Расплав-флюидные микровключения в алмазах месторождения им. М. В. Ломоносова (Архангельская алмазоносная провинция)

Abstract

Изучены расплав-флюидные включения в 11 алмазах месторождения им. М.В. Ломоносова (Архангельская алмазоносная провинция). Методом рентгеноспектрального анализа в них определен химический состав микровключений и получены дополнительные сведения по химическому составу методом ИК-спектроскопии. Впервые для алмазов Архангельской провинции установлена ведущая роль водосодержащих силикатно-карбонатных расплавов с широким диапазоном концентрации силикатных компонентов.Melt/fluid inclusions in diamonds provide material of parental mantle fluids or melts of diamond crystallization. It is necessary to expand the area of study of microinclusions in natural diamonds and their chemical compositions. The aim of this work is to study the melt/fluid inclusions in diamonds from Arkhangelsk kimberlite province (Lomonosov deposit). My work included the study of morphology of diamonds containing microinclusions, distribution of inclusions in the crystals. After preliminary examination, I selected representative crystals for further study by IR-spectroscopy and X-ray spectral analysis. After detailed examination under binocular, I selected 11 diamond crystals from a representative collection (31 crystals) selected samples belong to three types, according to the classification by Yu.l. Orlov: 1st, 2nd and 4th types. Polished slices were prepared from these crystals. I selected the areas enriched in microinclusions and studied them by cathodoluminescence and photoluminescence. Application of IR-spectroscopy allowed me to calculate the content of nitrogen defects, as well as the amount of water and carbonates in microinclusions. The nitrogen content in the studied diamonds ranges from 400 ppm until 1100 ppm. IR spectra of microinclusions in diamonds show the presence of water (3420, 1650 cm-1), carbonates (1430, 880 cm-1), and silicates (1050, 1015, 970 cm-1). The proportion of the phases varies considerably in different samples and almost constant within the same crystal. The molar proportion of H2O and CO2 (calculated from the carbonate phase) varies in microinclusions from 0.08 to 0.19 (H2O/(H2O+CO2). X-ray spectral analyses allowed me to study the composition of fluid/melt microinclusions and showed that they were carbonate-silicate with significant variations between these two components. It is important that microinclusions in diamonds studied did not contain chloride components even in the case of high concentrations of alkalis (K2O + Na2O), so that most of inclusions contained alkaline carbonate end-member. Comparison of the data obtained allowed me to conclude that the composition of microinclusions in diamonds from the Arkhangelsk province is the most similar to that in diamonds from the Internatsional’naya pipe (Yakutia).