| Popis: |
Varėna Iron Ore deposit (VIOD) is found in 1.89 Ga East Lithuanian-Latvian domain crystalline basement. The up-to-date research on the deposit is mainly descriptive, and its age and origin debated. In order to put time and pressure-temperature (PT) constrains on iron ore mineralization found in the deposit, rocks surrounding it were studied by means of chemical and isotopic approaches. Phase diagrams were constructed in order to evaluate the PT parameters. Samples of VIOD rocks were selected for detailed microstructural and chemical analysis, as well as pressure-temperature evaluation and monazite dating. In order to estimate the final stage of mineralization in the deposit, crosscutting granite veins were analysed by means of chemical and isotopic methods. The surrounding rock analyses showed that they are Si-rich metavolcanics, formed at ca. 1.83 Ga. After the peak metamorphic conditions at 620° C and 7 kbar, rocks experienced decompression at ca. 1.73 Ga, followed by a ca. 1.5 Ga thermal metamorphism up to 640° C at 3.5-4.5 kbar. Similar PT constrains can be implied to VIOD rocks based on mineral assemblages and calcite-dolomite thermometry. Monazite age of ca. 1.79 Ga and 1.5 Ga in VIOD rocks suggest that they have been metamorphosed simultaneously with the surrounding rocks. Magnetite analysis showed its formation during the regional metamorphism and local reheating during granitic melt emplacement at ca. 1.5 Ga, simultaneously with the AMCG suite to the south. |
