**4. Results**

### **4.1 Petrology of the Blatná suite**

Granitic rocks of the Blatná suite are formed by the Blatná hornblende-bearing biotite granodiorites and the Červená hornblende-biotite granodiorites. The Blatná granodiorites are medium-grained, usually equigranular rocks. Major components of these granodiorites are biotite (12–18 vol.%) formed by phlogopite-eastonite (Fe/ Fe + Mg 0.48–0.51, Al4+ 2.4–2.6 apfu (atoms per formula unit), Ti 0.20–0.43 apfu), plagioclase (An23–31) (40–42 vol.%), quartz (25–28 vol.%), K-feldspar (10–17 vol.%), and magnesiohornblende (0.2–0.7 vol.%) (**Figure 2**). The relatively rarely occurring porphyric variety contains K-feldspar phenocrysts, up to 1–2 cm big. Accessory minerals are represented by apatite, zircon, magnetite, titanite, and rare allanite.

The Červená granodiorites are medium-grained, equigranular to slightly porphyritic rocks, containing biotite (15–17 vol.%) formed by eastonite (Fe/Fe + Mg 0.44– 0.47, Al4+ 2.5–2.6 apfu, and Ti 0.28–0.38 apfu), plagioclase (An22–40) (28–41 vol.%), quartz (22–23 vol.%), K-feldspar (9–19 vol.%), and 1–2 vol.% hornblende (magnesiohornblende, actinolite) (**Figure 3**). Accessory minerals are represented by apatite, zircon, titanite, magnetite, and allanite. The Červená granodiorites display, in some cases, a strong planar fabric.

## **4.2 Chemical composition of the Blatná suite**

The representative chemical analyses of the Blatná suite are presented in **Table 1**. These granodiorites are high-K, calc-alkaline to shoshonitic, and metaluminous to slightly peraluminous rocks (A/CNK = mol. Al2O3/(CaO + Na2O+K2O)) = 0.8–1.2. Compared to the common I-type granites [10, 11], these granodiorites are enriched in

### **Figure 2.**

*Microphotograph of the Blatná granodiorite (Bt, biotite; Kfs, K-feldspar; Pl, plagioclase; Qz, quartz). Crossed polarizers.*

*Investigation of Accessory Minerals from the Blatná Granodiorite Suite, Bohemian… DOI: http://dx.doi.org/10.5772/intechopen.102628*

### **Figure 3.**

*Microphotograph of the Červená granodiorite (Bt, biotite; Kfs, K-feldspar; Pl, plagioclase; Qz, quartz). Crossed polarizers.*

Mg (1.0–3.4 wt.% MgO), Ba (838–2560 ppm), Sr. (257–506 ppm), Zr (81–236 ppm), Th (2–32 ppm), and U (2–15 ppm).

### **4.3 Accessory minerals association and textures**

The REE-, Zr-, and Y-bearing accessories in granodiorites of the Blatná suite are represented by apatite, zircon, and relatively rare occurred titanite and allanite. Apatite occurs usually in form of euhedral and subhedral grains (20–50 μm, rarely up to 100–120 μm) (**Figure 4**). Zircon usually occurs as small euhedral and subhedral grains (10–15 μm, rarely 50–70 μm). Both minerals are usually enclosed in biotite flakes. Apatite and zircon are sometimes zoned (**Figures 5** and **6**). Titanite occurs in relatively bigger, 100–200 μm, subhedral to euhedral grains (**Figure 7**). Allanite grains are 200–600 μm large, usually euhedral, interstitially grown between major mineral phases in the granodiorite groundmass (**Figure 8**). Its grains sometimes exhibit complex growth/alteration textures (**Figure 9**).

### **4.4 Apatite composition**

All analyzed apatites contain more F (3.0–4.5 wt.%) and less Cl (0.0–0.2 wt.%) (**Table 2**). Their content of Fe (0.02–0.27 wt.% FeO) and Mn (0.02–0.12 wt.% MnO) are low. Their contents of sulfur and natrium are also low (0.01–0.28 wt.% SO3, 0.01–0.09 wt.% Na2O). The concentrations of U and Th in analyzed apatite are low (0.01–0.09 wt.% UO2, 0.01–0.05 wt.% ThO2). The concentrations of REE and Y are usually under microprobe detection limits. In analyzed apatite, grains were found La/Y ratios from 0.0 to 0.4. Zonation of analyzed apatites, that could be observed in the backscattered images (BSE) is very rare and is coupled with different concentrations of Y and REE. Light parties of analyzed apatite grain are enriched in Y (0.31 wt. % Y2O3) and REE (0.13 wt.% Ce2O3) (**Figure 5**).


**Table 1.** *Representative chemical analyses of granodiorites.*
