Abstract:
Various types of hydrothermal veins with calcium zeolites: chabazite-Ca, stilbite-Ca, heulandite-Ca, laumontite and scolecite, associated with fluorapophyllite, prehnite, thaumasite, gypsum, and some other low-temperature minerals, are widespread within biotite-muscovite, nodular, biotite and horblend-biotite gneisses in the contact zone with iron quartzites of Olenegorskoye and Kirovogorskoye banded iron ore deposites. They were formed in the outer parts of iron ore bodies as a constituent of the process of nodular gneisses formation, due to reactions related to the silicon dioxide input from iron quartzites into biotite gneisses. Taking into consideration this geological position of the zeolite-bearing segregations, their con-cordance with the high-temperature textures of the host gneisses, and their age dating, it is possible to esti-mate their forming conditions (temperature from 200 down to 50 °C, and pressure from 300 down to 1 bar) as corresponding to the final stage of formation of the banded iron ore deposites.
