A review of nickel mineralisation and ore potential in the Arthrath intrusion, Aberdeenshire

Syn- to post-orogenic mafic-ultramafic intrusions of Ordovician age underlie extensive areas of the Caledonide belt in north-east Scotland. Scientific studies over the last forty years by Aberdeen University and the British Geological Survey (BGS) have revealed a complex assemblage of cumulate and other rock types in these bodies, locally altered and disrupted by late, high-temperature shearing. In detail the geology of most of these intrusions remains poorly known on account of the thick till deposits that cover most of the region.
\nSignificant magmatic nickel-copper sulphide mineralisation was discovered at two localities in these intrusions by Exploration Ventures Ltd (EVL) during a major exploration programme conducted between 1968 and 1973. Around the farms of Littlemill and Auchencrieve on the flank of the Knock intrusion EVL outlined a small deposit that has been intensely disrupted by shearing. At the second prospect, located in the Arthrath intrusion close to Ellon, disseminated and net-textured magmatic nickel-copper sulphide mineralisation was identified in five zones over a strike length of more than four kilometres. Anomalous concentrations of platinum-group elements (PGE) and cobalt are found locally in these zones. At Arthrath investigations by EVL and later workers have indicated that there has been much less tectonic disruption than in the Knock intrusion with the consequent preservation of thick intervals, locally exceeding 100 metres, of sulphide mineralisation.
\nReview of existing data in the light of deposit models for magmatic nickel-copper sulphide deposits worldwide suggests that there is good potential for the discovery of economic mineralisation of this type in the Arthrath intrusion. Further investigations are recommended to evaluate the potential in two settings in this body. First, given the limited drilling carried out to date and the lack of clear understanding of the controls on the known mineralisation, additional work is required to elucidate the lateral and vertical continuity of mineralisation identified by EVL. The second target is located in the broader area at the junction between the Arthrath intrusion and the larger Arnage mass to the west where investigations should be carried out to test the application of the conceptual model developed for the world-class Voisey’s Bay nickel-copper-cobalt deposit in Canada.
\nThe first stage of a future exploration programme should involve a thorough review by appropriate experts of the results of all previous work in the area. This should be followed by field investigations, including both geochemical and ground geophysical surveys and drilling. It is important that the programme at Arthrath take into account the results of work carried out in other parts of the region, such as Huntly-Knock, where the geology and mineralisation controls are better understood. Drill targets should be identified on the basis of the results of previous work, supplemented by new overburden/soil geochemistry and ground geophysical surveys (magnetic, electromagnetic and gravity). In order to acquire adequate data to identify an economic resource compliant with international reporting standards it is recommended that a diamond drilling programme of at least 15 boreholes be carried out in the most prospective zone identified from previous work and new surface investigations.

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