Abstract - There are two principal ways in which the basement is directly implicated in the formation of deposits within the Dinantian cover sequences of Ireland. Firstly, basement rocks are the likely source of metals, scavenged by deep circulation of hydrothermal fluids (e.g. Everett et al. 1999). Secondly, basement structures may be responsible for the localisation of the normal faults, which represent the main conduits for fluid flow (e.g. Johnston et al. 1996, Hitzman 1999). Here we review the main structural characteristics of Irish mineral deposits and consider the extent to which they can be linked to underlying basement controls.
Different models have been advanced for the formation of Irish Zn-Pb deposits though they all have several aspects in common (e.g. Johnston et al. 1996, Hitzman 1999). All of the models acknowledge that faults play a crucial role, acting as both the main conduits for transporting mineralising ore fluids and forming the main bounding structures to the deposits. Most models attribute the main phase(s) of mineralisation to a lower Carboniferous fluid flow regime prior to the compressive tectonism of the Variscan (Hercynian). There is also an emerging consensus of the importance of Caledonian basement structures in the localisation of Dinantian faults and related fluid flow. Using constraints from both Ireland and the UK we critically review structural aspects of Dinantian and later Variscan structures and argue that inheritance and reactivation of Caledonian structure are crucial elements of the structural history of Irish mineral deposits.
A review of structural constraints derived from onshore seismic datasets in the UK (e.g. Fraser & Gawthorpe 1990) and from outcrop and mine datasets in Ireland, highlights several features that are pertinent to the geometry and evolution of Irish mineral deposits.
Abstract of talk given to:
Geology and Mineralization in the pre-Carboniferous Rocks in Ireland and their Influence on Mineral Deposits in the Carboniferous, Irish Association of Economic Geologists Workshop, Westport, May 2002.