Nanoinclusions in microdiamonds from Neogenic sands of the Ukraine (Samotkan' placer): A TEM study Victor M. Kvasnytsya a, ⁎, Richard Wirth b a Institute of Geochemistry, Mineralogy and Ore Formation, National Academy of Sciences of Ukraine, Palladin Avenue 34, 03680 Kyiv-142, Ukraine b GeoForschungsZentrum Potsdam, Experimental Geochemistry and Mineral Physics, Telegrafenberg, 14473 Potsdam, Germany abstract article info Article history: Received 8 October 2008 Accepted 17 May 2009 Available online 18 June 2009 Keywords: Microdiamond Mineral inclusions Fluid inclusions ТЕМ Ukrainian shield Placer Mineral and fluid inclusions in seven microdiamonds (ca. 0.2 mm in diameter) from the Neogene, Samotkan' placer of the Ukrainian shield were investigated by TEM. Various types of submicron- or nanometre-sized inclusions such as olivine and orthopyroxene, Fe,Sn oxide and assemblages of mineral multi-phases were observed. In an octahedral microdiamond crystal numerous olivine and enstatite micro- and nanocrystals were observed. Their composition is close to that of other olivine and enstatite inclusions found in kimberlitic diamonds worldwide. An unusual feature of these minerals in the samples studied, however, is a relatively high NiO content: 0.50–0.80 wt.% in olivine (Fo 91.3–92.1 ) and 0.40–0.70 wt.% in enstatite (Fo 94.1–95.4 ). These peridotitic mineral associations represent the host (possibly lherzolitic mantle) in which the diamonds grew. The mean Mg# values of olivine and enstatite inclusions in Samotkan's microdiamond are, respectively, 91.43 and 94.83, which are closer to Mg#-values of these minerals in lherzolite, rather than in harzburgite assemblages (included in diamond). In addition, enstatite–clinoenstatite, K-richterite, graphite, and Fe,Sn oxide were also identified as nanoinclusions in Samotkan' diamond; the Fe,Sn oxides and magnetite were found in two microdiamonds of the transitional {111}+{110} form. The K-richterite and graphite have been attributed to epigenetic inclusions. The origin of Fe,Sn oxide is not clear. Assemblages of multi-phase, minerals were observed in four microdiamonds of variable morphology: octahedron, transitional {111}+{110} form, cube and cube-coated diamond. These phases belong to fluid- bearing inclusions and are enclosed in cavities which, as a rule, are not filled completely by the solid phases. The remainder of the volume is occupied by a fluid that for the most part has been released during sample preparation. In the majority of cases the multi-phase assemblages consist of carbonate, mica, rutile, ilmenite, apatite and sylvite. Carbonates are the most abundant phases in the fluid inclusions; they are calcium-rich carbonates, frequently with admixtures of Fe, Mg and Sr. The mica inclusions are enriched in silicon, with Si varying from ca. 6.7 to 7.0 a.p.f.u. The multi-phase mineral assemblages present in Samotkan's microdiamond are similar to fluid-bearing, microinclusions found previously in other diamond types (e.g., fibrous diamonds, the fibrous coat of coated diamonds or the internal clouds of octahedral diamonds) from kimberlites of different provinces worldwide. They represent the carbonate-, alkali-, and chlorine-rich mantle fluid composition present during crystallisation of the Samotkan's microdiamond. Judging from the composition of the multi-phase assemblages it may be assumed that the Samotkan's microdiamond grew from a carbonatitic to a slightly silicic melt, rich in alkali and volatile components. © 2009 Published by Elsevier B.V. 1. Introduction Inclusions in diamonds provide information about the mantle environment in which they grew, the composition of the fluid from which they formed and P–T conditions responsible for diamond growth. One can distinguish between primary (proto- and syngenetic) and epigenetic mineral inclusions, and primary multi-phase or fluid inclusions. Primary and epigenetic mineral inclusions in kimberlitic- and lamproitic-hosted diamond from almost all diamond-bearing pro- vinces of the world have been the subject of extensive study. Most frequently, the primary mineral inclusions are silicates such as garnet, olivine, and pyroxene, oxides (e.g., chromites) and sulphides (Sobolev, 1974; Meyer, 1987; Harris, 1992). The size of these crystalline inclusions varies over a wide range; from tens of nanometers up to a millimeter. These can indicate both mantle paragenesis (peridotitic or eclogitic) and also P–T parameters of diamond crystallisation. For example, the primary mineral inclusions in so-called “super-deep” diamonds such as ferropericlase in association with Mg, Si-and Ca,Si- “perovskite”, majoritic garnet, which have allowed estimates to be made of the depth of diamond crystallisation (lower mantle) (e.g., Harris et al., 1997; Davies et al., 1999; Stachel et al., 2000; Kaminsky Lithos 113 (2009) 454–464 ⁎ Corresponding author. E-mail address: kvasnytsya@ukr.net (V.M. Kvasnytsya). 0024-4937/$ – see front matter © 2009 Published by Elsevier B.V. doi:10.1016/j.lithos.2009.05.019 Contents lists available at ScienceDirect Lithos journal homepage: www.elsevier.com/locate/lithos