Barium-bearing micas of the muscovite-ganterite series from alkaline rocks of the Sredneziminsky ijolite-syenite-carbonaite massif (Eastern Siberia, Russia)
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Abstract:
Barium-bearing micas (BaO content from 1.2 to 18.7 wt %) were found in hydrothermally altered ijolites and alkaline syenite of the Sredneziminsky ijolite-syenite-carbonatite massif (Eastern Siberia, Russia). It occurs in the products of low-temperature replacement of cancrinite, in association with natrolite, analcime, calcite, diaspore/boehmite, celsian, and strontianite. Ba-bearing micas are represented by grains up to 1 mm, heterogeneous in chemical composition. The amount of Ba increases in the marginal parts of grains; enrichment of some layers in mica grains with barium is also observed. The main isomorphic substitution in muscovite corresponds to the scheme K++Si4+↔Ba2++IVAl3+. The empirical formula of barium-richest areas in one of the mica grains is (Ba0.54–0.56Sr0–0.09K0.46)∑1.02–1.06Al1.98–2.01(Si2.37–2.40All.60–1.63)∑4.00 O10(OH1.70–2.00F0–0.30)∑2.00, which corresponds to ganterite. The maximum content of BaO in the majority of muscovite grains of the Sredneziminsky massif is 14.0–14.9 wt % that is equal to 0.41‒0.44 apfu Ba. It is assumed that the source of barium in the hydrothermal solution was orthoclase containing 0.5–0.9 wt % BaO which underwent albitization at the post-magmatic stage. The widespread occurrence of sulfides in the rocks indicates low oxygen fugacity, which prevents the formation of barite and is favorable to the formation of Ba-bearing muscovite and celsian.Keywords:
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and complex are the two basic forms of the association of granitoid. This is also a general character of granitoid geology in south China. Compound massif means a that is spatially associated with several granitoid rocks at different ages. Thus the granitoid components are not geneticaly related with each other. The complex massife is meant to a that is associated with multiply differentiating ascending and emplacing magma from the same chamber. It is theoretically and pratically important to distinquish the two kinds of massifs.
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Natural muscovite treated hydrothermally under high pressures of argon and water takes up 70 to 90 times as much argon as the original muscovite contained. Muscovite synthesized under similar conditions from a colloidal gel contains even more argon. Muscovite synthesized in the presence of argon and water has cell dimensions about 0.3% larger than those of muscovite synthesized without argon present. --F. E. Ingerson.
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