Uranium and selected trace elements in granites from the Caledonides of East Greenland

AbstractThe Caledonian fold belt of East Greenland contains calc-alkaline granite (sensu lato) intrusions with ages ranging from c.2000 Ma to c.350 Ma. The Proterozoic granites have low U contents and the pre-Devonian Caledonian granites contents of U corresponding to the clarke value for U in granites. Some aspects of the geochemistry of U are discussed using U-K/Rb, U-Sr, U-Zr, and U-Th diagrams. Secondary enrichment and mineralization occurs in fractured and hydrothermally altered granites and rhyolites situated in or near a major NNE fault zone. The U is associated with iron oxides or hydrocarbons. It is suggested that the source of the mineralization was Devonian acid magma, which also acted as a heat source for circulating hydrothermal fluids.

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Petrogenesis of a late-stage calc-alkaline granite in a giant S-type batholith: geochronology and Sr–Nd–Pb isotopes from the Nomatsaus granite (Donkerhoek batholith), Namibia

International Journal of Earth Sciences ◽

10.1007/s00531-021-02024-w ◽

2021 ◽

Author(s):

S. Aspiotis ◽

S. Jung ◽

F. Hauff ◽

R. L. Romer

Keyword(s):

Partial Melting ◽

Mineral Assemblage ◽

Central Zone ◽

Calc Alkaline ◽

Pb Isotope ◽

Alkaline Granite ◽

Ti Oxides ◽

Eu Anomaly ◽

Environment Characteristic ◽

Southern Central

AbstractThe late-tectonic 511.4 ± 0.6 Ma-old Nomatsaus intrusion (Donkerhoek batholith, Damara orogen, Namibia) consists of moderately peraluminous, magnesian, calc-alkalic to calcic granites similar to I-type granites worldwide. Major and trace-element variations and LREE and HREE concentrations in evolved rocks imply that the fractionated mineral assemblage includes biotite, Fe–Ti oxides, zircon, plagioclase and monazite. Increasing K2O abundance with increasing SiO2 suggests accumulation of K-feldspar; compatible with a small positive Eu anomaly in the most evolved rocks. In comparison with experimental data, the Nomatsaus granite was likely generated from meta-igneous sources of possibly dacitic composition that melted under water-undersaturated conditions (X H2O: 0.25–0.50) and at temperatures between 800 and 850 °C, compatible with the zircon and monazite saturation temperatures of 812 and 852 °C, respectively. The Nomatsaus granite has moderately radiogenic initial 87Sr/86Sr ratios (0.7067–0.7082), relatively radiogenic initial εNd values (− 2.9 to − 4.8) and moderately evolved Pb isotope ratios. Although initial Sr and Nd isotopic compositions of the granite do not vary with SiO2 or MgO contents, fSm/Nd and initial εNd values are negatively correlated indicating limited assimilation of crustal components during monazite-dominated fractional crystallization. The preferred petrogenetic model for the generation of the Nomatsaus granite involves a continent–continent collisional setting with stacking of crustal slices that in combination with high radioactive heat production rates heated the thickened crust, leading to the medium-P/high-T environment characteristic of the southern Central Zone of the Damara orogen. Such a setting promoted partial melting of metasedimentary sources during the initial stages of crustal heating, followed by the partial melting of meta-igneous rocks at mid-crustal levels at higher P–T conditions and relatively late in the orogenic evolution.

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Petrogenesis of the synplutonic high-magnesian porphyritic dykes from the mafic-granitoid plutons of the East-European Craton, Voronezh crystalline massif

Геохимия ◽

10.31857/s0016-7525644356-371 ◽

2019 ◽

Vol 64 (4) ◽

pp. 356-371

Author(s):

R. A. Terentiev

Keyword(s):

Trace Elements ◽

Magma Chamber ◽

Earth Element ◽

Parent Magma ◽

Chrome Spinel ◽

Calc Alkaline ◽

East European ◽

Fine Grained ◽

Mineral Inclusions ◽

Metasomatized Mantle

This paper documents the data on high-Mg porphyrite dykes (PDs) from the mafic to felsic (~2.09 Ma) plutons of Elan complex (EC). The low-thickness (first centimeters) synplutonic dykes are characterized by sharp straight contacts without visible chilling zones, in contrast to the larger (up to 119 m) dykes that have gradual transitions. The dykes are fresh, porphyritic (bronzite, Al-enstatite, labradorite) and has fine-grained mainly quartzo-feldspathic (+biotite, sulfides, accessories, ±hypersthene) matrix. Based on geochemistry data the PDs are intermediate rocks (SiO2 = 58.9–60.3 wt. %) and plot into calc-alkaline series with high magnesian of whole rock (Mg# ~0.7) and felsic (68.9–70.2 wt. %) matrix (Mg# ~0.5). The PDs show differentiated rare-earth element patterns with negligible Eu anomalies. The bronzite phenocrysts varying sizes are characterized by block zoning and contain irregular inclusions of olivine (Mg# ~0.85), clinopyroxene (Mg# ~0.88), phlogopite (Mg# up to 0.94), labradorite, chrome spinel, graphite and sulfides. The Al-enstatite phenocrysts are practically sterile with respect to trace elements and mineral inclusions. The geochemical features as well as diffusion zones, reaction rims, and resorbed faces of the phenocrysts such as orthopyroxene and plagioclase indicate processes of recrystallization and/or partial dissolution of nonequilibrium crystals in the melt and indicate intratelluric nature of the dyke phenocrysts that cores are inherited from the EC derivatives/cumulate. The mineral thermometry estimates are: (1) the parent magma starting temperatures of 1200–1400 °С and (2) the EC crystallization temperatures 1080–1155 °С, (3) the PD emplacement temperatures 910–1070 °С. The petrogenetic model supposes the generation of EC high-temperature magmas similar to boninites from an upper metasomatized mantle. The melt is contaminated with continental crust lithologies. It implies the half-way evolved magma chamber in the crust. The PD melt, as a result of ending of the half-way magma chamber evolution, was emplaced into the still unheated EC plutons.

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Archaean U-Pb zircon ages from the Scoresby Sund region, East Greenland

Rapport Grønlands Geologiske Undersøgelse ◽

10.34194/rapggu.v134.7987 ◽

1987 ◽

Vol 134 ◽

pp. 19-24

Author(s):

B.T Hansen ◽

A.K Higgins ◽

B Borchardt

Keyword(s):

Fold Belt ◽

East Greenland

U-Pb analyses on zircons are reported for two rock colleetions from infracrustal complexes within the East Greenland Caledonian fold belt in the Scoresby Sund region. Calculated minimum ages range from 2800 to 2965 Ma, and are the oldest ages obtained in the region using this method.

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Regional geology and 1:500 000 mapping in North-East Greenland

Rapport Grønlands Geologiske Undersøgelse ◽

10.34194/rapggu.v148.8110 ◽

1990 ◽

Vol 148 ◽

pp. 16-20

Author(s):

N Henriksen

Keyword(s):

Geological Mapping ◽

Fold Belt ◽

East Greenland ◽

Regional Geology ◽

Field Mapping ◽

North East ◽

General Geology ◽

Geological Map

A three-year field mapping programme was initiated in 1988 aiming at regional geological studies and geological mapping in North-East Greenland between latitudes 75° and 78°N. This region encompasses relatively little known parts of the Caledonian fold belt and the overlying post-Caledonian sequences, which lie north of the better known regions of central East Greenland (Henriksen, 1989). Major aims of the programme include compilation a 1:500 000 geological map, and an understanding of the general geology of the region.

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Release of Uranium from Uraninite in Granites Through Alteration: Implications for the Source of Granite-Related Uranium Ores

Economic Geology ◽

10.5382/econgeo.4822 ◽

2021 ◽

Author(s):

Long Zhang ◽

Zhenyu Chen ◽

Fangyue Wang ◽

Noel C. White ◽

Taofa Zhou

Keyword(s):

Uranium Concentration ◽

Geochemical Data ◽

Uranium Deposits ◽

Bulk Rock ◽

Calc Alkaline ◽

Alkaline Granite ◽

Compositional Evolution ◽

High K ◽

Backscattered Electron ◽

Uranium Sources

Abstract Uraninite is the main contributor to the bulk-rock uranium concentration in many U-rich granites and is the most important uranium source for granite-related uranium deposits. However, detailed textural and compositional evolution of magmatic uraninite in granites during alteration and associated uranium mobilization have not been well documented. In this study, textures and geochemistry of uraninites from the Zhuguangshan batholith (South China) were investigated by scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The geochemical data indicate that the Longhuashan and Youdong plutons are peraluminous leucogranite, the Changjiang pluton is highly fractionated high-K calc-alkaline granite, and the Jiufeng pluton belongs to a high-K calc-alkaline association. Uraninites from the Longhuashan and Youdong granites have lower concentrations of ThO2 (0.9–4.0 wt %) and rare earth elements (REE)2O3 (0.1–1.0 wt %) than those from the Changjiang and Jiufeng granites (ThO2 = 4.4–7.6 wt %, REE2O3 = 0.7–5.1 wt %). Uraninites observed in the Longhuashan, Youdong, Changjiang, and Jiufeng granites yielded chemical ages of 223 ± 3, 222 ± 2, 157 ± 1, and 161 ± 2 Ma, respectively. The samples (including altered and unaltered) collected from the Longhuashan, Youdong, and Changjiang granites are characterized by highly variable whole-rock U concentrations of 6.9 to 44.7 ppm and Th/U ratios of 0.9 to 7.0, consistent with crystallization of uraninite in these granites being followed by uranium leaching during alteration. Alteration of uraninite, indicated by altered domains developing microcracks and appearing darker in backscattered electron (BSE) images compared to unaltered domains, results in the incorporation of Si and Ca and mobilization of U. In contrast, the least altered samples of the unmineralized Jiufeng granite have low U concentrations (5.3–16.4 ppm) and high ΣREE/U (13.6–49.4) and Th/U ratios (2.1–5.6), which inhibit crystallization of uraninite, as its crystallization occurs when the U concentration is high enough to exceed the substitution capacity of other U-bearing minerals. These results indicate that the Longhuashan, Youdong, and Changjiang granites were favorable uranium sources for the formation of uranium deposits in this area. This study highlights the potential of uraninite alteration and geochemistry to assist in deciphering uranium sources and enrichment processes of granite-related uranium deposits.

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An occurrence of polymorphic halloysite in granite saprolite of the Bayerischer Wald, Germany

Clay Minerals ◽

10.1180/claymin.1978.013.1.06 ◽

1978 ◽

Vol 13 (1) ◽

pp. 67-77 ◽

Cited By ~ 16

Author(s):

B.-M. Wilke ◽

U. Schwertmann ◽

E. Murad

Keyword(s):

Trace Elements ◽

Clay Minerals ◽

Iron Oxides ◽

Aqueous Phase ◽

Mixed Layer ◽

Thin Plates ◽

Low Crystallinity

AbstractXRD, DTA and IR patterns showed clay veins filling fissures in a granite of the Bayerischer Wald (eastern Bavaria) to consist mainly of hydrated halloysite of low crystallinity with traces of gibbsite, 2:1 (mixed layer) clay minerals and iron oxides. The halloysite forms thin plates which exhibit varying degrees and types of enrolment, resulting in platy, tubular and spheroidal crystals within the same sample. Concentrations of the trace elements Rb, Sr, Ba, Zr, Y, Ce, Pb, Zn and Cu indicate halloysite formation to have taken place via an aqueous phase under the influence of vadose waters circulating in fissures.

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