Geology
Ireland has a widely varied geological framework, with rocks ranging in age from Proterozoic (2500 million years ago) to the Present. The island can be divided into a number of mineral provinces that are endowed with a diverse suite of base and precious metals, and industrial minerals. These mineral provinces are described in brief below. For more details on the geology of Ireland, please visit the Geological Survey of Ireland website
Mineral Potential
In spite of its relatively small size (70,000 km2), Ireland has a notably diverse geology that is prospective for a wide range of mineral deposits. Large tracts of Ireland are underlain by metasediments and metavolcanics of Proterozoic and Lower Palaeozoic age. These rocks are known to contain significant base metal mineralization (e.g. copper at Avoca) and gold-bearing quartz veins. The latter style of mineralization has been the focus of extensive exploration efforts in Northern Ireland, and in 1999, an opencast gold mine was opened at Cavanacaw in Co Tyrone. The Lower Carboniferous limestones of the Irish Midlands (the Central Ireland Basin) are host to one of the great orefields of the world. Since 1960, fifteen significant zinc-lead deposits have been discovered, with six becoming producing mines. These include the world class mine at Navan, Co Meath. Ireland has been ranked first in the world in terms of zinc discovered per square kilometre, and second in the world with respect to lead. Ireland is Europe's largest zinc producer. Its three base metal mines account for some 32% of European zinc production, and they also produce 11% of its lead. Ireland's younger rocks contain significant deposits of industrial minerals, most notably the gypsum deposit at Kingscourt, Co Monaghan, that is found in an outlier of Permian rocks. A better appreciation of Ireland's mineral potential can be obtained by looking at the different Mineral Provinces.
North-Western Basement
The North-Western Basement province contains some of Ireland's oldest rocks, with Proterozoic gneisses overlain by metamorphosed sandstones, limestones and volcanics rocks. These are intruded by Palaeozoic granites. Demonstrated potential for base metals is shown by widespread 18th and 19th century workings, with many small mines and "trials" to be found. Quartz veins and shear zones are prime gold targets (e.g. Curraghinalt and Cavanacaw, both in Northern Ireland) and gold is also associated with massive sulphides (e.g. Glentogher, Co Donegal). Molybdenum-copper mineralization is associated with the Palaeozoic granites. There is potential for Rare Earth Elements in the province, and diamond and other gemstone targets have been identified in the far north of the province, in the Inishowen Peninsula. A number of types of dimension and ornamental stone have been exploited from this province, including the famed green Connemara marble.
Mayo-Curlew Basin
Significant gold deposits are known from Lower Palaeozoic rocks at Lecanvey and Cregganbaun in south Co Mayo. Other deposits in this province include talc-magnesite at Westport and the sub-economic Charlestown copper deposit.
Longford-Down Massif
Three principal groups of metallic mineral deposits occur in the Lower Palaeozoic rocks of the Longford-Down Massif. Firstly, there are vein deposits, mainly containing lead and zinc, but also including antimony and gold (e.g. Clontibret, Co Monaghan). A number of these vein deposits have been exploited historically. Secondly, stratiform iron-manganese deposits. Several of these deposits were worked during the late 19th century. Finally, there is minor copper-molybdenum mineralization associated with granites.
Leinster Massif
The Leinster Massif of Lower Palaeozoic metasediments and metavolcanics hosts the large low-grade copper-pyrite deposit at Avoca. There is sub-economic tungsten and lithium mineralization associated with the Leinster Granite. There is also potential for Rare Earth Elements, and there are numerous minor vein-type copper and lead deposits. Also of note is the historically mined alluvial gold deposit at Gold Mines River, in Co Wicklow.
Central Ireland Basin
The Central Ireland Basin is underlain by a sequence of Carboniferous sediments, where Lower Carboniferous limestones in a number of sub-basins host important zinc-lead deposits. Known zinc-lead deposits have been shown to contain more than fourteen million tonnes of zinc metal. Targets include stratabound Irish-type deposits in the basal Carboniferous (e.g. Navan, Tatestown, Oldcastle, Keel and Moyvoughly), the overlying Waulsortian limestones (Tynagh, Silvermines, Ballinalack, Galmoy and Lisheen) and stratigraphically higher crosscutting deposits (Harberton Bridge). Recent and current exploration has encountered significant zinc-lead mineralization at three localities in the southwestern part of the province viz. Caherconlish and Stonepark in Co Limerick, and Kilbreckan in Co Clare. Vein and massive replacement copper-silver deposits (Gortdrum, Aherlow, Mallow) are associated with the structurally controlled southern margin of the Basin. Significant industrial mineral deposits contain barite (Ballynoe and Tynagh), gypsum (Glangevlin), calcite (Kilbreckan) and dolomite (Bennettsbridge).
Munster Basin
In the Munster Basin, Devonian sandstones with minor volcanics are overlain by Carboniferous marine sandstones, shales, and limestones. Major folding and faulting took place during the Variscan Orogeny. Vein-hosted copper at Allihies and barite at Clonakilty (both in Co Cork) are amongst a variety of mineral deposits worked in the past. The Devonian sequences also contain potential palaeoplacer gold targets, while shale-hosted zinc-lead mineralization has been discovered in the Carboniferous strata.