Title: Metallogenesis of Cu deposits in Upper Palaeozoic sedimentary rocks, southern Ireland
Researchers: Juergen Lang, Dr Pat Meere
Today, the high demand for copper in all subjects of the electronic industries the interest in the historic copper findings of Southwest Ireland raised again, especially for international exploration companies. This research project aims to understand the sediment hosted and vein hosted copper mineralisations of Southern Ireland and their potential relationship to the copper-lead-zinc deposits in the Irish Midlands. For this study, we decided to choose the unique copper deposits of the Allihies mining district in West Cork, as well as smaller (historically mined) copper deposits on Sheep’s Head (Gortavallig) and Mizen Head (Crookhaven, Dhurode, Dereenalomane, etc.). The vein hosted copper mineralisation of Allihies is one of the largest copper deposits in Southwest Ireland. Sparse vegetation and nearly perfect outcrops give us a matchless opportunity to understand the pre-, syn- and post-Variscan structures and the subsequent fluid flow which developed the massive copper concentrations. Due to the beneficial nature of the research areas, we are able to use a perfect combination of different investigation methods from traditional field mapping, petrography and microthermometry to modern drone mapping techniques and geochemistry. The combination of these investigation types helps us to develop a workflow with the resulting opportunity to evolve a general understanding of the Munster Basin and the basement structures. With the gained knowledge about the regional structures and the hydrothermal fluid evolution, we want to provide a guideline for further mineral exploration procedures in Southern Ireland and possibly further locations of the Variscan Orogeny Belt.
The current hypothesis is that the Munster Basin and the South Munster Basin underwent an ongoing North-South extensional process (Pre-Variscan). This extension resulted in large scale early extensional faults (East-West) which formed the pathway for copper bearing hydrothermal fluids. The fluids developed fault parallel quartz veins (+/- copper) which have been slightly deformed, faulted and partially remobilised during the Variscan compression and its following relaxation. This “Allihies-Type” mineralisation with associated early extensional faults can probably be transferred all over the entire Munster Basin and its vein hosted copper deposits. It is possible, that the early extensional East-West faults are also the fluid pathways for the sediment hosted copper on Mizen Head. In that case, the host sediments must have had a high porosity which lead to a wide spread dissemination of the copper bearing fluids instead of (being stuck) as a quartz vein.
This project will address some fundamental questions related to the development of Cu deposits from key localities across southern Ireland. The core research questions relate to identifying the key structural and geochemical controls related to Cu mineralisation in Upper Palaeozoic sedimentary sequences. Central to this is determining whether there is a genetic link between the well-known Cu deposits of SW Ireland and those of the southern sector of the Irish Midland Orefield.