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DOI10.1016/j.oregeorev.2018.04.019
Differentiation of ironstone types by using rare earth elements and yttrium geochemistry - A case study from the Bahariya region, Egypt
Afify, A. M.1,2; Sanz-Montero, M. E.1; Calvo, J. P.1
通讯作者Afify, A. M.
来源期刊ORE GEOLOGY REVIEWS
ISSN0169-1368
EISSN1872-7360
出版年2018
卷号96页码:247-261
英文摘要

This paper deals with the geological and geochemical characterization of ironstone deposits encountered in two different sedimentary successions (upper Cretaceous and lower Cenozoic) in northern Bahariya, Egypt. The ironstones occur as uneconomic thin bands, lenses and concretionary beds in Cenomanian elastic rocks of the Bahariya Formation and as economic iron ore associated with Eocene carbonate depositional units. The ironstones contain similar iron-bearing minerals, mainly goethite and hematite, which display a variety of fabrics, i.e. concretionary, massive, stromatolitic-like, oolitic, pisolitic, reniform aggregates, boxwork, liesegang, geode-like and brecciated. The iron-rich minerals preferentially replaced and/or cemented the primary and diagenetic (mainly dolomite) carbonates. Preservation of fabrics, sedimentary structures and thickness of the precursor carbonates is conspicuous.


Whole-rock composition of the Cretaceous ironstones shows lower Fe(2)O(3)and MnO contents and relative enrichment in detrital-derived elements, namely Al, Zr and Nb, when compared with the Eocene ironstones, the latter showing enrichment in Fe, Mn, Si, and Ba oxides as well as Cu, Zn, Ni and Sr trace elements. Total REE content in the Cretaceous ironstones ranges widely from 70 to 348 ppm whilst the Eocene ironstones show quite low content, mostly from 1.96 to 31 ppm. Post Archean Australian Shale (PAAS)-normalized patterns of the upper Cretaceous ironstones display flat REE patterns, with small positive Eu and Pr, slightly negative Y and Ce anomalies which are close to unity and intermediate Nd concentrations (between 10 and 100 ppm). In contrast, PAAS-normalized REE + Y patterns of the Eocene ironstones display LREE positive slope with enriched flat HREE trend as well as negative Ce anomaly, positive Y and Eu anomalies, and low Nd concentration (in general less than 10 ppm).


Geochemical data along with sedimentary features of the upper Cretaceous and Eocene ironstones in Bahariya point to different origins in the two ironstone types, the former having been originated diagenetically whereas the latter were constrained by hydrothermal fluids. A syngenetic marine origin is ruled out for any of the studied ironstones. Higher amount of detrital derived elements as well as higher REE concentration in the upper Cretaceous ironstones than in the Eocene ironstones suggest some contribution from the associated elastic sediments. The negative Ce anomaly determined in both types indicates anoxic iron-rich solution that passed to oxidized surface. The presence of positive Y and Eu anomalies in the Eocene ironstones suggests that iron precipitation was favoured by hydrothermal reducing conditions, when slightly acidic fluids reached oxidizing alkaline waters.


英文关键词Geochemistry Rare Earth Elements Yttrium Ironstone Bahariya Egypt
类型Article
语种英语
国家Spain ; Egypt
收录类别SCI-E
WOS记录号WOS:000434004700015
WOS关键词WESTERN DESERT ; OOIDAL IRONSTONES ; IRON OOIDS ; RESERVOIR SANDSTONES ; KHATATBA FORMATION ; NAVAJO SANDSTONE ; MANGANESE OXIDES ; CENTRAL UTAH ; ORIGIN ; EVOLUTION
WOS类目Geology ; Mineralogy ; Mining & Mineral Processing
WOS研究方向Geology ; Mineralogy ; Mining & Mineral Processing
资源类型期刊论文
条目标识符http://119.78.100.177/qdio/handle/2XILL650/211897
作者单位1.Univ Complutense Madrid, Dept Petrol & Geochem, Fac Geol Sci, C Jose Antonio Novais 2, Madrid 28040, Spain;
2.Benha Univ, Fac Sci, Dept Geol, Banha 13518, Egypt
推荐引用方式
GB/T 7714
Afify, A. M.,Sanz-Montero, M. E.,Calvo, J. P.. Differentiation of ironstone types by using rare earth elements and yttrium geochemistry - A case study from the Bahariya region, Egypt[J],2018,96:247-261.
APA Afify, A. M.,Sanz-Montero, M. E.,&Calvo, J. P..(2018).Differentiation of ironstone types by using rare earth elements and yttrium geochemistry - A case study from the Bahariya region, Egypt.ORE GEOLOGY REVIEWS,96,247-261.
MLA Afify, A. M.,et al."Differentiation of ironstone types by using rare earth elements and yttrium geochemistry - A case study from the Bahariya region, Egypt".ORE GEOLOGY REVIEWS 96(2018):247-261.
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