In 1972 the government established a much closer link with active exploration when the Department of Industry contracted the Institute of Geological Sciences to undertake a reconnaissance search for base metals. In effect, an experienced team of field geologists, geochemists and geophysicists with back-up analytical services was required to locate new occurrences of base metals which, it was hoped, would subsequently attract mining companies. Because this Mineral Reconnaissance Programme appeared at a relatively late stage in Scotland's exploration history it was anticipated that it would be concerned mainly with deposits which were only marginally economic and consequently not immediately attractive to mining companies. Naturally this has meant that some projects have proved disappointing but recently the programme has received a welcome shot in the arm wit the announcement of a favourable conclusion to work being carried out at Vidlin, 25 km north of Lerwick, Shetland.

This concerns a 'pyrite bed', discovered by an officer of the Geological Survey as long ago as 1930 but not followed up (largely because it was not of the vein type of mineralisation then being sought) until a research student working with Dr. D. Flinn of Liverpool University noted the additional presence of chalcopyrite and the latter drew the attention of BGS to this. This was significant, for in the intervening years several economically viable 'stratabound' type sulphide ore bodies have been discovered in Scandinavia within schists which, though probably of Silurian age, have nevertheless strong similarities with those of Shetland. Initial geochemical tests carried out by IGS were encouraging and in 1975 a combined geological - geochemical - geophysical investigation was mounted which culminated in the spring of last year in a drilling programme which located a stratabound ore body 500 m long and up to 10 m thick, with the mineralised samples containing up to 12% copper, 1.7% zinc and 0.23% lead.

When the report on the investigation was published the mineral rights were obtained by a mining company and the result of their continuing exploration will decide whether the deposit is economically viable. The residents of the Vidlin area have the satisfaction of knowing that should the deposit be worked it will be by mining and not by opencast. Despite the as yet unproven viability of Vidlin the discovery of Scandinavian type massive sulphides in Scottish Dalradian rocks has given a considerable boost to other investigations being carried out by IGS in the Grampian Highlands which have located similar 'pyrite beds' but none with sizeable base-metal contents. By analogy with Vidlin, it is quite possible that sulphide deposits of economic proportions are present.

In passing, it is interesting to note  that the Vidlin mineralisation has several unusual features which distinguish it from most other Scottish copper deposits. In particular it is a stratabound body of pyrrhotitic ore, whilst the majority of Scottish occurrences comprise pyrite vein deposits. However, the most significant aspect of the Vidlin deposit is its close association with amphibolites - almost certainly the first recorded example in Scotland of a stratabound base-metal deposit interbedded with metamorphosed basic volcanic rocks. Perhaps the only comparable Scottish deposits are those at Craignure and Coille-Bhraghad on the wets side of Loch Fyne though these lack the volcanic associations and have relatively high nickel concentrations.

This note is published with the permission of the Department of Industry and the Director of the Institute of Geological Sciences.