Whole-rock geochemical, U-Pb and Sm-Nd isotope characteristics of the Dongueni Mont nepheline syenite intrusion, Mozambique

The Dongueni Mont nepheline syenite intrudes migmatitic paragneisses and siliciclastic metasediments of the Barue Complex, Mozambique. This study reports the whole-rock geochemical, U-Pb and Nd isotopic data of the nepheline syenite. The ferroan and alkalic geochemical characteristics are typical of alkaline rocks formed in a within-plate setting. The strong depletion in high field strength elements(HFSEs)(e.g. Ba, Nb, P,and Ti) and enrichment in large ion lithophile elements(LILEs)(e.g. Rb, Th, K, and Pb) are consistent with magmatism in a continental alkaline magmatic province associated with intracontinental rifting. Zircon U-Pb data yielded crystallization ages from 498 ± 19 to 562± 14 Ma,consistent with the Pan-African Orogeny and the inherited zircons yield an age of 1040 Ma, which supports the presence of a Mesoproterozoic crust. Theε_(Nd)(t) values from the nepheline syenite samples range from-15.1 to-16.1 and the T_(DM)values from 1.77 to 1.67 Ga, which indicate that the initial nepheline syenite magma formed from a tholeiitic or mantle source in a within-plate setting with crustal assimilation.

Nepheline Syenite Decomposition Using NaOH by Hydrothermal Reaction

Nepheline syenite is an important potassium-rich rock resource. Nepheline syenite powder was decomposed successfully by hydrothermal reaction using NaOH additive. Hydroxycancrinite (Na8(Al6Si6O24)(OH)2·2H2O ) solid and (K,Na)2SiO3 solution was obtained as a result of the hydrothermal reaction.

Evolution of technogenic landscapes by the example of apatite-nepheline ore concentration wastes

A primary soil-forming process can take place on the concentration waste of apatite-nepheline ores, whose biological recultivation was carried out more than 40 years ago. This process is characterized by the following features: forming of a thin litter with the content of organic carbon at the level of 8-12%, accumulation of humic substances in the sub-litter layer and the change of рН values. Microorganisms are biocatalysts of primary soil formation processes and one of the main factors that determine the specificity of this process. The prokaryotic complex of the newly formed soils, generated from nepheline sands, is considerably different from that of zonal soils on moraine sediments. The former ones are dominated by gram-positive bacteria, mainly actinobacteria, as well as by their filamentous forms (actinomycetes), whereas the latter ones are dominated by gram-negative bacteria. A common feature of invertebrate’s complexes in nepheline sands is the low species diversity, small-size and quickly development of microfauna and mesofauna representatives and the dependence of succession of microarthropods pioneer groups on the succession of bacteria and fungi.

Effects of Alkaline Additives on the Thermal Behavior and Properties of Cameroonian Poorly Fluxing Clay Ceramics

Ball clay and alkaline feldspars (syenite and nepheline syenite) were mixed with red kaolinite clay (rich in iron oxides but poor in fluxing oxides) and fired (1000°C - 1200°C) in order to improve certain characteristics of the obtained ceramics. The thermal behavior of the mixtures was monitored via Young modulus whereas linear shrinkage, water absorption, bulk density, flexural strength, microstructure and crystalline phases of fired products were examined. In the case of red clay-ball clay mixtures, the amount of mullite or cristobalite increased with heating temperature and the amount of additive, whereas the temperature at which there is an important sintering decreased with the increase of additive. In the ceramics produced from the mixtures of red clay-alkaline additive, contrary to mullite, the amount of cristobalite decreased with both the amount of additive and heating temperature. Also in the data of Young modulus, there was a decrease of temperature assigned to the beginning of densification. Additionally, incorporating at least 15% of alkaline additive to red clay and heating between 1050°C and 1200°C leads to ceramics with low water absorption (0.70% to 0.25%). However when using the same amount of additive and heating the mixtures at the same temperature, ceramics produced from nepheline syenite were denser than those obtained from syenite. Addition of ball clay or alkaline feldspars to kaolinite clay containing great amount of iron oxides and low fluxing oxides allows getting compact ceramics at reduced temperature.

A NEW MINERAL——FLUORBRITHOLITE-(CE)

: The new mineral fluorbritho!ite-(Ce)occurs in nepheline syenite-marble xenoliths, sodalite syenite xenoliths and pegmatite dikes at Mont St. Hilaire, Quebec. It is associated mainly with analcine ,microclme , aegirine , zircon , biotite, pyro-phanite. astrophyllite ?ancylite, natrolite,monaziie etc.The mineral is hexagonal ,P63/m -with a 9. 517(5) A , c 6. 983(4) A,c/a 0. 7337,? 547. 7(8) A3,Z=2. The strongest X-ray pmvder diffraction lines and their relative intensities (visual)are:2. 851(100),2. 821(30),2. 753(30),1. 970(20),1. 969(30)(for MSH-3).Fluorbritholite-(Ce) crystal is shown prismatic. Its colour is pale yellow, tan, reddish-brown. Streak colourless to pale brown ; Lustre adamantine ; Opaque to translucent; Hardness 5 ; Brittle; Cleavage { 0001 } distinct; Fracture even to conchoidal; Density 4. 66(1) (meas} or 4. Q6g/cm3(calc. ) ; Non-fluorscent. Optically umaxial (-). w 1. 792(5),? 1. 786(5) in Na light; Nonpleochroic.Electron microprobe analyses correspond to (CeL 69 La1.02Na0.82 Nd0.44 Sr0.30 Ca0.17 Mn0.17 Y0.09 Pr0.06 Th0.03 Fe0.01) ?4.32(Si232 P0.61 ) ?2.93 O11.81 F1.19,the ideal structural formula is(PEE,Ca)5(Si,P)3012F.Britholite-(Cc) and britholite-(Y) should be renamed re-spectively ,hydroxylbritholite-(Ce) and hydroxylbrithblite(Y) to be suggested in discussion section.

Petrogenesis and Tectonic Implications of Peralkaline A-Type Granites and Syenites from the Suizhou-Zaoyang Region,Central China

In this study, we present systematic petrological, geochemical, LA-ICP-MS zircon U-Pb ages and Nd isotopic data for the A-type granites and syenites from Suizhou-Zaoyang region. The results show that the peralkaline A-type granites and syenites were episodically emplaced in Suizhou-Zaoyang region between 450±3 and 441±7 Ma which corresponds to Late Ordovician and Early Silurian periods, respectively. Petrologically, the syenite-peralkaline granite association comprises of nephefine normative-syenite and alkaline granite in Guanzishan and quartz normative syenite and alkafine granite in Huangyangshan. The syenite-granite associations are ferroan to alkali in composition. They depict characteristics of typical OIB （oceanic island basalts） derived A-type granites in multi-elements primitive normalized diagram and Ybffa vs. Y/Nb as well as Ce/Nb vs. Y/Nb binary plots. Significant depletion in Ba, Sr, P, Ti and Eu indicates fractionation of feldspars, biotite, amphiboles and Ti-rich augite. The values of eNd（t） in Guanzishan nepheline syenite and alkaline granite are ＋1.81 and ＋2.26, respectively and the calculated two-stage model age for these rocks are 1 040 and 1 003 Ma, respectively. On the other hand, the Huangyangshan alkaline granite has eNd（t） values ranging from ＋2.61 to ＋3.46 and a relatively younger two-stage Nd model age values ranging from 906 to 975 Ma, respectively. Based on these data, we inferred that the Guanzishan nepheline syenites and granites were formed from fractional crystallization of OIB-like basic magmas derived from upweliing of metasomatized lithospheric mantle. The Huangyangshan quartz syenite and granite on the other hand, were formed from similar magmas through fractional crystallization with low input from the ancient crustal rocks. Typically, the rocks exhibit Al-type granite affinity and classified as within plate granites associated with the Ordovician crustal extension and the Silurian rifting.