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Frongoch Mine (Bron-y-Goch Mine; Llawynwnwch Mine), Pontrhydygroes, Upper Llanfihangell-y-Creuddyn, Ceredigion, Wales, UK

This page kindly sponsored by Steve Rust
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Latitude & Longitude (WGS84): 52° 21' 7'' North , 3° 52' 35'' West
Latitude & Longitude (decimal): 52.35222,-3.87639
GeoHash:G#: gcm1zf3mc
UK National Grid Reference:SN722744
Locality type:Mine
Köppen climate type:Cfb : Temperate oceanic climate
Other/historical names associated with this locality:Dyfed; Cardiganshire


Frongoch is located 15 km ESE of Aberystwyth. And was a major lead & zinc producer by nineteenth century standards. First mentioned in the late 1750's, and worked almost continuously to 1903. In the early working of Frongoch galena was the ore mineral, while sphalerite was either left standing in the mine or thrown on the dumps, with poor grade lead ore. When zinc ore could be sold for a profit the old lead stopes were stripped back for the sphalerite. This was mostly from the 1840's to end of the underground mines life in 1903. From 1924 to 1930 the dumps were reworked on a substantial scale. And up to the mid-1950's, a small dressing plant was used to reclaim lead and zinc ore from the dumps. The output from these later sporadic small scale dump workings is not recorded. Over the years the dump material has also been used for hardcore. In the mid to late 1990's this had greatly increased, but because of "environmental" concerns, it has stopped. Over recent years the concern of heavy metal out flow from the dumps has prompted the local council to attempt containment of the water in a holding lagoon. For some years there has been a wood-mill on the north east of the site. The wood shavings from the mill have covered large areas of the dumps in this area. As a result of this encroachment on the dumps, in 2003 a few hundred tons of the dump material were moved 200m further south on the mine site. The Sawmill has now stopped working as of 2012 and there is no further encroachment on the dumps.

Frongoch is one of the few mines in mid-Wales to use steam for working. In 1841 a 40-inch steam engine was working on the site. Not only was it used for pumping, but the water was reused to work some of the waterwheels. In the 1870's a 60-inch Cornish Beam engine was installed, pumping from a depth of 117 fathoms. The mine also used a 25-inch steam engine for winding and crushing.

Frongoch has a total estimated production of 61,000 tons of lead ore, and 50,000 tons of zinc ore. There are incomplete statistics for silver extracted from lead ore of 24,000 oz.

Geology:
The fault vein at Frongoch has been traced for about 3km but has been said to extend a further 2km WSW-ENE. A typical trend for veins in mid-Wales. Also quite usual for fault systems in this area is their discontinuous nature, commonly splitting up into many thin strings, and reuniting. Where the veinlets coalesced there was sometimes an improvement in ore quality. The fault cuts through Silurian mudstones/shales, arenites of the Devils Bridge Formation, of Llandovery age. In Frongoch mine the ore appears to have occurred were the veinlets came together. There also appears to have been two discontinuous ore shoots worked. One on the south, the other on the north side of the fault system. The main ore minerals were galena and sphalerite, which was found throughout the developed area. Although there was an increase in sphalerite in depth, with a decrease in galena.


Mineral List


50 valid minerals. 1 (TL) - type locality of valid minerals.

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org

Silurian
419.2 - 443.8 Ma



ID: 3185808
Paleozoic sedimentary rocks

Age: Silurian (419.2 - 443.8 Ma)

Lithology: Sedimentary rocks

Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529. [154]

Silurian
419.2 - 443.8 Ma



ID: 3160805
Silurian claystone

Age: Silurian (419.2 - 443.8 Ma)

Lithology: Major:{claystone}, Minor{sandstone,limestone}

Reference: Asch, K. The 1:5M International Geological Map of Europe and Adjacent Areas: Development and Implementation of a GIS-enabled Concept. Geologisches Jahrbuch, SA 3. [147]

Llandovery
433.4 - 443.8 Ma



ID: 2034671
Llandovery Rocks (Undifferentiated)

Age: Llandovery (433.4 - 443.8 Ma)

Lithology: Mudstone, siltstone and sandstone

Reference: British Geological Survey. DiGMapGB-625. British Geological Survey ©NERC. [23]

Data and map coding provided by Macrostrat.org, used under Creative Commons Attribution 4.0 License



This page contains all mineral locality references listed on mindat.org. This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in mindat.org without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.

References

Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
Rocks & Minerals: 23: 25.
BMS Database.
Bick, D.E. et al. (1996) British Mining No. 30 Northern Mine Research Society [Extensive history].
Green, D.I., Rust, S.A., and Mason, J.S. (1996) Classic British mineral localities: Frongoch mine, Dyfed. UK Journal of Mines & Minerals 17, 29-39. [Extensive mineralogy].
Cotterell, T.F. (2007) Cesàrolite from Frongoch Mine, Devil's Bridge, Ceredigion, Wales. Journal of the Russell Society, vol. 10, 55-56.
Cotterell, T.F. and Todhunter, P.K. (2007) Corkite and hinsdalite from Frongoch mine, Devil's Bridge, Ceredigion, Wales, including evidence to suggest that orpheite is a variety of hinsdalite. Journal of the Russell Society, 10, 57-64.
Green, D.I., Bridges, T.F., Rumsey, M.S., Leppington, C.M., and Tindle, A.G. (2008) A review of the mineralogy of the Roughton Gill Mines, Caldbeck Fells, Cumbria: Part 2 The Roughton Gill South Vein on Balliway Rigg. Journal of The Russell Society, vol. 11, 3-28. (referring to Cotterell 2007).
Cooper, M.A., Hawthorne, F.C., and Moffatt, E. (2009) Steverustite, Pb2+5(OH)5(Cu1+(S6+O3S2-)3)H2O)2, a new thiosulphate mineral from the Frongoch Mine Dump, Devils Bridge, Ceredigion, Wales: Description and crystal structure. Mineralogical Magazine, 73, 235-250.

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