Mineralogy and geochemistry of manganese and iron veins, Arndilly, Banffshire

Abstract

Synopsis Two veins, one composed of manganese oxides the other of iron oxides, occur 20 km south-east of Elgin in Grampian Region. They are hosted by the Dalradian (Lochaber Subgroup, Appin Group) Ben Aigan Quartzite which is intensely brecciated in some areas. The manganese vein is considered to be composed primarily of coronadite and wad, with minor hollandite and pyrolusite; the presence of romanechite in minor quantities has also been tentatively suggested. Goethite is the principal mineral of the iron vein, together with lesser hematite. Analysis of the vein material by ICP-atomic emission spectrometry revealed enrichments in Ag, Ba, Cu, Mo, Pb, Sb, V and Zn in all manganese specimens. Elevated levels of this diagnostic elemental assemblage in manganese oxides is known, from other studies, to be indicative of a hydrothermal influence. Although not of sufficient extent to be of economic significance in terms of manganese ore, the Arndilly deposit is considered, on the basis of geochemical and mineralogical evidence, to represent an oxide capping on stockwork-type mineralisation related to the Ben Rinnes granite. The whole of this area is regarded as prospective terrain.