Noble Metals Associated with Organic Matter, Kupferschiefer, Poland

Abstract

The Kupferschiefer contains from 0.3 to 30wt.% organic matter. Only 1–3% of the organic matter is soluble; the remaining 97–99% occurs as a tightly intermixed, immobile, clay-organic matrix. A major component of the organic matter is vitrinite, with lesser alginite.

The clay-organic matrix of the shale contains small accumulations of Au, Pt, and Pd, probably as organometallic compounds.

Thucholite is present locally, and contains inclusions of uraninite, brannerite, and noble metal minerals located at the boundary between optically isotropic and anisotropic components. The minerals were exsolved during graphitization of the isotropic component of the thucholite. The optically homogeneous organic matrix of the thucholite contains discrete inclusions of UO₂, brannerite and organic compounds of U, Au, Pt, and Ni varying in size from 0.008 to 0.02μm, as shown by electron microscopy. The anisotropic component of the thucholite is composed of three types of ordered domains distinguished by three different values of graphite ring thickness (c₀, nm): 0.672, 0.740, and higher.

During replacement of thucholite by calcite at the boundary of the two minerals, native Au, Ag, Bi, PbBi, AuPb₂, Pb, Pd-arsenides, Bi-sulfides, PbSe, and TiO₂ developed.

The organic matter of the Kupferschiefer was oxidized by mineralized fluids; the process of catalytic oxidation was controlled by transition metal catalysts and was locally enhanced by γ-radiation from uranium. As a result, insoluble sulfides of metal catalysts accumulated in economic quantities.