Title: An investigation of metal occurrence, sources and mobilization processes in selected Irish groundwaters associated with mines

Researchers: Sean Wheeler, Dr Tiernan Henry, Dr John Murray

Research Purpose: Rainwater has relatively low concentrations of all major and minor elements. However as it comes in contact with the surface, it reacts and picks up various elements depending on the nature of the ground and the environment. These reactions continue as the water makes its way into the subsurface. Minerals within the rock are dissolved and their constituents carried in the water. These stowaways can then react with each other, with water from other sources, with life (bacteria) and with oxygen in the water. Each of these processes has a different effect on the overall chemistry of the water. By sampling an analysing the chemistry of groundwater it is possible to make reasonable inferences about the journey it has taken, including what lithology it has passed through, what were the means of transportation (e.g. diffuse flow, conduit flow) and how long it has been in the ground. Sampling groundwater in concurrence with a drilling program can offer additional information beyond the specific point where the hole was drilled and is therefore a useful exploration tool. A primary goal of this project is to evaluate the application of groundwater geochemistry sampling and analyses as a tool for use in the mineral exploration industry. Mapping stream water and soil geochemistry has been proven to be an effective means of locating potential target sites prior to exploratory drilling. However, surface water will generally only give a unidirectional signal of surface chemistry and soil geochemistry tends only to indicate local shallow rock characteristics. Using these methods has enabled the discovery of many large shallow economic mineral deposits globally. Groundwater geochemistry however, has the potential to provide a 3-dimentional understanding of the subsurface (chemistry, lithology, structure), sometimes to significant depths. This may then enable the discovery of significant mineral deposits at greater depths than has been typically the case up to now. Simply put, the easy finds have already been made and new exploration methods are required to continue discovery and keep up with global demand for mineral resources. The Irish midlands are being used as the location to test the effectiveness of groundwater geochemistry as a subsurface exploration tool as there already exists a large amount of geochemical data from mining operations at Lisheen and Galmoy (less than 10km apart) in addition to detailed 3-dimentional models of the subsurface at each mine site.

The aims of the project are to investigate:

a) The regional and local flow patterns as determined at the mines during the pre-mine phase, and the pattern of flows observed during the operational and closure phases and to assess the footprint of the mine operation.

b) The basic hydrogeological system and its lithological, stratigraphic and structural controls.

c) Total metal concentrations in wells in the study areas to better understand the sources and mobilisation mechanisms of metals in groundwater in this region.