2011

Тезисы международной конференции

Рудный потенциал щелочного, кимберлитового

 и карбонатитового магматизма

Abstracts of International conference

Ore potential of alkaline, kimberlite

and carbonatite magmatism

Experimental modeling of the alkaline complexes mineralogenesis
Kotelnikov A.R., Kovalskii A.M., Kovalskaya T.N., Suk N.I.

Institute of Experimental Mineralogy, Chernogolovka, Russia, tatiana76@iem.ac.ru

Experimental study of the conditions of mineral genesis of alkaline complexes and application of the results to natural features is an important task, since such complexes are associated giant mineral deposits. Our team over the last years studied solid solutions of alkali pyroxenes, sodalite, thermodynamics clinopyroxene-biotite paragenesis, fluid regime of formation of post-magmatic associations. Also, the synthesis of many minerals, typical of alkaline complexes: sodalite ussingite, cancrinite, alkali pyroxene, gakmanit, etc. In this study, collected the latest research results.

Association clinopyroxene-biotite. Association of clinopyroxene and biotite - one of the most common in igneous, metamorphic and metasomatic rocks, including rocks of elevated alkalinity. Clinopyroxene - biotite geothermometer, built on the basis of empirical data on the composition of natural coexisting Cpx and Bi was proposed by L.L. Perchuk. However, with regard to alkaline rocks it is difficult to use due to lack of data on the thermodynamics of alkali pyroxenes and the influence of alkaline components in the distribution of magnesium and iron between pyroxene and biotite. As the starting materials used synthetic solid solutions of ternary clinopyroxenes (CPx-3) and synthesized at 650 º C and 1.5 kbar phlogopite and annite. Approach to equilibrium osuschestvyalsya from both sides. Initial compositions of minerals and the results of experiments on the cation exchange are presented in Table 1. Based on a 10 cation-exchange experiments obtained isotherm distribution of Mg and Fe between CPx-3, and Bi. (Fig.1). The distribution coefficient of Mg between clinopyroxene and biotite (KD) is described by the following equation of third order: ln (KD) = 0.65 + 3.30 * x -5.763 * x² -1.0911 * x³ (± 0.40), where x - mole fraction of Mg in clinopyroxene (x = Mg / (Mg + Fe^{2 +})). According to this equation to calculate the energy parameters of an asymmetric Margules model to describe the excess energy of mixing of solid solutions of clinopyroxenes (system Aeg - Di - Hed; aegirine mole fraction of 0.2 ± 0.04): W1 = -48.5 (16.2) and W2 = 24.1 (2.5) kJ / mol . Previously, we studied the balance of SPx-Bi for binary solid solutions of clinopyroxene (Kovalskii et al, 2008, 2009) and shows a nearly ideal miscibility in the series diopside - hedenbergite. Thus, we can conclude that increasing non-ideality of solid solution of diopside - hedenbergite when entering aegirine end-member. Based on data Perchuk (Perchuk, 1970) on natural parageneses clinopyroxene and biotite to 750 º C isotherm calculated excess energy of mixing of clinopyroxenes (Fig. 2).

At 750 º C and 1.5 kbar hydrothermal conditions studied the distribution of magnesium and iron between clinopyroxene (ternary alloys of the system Di-Hed-Aeg; XAegCPx = 0.2) and biotite (binary solid solutions Phl-Ann). It is shown that the distribution of Mg, Fe2 + between clinopyroxene and biotite imperfect, at low Mg ferrous iron enriched biotite, with XMgCPx> 0.7 is inverted and Fe2 + is redistributed in the CPx. Based on data on the distribution of Mg, Fe2 + between clinopyroxene and biotite calculated parameters Margules mixing model clinopyroxene, it is shown that the magnitude of the integrated excess mixing energy directly correlates with the mole fraction of the third end-member clinopyroxene (aegirine and jadeite).

Table 1. The experimental results of Mg and Fe exchange between clinopyroxene (CPx-3) and biotite (Ann – Phl range) at 750^oC and 1.5 kbar.  K_D=[X_Mg^CPx3*(1-X_Mg^Bi)]/[(1-X_Mg^CPx3)* X_Mg^Bi]

ln(K_D) = 0.65 + 3.30*x -5.763*x² -1.0911*x³ (±0.40)     (1)

Sodalite-bearing association. To date, according to data on the compositions of sodalite and the temperatures of their formation to estimate the minimum concentration of salts (NaCl, Na₂SO₄) in mineral-fluid: from 10-20 wt.% NaCl-eq. for 2-sodalite paragenesises to 1.5-3 wt.% NaCl-eq. for nozean containing paragenesis. Also estimated the mole fraction of sulfur in the fluid: 0.02 for 2-sodalite paragenesises and 0.04-0.27 for nozean-bearing parageneses (Suk et al, 2007). In the pegmatite body near the mountain Karnasurt found two types of sodalite: chlorine-and sulfur-containing sodalite. The results of our experiments are shown, that heterophase fluid was involved during Lovozersky massif pegmatite formation at 400 - 450°С and homogenius fluid - at 250°С, that correlate with the data Ustinov VI et al. (Ustinov et al, 2006), which is shown in the composition of minerals and their occurrence in the rocks.

Work is supported by RFBR grant № 10-05-00870

References:

Kovalsky A.M., T.N. Kovalskaya, A.R. Kotelnikov (2008) Calibration and application of mineral thermometer based on the study of clinopyroxene-biotite equilibrium. Abstracts of Annual Seminar of Experimental Mineralogy, Petrology and Geochemistry. Moscow, GEOKHI RAS, 22-23 april 2008, pp. 36-37. (in Russian)

Kovalsky A.M., T.N. Kovalskaya, A.R. Kotelnikov (2009) Experimental study of Mg and Fe distribution in the system clinopyroxene-biotite, thermometry of natural paragenesis. Abstracts of Russian youth scientific conference “Minerals: structure, properties, investigation methods”. Miass, IM Ural D. RAS, p. 38. (in Russian)

Perchuk L.L. (1970) Equilibria of rock forming minerals. M., Science, 392 p. (in Russian)

Suk NI, Kotelnikov AR, Kovalsky AM Mineral thermometry and fluid composition of sodalite syenites of the Lovozero alkaline massif. Petrology. 2007. v. 15, № 5, pp. 474-492. (in Russian)
Ustinov VI, Grinenko VA, Kotelnikov AR, Suk NI, Kovalskaya TN, Smirnova EP Thermometry sodalitsoderzhaschih breed associations and Tiksheozerskogo Lovozero alkaline massif. / / Proceedings of the National Conference of "geochemistry, petrology, mineralogy and genesis of alkaline rocks" 18-23 September 2006 Miass. 2006. s.267-272. (in Russian)