geological map of Great Britain. Based on May and Hansom (2003), and British Geological Survey.

Background

5

Aplite Quarries GCR site and the Red-a-VenMine GCR site, both in South-west England (butsee the cautionary note at the end of this chapter). In addition, some sites are of importance for being type localities, that is a site from which a mineral species new to sciencewas first described. For example, the Bage Mine GCR site in Derbyshire was the localityfrom which matlockite was first collected in1851 by the famous mineral collector BryceWright. The Benallt and Nant Mines GCR siteis the type locality for no less than three raremineral species (banalsite, pennantite and cymrite). The High Down Quarry GCR site, inDevon, is the type locality for wavellite; theBlagill Mine GCR site, in the Northern PennineOrefield, is the type locality for barytocalcite;and the Hingston Down Quarry and HingstonDown Consols GCR site in Cornwall is the type locality for arthurite. Other mineral type locali-ties which are GCR sites include ParysMountain, Botallack Mine and Wheal Owles,Penberthy Croft Mine, Cligga Head, andHope’s Nose. For some sites, however, the factthat it is a type locality is a subordinate interest, considering the importance for a particular featureor its place in a network of sites. The BotallackMine and Wheal Owles and the Cligga HeadGCR sites fall into this category.

Some mining districts in Great Britain havebeen studied in great detail and have become recognized worldwide as classic areas for understanding the processes of mineralization. Probably the most importantregions in this context are the South-westEngland mineral province, with seminal contributions by Dines (1956) and Hosking(1964), and the Northern Pennine Orefield, withthe classic accounts by Dunham (1948, 1990)and Dunham and Wilson (1985). Individualsites in these regions are difficult to recognize interms of their international importance; rather itis the network of sites which combine to give athorough appreciation of the mineralization history.

As a result of the diverse range of minerali -zation styles and the related exploitation activities in Great Britain there is a wealth of former mining sites which provide the opportunity to study the mineral deposits andtheir mineral parageneses, sometimes in situ,more commonly in the spoil heaps left over from the extractive activities. In South-west

England it has been estimated that there are over 2500 former mine sites (Alderton, 1993),while the Minescan survey in Wales (Bevins and Mason, 1997) determined over 1200 disused mine sites. However, not all minerali -zing processes lead to the generation of deposits of economic significance. Diageneticthrough to low-grade metamorphic processesgenerate mineral assemblages of petrogeneticimportance but of little economic significance.The development of zeolites is of commercialsignificance in other parts of the world but notin Great Britain. However, there are a smallnumber of sites of uniqueness in Great Britainthat are important for this GCR compilation,such as the Croft Quarry GCR site in theEnglish Midlands and the Dean Quarry GCRsite in South-west England. Certain areas ofGreat Britain, especially Wales and the LakeDistrict, are important regions worldwide for theoccurrence of low-grade prehnite-pumpellyitemetamorphic assemblages, although no sitesprovide sufficient field evidence to be listed;most of the information comes from detailedmicroscopic investigations of fine-grainedrecrystallization assemblages in basic igneousrocks, comprising chlorite, albite, prehnite,pumpellyite, epidote and actinolite, and morerarely laumontite and axinite. The presence ofpumpellyite metadomains described fromLlanelwedd Quarry in Wales by Bevins (1985),and Metcalfe et al. (1996) is perhaps a notableexception.

It has been the challenge of this GeologicalConservation Review of the mineralization inEngland and Wales to select those critical sitesfor understanding the history of mineralizing andmetallogenic processes across the region. Thefindings of this review have led to a total network of approximately 137 sites of mineralo -gical importance being listed for scheduling.The criteria for selection of the sites is exploredfurther later in this chapter.

The task of site selection has been greatlyaided by a number of systematic regionallybased reviews of the topographical mineralogyof Great Britain which have been published inthe last 20 years or so, covering the Lake District(Young, 1987a; Cooper and Stanley, 1990),South-west England (Embrey and Symes, 1987),Wales (Bevins, 1994), Scotland (Livingstone,2002), and most recently Northern England(Symes and Young, 2008). In turn, of course,

Mineralization in England and Wales: an introduction

6

these have drawn on even earlier regional studies, such as those by Pryce (1778) andCollins (1871) for South-west England, Mawe(1802) for Derbyshire, and Heddle (1901) forScotland, to name but a few. Until recently, onlythe work of Greg and Lettsom (1858) had presented in a single volume an overview of themineralogy of Great Britain and Ireland.However, Tindle (2008) has completely updatedthat volume, a monumental contribution which serves as an ideal companion volume tothe two Geological Conservation Review volumes detailing the mineralization of Englandand Wales, and of Scotland. The seminal works of Dines (1956), and Hoskins (1964)detailing the South-west England mineralprovince, and the classic accounts by Dunham(1948, 1990), and Dunham and Wilson (1985)for the Northern Pennine Orefield have beenmentioned above. Acknowledgement must also be made, however, to the comprehensivereview of the minerali zation of the British Islescompiled by Pattrick and Polya (1993), whichmany of the site reports in this volume drawupon.

GCR SITE SELECTION

The Geological Conservation Review was established with a view to identifying the mostimportant sites that require protection and conservation in order that the geological evolution and history of Great Britain can beunderstood. The aim is that these sites will benotified as Sites of Special Scientific Interest(SSSIs), under the current Wildlife andCountryside Act 1981. A full explanation of theGeological Conservation Review process and the relevant legislation, along with practical considerations of implementation of findingsare explained in Volume 1 of this series, AnIntroduction to the Geological ConservationReview (Ellis et al., 1996). The GCR has identified three fundamental site-selection criteria; international importance, presence ofexceptional features, and representativeness.Each site selected fits into at least one of thesecriteria, some into two and a few into all three.

The criteria for site selection in theMineralogy of England and Wales block followtwo main threads. Firstly, as listed in Table 1.1,

1. Sites representative of the mineralization history of England and Wales

1.1 Cambrian–Ordovician exhalative Mn and Fe mineralization, North Wales

Llyn Du Bach ComplexBenallt and Nant MinesTyllau Mwn

1.2 Ordovician porphyry copper mineralization,North Wales

Bryn-Coch and Capel HermonGlasdir MineMoel Hafod-OwenTurf Copper Mine

1.3 Lower Palaeozoic gold vein mineralization,North Wales

Cefn-Coch MineFoel-Ispri MineFriog Undercliff

1.4 Ordovician volcanism in North Wales

Lliwedd MineLlanberis MineCwm Tregalan–Shadow GullyLlyn Cwellyn MineFfestiniog Granite QuarryAfon StwlanBwlch Mine, DeganwyCae Coch MineParys Mountain

Table 1.1 Selection criteria for sites fundamental to understanding the mineralization of England and Wales,tabulated on the basis of geological time (section 1) and sites showing special features (section 2). Continuedopposite.

1.5 Syn-tectonic ‘Alpine-type’ veins in NorthWales

Manod QuarryCoed Llyn y GarneddPenrhyn Quarry

1.6 Ordovician volcanism in the Lake District

Coniston Copper MinesDale Head North and South VeinsSeathwaite Copper Mines

1.7 Ordovician- to Devonian-age intrusions of the Lake District

Carrock Mine–Brandy GillWet Swine GillBuckbarrow BeckWater CragLong Comb

1.8 Stratabound gold-arsenopyrite mineralization, Wales

Dolaucothi Mine

1.9 Post-orogenic (A1) lead-zinc-copper mineralization in Central Wales

Darren MineErglodd MineEaglebrook MineCwmystwyth MineBrynyrafr Mine

GCR site selection

7

1.10 Mineralization associated with Devonian volcanism in South-west England

Lidcott MineWheal Emily

1.11 Early Carboniferous extension-related mineralization – Mississippi Valley-type inWales and Shropshire (including A2 mineralization in Central Wales)

Ceulan Mine OpencastNantiago MineBrynyrafr MineNantymwyn MineCwmystwyth MineEaglebrook MineHalkyn MountainPool Park and South Minera MinesPennant MineGreat Orme Copper MinesHuglith MineSnailbeach Mine

1.12 Late Carboniferous–early Permian MississippiValley-type mineralization of the Lake District,and the Northern Pennine and South Pennineorefields

Eagle CragForce Crag MineLady’s Rake MineWest Rigg OpencutKillhope HeadSmallcleugh MineTynebottom MineScordale MinesSettlingstones MineWillyhole MineFallowfield MineClosehouse MineBlack Scar, Middleton TyasCumpston Hill North and South VeinsGreenhow (Duck Street) QuarryBlagill MineGunnerside Gill, SwaledaleFoster’s HushPike Law MinesSir John’s MineStonecroft MineDirtlow Rake and PindaleTreak CliffWindy KnollEcton Copper MinesMasson Hill MinesFall Hill Quarry

1.13 Late Carboniferous–early Permian mineralization associated with the Cornubian Batholith

SkarnsHaytor Iron MineRed-a-Ven Mine, Meldon

Pegmatites and aplitesTrevalour Downs PegmatiteMeldon Aplite QuarriesTremearne Par

Greisens, stockworks, etcCameron Quarry (endogranitic)St Michael’s Mount (endogranitic)

Cligga HeadMulberry Down Opencast (exogenetic)Great Wheal Fortune

TourmalinizationPriest’s Cove, Cape CornwallNanjizal Cove

Main-stage polymetallic veinsCameron QuarryCligga HeadWheal CoatesTrevaunance Cove, St AgnesWheal AlfredBotallack Mine and Wheal OwlesDevon United MineDevon Great ConsolsPenlee Quarry, NewlynHingston Down Quarry and ConsolsGreat Wheal Fortune

Cross-course mineralizationBotallack Mine and Wheal OwlesLockridge MinePenlee Quarry, NewlynPerran Beach to Holywell BayWheal PenroseDevon United Mine

Late-stage mineralizationSouth Terras Mine

1.14 Permian–early Triassic iron ores of Cumbria

Florence MineNab Gill Mine

1.15 Triassic Fe-Mn mineralization in the Mendipsand South Wales

Mwyndy MineOgmore CoastCompton Martin Ochre MineHartcliff Rocks Quarry

1.16 Triassic evaporites and arid weathering products

Ben KnowleGipsy Lane Brick PitWarren Quarry

1.17 Mineralization related to Mesozoic basinalextension in South Wales, the WelshBorderland and the Mendips

Ogmore CoastMachen QuarryBanwell CavesCharterhouse Lead OrefieldClevedon ShoreWurt PitDolyhir Quarry

1.18 Mesozoic–Tertiary sediment-hosted mineralization of the Cheshire Basin

Alderley Edge District

1.19 Pliocene to Pleistocene solution collapse andfill deposits in Derbyshire and Somerset

Portway Gravel PitsKirkham’s Silica SandpitsBanwell Ochre Caves

Table 1.1 Continued.

Mineralization in England and Wales: an introduction

8

Table 1.1 Continued.2. Sites showing other important

aspects of mineralogy in England and Wales

2.1 Supergene alteration

Turf Copper MineMynydd Nodol MineMachen QuarryParys MountainLlechweddhelyg MineFrongoch MineDrygill MineRoughtongill MineRed Gill MineBirk Fell Hawse MineDale Head North and South VeinsCarrock Mine–Brandy GillSeathwaite Copper MinesPikedaw Calamine and Copper MinesWillyhole MineFoster’s HushPike Law MinesNewhurst QuarryPenberthy Croft MineAlderley Edge District

2.2 Zeolitization

Dean Quarry, LizardCroft Quarry

2.3 Exceptional features

Glasdir MineMoel Hafod-OwenTurf Copper MineParys MountainCae Coch MineSnailbeach MineSeathwaite Graphite MineWater CragLong CombLady’s Rake MinePikedaw Calamine and Copper MinesFoster’s HushPike Law MinesTon Mawr QuarryTreak CliffCalton HillWurt PitGravel Hill MinePenberthy Croft MineBotallack Mine and Wheal OwlesHope’s NoseMeldon Aplite QuarriesAlderley Edge District

2.4 Aesthetic specimens

Roughtongill MineRed Gill MineDry Gill MineFlorence MineSmallcleugh MineScordale MinesBlagill MineSettlingstones MineFallowfield MineTreak CliffParys MountainManod QuarryHope’s NoseWheal Alfred

2.5 Rare mineral species/parageneses

Benallt and Nant MinesBwlch Mine, DeganwyParys MountainErglodd MineEaglebrook MineDolyhir QuarryLlechweddhelyg MineFrongoch MineSeathwaite Graphite MineBuckbarrow BeckLong CombWater CragWet Swine GillCarrock Mine–Brandy GillRoughtongill MineRed Gill MineDry Gill MineSeathwaite Copper MinesLady’s Rake MineTynebottom MineBlagill MineFallowfield MineSettlingstones MineClosehouse MineFoster’s HushGipsy Lane Brick PitWarren QuarryBotallack Mine and Wheal OwlesCligga HeadHope’s NoseMeldon Aplite QuarriesPenberthy Croft MineRed-a-Ven Mine, MeldonAlderley Edge District

2.6 Type localities

High Down QuarryBlagill MineFallowfield MineBage MineBenallt and Nant MinesParys MountainBotallack Mine and Wheal OwlesCligga HeadHingston Down Quarry and ConsolsHope’s Nose

2.7 Mining history significance

Seathwaite Graphite MineConiston Copper MinesDale Head North and South VeinsCarrock Mine–Brandy GillRoughtongill MineRed Gill MineSmallcleugh MineLady’s Rake MineScordale MinesSettlingstones MineBlagill MineFallowfield MinePikedaw Calamine and Copper MinesSir John’s MineGunnerside Gill, SwaledaleParys MountainCwmystwyth MineGreat Orme Copper MinesPike Law MinesAlderley Edge District

2.8 Understanding mineral sciences

Castle Hill QuarryWindy KnollTreak Cliff

GCR site selection

9

there is a group of sites (set 1.1 to 1.18), whichdemonstrate the mineralization history of Englandand Wales through time. Then there is a secondset of sites (set 2.1 to 2.8) which are includedbecause of a variety of exceptional features,including for example the range of rare mineralspecies present, the aesthetic qualities of specimensfrom the site, because they are type localities, orfor the exceptional mineralization featurespresent. Table 1.2 presents the same informationas in Table 1.1 but formatted to highlight thegeographical distribution of the sites on thebasis of the major mineralization areas describedin this volume, namely the Lake District(Chapter 2), the Northern Pennines (Chapter 3),the Southern Pennines of Derbyshire, butincluding also Cheshire, Leicestershire andShropshire (Chapter 4), Wales (Chapter 5), theMendip Hills (Chapter 6), and finally South-westEngland (Chapter 7). The geographical spreadof the sites is illustrated in Figure 1.2.

The international importance of the mineralsites in England and Wales has already beenhighlighted above. To these could be added the Botallack Mine and Wheal Owles GCR site, which is of international significance in providing evidence of varying stages of minerali -zation in the tin zone and the lower part of thecopper zone of the main-stage mineralizationassociated with the Cornubian Batholith.Unrelated to this scheduling, but indicative ofthe international importance of this site, is thefact that Botallack Mine was central to theinscription in 2006 of the ‘Cornwall and WestDevon Mining Landscape’ onto UNESCO’sWorld Heritage list.

There are a number of mineralogical sites inEngland and Wales which show the presence ofexceptional features. In Wales, the GlasdirMine GCR site represents a rare mineralizedexplosion pipe-breccia with mineralizationlinked to a porphyry copper system. The TreakCliff GCR site, with its deposits of ‘Blue John’fluorite, is undoubtedly unique; as is the TurfCopper Mine GCR site, associated with the Coedy Brenin porphyry copper deposit in southernSnowdonia. The Hope’s Nose GCR site isunique in Great Britain for the style of gold mineralization present, as well as being the typelocality for chrisstanleyite, while the celebratedgraphite deposit at the Seathwaite GraphiteMine GCR site has no counterpart in GreatBritain. Exceptional metasomatic cavity-fill mineral assemblages in Carboniferous carbonate

host-rocks are seen at the Ton Mawr QuarryGCR site, in South Wales. In Cornwall, thePerran Iron Lode, best seen at the Gravel HillMine GCR site, has no counterpart in the South-west England mineral province. Finally, theuniqueness of a number of type localities formineral species has been mentioned previously.

A number of sites listed have historic significance in the development of our under-standing of mineralization processes; perhapsone of the more important in progressing ourunder standing has been the debate over the origin of organic material associated with mineraldeposits, namely whether it is of biogenic orabiogenic origin. The GCR sites at Windy Knoll and Treak Cliff cover this, but mostimportantly this is the main criteria for listing ofthe Castle Hill Quarry GCR site, in the EnglishMidlands.

The criterion of representativeness aims toensure that all major elements of the mineraliza-tion are represented in the ultimate GCR site list.The majority of the sites listed in this volume fallinto this category. However, within this categorythere are inter-related sites, which highlight a particular geological phenomenon. For example, the GCR sites at Lliwedd Mine,Llanberis Mine and Cwm Tregalan–ShadowGully represent mineralization processes thathave been identified as being generated in theSnowdon volcanic caldera in Ordovician times,and which formed the basis of the model presented by Reedman et al. (1985).

However there are some regionally importantmineral sites that are not covered by the extensive listing in this volume. In some casesthis is because there are no localities that showany exceptional features or there are none thatexhibit the typical features of the suite any betterthan numerous other localities. It is importanttherefore to identify ‘regionally importantGeological/Geomorphological Sites’ (RIGS) torepresent such sites, even though this status carries no formal legal protection. Nevertheless,the importance of these sites needs to be recognized and recorded, facilitating conservationat a local level. In this volume there is no description, for example, of the claystone–ironstone nodule mineralization in the SouthWales Coalfield. Unfortunately, most of theimportant sites from which the mineralized nodules have been collected have been land-scaped, and presently no sites show evidence oftheir origin. Also, all but a few mines in the area

Mineralization in England and Wales: an introduction

10

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GCR site selection

11

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Mineralization in England and Wales: an introduction

12

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1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

1.1

01.1

11.1

21.1

31.1

4 1

.15

1.1

61.1

71.1

81.1

92.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

Sit

e n

ame

Cro

ft Q

uar

ry

*

New

hu

rst

Qu

arry

*

War

ren

Qu

arry

*

*

Gip

sy L

ane

Bri

ck P

it

*

*

Cal

ton

Hill

*

Mas

son

Hill

Min

es

*

Dir

tlo

w R

ake

and

Pi

nd

ale

*

Bag

e M

ine

*

Fall

Hill

Qu

arry

*

Tre

ak C

liff

*

I I

*

Win

dy

Kn

oll

*

*

Port

way

Gra

vel P

its

*

Kir

kham

’s S

ilica

Sa

nd

pit

s

*

Ect

on

Co

pp

er M

ines

*

Ald

erle

y Ed

ge D

istr

ict

*

*

*

*

*

Snai

lbea

ch M

ine

*

*

Hu

glit

h M

ine

*

Wa

les

Llyn

Du

Bac

h

Co

mp

lex

*

Ben

allt

an

d N

ant

Min

es

*

I I

Tyl

lau

Mw

n

*

Bry

n-C

och

an

d C

apel

H

erm

on

*

Tab

le 1

.2C

onti

nu

ed.

GCR site selection

13

Sit

es r

epre

sen

tati

ve o

f th

e m

iner

aliz

atio

n

his

tory

of

En

glan

d a

nd

Wal

es

Site

s sh

ow

ing

oth

er im

port

ant

asp

ects

of m

iner

alogy

in E

ngl

and

an

d W

ales

Sel

ecti

on

Cri

teri

a 1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

1.1

01.1

11.1

21.1

31.1

4 1

.15

1.1

61.1

71.1

81.1

92.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

Sit

e n

ame

Gla

sdir

Min

e

*

*

Mo

el H

afo

d-O

wen

*

*

Tu

rf C

op

per

Min

e

*

*

*

Foel

-Isp

ri M

ine

*

Cef

n-C

och

Min

e

*

Frio

g U

nd

ercl

iff

*

Lliw

edd

Min

e

*

Llan

beri

s M

ine

*

Cw

m T

rega

lan

– Sh

ado

w G

ully

*

Llyn

Cw

elly

n M

ine

*

Bw

lch

Min

e,

Deg

anw

y

*

*

Pary

s M

ou

nta

in

*

*

I *

* *

I

Cae

Co

ch M

ine

*

I

Ffes

tin

iog

Gra

nit

e Q

uar

ry

*

Afo

n S

twla

n

*

Man

od

Qu

arry

*

*

Co

ed L

lyn

y G

arn

edd

*

Pen

rhyn

Qu

arry

*

Do

lau

coth

i Min

e

*

Cw

mys

twyt

h M

ine

*

*

*

Bry

nyr

afr

Min

e

*

*

Dar

ren

Min

e

*

Erg

lod

d M

ine

*

*

Eag

lebr

oo

k M

ine

*

*

*

Tab

le 1

.2C

onti

nu

ed.

Mineralization in England and Wales: an introduction

14

Sit

es r

epre

sen

tati

ve o

f th

e m

iner

aliz

atio

n

his

tory

of

En

glan

d a

nd

Wal

es

Site

s sh

ow

ing

oth

er im

port

ant

asp

ects

of m

iner

alogy

in E

ngl

and

an

d W

ales

Sel

ecti

on

Cri

teri

a 1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

1.1

01.1

11.1

21.1

31.1

4 1

.15

1.1

61.1

71.1

81.1

92.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

Sit

e n

ame

Ceu

lan

Min

e O

pen

cast

*

Nan

tiag

o M

ine

*

Nan

tym

wyn

Min

e

*

Do

lyh

ir Q

uar

ry

*

*

Hal

kyn

Mo

un

tain

*

Poo

l Par

k an

d S

ou

th

Min

era

Min

es

*

Pen

nan

t M

ine

*

Gre

at O

rme

Co

pp

er

Min

es

*

*

Mw

ynd

y M

ine

*

To

n M

awr

Qu

arry

*

Ogm

ore

Co

ast

*

*

Mac

hen

Qu

arry

*

*

Llec

hw

edd

hel

yg

Min

e

*

*

Fro

ngo

ch M

ine

*

*

Myn

ydd

No

do

l Min

e

*

Men

dip

Hil

ls

Ban

wel

l Cav

es

*

Ban

wel

l Och

re C

aves

*

Ben

Kn

ow

le

*

Ch

arte

rho

use

Lea

d

Ore

field

*

Tab

le 1

.2C

onti

nu

ed.

GCR site selection

15

Sit

es r

epre

sen

tati

ve o

f th

e m

iner

aliz

atio

n

his

tory

of

En

glan

d a

nd

Wal

es

Site

s sh

ow

ing

oth

er im

port

ant

asp

ects

of m

iner

alogy

in E

ngl

and

an

d W

ales

Sel

ecti

on

Cri

teri

a 1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

1.1

01.1

11.1

21.1

31.1

4 1

.15

1.1

61.1

71.1

81.1

92.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

Sit

e n

ame

Cle

ved

on

Sh

ore

*

Wu

rt P

it

*

*

Co

mp

ton

Mar

tin

O

chre

Min

e

*

Har

tclif

f Ro

cks

Qu

arry

*

Sou

th-w

est

En

gla

nd

Mel

do

n A

plit

e Q

uar

ries

*

*

*

Prie

st’s

Co

ve, C

ape

Co

rnw

all

*

Tre

valo

ur

Do

wn

s Pe

gmat

ite

*

Tre

mea

rne

Par

*

Red

-a-V

en M

ine,

M

eld

on

*

*

Hay

tor

Iro

n M

ine

*

Bo

talla

ck M

ine

and

W

hea

l Ow

les

*

I

* *

Wh

eal C

oat

es

*

Lid

cott

Min

e

*

Wh

eal E

mily

*

Clig

ga H

ead

*

*

*

Cam

ero

n Q

uar

ry

*

St M

ich

ael’s

Mo

un

t

*

Tab

le 1

.2C

onti

nu

ed.

Mineralization in England and Wales: an introduction

16

Sit

es r

epre

sen

tati

ve o

f th

e m

iner

aliz

atio

n

his

tory

of

En

glan

d a

nd

Wal

es

Site

s sh

ow

ing

oth

er im

port

ant

asp

ects

of m

iner

alogy

in E

ngl

and

an

d W

ales

Sel

ecti

on

Cri

teri

a 1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

1.1

01.1

11.1

21.1

31.1

4 1

.15

1.1

61.1

71.1

81.1

92.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

Sit

e n

ame

Mu

lber

ry D

ow

n

Op

enca

st

*

Gre

at W

hea

l Fo

rtu

ne

*

Nan

jizal

Co

ve

*

Dev

on

Gre

at C

on

sols

*

Dev

on

Un

ited

Min

e

*

Tre

vau

nan

ce C

ove

, St

Agn

es

*

Perr

an B

each

to

H

oly

wel

l Bay

*

Lock

rid

ge M

ine

*

Sou

th T

erra

s M

ine

*

Wh

eal P

enro

se

*

Wh

eal A

lfre

d

*

*

Pen

bert

hy

Cro

ft

Min

e

*

*

*

Ho

pe’

s N

ose

*

* *

I

Hig

h D

ow

n Q

uar

ry

*

Hin

gsto

n D

ow

n

Qu

arry

an

d C

on

sols

*

*

Pen

lee

Qu

arry

, N

ewly

n

*

Gra

vel H

ill M

ine

*

Dea

n Q

uar

ry, L

izar

d

*

Tab

le 1

.2C

onti

nu

ed.

Mineralization history of England and Wales

17

have closed and so there is little chance of newexposures. To illustrate this episode of minerali -zation, a broad overview is presented, alongwith references to key publications.

The site reports are presented in this volume ona regional basis. In light of this, a brief overview ofthe major mineralization episodes in England andWales is presented in the following paragraphs.This is presented largely on a time basis, althoughit has not been possible yet to date accurately allof the mineralization events present.

MINERALIZATION HISTORY OFENGLAND AND WALES

The oldest significant mineralization determinedin Great Britain is the Besshi-style copper-zinc-gold mineralization which occurs in deformedLewisian Loch Maree Group metabasicsupracrustal rocks near Gairloch and which hasbeen shown to contain a sub-economic depositknown as the ‘Kerry Road sulphide deposit’ (seeJones et al., 1987). No rocks as old as theLewisian occur in England and Wales. Indeed,the oldest rocks in this region date back only toc. 700 Ma. These Neoproterozoic rocks formedpart of Eastern Avalonia, which was situated onthe north-east margin of Gondwana and wereassociated with subduction along this marginwhich generated magmatism and basin develop-ment. No significant mineralization episodeshave been determined in this region of southernBritain, although the Newhurst Quarry GCRsite in Leicestershire shows mineralization concentrated at the unconformable boundarybetween Neoproterozoic Charnian Supergrouprocks and overlying Triassic rocks, the minerali -zation being concentrated at this horizon becauseof lithological contrasts across the boundary.

Early Palaeozoic times saw the geological history of southern Britain dominated by theseparation of Avalonia from Gondwana and itsmigration towards Laurentia. Again, this periodwas dominated by basin generation and magmatism associated with the south-eastwardssubduction of Iapetus oceanic crust beneathAvalonia. Terranes identified in the LowerPalaeozoic sequences of England and Walesreflect the accretion of various crustal fragmentsas Avalonia drifted towards Laurentia. The earliest significant mineral deposits in the LowerPalaeozoic sequences of England and Walesrelate to sedimentary exhalative processes in

Cambrian times, generating bedded manganeseand iron silicate and carbonate deposits. Thisepisode is best seen at the Llyn Du BachComplex GCR site, with the mineralization beingdominated by rhodochrosite and kutnohorite,along with more minor spessartine, hematite,magnetite and ferropyrophanite. The structurallymore complex manganese mineral deposits atthe Benallt and Nant Mines GCR site are alsoconsidered to be sedimentary exhalative in origin, although here barium is more commonin association with the manganese, and the siteis important for the large number of rare, some-times well-crystallized manganese and bariumsilicates present, including banalsite, pennantite,cymrite and bannisterite, the site being the typelocality for the first three of those species.

Ordovician times were dominated by volcanicactivity, as noted above, linked to the south-eastwards subduction of Iapetus oceanic crust.The earliest eruptive events occurred in lateTremadoc to early Arenig times, with calc-alkaline magmas occurring in southernSnowdonia, forming the Rhobell VolcanicComplex, and in Pembrokeshire, forming theTreffgarne Volcanic Group. In Pembrokeshire,there is evidence for copper mineralization inthe Treffgarne area, as well as farther west,around Llandeloy, where contemporary dioriticintrusions are associated with a hidden porphyrycopper deposit (see Allen et al., 1976). However,exposures are slightly better developed in southern Snowdonia, where a major porphyrycopper deposit has been identified in the Coedy Brenin region, a system which represents oneof the oldest and best-preserved examples of aporphyry copper system in the world. The mineralization is associated with a suite ofaltered microtonalites and dolerites, comprisingthin veinlets and disseminations of pyrite andchalcopyrite. Fresh, primary mineralization israrely seen, the Bryn-Coch and Capel HermonGCR site offering the best opportunity to studythis mineralization episode. Associated with thismineralizing event, the Glasdir Mine GCR siterecords an intrusive explosion event, unique inthe southern Caledonide region, while the MoelHafod-Owen GCR site shows higher-level sinter-like textures within a breccia pipe, linked tofumarolic activity. A site unique to Great Britainis the Turf Copper Mine GCR site, where copper mobilized from the Coed y Brenin porphyry copper deposit has been precipitatedas native copper on organic matter in a peat bog.

Mineralization in England and Wales: an introduction

18

Figure 1.2 Map showing the locations of the mineralization GCR sites in England and Wales.

Mineralization history of England and Wales

19

Wales is renowned for its gold deposits, whichoccur in veins cutting Cambrian strata flankingthe Harlech Dome in the Dolgellau area, andalso unrelated stratabound gold-arsenic depositsin Upper Ordovician pyritic shales farther south,around Pumpsaint, at the Dolaucothi MineGCR site. The Dolgellau gold mineralization haslong been considered to have been generated inlate Silurian to early Devonian times, associatedwith Acadian deformation and metamorphism.However, more recently field relationships incliffs and wave-cut-platform exposures at the

Friog Undercliff GCR site have provided evidence which demonstrates that the veins arein fact pre-tectonic in age (Mason et al., 1999).The veins are now thought to have beenemplaced during depressuring and dewateringof sediments during post-tectonic uplift of theHarlech Dome. The veins typically exhibit book-and-ribbon textures as a result of repeated mineralizing events; these are well displayed atthe Cefn-Coch Mine GCR site. A four-stage paragenetic sequence has been determined(Mason et al., 2002). The richest gold levels

Figure 1.2 Continued.

Mineralization in England and Wales: an introduction

20

occur in irregular, so-called ‘bonanza-shoot’areas, which were once worked at the Foel-IspriMine GCR site.

Although for most of Ordovician times environments in Wales were dominated by basinal conditions, periodically through fromArenig to Caradoc times shallow-marine conditions prevailed, which led to the development of ooidal and pisolitic iron ore-beds. These were exploited as low-grade oresacross Snowdonia. They were ubiquitouslyaltered by low-grade metamorphic processes,while at the Tyllau Mwn GCR site the ore-bedhas been affected by contact metamorphism,leading to a rare assemblage containing chlorite,magnetite, stilpnomelane and apatite, whilstpreserving the original sedimentary ooidal textures.

Caradoc times saw a period of major volcanicactivity in southern Britain, especially in Walesand the Lake District, focused on the develop-ment of major calderas, notably the SnowdonCaldera in Wales, and the Scafell, Langdale andHaweswater calderas in the Lake District. TheSnowdon Caldera was thought to be responsiblefor the focus of an important episode of coppermineralization, as described by Reedman et al.(1985). Evidence for the pre-tectonic (Acadian)age for this mineralization is seen at the LliweddMine and Afon Stwlan GCR sites. There is someevidence of a zonation to the mineralization,for example lower-temperature arsenopyrite-bearing parageneses being present at theLlanberis Mine GCR site. A possible magmaticinput to Snowdon Caldera mineralization is suggested by the presence of minor tin andtungsten in magnetite- and hematite-bearingveins at the Cwm Tregalan–Shadow Gully GCRsite. Copper trials showing the presence of fluorite, and a range of bismuth and lead tellurides are present at the Llyn Cwellyn MineGCR site, located at the margin of the MynyddMawr riebeckite-bearing microgranite, while theFfestiniog Granite Quarry GCR site exposespipe-like bodies containing allanite and molybdenite, the pipes being considered to belate-stage magmatic features. To the north of theSnowdon Caldera a separate, minor volcaniccentre contains low-temperature lead-antimonymineralization at the Bwlch Mine GCR site,showing a number of rare lead antimonysulphosalt minerals in veins and irregularquartz-bearing patches in silicified rhyolitic ignimbrites. Caradoc-age volcanism has been

considered to have developed in a back-arcextensional tectonic setting, and elsewhere,away from the Snowdon Caldera, volcanicexhalative mineralization occurred, seen at theCae Coch Mine GCR site. This mine worked amassive stratiform pyrite deposit. The ParysMountain GCR site represents another volcanicexhalative deposit, although this is thought to be of early Silurian (Llandovery) age. The mineexploited a complex sulphide ore deposit, dominated by the extraction of copper on amajor scale. A well-developed gossan cap oncecovered the Parys Mountain deposit andalthough now removed, evidence is provided bysamples preserved in museum collections. Thisgossan contained an abundance of the lead sulphate anglesite, for which Parys Mountain isthe type locality.

In contrast, the Borrowdale Volcanic Group, ofCaradoc age, exposed widely in the Lake Districtand responsible for the dramatic mountainousscenery of the region, is considered to havedeveloped in a volcanic-arc environment on thebasis of the calc-alkaline character of the eruptedlavas. Copper mineralization cutting the volcanicsequences, seen at the Coniston Copper Mines,Seathwaite Copper Mines, and Dale HeadNorth and South Veins GCR sites has previouslybeen considered to be related to late Silurian toearly Devonian Acadian deformation and metamorphism. More recently, Millward et al.(1999) have argued that it is related to theOrdovician volcanic activity, as has been arguedin Wales.

Associated with this magmatic episode wasthe generation of a number of major intrusions,emplaced in the Ordovician to Devonian period.These were best developed in the Lake Districtand northern England, with relatively minorintrusive bodies and complexes being developed in Wales. The Eskdale Granite, in theLake District, has been determined to be ofCaradoc age, and at the Water Crag GCR sitegreisenization of country rocks has led to thedevelopment of remarkable quartz-topaz andquartz-andalusite rocks. Tungsten mineralizationat the Buckbarrow Beck GCR site also appearsto be related to the Eskdale Granite magmaticevent. The Long Comb GCR site comprises aunique assemblage in the Lake District, showingco-existing apatite and arsenopyrite togetherwith cobalt minerals in what is termed the‘Crummock Water thermal aureole’, linked to apostulated unexposed granitic intrusion. The

Mineralization history of England and Wales

21

Skiddaw Granite was emplaced in earlyDevonian times and was responsible for mineralization at the Carrock Mine–Brandy GillGCR site, the only economic tungsten minerali -zation identified to date in England and Walesoutside of the South-west England mineral field.The intrusion was also related to the antimony mineralization seen at the Wet Swine Gill GCRsite. To the east of the Lake District, two major concealed intrusions, the Weardale andWensleydale granites, had major influences onthe location and character of mineral deposits ofthe Northern Pennine Orefield (see below).

Final closure of the Iapetus Ocean led to collision between Avalonia and Laurentia, anevent termed the ‘Acadian Orogeny’. Early tectonic models attributed many mineralizationevents as being related to this episode; howeveras has been shown above some of these havebeen subsequently re-assigned to other ages,such as the Dolgellau gold deposits. In NorthWales, however, a distinctive mineral assemblageis present in syn-tectonic ‘Alpine-type’ veins,dominated by quartz-albite-chlorite but containing a suite of titanium dioxide mineralsincluding anatase, brookite and rutile, as seen atthe Manod Quarry GCR site. They occur alongwith the rare-earth-element-bearing phases monazite, xenotime and synchysite-(Ce). Their syn-tectonic origin is demonstrated clearly bythe presence of boudinaged dacite intrusionswith ‘Alpine-type’ mineralization occurring in theboudin necks. Similar veins occur at thePenrhyn Quarry GCR site, where they containspecular hematite and are hosted by Ordovicianmetabasite dykes cutting slates of Cambrian age.

The Central Wales Orefield contains two generations of mineral veins, which have beentermed the A1 ‘Early Complex’ veins and the A2‘Late Simple’ veins, the ages of which arethought to be early Devonian and earlyCarboniferous to Permian, respectively. Theveins commonly occupy the same fractures anddemonstrate re-activation over a considerableperiod of geological history. This is best demonstrated by complex, cross-cutting veinsystems at the Brynyrafr Mine GCR site, as wellas the dramatic and archaeologically importantCwmystwyth Mine GCR site. The A2 veins aredescribed later in this introduction. The A1veins predominantly trend ENE–WSW and typically comprise fractured country rockcemented by sulphide-bearing quartz. Lead,copper and silver were the predominant metals

worked but a range of other elements arepresent in minor amounts, namely zinc, antimony,nickel, cobalt, arsenic and gold. The DarrenMine, Erglodd Mine and Eaglebrook MineGCR sites contain mineral assemblages whichdemonstrate this complexity, the veins containing many uncommon, and sometimesrare, minerals, such as cobalt pentlandite, gersdorffite and tucekite. The veins are thoughtto have been generated in early Devonian timesas a result of post-Acadian orogenic relaxation.

The Acadian tectonic event in southernBritain led to the development of widespreadarid, terrestrial environments across much ofEngland and Wales in Devonian times. In thesouthernmost regions of England, however, laythe Variscides of northern Europe, a totally separate orogenic belt with a contrasting evolution. Devonian and Carboniferous timessaw the presence of a series of basins whichextended eastwards for around 800 km, throughto Germany, and comprised the RhenohercynianZone. These basins were associated with sporadic volcanism and minor mineralizationepisodes. Manganese ores are widespread ineast Cornwall and west Devon in strata of LowerCarboniferous age. At the Lidcott Mine GCRsite Carboniferous cherts are rich in manganese.It is not wholly clear when the manganese wasintroduced into the cherts, but it is almost certainly of volcanic origin. It is certainly notrelated to the main mineralization episodes inthis region which are linked to the intrusive history of the Cornubian Batholith (see later).Lead-antimony mineralization at the WhealEmily GCR site may well be linked to Devonianvolcanism, and is possibly epigenetic in origin,perhaps similar in origin to the Bwlch MineGCR site mineralization in North Wales.

Carboniferous times saw the establishment ofemergent to shallow-water conditions acrossmuch of southern Britain in environments thatled to the development of thick carbonatesequences, combined with shale accumulationsin peripheral basins. This combination led tothe subsequent localization of important lead-zinc-fluorite mineral deposits in the classic mining orefields of the Northern Pennine district (in the Alston and Askrigg blocks, butpossibly also expressed in the Lake District, tothe west), the Southern Pennine district, thenorth-east Wales (Halkyn–Minera) area, and theMendips. Mineral deposits in Central Wales andShropshire are also possibly linked genetically,

Mineralization in England and Wales: an introduction

22

representing a deeper structural expression.What was critical to these mineral deposits,which relate to so-called Mississippi Valley-type(MVT) mineralization, was the expulsion andmigration of fluids from basin environmentsfrom late Palaeozoic through to Mesozoic times. The mineralizing process is linked toperiods of active rifting, thermal subsidence andbasin inversion, which caused fluid expulsionfrom rapidly buried sediments. However insome cases it is still a matter of conjecture as towhich deposit relates to which mineralizingevent, while for other deposits there is criticalgeological evidence for their genesis, asdescribed below.

In the Northern Pennine Orefield a critical site in determining the age of the mineralizingevent is the Lady’s Rake Mine GCR site, which demonstrates that the lead and zinc mineralization present at this site very closelypost-dates the emplacement of the Whin Sill,which is now regarded as having taken placeduring the interval represented by the uncon -formity between upper Carboniferous and lowerPermian times. It has therefore been suggestedthat MVT mineralization of the NorthernPennine Orefield is of latest Carboniferous toearly Permian age.

A key feature in the localization of mineraliza-tion in the Northern Pennine Orefield is thepresence of the subjacent unexposedCaledonian intrusions, namely the Weardale andWensleydale granites. These controlled thedevelopment of the Alston and Askrigg blocks.These areas remained as positive highs frommid-Devonian times onwards which led to thedevelopment of thin, rhythmic, sedimentarycycle deposits, known as the ‘Yoredale facies’.The Alston Block is bounded to the north andsouth by the Stublick and Lunedale faults, passingrespectively into the Northumberland Basin andStainmore Trough. To the south of theStainmore Trough the Askrigg Block is defined atits southern extremity by the Craven Fault.Mineralization in the Alston Block is present as fissure-vein infills and metasomatic flatreplacements. The mineral veins show their richest development in the Great Limestone.Metasomatic flats are less common than the veinsand occur largely at vein intersections and in thecrests of small anticlines.

The Alston Block mineralization shows abroad concentric zoning, from inner to outer asfollows:

• fluorite-quartz-chalcopyrite-galena(+/– pyrrhotite and marcasite)

• fluorite-quartz-galena (+ sphalerite orsiderite)

• galena-quartz (+ sphalerite or siderite)• galena-barite (+ sphalerite or witherite)• barite-witherite-barytocalcite

The Killhope Head GCR site provides a finedemonstration of fissure-vein mineralization,along with iron-rich metasomatic replacementflat deposits in the Great Limestone, in the central fluorite zone, while the TynebottomMine GCR site provides excellent evidence forthe relationships between fissure veins andmetasomatic flats. The Smallcleugh Mine GCRsite shows extremely important exposures oflead- and zinc-rich metasomatic replacement flatmineralization within the Great Limestone. TheWest Rigg Opencut GCR site provides one ofthe finest examples of a Northern PennineOrefield vein and associated iron flat within theGreat Limestone. The Scordale Mines GCR sitedemonstrates vein and flat mineralization withinthe outer barite zone of the orefield, where themineralizing fluids were confined to theMelmerby Scar Limestone by the lithologicalcontrol of the Whin Sill and its adjacent, thermally altered shales. One of the densestconcentrations of mineralized veins and associated replacement deposits, however, isseen at the Pike Law Mines GCR site, which alsoshows extensive supergene mineralization. Oneof the major mineralized structures of the AlstonBlock is the Great Sulphur Vein, material fromwhich can be examined in spoil heaps at the SirJohn’s Mine GCR site. The Blagill Mine GCRsite lies in the outermost zone of the orefieldand is the type locality for barytocalcite. Finespecimens of barytocalcite are also found at theFoster’s Hush GCR site, where small exposuresof the mineral can be observed in situ in the parent vein, while the Closehouse Mine GCRsite represents a barium-rich mineral depositwhich includes a replacement of the Whin Sillintruded into the Lunedale Fault. Althoughlying outside of the Alston Block and in theNorthumberland Trough, the SettlingstonesMine GCR site, notable for the occurrence ofwitherite, and the Fallowfield Mine, alsonotable for witherite but especially for alstonite,are considered to represent the outermost zoneof the Alston Block mineralization, while spoilheaps at the Stonecroft Mine GCR site provide

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evidence of the lead and zinc mineralizationassociated with the Stublick Fault Zone.

The geological history of the Askrigg Block issimilar in most ways to the Alston Block,although the zonal distribution present in theAlston Block is by no means as discernable. TheGunnerside Gill (potential) GCR site, inSwaledale, represents a typical fissure-vein lead-fluorite-barite deposit, while the Greenhow(Duck Street) Quarry GCR site, at the southern-most extremity of the Askrigg Block, providesone of the finest examples of galena-fluorite vein mineralization in the area. At the easternmostand westernmost extremity of the Askrigg Blockoccur copper-bearing mineral veins, seen at theBlack Scar and Cumpston Hill North andSouth Veins GCR sites.

It is possible that this episode of mineraliza-tion has an expression farther to the west, in theLake District, where rich lead-zinc-dominatedmineralization is present, which has been estimated to be of Carboniferous age (Stanleyand Vaughan, 1982a). This episode of minerali -zation is especially well-developed at the ForceCrag Mine and Eagle Crag GCR sites.

The age of MVT mineralization farther south, in the South Pennine, or Peak District,Orefield is more contentious. Various lines ofevidence have suggested that the mineralizationmay be younger than that in the NorthernPennine Orefield, perhaps in the Triassic toJurassic age bracket. However, geothermal modelling and consideration of high heat-flowsassociated with extensive magmatic activityacross northern England favour a Westphalian toStephanian age. The mineralization, which isdominated by a simple sulphide mineralogy ofgalena and sphalerite, occurs principally inveins, which range from a millimetre to a fewmetres in thickness, and the veins commonlyshow crustiform textures. In addition, there area number of important flat deposits where shaleor volcanic horizons have acted as acquicludes.The mineralization is present chiefly in limestones of Asbian to Brigantian age and iscontrolled principally by stratigraphical andlithological, rather than structural, controls. Wall-rocks adjacent to veins are sometimes silicified.

The best example of vein mineralization in the South Pennine Orefield is seen at theDirtlow Rake and Pindale GCR site. Thismajor hydrothermal fissure, lying to the south ofCastleton, can be traced for over 6 km, and

varies between 3 m and 12 m in width. The site isimportant for showing a wide variety of minerali -zation styles, including breccia domes with silicafloors, as well as chimneys and pipes. In contrast, the mineralization at the Masson HillMines GCR site is an excellent example of areplacement fluorite-galena flat, where minerali -zing fluids have been trapped in limestonesbetween lavas and bentonites (‘wayboards’).Lavas, and to a lesser extent, mafic sills, occuracross the orefield, and at the Calton Hill GCRsite volcanic rocks contain a rare assemblage ofspinel lherzolite and harzburgite nodules.

Overall the South Pennine Orefield is hostedby a structure called the ‘Derbyshire Dome’, agentle anticlinal structure which is surroundedon all sides by younger Namurian strata. Small,peripheral anticlines expose inliers of Viseanlimestones, such as in the Ashover Anticline.These anticlines show crestal mineralizationassociated with hydrocarbons, as at the Fall HillQuarry GCR site, and provide an importantinsight into fluid-migration modelling. Fluoriteis common in mineralization at the crest of theDerbyshire Dome, and the unique variety ‘BlueJohn’ is found at the Treak Cliff GCR site, whileat the nearby Windy Knoll GCR site fluorite isaccompanied by a variety of solid and liquidhydrocarbons, possibly reflecting ponding of fluids in a structural trap.

There has been considerable debate not onlyconcerning the age of mineralization associatedwith the Derbyshire Dome but also as to thesource of the fluids. Originally a magmaticsource was favoured. The generally acceptedmodel now, however, is one of their derivationfrom adjacent sedimentary basins. Cycles ofactive rifting, thermal subsidence and basininversion would have been conducive to theexpulsion of fluids from the rapidly buried sediments. There has been much discussion asto which basin might be the source of the lead-zinc-fluorite-bearing fluids, including the NorthSea basins, or, closer to the Derbyshire Dome,the East Midland Basin, the Edale Gulf and theWidmerpool Trough. An apparent anomaly inthis model is the MVT mineralization at theEcton Copper Mines GCR site, which representsone of the few sites in England where copperwas worked from limestones of Carboniferousage. The Ecton Copper Mines lie on the marginof the Cheshire Basin, and hence a derivation offluids from the Cheshire Basin or the Irish SeaBasin has been proposed.

Mineralization in England and Wales: an introduction

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Further MVT mineralization occurs to thewest of the Cheshire Basin, in the North-eastWales Orefield, and indeed may be of similarderivation, with basinal fluids being driven outof the Cheshire Basin and the Irish Sea Basin.Again, the timing of mineralization is not whollyclear, but it is considered to be ‘Variscan’, whichaccords with ages from some of the lead-zincmineral veins in the Central Wales Orefield,which may well represent the deeper structuralexpressions of the carbonate-hosted veins, pipesand metasomatic flats seen in carbonate rocks ofCarboniferous age, as for example at the HalkynMountain GCR site. Here the mineralizationcomprises a simple galena-sphalerite-fluoriteassemblage, whilst farther to the south-east itbecomes dominated by sphalerite with quartz as a major gangue phase, as seen at the PoolPark and South Minera Mines GCR site.Mineralization at the Great Orme CopperMines GCR site is a further carbonate-hostedMVT deposit, but in this case copper is the dominant ore, and the deposit is considered tobelong to the ‘copper-dolomite’ class. ThePennant Mine GCR site, lying near to the out-crop of the mineralized Halkyn Mountain, showsbarite-witherite-calcite-sphalerite-galena-chalcopyrite mineralization cutting Silurian strata, which might well represent the deeper-level expression of the MVT mineralization, theveins having the same east–west orientationwhich predominates in the structurally higher-level Carboniferous sequences. The HuglithMine GCR site, in the West Shropshire Orefield,may also be related to this style of mineralizationbut at a deeper structural level, where copperand barite mineralization cutting Neoproterozoicquartzites is considered to be of Carboniferousage. The related nearby Snailbeach MineGCR site shows a greater abundance of galenaand also bitumens that might relate to aCarboniferous petroleum reservoir system.

As mentioned earlier, the Central WalesOrefield shows evidence of two mineralizingevents, the A1 (‘Early Complex’) veins of probable early Devonian age, and the A2 (‘LateSimple’) veins, of probable early Carboniferousto Permian age. The latter sometimes occupythe same lodes as the former, providing evidence of cross-cutting relationships and forthe re-activation of previously existing structures, such as at the Brynyrafr Mine andCwmystwyth Mine GCR sites. The A2 veinsshow simple galena-sphalerite-chalcopyrite

parageneses cutting brecciated mudstones, bestseen at the Ceulan Mine Opencast GCR site.Commonly the A2 mineralization shows crustiform textures similar to those in the MVTdeposits of the Pennine orefields. These are bestdeveloped at the Nantiago Mine GCR site. Arare A2 assemblage variation, containing ‘giant’quartz crystals, is present at the NantymwynMine GCR site.

Late Carboniferous times saw the generationof a foreland basin in South Wales, linked to theadvancing Variscan Orogen. High sedimentinputs led to thick accumulations of sandstonesand shales which, along with the compaction of abundant vegetation in fluvial and deltaic environments, led to the development of thethick sedimentary sequences of Namurian,Westphalian and Stephanian age. Claystone–ironstones of diagenetic origin developed andwere worked from numerous horizons in strataof Westphalian age, and indeed their presencewas fundamental to the industrial revolution inthis part of Great Britain. The claystone– ironstone horizons are important for the rangeof minerals present in cavities and cracks in thenodules, which contain well-crystallized, some-times doubly terminated quartz crystals, alongwith a range of sulphides, including galena,sphalerite, chalcopyrite, pyrite and marcasite, aswell as siegenite and millerite. Specimens ofneedle-like millerite sprays from South WalesCoalfield claystone–ironstone nodules are present in most major mineralogical museums.Academically the nodules are important becauseof the information that can be gained from studies of fluid inclusions in quartz and carbonate crystals, which permit modelling offluid flow in the evolving basin (Alderton andBevins, 1996; Alderton et al., 2004).Unfortunately, because of the demise of the coalindustry in Great Britain, accompanied by thelarge-scale removal of coal waste tips across theregion, there are no sites suitable for conserva-tion of the claystone–ironstone mineralization.

In latest Carboniferous times the major north-wards thrusting and propagation in southernBritain culminated in the Variscan Orogeny,which was followed by the emplacement of amajor intrusive body known as the ‘CornubianBatholith’. This occurred in the period295–270 Ma, and was accompanied by major,long-lasting hydrothermal activity which generated the wide range of mineral depositsseen in the South-west England mineral

Mineralization history of England and Wales

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province. A date of 269 ± 4 Ma has been proposed for the age of the main phase of mineralization. The evolution of this provincehas been reviewed and modelled by Alderton(1993), and more recently by Scrivener (2006).

Although carbonate-bearing rocks are relativelyrare in the region, small-scale, localized skarnsdid develop as a result of contact metasomatismand metamorphism during emplacement of thebatholith. The magnetite-hornblende depositsat the Haytor Iron Mine GCR site are an example of a skarn development of unusualnature for the mineral province. A site of international mineralogical interest is the Red-a-Ven Mine GCR site, lying at the north-west margin of the Dartmoor Granite, where LowerCarboniferous cherts, shales and minor lime-stones have been contact metamorphosed andmetasomatized. It appears that an initial chalcopyrite-arsenopyrite-pyrrhotite skarn hasbeen affected by later boron-rich fluids and further skarn development, leading to the presence of a range of rare mineral assemblagesand skarns with anomalously high tin levels.

Pegmatites and aplites developed during thefinal stages of consolidation of the granite. TheTremearne Par GCR site provides an excellentdemonstration of pegmatite-aplite relationshipswith the country rocks surrounding theTregonning–Godolphin Granite, while theTrevalour Downs Pegmatite GCR site showsthe development of large Li-rich micas. Of inter-national importance is the Meldon ApliteQuarries GCR site for being a unique examplein Great Britain of a sodium-potassium-lithiumaplite, containing a wide range of rare minerals,although as noted below a degree of cautionneeds to be exercised with some of the previously published accounts describing mineral occurrences from this locality and anumber of other localities described in this volume.

Greisens, sheeted-vein systems and stock-works are common in the province and havebeen considered to be relatively early featuresand accompany hydraulic fracturing of the hostrock. Both granite-hosted (endogranitic) andsediment-hosted (exogranitic) greisens occur,the former being observable at the CameronQuarry and St Michael’s Mount GCR sites,while the Mulberry Down Opencast exposesan exogranitic greisen and a low-grade tin stock-work. Spectacular greisen-bordered tin andtungsten veins occur at the Cligga Head and

the Great Wheal Fortune GCR sites.Tourmalinization is also widespread across theregion, as at the Nanjizal Cove GCR site, whilethe Priest’s Cove GCR site offers the opportunityto compare the genesis of magmatic tourmalinewith mineralized tourmaline development ofhydrothermal origin.

The main-stage mineralization is representedby steeply dipping fissure-veins which trendeast–west in the eastern part of the province,north-east–south-west in the central area, andnorth-west–south-west in the west and whosethickness is highly variable but perhaps mosttypically in the range 1–2 m. Individual lodestructures can sometimes be traced for a fewkilometres; the Devon Great Consols GCR siteis an exception, with the copper-bearing lodebeing worked over almost 4 km of continuoussection. They are dominated by tin and copper,but also carry tungsten, arsenic, lead and zinc.There is evidence for both lateral and verticalzonation, especially in relation to tin and copper, as seen in relationships between main-stage tin-copper mineralization at the CliggaHead, Trevaunance Cove, Cameron Quarryand Wheal Coates GCR sites. Copper-tin-arsenic main-stage mineralization is well developed at the Devon United Mine GCR site,with the arsenic possibly being derived fromunderlying mafic igneous rocks.

Some sites in the South-west England mineralprovince show evidence of multiple mineralizingepisodes; for example at the Penlee Quarry GCRsite four mineralizing events can be discerned,namely early pegmatites, contact metamorphism,main-stage tin-copper minerali zation, and finallylate cross-course mineralization (see below). Itis the Botallack Mine and Wheal Owles GCRsite that perhaps shows the greatest variety andrepresentation of mineralization events in theprovince which makes it a site of internationalmineralogical importance, reflected by theextensive mining of the area’s lodes and itsinscription in 2006 on UNESCO’s list of WorldHeritage Sites for the mining landscape. Thissite shows the development of skarn deposits, inthe subhorizontal sheet-like tourmaline- and cassiterite-bearing ‘floors’, such as the ‘GryllsBunny’, ‘carbonas’ (localized alteration associatedwith pipe-like bodies), main-stage tin-coppermineralization, and late cross-course mineraliza-tion containing lead, bismuth and uranium.

A suite of late veins, trending approximatelynorth–south, are termed the ‘cross-courses’.

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They chiefly comprise lead and zinc, along with fluorite and barite. They occur away from thegranite bodies and are considered to be low-temperature deposits. The cross-course mineralization bears a resemblance to MVT mineralization and it appears therefore that theorigin of the fluids was most probably as a resultof dewatering of adjacent Permo–Triassic red-bed sedimentary basins. The Lockridge MineGCR site, near Bere Alston, shows a typical N–S-orientated cross-course lode, with quartz carrying galena and sphalerite, along with some sphalerite. The mine was important, however,for the argentiferous nature of the galena. ThePerran Beach to Holywell Bay GCR site is afurther example of cross-course mineralization,being well exposed in cliff sections, and comprising comby quartz, galena and fluorite,with some siderite. In the Porthleven area, theWheal Penrose GCR site is related to three parallel N–S-trending cross-course lodes carrying quartz, galena, sphalerite, chalcopyriteand arsenopyrite. An example where there is a strong likelihood of host-rock influence oncross-course fluid composition is at the SouthTerras Mine GCR site, which contains uranium-bearing minerals. It is highly likely that thesource of the uranium was the nearby St AustellGranite. Finally, at the Devon United MineGCR site both main-stage and cross-course mineralization episodes can be discerned, thelatter ‘heaving’, or displacing, the earlier mineralized structures.

The effects of the Variscan Orogeny led to dramatic changes in the palaeogeography andclimate in early Permian times, combined with asteady northwards drift, away from the equatorialrainforest belt of the late Carboniferous period.The climate became more arid, and desert environments predominated. Critically, extensionmost probably linked to the onset of rifting ofthe proto-Atlantic led to the development of aseries of isolated and interconnecting basins. ByLate Permian times, a southwards transgressionfrom the Arctic Sea had led to the developmentof the Zechstein Sea (in the North Sea region)and the Bakevellia Sea (in the Irish Sea region).Similar conditions persisted into Triassic times,when, however, connections to a sea weresouthwards, to the Tethys Ocean. Within and atthe margins of these seas thick deposits of economically important evaporites developed,including gypsum, anhydrite, halite, K-rich salts(carnallite and sylvite) and celestine. The Ben

Knowle and Gipsy Lane Brick Pit GCR sites arerepresentative of evaporite develop ment in LateTriassic times. Beds and nodules of gypsumoccur in the Mercia Mudstone Group at GipsyLand Brick Pit. At Ben Knowle, gypsum andanhydrite in beds of similar age were convertedto celestine by the diagenetic addition of strontium from a Carboniferous source. TheWarren Quarry GCR site is a unique location forthe presence of the clay mineral palygorskite,which is thought to have precipitated at thejunction between Caledonian hornblendetonalite and mudstones of the Mercia MudstoneGroup as a result of weathering in an arid environment during late Triassic times.

Dinantian limestones in western and southernCumbria, the Forest of Dean, South Wales andthe Mendips contain important iron oxide(along with subordinate manganese) deposits,the age of which is still a matter of some debate.The most important economically were thehematite ores of the Cumbrian Orefield, whichoccur in a variety of forms, namely as veins alongfaults, stratiform replacement flats, and ‘sops’,which are dish-like dissolution hollows of karsticorigin, and which are unique to southernCumbria. It is currently considered that thesource of the iron was as a result of convectiveleaching of Permo–Triassic red-bed successionsin the Irish Sea Basin, with highly saline basinalbrines being driven up-dip by convection. Thetiming has been placed anywhere between pre-Permian to post-Triassic. The Florence MineGCR site in Cumbria provides the best exampleof replacement mineralization in the CumbrianOrefield, as well as being the source of excellentmuseum-quality specimens, especially of ‘kidneyore’ hematite. The hematite mineralization alsohas an expression in the underlying LowerPalaeozoic strata, being seen as veins comprising‘kidney ore’ hematite at the Nab Gill Mine GCRsite.

In South Wales, a series of hematite-goethitereplacement deposits in Dinantian limestoneswere worked at a number of mines in theLlanharri area, the largest being the LlanharryMine which closed as late as 1974. There is verylittle exposure remaining at any of the minedsites, although examples of the mineralizationdo occur at the Mwyndy Mine GCR site, withsimilar mineralization being seen in the Mendipsarea, at the Compton Martin Ochre Mine, theBanwell Ochre Caves, and the Hartcliff RocksQuarry GCR sites. There has been considerable

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debate not only concerning the origin of thisiron and manganese mineralization episode butalso its age. Evidence from the Ogmore CoastGCR site has helped constrain the age as beingpre-Jurassic, as syngenetic early Jurassic mineralization at that locality cuts limestonescontaining hematite veinlets and staining. Onthe basis of fluid-inclusion studies on samplesfrom Llanharry Mine the fluids are currently considered to be related to mixing of low-temperature, highly saline iron-bearing ground-waters with warmer, dilute fluids driven out ofthe adjacent Coal Measure sequences. It is infact considered that this episode of iron mineralization adjacent to the Permo–Triassicbasins may be linked to crustal extension associated with the opening of the proto-Atlanticin late Triassic times.

In the Cheshire Basin, continental aeolian andfluvial sandstones of mainly Mid-Triassic age inthe Sherwood Sandstone Group host a wide-spread barite mineralization and more localizedoccurrences of low-grade, Cu-dominated base-metal ores that are representative of the sediment-hosted, red-bed category of ore deposits. Thelatter are dominated by secondary species thatresult from alteration of primary sulphides andconsist mainly of copper carbonates, with arsenates, oxides and hydroxides containingcopper, lead, zinc, cobalt, nickel, vanadium andother elements. Mineralization is epigenetic andregarded as the result of the mixing of chloride-rich basinal brines and hydrocarbon fluids in thesandstones in structural traps beneath a sealformed by impermeable sediments of the over -lying Mercia Mudstone Group. Primary minerali -zation is regarded as having occurred either inLate Triassic to early Jurassic times or in the lateJurassic, with secondary alteration occurring inTertiary times in both cases. The Alderley EdgeDistrict GCR site is the classic site for the examination of this style of mineralization inGreat Britain and is uniquely accessible.

Evidence for a Mississippi Valley-type mineralizing episode is seen in the Mendip Hillsand Bristol area, extending across into SouthWales. It was veins associated with this eventthat led to the extraction of lead in these regionsas early as Roman times. The age of mineraliza-tion has been the subject of considerable debatebut there is now sufficient evidence to argue foran early Jurassic age. Critical evidence for thisage is seen at the Ogmore Coast GCR site,where syngenetic MVT is present which

indicates that fluids were exhaled into marginalLiassic sediments. Elsewhere in South Wales,this style of mineralization is seen exposed at theMachen Quarry GCR site. In the Mendipsregion, the Charterhouse Lead Orefield,Banwell Caves and Clevedon Shore GCR sitesare representative of this mineralizationepisode. The Wurt Pit GCR site is a large karstcollapse feature which exposes silicified lime-stones of early Jurassic age. The fluids responsiblefor the silicification are considered to be thoseresponsible for the Mendip Hills MVT deposits.The fluids responsible for the mineralization inSouth Wales are thought to have been basinalbrines expelled from the Bristol Channel Basin,while recent isotopic studies by Haggerty et al.(1996) have not only supported derivation ofthe Mendip Hills MVT fluids from basins ofMesozoic age but they conclude that a numberof different basins were involved, including theWessex Basin, the Central Somerset Basin, andagain the Bristol Channel Basin.

An anomalous episode of mineralization, carrying many rare mineral species, is seen at the Dolyhir Quarry GCR site, in the WelshBorderland. The nature of the mineralizationand its association with carbonates suggest thatit too might be an episode of MVT mineraliza-tion, possibly of the same age as the South Walesveins, with the fluids derived similarly from theBristol Channel Basin. This requires furtherstudies, however.

Many mineral deposits in England and Waleshave been subject to some form of weathering, especially the upper parts of the bodies, abovethe contemporary water-table, which have beenaffected by oxidation processes. The classicextreme end result of such processes is theleaching of most metals with the exception ofiron, leading to the development of a gossancapping to the ore deposit. Such a gossanoccurred at the Parys Mountain GCR site,which was particularly rich in fine specimens ofthe lead sulphate mineral anglesite and forwhich the site is the type locality. Remnants ofgossanous horizons are found elsewhere inWales, namely at the Frongoch Mine and theLlechweddhelyg Mine GCR sites, in the CentralWales Orefield, although it is likely that mostgossan cappings were removed in this area bythe effects of glaciation. In other cases metalsleached from the metalliferous minerals in ore-bodies have been transported downwards insolution, to precipitate above the contemporary

Mineralization in England and Wales: an introduction

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water-table as a variety of carbonates, sulphates,phosphates and arsenates. The Machen QuarryGCR site is renowned for the evidence of super-gene alteration of lead-bearing veins which arenow exposed by active quarrying. Spectacularanglesite crystals have been recovered from thislocality. In the Lake District the Red Gill Mine,Drygill Mine, and Roughtongill Mine GCRsites are widely recognized for the museum-quality lead, copper and zinc carbonates, sulphates, phosphates and arsenates of supergene origin, while in South-west Englandthe Penberthy Croft Mine GCR is of particularnote for the extreme range of supergene minerals present and the Wheal Alfred GCR siteis acknowledged as having yielded the finestpyromorphite specimens in the province. In the Northern Pennine Orefield supergenesmithsonite was worked from a deposit unique inthat area at the Pikedaw Calamine and CopperMines (potential) GCR site, while the WillyholeMine GCR site is of importance for the develop-ment of supergene greenockite derived from thealteration of sphalerite. A unique mineraldeposit of supergene copper mineralization isdeveloped at the Turf Copper Mine GCR site inNorth Wales, where in post-glacial times copperhas been leached from the largely hidden Coedy Brenin porphyry copper deposit and precipitated as native copper replacing organicmatter in a developing peat bog.

If copper-bearing solutions descend belowthe contemporary water-table and interact withprimary copper sulphides secondary enrichmentcan occur, leading to the generation of mineralssuch as bornite and djurleite, as seen at the BirkFell Hawse Mine, Seathwaite Copper Minesand Dale Head North and South Veins GCRsites in the Lake District, and the Alderley EdgeDistrict GCR site in Cheshire. Similar enrichmentprocesses are indicated to have occurred at theNewhurst Quarry GCR site in Leicestershire,where remnants of a chalcocite-bornite super-gene paragenesis is almost totally obliterated bya later oxidized association of copper salts.

It is clear that some of the supergene mineraldevelopment is of post-mining age; in othercases the age of the mineralization is equivocal.It has been suggested that some of the supergene alteration in the Lake Districtoccurred in Jurassic times, while the manganese

mineralization at the Mynydd Nodol Mine GCRsite in North Wales is thought to have developedfrom the leaching of Ordovician volcanic rocks inTertiary times. Two sites of mineralogical interest in Derbyshire have a part of their historylinked to processes operating as recently asPliocene–Pleistocene times. At the PortwayGravel Pits GCR site a solution-related collapsefeature on a mineralized vein, thought to havedeveloped in Pleistocene times, is filled withblocks of limestone and a distinctive quartz rock.At the Kirkham’s Silica Sandpits GCR site, theMiocene–Pliocene Brassington Formation comprises silica sands and kaolinitic clays ofcommercial value, and the site is noted for thepresence of the clay mineral metahallyosite,although its exact origin is not currently under-stood.

Finally, and very unfortunately, caution mustbe exercised in relation to the recording of mineral provenance, which has been highlightedby the deception that has been uncovered inrelation to specimens from the collection of thelate Arthur Kingsbury, now housed in theNatural History Museum. It has come to lightthat Kingsbury falsified the provenance of a significant number of his specimens, a situationwhich has only really come to light in the last10 years or so, following the detailed investiga-tions of the late George Ryback and curatorialstaff at the Natural History Museum (Ryback etal., 1998, 2001). Tindle (2008) has recently provided the most detailed information relatingto the scale of the fraud. What is relevant to this volume is that caution is required whenever siteaccounts describe mineral occurrences whichare based on published reports by Kingsbury.Some ten GCR mineral sites are in some wayimplicated to a greater or lesser degree in thisunfortunate situation, namely South TerrasMine, Carrock Mine–Brandy Gill, MeldonAplite Quarries, Tynebottom Mine, HingstonDown Quarry and Hingston Down Consols,Cligga Head, Red-a-Ven Mine, Alderley EdgeDistrict, Roughtongill Mine and High DownQuarry. In addition, of course, there have beensubsequent studies which have been based onKingsbury specimens, some of which now carrysuspect results, and finally Kingsbury donatedspecimens to others and so there may be fraudulent details in other mineral collections.