Geochemical studies of rare earth elements in the Portuguese pyrite belt, and geologic and geochemical controls on gold distribution

Abstract The newly discovered Bibole banded iron formations are located within the Nyong Group at the northwest of the Congo Craton in Cameroon. The Bibole banded iron formations comprise oxide (quartz-magnetite) and mixed oxide-silicate (chlorite-magnetite) facies banded iron formations, which are interbedded with felsic gneiss, phyllite and quartz-chlorite schist. Geochemical studies of the quartz-magnetite banded iron formations and chlorite-magnetite banded iron formations reveal that they are composed of >95 wt % Fe2O3 plus SiO2 and have low concentrations of Al2O3, TiO2 and high field strength elements. This indicates that the Bibole banded iron formations were not significantly contaminated by detrital materials. Post-Archaean Australian Shale–normalized rare earth element and yttrium patterns are characterized by positive La and Y anomalies, a relative depletion of light rare earth elements compared to heavy rare earth elements and positive Eu anomalies (average of 1.86 and 1.15 for the quartz-magnetite banded iron formations and chlorite-magnetite banded iron formations, respectively), suggesting the influence of low-temperature hydrothermal fluids and seawater. The quartz-magnetite banded iron formations display true negative Ce anomalies, while the chlorite-magnetite banded iron formations lack Ce anomalies. Combined with their distinct Eu anomalies consistent with Algoma- and Superior-type banded iron formations, we suggest that the Bibole banded iron formations were deposited under oxic to suboxic conditions in an extensional basin. SIMS U–Pb data indicate that the Bibole banded iron formations were deposited at 2466 Ma and experienced metamorphism and metasomatism at 2078 Ma during the Eburnean/Trans-Amazonian orogeny. Overall, these findings suggest that the studied banded iron formations probably marked the onset of the rise of atmospheric oxygen, also known as the Great Oxidation Event in the Congo Craton.

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Hydrological and soil geochemical controls of the abundance and fractionation patterns of rare earth elements in a periodically acidic Boreal stream

Geochemistry Exploration Environment Analysis ◽

10.1144/geochem.1.2.101 ◽

2001 ◽

Vol 1 (2) ◽

pp. 101-108 ◽

Cited By ~ 4

Author(s):

Mats Åström

Keyword(s):

Rare Earth ◽

Rare Earth Elements ◽

Geochemical Controls

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Geochemistry and Petrogenesis of Basic Paleogene Volcanic Rocks in Alamut Region

Earth Sciences Research Journal ◽

10.15446/esrj.v25n2.74025 ◽

2021 ◽

Vol 25 (2) ◽

pp. 237-245

Author(s):

Mehdi Nazari Sarem ◽

Mansour Vosoghi Abedini ◽

Rahim Dabiri ◽

Mohammad Reza Ansari

Keyword(s):

Rare Earth ◽

Rare Earth Elements ◽

Basaltic Magma ◽

Volcanic Rocks ◽

Geochemical Properties ◽

Deep Faults ◽

Microscopic Studies ◽

Rift Zones ◽

Geochemical Studies ◽

Low K

Structurally, the study area belongs to the tectonic range of the Central Alborz. The rocks were analyzed to detect main elements as well as rare and rare earth elements. Based on microscopic studies, the rocks in the region include basalt, trachyandesite and basaltic andesite with alkaline geochemical properties. According to geochemical studies, the early magma was affected by Nb, Ti, Ta, Eu negative anomalies, the enrichment of Rhizosphere rocks of rare earth elements (LRRE), high LREE/HREE ratio and low K/Nb ratio and high ratios of Th/Nb, La/Nb, Ba/Nb, Zr/ Nb magmatic contamination. The early basaltic magma has been formed of a garnet lherzolite mantle with phlogopite/pargasite by metasomatism at a pressure of 2.5-5.3 GPa at depths of more than 80-150 km. Structural evidence suggests the formation of these volcanic rocks in intercontinental rift zones. The formation of these rocks can be attributed to the effects of intercontinental extensional phases in deep faults during Eocene Alpine orogeny phases.

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