Laser-indused photoluminescence of apatite from carbonatites and phoscorites of ultrabasic-alkaline complexes of the Kola Peninsula, Russia
Sokolov S.V., Rassulov V.A.
All-Russian Institute of Míneral Resources (VIMS), Moscow, Russia
In many alkaline-ultrabasic complexes of different regions of the world, the carbonatites are associated with phoscorites − carbonate-bearing silicate-phosphorous-ferruginous rocks. Time and spatial accompaniment established between these rock series allowed to suggest their genetic unity.
The evidence of this proposition is based upon the following criteria (Sokolov, 1983): 1) adequate mineral composition relative to main, minor and accessory minerals and rather close chemical composition of the minerals of the same name; 2) similar geochemical specialization, expressed by enrichment in such components as Nb, Ta, Zr, U, Th, lanthanoids of cerium group, H2O, CO2, F; 3) coinciding or close by values of distribution coefficients of Ni, Ba, Fe between coexisting minerals; 4) identical isotopic composition of calcites (δ18О, δ13С).
In our earlier publications by the example of carbonatites and phoscorites of the Kovdor massif was shown, that calcites and apatites from these rocks are identical to each other by thermoluminescent properties (Sokolov, 1983), and apatites also on spectra of X-ray luminescence and photoluminescence (Sokolov, Rassulov, 2009).
At present work are given results of study of laser-induced (N-laser LGI-505, lexc = 337.1 nm) photoluminescence of apatite from the same rocks of three other massifs of the Kola Peninsula (Vuoriyarvi, Seblyavr, Turiy Mys).
The used equipment (its description is given in the article by Sokolov, Rassulov, 2004) has sensitivity to valent state of the elements-luminogenes and high spatial resolution (30-50 mm). According to the method of investigation (Rassulov, 2005), in each sample, besides integral spectrum, was measured spectrum with registration delay on 180 ms, on which were more distinctly expressed lines of the rare-earth centers with long afterglow (Sm3+, Dy3+, Tb3+, Eu3+).
Obtained by us results testify (see Figure): 1) on spectra of photoluminescence of studied apatites are present bonds of optic-active centres of manganese (constantly) and rare-earth elements (in different combinations) – Ce3+ (390/420 nm), Dy3+ (485 и 575 nm), Tb3+ (550 nm), Mn2+ (585 nm), Eu3+ (598 и 628 nm), Sm3+ (600 и 642 nm); 2) in apatites from phoscorites, as a rule, intensity of bands of lanthanoids and manganese is greater; analogous relations are established also in X-ray luminescence spectra of apatite (Sokolov, Rassulov, 2009).
Analysis of measured spectra shows, that apatites from both rock series in each massif are characterized by very similar spectra of photoluminescence (excluding insignificant differences), and at the same time they are different in one or another degree in individual massifs. Apatites of the Kovdor massif are strongly distinguished by weak display on spectra of rare-earth elements bands. The samples of these apatites represented earlier formations of phoscorites and carbonatites with green phlogopite. In other massifs the apatites belong to relatively late rocks with tetraferriphlogopite, which in addition to are enriched in rare-earth elements.
Rare differences in spectra of photoluminescence are expressed in that one of compared apatites from the Vuoriyarvi massif do not display bonds of Eu3+ (628 нм) and Sm3+ (642 нм), and at the Turiy Mys massif bond of Tb3+ (550 нм). These differences are not essential and might be caused by irregularity of distribution of optically active admixtures among zones (blocks) of apatite crystals or absence of the components (Na, OH, F), which compensate charges of trivalent rare-earth elements and by this way transfer them into luminogene category.
Conclusions: apatites from phoscorites and carbonatites of the alkaline-ultrabasic complexes of the Kola Peninsula are characterized by practically similar thermo-, X-ray-, and photoluminescent properties. This fact, in addition to earlier established ones, confirms once more genetic unity of phoscorites and carbonatites, which make up rare metal-phosphorous-ferruginous ores at the massifs Kovdor, Vuoriyarvi, Seblyavr, Turiy Mys.
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Fig. 1. Representative spectra of laser-induced photoluminescence of apatite from phoscorites (1-4) and carbonatites (5-8); z – spectra, resulting from registration delay of 180 ms. Massifs: Kovdor (1 and 5), Vuoriyarvi (2 and 6), Seblyavr (3 and 7), Turiy Mys (4 and 8). Spectra given without taking into account spectral function of the register.