scholarly journals The Malene metasedimentary rocks on Rypeø, and their relationship to Amîtsoq gneisses

1983 ◽  
Vol 112 ◽  
pp. 53-69
Author(s):  
R.F Dymek ◽  
R Weed ◽  
L.P Gromet
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Field Observation ◽  
Small Island ◽  
High Grade ◽  
Vertical Crustal Movement ◽  
Metasedimentary Rocks ◽  
Near Shore ◽  
Petrographic Study ◽  
Unconformable Contact

Two groups of Malene metasedimentary rocks on Rypeø, a small island south of Godthåb, have been studied in detail in order to evaluate their origin and relationship to older, adjacent Amîtsoq gneiss. Field observation shows that the metasediments range from massive to finely layered, and include an unusual pod-rock ('pseudoconglomerate'), which probably represents a series of deformed sedimentary layers (or lenses) of contrasting competence. Petrographic study indicates that the metasediments are quartz-rich, contain abundant plagioclase and biotite, and small but variable amounts ofsillimanite, muscovite, microcline and garnet. Rare earth elements (REE) in samples of four metasedimentary lithologies are similar to some published analyses of 'tonalitic' Amîtsoq gneiss. These observations suggest that the protolith of the Malene metasediments on Rypeø was dominated by sandstone type lithologies which evolved in a near-shore tidal to fiuviatile environment. These sediments were probably derived by weathering and erosion of Amitsoq gneiss and deposited unconformably on such a gneissic basement. Petrological study indicates that the Rypeø metasediments were metamorphosed to the beginning of Muse + Qtz breakdown (Musc-Sill-Kfsp transition zone), and locally underwent minor amounts of melting. The proposed original unconformable contact relationships, coupled with high-grade polymetamorphism - not only of the supracrustal rocks but also of Amitsoq gneiss - indicates substantial vertical crustal movement, perhaps as much as 75 km since the time of formation of Amitsoq gneiss at - 3750 Ma.

GENESIS AND AGE OF THE TOMTOR Nb AND RARE-EARTH DEPOSIT ORE SEQUENCE, NORTHEASTERN SIBERIAN PLATFORM

2021 ◽  
pp. 32-44
Author(s):  
Alexander Tolstov ◽  
Vladimir Cherenkov ◽  
Leonid Baranov
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Siberian Platform ◽  
High Grade ◽  
Geological Data ◽  
Magmatic System ◽  
Humid Climate ◽  
Stratigraphic Unit ◽  
Sedimentary Deposits ◽  
Hot Humid Climate

The northeastern Siberian platform (Republic of Sakha, Yakutia) hosts the Udzhinskaya province of alkaline ultrabasic massifs with carbonatites as final phases of magmatic system evolution; they form i ts central carbonatite core and are characterized by elevated Fe, Al and P concentrations. They also contain a complex of rare and rare-earth elements. Crust of laterite weathering of up to 400 m thick is present within the massifs. Phosphate, Nb, Y, Sc and TR content in crust of carbonatite weathering is much higher compared to unaltered rock differences. Their maximum values are in the sequence of specific sedimentary deposits f ormed a s denudation products of ore-bearing carbonatite crust precipitated in minor lake depressions and due to their intensive chemogenic transformation in hot humid climate. They are unique high-grade ores, with no world analogs in terms of mineral potential. Sometimes, these rocks are their natural concentrates averaging (in weight %) 7,21 Nb2O5, 0,578 Y2O3, 0,045 Sc2O3 and 10,16 TR2O3. The rocks composing the ore-bearing sequence show distinct evidence of sedimentary genesis: well-pronounced layered texture and facial zoning, presence of carbonized vegetable detrite and bacteriomorphic aggregates. Therefore, it is reasonable to regard a set of these formations as an independent stratigraphic unit, Tomtor sequence. Geological data suggest that it formed 340-280 Ma. Tomtor sequence can be an important prospecting criteria in prospecting for rare and rare-earth elements.

scholarly journals Geology, Apatite Geochronology, and Geochemistry of the Ernest Henry Inter-Lens: Implications for a Re-Examined Deposit Model

Minerals ◽  
2018 ◽  
Vol 8 (9) ◽  
pp. 405 ◽  
Author(s):  
Bradley Cave ◽  
Richard Lilly ◽  
Stijn Glorie ◽  
Jack Gillespie
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Rare Earth Element ◽  
Earth Element ◽  
Shear Zones ◽  
Light Rare Earth Element ◽  
Magmatic Fluid ◽  
Light Rare Earth ◽  
Metasedimentary Rocks ◽  
Copper Gold

The Ernest Henry Iron-Oxide-Copper-Gold deposit is the largest known Cu-Au deposit in the Eastern Succession of the Proterozoic Mount Isa Inlier, NW Queensland. Cu-Au mineralization is hosted in a K-feldspar altered breccia, bounded by two major pre-mineralization shear zones. Previous research suggests that Cu-Au mineralization and the ore-bearing breccia formed simultaneously through an eruption style explosive/implosive event, facilitated by the mixing of fluids at ~1530 Ma. However, the preservation of a highly deformed, weakly mineralized, pre-mineralization feature (termed the Inter-lens) within the orebody indicates that this model must be re-examined. The paragenesis of the Inter-lens is broadly consistent with previous studies on the deposit, and consists of albitization; an apatite-calcite-quartz-garnet assemblage; biotite-magnetite ± garnet alteration; K-feldspar ± hornblende alteration; Cu-Au mineralization and post-mineralization alteration and veining. Apatite from the paragenetically early apatite-calcite-quartz-garnet assemblage produce U–Pb ages of 1584 ± 22 Ma and 1587 ± 22 Ma, suggesting that the formation of apatite, and the maximum age of the Inter-lens is synchronous with D2 deformation of the Isan Orogeny and regional peak-metamorphic conditions. Apatite rare earth element-depletion trends display: (1) a depletion in rare earth elements evenly, corresponding with an enrichment in arsenic and (2) a selective light rare earth element depletion. Exposure to an acidic NaCl and/or CaCl2-rich sedimentary-derived fluid is responsible for the selective light rare earth element-depletion trend, while the exposure to a neutral to alkaline S, Na-, and/or Ca-rich magmatic fluid resulted in the depletion of rare earth elements in apatite evenly, while producing an enrichment in arsenic. We suggest the deposit experienced at least two hydrothermal events, with the first event related to peak-metamorphism (~1585 Ma) and a subsequent event related to the emplacement of the nearby (~1530 Ma) Williams–Naraku Batholiths. Brecciation resulted from competency contrasts between ductile metasedimentary rocks of the Inter-lens and surrounding shear zones against the brittle metavolcanic rocks that comprise the ore-bearing breccia, providing permeable pathways for the subsequent ore-bearing fluids.

Rare earth elements in volcanic rocks of the Buchans area, Newfoundland

1984 ◽  
Vol 21 (7) ◽  
pp. 775-780 ◽  
Author(s):  
D. F. Strong
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Volcanic Rocks ◽  
Ore Deposits ◽  
High Grade ◽  
Sulphide Deposits ◽  
General Tool ◽  
The Rare Earth

Rare earth elements (REE) were determined for 57 samples representative of the range of stratigraphic units, both mineralized and unmineralized, associated with the high-grade polymetallic volcanogenic sulphide deposits at Buchans, Newfoundland. These data do not indicate any features indicative of magmatic fractionation processes, e.g., enrichment of total REE or any europium depletion anomaly, in the mineralized relative to the unmineralized volcanics, suggesting that such processes did not play an important role in the formation of these ore deposits. These results also emphasize the need for caution in any attempts to use the rare earth elements as a general tool for discrimination between barren and mineralized volcanic sequences.

Geochemical and Nd isotopic compositions of the Palaeoproterozoic metasedimentary rocks in the Kongling complex, nucleus of Yangtze craton, South China block: implications for provenance and tectonic evolution

2017 ◽  
Vol 155 (6) ◽  
pp. 1263-1276 ◽  
Author(s):  
XIAO-FEI QIU ◽  
XIAO-MING ZHAO ◽  
HONG-MEI YANG ◽  
SHAN-SONG LU ◽  
NIAN-WEN WU ◽  
...  
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
South China ◽  
Chemical Weathering ◽  
Tectonic Setting ◽  
South China Block ◽  
Yangtze Craton ◽  
Metasedimentary Rocks ◽  
Isotopic Compositions ◽  
High Pressure Granulite

AbstractPalaeoproterozic metasedimentary rocks, also referred to as khondalites, characterized by Al-rich minerals, are extensively exposed in the nucleus of the Yangtze craton, South China block. Samples of garnet–sillimanite gneiss in the khondalite suite were collected from the Kongling complex for Nd isotopic and elemental geochemical study. These rocks are characterized by variable SiO2 contents ranging from 35.71 to 58.07 wt%, and have low CaO (0.45–0.84 wt%) but high Al2O3 (18.56–29.04 wt%), Cr (174–334 ppm) and Ni (42.5–153 ppm) contents. They have high CIW (Chemical Index of Weathering) values (90.4–94.7), indicating intense chemical weathering of the source material. The samples display light rare earth elements (LREE) enrichment with negative Eu anomalies (Eu/Eu*=0.40–0.68), and have flat heavy rare earth elements (HREE) patterns. The high contents of transition elements (e.g. Cr, Ni, Sc, V) and moderately radiogenic Nd isotopic compositions suggest that the paragneisses might be those of first-cycle erosion products of predominantly mafic rocks mixing with small amounts of felsic moderately evolved Archaean crustal source. Geochemical and Nd isotopic compositions reveal that at least some of the protoliths of Kongling khondalite were sourced from local pre-existing mafic igneous rocks in a continental arc tectonic setting. Combined with documented zircon U–Pb geochronological data, we propose that the Palaeoproterozoic high-pressure granulite-facies metamorphism, rapid weathering, erosion and deposition of the khondalites in the interior of the Yangtze craton might be related to a Palaeoproterozoic collisional orogenic event during 2.1–1.9 Ga, consistent with the worldwide contemporary orogeny, implying that the Yangtze craton may have been an important component of the Palaeoprotorozoic Columbia supercontinent.

scholarly journals Chemical fingerprint of iron oxides related to iron enrichment of banded iron formation from the Cauê Formation - Esperança Deposit, Quadrilátero Ferrífero, Brazil: a laser ablation ICP-MS study

2015 ◽  
Vol 45 (2) ◽  
pp. 193-216 ◽  
Author(s):  
Lucilia Aparecida Ramos de Oliveira ◽  
Carlos Alberto Rosière ◽  
Francisco Javier Rios ◽  
Sandra Andrade ◽  
Renato de Moraes
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Iron Oxides ◽  
Iron Ore ◽  
Redox Conditions ◽  
Iron Formation ◽  
High Grade ◽  
Banded Iron Formation ◽  
Iron Enrichment ◽  
Quadrilátero Ferrífero

<p>Chemical signatures of iron oxides from dolomitic itabirite and high-grade iron ore from the Esperança deposit, located in the Quadrilátero Ferrífero, indicate that polycyclic processes involving changing of chemical and redox conditions are responsible for the iron enrichment on Cauê Formation from Minas Supergroup. Variations of Mn, Mg and Sr content in different generations of iron oxides from dolomitic itabirite, high-grade iron ore and syn-mineralization quartz-carbonate-hematite veins denote the close relationship between high-grade iron ore formation and carbonate alteration. This indicates that dolomitic itabirite is the main precursor of the iron ore in that deposit. Long-lasting percolation of hydrothermal fluids and shifts in the redox conditions have contributed to changes in the Y/Ho ratio, light/heavy rare earth elements ratio and Ce anomaly with successive iron oxide generations (martite-granular hematite), as well as lower abundance of trace elements including rare earth elements in the younger specularite generations.</p>

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