Experimental study of fluid inclusions in Hakmanite from Karnasurt Mauntin, Lovosersky massif

Kovalskaya T.N^*, Kotelnikova Z.A.^**, Kotelnikov A.R.^*, Suk N.I.^*, Kovalsky A.M.^*, Goettlicher J.^***

^*IEM RAS, Chernogolovka, Moscow district, Russia, tatiana76@iem.ac.ru

^**IGEM RAS, Moscow. Russia

^*** Insitute for Synchrotron Radiation, Karlsruhe, Germanyљ

љљљљљљљљљљљљ Lovozersky alkaline massif is located in the central part of Kola peninsula and includes gigantic deposits of rare and radioactive elements. Data of alkalinity of post magmatic mineralgenetic solutions are necessary for understanding the features of mineralogenesis process for alkaline complexes. Sodalite (hakmanite) is a typical mineral of pegmatites of Lovozersky massif. Investigation of fluid inclusions in hakmanite (as it composition) supposes the conditions of it formation.

The composition of hakmanite was determined by the microbeam method. which showed two types of hakmanite in pegmatite №61 of Lovozersky massif – with Cl^- and Cl^- љand SO₄^2- anion groups. A slice of hackmanite has been cut, and sulfur K-edge X-ray absorption spectra have been measured in the fluorescence mode at the bulk X-ray absorption spectroscopy beamline (XAS) at ANKA using a five element Ge solid state detector (Canberra). A silicon 111 crystal pair was used as monochromator. Higher harmonics were eliminated by passing a mirror behind the monochromator. To minimize absorption caused by the atmosphere and by the windows of the ionization chamber a combined ionization-sample-chamber has been used at a nitrogen gas pressure of about 80 mbar. We have detected two types of sulfur K-edge XANES spectra in a sodalite (hackmanite) sample from Lovosero massiv, Kola peninsula: One indicates reduced sulfur species, the other one mainly sulfur as sulfate (fig. 1, 2). A suggestion how to attribute these species to the sodalite pahses has been given, but has to be checked by performing micro-X-ray diffraction at the same sample position where X-ray absorption spectra have been recorded.

Fig. 1. S K-edge XANES spectrum of an area at the slice of hakmanite where light pink colors dominate.

Fig. 2. S K-edge XANES spectrum of an area at the slice where blue colored parts have been observed.

We also investigated fluid inclusions in hakmanite (fig. 3). It is shown, that fluid inclusions in hakmanite contain water, crystal of salt and gas bubble. The thermometry of 3-phase fluid inclusions showed that the temperature of inclusion homogenization is about 200^о. The temperature of ice-melt in inclusions is from -6.5 to -4.4 ^оС. On the basis of these data we calculated the concentration of NaCl_eq in the fluid – 9.9 wt.%.

љWe carried out some experiments on synthesis of fluid inclusions in hakmanite. We used 1 M solution Na₂SO₄ and 2 M NaСl solution as a fluid component. The ratio shot/fluid was 1:6. High temperature gas pressure apparatus is љused to carry outљ the experiments. The charge ofљ the starting material was placed inside gold capsule Synthesis was carried out at Т=450њС and Р=1.5 kbar. The duration of the experiments was 31 days. The slices of hakmanite about 0,8*0,5 cm were used as starting materials. These slices were heated to 500њС and then were cooled in alcohol at room temperature. Synthesized fluid inclusions were investigated by thermo-cryometric method with

Linkam-600. We measured concentrations of Na₂SO₄ and NaСl solutions after experiments by flameless atomic absorption spectrometry method. We carried out the investigation of fluid inclusions in natrolite, which was found in the same pegmatite.

This study was financially supported by RFBR grants № 06-05-64904, № 07-05-00217, 07-05-00389, Russian Federation President grants МК-4797.2008.5 and Fund of native science support.