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Frongoch Mine (Bron-y-Goch Mine; Llawynwnwch Mine), Pontrhydygroes, Upper Llanfihangell-y-Creuddyn, Ceredigion (Dyfed; Cardiganshire), Wales, UK
Frongoch is located 15 km ESE of Aberystwyth. And was a major lead & zinc producer by ninetenth centry 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 where 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. 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. For some years there has been a woodmill 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 where moved 200m further south on the mine site.
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 25inch steam engine for winding and crushing.
Frongoch has a total estimated production of 61000 tons of lead ore, and 50000 tons of zinc ore. There are incomplete statistics for silver extracted from lead ore of 24000 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 discontinous nature, commonly spliting up in to 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, Llanddovery age. In Frongoch mine the ore appears to have occurred were the veinlets came to gether. There also appears to have been two discontinous 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 through out the developed area. Although there was an increase in sphalerite in depth, with a decrease in galena.
Mineral List
51 entries listed. 50 valid minerals. 1 type locality (valid mineral).
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References
- Rocks & Min.: 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. & Mason, J. S. (1996): Classic British mineral localities: Frongoch mine, Dyfed. UK Journal of Mines & Minerals 17, 29-39. [Extensive mineralogy].
Cooper, M.A., Hawthorne, F.C., 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.
- BMS Database.
- Bick, D. E. et al. (1996): British Mining No. 30 Northern Mine Research Society [Extensive history].
- Green, D. I., Rust, S. A. & Mason, J. S. (1996): Classic British mineral localities: Frongoch mine, Dyfed. UK Journal of Mines & Minerals 17, 29-39. [Extensive mineralogy].
Cooper, M.A., Hawthorne, F.C., 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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