Mineralogical Journal

3-16

Authors: V.M. Kvasnytsya

Summarized data on more than 120 diamond crystals from the Neogene (Baltska suite) and Quaternary alluvial sediments of the Dniester — Southern Bug interfluve and their basins were studied: 35 microdiamonds and 1 macrodiamond from the Neogene (Baltska suite) sands and 85 microdiamonds from alluvial sands. Using infrared microscopy, Raman spectroscopy and isotopic analysis of carbon a little more than four dozen microdiamonds (less than 0.5 mm in size) and one macrodiamond have studied in details. According to morphology, microdiamonds from the Neogene (Baltska suite) sands are mainly represented by cubes, octahedrons and rhombic dodecahedrons, as well as crystal fragments. Their photoluminescence is orange, green and yellowish green. Almost half of the crystals do not show luminescence under ultraviolet light. The macrodiamond and several microdiamonds are nitrogen-free crystals of type IIa by physical classification. According to Raman spectroscopy, they are relatively structurally more perfect than nitrogen-containing crystals. Microdiamonds from the alluvium of the Dniester and Southern Bug basins are represented in almost equal proportions by octahedrons and rhombic dodecahedrons, cubes and combination crystals, as well as crystal fragments. Photoluminescence of these diamonds is often orange and green, less common blue and yellow, and is absent for a significant part of the crystals. Among the investigated microdiamonds from the alluvium sands, 39% of the crystals are nitrogen-free type IIa diamonds, 31% of the crystals — Ia type diamonds, 15% of the crystals — Iab type diamonds and 15% of the crystals — Іb type diamonds. Microdiamonds from the alluvium of the Dniester basin have a wide range of δ13С values: from –24.79 to –3.14‰ (average –11.94‰). A specific feature of the microdiamonds of the Dniester — Southern Bug interfluve and their basins is the wide distribution of unique green rounded crystals among them — tetrahexahedrons and rhombic dodecahedrons. They are characterized by a high content of single nitrogen impurities (593—1106 ppm), a low degree of aggregation of nitrogen atoms (0—13%), and a narrow range of carbon isotopic composition values (average –11.53‰ δ13С). They are classified as endemic diamonds, which features indicate their local indigenous sources. The distribution of green microdiamonds was analyzed and an assumption was made about their genesis and the possible finding of their host sources. Issues of the origin of diamonds of the Dniester — Southern Bug interfluve and their basins, their possible crystallization medium, and host rocks are considered.

27-38

Authors: О.М. Ponomarenko, A.I. Samchuk, I.M. Lisna, L.V. Somka, I.A. Shvaika, L.I. Proskurka, I.D. Shvaika, K.V. Vovk

As a result of studying of the distribution of rare earth elements (REE) in apatites from metamorphic rocks that occurr as xenoliths (skialites) among Berdychiv granites and charnockites of the Podilsk block of the Dniester-Bug Megablock of the Ukrainian Shield, it was found that apatites of granulite-gneiss rocks are characterized by a low fractionation of REE with predominant light REE and sharp deficiency europium, which is characteristic of calc-alkaline rocks of other shields. As to the metamorphic rocks of the Bereznin stratum the maximum content of REE found in apatites is characteristic of melanocratic rocks which commonly found in the central zones of metamorphic xenoliths. At the contact with granitoids the content of REE decreases. All xenoliths became zonal due to the such factor as acid-basic ratio that control the differentiation of REE in mineral-forming environment. It has been suggested that the spectra of REE distribution found in apatites from metamorphic rocks, which occur as of xenoliths among granitoids, may indicate the nature of xenoliths. They can be either the substrate for these granitoids or occur as dyke or restite formations.

50-68

Authors: L.M. Stepanyuk, L. Shumlyanskyy, V.O. Gatsenko, T.I. Dovbush, S.A. Wilde, А.А. Nemchin, B. Bagiński, O.V. Bilan

The LA-ICP-MS method has been applied to the investigation of U-Pb and Lu-Hf isotope systematics in zircons from enderbitic gneiss that represents the main rock type in the Kosharo-Oleksandrivka open pit, and from amphibolite (metamorphosed ultramafite) that occurs as a body of non-defined shape hosted by enderbitic gneiss. The multigrain TIMS U-Pb dating method was applied to monazite from a charnockite vein that cuts through enderbitic gneiss. At least three zircon populations can be defined in enderbitic gneiss. The oldest (Paleoarchean) population is rather small and includes zircons that yielded an upper intercept age of 3325 ± 42 Ma. The biggest (Mesoarchean) population embraces zircon grains that plot along the regression line with the upper intercept age of 2850 ± 18 Ma, and lower intercept at 2092 ± 45 Ma. The Paleoproterozoic population plots near the lower intercept of the above mentioned regression line, its age has been defined as ca. 2100 Ma. The εHf value in zircons of the Mesoarchean population varies from 1.9 to –7.7, with a single value as low as –16.4. Paleoproterozoic zircons have εHf in a range –7.7 to –18.4. Amphibolite hosts two zircon populations. The first one has an upper intercept age of 2840 ± 31 Ma and variable Hf isotope composition (εHf — 7.7 to –9.9) that indicate mixing of juvenile mantle-derived and ancient crustal materials. The second population comprises a few zircons of the Paleoproterozoic (2078 ± 24 Ma) age that also had a mixed mantle-crustal source (εHf — 5.2 to –7.9). The late vein of charnockite yielded the U-Pb monazite age of 2015.3 ± 7.2 Ma. According to geothermobarometry, based on mineral composition determined by electron microprobe data, the studied rock association experienced granulite facies metamorphism at a temperature of 720—825 °С and pressure of 6.2—7.5 kbar.