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Address : Institute of Geological Sviences of National Academy of Sciences of Ukraine, Ukraine
Celebration date : 21 Sunday September 2008
Author name : Remezova, Olena

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  • Article title : Layered titanium-bearing intrusions of the Ukrainian Shield
    Article type : Other
    Location : International Geological Congress,oslo 2008

    Fulltext :

    On the Korosten’ pluton a number of gabbro intrusions is situated and the deposits of apatite-(titanomagnetite)-ilmenite ores are connected with them. They are confined with first phase of pluton forming, which took place in palaeproterozoic stage of tectono-magmatic activation where on the East-European platform the volcanic plutonic belts existed. The general feature is penetration of magma injection as one-act process. The space which is occupied today by such bodies was filled by homogenous melt and material of enclosed rocks was eroded. Sometimes the sides of fracture were extended by intruded magma with forming of magmatic chamber. Later the slow hardening of melt begin and it is accompanied by the sedimentation on the bottom of the chamber of the basic plagioclases and partly of olivine. General for intrusions is the selection of crystalline fraction which took place as process of consecutive accumulation of crystalline sediment layers on the bottom of chamber by gravitation. The presence of flow signs are explained by convectional streams in chamber. Crystalline sediment appears near the walls of chamber. All bodies are characterized by the accumulation of leucocrate varieties near the bottom. The active deposition of ore minerals was in middle and upper zones. All titanium-bearing intrusions carry hidden rhythmic stratification which connected with changes of ore minerals relationships, TiO2 content on a cross-section. In massifs the Ti-P mineralization is accompanied by the aureoles of weak anomalous concentrations of Cr, Co, V and some chalcophile elements related to the minerals–concentrators of these elements: titanomagnetite, olivines, pyroxenes, sulfides. On the Ukrainian shield gabbro-syenites intrusions are explored also. A magma which intrusions appeared from belongs to the lime-alkaline type. Crystallization was in near-bottom parts under the high pressure and temperatures. Often forming of gabbro-syenites complexes shows two opposite tendencies which depend on conditions. Different acidic-reduction conditions lead to the growth in remaining crystallization products silica and alkalis simultaneously. Therefore the stage of crystallization of olivine and pyroxene with growth of partial pressure can be changed by the crystallization of magnetite and titanomagnetite. In lower zone there is such order of mineral accumulation in melanocratic gabbro: apatite+ilmenite+titanomagnetite+olivine+plagioclase+pyroxene+potash feldspar. In leucocrate rocks the plagioclase is a single cumulative phase. The interstitial phases are represented by titanous augite and potash feldspar. The potash feldspar with pyroxenes becomes a cumulative phase only in syenites. In such cases, the role of mantle fluides, which are enriched on SiO2 and alkalis, litophile elements, occurred also. At forming of leucocrate varieties the greater part of alumina, Ca and Na is extracted, there is enrichment on potassium and silica and syenites of upper zone form.

     
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