Fig. 1: Stone tool, a stamp used to produce patterned gold discs. This remarkable stone die was used to make gold foil discs. It was found near Hacketstown, county Waterford, and is dated to circa 2200-1800 B.C.. Item 1948:33. Specimen on display at the Irish National Museum of Archaeology, in downtown Dublin, photographed in September 2019. The soils and bogs of Ireland have yielded large numbers of gold artefacts (Praeger, 1937, pp.285-289) but no particularly large (by modern standards) gold mines, though numerous smaller deposits and locally rich veins have been discovered.
"Rock of the Month # 223, posted for January 2020" ---
We start 2020 with a striking exhibit from Ireland. The Irish content is long overdue, and this is the first of three months'-worth of features from the Emerald Isle. Whereas the majority of stone tools studied by archaeologists are for utilitarian, day-to-day usage, such as knives, scrapers and projectile points, artistic creations such as beads are locally important. This month's example is especially noteworthy, an early example of a tool specific to the production of gold jewellery.
The National Museum of Ireland: Archaeology, beside Merrion Square, in the elegant Georgian core of Dublin just south of the Liffey river, houses antiquities from 7,000 B.C. to the late Medieval period and beyond. It was founded under an Act of 1877. A highlight of the public displays is an exhibit of the use of gold in ornaments and jewellery (Kelly, 2007, pp.15-21). The display of gold and bronze objects (as seen in 2019) is very impressive. The exhibits include:
Figs. 2-3: Stone tools, including the stamp of Figure 1, and an example of ancient Irish goldsmith work. The latter, item 1990:71, is from county Galway, circa 2000 B.C. Specimens on display at the Irish National Museum of Archaeology, in downtown Dublin, photographed in September 2019.
The artefacts on display in Dublin have analogues in Scotland, as shown by Alison Sheridan (in Clark, 2014, pp.39-59). Lunules are known in both countries, back to circa 2000 B.C., and one example shown by Sheridan is from Blessington, county Wicklow (ibid., p.41), on the west side of the Wicklow Mountains south of Dublin.
Ireland has a long mining history. Bronze Age copper mining in Cork and Kerry counties involved at least 74 mines of proven or probable early Bronze Age date (Craddock, 1980). 73 are of "Mount Gabriel type", exploiting syngenetic copper deposits in the Devonian Old Red Sandstone, at an average grade of 0.5% Cu, while the other deposit, at Derrycarhoon, exploited a larger, vein-type deposit. However, whereas Ireland had abundant copper and gold in the Wicklow and Kerry hills, tin (for converting copper to tougher bronze) required trade with Cornwall. Flat axes and gold insignia (lunulae) were traded for black cassiterite pebbles (Fox, 1964). Southwestern English and Irish Cu cannot be distinguished with certainty, since both have a high arsenic content (ibid., p.82).
Gold deposits of Ireland
Rocks of Caledonian age are the main host of known Au deposits in Ireland. Principal settings for gold in Ireland (McArdle, 1989; see also Steed and Morris, 1986; Simpson et al., 1989; Thompson et al., 1992; Wilkinson, 1996; Smyth, 2004; Lusty et al., 2011) include: (1) the Avoca area, in volcanogenic massive sulphides, quartz veining and banded iron formation; (2) quartz veins and lower Paleozoic wallrocks in south Mayo; (3) stibnite- arsenopyrite veins of Clontibret in the Longford-Down inlier; and (4) Au associated with sulphide deposits in the Dalradian of west Ireland, as in Connemara (see e.g., Parnell et al., 2000). The Curraghinalt gold deposit in N.Ireland is a high-grade Au deposit, with the metal hosted by at least ten quartz-carbonate veins. At one point (Anon, 2013) the estimated endowment included measured resources of 0.02 MT grading 21.51 ppm Au, indicated resources of 1.11 MT grading 12.84 ppm Au and inferred resources of 5.45 MT grading 12.74 ppm Au. Curraghinalt, at an aggregate resource of 2.77 million ounces, is the largest-known Au deposit in the Sperrin Mountains of Northern Ireland. The gold mineralization in the quartz-sulphide veins in Dalradian metasediments has been dated to the Grampian event of the Caledonian orogeny, between 462.7 and 452.8 Ma (Rice et al., 2016).
The next consideration, having determined the use of the tools, and surveyed the local geology, is the source of the metal itself, which may be either near or far (or both). Gold metal tends to contain impurities, most often silver, but also copper, iron and other elements. Provenance can be constrained by analyses of gold in both ore and artefacts. One finding is the recognition of gold recycling by the remelting of artefacts (Cahill et al., 1997). As noted in the previous section, there was ample gold found in Ireland in ancient times, probably mostly in stream gravels (placer gold) where the metal would be concentrated in heavy-mineral sands, having been released from its bedrock sources by weathering.
Anon (2013) Dalradian seeks to optimize Curraghinalt. Northern Miner 99 no.39, 23, 11 November.
Cahill,M, Chapman,RJ, Leake,RC, Shell,CA, Taylor,JJ, Warner,RB and Watling,RJ (1997) Identification of the exploitable gold ores of Britain and Ireland and their relation to early prehistoric gold artefacts: recent advances with LA-ICP-MS analysis. Metals in Antiquity conference, Harvard University, Abstracts volume, p.17.
Clark,NDL (2014) Scottish Gold: Fruit of the Nation. Neil Wilson Publishing Limited / The Hunterian, University of Glasgow, 112pp.
Craddock,PT (editor) (1980) Scientific Studies in Early Mining and Extractive Metallurgy. British Museum Occasional Paper No.20, 175pp.
Fox,A (1964) South West England. Ancient People and Places 41, Thames and Hudson, London, 254pp.
Kelly,EP (2007) Guide to the National Museum of Ireland: Archaeology. National Museum of Ireland, Dublin, 48pp.
Lusty,PA, Naden,J, Bouch,JJ, McKervey,JA and McFarlane,JA (2011) Atypical gold mineralization in an orogenic setting - the Bohaun deposit, western Irish Caledonides. Econ.Geol. 106, 359-380.
McArdle,P (1989) Geologic setting of gold mineralization in the Republic of Ireland. TIMM B98, 7-12.
Parnell,J, Earls,G, Wilkinson,JJ, Hutton,DHW, Boyce,AJ, Fallick,AE, Ellam,RM, Gleeson,SA, Moles,NR, Carey,PF and Legg,I (2000) Regional fluid flow and gold mineralization in the Dalradian of the Sperrin Mountains, Northern Ireland. Econ.Geol. 95, 1389-1416.
Praeger,RL (1937) The Way that I Went. Collins Press Ireland, 2nd edition, xii+394pp., republished 2014.
Rice,CM, Mark,DF, Selby,D, Neilson,JE and Davidheiser-Kroll,B (2016) Age and geologic setting of quartz-vein-hosted gold mineralization at Curraghinalt, Northern Ireland: implications for genesis and classification. Econ.Geol. 111, 127-150.
Simpson,PR, Gallagher,MJ, Green,PM, Middleton,RS, Raiswell,R and Williams,RAC (1989) Gold mineralization in relation to the evolution of extensional volcano-sedimentary basins in the Scottish Dalradian and Abitibi belt, Canada. TIMM B98, 102-117.
Smyth,D (2004) Orientation biogeochemical prospecting studies in Ireland. Geochemistry: Exploration, Environment, Analysis 4, 87-95.
Steed,GM and Morris,JH (1986) Gold mineralization in Ordovician greywackes at Clontibret, Ireland. In `Turbidite-Hosted Gold Deposits' (Keppie,JD, Boyle,RW and Haynes,SJ editors), GAC Spec.Publ. 32, 186pp., 67-86.
Thompson,SJ, Shine,CH, Cooper,C, Halls,C and Zhao,R (1992) Shear-hosted gold mineralization in Co. Mayo, Ireland. In `The Irish Minerals Industry, 1980-1990' (Bowden,AA, Earls,G, O'Connor,PG and Pyne,JF editors), Irish Association for Economic Geology, Dublin, 436pp., 21-37.
Wilkinson,JJ (1996) Faulting, fluid pressure fluctuations and gold mineralisation at the Croagh Patrick quartz-gold vein deposit, county Mayo, Ireland. GSA Abs.w.Progs. 28 no.7, 152, Denver.
Visit the "Rock of the Month" Archives!