Title: 3D Modelling of geological and geophysical data from the Irish midlands
Researchers: Dr John Conneally, Prof. John Walsh
The Irish midlands are a globally important source of base metals, however due to poor exposure over much of the area, the detailed structure of this region is relatively poorly understood. Recent exploration projects have involved the acquisition of a number of 2D seismic reflection profiles over potentially prospective areas. Traditional exploration geophysical techniques such as gravity, magnetics and electromagnetics typically produce a horizontal slice at a relatively shallow depth, which when combined with 2D seismic sections tied to boreholes provide important controls on the 3D geological structure of the area. In addition to the data provided by the industry partners, published outcrop mapping from the GSI and new high quality geophysical datasets acquired by the Tellus project are now available for the area covered by this project. This project aims to integrate these data types to build a geologically robust 3D model for a large portion of the northern part of the Irish midlands. This work will lead to a greater understanding of the structural style of the Irish type deposits and may have a role in identifying potentially prospective areas and in de-risking future exploration in this region. The discovery and management of raw material and groundwater resources in Ireland is critically dependent on the existence of high quality models of the subsurface. 3D modelling of both geological and geophysical data provide much improved constraints on basin structure and evolution, and on the precise nature of fault-related and stratigraphically controlled fluid flow and associated localisation of mineralisation.
This project specifically involves the building of 3D models based on onshore seismic reflection data, and is an essential complement to the modelling work being performed on the Irish Zn-Pb Orefield. Technical issues which the research will explore include the following: (i) Definition of links between structure and depositional facies. (ii) Significance of the geometry and structure of bounding faults, including segmentation, relays and fault zone complexity, in providing feeders and localising mineralisation. (iii) The geometry and effects of within-deposit faults on mineralisation, including their role as conductive pathways and/or barriers/baffles to flow. (iv) The spatial distribution of different breccia types and their impact on mineralisation. (v) The geometry of later faults and associated structures of Variscan and Tertiary age.
The resulting models and improved understanding will provide an improved backdrop to future minerals exploration and research. The primary data used in this project to define the 3D structure of the subsurface is seismic reflection data, the coverage of this data onshore Ireland is generally sparse and where coverage is poor, other data is used to constrain the locations of structures. There are five areas covered by reflection seismic data in the Irish onshore, these areas are the Navan area (Seismic data courtesy of Boliden Tara Mines DAC), the north midlands area, including data covering counties Westmeath, Longford, Kildare, Meath, Offaly and Cavan, (data courtesy of Teck Ireland), One 2D line is currently available in the Tullamore area (data courtesy of Geological Survey of Ireand), the Kilbricken area Co. Clare (data courtesy of Hannan Metals), the Castlecomer syncline, including data from counties Laois, Kilkenny and Carlow and the Loop Peninsula Co Clare (data courtesy of Petroleum Affairs Division). In most areas the seismic data is strongly constrained by borehole data, (Courtesy of Boliden Tara Mines DAC, Teck Ireland, Hannan Metals, Minerals Ireland, Geological Survey Ireland, and Petroleum Affairs Devision), the drilling dataset is much more aerially extensive than the seismic dataset providing important constraints for other areas of the Irish onshore.