Carbonatites Research Papers - Academia.edu (original) (raw)

1. Definitionen............................................................2 2. Historische LS-Kunde, Paragenesen....................5 2.1 Einteilungen von LS...............................................5 2.2 Einteilung von... more

1. Definitionen............................................................2
2. Historische LS-Kunde, Paragenesen....................5
2.1 Einteilungen von LS...............................................5
2.2 Einteilung von Erz-LS.............................................6
2.3 Paragenesen..........................................................7
2.4 Granitoide LS.........................................................8
3. Vereinfachte genetische Klassifikation der LS...11
3.1 Magnetogene Erz-LS............................................12
3.2 Verwitterungs-LS, Pegmatite.............................. 13
3.3 Sedimentäre LS....................................................13
3.4 Hydrothermale LS................................................14
4. Genetische Einteilung..........................................20
4.1 Ozeanforschung...................................................21
4.2 Plattentektonik.....................................................22
4.3 Vulkanismus........................................................22
4.4 Neue Mechanismen zur LS-Bildung..................23
4.5 Sedimentologie...................................................23
4.6 Petrologie............................................................24
5. Ausgewählte LS..................................................24
5.1 Witwatersrand Becken LS..................................24
5.2 Bushveld LS........................................................24
5.3 Die Sudbury LS...................................................26
6. Kompatible und inkompatible Elemente...........27
7. Geochemie der Kristalle ......................................29

This work focus on the characterization of a recently discovered pair of carbonatites named as Joca Tavares Carbonatite and Tres Estradas Carbonatite, their identification on Rio Grande do Sul count up to 529 global carbonatites... more

This work focus on the characterization of a recently discovered pair of carbonatites named as Joca Tavares Carbonatite and Tres Estradas Carbonatite, their identification on Rio Grande do Sul count up to 529 global carbonatites occurrences. The main objectives of this project are to macroscopic petrography, spatial and structural characterization of each body, its structural control and wallrock relationships and regional geological setting of the carbonatites in the Rio Grande do Sul shield. This work ends with making of a GIS system data . The study started with the collection and integration of diverse information surrounding the occurrences and involved detailed analysis of remote sensing (satellite and aerial) images plus airborne geophysical data. Thus the products generated were associated to field lithological verification, petrographic description of rock samples and in situ structural measurements. Tres Estradas Carbonatite are hosted by basement gneisses (Santa Maria Chico Granulitic Complex) and show oriented foliation to northeast direction, often folding. Hence, Tres Estradas is classified as a linear type carbonatite. The Joca Tavares Carbonatite is intruded along contact between Arroio Marmeleiro metamorphics and Cerro do Bugio siliciclastics and did not show foliation and is classified as a central type carbonatite. Both are situated near to significant NE-NW faults intersections. It is possible to conclude that the Joca Tavares and Tres Estradas were located at specific sites pointed by the NE and NW crossing faults. The northwest oriented Suspiro-Linhares Fault Zone (Ibare Lineament) consists of the main structural control of carbonatites ocurrences, this lineament delimits the boundary between upper crustal rocks of the Palmas Group and the deepest exposed crust (Santa Maria Chico Granulitic Complex). This project organized and generate a significant amount of data approaching the carbonatitic rocks on Rio Grande do Sul.

The Stirone River section in the Italian Northern Apennines hosts a rare example of Pliocene age hydrocarbon-imprinted carbonates in the Mediterranean Basin associated with deep-water hemipelagic lithologies. These include meter-sized,... more

The Stirone River section in the Italian Northern Apennines hosts a rare example of Pliocene age
hydrocarbon-imprinted carbonates in the Mediterranean Basin associated with deep-water hemipelagic
lithologies. These include meter-sized, dolomite-cemented chimneys, micritic brecciated limestones,
lucina-mudstones and chemosymbiotic bivalve shells. Some such chimneys show d13C values as low
as 37.5‰ VPDB, suggesting subsurface precipitation of authigenic dolomite induced by anaerobic
oxidation of methane triggered by consortia of sulphate reducing bacteria. These carbonates are interpreted
as part of the plumbing system related to hydrocarbon expulsion onto the seafloor, resulting from
hydrocarbon-enriched defluidization processes dated at an interval at 3.6 e 3.3 Ma and associated with
the thrust-related “Salsomaggiore structure”.

The carbonatite of Mabounié (Gabon), first described in 1988 [1], is a complex igneous intrusion approximately 2.3 km in diameter hosted in Paleoproterozoic fenitized gneisses and migmatites. Numerous mineralogical and geochemical studies... more

The carbonatite of Mabounié (Gabon), first described in 1988 [1], is a complex igneous intrusion
approximately 2.3 km in diameter hosted in Paleoproterozoic fenitized gneisses and migmatites.
Numerous mineralogical and geochemical studies were conducted in the twenty years following its
discovery ([2-4], BRGM, pers. comm.) that led to the discovery of a polymetallic lateritic ore deposit
above the intrusion. In the present work, new petrographic studies are reported on fresh drill core samples
obtained within the framework of the Maboumine project.
The carbonatite is heterogeneous sövite, crosscut by a few dikes of rauhaugite (dolomite-rich
carbonatite). The mineralogy varies strongly along magmatic bedding, schlieren patches and
hydrothermally recrystallized areas [4]. Apatite-sövite and phlogopite-sövite are common and intermixed
with each other, and contain a variable amount of Ti-rich magnetite (in some cases, up to 40 vol.% of the
rock). Other accessory minerals include rare-earth carbonates, ilmenite, pyrochlore, zircon, baddeleyite,
calzirtite and zirconolite.
In the lateritic profile developed above the carbonatite suite, the lowermost horizon consists of
massive phosphates and is characterized by the dissoluion of carbonates; it is followed by “ribbon”
laterites characterized by the breakdown of apatite, and finally by an iron-oxide-rich horizon at the
surface of the deposit. Even though pyrochlore is affected by different processes and its composition
changes slightly across the profile [3], this mineral remains the main carrier of rare metals (Nb, Ta) and
rare earth elements, which are concentrated upward mainly in the “ribbon” ore.

The South Qinling orogen in central China hosts carbonatites occurring as stocks associated with syenites and collectively regarded as the Miaoya intrusive complex. The complex hosts economic resources of rare-earth elements (REE) and Nb.... more

The South Qinling orogen in central China hosts carbonatites occurring as stocks associated with syenites and collectively regarded as the Miaoya intrusive complex. The complex hosts economic resources of rare-earth elements (REE) and Nb. The Miaoya syenites are strongly metasomatized at the contact with the carbonatites and cross-cut by carbonate and felsic veinlets. Small oscillatory-zoned crystals of zircons from the syenites give a concordant U–Pb age of 147 ± 0.5 Ma, which differs significantly from the ages of both large magmatic zircon grains from the syenites and primary monazite from the carbonatites (766 Ma and 234 Ma, respectively). To account for the possibility that the Miaoya syenites are coeval and cogenetic with the carbonatites, the trace-element budget of both rock types was examined in detail. The Miaoya carbonatite contains primary REE-rich fluorapatite and monazite, which precipitated earlier than the rock-forming REE-poor calcite, indicating that the primary carbonatitic magma was rich in REE. The compositions of the parental syenitic and carbonatitic magmas, calculated on the basis of the trace-element composition of primary fluorapatite in the two rock suites, show that the carbonatitic magma contained higher Sr and REE (La–Tb), but lower Ba, Pb, Th, U, Nb and Ta levels in comparison with the syenitic melt. These differences are inconsistent with derivation of the Miaoya rocks from a homogeneous carbonate–silicate melt by immiscibility or crystal fractionation. It is therefore concluded that the carbonatitic magma at Miaoya was generated directly in the mantle. Emplacement of the carbonatites in the South Qinling orogen marked transition to a postorogenic regime, and was preceded by oceanic crust subduction and closure of the Mianlue Ocean in the Triassic. Our models show that melting of the Mianlue crust and up to 10 wt.% of sediments cannot produce the levels of REE enrichment observed in the Miaoya carbonatites. More complex models, involving recycling of the Mianlue oceanic crust and a REE-rich carbonate liquid from an old deep-seated mantle source are required to explain the observed trace-element characteristics of the Miaoya carbonatites.

We report here, for the first time, on the new finding of extrusive calciocarbonatite (alvikite) rocks from the Pleistocene Mt. Vulture volcano (southern Italy). These volcanic rocks, which represent an outstanding occurrence in the... more

We report here, for the first time, on the new finding of extrusive calciocarbonatite (alvikite) rocks from the Pleistocene Mt.
Vulture volcano (southern Italy). These volcanic rocks, which represent an outstanding occurrence in the wider scenario of the
Italian potassic magmatism, form lavas, pyroclastic deposits, and feeder dikes exposed on the northern slope of the volcano. The
petrography, mineralogy and whole-rock chemistry attest the genuine carbonatitic nature of these rocks, that are characterized by
high to very high contents of Sr, Ba, U, LREE, Nb, P, F, Th, high Nb/Ta and LREE/HREE ratios, and low contents of Ti, Zr, K, Rb,
Na and Cs. The O–C isotope compositions are close to the “primary igneous carbonatite” field and, thus, are compatible with an
ultimate mantle origin for these rocks. The Sr–Nd–Pb–B isotope compositions, measured both in the alvikites and in the silicate
volcanic rocks, indicate a close genetic relationship between the alvikites and the associated melilitite/nephelinite rocks.
Furthermore, these latter products are geochemically distinct from the main foiditic-phonolitic association of Mt. Vulture. We
propose a petrogenetic/geodynamic interpretation which has important implications for understanding the relationships between
carbonatites and orogenic activity. In particular, we propose that the studied alvikites are generated through liquid unmixing at
crustal levels, starting from nephelinitic or melilititic parent liquids. These latter were produced in a hybrid mantle resulting from
the interaction through a vertical slab window, between a metasomatized mantle wedge, moving eastward from the Tyrrhenian/
Campanian region, and the local Adriatic mantle. The occurrence of carbonatite rocks at Mt. Vulture, that lies on the leading edge
of the Southern Apennines accretionary prism, is taken as an evidence for the carbonatation of the mantle sources of this volcano.
We speculate that mantle carbonatation is related to the introduction of sedimentary carbon from the Adriatic lithosphere during
Tertiary subduction.

Zircon grains from two Precambrian carbonatites from Fennoscandia (Siilinjärvi and Tiksheozero) were studied by in-situ geochemical and isotope methods. Zircon domains which preserved primary mantle signatures were identified by a... more

Zircon grains from two Precambrian carbonatites from Fennoscandia (Siilinjärvi and Tiksheozero) were studied
by in-situ geochemical and isotope methods. Zircon domains which preserved primary mantle signatures were
identified by a combination of microscopic investigations of thin sections of the carbonatite rocks and separated
zircon grains (optical microscopy, optical microscopy combined with cathodoluminescence (OM–CL), and scanning
electron microscopy). All studied samples show evidence for alteration processes caused by infiltration of
late-stage carbonatite melt/s or fluid/s. This led to different changes in the geochemistry and isotope composition
of altered zircon domains. For the 2.6 Ga old Siilinjärvi carbonatite complex, zircon grains underwent solid state
recrystallization mainly at their rims. Zircon cores often preserved primary mantle signatures and register high
HREE/LREE ratios, undisturbed U–Pb ages, εHf values close to CHUR (chondritic uniform reservoir), and δ18O
values typical for the mantle. The solid state recrystallization of zircon occurred mainly in contact with a
late-stage carbonatite melt or fluid and led to (i) diffusion driven loss of HREE, Th, and U, (ii) partial disturbance
of theU–Pb system, (iii) a small shift of the δ18O toward lower values, and (iv) higher CL intensities in such zircon
domains. Contrarily, zircons from the 2.0 Ga old Tiksheozero complex underwent a coupled dissolution–
reprecipitation process. Dissolved–reprecipitated zircon domains typically have a distinctive patchy texture in
BSE images and sometimes contained abundant micro-inclusions of calcite, phlogopite, apatite, and baddeleyite.
The EDS spectra documented that these non-luminescent zircon regions have much higher concentrations of Ca
(and sometimes Fe) indicating an “impure” zircon composition. In addition, many trace elements are highly
enriched in such “impure” zircon. Enrichment of Th (and to a lower degree of U) resulted in high Th/U ratios
(>1) and disturbance of the U/Pb ages. Hf and O isotope values varied widely even within a single zircon
grain. Isotope signatures attest a complex crystallization history of carbonatites and can best be interpreted as
melt mixing processes of different carbonatite melt pulses. The non-luminescent reprecipitated zircon domains
in Tiksheozero are often rimmed by zircon with high CL-intensity recrystallized in a solid state aswell as by new
zircon overgrowths. These zircon regions consist of pure zircon without elevated concentrations of Ca and Fe.
Solid state recrystallization was accompanied by annealing that caused volume loss resulting in fractures that
are now frequently filled with calcite (often containing a minor proportion of apatite) and phlogopite which
sampled the withdrawn elements from the recrystallized zircon. Co-crystallizing calcite may thus lead to HREE
depletion in newly grown zircon. It is expected that interaction with carbonatite melts can lead to similar
changes in zircon grains from other sub-continental mantle rocks. Then, the primary geochemical and isotope
systems of zircon may be changed despite its chemical and physical robustness. Infiltration of late-stage
carbonatite melts seems to be a common process within many carbonatitic rocks that may hamper to determine
the primary geochemical and isotope signatures of carbonatitic zircons.

Carbonate rocks at the Bayan Obo giant rare earth element (REE) – Nb – Fe ore deposit, Inner Mongolia, China are divided into four categories: sedimentary limestone and dolostone (H8 s), deformed mineralized coarse-grained dolomite marble... more

Carbonate rocks at the Bayan Obo giant rare earth element (REE) – Nb – Fe ore deposit, Inner Mongolia, China are divided into four categories: sedimentary limestone and dolostone (H8 s), deformed mineralized coarse-grained dolomite marble (H8 c) and fine-grained dolomite marble (H8 f), and carbonatite dikes (D), based on their texture, mineral assemblage and geological occurrence. Although the sedimentary carbonate rocks (H8 s) show weak deformation north of the Kuangou fault zone, this unit is not metamorphosed, which occurs together with quartz sandstone, sandstone and shale, comprising the Middle Proterozoic Bayan Obo Group. In contrast, the mineralized fine-to-coarse-grained dolomitic marbles (H8 f and H8 c) that occur to the south of the Kuangou fault zone are sheared, deformed and metamorphosed. The H8 c consist mainly of dolomite associated with apatite, magnetite, minor pyrochlore, and sodic amphibole. Dolomite in the main ore-bearing unit (H8 f) occurs with magnetite, monazite, bastnaesite, and parisite. Fine-grained monazite occurs as fracture fillings in dolomite. Electron microprobe data show that dolomite and/or ankerite in the ore-bearing rocks (H8 c and H8 f) are similar to carbonatite dikes (D) occurring within 3.5 km northeast of the deposit. These carbonates contain high MnO (>0.50 wt.%) and SrO (>0.15 wt.%) as is typical of carbonatites; this contrasts with very low MnO and SrO (< 0.1 wt.%) in typical sedimentary limestone and dolostone (H8 s). The variation of MnO and SrO content in dolomite from the ore-bearing dolomite marbles may be interpreted by fractional crystallization of a carbonatitic magma, which results in REE enrichment in the evolved residual magma. This interpretation is consistent with their field relations, trace element geochemistry, stable isotopes, and 87 Sr/ 86 Sr ratios. The MnO and SrO contents of carbonate minerals may be used as important chemical characteristics to identify their genesis. MnO and SrO contents in carbonate minerals higher than 0.15 wt.% are used as indicators to distinguish carbonatite from sedimentary carbonate rocks. These criteria together with fenitization may be taken as critical signatures to separate carbonatites from sedimentary carbonate rocks, even when both were metamorphosed to marbles.

Most studies of compositional heterogeneities in the mantle, related to recycling of crustal sediments or delaminated subcontinental lithosphere, come from oceanic setting basalts. In this work, we present direct geochronological and... more

Most studies of compositional heterogeneities in the mantle, related to recycling of crustal sediments or delaminated subcontinental lithosphere, come from oceanic setting basalts. In this work, we present direct geochronological and geochemical evidence for the incorporation of recycled crustal materials in collision-related carbonatites of the South Qinling orogenic belt (SQ), which merges with the Lesser Qinling orogen (LQ) to separate the South and North China Blocks. The SQ carbonatites occur mainly as stock associated with syenites. The data presented here show that zircon from the syenites yields an age of 766 ± 25 Ma, which differs significantly from the age of primary monazite from the carbonatites (233.6 ± 1.7 Ma). The syenites contain lower initial 87Sr/86Sr and higher εNd values. This indicates that the carbonatites do not have genetically related with the silicate rocks, and were directly derived from a primary carbonate magma generated in the mantle. The carbonatites show a Sr–Nd isotopic signature similar to that of the chondritic uniform reservoir (CHUR), and parallel Sm–Nd model ages (TCHUR) of 190–300 Ma. However, the rocks have extremely variable Pb isotopic values straddling between the HIMU and EM1 mantle end-members. Most carbon and oxygen isotopic compositions of the SQ carbonatites plot outside the field for primary igneous carbonates. Their δ13C shows higher value than a ‘normal’ mantle, which implies an incorporation of recycled inorganic carbon. The carbonatites were emplaced close to the Mianlue suture, and followed the closure of the Mianlue ocean and Triassic collision of the South and North China Blocks. However, direct melting of the subducted Mianlue oceanic crust characterized by high εNd and low (EM1-like) 206Pb/204Pb values cannot explain the CHUR-like Nd signature and the Pb isotopic trend toward HIMU in the SQ carbonatites. We conclude that their parental magma was derived from a source incorporating the Mianlue oceanic crust mixed with an asthenospheric (or deeper) material characterized by high Pb and low Nd isotopic values. This material represents a deep-seated Proterozoic carbonate component recycled via mantle convection or localized upwelling. Notably, this model cannot explain the isotopic compositions of the Late Triassic (209–221 Ma) carbonatites in the LQ, characterized by a mantle-derived δ13C, but EM1-like Sr–Nd–Pb isotopic compositions. This signature is best explained in terms of delamination of the lower continental crust thickened during the collision of the South and North China Blocks, and partial incorporation of the delaminated material into the LQ mantle source. Modeling of the measured Sr–Nd–Pb isotopic variations suggests that the source of the LQ carbonatites could be produced by mixing of 80–85% of mantle material and 15–20% of delaminated lower continental crust. The emplacement of the SQ and LQ carbonatites marked a gradual transition from a compressional tectonic regime, brought about by the collision of the South and North China Blocks to intra-orogenic extension in the waning stages of the Triassic orogeny.

We investigated the isotope composition (O, C, Sr, Nd, Pb) in mineral separates of the two Precambrian carbonatite complexes Tiksheozero (1.98 Ga) and Siilinjärvi (2.61 Ga) from the Karelian–Kola region in order to obtain information on... more

We investigated the isotope composition (O, C, Sr, Nd, Pb) in mineral separates of the two Precambrian carbonatite complexes Tiksheozero (1.98 Ga) and Siilinjärvi (2.61 Ga) from the Karelian–Kola region in order to obtain information on Precambrian mantle heterogeneity. All isotope systems yield a large range of variations. The combination of cathodoluminescence imaging with stable and radiogenic isotopes on the same samples and mineral separates indicates various processes that caused shifts in isotope systems. Primary isotope signatures are preserved in most calcites (O, C, Sr, Pb), apatites (O, Sr, Nd), amphiboles (O), magnetites (O), and whole rocks (Sr, Nd). The primary igneous C and O isotope composition is different for both complexes (Tiksheozero: δ 13 C = − 5.0‰, δ 18 O = 6.9‰; Siilinjärvi: δ 13 C = −3.7‰, δ 18 O = 7.4‰) but very uniform and requires homogenization of both carbon and oxygen in the carbonatite melt. The lowest Sr isotope ratios of our carbonates and apatites from the Archaean Siilinjärvi (0.70137) and the Palaeoproterozoic Tiksheozero (0.70228) complexes are in the range of bulk silicate earth (BSE). Positive ε Nd values of the two carbonatites point to very early Archaean enrichment of Sm/Nd in the Fennoscandian mantle. No HIMU components could be detected in the two complexes, whereas Tiksheozero carbonatites give the first indication of Palaeoproterozoic U depletion for Fennoscandia. Sub-solidus exchange processes with water during emplacement and cooling of carbonatites caused an increase in the oxygen isotope composition of some carbonates and probably also an increase of their 87 Sr/ 86 Sr ratio. A larger increase of initial Sr isotope ratios was found in carbonatized silicic rocks compared to carbonatite bodies. The Svecofennian metamorphic overprint (1.9– 1.7 Ga) caused reset of Rb/Sr (mainly mica) and Pb/Pb (mainly apatite) isochron systems.

Melilite and wollastonite from the Colle Fabbri stock contain silicate melt and silicate-carbonate inclusions. The homogenization temperatures of silicate inclusions are within the magmatic temperature range of mantle ultrabasic melts:... more

Melilite and wollastonite from the Colle Fabbri
stock contain silicate melt and silicate-carbonate inclusions.
The homogenization temperatures of silicate inclusions are
within the magmatic temperature range of mantle ultrabasic
melts: about 1,320±15 °С. Their composition is melilititic
and evolves to the composition of leucite tephrite and phonolite.
The composition of silicate-carbonate inclusions are
high SiO2, Ca-rich, enriched in alkalies and are similar to
that of inclusions of carbonatite melts in the minerals of
melilitolites of other intrusive ultramafic complexes. They
are also similar to the compositions of metasomatized travertine
covering the melilitolite stock. The presence of primary
silicate and silicate-carbonate inclusions evidences
that the melilitite magma from which melilitolites of Colle
Fabbri crystallized was associated with carbonatite liquid.
This liquid was highly fluidized, mobile and aggressive.
Actively interacting with overlying travertine, the liquid
enriched them with alkalies, aluminosilicates and incompatible
elements, which resulted in the equalization of their
compositions. Heterogeneous compositional dominions
were formed at the contact between melilitolite and wall
pelites. In the minerals of these contact facies high-Si melt
inclusions of varying composition have been observed.
Their occurrence is related to the local assimilation by the
high-temperature melilitite magma of pelitic country rocks.
The content of incompatible elements in melilitite melts and
melilitolites is higher than the mantle norm and they have
peculiar indicator ratios, spectra, Eu/Eu* ratio, which suggest
a peculiar mantle source.

The assemblage clinopyroxene + magnesite was observed in Earth's high-pressure metamorphic samples , and its stability in subducting slabs was confirmed by experiments. Recent studies also suggested that the fO2 variations observed in SNC... more

The assemblage clinopyroxene + magnesite was observed in Earth's high-pressure metamorphic samples , and its stability in subducting slabs was confirmed by experiments. Recent studies also suggested that the fO2 variations observed in SNC meteorites can be explained by polybaric graphite-CO-CO2 equilibria in the Martian mantle. Although there is no direct evidence for the stability of the cpx + mc assemblage in Mars mantle, its high pressure– high-temperature decomposition to cpx + fo + CO2 makes it a good analogue for the source of carbon metasomatism,
in particular, to study nakhlites formation. Iron, which is present in the Earth’s and Martian mantles, may, however, influence the speciation of carbon. We performed
experiments on a clinopyroxene + magnesite assemblage at 1.8 and 3.0GPa and temperatures corresponding to the Earth’s and Martian mantles. The role of iron and of fO2 was investigated by (1) replacing all or part of the magnesite by siderite
FeCO3, (2) adding Fe0 and (3) using graphite C capsules. A carbonate-silicate melt forms at both Earth and Mars conditions. Clinopyroxene and olivine are the main solid phases in the iron-free experiments. Fe2+ and Fe0 decrease their melting
temperatures and increase the silicate fraction in the melt. The produced carbonate-silicate melts may be involved in the formation of some carbon-rich lavas on Earth (e.g., carbonatites, ultramafic lamprophyres, or kamafugites). Our results may also be used to interpret ophiolite samples or inclusions. In particular, we show that wustite may form in equilibrium with carbonate-silicate melt in opx-(and silica-) poor regions
of the mantle below 3 GPa. Our results also confirm the hypothesis of carbon metasomatism in the Martian nakhlites source. Immiscibility or reduction could explain the absence or rarity of C in Martian lavas.

In recent years, there has been increasing concern regarding the chemical impact of agricultural activities on the environment so it is necessary to identify contaminants, and/or characterise the sources of contamination. In this study, a... more

In recent years, there has been increasing concern regarding the chemical impact of agricultural activities on the environment so it is necessary to identify contaminants, and/or characterise the sources of contamination. In this study, a comprehensive chemical characterisation of 27 fertilisers of different types used in Spain has been conducted; major, minor and trace elements were determined, including rare earth elements. Results show that compound fertilisers used for fertigation or foliar application have low content of heavy metals, whereas fertilisers used for basal and top dressing have the highest content of both REE and other heavy metals. REE patterns of fertilisers have been determined in order for them to be used as tracers of fertilisers in future environmental studies. Furthermore in this work REE patterns of fertilisers are used as tracers of the source of phosphate in compound fertilisers, distinguishing between phosphorite and carbonatite derived fertilisers. Fertilisers from carbonatites have higher contents of REE, Sr, Ba and Th whereas fertilisers from phosphorites have higher contents of metals of environmental concern, such as Cd, U and As; and the sum of the heavy metals is higher. Some of the analysed fertilisers have Cd concentrations that exceed maximum values established in some countries and can be expected to produce long-term soil accumulation. Furthermore, other elements such as U, As and Cr are 10–50 times higher in concentration than those of Cd, but there is no legislation regarding them, therefore it is necessary to regulate fertiliser compositions in order to achieve environmental protection of soils and waters.

Kimberlite is an igneous rock, which sometimes contains diamonds. It is named after the town of Kimberley in South Africa, where the discovery of an 83.5-carat (16.70 g) diamond called the Star of South Africa in 1869 spawned a diamond... more

Kimberlite is an igneous rock, which sometimes contains diamonds. It is named after the town of Kimberley in South Africa, where the discovery of an 83.5-carat (16.70 g) diamond called the Star of South Africa in 1869 spawned a diamond rush and the digging of the open-pit mine called the Big Hole.

Résumé/Abstract The Geological Survey of Venezuela, Ministry of Energy and Mines, is updating the metallogenic map of the country as a part of the UNESCO Project Metallogenic Map of the World. Important new large ore deposits, such as the... more

Résumé/Abstract The Geological Survey of Venezuela, Ministry of Energy and Mines, is updating the metallogenic map of the country as a part of the UNESCO Project Metallogenic Map of the World. Important new large ore deposits, such as the extensive Km 88 zone in ...

THE existence of carbonatite magmas has been generally accepted1, but their origin remains uncertain. The more favoured petrogenetic models include: (1) direct partial melting of the upper mantle2-5 (2) fractional crystallisation of... more

THE existence of carbonatite magmas has been generally accepted1, but their origin remains uncertain. The more favoured petrogenetic models include: (1) direct partial melting of the upper mantle2-5 (2) fractional crystallisation of CO2-rich alkaline silicate magma6; and (3) separation of an immiscible carbonate melt from an initially homogeneous CO2-rich alkaline silicate magma7-10. Experiments have shown all of these processes to be feasible5-7, and each may generate the geochemical characteristics of carbonatite, such as enrichment in rare earths and other incompatible trace and minor elements11,12, and low 87Sr/86Sr ratios13. Here we discuss the role of immiscibility, and report new experimental data which demonstrate for the first time that liquid immiscibility does occur between silicate and carbonate liquids of the compositions found in nature.

Mediterranean lamproites from Spain, Italy, Serbia and Macedonia are mantle-derived ultrapotassic volcanic rocks that occur exclusively in postcollisional, extension-related geodynamic settings within the Alpine–Himalaya orogenic belt.... more

Mediterranean lamproites from Spain, Italy, Serbia and Macedonia are mantle-derived ultrapotassic volcanic rocks that occur exclusively in postcollisional, extension-related geodynamic settings within the Alpine–Himalaya orogenic belt. Previous studies inferred them to be multi-component melts, originating by mixing of several mantle end-members: (1) provenance-controlled crust-contaminated mantle component(s), (2) an ultra-depleted mantle component, and (3) a component ultimately derived from the convecting mantle. Hf isotope ratios of Mediterranean lamproites reported here cover a large range of εHf values from 0 to −15, for less variable εNd −2 to −13, providing further evidence for a lithospheric origin. The Hf isotope data help to distinguish two regionally distinct crustal components both derived from zircon-bearing protoliths similar to turbiditic sediments typical for continental margins. The Hf isotopes provide unique insights into mantle mixing processes by constraining the geochemistry of the component derived from the convective mantle. This component is rich in Sr and Nb, has low Ti and HFSE4+/LREE, and isotopic compositions similar to OIB. In Hf–Nd isotope space, this component is responsible for the decoupling of Hf and Nd isotopic ratios, already recognized in lamproites worldwide. This deviation results from a strongly curved hyperbolic mixing between a proto-lamproitic melt and a small, but significant contribution from carbonatitic melts ultimately derived from the convective mantle.►Mediterranean lamproites originated by mixing of several mantle end-members. ►The Hf isotope data distinguish two regionally distinct crustal components derived from turbiditic sediments. ►The convective mantle component has isotopic compositions similar to OIB. ►This component is responsible for the decoupling of Hf and Nd isotopic ratios. ►This deviation results from a hyperbolic mixing between a proto-lamproitic melt and carbonatitic melts.

The new mineral umbrianite, ideally K7Na2Ca2[Al3Si10O29]F2Cl2, was discovered as an essential groundmass mineral in melilitolite of the Pian di Celle volcano, Umbria, Italy. It forms rectangular, lamellar or lath-shaped crystals (up to 25... more

The new mineral umbrianite, ideally K7Na2Ca2[Al3Si10O29]F2Cl2, was discovered as an essential groundmass mineral in melilitolite of the Pian di Celle volcano, Umbria, Italy. It forms rectangular, lamellar or lath-shaped crystals (up to 25 x 30 x 200 μm in size), typically flattened on {010}, and sheaf-like aggregates (up to 200-500 μm across). Umbrianite is mainly associated with kalsilite, leucite, fluorphlogopite, melilite, olivine (Fo>60), diopside, nepheline, Ti-rich magnetite, fluorapatite, cuspidine–hiortdahlite series minerals, götzenite, khibinskite, monticellite-kirschsteinite, westerveldite, various sulfides and peralkaline silicate glass.
The empirical formula (based on Si+Al+Fe3+=13) for the holotype umbrianite (mean of 58 analyses) is (K6.45Na0.35(Sr,Ba)0.01)Σ6.81(Na1.22Ca0.78)Σ2.00(Ca1.85Mg0.13Mn0.01Ti0.01)Σ2.00[(Fe3+0.34Al3.06Si9.60)Σ13.00O29.00]F2.05Cl1.91(OH)0.04. The X-ray diffraction powder-pattern (MoKα -radiation) shows the strongest lines {d [Å](Iobs)} at: 9.65(100), 6.59(97), 3.296(77), 3.118(70), 2.819(53), 2.903(52), 6.91(43). The unit-cell parameters and space group are: a = 7.0618(5), b = 38.420(2), c = 6.5734(4) Å, V = 1783.5(2) Å3, Pmmn, Z = 2. The calculated density is 2.49 g/cm3. The crystal structure of umbrianite has been refined from X-ray single-crystal data to R1 = 0.029 %. R = 0.0941. The strong bands in the Raman spectrum of umbrianite are at: 525, 593, 735 and 1036 cm-1. Umbrianite from Pian di Celle is unstable to postmagmatic alterations and partially or completely replaced by Ba-rich hydrated phases, and one of them is very close to günterblassite. Umbrianite and günterblassite represent a new structural type of phyllosilicates with triple-layer Si-Al tetrahedral blocks. The structural and chemical comparison of these minerals with members of the rhodesite silicate mero-plesiotype series (double-layer block) and mountinite family (single-layer block) is given.

Inclusions of calcite within large euhedral apatite crystals from the pyroxenite-carbonatite-syenite complex of Sevattur, Tamil Nadu, south India, were identified to represent inclusions of a primary carbonatitic melt (calcite I) from... more

Inclusions of calcite within large euhedral apatite crystals from the pyroxenite-carbonatite-syenite complex of Sevattur, Tamil Nadu, south India, were identified to represent inclusions of a primary carbonatitic melt (calcite I) from which the apatites have crystallized. The apatites themselves are embedded into a younger batch of calcite-carbonatitic melt (calcite II). Using the synchrotron XRF microprobe at beamline L at HASYLAB/DESY (Hamburg), the concentrations of the trace elements Ba, Sr, Y, Zr, Th, La, Ce, Nd, Sm, Gd, Dy, and Er were determined both in melt inclusions as well as in host apatites and younger carbonatite matrix. Unexpected high REE concentrations were found not only in apatite but also in calcite, especially of the younger matrix phase, in agreement with the whole rock geochemistry. The data reveal an equilibrium distribution between melt inclusions and host apatite that allows the calculation of partition coefficients D = C i Ap / C i Cc=melt for elements of interest. Assuming 9% crystallization of the melt, which can be calculated from the whole rock analyses, the composition of the primary carbonatite melt prior to apatite crystallization can be determined. This composition is, with the exception of only few elements, nearly equal to that of the younger matrix carbonatite melt (calcite II), and thus gives evidence for the existence of different pulses of carbonatite melt during crystallization and consolidation of the carbonatite body. The results allow new insights into the processes of trace element and REE distribution between the two major igneous components of carbonatites and thus into the question of carbonatitic fractionation processes. The data reveal that mere apatite crystallization and fractionation does not lead to enriched REE compositions during carbonatite evolution but lowers their concentrations in the residual melts. But alternatively, if segregated apatite is collected and incorporated by a new melt batch, the overall REE of this melt will be increased.

The Cape Verde volcanic archipelago, located in the oceanic portion of the African plate some 500km west of the Senegal coast, is renowned for the occurrence of carbonatites on at least 5 of its 10 islands. In this study we report the... more

The Cape Verde volcanic archipelago, located in the oceanic portion of the African plate some 500km west of the Senegal coast, is renowned for the occurrence of carbonatites on at least 5 of its 10 islands. In this study we report the occurrence of about twenty new small outcrops of extrusive carbonatites on Brava Island (64km2), the south-westernmost island of

Carbonatites are very rare in oceanic environments, where they have been reported only at the Canary and Cape Verde islands in the Atlantic Ocean. In the Canary archipelago, calciocarbonatites occur only on the island of Fuerteventura, in... more

Carbonatites are very rare in oceanic environments, where they have been reported only at the Canary and Cape Verde islands in the Atlantic Ocean. In the Canary archipelago, calciocarbonatites occur only on the island of Fuerteventura, in clear spatial and temporal association to ...

Monazite structural group includes arsenates, phosphates, and silicates, with general formulae A B O4 , (A = Bi, Ca, Rare Earth Elements, Th, U and B = As5+, P5+, Si4+). Among them, the phosphate monazite is the most abundant independent... more

Monazite structural group includes arsenates, phosphates, and silicates, with general formulae A B O4 , (A = Bi, Ca, Rare Earth Elements, Th, U and B = As5+, P5+, Si4+). Among them, the phosphate monazite is the most abundant independent Rare Earth Element mineral, occurring in several geological sites. It presents a variable composition and morphology and has strong chemical and physical stability. This paper presents a review about this mineral, particularly for monazite associated with carbonatite complexes. Detailed study of the composition of monazite will improve geochemical and petrological interpretations. In the economic field, monazite is, with bastnaesite, an ore mineral present in the main deposits in the world; its morphological and composition characteristics have influence in ore quality and in efficiency of concentration processes. Since the seventhies, its importance reachs the environmental field and his highly stable structure has been investigated as model for a ...

South Nam Xe carbonatites are located in northwest Vietnam and include calcio-and ferro-carbonatite dikes. This investigation on their petrography, mineralogy and whole rock chemistry aims to constrain temporal emplacement sequence of the... more

South Nam Xe carbonatites are located in northwest Vietnam and include calcio-and ferro-carbonatite dikes. This investigation on their petrography, mineralogy and whole rock chemistry aims to constrain temporal emplacement sequence of the carbonatites during their evolution. The calciocarbonatites are supposed to be formed in the first or second stage due to massive coarse-grained texture with an assemblage of calcite, typical magmatic alkaline silicates (aegirine, arfvedsonite), biotite, fluorapatite and magnetite. Their calcites show a high CaO/(MgO + Fe 2 O 3 + MnO) ratio and a predominance of SrO over MnO (SrO = 3.81-3.98 wt.%; MnO = 0.66-0.78 wt.%). Rare earth elements (REE) tend to participate in rock-forming minerals rather than in isolated REE minerals. The ferrocarbonatites are composed of magmatic and hydrothermal varieties and assumed to be formed in the third and/or fourth stage. Major minerals of the former include zoned ankerite, Sr-rich calcite, subhedral feldspar crystals, phlogopite and magnetite; fluorapatite, monazite and REE carbonates are minor resulting in a moderate REE concentration of 43,200 ppm. Meanwhile, the latter is predominant by syntax-texture REE fluorcarbonates and (Ba,Sr) sulphates. Further, the highest REE concentration (163,900 ppm) of the rock coupled with abundance of volatile minerals (fluorite, fluorcarbonates, sulphides) and 18 O enrichment in the calcites (δ 18 O V-SMOW = 12.01-13.26‰) is probably attributed to hydrothermal subjection in the last stage.