Strontium and Barium Minerals in Alkaline Rocks of the Bolshetagninsky Ijolite-Syenite-Carbonatite Massif (Southwestern Margin of the Siberian Craton)

The paper displays data on Sr- and Ba-bearing minerals occurring in melteigite, ijolite, urtite, and nepheline syenite of the Bolshetagninsky ijolite-syenite-carbonatite massif. At the magmatic stage, strontium enters as an isomorphic admixture into calcite (SrO = 0.5–1.9 wt %) and fluorapatite (SrO = 0.6–2.6 wt %), while barium mainly enters in phlogopite and annite. Zonal phlogopite in urtite contains up to 8.4 wt % BaO (24 mol. % of kinoshitalite component); interstitial calcite in the same rock contains small ingrowths of barytocalcite. Stronalsite, strontianite, crichtonite, henrimeyerite, barite, celestite, Sr-bearing fluorcalcipyrochlore, Sr-bearing muscovite, and epidote have crystallized at the high-temperature postmagmatic stage. In the exocontact zone of the carbonatite stock, ijolite and nepheline syenite underwent biotitization, carbonatization, and K-feldspathization, followed by chloritization and formation, in some spots, of hyalophane and celsian segregations and veinlets. The formation of Ba-bearing muscovite and Ba-bearing manganese hydroxides took also place at the low-temperature hydrothermal stage. The presence of hyalophane and celsian in altered alkaline rocks is a peculiarity of the Bolshetagninsky massif, indicating the low activity of \({\text{SO}}_{4}^{{2 - }}\) in hydrothermal solutions.