Vivianite mineralization at the Zapadno-Biklyanskoye deposit of bentonite clays

For the first time, vivianite mineralization was observed in the West-Biklyanskoye bentonite clay deposit quarry. Vivianite occurred as radiating nodules, secretions, crusts, and earthy aggregates of bright blue color. The host rocks were deluvial loams enriched with syngenetic organic matter originating from the remains of anaerobic microbial colonies. The quarry site with the inclusions of vivianite aggregates was confined to a former bog area, as evidenced by the presence of peat layers in the roof of the sections. In areas where bog deposits were absent, no vivianite mineralization was found along the quarry walls. The formation of vivianite aggregates is therefore associated with the infiltration of bog waters containing mobile forms of iron and phosphorus compounds into the underlying deluvial loams. A continuous input of nutritious organic substances stimulated the proliferation of anaerobic microorganisms within these sediments. Their metabolic activity led to the concentration of mineral phases and the crystallization of vivianite and pyrite grains, which coalesced into aggregates. The change from reducing to oxidizing conditions contributed to the development of limonite crusts composed of goethite and hydrogoethites on top of the vivianite and pyrite aggregates.