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.

1104 DUDKIN, SANDIMIROV Table 1. Compositions of lacustrine, riverine, and underground waters in the region of the Khibiny alkaline massif and the area affected by the discharge of the ОАО Apatit concentrating mill (mg/1) Component 1 2 3 4 5 6 7 8 pH 7.2 7.08 7.16 7.08 6.9 8.1 7.7 7.43 Ca 4.0 3.30 0.63 0.44 1.2 0.5 3.65 4.01 Mg 1.3 1.02 0.07 0.11 0.24 0.16 1.03 1.03 Na 7.5 5.52 4.5 6.40 6.44 9.43 16.2 17.0 К 1.17 1.17 0.76 - - 2.54 2.74 so4 3 9.41 2.05 2.8 2.88 3.25 26.9 26.9 Cl 1.8 2.28 0.52 1.4 1.07 1.35 5.29 5.03 P04 0.008 0.002 - - - - 0.001 0.001 Si (NO, + NOo) 0.6 1.46 1.3 1.44 1.75 1.75 0.14 0.23 Al - 0.022 0.03 0.054 0.087 0.074 0.085 0.091 Fe - 0.022 0.02 0.28 - - 0.034 0.055 Cu <0.005 0.004 - - - - 0.004 0.004 Zn <0.005 0.007 - - - - 0.001 0.015 Mn - 0.022 0.003 0.002 - - 0.009 0.014 Sr - 0.042 0.005 0.056 - - 0.063 0.070 Note: (1) Limiting natural composition of Lake Imandra waters estimated by Moiseenko et al. [6]; (2) composition of Lake Imandra waters in the control zone located in the area of the combined influence of local industrial enterprises, after Moiseenko et al. [6]; (3) and (4) the minimum and maximum contents of mineral components in the surface waters far away from plants and sites of industrial water discharge [7]; (5) and (6) the same for underground waters [7]; (7) and (8) compositions of Lake Imandra waters in the zone affected by the discharge of concentrating mills (7) near the surface and (8) at the bottom according to our data, analyst L.P. Kudryavtseva (Institute of the Industrial Ecology Problems of the North, Kola Scientific Center, Russian Academy of Sciences). Previous physicochemical modeling by means of the Selector program [11, 12] showed [13] that the composition of the Khibiny fissure (infiltration) weath­ ering crusts corresponds to the humid conditions of midlatitudes [14]. However, an increase in water pH up to 7.5-8.1 depresses the replacement of primary miner­ als with depth even in the ground nepheline sands pro­ duced as tailings from apatite concentration. The calcu­ lated rates of the formation of supergene phases under the conditions of the Far North suggest that the first traces of presently forming hydromica-montmorillonite weather­ ing residues will be visible after 300-400 years [13]. Physicochemical computer simulation showed [13] that, during the formation of secondary phases under the influence of atmospheric waters percolating through nepheline sands, the composition of water must be less saturated in the rock components than that observed in present-day natural waters. This once more indicates that water-rock interaction is not limited to the formation of weathering crusts [1, 15]. The dissolution of Khibiny minerals, including nepheline, could exert a significant influence on the water composition [2, 4, 5]. Nepheline crystals are covered by a thin film of gray or grayish brown hal- loysite (or metahalloysite) and iron hydroxides at the drying rocky surface subjected to the maximum atmo­ spheric influence, with no visible alteration beneath it. The rock remains fresh beneath the film. However, deep hollows at the place of nepheline crystals can be observed on the bottom of permanent streams and run­ ning-water lakes. In such cases, the slow dissolution of nepheline is obvious. The content of rapidly dissolving minerals [2, 5] in the Khibiny is not significant in general. At relatively low pH values of 5.8-6.5, significant amounts of Na, K, and Ca can be extracted from abundant nepheline and feldspathoids, and S and Cl are released from sodalite [2,4]. The Khibiny rocks usually contain no more than 0.01% S and Cl and occasionally up to 0.10% S 04. The content of F, the most mobile element of the Khibiny apatite deposits, is often 0.04-0.40%. It occurs in fluorapatite, amphiboles, biotite, and easily soluble natural NaF (villiaumite). When a borehole penetrates a local villiaumite accumulation, the F content in the water may initially increase up to 0.4-2.25 mg/1 and then decrease rapidly. The main repository of Cl and S in the Khibiny rocks is sodalite, including sulfate-sodalite. According to Dorfman [2], the indications of sodalite dissolution appear very rapidly, within a few hours. Sulfate- sodalite is a rare mineral of alkaline pegmatites, while significant amounts of chlorine-sodalite occur as rims replacing nepheline. According to Kostyleva-Labunts- ova et al. [4], the content of sodalite in the Khibiny rocks locally reaches 2%. Detailed mineralogical anal­ ysis showed that the ijolites, urtites, and apatite-ne- pheline rocks contain 0.2-0.7% sodalite [16]. The Khibiny sodalite contains 5.66-6.55% Cl, and rare sul- fate-sodalite (hackmanite) contains 6.05-6.92% Cl and 0.29-0.77% S [4]. GEOCHEMISTRY INTERNATIONAL Vol. 45 No. 11 2007