Igneous and metamorphic coastlines have long been associated with the formation and supply of offshore heavy mineral sands, notably, in areas with high-energy coastlines. The NW of Ireland has a very old and complex geologic history, presenting Precambrian gneisses, schists and psammites as well as Caledonian granites and Ordovican ophioloites. These orthogneiss (Lewisian), basinal metasediments (Dalradian), Terman granite (Caledonian) and Deer Park ophiolites (Ordovician) are the likely source of heavy mineral concentrations found on strandlines of many beaches in the area and it is speculated that the same sediments may be forming marine offshore placers. However, their existence, provenance and economic viability are, until now, unassessed. Placer deposits form as detrital sediments undergo density-driven sorting during erosion, transport or deposition (Garzanti, 2007) and have proven to be a highly lucrative ore type deposits yielding gold, tin, REEs, titanium, uranium and diamonds, amongst others. (Geoghegan, 1989) identified a number of potential sites for offshore deposits around the coast of Ireland and prospecting licences were requested by Burmin Exploration in the 1990s to survey the seabed. It was estimated that a substantial heavy mineral concentration is located in Blacksod Bay (Mayo) with a sediment thickness of 3-11 metres in places. With the advancement of seabed mapping techniques and methods to geochemically fingerprint sediments, exploration of these types of deposits can be greatly benefited. In addition, research of this type can lend to better exploration targeting, understanding of mineral concentration mechanisms and littoral to marine sediment transport pathways and exchanges.
– determine the heavy mineral sand resource for a number of known sites offshore Ireland
– understand the provenance and transport pathways of the heavy minerals from source to sink at target sites
– understand the mineral concentration mechanism and environmental controls constraining the resources
– apply this knowledge to develop a pathway for more focussed offshore mineral sand exploration approaches and target area identification