Formation of interbasaltic laterite horizons in NE Ireland by early Tertiary weathering processes

Geochemical and quantitative mineralogical analyses have been carried out on laterites that formed during the early Tertiary (Palaeocene) in Northern Ireland. Enrichment/depletion patterns have been identified for major, minor and trace (including rare earth) elements related to breakdown of the primary minerals plagioclase, augite and olivine and formation of secondary oxides and clay minerals. Maximum concentrations of Si, Mn, Mg, Ca, Na, K and Sr were found to occur in the parent basalt whereas concentrations of Ti, Fe, Pb, Th, U, Cr, Nb, Rb, Ba, V and Zr are at a maximum in the highly weathered iron crust. Redistribution of Al, Cu and Ni occurred during lateritization with these elements leached from the uppermost iron crust horizon and reprecipitated further down the weathering profile. Weathering caused mobilization and fractionation of the rare earth elements with the light rare earth elements leached preferentially to the heavy rare earth elements.