Crystalline manganese oxides in till, from Bridge of Don, Aberdeen

Abstract

Synopsis Highly crystalline manganiferous blocks consisting mainly of manganite and pyrolusite occur in a supraglacial flow till. Field evidence indicates that mineralization, which is of high chemical purity and notably free of iron, occurred in situ. The segregation of manganese from iron probably occurred as a result of selective dissolution of manganese in waterlogged organic-rich soil or sediment. Manganese and associated barium may have been transported by groundwater to its present location largely in the form of colloidal hydrous manganese dioxide. Initial deposition appears to have been localized by impersistent clay bands, with further deposition being catalysed by previously deposited manganese oxides. Local topography and depth of the clay bands relative to a fluctuating water table were probably critical in localizing the mineralization.

An ancient manganese-iron deposit of freshwater origin, Islay, Argyllshire

“…Although the presence of pyrolusite is frequently recorded in the early mineralogical literature, this cannot be considered as a reliable identification, but should more realistically be regarded as a field-term applied to any hard, blue-black, crystalline manganese oxide. Despite its supposed widespread occurrence, pyrolusite has been identified by modern techniques at only three other localities in Scotland; in a manganese vein at Arndilly, Banffshire (Nicholson 1986); in the Lecht manganiferous ironstone, Banffshire (Nicholson 1987b); and within manganite blocks in glacial till in Aberdeenshire (Chew 1978). In each case it is only a minor constituent.…”