Tellurium and Selenium in Black Shales and Related Lithologies
Increasing interest and potential demand for the elements tellurium (Te) and selenium (Se), requires an improved understanding of the mechanisms controlling their mobility in the Earth's crust. Black shales are known to contain elevated concentrations of Te and Se and as such act as a potential...
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| Format: | Dissertation |
| Language: | English |
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ProQuest Dissertations & Theses
01-01-2021
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| Online Access: | Get full text |
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| Summary: | Increasing interest and potential demand for the elements tellurium (Te) and selenium (Se), requires an improved understanding of the mechanisms controlling their mobility in the Earth's crust. Black shales are known to contain elevated concentrations of Te and Se and as such act as a potentially large sink of these elements in the crust. In this thesis, whole rock geochemistry and detailed mineralogical analysis of black shales and related lithologies is undertaken to gain a better understanding the factors controlling Te and Se enrichment. Whole rock analysis of black shales and pelites from Britain and Ireland identifies mean concentrations of 0.07 ppm (Te) and 2.03 ppm (Se) in the majority of deposits with significantly elevated concentrations in certain samples. Mineralogical, isotopic and correlation analysis indicate that the depositional enrichment of Te and Se within black shales is controlled by the availability of Te and Se in the depositional waters. Periodic increases in atmospheric O2 concentrations through geological time, specifically during the Ediacaran and the Carboniferous, resulted in a higher flux of Te and Se to oceanic basins and higher concentrations of Te and Se in the resultant shales. Within black shales, Te is concentrated within organic matter, while Se is concentrated within diagenetic pyrite and organic matter. Both Te and Se are readily liberated from black shales at surface through oxidation and leaching by groundwater. During metamorphic recrystallisation of black shales, mobilisation of Te and Se occurs, forming concentrated enrichments associated with pyrite. Magmatic assimilation provides a potential enrichment mechanism for Te and Se from shales and pelites. Assimilation of Dalradian pelites within Ordovician intrusions has formed Te and Se enriched graphitic deposits. A similar crustal assimilation mechanism may have occurred in other deposits, producing hyper-enriched Te and Se deposits based on shale protoliths. |
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