Inorganic geochemistry and mineralogy of unit B, Duaringa oil shale deposit

Abstract

Chemical and mineralogical analyses are presented for a continuous sequence of samples over the full stratigraphic section of Unit B, Duaringa oil shale deposit. Correlation techniques and electron microprobe analysis have been used to determine element and mineral associations and the composition of manganoan siderites. The work presented provides a detailed chemical and mineralogical description of the unit. The geochemistry and mineralogy of Duaringa oil shales is similar to that of other Tertiary oil shales excepting that the composition of manganoan siderite crystals is unusually variable. A number of minerals show systematic trends with stratigraphie depth and oil shale grade in Unit B. In particular, pyrite correlates positively and manganoan siderite correlates negatively with oil shale grade. Manganoan siderites were inversely variable in manganese and iron content within individual grains. Manganese contents increased progressively from 1 wt% MnO at the extremities to as much as 15 wt% MnO in the central regions of some grains. This may reflect decreasing availability of manganese in the pore liquors as crystallization proceeded during early diagenesis.