Geological and structural characteristics of deep-level rock mass of the Udachnaya pipe deposit

For hard rock massifs, structural disturbance is a key indicator of mining structure stability. The presence of intersecting structural elements in the massif reduces rock strength and leads to formation of potential collapse structures. In addition to that, disjunctive deformations that penetrate rock strata serve as channels for fluid migration and connect aquifers into a single system. It was established that the largest of them –faults of east-northeastern, northeastern and northwestern directions – form the kimberlite-bearing junction of the Udachnaya pipe. These faults represent zones of increased fracturing, brecciation and tectonic foliation, distinguished from adjacent areas by increased destruction of the rock mass. Specifics of tectonic fracture distribution within structural and lithological domains are determined by the presence of multidirectional prevailing systems of tectonic fracturing, as well as by differences in their quantitative characteristics. With some exceptions, the main systems form a diagonal network of fractures (northeastern – northwestern orientation), which is typical for larger structural forms – faults. Despite the differences in dip orientation of the systems, most of them correspond to identified directions, which is typical for both kimberlites and sedimentary strata. Overall disturbance of the massif, expressed in terms of elementary block volume, reaches its peak in the western ore body. For such type of deposits, friction properties of fracture structures have average values. Consideration of geological and structural data in the design and development of new levels of the deposit will allow to maintain the necessary balance between efficiency and safety of performed operations.

Sulfur isotopic compositions of the lithospheric mantle sulfides from the Udachnaya pipe (Yakutia)

<p>Sulfide inclusions in Neoproterozoic West African diamonds have revealed mass-independently fractionated sulfur isotopes in them [Smit et.al., 2019]. This feature is a sign of Archean surface changes traced in the mantle. Here we present an S isotope study of the unique fresh mantle deep-seated peridotites, eclogites and pyroxenites with rare or without any secondary alterations from the Udachnaya-East pipe. This research will give better understanding the role of subduction in the formation of the lithospheric mantle under the Siberian craton. Sulfur isotopes (<sup>34</sup>S/<sup>32</sup>S which is denoted as δ<sup>34</sup>S) were measured in the sulfides from eclogites, peridotites and pyroxenites using an Isoprime isotope ratio mass spectrometer (IRMS) with classic configuration with 4 collectors. The sulfides from eclogites are pyrrotite, pentlandites and chalcopyrites. They have δ<sup>34</sup>S values from +0,67 to +3,08 per mil (‰). Sulfides in peridotites are pyrrotite-pentlandite-chalcopyrites assemblages and they have δ<sup>34</sup>S values from +0,22 to +3,55 ‰. These δ<sup>34</sup>S values from eclogites and peridotites are broadly overlap with the field for depleted mantle and chondrites (-1,9 to +0,35‰) [Labidi et.al., 2013; 2014]. Sulfides from pyroxenites are pyrrotite and they have δ<sup>34</sup>S values from -3,62 to +1,49 ‰. These δ<sup>34</sup>S values have a wider range than the estimates for depleted mantle. The δ<sup>34</sup>S values in our samples are close to those in the depleted mantle, but still have deviation from it and do not fractionated. Our data did not detect mass-independently fractionated sulfur isotopes in the mantle samples from the Udachnaya pipe. Thus subduction of the earth’s crust did not play role in the values of sulfur isotopes of the lithospheric mantle sampled by Udachnaya kimberlite pipe. The source of sulfur in these rocks probably was the astenospheric mantle.</p><p>References</p><ol><li>Smit et. al., 2019</li> <li>Labidi et. al., 2013; 2014</li> </ol><p>This study was supported by the Russian Foundation for Basic Research № 18-05-70064</p>

The nature of philogopite-ilmenite and ilmenite paragenesises in deep-seated xenoliths from Udachnaya kimberlite pipe

The article describes the petrography and mineralogy of xenoliths ilmenite-phlogopite containing deformed and granular peridotites from the Udachnaya-Eastern pipe. The age of pholopite porphyroclast from the studied deformed xenoliths matches with age of phlogopite megacryst and itself hosted kimberlites from Udachnaya pipe indicating the following processes closed in time: 1) crystallization of the low-Cr megacryst association; 2) deformation of rocks on the mantle lithosphere - asthenosphere border during the kimberlite-forming cycle; 3) formation of protokimberlite melts.