Using machine learning to identify indicators of rare earth element enrichment in sedimentary strata with applications for metal prospectivity

Rare Earth Element Adsorption to Clay Minerals: Mechanistic Insights and Implications for Recovery from Secondary Sources

“…The higher REE concentrations in brines also corresponded with shales and mudstones having the highest REE concentrations in the Western Canada Sedimentary Basin. 23 This relationship could indicate water-rock interactions with fine-grained materials being the main source of REE in the brines, which is supported by leaching experiments from rocks of the Iberian Pyrite Belt, where REE normalization patterns were transferred from rocks into solution, indicating water-rock interactions as an important source of REE to the waters. 21 However, determining the source of the REE could be considerably more complicated.…”

“…Additionally, lithology and the geologic history of the basin can also be significant factors; Bishop et al also found that REE concentrations were higher in brines hosted in clastic-dominated formations with the highest concentrations in formations with a higher fine-grained component. The higher REE concentrations in brines also corresponded with shales and mudstones having the highest REE concentrations in the Western Canada Sedimentary Basin . This relationship could indicate water-rock interactions with fine-grained materials being the main source of REE in the brines, which is supported by leaching experiments from rocks of the Iberian Pyrite Belt, where REE normalization patterns were transferred from rocks into solution, indicating water-rock interactions as an important source of REE to the waters .…”

“…For example, the shales of the Iberian Pyrite Belt could be a significant source of REE to AMD waters, where their transport at neutral to basic pH conditions is dominated by particulate phases including clays . Analysis of a global data set of REE in sedimentary strata revealed that fine-grained clastic rocks are more enriched in REE than carbonates, evaporites, and sandstones, while REE concentrations in formation waters of Saskatchewan, Canada were highest in formations predominantly composed of fine-grained clastics . Clay and detrital minerals are commonly the major REE-bearing phases in coals and can be transferred into their ashes following combustion. , Although the importance of the relationship between REE and clay minerals is well established for secondary sources, surprisingly, there is a dearth of information regarding the binding behavior of REE to clay mineral surfaces in aqueous settings.…”

Rare Earth Element Speciation in Coal and Coal Combustion Byproducts: A XANES and EXAFS Study

“…Supporting this assertion, it has been found through leaching and SEM-EDS that most REE-bearing minerals in CCBs from the Powder River Basin were encapsulated in an aluminosilicate matrix . Further, statistical analyses of sedimentary lithologies indicated that due to their strong relationship with other detritally sourced elements, REE may be transported in their host mineral phase from their source and incorporated into clastic sediments in coal deposits . Since the melting point of xenotime (∼2000 °C) is higher than typical coal boiler temperatures, it would likely be preserved in the ashes following combustion .…”

“…49 Further, statistical analyses of sedimentary lithologies indicated that due to their strong relationship with other detritally sourced elements, REE may be transported in their host mineral phase from their source and incorporated into clastic sediments in coal deposits. 50 Since the melting point of xenotime (∼2000 °C) 51 is higher than typical coal boiler temperatures, it would likely be preserved in the ashes following combustion. 13 Results here indicate that the REE species are not significantly transformed during the combustion process and the more refractory phosphate minerals, such as xenotime and monazite, or silicate minerals, such as zircon, are preserved and are dispersed throughout the ash particles.…”