Mineral investigations in the Northumberland trough : part 4, The Bewcastle area

Broad similarities between the tectonosedimentary setting of the Northumberland-Solway Basin and the extensively mineralised rocks of the Irish Midlands (Plant and Jones, 1991; Andrew, 1993) prompted the MRP to carry out exploration surveys for carbonate-hosted base-metals along a 70 km strike-parallel zone at the northern margin of the Solway-Northumberland Basin (Colman et al., 1995). This report describes the results of geochemical reconnaissance and limited follow-up sampling over the Lower Carboniferous rocks of the Bewcastle Anticline undertaken as part of these investigations. Situated only about 10 km south-east of the basin margin, the Bewcastle Anticline is considered to be a favourable environment for stratabound base-metal mineralisation because of the presence there of early Dinantian intrabasinal growth faults active during deposition of Lower Border Group (Courceyan-Chadian) carbonates and siliciclastics. By analogy with Irish-style SEDEX mineralisation these synextensional faults are the· most likely sites for metalliferous fluids expelled from deeper structural levels within the basin. Mafic lavas, which mark an early period of extensional fracturing at the basin margin, and are locally associated with mineralising hydrothermal activity, are of minor occurrence in the Bewcastle district, but may be more extensive at shallow depth in the core of the anticline or in the hanging wall block of growth faults.