THE BURANNYI SITE: THE ORE HORIZON STRUCTURE TOMTOR DEPOSIT ( <i>Sakha Republic, Yakutia</i> )

The Tomtor Complex of ultramafic rocks and carbonatites is located in the north of the Sakha Republic (Yakutia). Unique Sc-Y-Nb-REE ores of the Burannyi site (Tomtor deposit) are cryptogranular and have high contents of Nb2O5, REE2O3, Y2O3, and Sc2O3. Thin-layered ore bodies are stratified formations that presumably occur in weathering crust depressions. Based on modeling the shape of the roof and ore body base, as well as the overlying Permian continental and Jurassic marine sediments of the Burannyi site, the structural and morphological features of the ore layer were identified, using the QGis (QGIS.ORG Association, Switzerland) and Micromine (Micromine Pty Ltd., Australia) software packages. High-grade ores of the Burannyi site lie on an irregular surface. In the base of the ore layer there are two isolated depressions, the Northern and the Southern, which in turn are complicated by basins of various sizes. There are ten basins in the Northern Depression and four in the Southern Depression. The basins form linear structures that coincide with faults identified during exploration. Only four basins in the northern part of the site are completely filled with ore matter. Others are partially filled with ore, and the remaining volume is occupied by Permian coarse-grained clastic coalbearing sediments. In the Southern Depression, the proportion of basins filled with ore material is the lowest; the deepest basin is filled with ore by only 25%. It is assumed that this difference is caused by different times of basin formation. Developing the hypothesis that the ores are sediments of a thermal reservoir, we suggest that the formation of basins at the ore layer base occurred as a result of hydrothermal (phreatic) explosions. The presence of tectonic breccia confirms the occurrence of fast high-pressure processes in the Tomtor Complex.