Cenozoic diamondiferous depressions of the southern part of polyudov ridge (Vishera diamond area)

Abstract

In the West-Ural zone of folding within the southern part of the Polyudov Ridge, Cenozoic diamondiferous deposits are identified that carry out the Volyn-Kolchim, Ilya-Vozhsk, Western and Burkochim paleo-depressions. They are developed mainly from the contact of the Lower Silurian carbonate rocks and terrigenous Vendian-Cambrian rocks, forming elongated negative forms in terms of up to 7.6 km long, and in cross section a trough-shaped profile up to 1.1 km in size with elements of V-shaped incisions across reach 0,13 km. Depression`s deposits have polyfacial genesis, usually divided into five (up to nine) diamondiferous (aQIII, ldQII, d-pQII, d-pN, eMZ-Р) and upper non-diamond-bearing (dQIV) layers. According to morphology and lithological characteristics, the studied depressions are attributed to the corrosion-erosion type of the Cenozoic time. The mineral composition is predominantly goethite-illite. The heavy fraction of sedimentary depressions is similar and corresponds to the leucoxene-tourmaline-zircon association. Fine minerals of the lenses and interlayers along cracks are represented by smectites and halloysite. The composition of the heavy fraction of the Neogene layers is similar to that of the Takatin- -time and Kolchim-time sandstones. It is dominated by zircon (up to 90%), to a lesser extent tourmaline (up to 20%), leucoxene (up to 20%), rutile (up to 9%). A significant proportion belongs to authi-genic minerals - limonite, hematite, pyrite. The placer formation of these depressions assumes a large role of the Pre-Latino and Meso-Cenozoic chemical weathering crusts, and they are essentially intermediate formations between the weathering crust and the products of their redeposition in the channel alluvium, which was developed by dredging until recently.