Frongoch Mine (Bron-y-Goch Mine; Llawynwnwch Mine), Pontrhydygroes, Upper Llanfihangell-y-Creuddyn, Ceredigion, Wales, UK
|Latitude & Longitude (WGS84):||52° 21' 7'' North , 3° 52' 35'' West|
|Latitude & Longitude (decimal):||52.35222,-3.87639|
|UK National Grid Reference:||SN722744|
|Köppen climate type:||Cfb : Temperate oceanic climate|
|Other/historical region 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.
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.
50 valid minerals. 1 (TL) - type locality of valid minerals.
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
419.2 - 443.8 Ma
|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. 
419.2 - 443.8 Ma
433.4 - 443.8 Ma
|Llandovery Rocks (Undifferentiated)|