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.

ISSN 0016-7029, Geochemistry International, 2007, Vol. 45, No. 11, pp. 1103-1110. © Pleiades Publishing, Ltd., 2007. Original Russian Text© O.B. Dudkin, S.S. Sandimirov, 2007, published in Geokhimiya, 2007, No. 11, pp. 1195-1202. Geochemistry of Water-Rock Interaction in the Area of the Khibiny Alkaline Massif О. B. Dudkin" and S. S. Sandimirov* aGeological Institute, Kola Scientific Center ; Russian Academy o f Sciences, ul. Fersmana 14, Apatity, Murmansk oblast, 184209 Russia e-mail: Dudkin®geoksc.apatityru b Institute o f Industrial Ecology Problems o f the North, Kola Research Center, Russian Academy o f Sciences, ul. Fersmana 14, Apatity, Murmansk oblast, 184209 Russia Received May 19, 2006 Abstract —The interaction of natural and industrial waters with the rocks and apatite ores of the Khibiny alka­ line massif was studied to estimate the extent of anthropogenic influence on natural processes. The abundance of the major rock-forming elements of the nepheline syenites and foidolites in the natural waters indicates that dissolution of nepheline and feldspathoids in natural water plays a significant role under the conditions of slow weathering in the Far North. Experiments showed that fine nepheline particles are transformed into amorphous phases at a fixed water volume at 18-20°C and pH 7.5-8.1. This process became observable already within the first day and continued for months. It is possible in stagnant reservoirs of natural waters and clearly expressed in industrial settling tanks. This is supported by the high content of amorphous phases enriched in Na, К, Al, and Si in the top layer of lacustrine sediments at the zone affected by the sewage of a concentrating mill. 10.1134/S0016702907110031 INTRODUCTION Under the conditions of slow weathering in the regions of the Far North, different processes of water- rock interaction must be clearly expressed [1]. Many minerals of Khibiny rocks actively interact with water [2-5]. Mining and concentrating operations extract tre­ mendous volumes of bedrocks into the supergene zone, where the surface area of their exposure to atmospheric agents increases considerably Using the available data, we attempted to determine the conditions of water sat­ uration in the major elements of a number of rock- forming minerals, taking into account the role of fine mineral particles. We studied the rocks of the Khibiny apatite- nepheline deposits, whose compositions were studied in detail in [2, 4]. The following element groups were analyzed in waters [6, 7]: weakly mobile major ele­ ments (Al, Si, and Ca); highly mobile major elements (Na and K); and minor components not very common in the Khibiny rocks but showing the highest mobility (S04 and Cl) [8]. The choice of these elements is justi­ fied by Table 1. The available data indicate insignificant chemical variations in the surface waters of the Khibiny Massif and adjacent areas (Table 1, an. 3, 4). Under­ ground waters have elevated contents of Na, Al, and Si (Table 1, an. 5, 6). Hence, the discharge of underground waters can significantly affect the composition of sur­ face waters. However, anomalously high concentra­ tions of Na (up to 16 mg/1), К (up to 3.8 mg/1) [7], and Al (up to 0.096 mg/1) were also detected in some cases in the surface waters collected far from mines and con­ centrating plants. These contents are close to the con­ stantly high contents of these elements in the water of Lake Imandra near the site of sewage discharge from concentrating mills [6] (Table 1, an. 7, 8). INTERACTION OF MINERALS AND NATURAL WATERS It is usually thought that the main geochemical fac­ tor of water-mineral interaction in the supergene zone is the formation of weathering crusts. Weathered rocks were first reported in the Khibiny Massif by Chirvinskii [9]. Fissure (infiltration) weathering residues of pregla­ cial origin were found and studied in detail by Dorfman [2]. Their age was estimated as Pleistocene-Miocene on the basis of their hydromica-montmorillonite com­ position [10]. Topographically, the fissure residues are expressed as ravines, creek beds, and mountain valleys overlain by glacial deposits. They are composed at depth of hydromica, montmorillonite, and iron hydroxides replacing the rocks, and their fissures are mainly filled with montmorillonite (Fig. 1). There are also zeolites, secondary carbonate-hydroxide-fluorapatite, and minor opal and kaolinite [3]. In addition, a wide diversity of supergene minerals replace pyroxene, titanite, and acces­ sory minerals of the agpaitic association [2,4]. 1103