Local Geology
The mountains surrounding Allihies consist predominantly of Old Red Sandstone dating from the Devonian Period, approximately 530 m.y. (million years). The rocks were formed from sediments produced under extreme desert conditions, such as now existing in the Sahara Desert.
Minerals found at various mines:
Dooneen Mine – Opened 1812
Minerals Found: Atacamite, Botallackite, Chalcanthite, Copper, Cuprite,Langite.
Co-ordinates: 51.64833,-10.05583
Mountain Mine – Opened 1813
Minerals Found: Bournonite, Brochantite, Calcite, Chalcocite , Chalcopyrite, Connellite, Devilline,Langite,Pyrite,Quartz,Siderite, Sphalerite.
Co-ordinates: 51.64806,-10.03750
The Man Engine House has recently been restored by the Mining Heritage Trust of Ireland. It’s been observed that the large stopes, have fine crystalline crusts of langite and brochantite which formed when the mine started to be disused.
Caminches Stamp Mill – Opened 1818
Minerals Found:Malachite,Quartz.
Co-ordinates: 51.6394444444, -10.0302777778
Caminches Mine – Opened 1818
Minerals Found: Chalcopyrite, Quartz.
Co-ordinates: 51.6455555556, -10.0308333333
Ore was extracted from a 116 metres long, north-northeast trending vein with a slight “S” bend, extending down to 400 metres.
Field trip in the Main Mountain mine with the Mining Heritage Trust of Ireland.
Knealoge Mine – Opened 1842
Minerals Found: Quartz
Co-Ordinates: 51.6291666667, -10.0425
Coom Mine – Opened 1870
Minerals Found: Chalcopyrite, Quartz.
Co-ordinates: 51.6452777778, -10.0266666667
The target for ore extraction was an east-west vein with a slight “Z” bend, extending from the southern end of the Caminches vein.
During the last two centuries, commercial interest lay in metalliferous (Quartz)veins containing copper minerals injected into fractures coursing variously east to west or north-north-east within the Devonian sediments.
The main ore mineral formerly extracted in course of working the Allihies mines was chalcopyrite (copper-iron-sulphide) together with as little as possible of worthless quartz (silicon dioxide). Other sulphides produced in lesser quantities were tetrahedrite (copper/antimony) and pyrite (iron) plus minor quantities of chalcocite (copper) and molybdenite (molybdenum).
This specimen of Rhodochrosite in our museum, represents something much greater than just a pretty calcite rock. Often associated with silver deposits, Rhodochrosite is found in few locations worldwide where a high concentration of manganese minerals reside.
Between 1870 and 1915, 65% of the population of Beara left the South West of Ireland behind, in order to seek greater fortunes with silver mining in Butte, Montana, where an abundance of Rhodochrosite had been found.
Today, demographics suggest that over 20% of Butte has Irish links, making it the statistically the most Irish-American metropolitan/micropolitan city in the US.
Devonian sedimentary rocks form much of west County Cork, consisting largely of the compressed, sheared, contorted siltstones and sandstones of the Variscan mountain building episode. Around Allihies, they extend eastward from the coast, and inland into the mountains beyond the village.
Where veins of either direction intersect one another, an S or Z bend is sometimes formed, often enriched in copper minerals.
Upon visiting sites of former mine waste dumps you may observe remaining rock debris stained strongly red or orange. This is due to hydration of iron oxide and/or oxidation of iron sulphide, producing the hydrated iron oxide mineral, limonite. In other places waste rock is stained green by the oxidation of copper sulphides to form copper carbonate, malachite.
Field Trip Gallery
The Allihies Copper Mine Museum offers guided tours of the mines which is highly recommend, the museum also has an extensive section on the Geology and mineralogy of the region which is well worth a visit.
Quite recently the Allihies Copper Mine Museum have started a ‘Mineral Hunt’ which is a free event with the aim of educating budding or amateur geologists with a wealth of information on the geological landscape in the area. Well worth investing your time with, with prizes on offer for the best discovery as well as great fun! Be sure to check out or event calendar or facebook page for future announcements.