Mineralogical-geochemical features of rocks of small intrusions and dikes of the Evenk group of gold-silver deposits

Small intrusions and dikes of gabbroids represented by two geochemical types (potassium and sodium specialization) are studied. 87Sr/86Sr values (0.705) in the monzogabbros lie within the range common to the back parts of the active continental margins, while the gabbroids of sodium specialization possess high values of this ratio (0.708), which probably results from the contamination of the melt by the crust substance. Epithermal gold-silver deposits of the Evenk region are paragenetically associated with small intrusions of the Upper-Cretaceous granodiorite-porphyries and dacites. Rare element composition and 87Sr/86Sr values (0.705) in the granitoids are typical of the magmatites of active continental margins of the Andean type. 20 refs.; 4 figs.; 8 tabs