Main Mineral Provinces of Ireland
Ireland has a widely varied geological framework, ranging from Proterozoic to the Present, that includes a number of mineral provinces (see inset map) endowed with a diverse suite of base and precious metals as well as industrial mineral deposits. The geology of these mineral provinces are briefly summarized below.
This province contains Pre-Dalradian orthogneisses overlain by variably metamorphosed Dalradian clastics, carbonates and volcanics, that are intruded by Palaeozoic granites. Demonstrated potential for base metals is shown by widespread 18th and 19th century small workings, allied with the presence of stratabound base metal and barite mineralization. Quartz veins and shear zones are prime gold targets (e.g. Curraghinalt, Cavanacaw) and gold is also associated with massive sulphides (e.g. Glentogher). Porphyry style Mo-(Cu) deposits and variously mineralized skarns are associated with the Palaeozoic granites. Diamond and other gemstone targets have recently been identified in the far north of the province in the Inishowen Peninsula. A number of types of dimension and ornamental stone have also been exploited from this province, including the famed green Connemara marble.
The Lower Palaeozoic in Ireland consists of turbidite sequences and associated acidic or calc-alkaline volcanics, that were deformed and metamorphosed (up to greenschist facies) during the Caledonian Orogeny. Major granitoid intrusions were emplaced in the Lower Palaeozoic sequence during the early Devonian.
Three principal groups of metallic mineral deposits occur in the Longford-Down inlier: Epigenetic vein deposits, mainly composed of Pb and Zn, but also including Sb-As-Au (e.g. Clontibret). A number of these vein deposits have been exploited historically. Stratiform manganiferous iron deposits of probable volcano-sedimentary origin. Several of these deposits were worked during the late-19th century. Minor porphyry copper type Cu-Mo mineralization associated with small granodiorite intrusions.
This area hosts the large low-grade VMS Cu-pyrite deposit at Avoca, sub-economic W and Li mineralization associated with the Leinster granite batholith, numerous minor vein-type Cu and Pb deposits and the historically mined alluvial gold deposit at Gold Mines River.
Significant vein/shear hosted gold deposits are known at Lecanvey and Cregganbaun. Other deposits in this province include talc-magnesite at Westport and the Charlestown Cu deposit, centred upon a shallow dacitic intrusive.
Mineral Deposits of Ireland
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In this province, Devonian terrestrial clastics with minor volcanics are overlain by Carboniferous marine sandstones and shales with subordinate carbonates. Major folding and strike-slip faulting took place during the Variscan Orogeny. Vein-hosted Cu (Allihies) and barite (Clonakilty) are amongst a variety of mineral deposits worked in the past. The Devonian sequences contain potential palaeoplacer gold targets, while shale-hosted Zn-Pb mineralization has recently been discovered in the Carboniferous strata.
Central Ireland Basin
Thick Lower Carboniferous carbonates in a number of sub-basins are the host in this important zinc-lead province. Known Zn-Pb deposits contain some 14Mt of zinc metal. Target horizons are stratabound Irish-type deposits in the basal Navan Group (Navan, Tatestown, Oldcastle, Keel, Moyvoughly), the overlying Waulsortian limestones (Tynagh, Silvermines, Ballinalack, Galmoy, Lisheen) and stratigraphically higher crosscutting deposits of MVT type (Harberton Bridge). Vein and massive replacement Cu-Ag deposits (Gortdrum, Aherlow, Mallow) are associated with the structurally controlled southern margin of the Basin. Other significant deposits include barite (Ballynoe, Tynagh), gypsum (Glangevlin), calcite (Kilbreckan) and dolomite (Bennettsbridge). There are also potential Carlin-type gold targets in major structural zones (Navan-Silvermines, Mallow).