Growth dissymmetrization of rare earth element distribution and the Sm-Nd isotope system in fluorite crystals of the Nordvik deposit (Taymyr)

Abstract

Mineralogists and physicist have long been interested in the nature and regularities of the zonal‐sectoral structure of mineral monocrystals, but in many cases they have not found adequate explanation. In some works it was shown that dissymmetrization of physical features observed for such objects to a significant degree was connected with fractionation of trace elements and atomic groups by symmetrical nonequivalent facets of the growing crystal. For example, D. Rakovan et al. [1] has revealed a strongly expressed sectoral zonality in the distribution of trace rare earth elements (REE) in crystals of natural apatite with the help of synchrotron X-ray fluorescence microanalysis (SXRFMA). Analogous but weaker and ambiguously revealed effects have also been established for fluorite from several American deposits [2]. In [3] we used the method of high-resolution X-ray luminescence spectroscopy and discovered a special type of fluorite crystals of cuboctahedral habit (KOF‐1 type) characterized by distinctly revealed separation of “light” (LLn) and “heavy” (HLn) trace lanthanoid ions in different pyramids of growth of one growth zone of crystal. Among such objects, cuboctahedral fluorite crystals from the Nordvik deposit (Taymyr) are investigated in detail in this work. The deposit of optical fluorite Nordvik is located in the Uryung‐Tumus peninsula of the Khatanga Gulf and is connected with one of the salt dome and oil-bearing structures situated within the Enisey‐Khatanga basin. Fluorite mineralization is mainly connected with the cap rock carbonate blocks. The peculiarities of the fluorite genesis and geological structure of the Nordvik deposit were described earlier [4‐6]. Two transparent and colorless fluorite crystals of rare (for the Nordvik deposit) cuboctahedral habit were used in our investigation. Crystals of about 4 cm in diameter were sampled from the fluorite‐calcite veinlet localized in the lowest part of the dolomitic cap rock of the Nordvik deposit western flank. According to the data of thermobarogeochemical investigation (E.V. Tolmachev), both crystals were formed from hydrothermal solutions under the temperature 340‐370 ° C. 1