scholarly journals Nb–Ta mineralization in Ti-oxide minerals from the Bagolyhegy Metarhyolite Formation (Bükk Mountains, NE Hungary)

2021 ◽  
Keyword(s):  
Mineral Assemblage ◽  
Metamorphic Rocks ◽  
Low Grade ◽  
High Field Strength ◽  
Fine Grained ◽  
Ree Mineralization ◽  
Icp Ms ◽  
Oxide Minerals ◽  
Rock Suite ◽  
Mesozoic Rock

Abstract The foliated low-grade metamorphic rocks of the Triassic Bagolyhegy Metarhyolite Formation, mainly of pyroclastic origin, host post-metamorphic quartz-albite veins containing abundant tourmaline and occasionally rutile/ilmenite. The study of the Ti-oxide-mineralized veins with SEM-EDX revealed an unusual mineral assemblage comprising fine-grained Nb–Ta-bearing oxides (columbite-tantalite series, fluorcalciomicrolite and other Nb–Ti–Y–Fe-REE-oxide minerals) intergrown with Nb-rich polymorphs of TiO2 (anatase, rutile), ilmenite and zircon enriched with hafnium. This high field strength elements (HFSE)-bearing paragenesis is unexpected in this lithology, and was not described from any formation in the Paleozoic-Mesozoic rock suite of the Bükk Mountains (NE Hungary) before. The host metavolcanics are significantly depleted in all HFSE compared to the typical concentrations in felsic volcanics and the mineralized quartz-albite veins have even lower Ti–Nb–Ta concentration than the host rock, so the mineralization does not mean any enrichment. From proximal outcrops of the Triassic Szentistvánhegy Metavolcanics, potassic metasomatized lenses with albite-quartz vein fillings containing rutile/ilmenite are known. We studied them for comparison, but they only contain REE mineralization (allanite-monazite-xenotime); the Nb–Ta-content of Ti-oxide minerals is undetectably low. LA-ICP-MS measurements for U–Pb dating of Hf-rich zircon of the Nb–Ta-rich mineral assemblage gave 71.5 ± 5.9 Ma as lower intercept age while dating of allanite of the REE mineralized quartz-albite veins gave 113 ± 11 Ma as lower intercept age. The REE-bearing vein fillings formed during a separate mineralization phase in the Early Cretaceous, while the Nb–Ta mineralization was formed by post-metamorphic alkaline fluids in the Late Cretaceous., controlled by fault zones and fractures.

TEM/AEM characterization of fine-grained clay minerals in very-low-grade rocks: Evaluation of contamination by empa involving celadonite family minerals

1996 ◽  
Vol 54 ◽  
pp. 694-695
Author(s):  
Gejing Li ◽  
D. R. Peacor ◽  
D. S. Coombs ◽  
Y. Kawachi
Keyword(s):  
Electron Microscopy ◽  
Volcanic Rocks ◽  
Analytical Electron Microscopy ◽  
Metamorphic Rocks ◽  
New Mineral ◽  
Chemical Compositions ◽  
Low Grade ◽  
Fine Grained ◽  
Depth Analysis ◽  
Mineral Aggregates

Recent advances in transmission electron microscopy (TEM) and analytical electron microscopy (AEM) have led to many new insights into the structural and chemical characteristics of very finegrained, optically homogeneous mineral aggregates in sedimentary and very low-grade metamorphic rocks. Chemical compositions obtained by electron microprobe analysis (EMPA) on such materials have been shown by TEM/AEM to result from beam overlap on contaminant phases on a scale below resolution of EMPA, which in turn can lead to errors in interpretation and determination of formation conditions. Here we present an in-depth analysis of the relation between AEM and EMPA data, which leads also to the definition of new mineral phases, and demonstrate the resolution power of AEM relative to EMPA in investigations of very fine-grained mineral aggregates in sedimentary and very low-grade metamorphic rocks.Celadonite, having end-member composition KMgFe3+Si4O10(OH)2, and with minor substitution of Fe2+ for Mg and Al for Fe3+ on octahedral sites, is a fine-grained mica widespread in volcanic rocks and volcaniclastic sediments which have undergone low-temperature alteration in the oceanic crust and in burial metamorphic sequences.

Zussmanite in ferruginous metasediments from Southern Central Chile

1998 ◽  
Vol 62 (6) ◽  
pp. 869-876 ◽  
Author(s):  
H.-J. Massonne ◽  
F. Hervé ◽  
O. Medenbach ◽  
V. Muñoz ◽  
A. P. Willner
Keyword(s):  
Chemical Composition ◽  
Metamorphic Rocks ◽  
Stability Field ◽  
Low Grade ◽  
Central Chile ◽  
X Ray ◽  
Fine Grained ◽  
Southern Central ◽  
Similar Phase

AbstractZussmanite KFe13[AlSi17O42](OH)14, a modulated 2:1 layer silicate, has so far been found only in iron-rich metasediments from Laytonville, California (Agrellet al.), 1965). A new occurrence is reported here from Punta Nihue north of Valdivia, Chile, in banded stilpnomelane-schists. These are intercalated in the ‘Western Series’, a complex of low-grade metamorphic rocks with local high-pressure, low-temperature overprint (e.g. blueschists).The rock contains conspicuous porphyroblasts of zussmanite of mm size and is composed of chemically distinct bands with the subsequent assemblages: (1) zussmanite-stilpnomelane-quartz, (2) siderite-quartz±stilpnomelane (3) apatite-stilpnomelane-quartz±siderite. The chemical composition of zussmanite, (K0.80Na0.05Ba0.01)(Fe11.292+Mg1.11Mn0.25Fe0.143+Cr0.01Al0.19Ti0.01)[Al1.23Si16.77O42](OH)14, its optical properties and X-ray data correlate well with the Californian occurrence. Additionally, we present new IR data. In type (2) bands of fine-grained crystals of a K,Al poor mineral formed from siderite and quartz. Its chemical composition is close to that of zussmanite. A similar phase was also reported from Laytonville, California (Muir Wood, 1980).The rarity of rock-forming zussmanite can be explained by its occurrence in strongly Fe-rich and reduced rocks, as well as, by a possibly narrowP-Tstability field.

The thermometric significance of magnetite in low grade metamorphic rocks

1964 ◽  
Vol 262 (7) ◽  
pp. 904-917 ◽  
Author(s):  
M. I. Abdullah ◽  
M. P. Atherton
Keyword(s):  
Metamorphic Rocks ◽  
Low Grade

Zircon ages and the distribution of Archaean and Proterozoic rocks in the Rauer Islands

1993 ◽  
Vol 5 (2) ◽  
pp. 193-206 ◽  
Author(s):  
P. D. Kinny ◽  
L. P. Black ◽  
J. W. Sheraton
Keyword(s):  
Granulite Facies ◽  
Metamorphic Rocks ◽  
Low Grade ◽  
High Grade ◽  
Ion Microprobe ◽  
Rock Interaction ◽  
Mafic Rocks ◽  
Grade Fluid ◽  
Vestfold Hills ◽  
Intrusive Suite

The application of zircon U-Pb geochronology using the SHRIMP ion microprobe to the Precambrian high-grade metamorphic rocks of the Rauer Islands on the Prydz Bay coast of East Antarctica, has resulted in major revisions to the interpreted geological history. Large tracts of granitic orthogneisses, previously considered to be mostly Proterozoic in age, are shown here to be Archaean, with crystallization ages of 3270 Ma and 2800 Ma. These rocks and associated granulite-facies mafic rocks and paragneisses account for up to 50% of exposures in the Rauer Islands. Unlike the 2500 Ma rocks in the nearby Vestfold Hills which were cratonized soon after formation, the Rauer Islands rocks were reworked at about 1000 Ma under granulite to amphibolite facies conditions, and mixed with newly generated felsic crust. Dating of components of this felsic intrusive suite indicates that this Proterozoic reworking was accomplished in about 30–40 million years. Low-grade retrogression at 500 Ma was accompanied by brittle shearing, pegmatite injection, partial resetting of U-Pb geochronometers and growth of new zircons. Minor underformed lamprophyre dykes intruded Hop and nearby islands later in the Phanerozoic. Thus, the geology of the Rauer Islands reflects reworking and juxtaposition of unrelated rocks in a Proterozoic orogenic belt, and illustrates the important influence of relatively low-grade fluid-rock interaction on zircon U-Pb systematics in high-grade terranes.

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