The nickeliferous Elan complex of the Voronezh Crystalline Massif: composition and nomenclature of the rocks

Abstract

Introduction: In the structure of the Precambrian foundation of the Voronezh Crystalline Massif, subvolcanic bodies were detected that were attributed to the Elan norite-diorite complex. Two large sulphidic nickel deposits, Elan and Elki, are associated with it. The discrepancy between the traditional names of the rocks of the complex and the existing classifications stimulated us to publish this paper. Methodology: Detailed petrochemical and petrographic studies were carried out. Results and discussion: The Elan and Elki petrotypical plutons are subdivided into cumulative, differentiated, and dyke series. The rocks are part of the medium and acid formations of the calc-alkaline series; with the exception of cumulates, which are in the boundary region between the medium and main groups. The differentiated series is common and consists of ultra-magnesium granitoids. It forms continuous rows of: (1) biotite-orthopyroxene meladiorite – quartz meladiorite – quartz melamonzodiorite – melagranodiorite and (2) hornblende-biotite, biotite, and quartz diorite – tonalite – granodiorite – monzogranite. The cumulates are represented by melanorite, plagioorthopyroxenite, quartz-containing melanorite, and quartz melagabbrodiorite, as well as hornblendite, hornblende melagabbro, and quartz melagabbrodiorite. Conclusions: The conclusion was made about the need to review the composition of the complex (the proposed new name: melanorite – quartz meladiorite – granodiorite Elan complex). It has been proposed to use the determined varieties in geological exploration to carry out the petrographic control of sulphide mineralisation.