In the limits of the Kovdor massif (Kola Peninsula, Russia) two large deposits are situated – phlogopite and rare metal-apatite-magnetite. Coarse-grained diopside-phlogopite-olivine rocks and restricted to them vein-like pegmatoid bodies with commercial mica compose phlogopite complex (Rimskaya-Korsakova, Krasnova, 2002). Rare metal-apatite-magnetite mineralization is presented by calcite(±dolomite)-bearing phoscorites and analogous with them by mineral composition carbonatites (Sokolov, 1983).
A number of researches (V.I.Ternovoy, E.M.Epshtein and some others) considered, that both deposits arised simultaneously as a result hydrothermal-metasomatic process and have similar mineral composition. However, comparison analysis of geological, geochronological and mineralogy-geochemical data along with results of thermobarogeochemical study of melt and fluid inclusions in rock-forming minerals of ores displayed considerable and important distinctions between these deposits, that allowed us to relate them to magmatic formations, but different genetic type (Sokolov, 2006).
The luminescence investigation techniques is used successfully for revealing such mineral features, which could be used as diagnostic signs or are typomorphic for definite geologic environments. With the aim of supporting of different nature of the mentioned deposits were studied X-ray luminescence (XL) and laser-induced photoluminescence (PL) of apatite. This mineral is wide distributed in the cited ores, and, as known (Portnov, Gorobets, 1969), is characterized by definite luminescence spectra in deposits of different genetic (formation) type.
Spectra of X-ray luminescence (n = 16), were obtained using monofractions of apatite with mass of 20-50 mg, collected from phlogopite ores with modify ratio of rock-forming minerals (olivine, diopside, phlogopite, apatite) and various by composition phoscorites (apatite-forsterite, apatite-forsterite-magnetite, calcite-forsterite-magnetite) and carbonatites (forsterite-calcite and phlogopite-calcite). Spectra of photoluminescence (n = 44) were measured on apatite grains from the same samples. Spectra contain luminescence bonds of optic-active centres of rare-earth elements and manganese: Ce3+ (390 nm), Eu2+ (450 nm), Dy3+ (485 and 575 nm), Tb3+ (490 and 550 nm), Sm3+ (565, 600, and 642 nm), Mn2+ (585 nm), Eu3+ (620 and 628 nm). Initiation of a REE-centres, probably, is caused by the presence of isomorphic sodium, which manifests itself as a compensator of superfluous positive charge, created by the lanthanides.
|
|
|
|
|
|
|
|
|
|
|
|
Representative spectra of X-ray luminescence (1-4) and laser-induced photoluminescence (5-8) of apatite from phlogopite deposit (1 and 5), calcite ijolites (2 and 6), and rare metal-apatite-magnetite deposit – phoscorites (3 and 7) and carbonatites (4 and 8); z – spectra, resulting from registration delay of 180 ms. Spectra given without taking into account spectral function of the register.
X-ray luminescence spectra of apatite from phlogopite ores differ from apatite spectra from phoscorites and carbonatites: 1) by a greater amounts of bonds of REE luminogens (Tb3+, Sm3+); 2) reduced intensity of a luminescence, attaining correspondingly, 350-1900 и 2450-4770 relative units (Fig. 1, 3, 4). At the same time they are identical with spectra of apatite from calcite ijolites, enclosing apatite-magnetite deposit (Fig. 1 and 2), which corresponds with their mutual belonging to silicate system, while rare metal-apatite-magnetite ores by their composition represent silicate-phosphate-oxide and carbonate rocks.
Photoluminescence of apatite was generated by laser radiation (lexc = 337.1 nm), under influence of which the mineral displays blue (or lilac-blue) luminescence with vary intensity. According to the used method (Rassulov, 2005), in one point of each grain were measured two PL-spectra – integral by time and with registration delay of 180 ms later on laser impulse, what allow to fix the weak lines of the centers with long afterglow (Sm3+, Dy3+). Photoluminescence spectra, like X-ray luminescence spectra, make up also two groups, corresponding to apatites: 1) from rocks of phlogopite complex and calcite ijolites and 2) from phoscorites and carbonatites. The first group possess luminescence bonds of Eu2+, Dy3+, Tb3+, Eu3+, Sm3+ (Fig. 5 and 6) and the second one has distinct manifested only bonds of Ce3+ and Mn2+ (Fig. 7 and 8).
Conclusions: the results of investigation of apatite luminescence confirm difference of ores of phlogopite and rare metal-apatite-magnetite deposits and testify to genetic unity of phoscorites and carbonatites in composition the last.
References:
Portnov A.M., Gorobets B.S. The luminescence of apatite from different types of rocks // Doklady of the Academy of Sciences USSR. 1969. Vol. 184. № 1. P. 199-202. (in Russia).
Rassulov V.A. Local laser luminescent spectroscopy of minerals (on example of zircon). Methodical recommendations № 156. М. VIMS. 2005. 16 p. (in Russia).
Rimskaya-Korsakova O.M., Krasnova N.I. Geology of the deposits of the Kovdor massif. St.-Petersburg. 2002. 146 p. (in Russia).
Sokolov S.V. The genetic unity of apatite-magnetite ores and carbonatites in alkali-ultrabasic intrusions // Geochem. Internat. 1983. Vol. 20. P. 86-98.
Sokolov S.V. Genetic relationships between apatite-magnetite and phlogopite deposits of the Kovdor massif (Kola Peninsula, Russia). 12th Quadrennial IAGOD Symposium 2006. Moscow. 2006. Abstracts e-book, №356.