Open questions: Gwynedd

Where sources disagree, MineArchive keeps both accounts rather than picking one; where a fact could not be settled, the record says so. 28 such claims on 20 records. All regions.

Aberllefenni Slate Quarry

• Aberllefenni is reputed to be the longest continually operated slate mine in the world, closing in 2003. (uncertain)
• The quarry employed around 190 men at its peak around 1890, falling to around 40 by 1950 and just 3 at closure in 2003. (uncertain)

Alexandra Quarry

• Eight men were killed at the quarry between 1895 and 1913; in 1907 a locomotive boiler explosion on the quarry tramway killed one passenger and severely scalded the driver, resulting in £50 fines for both the agent and the company. (uncertain)

Braichgoch Slate Mine

• The Corris Mine Explorers history dates the Braich Goch Slate Quarry Company to 1864, while Wikipedia's account has the Birley family establishing Braich Goch Slate Quarry Ltd on purchasing the lease in 1859. (disputed)

Clogau Gold Mine

• Every British royal wedding ring since 1923, when the future Queen Elizabeth The Queen Mother married the Duke of York, has reputedly been made from a nugget of Welsh gold sourced from Clogau — including those of Queen Elizabeth II, Princess Diana, and Meghan Markle in 2018. (uncertain)
• A 2022 report describes extensive surviving surface infrastructure at Clogau, including a horse whim, the ruins of a mine office and workshop, and remnants of a steam-powered mill, alongside stopes and deep shafts on the St David's and No. 2 levels either side of the hill's central fault. (uncertain)
• The BGS mine-plans catalogue holds a BGS plan titled 'Clogau' (catalogue KP19209, undated in the catalogue); the catalogue gives no location and the plan's details do not clearly tie it to this working, so it may belong to another of the same name. (uncertain)

Coetmor Quarry

• The Royal Commission's study states that the standard gauge railway reached Bethesda in 1884 and that its terminus, on the north side of the town, was built on land reclaimed from the Coetmor Quarry tip. (disputed)
• The Dyffryn Ogwen community history instead says the 1884 station was built on the rubble tips of the former Bird's Lodging slate quarry. (disputed)

Cwmorthin Slate Mine

• A July 2014 report describes severely deteriorated conditions in the Old Vein workings, with numerous roof falls and delaminating slabs, alongside abandoned mining carts still standing on Floor B and miners' barracks visible from the surface. (uncertain)

Dinorwig Slate Quarry

• A 2023 report describes the quarry's upper levels, including the Australia Mill and its compressor house, as remaining in 'remarkable condition, with many of the buildings and artifacts remaining in place', preserved by minimal disturbance since closure. (uncertain)

Diphwys Casson Quarry

• Coflein and a 2020 site survey both record small-scale extraction continuing to 1925; Wikipedia instead describes a 1920s reopening lasting seven years before a final 1955 closure. (disputed)

Dorothea Quarry

• The 68-inch Cornish beam engine was designed by Nicholas Trestrail and built by Holman Brothers of Hayle; work began in April 1905 and the engine was set going in June 1906. (disputed)
• The Cornish beam engine is recorded as installed in 1904. (disputed)

Llechwedd Slate Caverns

• According to the traditional account, unpaid workers continued searching after funding ran out and struck the rich 'Old Merioneth Vein' within weeks, securing the quarry's future. (disputed)

Maenofferen Quarry

• Underground production ended in November 1999 according to Wikipedia, Coflein and TheTimeChamber, but November 1998 according to Festipedia; the accounts disagree by a year. (disputed)

Moelwyn Quarry

• The quarry ran basic literacy classes for its workforce in the 1860s, which were, on one account, visited by the sitting Prime Minister, Lord Palmerston. (uncertain)

Nant Gwrtheyrn Quarries

• Nant Gwrtheyrn's own history dates the first sett quarry in the valley to 1851 under Hugh Owen of Anglesey, with the Liverpool firm Kneeshaw and Lupton taking control in 1861; other accounts give 1861 as the opening date and Kneeshaw and Lupton as the opener, while Coflein says only that modern quarrying started shortly after 1850. (uncertain)

Prince Edward Gold Mine

• Mindat dates the ring bar to 1935; Princess Marina married in November 1934. (disputed)
• One trip report says the mine was probably first worked around 1885. (uncertain)
• Two trip reports say gold for Edward's 1911 investiture as Prince of Wales came from the mine and gave it its name; Mindat does not mention this. (uncertain)

Sygun Copper Mine

• A 2022 report on mining remains in the hills around Sygun describes waterlogged, dark adits and the surviving structure of an aerial ropeway at nearby Cwm Bychan, noting that the accessible workings show only minor mineralisation and appear to be exploratory trials rather than productive workings. (uncertain)

Tonfanau Quarry

• The quarry closed in 1998, 106 years after opening, under Hanson, with most of the plant and machinery removed. The same Wikipedia article states elsewhere that a granite quarry existed north of the village only 'until 1992'. (disputed)

Trefor Granite Quarry

• Coflein and the People's Collection Wales record give the quarry's closure as 1963. (disputed)
• History Points gives the closure as 1971, and Wikipedia's article on the village says large-scale industry ended with closure in 1960. (disputed)

Turf Copper Mine

• Buddlepit gives working dates of 1824-47 and 183 oz of gold recovered 1854-65, figures its Dolfrwynog page attributes to Dolfrwynog; unresolved. (disputed)

Tyddyn Gwladys Mine

• A photograph in the Meirionnydd Archives shows the interior of gold miners' barracks, identified with a query as Tyddyn Gwladys. (uncertain)

Tymawr West Quarry

• The Ordnance Survey maps of 1889 and 1900 show the Nantlle Vale Slate Quarry here, in existence in 1882 and closed about 1910, afterwards apparently divided between Ty Mawr West and Ty Mawr East. (uncertain)