Mineral investigations in the Northumberland trough : part 1, Arnton Fell, Borders, Scotland

Recognition that the tectonosedimentary environment of the Solway-Northumberland basin is broadly similar to the Lower Carboniferous base-metal province of the Irish Midlands prompted the BGS Mineral Reconnaissance Programme to initiate a drainage survey over the post-Silurian unconformity in southern Scotland in the early 1970's (Haslam, 1972). A follow-up survey in the area to the south-west of Langholm in 1975 traced anomalous Pb and Zn values to a small outcrop of sandstone containing disseminated galena within the 'cementstone' facies of the Lower Border Group close to the contact of the basal Carboniferous Birrenswark lavas. Subsequently, soil and deep overburden studies followed by diamond drilling identified sub-economic base metal concentrations in Lower Border Group rocks extending along 4 km of regional strike (Gallagher et al., 1977). Reconnaissance panned concentrate sampling continued in 1976 to the north-east of Langholm, successfully identifying a number of mainly Zn, Ba and minor Pb anomalies indicative of further mineral occurrences along the northern margin of the basin, but detailed investigations to trace these anomalies to source was not undertaken at that time. A systematic drainage survey of southern Scotland as part of the BGS Geochemical Baseline Survey of the Environment (G-BASE) in the period 1981 - 85, provided high-quality stream sediment data for the area which identified the presence of anomalous base metal zones close to the basin margin (British Geological Survey, 1993). In 1992 a new MRP project aimed at stimulating mineral exploration interest in the northern margin of the Northumberland-Solway basin was instigated. It was prompted by the completion of a multidisciplinary study into the analysis of spatially-related datasets and mineral deposit modelling for carbonate-hosted mineral deposits in northern England (Jones et al., 1994). An evaluation of MRP panned concentrate data and G-BASE stream sediment data in conjunction with geological and geophysical information revealed the presence of distinct patterns of metalliferous element enrichment partly coincident with north-east trending Dinantian growth faults developed along the northern basin margin. Comparison of the regional patterns for Pb, Zn, Cu and Ba in the two sample media (Colman et al., 1995), concluded that panned concentrates were the preferred sample type for tracing the source of base-metal mineralisation. Several areas prospective for stratabound base-metal mineralisation were identified, and the results of follow-up investigations in the first and most northerly of these target areas, are presented in this report. The project area is situated in the Roxburgh District of the Scottish Borders, 15 - 20 km north-east of Newcastleton and about the same distance south-east of Hawick. It lies within the Ordnance Survey 1:50,000 map sheet 80 (The Cheviot Hills), and British Geological Survey 1:50.000 map sheet 17E (Jedburgh). Mature coniferous plantations cover the entire area apart from a narrow east-west strip of land separating Forestry Commission in the north from private forestry in the south. The relief is moderate to steep, rising from about 200 m in the valley bottoms to nearly 600 m on Peel Fell at the eastern edge of the area. Extensive deposits of peat, generally 1 - 2 m thick, overlie glacial deposits which mainly comprise a clay-rich, grey-brown till averaging 3 m in thickness, but locally exceeding 6 m on the lowest ground. The headwaters of two river systems, the Liddel Water (- Peel Burn - Wormscleuch Burn) and the Jed Water (- Raven Burn) catchments, drain to the south and north respectively from a central watershed at Wheelrig Head [NT 615 015] (Figure l). Outcrop is sparse being limited mainly to the upper reaches of the more deeply incised stream sections. forestry tracks, and one or two small quarries and other excavations for local road stone supplies.