Gold Potential of the Dalradian Rocks of North-West Northern Ireland: Prospectivity Analysis Using Tellus Data
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Gold potential of the Dalradian rocks of north-west Northern Ireland: prospectivity analysis using Tellus data Internal Report OR/08/039 BRITISH GEOLOGICAL SURVEY INTERNAL REPORT OR/08/039 Gold potential of the Dalradian rocks of north-west Northern Ireland: prospectivity analysis using Tellus data PAJ Lusty, PM McDonnell, AG Gunn BC Chacksfield and M . Cooper Keywords Northern Ireland, prospectivity analysis, gold Front cover The Owenkillew Valley, Tyrone, Northern Ireland (Photo: P. McDonnell) Bibliographical reference PAJ LUSTY, PM MCDONNELL, AG GUNN, BC CHACKSFIELD AND M COOPER. 2009. Gold potential of the Dalradian rocks of NW Northern Ireland: prospectivity analysis using Tellus data. British Geological Survey Internal Report, OR/08/39. 74pp. Copyright in materials derived from the British Geological Survey’s work is owned by the Natural Environment Research Council (NERC) and/or the authority that commissioned the work. You may not copy or adapt this publication without first obtaining permission. Contact the BGS Intellectual Property Rights Section, British Geological Survey, Keyworth, e-mail [email protected]. You may quote extracts of a reasonable length without prior permission, provided a full acknowledgement is given of the source of the extract. Maps and diagrams in this book use topography based on Ordnance Survey mapping. © NERC 2009. All rights reserved Keyworth, Nottingham British Geological Survey 2009 BRITISH GEOLOGICAL SURVEY The full range of our publications is available from BGS shops at British Geological Survey offices Nottingham, Edinburgh, London and Cardiff (Welsh publications only) see contact details below or shop online at www.geologyshop.com BGS Central Enquiries Desk Tel 0115 936 3143 Fax 0115 936 3276 The London Information Office also maintains a reference collection of BGS publications, including maps, for consultation. email [email protected] We publish an annual catalogue of our maps and other publications; this catalogue is available online or from any of the Kingsley Dunham Centre, Keyworth, Nottingham NG12 5GG BGS shops. 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Garth Earls, Director GSNI, provided expert information and advice on gold in the Dalradian rocks of Northern Ireland and made many suggestions to improve this and future studies. i Contents Acknowledgements ......................................................................................................................... i Contents .......................................................................................................................................... ii Summary ....................................................................................................................................... vi 1 Introduction ............................................................................................................................ 1 2 Geological setting ................................................................................................................... 4 2.1 Geology of the Newtownstewart sheet ........................................................................... 4 3 An introduction to prospectivity analysis ............................................................................ 5 Mineral deposit models and key exploration criteria ................................................................ 7 3.1 Orogenic gold deposits ................................................................................................... 7 3.2 Orogenic gold deposits in Northern Ireland ................................................................... 8 Data and data processing ............................................................................................................ 15 3.3 Geology ........................................................................................................................ 15 3.4 Structure ........................................................................................................................ 16 3.5 Geophysics .................................................................................................................... 16 3.6 Geochemistry ................................................................................................................ 25 3.7 Mineral occurrences ..................................................................................................... 32 4 Application of Fuzzy Logic modelling to the study area .................................................. 32 Results .......................................................................................................................................... 47 4.1 Regional prospectivity analysis .................................................................................... 47 4.2 Detailed prospectivity analysis of the Newtownstewart sheet ..................................... 54 4.3 The effect of assigning intra-Dalradian rankings ......................................................... 56 5 Discussion and conclusions .................................................................................................. 69 6 Recommendations for further work ................................................................................... 71 References .................................................................................................................................... 71 FIGURES Figure 1 Major Caledonian structures and the location of significant gold deposits in Britain and Ireland. DL, Donegal Lineament; OL, Omagh Lineament; CB, Cregganbaun; CP, Croagh Patrick, CV, Cavanacaw, CT, Curraghinalt; CL, Clontibret, GH, Glenhead; L, Leadhills; CN, Cononish; CL, Calliacher-Urlar Burn (Adapted from Parnell et al. 2000). …………….1 Figure 2 The distribution of exploration and mining licences in Northern Ireland, March 2008. A cluster of licences is present over the Dalradian rocks of the Sperrin Mountains (shown by the red outline). ...................................................................................................................... 2 ii Figure 3 The location of the study area and the main gold deposits. The Newtownstewart map sheet area, selected for detailed analysis, is outlined by the dashed line. ............................. 3 Figure 4 Geology of the Newtownstewart sheet (GSNI, 2007). .................................................. 6 Figure 5 The location of the Curraghinalt and Cavanacaw deposits and other occurrences of auriferous vein style mineralisation…………………………………………………………10 Figure 6 Generalised geology of the study area showing the groupings used in the prospectivity analysis. ................................................................................................................................. 17 Figure 7 Reduced to pole magnetic anomaly map. ...................................................................... 18 Figure 8 Magnetic pseudogravity horizontal gradient anomaly map. .......................................... 19 Figure 9 Electromagnetic field apparent resistivity anomaly map. .............................................. 20 Figure 10 Residual Bouguer gravity anomaly map. ..................................................................... 21 Figure 11 Digitised lineaments derived from the Tellus geophysical survey and the regional gravity dataset for the regional scale analysis. ...................................................................... 22 Figure 12 Lineaments derived from the Tellus geophysical data over the Newtownstewart map sheet. ...................................................................................................................................... 24 Figure 13 The distribution of gold in Tellus stream-sediment samples. ...................................... 26 Figure 14 The distribution of silver in Tellus stream-sediment samples. ...................................