Sandimirov S.S. Geochemisrty of water-rock interaction in the area of the Khibiny alkaline massif. Geochemisrty International. 2007, T.54, №11, p. 1103-1110.

1106 DUDKIN, SANDIMIROV Table 3. Composition of water (mg/l) after experiments (a) on the opening of rock pores in water and (b) on the interaction of finely ground apatite-nepheline rock with a fixed water volume Component la 2a 3a 4b 5b pH 7.31 7.74 7.48 7.94 8.05 Ca mg/1 2.83 5.36 0 2.87 3.05 Mg mg/1 0.30 0.42 0.03 0.19 0.04 Na mg/1 11.3 12.6 12.8 2.63 10.1 К mg/1 6.4 7.4 4.2 4.4 2.91 S04mg/1 2.75 2.98 2.52 0.43 0.2 Cl mg/1 3.38 2.1 4.8 0.39 0.30 Ptot Mg/1 - - - 1.94 3.2 Si |ig/l (NO, + N 02) - - - 0.62 4.77 Al |ig/l 2.15 2.11 1.88 0.59 0.76 Fe |itg/l 0.45 0.74 0.84 0.058 0.11 Cu |ig/l 0.010 0.010 0.003 0.002 0.001 Zn |ig/l 0.045 0.047 0.008 0.003 0.001 Mn |LLg/l 0.019 0.037 0.027 0.002 0.001 Sr |ig/l 0.216 0.845 0.019 0.28 0.19 Note: The compositions of water after interaction: (la) with apatite-nepheline ore, (2a) with urtite, and (3a) with sodalite pegmatite. The compositions of water after interaction with a finely ground sample of apatite-nepheline ore: (4b) for three days and (5b) for three months. bedrocks, which leads to the extensive opening of pre­ viously closed pores. There is another physical factor related to rock dis­ integration that could provide a rapid saturation of nat­ ural waters in the components of endogenous minerals. It is well known that fine particles (nanoparticles) can be decomposed in water within minutes or even sec­ onds [19, 20, etc.]. According to the available data, this process can be expected for the rock-forming minerals of the Khibiny apatite deposits, primarily, for nepheline. Under natural conditions, mud-sized (dust) mineral particles can be formed during rock collapses, avalanches, and mudflows. In addition to these natural factors, which may control the composition of surface waters already at the heads of mountain streams, of great importance must be the anthropogenic factor, the crushing of minerals during mining operations and ore concentration. The behavior of fine mineral particles of apatite ore in water was studied by the example of a banded ore from the Yukspor deposit of the following composition (wt %): nepheline 42, apatite 38, pyroxene 12, titanite 3, Ti-magnetite 1, and feldspar 2. The major-element composition of this ore is (wt %) SiO, 25.50, TiO, 0.52, АШ 3 18.90, Feo03 2.29, CaO 19.00, Na,О 10.82, K ,0 3.12, and P20 5 16.63. Small portions of the sample were ground in an agate mortar. The 5-g powder aliquots were mixed with 250 ml of distilled water and periodically stirred. The experiments lasted three days and three months. At the end of experiments, the products were settled for a day, without the addition of any reagents. The obtained solu­ tion was filtered through a 0.45-|im membrane filter and analyzed. The compositions of solutions obtained by the interaction of finely ground samples with water (Table 3, an. 4b and 5b) are comparable with that of nat­ ural waters (Table 1). An X-ray amorphous precipitate was retained on the filter after water purification. Its emission spectral analysis revealed high contents of Si, Al, and Na. The weight loss of powders obtained by drying at room temperature varied from 10 to 18%. Their X-ray diffraction patterns showed the presence of dispersed phases, which were especially abundant in experiments with a fixed water volume contacting the sample for 3 months (Fig. 2). The presence of dispersed phases was confirmed by IR spectrometry (O.A. Zalkind, Institute of Rare Ele­ ment and Mineral Chemistry and Technology, Kola Research Center, Russian Academy of Sciences). The X-ray diffraction patterns of the powders showed that an increase in the extent of dispersion was accompa­ nied by a decrease in the content of crystalline nepheline relative to apatite. This observation was con­ firmed by the analysis of pelleted samples using an MS-46 microprobe (Fig. 3). The samples were ana­ lyzed with а 100 -дт beam in ten points, and the aver­ age composition was then calculated. The obtained data showed that fine nepheline particles are unstable in atmospheric water even at high pH values, when they transform slowly into amorphous phases. The lake waters of the Khibiny Massif contain 0.001-0.003 mg/1 phosphorous, which is only slightly higher than the average content in natural waters [21]. It can be suggested that apatite particles smaller than GEOCHEMISTRY INTERNATIONAL Vol. 45 No. 11 2007