The concentration and distribution of U, its decay products, and other trace elements in reduction centres in sandstones of Late Pennsylvanian – Stephanian age from Pugwash Harbour, Nova Scotia were determined by chemical analyses and autoradiography.Bulk analyses showed U enrichment up to 150 times in reduction centres relative to oxidized host rock. In the host rock U and 226Ra were in radioactive equilibrium; in the reduction centres there was up to seven times as much U as 226Ra activity. Cu, Ni, As, and Hg were also more concentrated in the centres than in the host rock. Carbon was only slightly or not at all elevated and Fe was considerably depleted in the centres.Autoradiograph patterns from gamma rays, alpha particles, and fission tracks from the centres were found to be identical to each other, and the highest track densities coincided with the dark areas of the centres. In detail they revealed fine complex zoning. In dark bands U was concentrated in submicron grains from which fission tracks, too numerous to be counted, radiated. Alpha tracks from these areas gave calculated U concentrations of up to 13 000 ppm.The element disproportionation between host and centre and the disequilibrium between parent U and daughter 226Ra in the centres suggest microredox systems still active today.Chemical and microprobe analyses indicate oxides and sulfides of trace and minor elements to be responsible for the dark colouration of these centres.

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