Altered kimberlites of the Vakunaika river: new data and prospects

Prospecting for diamonds and their sources started in the Irkutsk region in 1947. After the large diamond deposits were discovered in Yakutia, the high-scale diamond prospecting in the Irkutsk region was nearly abandoned for a number of reasons though there were numerous diamond crystals found in the alluvium of the major watercourses in the north and south of the region. The general search for diamonds in the platform part of the region was conducted by geological survey and dedicated research projects. However, the half-century prospecting failed to identify primary diamond sources in the platform part of the Irkutsk region. The described territory belongs to the Lower-Tunguska (Nepa-Chona) diamond province. Its diamond content is attributable to the magmatic, lithologic-stratigraphic, tectonic, mineralogical, and geomorphological factors. The diamond-bearing prospects of the area were determined by the many-year exploration conducted by the Irkutsk Geology Directorate (“PGO Irkutskgeologia”), the Amakinskaya survey party (“PGO Yakutskgeologia”), and by the dedicated projects of the research-and-production organizations of the USSR and Russian Federation. The heavy mineral sampling identified pyropes and chromespinelides, the minerals that are paragenetically associated with diamonds, in most of the watercourses of the area. LLC Angarsk Investment Company has been prospecting for diamonds in the Irkutsk region including the Katangsky district, since 2006. The aim of the exploration is to identify primary diamond sources, the research object being Verkhnechonskaya license area (hereinafter, Irkutsk area). The research methods include reconnaissance traverse, heavy mineral sampling in small volumes and from depth, ground-based magnetometry, prospecting and core drilling to verify the geophysical and mineralogical anomalies identified by the previous diamond prospecting operations, analytical and laboratory studies, and processing of the obtained data. One of the most significant research results is the discovery of the rocks of kimberlite nature. For the first time, the search in the Siberian platform area has identified formations that resemble kimberlites by their mineralogical, geochemical and petrochemical data. The formations have been provisionally named altered kimberlites. The rocks had been subjected to the intensive superimposed processes that nearly completely altered their original appearance and composition. They form a diatreme of complex morphology, the structure of which shows the signs of repeated tectonic shifts. The structural and tectonic conditions of the diatreme are in many respects similar to those of the kimberlite pipes in the Yakutia diamond-bearing province. The main conclusion is that the discovery of the ultrabasic rocks of the kimberlite group allows us to consider the primary diamond potential of the northern areas in the Irkutsk region to be very high.

altered kimberlites, Irkutsk area, pipe, diamond-bearing, kimberlite fields