The identification of various types of geochemical stream sediment anomalies in Northern Ireland

A regional geochemical stream sediment survey of part of Northern Ireland led to the recognition of three types of base metal anomaly of exploration interest. These were significant anomalies of both elastic and hydromorphic origin, and non-significant hydromorphic anomalies in several upland areas. The significant anomalies are derived from Pb-Zn-Cu mineralization, whereas the non-significant anomalies are due to the leaching of Zn and other metals from acidic and/or gleyed soils and subsequent concentration in stream channels by coprecipitation with manganese oxides. Significant hydromorphic anomalies can be identified on the basis of abnormal Zn/Mn ratios and significant elastic anomalies on the basis of anomalous Pb contents. It is of the utmost importance to distinguish the dispersion mechanisms. Regional variations in bedrock geochemistry may only be identified when consideration is given to local dispersion mechanisms and account taken of the effects of variations in the surface environment on stream sediment composition. Changes in vegetation and land use may lead to rapid alterations in the nature of the dominant dispersion mechanisms.