Stratabound barium-zinc mineralisation in Dalradian schist near Aberfeldy, Scotland. Final report

The discovery and preliminary assessment of stratabound barium-zinc mineralisation in Dalradian metamorphic rocks near Aberfeldy (outlined in MRP Report No. 26) resulted from co-ordinated geological, geochemical, geophysical and mineralogical studies, full details of which are presented here. The presence of an extensive zone of mineralisation in the area was recognised initially by a geochemical drainage survey and , reconnaissance geological mapping. Subsequently, more detailed mapping and drainage sampling were supplemented by VLF-EM geophysical surveys, overburden and rock sampling, and shallow drilling. The VLF-EM technique successfully delineated resistive rocks within the generally conductive graphitic schists and proved a valuable mapping aid in areas of poor exposure. The mineralised zone is defined by the presence of bedded baryte, sulphide concentrations, quartz-celsian rock and micaceous schists in which the muscovite is barium-rich. It varies in thickness from about 60 m to 110 m and extends, at least intermittently, over 7 km of strike and through a vertical interval of 370 m. Individual baryte bands are 2.3-l 5.5 m thick and may extend along strike for up to 1.8 km. The greatest sulphide concentration is in carbonate rock assaying 8.5% Zn and 3.6% Pb over 4.3 m. Other unusual constituents of the mineralised zone are the barium silicates hyalophane and cymrite and the chromian muscovite fuchsite. It is concluded that the mineralisation is of synsedimentary origin, involving the introduction of metal-rich hydrothermal brine into an euxinic basin.