Exploration for stratabound mineralisation in the Argyll Group (Dalradian) of north-east Scotland

The Mineral Reconnaissance Programme (MRP) identified several horizons of stratabound mineralisation within the Argyll Group during investigations of the Dalradian Supergroup in Scotland between 1973 and 1987. These included the multi-million tonne Aberfeldy baryte deposits. Most of the discoveries were made in the central and south-western Scottish Highlands, where the Dalradian succession is well recognised. The Dalradian of north-east Scotland, because of its poorer exposure and greater complexity, did not receive the same level of attention. The project reported here was set up to assess the potential of the Argyll Group in north-east Scotland for stratabound mineralisation, based on the geological models developed in the central Highlands. An initial desk study involved the digitisation (where necessary), integration and review of the following datasets: (i) geological mapping, including the results of new BGS mapping, (ii) BGS airborne aeromagnetic data, (iii) BGS geophysical ground survey results, (iv) BGS Geochemical Baseline Survey of the Environment drainage data, (v) existing MRP data, (vi) BGS traverse-based soil sampling results, and (vii) datasets collected by Exploration Ventures Ltd, principally detailed airborne and ground geophysical information. Assessment of these datasets identified three broad areas which contained geochemical, geophysical and geological features that merited examination to determine their sources and indicate the potential for economic stratabound mineralisation. These areas were Ballater-Strathdon, Upper Deveron and Huntly-Portsoy. Geochemical and geophysical ground surveys were carried out in parts of all three of these areas and followed-up locally by pitting and trenching to clarify, the sources of individual anomalies. The studies indicated that the areas with the most potential for stratabound mineralisation occur to the east of the Portsoy Lineament and/or in rocks which cannot be easily correlated with Argyll Group rocks elsewhere. These rocks tend to be lithologically different from the typical Argyll Group sequence and are generally more fractured, sheared, brecciated and altered. The most promising area for the discovery of stratabound mineralisation is considered to be in the Upper Deveron area at Wellheads. Here, high levels of lead and zinc in overburden are probably enhanced by hydromorphic processes, but the source of the lead has been traced to quartzites and the zinc to adjacent pelites within the Corinacy Pelite Member of the Blackwater Formation. The predominantly lead-zinc mineralisation is similar to that at Glenshee and Dericambus. Detailed VLF EM and IP surveys are recommended to assist in defining trenching and drilling targets. Lead and coincident IP anomalies at Succoth-Gouls also merit follow-up investigation. In the Ballater-Strathdon area a large EM and magnetic anomaly on Creagan Riabhach, although apparently low in base-metal content, merits further investigation on the grounds that: (1) a significant amount of sulphide mineralisation is present at shallow depth, (2) there is good evidence for stratabound mineralisation, and (3) the rocks are thought to be similar to the Ben Lawers Pyrite, where copper mineralisation occurs sporadically. In the Upper Donside part of the Ballater-Strathdon area several lead-zinc anomalies have been identified from drainage sampling, but very little mineral-exploration work has been carried out over the c. 10 km strike length of the Argyll Group metasedimentary rocks. The Glenbuchat Graphitic Schist Formation has a volcanic component here, providing the potential for hydrothermal mineralisation. In the Glen Avon part of the area lead and zinc drainage anomalies have been identified and their potential is enhanced by proximity to the Lecht mineralisation.