The Dalradian rocks of the Lecht, NE Scotland: stratigraphy, faulting, geochemistry and mineralisation

Abstract

ABSTRACTAir photo interpretation and geochemistry have been used to supplement sparse field data in compiling a reconnaissance geological map of the area around the Lecht. Upper Appin and lower Argyll Group rocks are exposed, the best marker horizons being correlatives of the Appin and Jura Quartzites. Scatter plots, Q mode factor analysis and Pearson correlation coefficients of geochemical data were successfully used in the correlation of the pelite and limestone outcrops. The presence of major recumbent folds is inferred. The area is cut by numerous minor faults which are thought to be related to a major transcurrent fault, the probable north-eastern continuation of the Loch Tay fault, which was active in Lower Old Red Sandstone times.The Lecht manganiferous ironstone is a seepage-bog ore type deposit derived by weathering of the local Dalradian sequence. Despite intensive leaching, this sequence still shows anomalously high levels of several elements, particularly Mn, Ba and Zn. In addition, stratiform sphalerite and manganiferous garnet are present in Blair Atholl Subgroup limestone and pelite horizons, respectively. Mineralogical and geochemical evidence suggests the presence of Zn–Pb–(Ag)–(?Au) exhalative mineralisation within the upper Appin Group Dalradian of the region, of which the Lecht represents the distal manganiferous expression.