The Carrock Fell Tungsten Veins

THE CARROCK FELL TUNGSTEN VEINS

The UK’s only tungsten producer outside of Cornwall & Devon

Colin J Andrew Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014

Lough Doon Carrock Crossdoney

Ballinglen

Cligga Castle an Dinas Hemerdon

Tungsten mineralization in the British Isles Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 History

MillMine in 1915 Workings & Plant 1913 Miners at Carrock in 1911

. Carrock Mine, was probably the first location in the UK to be worked primarily for tungsten. It was tried initially as a lead / copper prospect in the 1850’s and 1870’s but soon failed and was then re-opened for tungsten in 1902, being taken over by the German-run “Cumbrian Mining Company” in 1906. In 1913 British interests took over and the mine was worked for the duration of the First World War. Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 History

Miners at Carrock in 1942

. In 1942 as renewed conflict increased demand for the metal, which resulted in the Ministry of Supply conducting exploratory work by sappers of the Royal Canadian Engineers, who drove some 790m of horizontal and vertical development to define approximately 51,500 tonnes grading 1.29% WO3 the mine did not go into production and was abandoned the following year. Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 History Mill under construction in 1972

. Further underground development work was carried out in the early 1970’s and a new mill erected, but the mine closed shortly after. Renewed interest in April 1977 led to further exploratory work and the mine was reactivated at a mining rate of ~16,000tpa before it closed in October 1981 subsequent to a dramatic fall in the price of tungsten concentrates and the plant dismantled and site cleared in Spring 1988.

. During its life the mine yielded over 110,000 tonnes of ore grading 1.08% WO3 Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014

Carrock Fell in March 1972.

Entrance to the “Canadian” or No. 1 crosscut (left) View up Grainsghyll towards the plant under construction (above) Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014

View from Coomb Height, January 1980 Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014

View along Harding North, No. 1 Level. Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014

Mining in 1977 Mining in 1977

View along Harding North, No. 1 Level. Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014

Carrock Fell, today. Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 Geological Setting . The Lake District lies in the southern paratectonic Caledonide belt of northern England.

. Ordovician flysch-type turbidite greywackes of the Skiddaw Group are succeeded conformably by tholeitic submarine volcanics of the Eycott Group.

. The Eycott Group is overlain unconformably by the Borrowdale Volcanic Group comprising calc- alkaline volcanics of Llandeilo age overstepped by a thick sequence of Silurian turbidite greywackes.

. The Carrock Fell Complex is a lensoid mass of gabbros and related granophyric hybrids elongated parallel to the local Caledonian trend and thought to be pene-contemporaneous with the Eycott volcanics. Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 Regional Geology

. End-Silurian polyphase orogenic deformation was followed by the emplacement of early Devonian discordant, post-tectonic granites (Skiddaw, Shap and Weardale). Regional gravity surveys suggest they coalesce with Ordovician granites (Eskdale and Ennerdale) at depth to give an extensive composite batholith beneath the Lake District. . The Carrock Fell deposit is genetically and spatially related to the post-tectonic Skiddaw Granite (398±8 Ma), a peraluminous biotite granite pluton. Rundle – (1992) Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 Lake District Granites

Skiddaw Granite

Threlkeld Microgranite

Ennerdale Granophyre Shap Granite

Eskdale Granite Outcrop of granite cupolas

3D visualization of the calculated depth to the Lake District Batholith Data from M.K.Lee (1986) Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 Geological Setting

. The Skiddaw Granite is seen in three small inliers with the northernmost at Grainsghyll being variably greisenized showing a clear northwards gradation from biotite granite to greisen.

. Apatite, rutile, pyrite and arsenopyrite occur in the greisen.

After Eastwood et al (1968). Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 Age of Intrusion & Mineralization

398·8 ± 0·4 Ma and 392·3 ± 2·8 Ma (molybdenite Re–Os) T.J.Shepherd, R.D.Beckinsale, C.C. Rumdle & J. Durham (1976) D. Selby; J. Conliffe; Q. G. Crowley; M. Feely (2008) . K-Ar dating can not distinguish between cooling of the Skiddaw granite, greisen formation and tungsten mineralization (minimum age of granite intrusion, 392 ± 4 Ma; mean age of mineralization alteration, 385 ± 4 Ma) suggesting that they occurred within a relatively short space of time. Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 Local Geology

. Crossing Grainsghyll a number of well developed N-S dominantly quartz veins, carry wolframite, scheelite, arsenopyrite, pyrite, pyrrhotite, sphalerite and ankerite along with accessory molybdenite, chalcopyrite, bismuthinite, apatite, dolomite, calcite, fluorite and muscovite with rare joseite, cosalite, cassiterite and native gold. Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014

View from Coomb Height, June 1979

Smith Vein Harding Vein

Emerson Vein

“Canadian” or No 1 Level Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 Section of workings on Harding Vein

Stopes 1906-1917 25,116 tonnes mined for 19,000 MTU WO3

Stopes 1972-1978 25,000 tonnes mined for 33,000 MTU WO3

Stopes 1978-1981 60,000 tonnes mined for 67,000 MTU WO3

Average mined grade = 1.081% WO3 Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014

View along Harding North, No. 1 Level. Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014

. Mineralization is represented by a series of N-S tungstaniferous quartz veins contained within greisenized wallrock at the margin of the granite, and extending outwards into the gabbros. Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 Mineralization . Economic mineralization is usually developed over a 400-600m strike section across the granite contact, and for the Harding Vein has been proved for 150m above the main adit level. The richest ore-shoots are contained within biotite-rich melanogabbros close to the hornfels contact.

. Further north, within the leucogabbros, ore-shoots are confined to narrow E-W belts of pyroxene-hornblende granulites considered to be relic masses of andesitic lava incorporated into the gabbro magma (“kersantites”).

Section on Harding Vein showing ore shoots (stopes) Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 Mineralization

. In the greisen the veins appear to occupy master joints with well defined walls.

. On passing into the highly fractured gabbros the veins become strongly braided, with individual components showing a complex, short time-scale chronology, suggesting repeated opening along the same fracture zone. Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 Mineralization

. The veins are associated with extensive zones of pervasive argillic wallrock alteration and are also extensively finely veined by ferroan dolomite. Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 Vein Mineralization Styles

Comb-like groups of wolframite blades (35 to 55 mol.% hubnerite) Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 Vein Mineralization Styles

Rich early wolframite quartz vein in greisenized granite. Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 Vein Mineralization Styles

Both early wolframite-bearing quartz and later arsenopyrite / marmatite / scheelite Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 Vein Mineralization Styles

Complex multi-stage vein with late ankerite-fill Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 Vein Mineralization Styles

Some vugs in the early quartz veins were sites for deposition of scheelite and sulphides before becoming filled by late carbonates. Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 Carrock Scheelite / Wolframite

Daylight and SW UV Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 Carrock Scheelite / Wolframite

SW UV Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 Carrock Scheelite

Daylight Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 Carrock Scheelite

SW UV Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014

JoseiteJoseite Krupkaite

. Many rare bismuth sulphosalts have been recorded in the Carrock veins including Joseite A and B, Cosalite, Krupkaite, Aikinite, Ingodite, Grunlingite, Hedleyite Cosalite Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 Vein Mineral Paragenesis

STAGE 2 Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 Mineral Paragenesis

. In the veins, a wolframite-scheelite-apatite assemblage pre-dates a scheelite-arsenopyrite-pyrite (plus other sulphides) assemblages.

. Contemporaneous greisenisation involved loss of Na, Cr, Ca and Ba from granite, but Si and K were retained while B, Be and Al increased slightly. Sn also increased but is always a trace constituent, and F appears to have decreased. Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 Fluid Inclusion Data

T. K. Ball , N. J. Fortey & T. J. Shepherd (1985)

Temperatures of mineralization declined from a peak near 350oC to 170oC, and the hydrothermal fluid contained about 6 wt% NaCl and 3 wt% NaHCO3. Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 Fluid Inclusion Data

400 Early 40 Scheelite

Apatite 30

300 Quartz Quartz o 20 Th C Ankerite Early

Sulphides Number Quartz 10 200 Early Scheelite Fluorite Ankerite Fluorite Early quartz 0 Apatite

100 80 160 240 320 Relative Time o Th C

T. K. Ball , N. J. Fortey & T. J. Shepherd (1985)

80 T. K. Ball , N. J. Fortey & T. J. Shepherd (1985)

70 2 60 Margin / CO

450 Centre O

2 50 H

30 -250 -200 -150 -100 -50 0 50 100 150 200 250 300 350 400 450

Increase in water to CO2 ratios away from contact Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 Hydrothermal Fluids

. Mineralizing fluids were moderately saline with high Na/K, enriched in tungsten and periodically charged with CO2; compared with magmatic fluids the mineralizing fluids were depleted in δ18O.

. During the period of quartz deposition there is a significant decrease in CO2.

. At any point along the vein, the early fluids are hottest.

. Spatial variation is related to proximity to the granite contact.

. The CO2 content of the late fluids is consistently less than that of the early fluids and is independent of wall rock lithology.

T. J. Shepherd & P. Waters (1984) Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014 Conclusions (1)

. Tungsten mineralization at Carrock Fell Mine comprises wolframite and scheelite in polyminerallic quartz veins which traverse the Grainsgill Granite cupola and surrounding country rocks. In the veins, a wolframite-scheelite-apatite assemblage pre-dates a scheelite- arsenopyrite-pyrite (plus other sulphides) assemblages.

. Temperatures of mineralization declined from a peak near 350oC to 170oC, and the hydrothermal fluid contained about 6 wt% NaCl and 3 wt% NaHCO3.

. Zones of intense alteration (greisenisation) contain high concentrations of quartz-hosted fluid inclusions resulting from penetration of the granite by fluid chemically similar to that in the vein quartz.

. The W-rich, Sn-poor nature of the mineralization may relate to the weakly saline, F-deficient but CO2-rich fluid chemistry.

. The zone of maximum flow, which extends 0-400m out from the granite contact, is characterised by high H2O / CO2 ratios and corresponds closely with the known distribution of high-grade oreshoots..

. The latest ankerite dominated stage temperatures were below 150oC, and the fluid is estimated to have contained approximately 12 wt% NaCl and 15 wt% CaCl2. Carrock Fell Tungsten Deposit IAEG Weekend Course – May 2014