Minerals of Rare Earth Elements in High-Phosphorus Ooidal Ironstones of the Western Siberia and Turgai Depression

Maxim Rudmin,Elshan Abdullayev,Igor Reva,Aleksey Mazurov,Aleksey Ruban,Ella Sokol,Andrey Kudryavtsev,Oleg Tolkachev

doi:10.3390/min10010011

Abstract

The aim of this research was to study the rare earth (REE) minerals in ooidal ironstone deposits of the West Siberian basin and the Turgai depression. Authigenic minerals (monazite and cerite) were described, and their main mineral form was identified as light rare earth element phosphate (LREE-phosphate) in this study. LREE-phosphate is included in ferruginous ooids, peloids, and oncoids and forms a consistent mineral association with Fe-hydroxides (goethite and its hydrated amorphous derivatives) and Fe-rich layered silicates (Fe-illite-smectite, chamosite, berthierine). The constancy of the mineral association in two deposits of different ages indicates a general mechanism behind the formation of these minerals. LREE-phosphates (authigenic monazite) are characterized by microscopic sizes (up to 24 μm), diverse morphology (mainly spherical or xenomorphic), and occupy spaces between the micro-cortex in ferruginous spheroids. This mineral can be found in other deposits of ooidal ironstone. According to its mineralogical and chemical characteristics, LREE-phosphate mainly belongs to the authigenic (nodular or “gray”) monazite. However, the incomplete (not 100%) correspondence of Kikuchi bands with the reference monazite does not allow its reliable identification. Based on its small size, chemical leaching or bacterial interaction is recommended to extract REE from ooidal ironstone while predicting the associated removal of phosphorus from iron ore due to its dominant phosphate mineral form. Ooidal ironstone should be considered a complex deposit and an unconventional natural type of REE ores as an example of the largest Bakchar and Lisakovsk deposits.

Highlights

The ooidal ironstone is a chemogenic sedimentary rock that was formed during the PhanerozoicEon [1,2,3]
Identification was performed with an electron beam energy of 20 kV and beam current of 10 nA. Both terrigenous and authigenic rare earth (REE)-bearing minerals were found in both ooidal ironstone deposits
Monazite dominates among terrigenous REE minerals occurring as relatively large grain fragments while xenotime is of secondary importance

Summary

Introduction

The ooidal ironstone is a chemogenic sedimentary rock that was formed during the PhanerozoicEon [1,2,3]. The ooidal ironstone is a chemogenic sedimentary rock that was formed during the Phanerozoic. These ores are characterized by a high content of bulk iron and a low content (or complete absence) of detrimental impurities of phosphorus relative to the goethite ore. The ooids contain relatively high contents of Si, Al, Mg, P, K, Ti, and V, as well as rare earth elements (REEs) [18,19,20]. Phosphorus occurs in ooidal ironstones as a mechanical admixture, adsorbed form [14,21,22,23,24,25], or an individual authigenic mineral [8,26,27,28]

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