**5. Mineralogy and mineral chemistry of allanite**

Allanite in these rock types occurs as a rare accessory mineral. It forms in these rocks relatively bigger grains (300–500 μm) and usually occurs on grain boundaries of biotite and plagioclase. Electron microprobe data show that the chemical composition of the epidote-group minerals in analyzed granitic rocks of the Moldanubian batholith varies greatly (**Table 1**). Studied allanites often exhibit irregular alteration, usually along their grain rims without any zoning of unaltered parties. In the BSE images, highly altered allanite parties on their rims are dark (**Figure 2A**). These highly altered parties are enriched in Si, Ti, and Th and depleted in Ca, Fe, Mn, La, and Ce. The altered allanite parties also display lower total analytical sum, which could indicate their hydration. In some other cases, irregular bright parties of BSE in altered allanite grains were found. These bright parties are enriched in Fe and depleted in Si, Ti, Ca, and Th (**Figure 2B**).

Analyzed epidote-group minerals without visible alteration contain 30.9– 36.1 wt.% SiO2, 10.1–17.8 wt.% CaO, 8.8–15.1 wt.% FeO, and 13.0–24.4 wt.% REE2O3. The magmatic zoning observed in some analyzed allanite grains (**Figure 2C**–**E**) seems to be caused by variations in Fe, Ca, Th, and REE contents and Fe3+/(Fe3+ Fe2+) ratio. Allanites from the Schlieren granites and Freistadt suite are relatively Al-poor (Al = 1.3–1.8 atoms per formula unit, apfu) and display variable Feox = (Fe3+/(Fe3+ + Fe2+)) ratio (0.2–0.5). Allanites from the diorite 1 are enriched in Al (1.8–1.9 apfu). Distinctly greater Al enrichment occurs in allanites from microgranodiorites (up to 2.2 apfu). These allanites also display higher Feox = (Fe3+/(Fe3+ Fe2+)) ratio without any zoning (**Figure 2F**). All analyzed allanites are Mn-poor with its concentrations from 0.01 to 0.04 apfu.

**25**

**Table 1.**

*b.d.l.—below detection limit and apfu—atoms per formula unit.*

*Selected representative microprobe analyses of allanite.*

*Allanite from Granitic Rocks of the Moldanubian Batholith (Central European Variscan Belt)*

Schlieren granite

Sample 1714-16 1714-19 1724-11 1633-7 1633-12 532-30 Suite Weinsberg Weinsberg Weinsberg Freistadt Freistadt Dykes

SiO2 35.97 34.74 32.01 31.47 31.67 32.36 TiO2 1.28 1.29 1.22 1.06 1.20 1.17 Al2O3 14.88 14.38 15.78 13.45 14.06 14.69 FeO 8.66 9.33 13.43 15.10 15.20 14.94 MnO 0.43 0.52 0.30 0.41 0.47 0.21 MgO 0.92 1.10 0.91 1.52 1.16 0.24 CaO 11.04 10.89 10.62 10.78 11.34 12.48 La2O3 5.15 4.89 6.67 7.40 6.46 5.37 Ce2O3 8.89 9.47 12.29 11.48 10.95 8.96 Pr2O3 0.61 0.78 1.25 1.09 1.09 0.87 Nd2O3 1.91 2.46 3.59 2.85 2.87 2.92 Sm2O3 0.07 0.21 0.29 0.08 0.26 0.52 Gd2O3 0.00 0.23 0.22 0.16 0.12 0.22 Dy2O3 0.00 0.00 0.01 0.17 0.19 0.08 ThO2 2.80 2.33 0.20 1.12 1.10 0.10 UO2 0.04 0.05 0.01 0.02 0.01 b.d.l. Total 92.65 92.67 98.80 98.16 98.15 95.13

Si 3.42 3.35 3.04 3.06 3.05 3.12 Ti 0.09 0.09 0.09 0.08 0.09 0.09 Al 1.66 1.63 1.77 1.54 1.60 1.67 Fe2+ 0.69 0.75 1.07 1.23 1.23 1.20 Mn 0.04 0.04 0.02 0.03 0.04 0.02 Mg 0.13 0.16 0.13 0.22 0.17 0.03 Ca 1.12 1.13 1.08 1.12 1.17 1.29 La 0.18 0.17 0.23 0.25 0.23 0.19 Ce 0.31 0.33 0.43 0.43 0.39 0.32 Pr 0.02 0.03 0.04 0.04 0.04 0.03 Nd 0.07 0.09 0.12 0.11 0.10 0.10 Sm 0.00 0.01 0.01 0.01 0.01 0.02 Gd 0.00 0.01 0.01 0.00 0.00 0.01 Dy 0.00 0.00 0.00 0.01 0.01 0.00 Th 0.06 0.05 0.00 0.03 0.02 0.00 U 0.00 0.00 0.00 0.00 0.00 0.00

Diorite 1 Margin Margin Micro-

granodiorite

*DOI: http://dx.doi.org/10.5772/intechopen.86356*

Schlieren granite

Variety wt.%

apfu, O = 12.5


*Allanite from Granitic Rocks of the Moldanubian Batholith (Central European Variscan Belt) DOI: http://dx.doi.org/10.5772/intechopen.86356*

### **Table 1.**

*Rare Earth Elements and Their Minerals*

zircon, ilmenite, magnetite, titanite, and allanite.

ite, titanite, apatite, rutile, zircon, and rare allanite.

depleted in Si, Ti, Ca, and Th (**Figure 2B**).

**5. Mineralogy and mineral chemistry of allanite**

The Schlieren granites of the Weinsberg suite are represented by biotite granites consisting of plagioclase (An20–40) (32–50 vol.%), K-feldspar (7–37 vol.%), quartz (18–34 vol.%), and biotite (annite, Fe/Fe + Mg = 0.53–0.55, Al4+ = 2.10–2.13, and Ti = 0.23–0.42 atoms per formula unit (apfu)), (6–32 vol.%). Amphibole was also frequently present (up to 5 vol.%). Accessory minerals are represented by apatite,

The biotite diorites (diorite 1) of the Weinsberg suite consist of plagioclase (An37–39), (50–53 vol.%), biotite (annite, Fe/Fe + Mg = 0.65–0.66, Al4+ = 2.22–2.93,

Accessory minerals are represented by ilmenite, apatite, zircon, titanite, allanite,

Ti = 0.30–0.50 apfu), (6–17 vol.%) and muscovite (0–1 vol.%). Accessory minerals

The microgranodiorites from the eastern margin of the Klenov pluton consist of plagioclase (An25–54), K-feldspar, quartz, biotite (annite, Fe/Fe + Mg = 0.60–0.68, Al4+ = 1.68–2.30, and Ti = 0.13–0.47 apfu), pyroxene (Fe-augite), and amphibole (ferro-actinolite to Mg-hornblende). Accessory minerals are represented by ilmen-

Allanite in these rock types occurs as a rare accessory mineral. It forms in these rocks relatively bigger grains (300–500 μm) and usually occurs on grain boundaries of biotite and plagioclase. Electron microprobe data show that the chemical composition of the epidote-group minerals in analyzed granitic rocks of the Moldanubian batholith varies greatly (**Table 1**). Studied allanites often exhibit irregular alteration, usually along their grain rims without any zoning of unaltered parties. In the BSE images, highly altered allanite parties on their rims are dark (**Figure 2A**). These highly altered parties are enriched in Si, Ti, and Th and depleted in Ca, Fe, Mn, La, and Ce. The altered allanite parties also display lower total analytical sum, which could indicate their hydration. In some other cases, irregular bright parties of BSE in altered allanite grains were found. These bright parties are enriched in Fe and

Analyzed epidote-group minerals without visible alteration contain 30.9– 36.1 wt.% SiO2, 10.1–17.8 wt.% CaO, 8.8–15.1 wt.% FeO, and 13.0–24.4 wt.% REE2O3. The magmatic zoning observed in some analyzed allanite grains

(**Figure 2C**–**E**) seems to be caused by variations in Fe, Ca, Th, and REE contents and Fe3+/(Fe3+ Fe2+) ratio. Allanites from the Schlieren granites and Freistadt suite are relatively Al-poor (Al = 1.3–1.8 atoms per formula unit, apfu) and display variable Feox = (Fe3+/(Fe3+ + Fe2+)) ratio (0.2–0.5). Allanites from the diorite 1 are enriched in Al (1.8–1.9 apfu). Distinctly greater Al enrichment occurs in allanites from microgranodiorites (up to 2.2 apfu). These allanites also display

higher Feox = (Fe3+/(Fe3+ Fe2+)) ratio without any zoning (**Figure 2F**). All analyzed allanites are Mn-poor with its concentrations from 0.01 to

The biotite granodiorites of the "marginal variety" of the Freistadt suite consist of plagioclase (An25–37), (32–68 vol.%), quartz (12–32 vol.%), K-feldspar (3–27 vol.%), biotite (annite, Fe/Fe + Mg = 0.44–0.62, Al4+ = 2.09–2.28, and

are represented by apatite, zircon, ilmenite, titanite, monazite, and allanite.

Ti = 0.37–0.45 apfu), (15–20 vol.%), K-feldspar (8–12 vol.%), amphibole (Mg-hornblende), (3–10 vol.%), and pyroxene (Fe-augite), (1–5 vol.%).

**4. Petrography**

and thorite.

**24**

0.04 apfu.

*Selected representative microprobe analyses of allanite.*

### **Figure 2.**

*BSE images of allanite, A—partly altered allanite grain from biotite granodiorite of the Freistadt suite, B—highly altered allanite grain form the Schlieren granite, C and D—zoned allanite grains from the diorite 1, E—allanite grain from the Schlieren granite, and F—allanite grain from microgranodiorite. Aln—allanite, Ap—apatite, Bt—biotite, Ilm—ilmenite, Kfs—K-feldspar, Qz—quartz, Pl—plagioclase, and Ttn—titanite.*

The majority of analyzed allanites represent substitution between ferriallanite and allanite. Only allanites from the microgranodiorites display substitution between allanite and clinozoisite (**Figure 3**).

All analyzed allanites display variable concentrations of REE with preference of Ce over La. The Ce is predominant in all analyzed allanite grains over other REE studied here; they are thus identified as allanite-(Ce). The highest concentrations of Ce were found in allanites from diorite 1 (0.31–0.41 apfu). The lowest concentrations of Ce display allanites from the youngest microgranodiorite dykes (0.14–0.32 apfu).

**27**

internal zoning was found (**Figure 2C** and **D**).

**6. Discussion**

*Petrík et al. [21].*

**Figure 3.**

*Allanite from Granitic Rocks of the Moldanubian Batholith (Central European Variscan Belt)*

For allanite, two main substitutions occur, namely the epidote-allanite and the allanite-ferriallanite substitutions [2, 21]. For analyzed allanites from the Weinsberg and Freistadt suites, the allanite-ferriallanite substitution is significant. Similar substitution was found by Petrík et al. [21] in allanites from the I-type granitic rocks of the Sihla tonalite suite in the Western Carpathians. Some highly altered allanite grains which were found in the Schlieren granite (**Figure 2B**) exhibit irregular zonation, which is very similar with the "mushroom-shaped areas" described by Poitrasson [22] from anorogenic granites of Corsica (southeast France). However, in the case of altered allanites from the Schlieren granite, the altered parties are depleted in Si, Ti, Ca, and Th, but enriched in Fe. Some other allanite alteration was found on allanite rims that occurred in the allanite from the Freistadt granodiorite (**Figure 2A**). In this case, the altered allanite rim is enriched in Si, Ti, and Th. Similar enrichment of Th was also found in altered alanites from anorogenic granites of Corsica (southeast France) and in allanites from the Casto granite of Idaho (USA) [22, 23]. Alterations of allanite which were found in allanites from the Schlieren granite and Freistadt granodiorite could be very probably explained by later late- and post-Variscan alteration of the Moldanubian batholith, which was connected with Pb-Zn and U-mineralization, which occurs in this region. The allanite grains display in some cases three types of zoning, as revealed in BSE images: (1) oscillatory zoning [1, 24], (2) normal growth-induced magmatic zoning [2, 22], and (3) complicated internal zoning consisting of a patchwork of domains variable in brightness [21]. In allanite grains from diorite 1, complicated

 *+ Fe2+) after* 

*Plot of REE + Y + Th + Mn + Sr. (apfu) vs. Al (apfu) with isolines of the ratio Feox = Fe3+/(Fe3*

*DOI: http://dx.doi.org/10.5772/intechopen.86356*

*Allanite from Granitic Rocks of the Moldanubian Batholith (Central European Variscan Belt) DOI: http://dx.doi.org/10.5772/intechopen.86356*

**Figure 3.**

*Rare Earth Elements and Their Minerals*

**26**

**Figure 2.**

*and Ttn—titanite.*

(0.14–0.32 apfu).

The majority of analyzed allanites represent substitution between ferriallanite

*BSE images of allanite, A—partly altered allanite grain from biotite granodiorite of the Freistadt suite, B—highly altered allanite grain form the Schlieren granite, C and D—zoned allanite grains from the diorite 1, E—allanite grain from the Schlieren granite, and F—allanite grain from microgranodiorite. Aln—allanite, Ap—apatite, Bt—biotite, Ilm—ilmenite, Kfs—K-feldspar, Qz—quartz, Pl—plagioclase,* 

All analyzed allanites display variable concentrations of REE with preference of Ce over La. The Ce is predominant in all analyzed allanite grains over other REE studied here; they are thus identified as allanite-(Ce). The highest concentrations of Ce were found in allanites from diorite 1 (0.31–0.41 apfu). The lowest concentrations of Ce display allanites from the youngest microgranodiorite dykes

and allanite. Only allanites from the microgranodiorites display substitution

between allanite and clinozoisite (**Figure 3**).

*Plot of REE + Y + Th + Mn + Sr. (apfu) vs. Al (apfu) with isolines of the ratio Feox = Fe3+/(Fe3 + Fe2+) after Petrík et al. [21].*

## **6. Discussion**

For allanite, two main substitutions occur, namely the epidote-allanite and the allanite-ferriallanite substitutions [2, 21]. For analyzed allanites from the Weinsberg and Freistadt suites, the allanite-ferriallanite substitution is significant. Similar substitution was found by Petrík et al. [21] in allanites from the I-type granitic rocks of the Sihla tonalite suite in the Western Carpathians. Some highly altered allanite grains which were found in the Schlieren granite (**Figure 2B**) exhibit irregular zonation, which is very similar with the "mushroom-shaped areas" described by Poitrasson [22] from anorogenic granites of Corsica (southeast France). However, in the case of altered allanites from the Schlieren granite, the altered parties are depleted in Si, Ti, Ca, and Th, but enriched in Fe. Some other allanite alteration was found on allanite rims that occurred in the allanite from the Freistadt granodiorite (**Figure 2A**). In this case, the altered allanite rim is enriched in Si, Ti, and Th. Similar enrichment of Th was also found in altered alanites from anorogenic granites of Corsica (southeast France) and in allanites from the Casto granite of Idaho (USA) [22, 23]. Alterations of allanite which were found in allanites from the Schlieren granite and Freistadt granodiorite could be very probably explained by later late- and post-Variscan alteration of the Moldanubian batholith, which was connected with Pb-Zn and U-mineralization, which occurs in this region.

The allanite grains display in some cases three types of zoning, as revealed in BSE images: (1) oscillatory zoning [1, 24], (2) normal growth-induced magmatic zoning [2, 22], and (3) complicated internal zoning consisting of a patchwork of domains variable in brightness [21]. In allanite grains from diorite 1, complicated internal zoning was found (**Figure 2C** and **D**).

The allanite-clinozoisite substitution that is significant for allanite from microgranodiorites occurring in the eastern margin of the Klenov pluton was also found in allanites from epidote-bearing tonalites in the Bell Island pluton, Canada [25].
