A mineralogical tour of Ireland (Part 1): Leinster
Stephen Moreton (UK)
The island of Ireland has much to offer the mineral collector, but is relatively unknown to most. This may in part be due to a lack of published information, although, for years, the troubles in the north also served to deter visitors for many years. This series of articles briefly summarises the principal mineral locations on a region by region basis.
As the island is divided into four regions, Leinster, Munster, Connaught and Ulster (Fig. 1), which are in turn subdivided into counties, it seems appropriate to cover the island in this way. As the main ferry terminals for the Irish Republic are in Leinster many a trip to the country will start here. Leinster occupies the southeast region of the island and is the driest (or rather least wet) part of Ireland. Geologically, it offers the largest granite batholith in the British Isles, complete with metamorphic aureole, Carboniferous and Ordovician sediments and a scattering of basic igneous intrusions.
County Wicklow dominates the mineral scene in Leinster. Fractures along the margin of the Wicklow granite have acted as conduits for much later mineralising solutions, giving rise to lead/zinc veins. These reach their best development in Glenmalure, Glendasan and Glendalough.
Fine schieferspar calcite and dark brown sphalerite have recently been found in Glendasan, while some of the higher tips have yielded pretty crystalline crusts of pyromorphite and micro-wulfenite.
Small specimens of cerussite, linarite, chrysocolla and other secondary minerals also await the patient collector. Cruciform twinned harmotome has been known from the district for over a century but is exceedingly scarce. Glendalough is particularly pretty and offers ancient monastic ruins for those who do not fancy the three kilometre walk along the miner’s track to the mines at the top of the valley (Fig. 3).
A little to the south is the village of Avoca, where the popular TV series “Ballykissangel” was filmed. The enormous abandoned copper and pyrite mines straddle the valley, and can hardly be missed. The ore was massive, cupriferous pyrite, with local concentrations of lead, zinc and even gold. In the nineteenth century, native copper was found crystallised in fractures in the slate down to depths of 40 fathoms (73m), but the huge modern opencasts have obliterated the best localities. Blue crusts of water soluble chalcanthite can still be found at the bottom of the Tigroney open pit above the east side of the valley.
Nearby is the legendary Gold Mines River. In 1795, so the story goes, a local school teacher called Dunahoo suddenly began living beyond his apparent means. He also kept disappearing for periods of time. Curious, his wife followed him one day to see where he was going and saw him digging in a stream. Thinking he had gone mad, she told others. They were not so naïve and a gold rush ensued. In the subsequent scramble, as much as a third of a tonne may have been recovered, including a whopping 22 ounce nugget before the government sent in the troops to disperse the crowds.
Systematic placer mining then began, with the primary objective being to discourage the locals from gathering, not to make a profit. Extensive trials failed to locate the bedrock source, but it was found that the locals had been so inefficient that their own waste proved remunerative when reworked. When the government gave up some years later, various private adventurers and companies gave it a try but failed to make it pay. The depth of the overburden was, and still is, the major obstacle as bedrock exposures were limited.
Nowadays, the richest section of the river is in the middle of a dense forestry plantation inhabited by billions of flies. If one can battle through the undergrowth – and endure the subsequent aerial onslaught – specks and grains of gold can still be readily panned. The neighbouring streams are also auriferous, although to a lesser degree.
Elsewhere in Wicklow, in the 1990s, good drusy epidote was found in Parnell quarry, which works a pyroxene diorite intrusion near Arklow. The thin veins have since been quarried away. The old iron mine at Cloghlea, near Blessington, has yielded fine stalactitic, botryoidal and chatoyant goethite.
If one heads north one encounters Co. Dublin, where lead and native silver were mined at Ballycorus. The silver was very restricted and not to be found nowadays. Waste from the little opencast below the smelter chimney does yield cerussite together with micro linarite and micro acicular brown pyromorphite.
On the coast at Killiney is a small lead mine, where reaction with seawater has formed phosgenite in the oxidising ore. “A similar deposit is being extracted at Galmoy, in Co. Kilkenny, but another at Keel, Co. Longford proved uneconomic when tested in the 1960s. The old granite quarries at Glencullen once yielded green beryl prisms with black schorl, but they have been disused and flooded for many years. The River Dodder offers alluvial gold. Further north, in County Meath, is Europe’s largest zinc mine at Navan. It is an entirely underground operation, working an enormous stratabound deposit of fine-grained iron/zinc/lead sulphide ore. All waste is backfilled into the enormous stopes.
Heading south from Wicklow, one encounters Europe’s largest lithium pegmatite belt in the Blackstairs Mountains of Counties Wicklow and Carlow. Pink spodumene (kunzite) has been reported but is elusive. The green variety – hiddenite – is known from drill core only. Mostly, the localities consist of white spodumene laths in pegmatite boulders along the sides of fields. There are no outcrops. The largest crystals, up to around 20cm, are in boulders at the bottom of a field behind the derelict Aclare House.
At another of these occurrences, Moylisha, cassiterite crystals over 2cm across were found in matrix, but these are now lost in a forestry plantation. At Stranakelly, boulders of pink lithian muscovite, with tiny blue apatite crystals, were found. On Tomduff hill, an andalusite prospect was also evaluated but found to be uneconomic. The finger-size pinkish crystals in white quartz are unusually good for the species. Some of the streams yield specks of gold, but cannot compete with Gold Mines River.
In the extreme southeast is County Wexford. An old lead and copper mine at Caim, in the north of the county, offers micro specimens of the usual secondaries. Further south, gold can be panned around Forth Mountain, but the streams are small and difficult of access, being on private farmland. The peninsula of Hook Head offers good mackerel fishing and complete crinoids, but Irish palaeontologists are possessive of the latter and get upset whenever someone takes them. Better to let the sea destroy them instead it seems.
From here we are now well positioned to head west into Co. Waterford and begin our exploration of Munster, home of Ireland’s richest copper mines, rare phosphates and fine rock crystals.
Introducing Mineralogy, by John Mason, Dunedin Academic Press, Edinburgh (2015), 118 pages (Paperback), ISBN: 978-17-80460-28-4.
Minerals of Britain and Ireland, by A G Tindle, Terra Publishing (2008), 624 pages (Hardback), ISBN: 978-19-03544-22-8.
Rocks and minerals: The definitive visual guide, by Ronald Louis Bonewitz, Dorling Kindersley (2008), 356 pages (Hardback), ISBN: 978-14-05328-31-9.