I think that the following paper will give you precise answers to your question:

ESTIMATING P-T CONDITIONS OF GARNET GROWTH WITH ISOCHEMICAL PHASE-DIAGRAM SECTIONS AND THE PROBLEM OF EFFECTIVE BULK-COMPOSITION

By:

DOUGLAS K. TINKHAM AND EDWARD D. GHENT Department of Geology and Geophysics, University of Calgary, Calgary, Alberta T2N 1N4, Canada

In:

The Canadian Mineralogist Vol. 43, pp. 35-50 (2005)

Best regards,

Guenter Grundmann

@ Guenter Grundmann, I will read it

Thank you Sir

Dear Mr. Bekele,

the Mn content of garnet in pegmatites corresponds to the Mn content in phosphates be it manganiferous apatite or one of the many Mn-Fe-bearing phosphate s.s.s.. Translated into the depth of formation, the pegmatites and aplites bearing spessartite developed at greater depth than the pegmatites enriched in Mn-bearing phosphates. So far it is a field observation.

If you need some literature let me know this.

With kind regards

H.G.Dill

Harald G. Dill yes indeed I need any relevant literature

Thank u very much, Sir

Barsisa Bekele

Dear Mr. Bekele:

Please find attached some hints. Excluding the book, I can send you may papers on request.

Schaaf, P., Sperling, T., Müller-Sohnius, D., 2008. Pegmatites from the Bavarian Forest, SE Germany: geochronology, geochemistry and mineralogy. Geol. Bavarica 108, 204–303.

Dill HG, Skoda R (2015) The new Nb-P aplite at Reinhardsrieth: a keystone in the lateral and depth zonations of the Hagendorf-Pleystein Pegmatite fi eld, SE Germany. Ore Geol Rev 70:208–227

DILL, H.G. (2015) The Hagendorf-Pleystein Province: The center of pegmatites in an ensialic orogen.- Modern Approaches in Solid Earth Sciences,

Springer, Dortrecht, Heidelberg, London, New York, ISBN-978-3-319-18805-8, 475 pp.

cited from above:

It is true that pegmatite-related garnet is specialized in spessartite, but per se is

no marker for lithium as numerous examples show. Garnet with from the Bayerischer Wald with Spess 57 through Spess 67 are unrelated to any lithium concentration (Schaaf et al. 2008). By contrast the most elevated Li concentration at Hagendorf is not correlated with Mn-dominated garnet. Manganiferous garnet may point to higher temperatures in the study area, but has to be treated in the pegmatite province,

proper, together with apatite and in the marginal zone looked at vis-à-vis minerals

like biotite. Spessartite-bearing almandine s.s.s. coupled with the above

phosphates and silicates are marker for the depth of formation or the present-day

level of erosion and they might be used to predict the presence of Mn-bearing phosphates

in a pegmatite province. As the Mn is captured throughout the crystallization

of silicates, e.g., garnet, in the course of the evolution of the melt, the systems gets

depleted in Mn and rules out the precipitation of a wide range and high quantity of

primary or secondary Mn phosphates during subsequent stages (Table 4.1)....

With kind regards

H.G.Dill

Thank you very much Sir Harald G. Dill I will read them

Various factors can influence this - P-T conditions and also initial composition from which the granites/pegmatites are melted.

Contrib. Mineral. Petrol. 65, 59-67 (1977) Contributions to Mineralogy and Petrology 9 by Springer-Verlag 1977 Garnet in Silicic Liquids and Its Possible Use as a P-T Indicator T. H. Green