Chromium-rich illite/smectite in the basal Balinka Conglomerate of the Upper Carboniferous-Permian Boskovice Basin (Bohemian Massif)

The Upper Carboniferous polymictic Balinka Conglomerate was deposited along the western margin of Boskovice Basin (eastern part Bohemian Massif). Angular aggregates deep-green chromium-rich interstratified clay mineral R1-illite(0.8)/smectite (I/S) are present exclusively in basal this unit. textural position chromium-bearing I/S (0.77–2.88 wt.% Cr 2 O 3 ; 0.040–0.153 apfu Cr) conglomerate matrix indicates a genetic link with highly altered chromium spinel, which is preserved relics. source Cr-rich spinelides serpentinized peridotites adjacent Moldanubicum (Gföhl Unit). formation related to diagenetic processes matrix. fluids would have relatively high fugacity CO and activity K + . K/Ar ages 284.1 ± 7.7 276.3 7.4 Ma (lower Permian – Kungurian/Artinskian age) confirmed origin I/S.