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This document is with a copy of the following article published by the Mining Heritage Trust of Ireland. It is provided for non-commercial research and educational use. The Mining Heritage Trust of Ireland formally ceased its existence in 2019 but has provided a continuing website of resources with free access for those interested in the activities of the organisation in its various formats from 1996-2019, and in Irish mining heritage in a broader sense. Mighall, T., Timpany, S., Critchley, M. F., Martinez Cortizas, A., Silva Sanchez, N., (2013) ‘A palaeoecological assessment of the impact of former metal mining at Glendalough, County Wicklow’ Journal of the Mining Heritage Trust of Ireland, 13, pp. 9-22 Copyright of this article remains with the Mining Heritage Trust of Ireland whose archives, intellectual assets and library have been transferred to the Natural History Division of the National Museum of Ireland. Please contact [email protected] for any enquiries relating to the MHTI. This cover page must be included as an integral part of any copies of this document. A PALAEOECOLOGICAL ASSESSMENT OF THE IMPACT OF FORMER METAL MINING AT GLENDALOUGH, COUNTY WICKLOW IRELAND Timothy M. Mighall, Scott Timpany, Martin F. Critchley, Antonio Martinez Cortizas and Noemi Silva Sanchez Abstract: This paper presents the preliminary findings of a palaeoecological and geochemical study of a peat core sampled to reconstruct the environmental history at Glendalough and Glendasan, County Wicklow, in order to search for signs of undocumented early metal mining. An increase in lead concentrations raises the intriguing possibility of mining in the Glendalough area from the eleventh century onwards and in particular, a rapid growth from the fifteenth century. This phase of increased lead pollution coincides with the gradual loss of woodland in the area. Journal ofthe Mining Heritage Trust ofIreland, 13, 2013, 9-22. INTRODUCTION acqms1t1on and analysis of a peat core obtained from an ombrotrophic (rain-fed only) blanket bog in the vicinity of the This paper presents the preliminary findings of a Glendalough/Glendasan mines in the uplands of County palaeoecolog ical and geochemical study of a peat core Wicklow. sampled to reconstruct the environmental history at Glendalough and Glendasan, County Wicklow. The work The aims of the research were threefold. Firstly, to reconstruct formed part of the Metal Links: Forging Communities Together the vegetation and fire history from the peat core through the lnterReg IVA project which deals with mining communities in use of microfossil (pollen, non-pollen palynomorphs [fungal Wales (Mid-Wales and Anglesey) and Ireland (Glendalough spores (NPPs)] and microscopic charcoal analysis. Secondly, and Copper Coast, County Waterford). All of these areas were to construct a chronology for the sequences using radiocarbon mined extensively during the nineteenth century for lead and dating and thirdly, to reconstruct atmospheric dust and metal copper, with the lead mines at Glendalough and Glendasan being the most important nineteenth century lead producers in pollution histories using peat geochemistry. Ireland (Schwartz and Critchley 2012, 5). However, archaeological investigations in Wales and England GEOLOGY, MINERALISATION AND (Timberl ake 2009) have demonstrated that metalliferous KNOWN MINING HISTORY mining, principally for copper ores, started as far back as the The underlying geology of the Glendalough area is over 400 Bronze Age in some areas. In Ireland, with the exception of million years old and was formed during the Caledonian the Bronze Age copper mines of Ross Island near Killamey and South West Cork (O'Brien 2004; 1994), there has been orogeny (Phillips 200 I). Around 430 million years ago, the very little scientific investigation of early metal mining. area that became the Wicklow Mountains was situated on the References to ' Danes workings' appear in eighteenth and fringes of an equatorial microcontinent to the south of the nineteenth works of reference (for example, O' Halloran 1772, Iapetus Ocean named Avalonia. Mud, silt and mixed coarse­ notes the Ross Island Mines were widely believed to be the fine sediments from turbidity flows were deposited on the work of the 'Danes') yet no evidence is given for their dating. ocean floor and there was local volcanic activity giving rise to ash deposits, lavas and local igneous intrusions. As the At Glendalough, the co-location of lead-zinc mineralisation continental plates moved towards each other, the Iapetus with the monastic settlement of St Kevin (also known as the Ocean began to close and Avalonia drifted into northern Seven Churches), founded in the sixth century and which latitudes, colliding first with the continent of Baltica and then attained its zenith between the tenth and twelfth centuries, with Laurentia to form the supercontinent of Euramerica. The raises the intriguing possibility of a probable link between the Iapetus closed completely at the end of the Silurian period Monastic City and the working of metallic minerals (see Fig. (443 -415 million years ago). High pressure and high I). Undisturbed and slowly accumulating peat can preserve a temperatures accompanied the closure, resulting in record of particles (such as pollen, charcoal and mineral dust) metamorphism of the ancient ocean sediments to form the which fall from the air onto its surface and are buried by slates and greywackes which now outcrop at Glendalough. subsequent layers of peat. So, in the context of possible pre­ nineteenth century mining at Glendalough and a link with the Around 400 million years ago (towards the end of Caledonian monastic settlement, the Metal Links project funded the orogeny) the Wicklow Mountains were intruded by a granite 9 Journal ofthe Mining Heritage Trust ofIreland No. 13 Fig. 1. The valleys of Glendalough (left )and Glendasan (right) with Camaderry Mountain between. The Monastic City of Glendalough can be seen centre right. The mine workings in Glendalough and Glendasan were joined by workings that extended right through Camaderry Mountain in the mid-nineteenth century. The peat core sample was taken from an area of rain fed blanket bog on the north west slope of Camaderry Mountain. Photograph with kind permission of the Glendalough Mining Heritage Project batholith, known as the Leinster Granite, the largest continuous weathered lode is the South Luganure Lode uphill from the area of granite in Ireland and Britain (O'Connor and Briick Old Luganure Adit, where a gully marks its course. It is likely 1978). The heat generated by this process created an aureole than any pre-nineteenth century mining would have been of schists: metamorphosed slates and shales. Superheated undertaken only on visible outcrops in remote uplands areas fluids driven by the heat of the granite leached lead and other such as this. metals from the schists and deposited these along sub-vertical cracks in the granite close to the margin with the schists to Current narratives of the Glendalough area in County Wicklow form mineral lodes (McArdle et al 1978). The lodes are focus almost exclusively on its monastic heritage. Yet, from typically composed of galena (lead sulphide), lesser sphalerite the thirteenth century, the area has been witness to significant (zinc sulphide) and minor pyrite (iron sulphide), chalcopyrite industry that has had a profound impact on its geomorphology. (copper sulphide) and native silver, along with rock of little or In the seventeenth century, large iron smelting works were no commercial value such as quartz and barite. Repeated established in southern County Wicklow at Carnew, by episodes of glaciation during the Quaternary (2.58 Ma to Welshman, Calcott Chambre, who leased Camew Castle in present), further weathered and sculpted the stumps of the I 619 (History of Parliament). Protestant colonisers arrived in Caledonian Mountains to reveal the Leinster granite which the southern part of the county during the second half of the form the spine of the present day Wicklow Mountains. The seventeenth century to settle close to the forest of Shillelagh relentless flow of glaciers exposed the mineral veins in the that was exploited for its vast quantities of oak as a source of sides of the characteristic U-shaped valleys of G lendasan, charcoal; many of these immigrants were skilled specialists Glendalough and Glenmalure and created the ribbon lakes in such as bellows makers, founders, finers and hammer men, Glendalough and corries dammed by moraine such as Lough who worked in the local ironworks to smelt the iron ore Nahanagan (Synge 1973). shipped from Bristol. The known lodes rarely show mineral or even gangue (friable Around this time in Glendalough too, the need to supply quartz and siderite) at the surface, and where not masked by charcoal for smelting works resulted in a 'smash and grab' scree, moraine or bog, the hydrothermally altered and softened operation where all available wood was felled for cordage, granite which accompanies the strong mineralisation weathers laying waste to the landscape by denuding it of its deciduous to noticeable depressions. The most visible evidence of a tree cover. Around 83 identified charcoal burning platforms 10 A palaeoecological assessment ofthe impact offormer metal mining in Glendalough 307000 308000 300000 3f1000 302000 0 0 0 0 Mine 0 ~ "' .... Dressing floor ; 57 Spot height d Monastic site - Majorvein Brockagh Mountain 0 0 - Minorvein 0 • 557 500 0) 0) Sampling ■ -. --400' -· 698 0 site 0 0 •

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