Variations in Chemical Compositions of Titanite Group Minerals from Ore Skarns in the Ladoga Lake Region (South Karelia, Russia)

Titanite, Al- and F-enriched titanite, tin-bearing titanite, and malayaite from ore skarns in the Ladoga Lake region have been studied. The composition of these minerals from skarns with W–Zn–Pb–Bi (Latvasyrja, Jokiranta) and Sn–Zn–Cu–Fe–In (Pitkäranta mining district) mineralization, related genetically to S- and A-type granites, was analyzed. For the first time, Al-rich (Al2O3, 5–7 wt %) and F-rich (~3%) titanite was detected in ore deposits and occurrences in Karelia. The isomorphic substitutions in titanite from skarns with different metallogenic specialization were considered. It is shown that the following isomorphic schemes are realized for studied titanite: (Al, Fe) 3+ + F– ↔ Ti4+ + O2–; (Al, Fe) 3+ + (OH) – ↔ Ti4+ + O2–, where Al Fe (skarns with W–Zn–Pb–Bi mineralization), and Sn4+ ↔ Ti4+ (skarns with Sn–Cu–Fe–Zn–In mineralization). The Sn-bearing titanite from Sn-bearing skarns almost always Fe-bearing, which seems to be due to high Fe of rapakivi granites containing biotite and other mafic minerals with Fe# > 0. 9. The high Fe content is preserved at the postmagmatic stage, which resulted in the formation of columbite- (Fe), synchysite- (Fe), and marmatite. The formation of titanite enriched in aluminum and fluorine was controlled by protolith and fluid compositions rather than temperature and pressure (500°C, 5 kbar). Crystallization of this titanite in Jokiranta ore occurrences took place during a post-ore-forming process, potentially capable to the remobilization of base-metal ores.