scholarly journals Zirconosilicates in the kakortokites of the Ilímaussaq complex, South Greenland: Implications for fluid evolution and high-field-strength and rare-earth element mineralization in agpaitic systems

2016 ◽  
Vol 80 (1) ◽  
pp. 5-30 ◽  
Author(s):  
A. M. Borst ◽  
H. Friis ◽  
T. Andersen ◽  
T. F. D. Nielsen ◽  
T. E. Waight ◽  
...  
Keyword(s):  
Rare Earth ◽  
High Field ◽  
Earth Element ◽  
Secondary Mineral ◽  
High Field Strength ◽  
Ree Mineralization ◽  
Subsequent Decrease ◽  
Fluoride Complexes ◽  
Mineral Assemblages ◽  
High Concentrations

AbstractThe layered agpaitic nepheline syenites (kakortokites) of the Ilímaussaq complex, South Greenland, host voluminous accumulations of eudialyte-group minerals (EGM). These complex Na-Ca-zirconosilicates contain economically attractive levels of Zr, Nb and rare-earth elements (REE), but have commonly undergone extensive autometasomatic/hydrothermal alteration to a variety of secondary mineral assemblages. Three EGM alteration assemblages are recognized, characterized by the secondary zirconosilicates catapleiite, zircon and gittinsite. Theoretical petrogenetic grid models are constructed to assess mineral stabilities in terms of component activities in the late-stage melts and fluids. Widespread alteration of EGM to catapleiite records an overall increase in water activity, and reflects interaction of EGM with late-magmatic Na-, Cl- and F-rich aqueous fluids at the final stages of kakortokite crystallization. Localized alteration of EGM and catapleiite to the rare Ca-Zr silicate gittinsite, previously unidentified at Ilímaussaq, requires an increase in CaO activity and suggests post-magmatic interaction with Ca-Sr bearing aqueous fluids. The pseudomorphic replacement of EGM in the kakortokites was not found to be associated with significant remobilization of the primary Zr, Nb and REE mineralization, regardless of the high concentrations of potential transporting ligands such as F and Cl. We infer that the immobile behaviour essentially reflects the neutral to basic character of the late-magmatic fluids, in which REE-F compounds are insoluble and remobilization of REE as Cl complexes is inhibited by precipitation of nacareniobsite-(Ce) and various Ca-REE silicates. A subsequent decrease in F– activity would furthermore restrict the mobility of Zr as hydroxyl-fluoride complexes, and promote precipitation of the secondary zirconosilicates within the confines of the replaced EGM domains.

scholarly journals Supplemental Material: Quantifying metasomatic high-field-strength and rare-earth element transport from alkaline magmas

2021 ◽  
Author(s):  
Krzysztof Sokół ◽  
et al.
Keyword(s):  
Rare Earth ◽  
Field Strength ◽  
High Field ◽  
Earth Element ◽  
Estimation Method ◽  
Model Description ◽  
High Field Strength ◽  
Data Standardization ◽  
Element Transport ◽  
Alkaline Magmas

Petrographic information, parameterization of the Grant model, description of the HFSE tonnage estimation method, and supplemental tables of whole-rock data, standardization, and HFSE volume-tonnage calculations.<br>

scholarly journals Supplemental Material: Quantifying metasomatic high-field-strength and rare-earth element transport from alkaline magmas

2021 ◽  
Author(s):  
Krzysztof Sokół ◽  
et al.
Keyword(s):  
Rare Earth ◽  
Field Strength ◽  
High Field ◽  
Earth Element ◽  
Estimation Method ◽  
Model Description ◽  
High Field Strength ◽  
Data Standardization ◽  
Element Transport ◽  
Alkaline Magmas

Petrographic information, parameterization of the Grant model, description of the HFSE tonnage estimation method, and supplemental tables of whole-rock data, standardization, and HFSE volume-tonnage calculations.<br>

scholarly journals Quantifying metasomatic high-field-strength and rare-earth element transport from alkaline magmas

Geology ◽  
2021 ◽  
Author(s):  
Krzysztof Sokół ◽  
Adrian A. Finch ◽  
William Hutchison ◽  
Jonathan Cloutier ◽  
Anouk M. Borst ◽  
...  
Keyword(s):  
Rare Earth ◽  
Field Strength ◽  
Rare Earth Element ◽  
High Field ◽  
Earth Element ◽  
Chemical Interaction ◽  
Hydrothermal Systems ◽  
Initial Reaction ◽  
High Field Strength ◽  
Alkaline Magmas

Alkaline igneous rocks host many global high-field-strength element (HFSE) and rare-earth element (REE) deposits. While HFSEs are commonly assumed to be immobile in hydrothermal systems, transport by late-stage hydrothermal fluids associated with alkaline magmas is reported. However, the magnitude of the flux and the conditions are poorly constrained and yet essential to understanding the formation of REE-HFSE ores. We examined the alteration of country rocks (“fenitization”) accompanying the emplacement of a syenite magma at Illerfissalik in Greenland, through analysis of changes in rock chemistry, mineralogy, and texture. Our novel geochemical maps show a 400-m-wide intrusion aureole, within which we observed typically tenfold increases in the concentrations of many elements, including HFSEs. Textures suggest both pervasive and structurally hosted fluid flow, with initial reaction occurring with the protolith’s quartz cement, leading to increased permeability and enhancing chemical interaction with a mixed Ca-K-Na fenitizing fluid. We estimated the HFSE masses transferred from the syenite to the fenite by this fluid and found ~43 Mt of REEs were mobilized (~12% of the syenite-fenite system total rare-earth-oxide [TREO] budget), a mass comparable to the tonnages of some of the world’s largest HFSE resources. We argue that fenite can yield crucial information about the tipping points in magma evolution because retention and/or loss of volatile-bonded alkali and HFSEs are key factors in the development of magmatic zirconosilicate-hosted HFSE ores (e.g., Kringlerne, at Ilímaussaq), or the formation of the syenite-hosted Nb-Ta-REE (Motzfeldt-type) roof-zone deposits.

Geophysical interpretation of U, Th, and rare earth element mineralization of the Bokan Mountain peralkaline granite complex, Prince of Wales Island, southeast Alaska

2014 ◽  
Vol 2 (4) ◽  
pp. SJ47-SJ63 ◽  
Author(s):  
Anne E. McCafferty ◽  
Douglas B. Stoeser ◽  
Bradley S. Van Gosen
Keyword(s):  
Rare Earth ◽  
Rare Earth Element ◽  
Earth Element ◽  
Gamma Ray ◽  
Outer Edge ◽  
Peralkaline Granite ◽  
Ree Mineralization ◽  
Granite Complex ◽  
Oxide Minerals ◽  
High Concentrations

A prospectivity map for rare earth element (REE) mineralization at the Bokan Mountain peralkaline granite complex, Prince of Wales Island, southeastern Alaska, was calculated from high-resolution airborne gamma-ray data. The map displays areas with similar radioelement concentrations as those over the Dotson REE-vein-dike system, which is characterized by moderately high %K, eU, and eTh (%K, percent potassium; eU, equivalent parts per million uranium; and eTh, equivalent parts per million thorium). Gamma-ray concentrations of rocks that share a similar range as those over the Dotson zone are inferred to locate high concentrations of REE-bearing minerals. An approximately 1300-m-long prospective tract corresponds to shallowly exposed locations of the Dotson zone. Prospective areas of REE mineralization also occur in continuous swaths along the outer edge of the pluton, over known but undeveloped REE occurrences, and within discrete regions in the older Paleozoic country rocks. Detailed mineralogical examinations of samples from the Dotson zone provide a means to understand the possible causes of the airborne Th and U anomalies and their relation to REE minerals. Thorium is sited primarily in thorite. Uranium also occurs in thorite and in a complex suite of [Formula: see text] oxide minerals, which include fergusonite, polycrase, and aeschynite. These oxides, along with Y-silicates, are the chief heavy REE (HREE)-bearing minerals. Hence, the eU anomalies, in particular, may indicate other occurrences of similar HREE-enrichment. Uranium and Th chemistry along the Dotson zone showed elevated U and total REEs east of the Camp Creek fault, which suggested the potential for increased HREEs based on their association with U-oxide minerals. A uranium prospectivity map, based on signatures present over the Ross-Adams mine area, was characterized by extremely high radioelement values. Known uranium deposits were identified in the U-prospectivity map, but the largest tract occurs over a radioelement-rich granite phase within the pluton that is likely not related to mineralization. Neither mineralization type displays a well-defined airborne magnetic signature.

Origin of the Late Devonian Weekend lamprophyre dykes, Meguma Zone, Nova Scotia

1993 ◽  
Vol 30 (12) ◽  
pp. 2295-2304 ◽  
Author(s):  
M. C. Tate ◽  
D. B. Clarke
Keyword(s):  
Rare Earth ◽  
Field Strength ◽  
Rare Earth Element ◽  
High Field ◽  
Earth Element ◽  
High Field Strength Element ◽  
Late Devonian ◽  
High Field Strength ◽  
Element Abundances ◽  
Depleted Mantle

The Weekend dykes consist of 10 Late Devonian spessartite lamprophyres cropping out within the allochthonous Meguma lithotectonic terrane of the northern Appalachians. The dykes have characteristic panidiomorphic textures, with seriate phenocrysts of amphibole, clinopyroxene, and rare biotite set in a groundmass of intergrown plagioclase, K-feldspar, and quartz, with deuteric calcite and epidote. All dykes intruded during one magmatic episode (ca. 370 Ma) following terrane accretion of the Acadian Orogeny. The unaltered Weekend dykes show restricted major element variation (SiO2 54–58 wt.%, Al2O3 14–16 wt.%, MgO 7–11 wt.%, and total alkalies 2.4–5.5 wt.%) and have high Mg# (71–80) and moderate to high concentrations of Ni (69–278 ppm) and Cr (390–992 ppm). Large ion lithophile element (e.g., Sr, Ba 294–1194 ppm) and light rare earth element (13–67CN) abundances are high relative to high field strength element (e.g., Nb, Ta, Y 0.45–26 ppm) and heavy rare earth element (6–30CN) abundances. Geochemical variation largely corresponds to minor phenocryst fractionation, but high Mg# indicate the primitive nature of most dykes and preclude significant evolution of lamprophyric magmas in the crust. Incompatible element enrichments coupled with depleted mantle high field strength element abundances probably require a melt derived from reenriched lithospheric mantle sources, whereas Nb depletion and the volatile-rich mineralogy suggest metasomatic contributions from subducted ocean lithosphere. Geochemical comparisons with continental margin arc basalts and immobile element tectono-magmatic discrimination reinforce a subduction model for the Weekend dykes and strongly suggest active subduction prior to the emplacement of the Meguma terrane.

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