ABSTRACT
Dark organic-rich concretions and bands occur in the white-grey sandstones, usually 1.5-2m below the copper-bearing shale, often in one horizon, spatially related to the discontinuous finer-grained, clay- and organic-rich dark bed. Three major types of the concretions (I – black and dark-gray; II – transitional two-colored: dark-gray and red;, III – red) have been described and their origin presented.
