Geochemistry and mineralogical residences of trace elements in oil shales from the Condor deposit, Queensland, Australia

Abstract

Stratigraphically selected samples from several bore cores were chemically analysed for trace elements using neutron activation analysis and X-ray fluorescence spectrometry. Inter-element correlation techniques, selective leaching procedures, X-ray diffraction and electron microprobe analyses were used to establish geochemical associations and specific mineralogical residences for a comprehensive range of elements. Abundances and mineralogical residences have been determined for a comprehensive range of trace elements in Condor oil shale. Trace-element abundances are generally similar to or less than those reported for an average shale. The exceptions are pyritic S, inorganic N and Mn which are often above normal abundances and together with As, are of possible environmental concern during processing. The results provide a definitive chemical and mineralogical characterization of the oil shale and identify the major mineralogical residences of the important trace elements. S, As, Ni and Co occur mainly in the mineral pyrite, while Mn is resident in siderite and magnesian siderite. S, Ni and Co also occur, to a lesser extent in the kerogen. Inorganic N occurs in the ammonium feldspar, buddingtonite, which formed by diagenetic replacement of K-feldspar. A sound basis is established for studies of mineral reactions during retorting, spent shale combustion and waste disposal.