Institute of Applied Geoscience (IAG)

Structural controls of orogenic gold in Northern Ireland and wider implications to orogenic gold mineralization models

A NERC CASE PhD project (Mr James Shaw)

Supervisors: Dr Taija Torvela and Dr Rob Chapman (SEE); Dr Mark Cooper (Geological Survey of Northern Ireland); Dr Greg Hope (Dalradian Resources Inc.).

This project synthesizes both regional and deposit-scale studies to illuminate gold mineralization controls and processes in the Grampian terrane of Northern Ireland: Detailed deposit investigation at Dalradian Resources’ Curraghinalt Mine are integrated with wider analysis of regional tectonic and structural evolution to contribute not only to our understanding of ore genesis at the UK’s most important gold prospect, but also to clarifying the more general structural controls influencing the location and genesis of the Curraghinalt deposit. These studies will underpin a consideration of orogenic gold models and gold deposit genesis in similar settings globally. The project will also have significance in informing future regional exploration strategies in Northern Ireland.

Structural controls of orogenic gold are varied and the understanding of the effect of the larger-scale tectonic and structural evolution on the ore deposit formation are still relatively poorly understood. This project studies the regional structural context of specific localities hosting economically important gold mineralization with a view to developing hypotheses which account for the structural location of these occurrences. In this way we aim to investigate whether generic controls may inform existing models for orogenic gold genesis on one hand and regional exploration on the other hand. An important outcome of the study is to apply this new understanding of gold localization to other orogenic gold districts in order to contribute to the ongoing academic debate on the nature of these deposits. 

Good field areas that are both easily accessible and have a reasonable amount of background data are valuable assets in the global efforts of elucidating the debate on orogenic gold genesis. Decent field areas are, however, fairly rare. Northern Ireland provides an excellent basis for study owing to the development of the economically significant gold mineralization at Curraghinalt and Cavanacaw, recent detailed geological mapping by the Geological Survey of Northern Ireland (GSNI), and the Tellus program which has generated a state-of-the-art integrated geochemical and geophysical database. Several other gold localities in NI have been reported including detrital gold in various river catchments where there are no known bedrock sources and glacial cover is thick. The UK Caledonides are contiguous with the auriferous terranes along the eastern seaboard of North America which have a long history of gold extraction, such that there is a real potential for further important discoveries.  Northern Ireland has only relatively recently become a focus of exploration and this project offers exciting opportunities to address the fundamental questions of the localization and genesis of gold mineralization, while also considering highly relevant exploration questions.

This project focusses on the regional setting of the Curraghinalt Deposit in the Sperrin Mountains (e.g. Dalradian Resources Inc, 2016), where a mine is currently under development. The Curraghinalt gold is hosted by sub-parallel auriferous quartz veins, formed within the Neoproterozoic (Dalradian) metasediments thrusted over an Ordovician island arc (Tyrone Igneous Complex; e.g. Cooper et al., 2011; Hollis et al., 2012; Standish et al., 2014; Rice et al., 2016). Numerical analysis implies that the veins are more clustered than expected from a random distribution (McCaffrey & Johnston, 1996) which in turn suggests that the veins may be linked to a more regional structural pattern. Recent mapping by the Geological Survey of Northern Ireland (GSNI) and the availability of extensive geophysical and geochemical data sets (Tellus Surveys) provide an excellent basis to investigate regional structural evolution and its relationship to the mineralization.

Aims and objectives

The project aims at investigating the structural setting of gold mineralization in NI, in the context of the Caledonian/Acadian orogenic belt in N America and Scandinavia, and addressing the implications to the orogenic gold formation models globally. The specific research questions are: 

i.          What is the detailed structure of the Curraghinalt ore body? How does it link to the regional tectonic and structural evolution – e.g. are shear zone/vein interactions important?

ii.          Are there characteristic structural signatures associated with the Cavanacaw deposit and smaller ‘regional’ veins, and do they differ from those at Curraghinalt?

iii.         What is the effect of lithological variations and pre-existing boundaries/structures to ore localisation?

iv.        Can detailed geochemical, geomechanical, and/or microanalytical investigations tell more about the relative timing and/or stress field conditions of the vein formation at different sites?

v.         Is the structural setting of NI deposits replicated elsewhere in the Caledonian/Acadian belts and/or in other global, know orogenic gold deposits? What are the implications to the debated models for orogenic gold formation and for the generic considerations in locating the exploration targets with the most economic potential?

The specific objectives include 3D-4D model building based on data collection and analysis through field work (both underground and surface mapping), analysis of drill core samples, and from the Tellus database which will be made available to the project through the involvement of GSNI. Other key objectives include e.g. microanalytics, geomechanics, and detailed vein geochemistry, in order to shed light on the more generic aspects of orogenic gold genesis.

References

Cooper, M.R., Crowley, Q.G., Hollis, S.P., Noble, S.R., Roberts, S., Chew, D., Earls, G., Herrington, R. & Merriman, R.J. 2011. Age constraints and geochemistry of the Ordovician Tyrone Igneous Complex, Northern Ireland: implications for the Grampian orogeny. Journal of the Geological Society, London, 168, 837-850.

Dalradian Resources Inc., 2016. Technical Report for the Northern Ireland Gold Project, Northern Ireland. SRK report 3CD016.000, 169 p.

Hollis, S.P., Roberts, S., Cooper, M.R., Earls, G., Herrington, R.J., Condon, D.J., Cooper, M.J., Archibald, S.M. & Piercey, S.J. 2012. Episodic-arc ophiolite emplacement and the growth of continental margins: Late accretion in the Northern Irish sector of the Grampian-Taconic orogeny. GSA Bulletin, 124, 1702–1723.

McCaffrey, K.J.W., and Johnston, J.D., 1996, Fractal analysis of a mineralised vein deposit: Curraghinalt gold deposit, County Tyrone: Mineralium Deposita, 31, 52–58.

Rice, C.M., Mark, D.F., Selby, D., Neilson, J.E. and Davidheiser-Kroll, B. 2016. Age and Geologic Setting of Quartz Vein-Hosted Gold Mineralization at Curraghinalt, Northern Ireland: Implications for Genesis and Classification. Economic Geology, 111, 127-150

Standish, C.D., Dhuime, B., Chapman, R.J., Hawkesworth, C.J., and Pike, A.W.G., 2014, The genesis of gold mineralization hosted by orogenic belts: A lead isotope investigation of Irish gold deposits: Chemical Geology, 378, 40–51.

 

 

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