Mines with Slate and Regional Metamorphism

33 linked mines · Geology: Slate and Regional Metamorphism

Listed only where MineArchive's own research gives a reasonable evidential basis for the connection — not every mine where this geology might plausibly apply.

Mine	Region	Worked	Commodities	Connection
Bagalow Quarry	Cornwall	1834–Early 20th century	Slate, Limestone	(well documented example) Upper Devonian and Lower Carboniferous mudstones recrystallised so that they split along a cleavage cutting across the bedding — the process that makes a roofing slate, and the reason this cliff was worth working.
Ballachulish Slate Quarries	Highland	1693–1955	Slate	(well documented example) The mine's own recorded geology explicitly describes a metamorphic rock formed from Dalradian-age mudstones.
Bank Wood Quarry	Cumbria	1902–Abandoned by 1905	Slate	(well documented example) The quarry worked Borrowdale Volcanic Group slate, the regionally metamorphosed Ordovician tuffs of the central Lake District.
Bellstone Quarry	Pembrokeshire	1825–Disused by 1891	Slate	(well documented example) The quarry worked the slate of the Preseli Hills at the south-western end of the Welsh slate belt, on the same hillside as Rosebush.
Boscastle Slate Quarries	Cornwall	No reliable opening date has yet been located.–No reliable closure date has yet been located.	Slate	(well documented example) Lower Carboniferous slates of the Barras Nose formation resting on Upper Devonian rocks, the best of them blue and green at the foot of the cliffs.
Braichgoch Slate Mine	Gwynedd	1787 (lease); working at Braich Goch from 1836–1970 or 1971	Slate	(well documented example) The mine worked slate of the Cambrian slate belt of Snowdonia, the regionally metamorphosed sequence worked across the Corris quarries.
Cilgerran Quarries	Pembrokeshire	Worked by the 19th century; the stone used since the medieval period–No reliable closure date has yet been located.	Slate	(well documented example) The quarries worked the slate exposed in the gorge the Teifi has cut below Cilgerran, a hard building stone rather than a fine roofing slate.
Coetmor Quarry	Gwynedd	Before 1850–1860s (absorbed by Pantdreiniog)	Slate	(historical documentary reference) One of the smaller workings in the Cambrian slate belt of Dyffryn Ogwen; the link rests on the quarry's location and commodity rather than on any description of its own veins, none having been found.
Cove Quarries, Coniston	Cumbria	By c. 1855 (local account); returned from 1900–Sep 1934 (List of Mines); worked into mid-20th c. by local account	Slate	(historical documentary reference) The Cumbria Industrial History Society describes the Old Man's silver-grey slate as cleaved tuffs of the Borrowdale Volcanic Group.
Croesor Quarry	Gwynedd	1846 (small-scale); companies formed by 1861–1930	Slate	(well documented example) The mine's own recorded geology explicitly describes working slate beds within the Cambrian slate belt of Snowdonia.
Deeside and Moelfferna Quarries	Denbighshire	Deeside 1870, Moelfferna 1876–1947	Slate	(well documented example) The quarries worked the north-eastern end of the Ordovician slate belt that runs across mid Wales from Tywyn to Chirk, where shales and mudstones were compressed and metamorphosed into slate.
Delabole Slate Quarry	Cornwall	from Working recorded from at least the mid-1200s	Slate	(well documented example) Devonian mudstones cleaved to slate — and cleaved so consistently over so large a body that one pit could be worked for seven centuries without moving.
Diphwys Casson Quarry	Gwynedd	1760s (Methusalem Jones)–Sources disagree: Coflein and a 2020 site survey both give small-scale extraction continuing to 1925	Slate	(well documented example) Diphwys Casson worked Ordovician slate veins typical of the wider Ffestiniog district's regionally metamorphosed mudstone sequence.
Dorothea Quarry	Gwynedd	1820s–1970	Slate	(well documented example) A textbook case of cleavage controlling mine design: the Nantlle slate stands near-vertical, so Dorothea had to be worked as deep pits below the water table rather than as hillside chambers.
Easdale Slate Quarries	Argyll and Bute	1745 (earlier working recorded from 1168)–1911 (Easdale quarries); wider Slate Islands industry to 1950s	Slate	(well documented example) The mine's own recorded geology explicitly describes working Dalradian slate.
Gillow Slate Quarry	Cornwall	Possibly from the 17th century–Disused by 1896	Slate	(well documented example) Upper Devonian and Lower Carboniferous mudstones recrystallised so that they split along a cleavage across the bedding — the metamorphic process that makes a roofing slate, as this record's geology describes.
Honister Slate Mine	Cumbria	from Late 17th century	Slate	(well documented example) Borrowdale Volcanic Group ash cleaved into slate — the same process as Wales, but on volcanic rock rather than mudstone, which is where the green comes from.
Lag Bank Quarry	Cumbria	Returned from 1927–Returned to 1945; no closure date located	Slate	(well documented example) Coniston green slate is metamorphosed Borrowdale Volcanic Group ash, the regionally metamorphosed sequence worked across the central Lake District.
Llechwedd Slate Caverns	Gwynedd	1846–1970s (working quarry); reopened 1972 as a visitor attraction	Slate	(well documented example) The mine's own recorded geology explicitly describes working Cambrian slate beds.
Llwyngwern Quarry	Powys	By 1828–1941	Slate	(well documented example) The quarry worked a minor outcrop of the Ordovician slate belt on the western flank of Mynydd Llwyn-gwern, away from the main veins around Corris and Aberllefenni.
Marchlyn Quarry	Gwynedd	Late working of Dinorwic; no opening date located–1969 (with Dinorwic)	Slate	(well documented example) Marchlyn worked the Cambrian slates of the Llanberis belt, cut as galleries into the mountainside in the Dinorwic manner rather than mined in chambers.
Oakeley Quarry	Gwynedd	1818 (Holland's original lease); consolidated as Oakeley Quarry in 1883–1969 (underground); final closure 2010 (surface, after subsidence)	Slate	(well documented example) The mine's own recorded geology explicitly describes working the Cambrian slate beds of the Ffestiniog district.
Palmerston Quarry	Gwynedd	1825 (Welsh Slate Company lease)–1883; absorbed into Oakeley	Slate	(well documented example) A single Cambrian slate vein reached at different heights on the mountain above Rhiwbryfdir by three separate quarries, Palmerston being the lowest and running directly beneath the Middle Quarry in the same vein; worked underground in chambers from 1840 once surface slate was exhausted.
Pen-yr-Orsedd Quarry	Gwynedd	1816–1979	Slate	(well documented example) Near-vertical Cambrian cleavage again dictating the mine plan: deep pits rather than hillside chambers, and therefore a permanent haulage problem that the Blondin was bought to solve.
Penmachno Quarry	Conwy	1818–1962	Slate	(well documented example) Ordovician slate of the Ffestiniog district's north-eastern edge, worked in the North Vein from galleries and underground chambers.
Penrhyn Quarry	Gwynedd	1770s–Still active	Slate	(well documented example) The mine's own recorded geology explicitly describes working a major deposit of Cambrian slate.
Quay Foot Quarry	Cumbria	Working by the mid-19th century–Not returned after 1930	Slate	(well documented example) Borrowdale Volcanic ash and tuff compressed until it splits along a cleavage — the green slate of the valley, whose veins run from Honister down to small workings like this one, as this record's geology describes.
Rhosydd Quarry	Gwynedd	worked from 1840; Rhosydd Slate Company formed 1853–1930 (final reopening attempt failed 1948)	Slate	(well documented example) The mine's own recorded geology explicitly describes the Old Vein as part of the Cambrian Ffestiniog Flags, ash and mudstone cleaved by regional metamorphism into workable slate.
Tilberthwaite	Cumbria	worked from the late 16th/early 17th century (Elizabethan)–copper mining ceased 1942; slate quarrying continued intermittently to 2001	Copper, Lead, Slate	(well documented example) The mine's own recorded geology explicitly describes slate quarried from the district's Ordovician rocks.
Tintagel Slate Quarries	Cornwall	15th century–1937	Slate	(well documented example) The record describes Upper Devonian and Lower Carboniferous slate worked for roofing along the north Cornish coast, with the quality varying systematically with height in the cliff — the slate near sea level being better than that above.
Troutbeck Park Green Slate Works	Cumbria	In the returns from 1883–Standing by 1894	Slate	(well documented example) The works took Lakeland green slate of the Borrowdale Volcanic Group, volcanic ash compacted and cleaved by later earth movement so that it splits along the cleavage.
Votty and Bowydd Quarry	Gwynedd	Bowydd worked from c. 1800, commercial from 1833; merged with Votty in 1870–1963	Slate	(well documented example) The mine's own recorded geology explicitly describes Cambrian slate beds of the Ffestiniog district.
Yew Craggs Quarry	Cumbria	Working by the early 18th century–Closeheads abandoned 1963	Slate	(well documented example) Borrowdale Volcanic ash and tuff compressed until it splits along a cleavage — the green slate of Honister, whose veins run from crag to crag across the hause as this record's geology describes.

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