Have a look at this power point to see the roles of various incompatible elements,from(Ta and Ni inclusive)can be applied.

Dear Ahmed,

I have attached a link. I think this article can be very useful for you.

Best Regards

http://www.sciencedirect.com/science/article/pii/001670379500215L

Hi Ahmed,

The variable partitioning behaviour of Nb and Ta between melt and restite during partial melting depends strongly on geodynamic setting, and on the presence and stability of Ti-bearing refractory accessory minerals in the melting environment (especially rutile, titanite), or on the involvement of Ti-bearing phases such as titanomagnetite and ilmenite during fractionation.  

For example, the retention of Nb and Ta in refractory rutile within the downgoing eclogite slab as it undergoes dehydration and/or melting, has frequently been invoked as the underlying cause of their relative deficiency in the continental crust.

Hoffmann (1988) gives a good discussion the first-order differences in geochemical compatibility of Nb and Ta (as well, incidentally, as Pb) between the generation of oceanic and continental crust.

McDonough (1991) discusses in detail the role of residual phases in subduction zone partitioning of HFSE and Nb in particular.

Of course the literature on this topic is voluminous but I picked out below a couple of more recent studies which might be of further interest to you.

Hope this helps

Graham

Hofmann, Albrecht W. "Chemical differentiation of the Earth: the relationship between mantle, continental crust, and oceanic crust." Earth and Planetary Science Letters 90.3 (1988): 297-314. (Available on Researchgate)

McDonough, W. F. "Partial melting of subducted oceanic crust and isolation of its residual eclogitic lithology." Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences 335.1638 (1991): 407-418. Available at: http://www.geol.umd.edu/~rudnick/PDF/McDonough_PTRSL_1991.pdf

Schmidt, Alexander, et al. "HFSE systematics of rutile-bearing eclogites: new insights into subduction zone processes and implications for the earth’s HFSE budget." Geochimica et Cosmochimica Acta 73.2 (2009): 455-468. (Available on Researchgate)

Nebel, O., et al. "Deep mantle storage of the Earth’s missing niobium in late-stage residual melts from a magma ocean." Geochimica et Cosmochimica Acta 74.15 (2010): 4392-4404. (Available on Researchgate)

What late stage magmatic melts are you worrying about? Nb and Ta can become quite enriched in (per)alkaline magmas, and then either form their own minerals (columbite-tantalite series), or partition in other oddball minerals (astrophyllite, rinkite, lorenzonite).

Hi every body,

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I'm really thank all of you very much and greatly appreciate your consideration and cooperation.

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I'm worry about the behaviour of these elements during magmatic fractionation generally but especially during fractionation of granites and pegmatites of the LCT family where primary Nb and Ta deposits can be divide ito three main types, on the basis of the igneous rocks with which they are associated:

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1. Carbonatites 2. alkaline to peralkaline granites and syenites 3. granites and pegmatites of the LCT (Li-Cs-Ta) family

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Now I have some information but i'm not sure about them:

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If we have mantle source enriched in Nb and Ta, these elements can substitute for major ions in some common oxide groups such as rutile and ilmenite then during partial melting of this source these elements like the melt so they still into the melt until they reach late stages of differentiation ...

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In case of peralkaline melts which produced of low degrees of partial melting in an undepleted enriched mantle source. A key characteristic of such magmas is their ability to evolve to high Cl and F contents.

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It is known that elevated concentrations of alkalis and F in these magmas increase the solubility of the REE and HFSE by promoting formation of alkali-fluoride complexes with them thereby providing a mechanism for transporting these elements.

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Nb and Ta have high ionic potential and they are particularly insoluble but existance of fluorine and formation of fluoride complexes that improve the solubility of them into the magmatic melt and by differentiation the concentrations of these elements increased (because of their substitutions are energetically unfavorable) in the residual melt then by increasing of water vapor in the melt the fluoride complexes hydrolyzed so, that liberate the comlexed elements and forced to form their minerals (oxide group minerals) like columbite-tantalite or existed in other oxide minerals like pyrochlore, perovskite and others ...

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is that was right ?

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best regards for all

Sounds OK to me. There are of course also other ways to reduce fluorine activity - if somehow Ca wasn't in the system before, and it is introduced, the the formation of fluorite will limit the fluorine activity.

Please look this paper:

Münker C., Wörner G., Yogodzinski G., Churikova T. Behavior of high field strength elements in subduction zones: constraints from Kamchatka–Aleutian arc lavas. Earth and Planetary Science Letters 224 (2004) 275– 293.

http://community.dur.ac.uk/yaoling.niu/MyReprints-pdf/2011NiuRSC.pdf

Artur, I hope you are keeping track of whether those oddly mobile elements are not financing some warlord in deepest darkest Africa! ;-)

I really thank all of you again for this effective and important information and researches ...

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Of course I interested in Niobium and tantalum geochemistry (geology in general) and their amazing applications because of their special properties which determine their primary uses like resistance to corrosion, high melting point and superconductor properties that make them indispensable twins.

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Consequently they used in many of industries like steel industry where niobium is used in nickel, cobalt and iron-based superalloys for high-temperature applications in jet engines, rocket subassemblies and other amazing uses, whereas tantalum has a unique ability to store and release energy, which is why the electronics industry consumes more than one-half of tantalum production .

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Coltan is considered as conflict mineral resource, basically this concept is completely refused by me.

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What is the meaning of grabbing the mineral resources of any country only for funding their war and fighting that cause killed a lot of peoples instead of seeking to solve these problems about these conflict zones ?!!

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https://www.warchild.org.uk/issues/congo-conflict-minerals

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Best regards for all.

Dear Mr. Tarek,

Niobium and tantalum are concentrated apart in two different rock types so as to sold for a profit.

Magmatic niobium-tantalum-scandium deposits

1.Sn-Ta-Nb-Sc concentrations in calcalkaline and alkaline

  1.1 Granites

  1.2 Pegmatites

2. Nb- enriched deposits related to alkaline igneous complexes and carbonatites

  2.1 Pyrochlore-dominated concentric shell-type intrusions and carbonatites

  2.2 Nb-perovskite-dominated lakkolites

These are lithophile elements which tend to form Nb-Ta oxides (e.g. columbite s.s.s). The preferential concentration is given below.

Intrusive rocks

Ultrabasic rocks(dunites, pyroxenite etc.) 0.7 ppm Ta 6 ppm Nb

Basic rocks (gabbros etc.) 0.7 ppm Ta 12 ppm Nb

Intermediate rocks (diorite, granodiorite) 1.1 ppm Ta 11 ppm Nb

Granite 2.6 ppm Ta 15 ppm Nb

Alkaline igneous rocks (syenite etc.) 11.0 ppm Ta 133 ppm Nb

Effusive rocks

Basic rocks (basalt etc.) 3.5 ppm Ta 47 ppm Nb

Intermediate rocks (andesite) 11.2 ppm Ta 63 ppm Nb

Rhyolite 9.8 ppm Ta 37 ppm Nb

Alkaline effusive rocks 14.4 ppm Ta 204 ppm Nb

Nb and Ta have great similarities in their ionic radii (Nb: 0.69 A, Ta: 0.68 A) and occur both in the same valence state (5+). They form minerals of complete solid solution series with the general formula AxByOz

A: Na, Ca, Ba, Th, Pb, REE, Zr, Fe 2+

B: Nb, Ta, Ti, Fe 3+ , Sn, Hf, W, Al

C: O, OH, F

The contents of Nb and Ta increase during differentiation of intrusive rocks. The ionic radii of Nb and Ta prevents them from being accomodated in the crystal lattice of common rock-forming minerals and leave these elements in solutions until the pegmatitic stage of alkaline and calcalkaline magmas. Nb prefers late-stage differeniates of alkaline intrusions (see pyrochlore-dominated alkaline igneous intrusions and carbonatites) and Ta acidic calkakline intrusives (Sn-Ta pegmatites)

Nb-Ta mineralization are encountered in the apical parts of alkaline pegmatites and alkaline granites where they are asociated in time and space with albitization. Nb and Ta develop niobates and tantalates containing REE ( cassiterite- and albite –enriched granites in Nigeria)

In acidic highly differentiated calcalkaline igneous rocks columbite with Ta prevailing over Nb are common.

Nb-Ta minerals are redeposited together with cassiterite in alluvial and fluvial placer deposits where they can reach economic grades.

Ta may be incorporated into the lattice of cassiterite to as much as 4 % Ta2O5. Cassiterite, columbite and tapiolite (Fe2+0.8Mn2+0.2Ta1.8Nb0.2O6) do not form s.s.s. During smelting of cassiterite considerable quantities of Ta and Nb may be extracted from the slags.

I presented it in a short-cut-way as to do not drown you in too much text.

As far as the pegmatites are concerned I refer to:

DILL, H.G. (2015) Pegmatites and aplites: Their genetic and applied ore geology.- Ore Geology Reviews 69: 417-561.

Best regards

H.G.Dill

 I recommend you one proper paper which detailedly introduce the fractination process of Niobium and Tantalum. i exepect it is useful for you.

Mantle melts (alkali-carbonatitic, but also basaltic) extract both elements into the crust, compared with primitive mantle, although Nb is preferrred over Ta (Chakhmouradian 2006). Preferential titanite over rutile melting in subducted oceanic crust generates melts with very high Nb/Ta (John et al. 2011). With a crustal abundance of 12-20 ppm, niobium is more abundant than tantalum (1-2 ppm; http://earthref.org/GERM/ GERM Earth Reservoir Database). Both elements are enriched in highly differentiated granites, in alkali granites and syenites, in carbonatites and in rare-metal granites and pegmatites. Niobium outweighs tantalum in carbonatites and syenites, whereas tantalum reaches higher concentration in granites and pegmatites (cf. “tin granites”; Figure 1.18). In peraluminous granites (i.e., with an Al2O3/(CaO + Na2O + K2O) ratio (A/CNK) >1), Nb/Ta ratios vary from

Dear Prof. Dr. Walter L. Pohl, Thank you very much for your interest and cooperation. 

I am working on research about Nb & Ta as a graduation project from about eight months ago and close to completion. 

currently, I have nearly enough information about the origin of Nb & Ta into arc rocks and post-collision peraluminous rare-metal granites, pegmatites, carbonatites and alkali rocks.

But still I have a question, is there a relation between decreasing in Nb/Ta ratio and fluorine content in the melt led to fractionation of Ta from Nb during post magmatic alteration stage of rare-metal granite and pegmatite evolution ? is that related to fluorine complexion?  According to (Wang et al. 1982) showed that Nb and Ta fluorine complexes have different thermal stabilities where Ta-fluorine complexes are more mobile and stable to lower temperature than Nb-bearing complexes, therefore, Nb tends to crystallize from the melt in earlier stages that may enhance the enrichment of tantalum in farther late stages. Where fluorine tends to partition more strongly into the silicate melt (DF fluid/melt = 0.2-0.3) than into the aqueous fluid and is, therefore, generally not present as a complexing agent for metals in the fluid hydrothermal phase.

By the way, your book about "Economic Geology Principles and Practice (2011)" is really amazing and very helpful thanks again.

Best regards.

Hi Ahmed,

in addition to the very informatif comments above, I'd like to share with you some more informations. As HFSE Nb, Ta, Zr and Hf are very resistant to alteration and therofore they likely used to truck and understand to evolution of magmas as well as they are useful in tectonic discrimination diagrams. Nb-Ta and Zr-Hf are chemicaly very similar twins and hence, they are expected to not fractionate from each other during diffrentiation, however such fractionation is often observed in magmatic rocks leading for example to positive or negative correlations between Nb/Ta and Zr/Hf ratios with increasing differentiation. As mentioned by Prof. W.L. Pohl one of the reasons could be a result of the fractional crystallization of Ti bearing phases like rutile, titanite and ilmenite (John et al. 2011; Mallmann et al. 2014). Some authors (Hui et al., 2011; Niu, 2012) propose the process of “mass-dependent fractionation during magmatism” to explain Nb-Ta and Zr-Hf fractionation in magmatic systems. They suggest that the lighter elements 90-96Zr and 93Nb would behave more incompatible than the heavier elements 174-180Hf and 181Ta in magmatic processes. The presence of halogens like F and Cl could play an important role  to facilitate the transport of the HFSE in the magma and the hydrothermal fluids, forming e.g. HFSE-F complexes which could lead to high enrichment of some HFSE (Agangi et al., 2010; Demartis et al., 2014; Sheard et al., 2012; Timofeev et al., 2015). High concentration of complexing ligands allowed HFSE to be transported in solution and to behave more incompatible as expected.