Stratiform barium enrichment in the Dalradian of Scotland

Abstract

A stratigraphic zone of calcareous schist containing barite and/or barium silicates with minor sulfides occurs at the top of the Ben Eagach Schist near Loch Lyon in the metamorphosed and highly deformed Middle Dalradian rocks (ca. 600 m.y.) of the Grampian Highlands. The Ben Eagach Schist consists of graphitic schist, micaceous schist, and quartzite and is approximately 200 m thick on Beinn Heasgarnich. The mineralized zone is 1 to 3 m thick, containing 4.5 percent Ba and 0.2 percent Zn at its type section, and occurs over at least 4 km of strike. The main barium-bearing mineral is muscovite with up to 10.3 percent BaO; hyalophane is usually present as the coexisting feldspar. Though not everywhere present, barite comprises as much as 11 percent (modal) of the schist and is associated with manganoan calcite. At one locality the zone is celsian rich with pyrrhotite as the main sulfide. Pyrite and minor sphalerite are the most common sulfides, but traces of galena and chalcopyrite also occur.The newly discovered barium-enriched zone is the lateral equivalent of substantial strata-bound barite and sulfide deposits, with associated barium silicates, which occur in the Aberfeldy area some 45 km to the east-northeast. The zone is interpreted as having formed in a short-lived shelf area adjacent to a second-order basin (Easdale) immediately southwest of a similar basin centered on Aberfeldy, where the barite deposits are believed to define small third-order basins, the development of which was controlled by rift-related faulting. The Ben Eagach Schist and associated Middle Dalradian formations of the Aberfeldy and adjacent basins have considerable potential for further exploration.