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.

GEOCHEMISTRY OF WATER-ROCK INTERACTION 1105 To test the hypothesis of rapid saturation of natural waters in sodalite constituents, including S and Cl, its interaction with distilled water was experimentally mod­ eled using three samples of unaltered rock (Table 2). The samples were taken in 1959 from depths of 130-240 m in the boreholes located above mining pits and far away from possible industrial and domestic discharges and have been stored since then in a dry room for 36 years. The samples were crushed in a water environment, with the minimum yield of fine-grained fractions. The 1-3 cm rock fragments were splintered to 5.0-0.3 mm to obtain no more than 10% of the <0.315 mm fraction. Then, the rock chunks were washed to remove dust and fine par­ ticles. A 10-g aliquot of crushed rock was loaded into a large agate mortar, mixed with 150 cm3 distilled water, and carefully crushed. The sample was kept for 10 min, after which water was collected, examined for visible suspensions, filtered through a 0.45 |im membrane fil­ ter, and analyzed (analyst L.P. Kudryavtseva). It was planned that the time of water-rock interac­ tion would be increased. However, the compositions of the obtained solutions (Table 3, an. la -3 a) appeared to be similar to that of natural waters (Table 1). The con­ tents of S04 and some cations (Na, K, Mg, and Al) in the experimental solutions were weakly dependent on the presence of sodalite in the samples, which presum­ ably indicates the presence of concentrated liquid inclusions or easily soluble salts in the pores of rocks. The possible role of the so-called buried waters (capil­ lary or film water [1]) in the modern system of water monitoring was noted during the hydrogeological work in the Kola Peninsula. The easily soluble pore phases could be formed in the rocks owing to the penetration of drill mud during prospecting operations; on the other hand, they could occur as inclusions retained from the time when the rock was located at a considerable depth. The elevated contents of hydrocarbon gas phases in the Khibiny rocks were in some cases accompanied by the occur­ rence of soda [17]. Physicochemical computer model­ ing showed the principal possibility of soda formation in the Khibiny rocks during slow interaction of nepheline with hydrocarbon gases in a moist environ­ ment [18]. It is possible that the recent natural waters inherit in part the composition of waters buried during the pregla­ cial period simultaneously with the development of Fig. 1. Steeply dipping supergene fissure zone in the lens- banded ore of an apatite-nepheline deposit. The light-col- ored veinlets are mainly composed of montmorillonite with small grains of opal and secondary apatite. The lens-banded ore is replaced by hydromica, montmorillonite, and iron hydroxides in the fissure zone. areal weathering mantles, which preserved as relics of infiltration fissure residues. The repeated formation and thawing of ice sheets in the Khibiny Massif had to affect the state of the pore space of the rocks and result in the redeposition, filtration, and drying of pore inclu­ sions in the rocks. Currently, the most active exogenous process in the Khibiny Massif is the disintegration of Table 2. Mineral compositions of the rock samples (wt %) Rock Nepheline Feldspar Pyroxene and amphibole Sodalite Apatite Other minerals Banded ore of the Yukspor deposit 48 2 8 <1 33 8 Urtite, Mt. Yukspor 65 5 21 <1 3 5 Sodalite zone of pegmatite in Yukspor nepheline syenite 0 21 7 70 0 2 GEOCHEMISTRY INTERNATIONAL Vol. 45 No. 11 2007