Victor V. Sharygin

Melt inclusions in olivine phenocrysts in unaltered kimberlites from the Udachnaya-East pipe, Yakutia: Some aspects of kimberlite magma evolution during late crystallization stages

The results of a complex study of melt inclusions in olivine phenocrysts contained in unaltered kimberlites from the Udachnaya-East pipe indicate that the inclusions were captured late during the magmatic stage, perhaps, under a pressure of <1 kbar and a temperature of ≤800°C. The inclusions consist of fine crystalline aggregates (carbonates + sulfates + chlorides) + gas ± crystalline phases. Minerals identified among the transparent daughter phases of the inclusions are silicates (tetraferriphlogopite, olivine, humite or clinohumite, diopside, and monticellite), carbonates (calcite, dolomite, siderite, northupite, and Na-Ca carbonates), Na and K chlorides, and alkali sulfates. The ore phases are magnetite, djerfisherite, and monosulfide solid solution. The inclusions are derivatives of the kimberlite melt. The complex silicate-carbonate-salt composition of the secondary melt inclusions in olivine from the kimberlite suggests that the composition of the kimberlite melt near the surface differed from that of the initial melt composition in having higher contents of CaO, FeO, alkalis, and volatiles (CO2, H2O, F, Cl, and S) at lower concentrations of SiO2, MgO, Al2O3, Cr2O3, and TiO2. Hence, when crystallizing, the kimberlite melt evolved toward carbonatite compositions. The last derivatives of the kimberlite melt had an alkaline carbonatite composition.

Carbonate-chloride enrichment in fresh kimberlites of the Udachnaya-East pipe, Siberia: A clue to physical properties of kimberlite magmas?

Kimberlites, the deepest terrestrial magmas and the principal source of diamonds, must have low viscosity and high buoyancy, which govern their exceptionally fast transport from mantle depths to the surface. Appreciation of the rheological properties of kimberlite magmas relies on research into their temperatures and compositions. Understanding of the alkali and volatile element budget is central to these studies, but is hampered by contaminated and altered compositions of kimberlites worldwide. Kimberlites of the diamondiferous Udachnaya-East pipe (Siberia) are exceptionally fresh, with low H2O (<0.5 wt%), but high CO2 (up to 14 wt%), Cl (up to 6 wt%), and alkalies ( up to 6 wt% Na2O and 2.0 wt% K2O). After crystallization of olivine the kimberlite melt evolved towards essentially carbonate-chloride compositions. The groundmass assemblage and compositions of the Udachnaya-East kimberlite resemble modern halogen-rich natrocarbonatite lavas from the Oldoinyo Lengai volcano. Rheological measurements on the Oldoinyo Lengai lavas can be used to constrain properties of the kimberlite magma.

Chemical Composition of Nyerereite and Gregoryite from Natrocarbonatites of Oldoinyo Lengai Volcano, Tanzania

Alkali carbonates nyerereite, ideally Na2Ca(CO3)2 and gregoryite, ideally Na2CO3, are the major minerals in natrocarbonatite lavas from Oldoinyo Lengai volcano, northern Tanzania. They occur as pheno- and microphenocrysts in groundmass consisting of fluorite and sylvite; nyerereite typically forms prismatic crystals and gregoryite occurs as round, oval crystals. Both minerals are characterized by relatively high contents of various minor elements. Raman spectroscopy data indicate the presence of sulfur and phosphorous as (SO4)2− and (PO4)3− groups. Microprobe analyses show variable composition of both nyerereite and gregoryite. Nyerereite contains 6.1–8.7 wt % K2O, with subordinate amounts of SrO (1.7–3.3 wt %), BaO (0.3–1.6 wt %), SO3 (0.8–1.5 wt %), P2O5 (0.2–0.8 wt %) and Cl (0.1–0.35 wt %). Gregoryite contains 5.0–11.9 wt % CaO, 3.4–5.8 wt % SO3, 1.3–4.6 wt % P2O5, 0.6–1.0 wt % SrO, 0.1–0.6 wt % BaO and 0.3–0.7 wt % Cl. The content of F is below detection limits in nyerereite and gregoryite. Laser ablation ICP-MS analyses show that REE, Mn, Mg, Rb and Li are typical trace elements in these minerals. Nyerereite is enriched in REE (up to 1080 ppm) and Rb (up to 140 ppm), while gregoryite contains more Mg (up to 367 ppm) and Li (up to 241 ppm) as compared with nyerereite.

New mineral data from the kamafugitecarbonatite association: The melilitolite from Pian di Celle, Italy

SummaryA detailed mineralogical investigation of a Pian di Celle sill rock (San Venanzo, Italy), classified asmelilitolite and associated withvenanzite and carbonatitic pyroclasts, revealed new and rare mineral parageneses, considered as characteristic of thekamafugite-carbonatite association. These are formed by several accessory minerals, including minerals of the cuspidine family, götzenite, khibinskite, minerals of the rhodesite- delhayelite- macdonaldite family, pyrrhotite, bartonite and (Fe, Ni, Co) monoarsenide, mostly optically and chemically identified also in fluid inclusions. The chemical composition of these minerals and their probable crystallisation succession, deduced from textural relationships, demonstrates extensive atomic substitutions, notably for Ca, Ti, Mg and alkali, essentially reflecting high concentrations of REE, Sr, Ba, Nb and Zr, which significantly varied during crystallisation. Molecular alkali excess over Al and high Ca content in (H2O, F, CO2)-rich, Siundersaturated liquid(s) are considered the dominant factors in controlling the stability of disilicate-type minerals. Separation of the carbonatite liquid from the silicate magma, constrained by textural and fluid inclusion data, was fundamental in moving the residuum onto a strongly peralkaline trend which stabilised the sulphides under changed redox conditions.ZusammenfassungEine eingehende mineralogische Untersuchung eines Lagerganges von Pian di Celle, der als Melilitolit klassifiziert and mit Venanzit and karbonatitischen Pyroklasten assoziiert ist, ergab neue and seltene Mineral-Paragenesen, die als charakteristisch für die Kamafugit-Karbonatit-Assoziation gelten. Diese bestehen aus verschiedenen akzessorischen Mineralien, darunter Perovskit, Cuspidin, Götzenit, Khibinskit, Delhayelit, Macdonaldit, Bardonit and (Fe, Ni, Co) Monoarsenit; diese werden in Flüssigkeitseinschlüssen mit optischen and chemischen Methoden identifiziert. Die chemische Zusammensetzung dieser Minerale and ihre wahrscheinliche Kristallisationsabfolge, aus texturellen Beziehungen abgeleitet, zeigt extensive Substitutionen, vor allem für Ca, Ti, Mg and Alkelien, die im wesentlichen hohe Gehalte an SEE, Sr, Ba, Mb and Zr andeuten, die während der Kristallisation beträchtlichen Schwankungen unterlagen. Molekularer Alkali überschuß über Al in (H2O, F, CO2)-reichen Si-untersättigten Fluiden werden als wichtigste Faktoren für die Stabilität von Mineralen des DisilikatTyps gesehen. Trennung des Karbonatites vom Silikat, die durch texturelle und Flüssigkeitseinschluß-Daten genau fixiert werden konnte, war wichtig für die Verschiebung des Residuums auf einen deutlich peralkalinen Trend, welcher die Sulfide unter veränderten Redox-Bedingungen stabilisieren konnte.

Djerfisherite in the Udachnaya-East pipe kimberlites (Sakha-Yakutia, Russia): paragenesis, composition and origin

Djerfisherite, an unusual potassium- and chlorine-bearing sulphide K6Na(Fe,Ni,Cu)(24)S26Cl, is found in remarkably fresh rocks of the Udachnaya-East kimberlite pipe, including several varieties of kimberlite and a kimberlite-hosted phlogopite-spinel lherzolite xenolith. In both kimberlite breccia and monticellite kimberlite djerfisherite is a common groundmass mineral. Djerfisherite is also present as a daughter phase in olivine-hosted inclusions of trapped carbonate-chloride melt and sulphide melt. The mineral is present as irregular or rounded grains (up to 80-100 mu m) in association with magnetite and pyrrhotite in the kimberlite groundmass, and together with carbonates, Na-K-chlorides, silicates, magnetite, sulphates and Fe-Ni-sulphides in melt inclusions. Djerfisherite in the lherzolite xenolith is mainly interstitial (up to 100 mu m) and commonly rims primary mantle sulphides that show clear signs of replacement. Broad compositional variations in Fe, Ni and Cu are common in djerfisherite from different occurrences of the Udachnaya-East pipe. Textural relations, heating stage experiments with melt inclusions and compositional data, suggest a late magmatic origin of djerfisherite in the Udachnaya-East kimberlite groundmass, at shallow depths and at T <= 800 degrees C. In contrast, djerfisherite in the lherzolite xenolith appears to be a product of direct precipitation from evolved kimberlite magma infiltrating into lithospheric xenoliths or reactions of evolved kimberlite fluids/melts with primary minerals in xenoliths.

Gas Fire from Mud Volcanoes as a Trigger for the Appearance of High-Temperature Pyrometamorphic Rocks of the Hatrurim Formation (Dead Sea Area)

Rock complexes of the Hatrurim Formation are largely confined to axial parts of gentle anticlinal uplifts. The rocks are partly localized in the complicating synclines on near-horizontal Campanian strata (Mishash Formation). The platform cover of this area is crosscut by a young rift valley and is divided by faults into blocks. The Hatrurim basin hosted in one of the blocks associates with the synclinal structure (8 × 5 km), the eastern limb of which is bordered by listric walls of the Dead Sea Rift valley (Fig. 3). The block is surrounded by anticlines with small gas (Zoar, Kidod, and Haqanaim) and oil (Zuk-Tamrur and Gurim) traps. The rift valley is characterized by salt diapirism (Sdom Dome). Asphaltene, bitumen, and oil occurrences are observed in coastal areas of the Dead Sea [8]. Numerous natural cataclysms related to bitumen burning and gas explosions are mentioned in biblical history. The landscapes of the Hatrurim, Ma’ale Adummim, Jabel Harmun, and Hyrcania complexes are distinguished in the surrounding cuesta topography characteristic of sedimentary sequences of the Judea Mountains and the Negev Desert. The relief of the Hatrurim basin is marked by several hundred newly formed cones largely composed of mud breccia. In some places, the breccias are characterized by vague bedding discordant with that of host sedimentary rocks. In the southern part of the basin, small individual cones and their chains are located on the eroded surface of the phosphorite and cherty Mishash Formation. In the north, large cones crown the mud breccia. The Ma’ale Adummim and Hyrcania complexes are characterized by a specific relief (truncated cones a few kilometers across at the base and an order of magnitude lower in height). The MZ complexes (particularly, Maqarin) in Jordan are feebly marked. Breccias are distributed through the entire section of the Hatrurim basin (Fig. 4). Rock fragments are composed of chalk, marl, and dolomite with subordinate cherts and phosphorites of the Mishash Formation.

Shulamitite Ca3TiFe3+AlO8 – a new perovskite-related mineral from Hatrurim Basin, Israel

Shulamitite, ideally Ca 3 TiFe 3+ AlO 8 , is a mineral intermediate between perovskite CaTiO 3 and brownmillerite Ca 2 (Fe,Al) 2 O 5 . It was discovered as a major mineral in a high-temperature larnite-mayenite rock from the Hatrurim Basin, Israel. Shulamitite is associated with larnite, F-rich mayenite, Cr-containing spinel, ye9elimite, fluorapatite, and magnesioferrite, and retrograde phases (portlandite, hematite, hillebrandite, afwillite, foshagite and katoite). The mineral forms reddish brown subhedral grains or prismatic platelets up to 200 μm and intergrowths up to 500 μm. The empirical formula of the holotype shulamitite (mean of 73 analyses) is (Ca 2.992 Sr 0.007 LREE 0.007 )(Ti 0.981 Zr 0.014 Nb 0.001 )(Fe 3+ 0.947 Mg 0.022 Cr 0.012 Fe 2+ 0.012 Mn 0.001 )(Al 0.658 Fe 3+ 0.288 Si 0.054 )O 8 . The X-ray diffraction powder-pattern (Mo Kα -radiation) shows the strongest lines {d [A]( I obs )} at: 2.677(100), 2.755(40), 1.940(40), 11.12(19), 1.585(17), 1.842(16), 1.559(16), 3.89 (13), 1.527(13). The unit-cell parameters and space group are: a = 5.4200(6), b = 11.064(1), c = 5.5383(7) A, V= 332.12(1) A 3 , Pmma, Z = 2. The calculated density is 3.84 g/cm 3 . The crystal structure of shulamitite has been refined from X-ray single-crystal data to R 1 = 0.029 %. No partitioning among octahedral sites was found for Ti and Fe 3+ in the structure of shulamitite, these cations are randomly distributed among all octahedra indicating an example of “valency-imposed double site occupancy”. The strong bands in the Raman spectrum of shulamitite are at: 238,250, 388,561, and 742 cm −1 . Shulamitite from the Hatrurim Basin crystallized under combustion metamorphism conditions characterized by very high temperatures (1150−1170 °C) and low pressures (high- T -region of the spurrite-merwinite facies). Chemical data for shulamitite and its Fe-analog from other metacarbonate occurrences (natural and anthropogenic) are given here.

Magma chamber-scale liquid immiscibility in the Siberian Traps represented by melt pools in native iron

Magma unmixing (i.e., separation of a homogeneous silicate melt into two or more liquids) is responsible for sudden changes in the evolution of common melts, element fractionation, and potential formation of orthomagmatic ore deposits. Although immiscible phases are a common phenomenon in the mesostasis of many tholeiitic basalts, evidence of unmixing in intrusive rocks is more difficult to record because of the transient nature of immiscibility during decompression, cooling, and crystallization. In this paper, we document a clear case of liquid immiscibility in an intrusive body of tholeiitic gabbro in the Siberian large igneous province, using textures and compositions of millimeter-sized silicate melt pools in native iron. The native iron crystallized from a metallic iron liquid, which originated as disseminated globules during reduction of the basaltic magma upon interaction with coal-bearing sedimentary rocks in the Siberian craton. The silicate melts entrapped and armored by the native iron are composed of two types of globules that represent the aluminosilicate (60–77 wt% SiO2) and silica-poor, Fe-Ti-Ca-P–rich (in wt%: SiO2, 15–46; FeO, 15–22; TiO2, 2–7; CaO, 11–27; P2O5, 5–30) conjugate liquids. Different proportions and the correlated compositions of these globules in individual melt pools suggest a continuously evolving environment of magmatic immiscibility during magma cooling. These natural immiscible melts correspond extremely well to the conjugate liquids experimentally produced in common basaltic compositions at <1025 °C. Our results show that immiscibility can occur at large scale in magma chambers and can be instrumental in generating felsic magmas and Fe-Ti-Ca-P–rich melts in the continental igneous provinces.

Fayalite and kirschsteinite solid solutions in melts from burned spoil-heaps, South Urals, Russia

Individual grains of calcian fayalite and ferroan kirschsteinite, as well as fayalite-kirschsteinite intergrowths are observed in the groundmass of basic crystallised melts, or parabasalts, from burned spoil-heaps of the Chelyabinsk brown-coal basin. Exsolved fayalite and kirschsteinite rims surround the grains of fayalite and early Mg-Fe olivine. The chemical study of the olivines has shown that during their crystallisation they were becoming enriched in fayalite and larnite and depleted in forsterite. The intergrowths of ferroan kirschsteinite (> 20 wt.% of CaO) and calcian fayalite ( 8.5 wt.%. The exsolution temperatures were estimated to 980-800 °C. The main reasons for the appearance of the Ca-Fe olivine in the parabasalts are the composition of the initial melt enriched in FeO and CaO, fractional crystallisation resul ting in further enrichment in iron of the residual low-silica melt, and reducing conditions during olivine crystallisation and exsolution.

Specificity of pyrometamorphic minerals of the ellestadite group

Numerous rare and new mineral species are synthesized during the process of pyrometamorphism (Gross, 1977; Chesnokov et al., 1987; Chesnokov and Shcherbakova, 1991; Chesnokov, 1999), including silicooxides, chloride-, fluoride, and sulfate-silicates, carbonate-sulfides, chloride-oxides, etc. Having made sense of numerous findings of compounds of this type, Chesnokov (1999) set forth the concept of the crystallochemical transition at extreme temperatures attaining 1200–1450°C in pyrogenic systems. First of all, intertype transitions (oxygen-bearing-oxygen-free) and interclass transitions (chloride-silicate, carbonate-sulfide, chlorideoxide) are realized. The specificity of pyrometamorphic mineral assemblages consists in the abundance of silicates with additional anions (F−, Cl−, (CO3)2−) (Sokol et al., 2005). Minerals of the ellestadite group Ca10(SiO4)3 − x(SO4)3 − x(PO4)2x(OH,F,Cl)2 are a spectacular example of these features. In the general case, they are silicate-sulfate-phosphate-hydroxide-chlorides-fluorides. The detailed description of these minerals based on the study of the original collection of pyrometamorphic minerals is presented in this paper.