A Study of Potash Fenitization around the Brent Crater, Ontario,—A Paleozoic Alkaline Complex

1971 ◽  
Vol 8 (5) ◽  
pp. 481-497 ◽  
Author(s):  
K. L. Currie
Keyword(s):  
Geometric Form ◽  
Potash Feldspar ◽  
Alkaline Complex ◽  
Carbonatite Complex ◽  
The West ◽  
Granitoid Gneisses ◽  
Chemical Trends

Fractured and brecciated granitoid gneisses around and within the Brent Crater display progressive chemical and mineralogical changes due to metasomatism, culminating in potassic, silica-undersaturated metasomatic rocks. In the metasomatized rocks, potash feldspar increases in amount and degree of triclinicity with increasing metasomatism, while quartz and plagioclase decline in amount. Calcite of carbonatitic isotopic character is found in some of the breccia matrices. Alkaline ultrabasic dikes, identical in chemistry, petrography, and radiometric age to those of the Nippissing alkaline petrographic province, cut the breccia. Potassic trachyte, which appears to form dikes and lenses within the crater, may be the result of anatexis of potassic metasomatites. The geometric form, petrography, and chemical trends of the metasomatized rocks are virtually identical to those of the fenite aureole of the Callander Bay alkaline carbonatite complex, 42 miles (67.6 km) to the west, suggesting that they result from a fenitization process in which potassium rather than sodium is enriched.

Potash-trachytes and ultra-potassic rocks associated with the carbonatite complex of the Toror Hills, Uganda

1965 ◽  
Vol 35 (270) ◽  
pp. 363-378 ◽  
Author(s):  
D. S. Sutherland
Keyword(s):  
Close Similarity ◽  
Chemical Analyses ◽  
Potash Feldspar ◽  
Carbonatite Complex ◽  
Modes Of Occurrence ◽  
First Time ◽  
Potassic Rocks ◽  
Eastern Uganda

SummaryRocks containing a high percentage of potash feldspar are described for the first time from the Toror Hills in the Karamoja district of eastern Uganda. They include feldspathic fenites, intrusive feldspathic fenite-breccias, potashtrachytes, and orthoclasites. Petrographic data and chemical analyses show the close similarity in composition of these rocks despite their widely differing textures and modes of occurrence. The potash metasomatism associated with the emplacement of carbonatite, and the subsequent mobilization of these feldspathic fenites are compared with similar phenomena observed at other carbonatite centres. The problem of the mechanism of mobilization is discussed.

scholarly journals On the age of pyrochlore carbonatites from the Ilmeno-Vishnevogorsky Alkaline Complex, the Southern Urals (insights from Rb-Sr and Sm-Nd isotopic data)

LITOSFERA ◽  
2020 ◽  
Vol 20 (4) ◽  
pp. 486-498
Author(s):  
I. L. Nedosekova ◽  
V. A. Koroteev ◽  
T. B. Bayanova ◽  
P. A. Serov ◽  
V. I. Popova ◽  
...  
Keyword(s):  
Mass Spectrometer ◽  
Southern Urals ◽  
Tectonic Activity ◽  
Ionization Mass ◽  
Alkaline Complex ◽  
Carbonatite Complex ◽  
The Southern Urals ◽  
Scientific Center ◽  
Linear Type ◽  
Isotopic Compositions

Research subject. In this research, we carried out Sm-Nd- и Rb-Sr-dating of pyrochlore carbonatite from the Vishnevogorsky niobium deposit, Ilmeno-Vishnevogorsky Alkaline Complex, Southern Urals. IVC is located in the Ural fold region and is a carbonatite complex of the linear type. Rare metal (Nb-Zr-TR) deposits and occurrences are related to IVC. The age and the duration of IVC deposits formation remains a matter of debate. To determine the age of IVC carbonatites and related niobium ore, we measured Sm-Nd and Rb-Sr isotopic compositions and concentrations of the elements in the minerals (pyrochlore, calcite, apatite, biotite) and bulk sample of pyrochlore carbonatite. Materials and methods. The Sm and Nd isotopic compositions and concentrations were determined on a Finnigan MAT-262L (RPQ) seven-collector mass spectrometer in the static regime at the Geological Institute of the Kola Scientific Center, Apatity, Russia. The Sr and Rb isotopic compositions and concentrations were determined on thermos-ionization mass spectrometer Triton Plus (“Geoanalitik”, IGG UD RAN, Ekaterinburg, Russia). Results. Age of pyrochlore carbonatites from ore zone 140 (Vishnevogorsky deposit, IVC) defined by Sm-Nd and Rb-Sr isotopic methods. Mineral Sm-Nd-isochron (5 points) indicated age 229 ± 16 Ma, mineral Rb-Sr-isochron (5 points) showed similar age 250.5 ± 1.2 Ma. Conclusions. Results Sm-Nd и Rb-Sr dating indicate that the pyrochlore сarbonatites of ore zone 140 crystallized ≈ 250 Ma ago, at the stage of the postcollisional extension, possibly, in connection with exhumation complex, which was accompanied by decompression, partial melting of rocks, involving fluids, dissolution and precipitation of Ordovician-Silurian alkaline-carbonatitе complex. Thus, the formation of the IVC carbonatites and related Nb-ore, which began in Silurian (S), continued in Permian (P) and Triassic (T1-2) and was associated with the post-collision stage of tectonic activity in the Ural Fold Belt.

The Early Proterozoic carbonatite complex of Angico dos Dias, Bahia State, Brazil: geochemical and Sr-Nd isotopic evidence for an enriched mantle origin

2003 ◽  
Vol 67 (5) ◽  
pp. 1039-1057 ◽  
Author(s):  
P. Antonini ◽  
P. Comin-chiaramonti ◽  
C. B. Gomes ◽  
P. Censi ◽  
B. F. Riffel ◽  
...  
Keyword(s):  
Large Scale ◽  
Alkaline Complex ◽  
Carbonatite Complex ◽  
Early Proterozoic ◽  
Isotopic Signatures ◽  
Enriched Mantle ◽  
Mantle Sources ◽  
Northern Side ◽  
Very High ◽  
Potassic Magmatism

AbstractBorehole samples of carbonatites and phlogopite-pyroxenites from the Angico dos Dias (AdD) intrusive alkaline complex, State of Bahia, Brazil, have been investigated in terms of mineralogy, geochemistry and C-O-Sr-Nd isotopes. The AdD complex, of Early Proterozoic age (2 Ga), intrudes the northern side of the São Francisco Craton. Mineralogy and petrography indicate that the studied rocks only partially preserved their magmatic textural features owing to their metamorphic re-equilibration (greenschist facies). The REE contents and LREE/HREE ratios of the AdD carbonatites are very high (mean 3979±718 ppm and La/Yb = 215±23, respectively), as for most Precambrian magmatic carbonatites. The AdD carbonatites are also enriched in 18O (δ18O = 11.9 to 15.8‰), possibly due to secondary processes (e.g. metamorphism, alteration) whereas carbon isotopes are in the range of ‘primary carbonatites’ (δ13C = –5.7 to –7.1‰). Most of the initial 87Sr/86Sr and 143Nd/144Nd values of the studied carbonatites were not appreciably modified by secondary processes. Their εtSr and εtNd values (20.0 to 25 and 0.7 to –4.5, respectively) indicate enriched mantle sources very different from the ‘depleted’ ones related to many Precambrian carbonatites from North America (0.6 –2.6 Ga) and Africa (0.5 –2.0 Ga). The Early Proterozoic Sr-Nd isotopic signatures of the AdD carbonatites are similar to those of the Early Cretaceous carbonatites from the Paraná basin. The latter carbonatites show a great isotopic variability ranging from Bulk Earth to the related potassic magmatism from Asunción-Sapucai graben in the Eastern Paraguay (K-ASU magmatism: εtSr = 35 to 50 and εtNd = –12 to –20). The very similar isotopic compositions of Precambrian and post-Palaeozoic carbonatites worldwide indicate that the subcontinental mantle variability lasted for long periods of time and indicate a large-scale mantle heterogeneity.

scholarly journals The Syenite–Carbonatite Complex of Ihouhaouene (Western Hoggar, Algeria): Interplay Between Alkaline Magma Differentiation and Hybridization of Cumulus Crystal Mushes

2021 ◽  
Vol 8 ◽  
Author(s):  
A. Djeddi ◽  
F. Parat ◽  
J.-L. Bodinier ◽  
K. Ouzegane ◽  
J.-M. Dautria
Keyword(s):  
Alkaline Complex ◽  
Carbonatite Complex ◽  
Slow Cooling ◽  
Silicate Minerals ◽  
Rock Types ◽  
Evolutionary Scheme ◽  
Silicate Liquids ◽  
Rock Suite ◽  
Highly Evolved ◽  
Carbonate Melt

The 2 Ga-old Ihouhaouene alkaline complex (Western Hoggar, Algeria) is among the oldest known carbonatite occurrences on Earth. The carbonatites are calciocarbonatites hosted by syenites, the predominant rock type in the complex. Both rock types are characterized by medium-grained to pegmatitic textures and contain clinopyroxene, apatite, and wollastonite, associated with K-feldspar in syenites and a groundmass of calcite in carbonatites. The rock suite shows a continuous range of compositions from 57–65 wt.% SiO2 and 0.1–0.4 wt.% CO2 in red syenites to 52–58 wt.% SiO2 and 0.1–6.5 wt.% CO2 in white syenites, 20–35 wt.% SiO2 and 11–24 wt.% CO2 in Si-rich carbonatites (>10% silicate minerals), and <20 wt.% SiO2 and 24–36 wt.% CO2 in Si-poor carbonatites (<5% silicate minerals). Calculation of mineral equilibrium melts reveals that apatite and clinopyroxene are in disequilibrium with each other and were most likely crystallized from different parental magmas before being assembled in the studied rocks. They are subtle in the red syenites, whereas the white syenites and the Si-rich carbonatites bear evidence for parental magmas of highly contrasted compositions. Apatite was equilibrated with LREE-enriched (Ce/Lu = 1,690–6,182) carbonate melts, also characterized by elevated Nb/Ta ratio (>50), whereas clinopyroxene was precipitated from silicate liquids characterized by lower LREE/HREE (Ce/Lu = 49–234) and variable Nb/Ta ratios (Nb/Ta = 2–30). The Si-poor carbonatites resemble the Si-rich carbonatites and the white syenites with elevated REE contents in apatite equilibrium melts compared to clinopyroxene. However, apatite equilibrium melt in Si-poor carbonatite shows a majority of subchondritic values (Nb/Ta<10) and clinopyroxene has chondritic-to-superchondritic values (Nb/Ta = 15–50). Although paradoxical at first sight, this Nb-Ta signature may simply reflect the segregation of the carbonatite from highly evolved silicate melts characterized by extremely low Nb/Ta values. Altogether, our results suggest an evolutionary scheme whereby slow cooling of a silico-carbonated mantle melt resulted in the segregation of both cumulus minerals and immiscible silicate and carbonate melt fractions, resulting in the overall differentiation of the complex. This process was however counterbalanced by intermingling of partially crystallized melt fractions, which resulted in the formation of hybrid alkaline cumulates composed of disequilibrium cumulus phases and variable proportions of carbonate or K-feldspar.

A Study of Fenitization Around the Alkaline Carbonatite Complex at Callander Bay, Ontario, Canada

1971 ◽  
Vol 8 (5) ◽  
pp. 498-517 ◽  
Author(s):  
K. L. Currie ◽  
John Ferguson
Keyword(s):  
Oxygen Fugacity ◽  
Total Acidity ◽  
Charge Balance ◽  
Potash Feldspar ◽  
Carbonatite Complex ◽  
Chemical Changes ◽  
Sulfur Fugacity ◽  
Granitoid Rocks ◽  
Calcium And Magnesium ◽  
Alkali Chlorides

Fenitization in granitoid rocks is first noticeable in the form of hematite veinlets, accompanied by increased ordering of potash feldspar. With increasing fenitization, plagioclase is converted to albite plus calcite, and K-feldspar progressively converted toward maximum microcline. Acmitic pyroxenes become increasingly abundant. The chemical changes producing these effects consist of the substitution of sodium plus another cafemic ion for silicon in such a way as to maintain charge balance. The fenitizing fluid was essentially an NaCl brine, roughly 1 molal in alkali chlorides, and 0.01 molal total acidity. The content of iron, calcium, and magnesium was high. The oxygen fugacity was near 10−17 bars (hematite–magnetite), and the sulfur fugacity near 10−12 bars. Fenitization may have occurred at temperatures as high as 700°, but the main fenitization took place at temperatures slightly above 500° and fenitization ceased at about 450°. Pressures were low, probably less than 500 bars. The source of the fenitizing solutions was carbonatite, which in turn was derived from nephelinitic magma.

scholarly journals Magmatic origin and petrogenesis characterization of syenite rock from Pakkanadu alkaline complex, Southern Granulite Terrain, India: Implication on emplacement and petrogenetic history

2021 ◽  
Vol 13 (4) ◽  
pp. 1214-1224
Author(s):  
P. Gangatharan ◽  
K. Anbarasu ◽  
M. Satyanarayanan
Keyword(s):  
Rare Earth ◽  
Rare Earth Element ◽  
Tamil Nadu ◽  
Earth Element ◽  
Alkaline Complex ◽  
Carbonatite Complex ◽  
Study Region ◽  
Magmatic Origin ◽  
South Indian ◽  
Granulite Terrain

The present study mainly focused on understanding the magmatic origin and petrogenesis characterization based on the Petrography, major, trace and Rare Earth Element (REE) signatures in the alkaline syenite from Pakkanadu alkaline carbonatite complex. The alkaline plutons from South Indian granulite terrain are intruded along with Archaean epidote-hornblende gneisses. The study area was carbonatite complexes of Tamil Nadu and is characterized by a group of rock associations Carbonatite-Syenite-Pyroxenite - Dunite. From Harker various patterns Pakkanadu alkaline complex syenite showed increasing trends of SiO2, Al2O3, Na2O + K2O opposite to decreasing order of CaO, Fe2O3, MgO, TiO2, P2O5 and MnO trend, suggest fractionation of clinopyroxene, hornblende, sphene, apatite and oxide minerals and feldspar that ruled the fractionation. The concentration of trace elements enriched in Large Ion lithophile elements  (LILE) (Ba, Sr, and Rb) elements and High Field Strength Elements (HFSEs) indicated that the dyke intrusion by differentiation of magma from a mantle source. Rare earth element (REE) distribution of Light rare earth element (LREE) enriched and High rare earth element (HREE) depleted pattern show strongly fractionated pattern with moderate Eu anomalies. Plots of tectonic discrimination diagrams of Pakkanadu samples fall in the field of syn-COLG field to the VAG syn- COLG field.     For the first time, this type of study was carried out in the study region in a detailed manner. The present study significantly exposed the petrography, petrogenesis and magmatic origin process in the Pakkanadu alkaline carbonatite complex. 

Enumeration and Identification of Asbestos Fibres in Water

1974 ◽  
Vol 32 ◽  
pp. 526-527 ◽  
Author(s):  
O. Mudroch ◽  
J. R. Kramer
Keyword(s):  
Water Supply ◽  
Water Samples ◽  
Drainage Basin ◽  
Lake Superior ◽  
Research Work ◽  
List Type ◽  
The West ◽  
Asbestos Fibre ◽  
Amphibole Asbestos

Approximately 60,000 tons per day of waste from taconite mining, tailing, are added to the west arm of Lake Superior at Silver Bay. Tailings contain nearly the same amount of quartz and amphibole asbestos, cummingtonite and actinolite in fibrous form. Cummingtonite fibres from 0.01μm in length have been found in the water supply for Minnesota municipalities.The purpose of the research work was to develop a method for asbestos fibre counts and identification in water and apply it for the enumeration of fibres in water samples collected(a) at various stations in Lake Superior at two depth: lm and at the bottom.(b) from various rivers in Lake Superior Drainage Basin.

The fight to save Uganda’s White Rhino

1964 ◽  
Vol 2 (01) ◽  
pp. 6-12
Keyword(s):  
The West ◽  
West Nile ◽  
White Rhino

In the West Nile District of Uganda lives a population of white rhino—those relies of a past age, cumbrous, gentle creatures despite their huge bulk—which estimates only 10 years ago, put at 500. But poachers live in the area, too, and official counts showed that white rhino were being reduced alarmingly. By 1959, they were believed to be diminished to 300.

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