First finds of platinoids in black-shale sequences of the Bureya Massif (Khabarovsk Region and Jewish Autonomous Okrug)

The problem of the platinum-metal potential in black-shale sequences has recently attracted the attention of geologists [1‐5], since highly carbonaceous rocks of different origins are considered to represent the most probable future nontraditional natural source of gold and platinoids. Black shales with high carbon contents are widespread in the Bureya Massif. Single chemical analyses revealed in them elevated concentrations of platinoids ranging from 0.0 n to n g/t [6]. The forms of platinoids occurring in these rocks remain, however, unknown, which hampers the assessment of their recoverable reserves and development of technologies for their extraction. In this connection, the purpose of this work is the study of the composition, morphology, and grain-size of platinoids in these rocks. Using the method of the scanning electron microscopy with an energy-dispersion analyzer (SEM-EDA), we found and first studied platinoids in black shales of the Sutyr and Kimkan sequences in the eastern Bureya Massif. These sequences represent constituents of the Upper Riphean‐Lower Cambrian Khingan Group. They are subjected to greenschist metamorphism, structurally uniform, and characterized by elevated carbon contents. The Sutyr Sequence ( PR 1 st ) constitutes an extended (75 × 5 km) tectonic block in the Khingan deep-seated fault zone. It is largely composed of carbonaceous shales, phillites, and metasiltstones with C org concentrations of 1 to 22%. Shales are sulfidized to different extents and enclose locally thin quartz stringers. Sulfides (pyrite and subordinate pyrrhotite, chalcopyrite, arsenopyrite, covelite, and marcasite) form fine-grained (up to 1 mm) impregnation, rare stringers, and lenses up to 0.5‐2.0 cm long. Carbonaceous material consists of fine dispersed amorphous matter and fine graphite scales sized 0.01‐0.03 mm. The semiquantitative analyses revealed gold, platinum, and palladium (up to 0.1, 0.04, and 0.01 g/t, respectively) in rocks of the sequence. Based on the lithological features, the Kimkan