Home – Home – Jornals – Russian Geology and Geophysics 2018 number Неопубликованное

Carbonatite breccias (CBs) were discovered in the Tomtor Massif (Complex) (TM), which hosts the largest REE-Nb-Sc-Y ore deposit, by holl G2 in the northern Buranny area. CBs are petrographically complex rocks consisting of fragments of dolomite, dolomite-ankerite, ankerite and calcite carbonatites with significant contents of F-REE carbonates, pyrite, and fluorite. CBs show signs of fragmentation of carbonatites and calcite rocks, as well as the movement of these fragments by younger melt-brine enriched in CO2, F, S, and REE, and its interaction with the fragments. The studied rocks are classified as magmatic-fluidogenic and fluidogenic breccias, which provide a unique source of information on the rock composition and processes occurring at deep levels of the TM. The distribution pattern of trace elements in the KB, presented in spider diagrams, largely corresponds to the distribution of these elements in carbonatites and uniquely rich Nb-REE ores of the upper ore horizon of the TK. Spider diagrams reveal enrichment in Th, Nb, La, Ce, and Nd and depletion in U, K, Sr, Zr, Hf, and Ti, as in other carbonatite complexes of the world (including those with breccias). The REE distribution shows enrichment in MREE and HREE. The formation of the KB is accompanied by the crystallization of REE minerals with a composition unique to the TK, primarily synchysite-(Ce), parisite-(Ce) and/or bastnaesite-(Ce), cebaite-(Ce), and burbankite. Crystallization of REE-fluorcarbonates is associated with the process of dolomite replacement by ankerite, on the one hand, and the maximum amount of these minerals, as well as cebaite-(Ce) and burbankite, is recorded in calcite rocks in association with fluorite and pyrite, on the other hand. It is shown that the position of the δ¹⁸O and δ¹³C‰ composition points in KB fragments and in the interfragmentary space form a dependence with a high correlation coefficient value, close to the trend characterizing the process of mixing of C and O isotopes of carbonatites and sedimentary carbonates. However, this conclusion contradicts the data on high contents of REE, Nb. P and other elements typomorphic for carbonatites with increasing δ¹⁸O and δ¹³C‰ values and is a result of the transformation of carbonates by a low-temperature deuteric fluid. For the first time, the obtained comprehensive data on KB allow us to consider these formations as a new type of mineralization for TK.