Dear Mr. Hassan,

from you question I learnt that you refer to the so-called "ironstones" which is the most widespread type of sedimentary Fe ore deposit during the late Precambrian, Paleozoic, Mesozoic and even Cenozoic. In contrast to the BIF, this Fe accumulation took place under an oxygen-enriched atmosphere. I have added two papers  which may direct your thoughts to this type of Fe concentration and the REE distribution in particular.

Graf, J. L.; O'Connor, E. A.; van Leeuwen, P. 1994 Rare earth element evidence of origin and depositional environment of Late Proterozoic ironstone beds and manganese-oxide deposits, SW Brazil and SE Bolivia. Journal of South American Earth Sciences, 7, 115-133.

Moëlo, Y.; Rouer, O.; Bouhnik-Le Coz, M. 2008. From diagenesis to hydrothermal recrystallization: polygenic Sr-rich fluorapatite from the oolitic ironstone of Saint-Aubin-des-Chateaux (Armorican Massif, France. European Journal of Mineralogy 20 ,  205 - 216.

If you have a look at:

ZITZMANN, A. (Editor) 1977 The iron ore deposits of Europe and adjacent areas. Bundesanstalt für Geowissenschaften und Rohstoffe, Hannover 418 pp.

you will get an almost complete insight into the "ironstone deposits" and based upon this monograph you can select chemical papers, including those dealing with REE for your studies.

Best regards

Harald G. Dill

Dear Kenneth:

I feel fine with this way of getting in  touch.

I have used this way of distinction which is a rather simplistic one and I would like to express it again as follows:

Banded Iron Formation (BIF) / Achaean : reducing atmosphere

Ironstone deposits / Late Proterozoic and younger: oxidizing atmosphere.

I have used only the common way of attribution among economic geologists. I hope you will agree as a chemist with this separation.

The terms "oxygenated" and "oxygen-enriched" I would use in this Q & A  as synonymous. But I am aware of some slight differences. Sorry for that, that I might have been a bit too  sloppy as to my wording and the use of technical terms.

Best regardsHarald

Dear Kenneth:

Thank you for this update.

Harald

Dear Dr Jubril Hassan

Kindly you are encouraged to find the classical book from Sir Goldsmits 1954 in Geochemistry and also Dr Henderson 1984 in Rare earth element Geochemistry.

Thank you

Regard's

Zolhizir bin Daud

The whole rock Cerium anomaly considered as a geochemical parameter that characterizes paleo-oceanographic chemical conditions related to relative eustatic sea-level changes independent of sedimentological considerations. There is no general agreement as to the mechanism for Ce-depletion in seawater and enhancement in sediments, even though scores of observations have been made by the scientists. Estimates show that at pH > 7.5; Ce (OH)4 precipitates with Fe-Mn-Al-Ti-oxy-hydroxide, forming coatings on carbonate minerals.

In oxic conditions, Ce is less readily dissolved in seawater, so that oxic seawater is more depleted with respect to Ce, while oxic sediments are more enhanced with respect to Ce. A negative Ce anomaly is indicated in which organisms extract phosphate from oxic seawater (Wright et al.,op. cit.). In suboxic seawater, Ce-bearing sediments are mobilized and Ce is released into the water column resulting in a less negative to a positive anomaly in seawater (DeBaar et al., 1985, 1988; DeBaar, 1991; Sholkovitz and Schneider, 1991); in anoxic sediments, Ce is depleted and the sediments show a negative anomaly but increasing values indicate more oxic conditions (Murray et al., 1990, 1991); Ce anomaly is dictated by the eustatic changes of sea level. During a transgression, the bottom waters would become more anoxic and the Ce whole-rock anomaly more negative but during a regression, the bottom waters would become more oxic and the Ce whole-rock anomaly would be more positive. During marine transgression, there will be less deposition of Ce (OH)4 enriched sediments transported into deeper waters, giving a relative "negative" anomaly.

The chondrite REE pattern and Europium (Eu) anomaly and the ratio of LREE/HREE can be regarded as an effective indicator of provenance composition (Taylor and Mclennan, op. cit.). Higher LREE/HREE ratios and negative Eu anomalies are generally found in felsic rocks, whereas the mafic rocks exhibit lower LREE/HREE ratios and no or small Eu anomalies (Cullers, 1994). The TTG (tonalite-tronjhemite-gneiss) rocks exhibit very high LREE /HREE ratios and no or small positive Eu anomalies (Cullers and Graf, 1984).

The above comments are compiled from the published work on general observations on Ce and Eu anomalies. It is well understood that the prevailing oxygen rich environment help deposition of Iron Stones globally. Derivation of sediments from its appropriate provenance adds the Eu anomaly.

Thanks

D. Majumdar

India

Hi Jubril,

I have worked on the upper Cretaceous  oolitic ironstones, Aswan, Egypt. I found a possible increase in LREE/HREE can be related to weathering overprinting. Aswan ironstone contain early diagenetic fluorapatite and it is corroded  by sulphate-bearing solution derived from oxidation of sulphides in the ironstones. This results in formation of crandalite-goyazite  solid solution series (see Al sulphate phosphate minerals (Dill, 2001). These APS minerals are too fine to be realized by optical microscope and can be observed by SEM. These minerals are rich in LREE over HREE. I attached my paper about the oolitic ironstones of Egypt for you to read. 

if your study on the Cretaceous ironstones of Nigeria, it is possibly that these deposits have underwent phases of chemical weathering under humid and warm climate dominated in N Africa.

Positive Ce anomaly emerges in deeply weathered and lateritic profiles where soluble Ce3+ oxidizes to insoluble, stable Ce4+ and is hosted in secondary REE minerals (Braun et al. 1990; Borges et al. 2008).

Positive Eu anomaly can be related to strongly reducing condition during diagenesis (Schieber, 1988).

Best regards

Walid

thanks sir. i have read and appreciated these paper, i got online in 2015 and learnt a lot from it. 

General views about the positive Eu anomaly is that feldspar rich magmatic rocks as the provenance of ironstone. Deposition of  ironstones in oxidation environment may be a reason for the positive Ce anomaly. The reason is:

In oxic conditions, Ce is less readily dissolved in seawater, so that oxic seawater is more depleted with respect to Ce, whereas oxic sediments are more enhanced with respect to Ce. Organisms extracting phosphate from oxic seawater show a negative Ce anomaly, whereas Fe oxide-rich oxic sediments, such as red clay, have a positive Ce anomaly. Conversely, in suboxic seawater Ce bearing sediments are mobilized so that Ce is released into the water column resulting in a less negative to a positive anomaly in seawater.

If you are interested to know more you can consult the following papers: DeBaar et al., 1985, 1988; DeBaar, 1991; Sholkovitz and Schneider, 1991.

Good luck to you.

Regards

D. Majumdar

thanks Salama, i have read through your work from the onset and duly appreciate your contribution 

thanks Prof. Kenneth M. Towe , really Appreciate your effort.

Positive Ce anomaly is related to hydrogenous (seawater sourced)Fe oxyhydroxides. Whereas, positive Eu anomaly and negative Ce anomaly is related to modern submarine hydrothermal sulfides, of Fe-oxyhydroxides.

I recommend Kenneth's answer

Best Regards

I found Eu positive anomalies for clays what are possible reasons to find this

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