**2. Geological setting**

The Central Bohemian plutonic complex is a large composite magmatic body that occurred in the central part of the Bohemian Massif between Prague and Klatovy. This plutonic complex represents according to its mineralogical and geochemical compositions the most fractionated Variscan magmatic body in the Bohemian Massif (**Figure 1**). The most widespread rock types that occurred in this complex are amphibole-biotite granodiorites accompanied by biotite granites, tonalites, and melagranites (durbachites) [1–3]. The Blatná suite occurred in the south-west part of magmatic complex is formed by the Blatná hornblende-bearing biotite granodiorites and the Červená hornblende-biotite granodiorites. Other petrographic varieties of the Blatná suite are the Klatovy and Kozárovice granodiorites and tonalites occurring in the southwestern part of the Central Bohemian magmatic complex (**Figure 1**). The Blatná granodiorites intruded during the Variscan magmatic event (346.7 1.6 Ma, U/Pb TIMS analyses on zircon) [2].

*Geologic map of the Central Bohemian Plutonic complex, modified from [1].*

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

## **3. Materials and methods**

Detailed mineralogical and geochemical investigations of the Blatná and Červená granodiorites were carried out on a representative suite of the 37 rock samples which were taken predominantly from boreholes performed by the Czechoslovak Uranium industry (ČSUP, recently DIAMO) during their exploration activities (1978–1989) in this area [4, 5]. The contents of major elements were determined by a standard XRF method, using the Philips PW 1410 spectrometer at the Geochemical laboratories of the Czechoslovak Uranium Industry (Stráž under Ralsko, Northern Bohemia). The FeO content was measured via titration, whereas the H2O content was determined gravimetrically. The contents of selected trace elements were determined also by a standard XRF method, using the Philips PW 1410 spectrometer at the chemical laboratory of the Unigeo Brno Ltd. in Brno, Moravia. The content of U and Th was determined by gamma spectrometry using a multichannel spectrometer at Geophysics Brno Ltd., also in Brno, Moravia. The content of REE was quantified by inductively coupled plasma mass spectrometry (ICP MS) at Activation Laboratories Ltd., Ancaster, Canada, using a Perkin Elmer Sciex ELAN 6100 ICP mass spectrometer, following standard sample preparation procedures involving lithium metaborate/tetraborate fusion and acid decomposition. All chemical analyses were calibrated against international reference materials.

Approximately 140 quantitative electron microprobe analyses of apatite, zircon, allanite, titanite, and selected rock-forming minerals (plagioclase, K-feldspar, and biotite) were collected from representative samples of the Blatná suite. All these minerals were analyzed in polished thin sections. The back-scattered electron (BSE) images were acquired to study the internal structure of mineral aggregates and individual mineral grains. The abundances of all chemical elements were determined using a CAMECA SX 100 electron probe micro-analyzer (EPMA) operated in wavelength-dispersive mode at the Department of Geological Sciences, Masaryk University in Brno. The accelerating voltage and beam currents were 15 kV and 20 or 40 nA, respectively, and the beam diameter was 1–5 μm. The peak count time was 20 s, and the background time was 10 s for major elements. For the trace elements, the times were 40–60 s on the peaks, and 20–40 s on the background positions. The following standards, X-ray lines and crystals (in parentheses), were used: AlKα, sanidine (TAP); CaKα, fluorapatite (PET); CeLα, CePO4 (PET); ClKα, vanadinite (LPET); DyLα, DyPO4 (LLIF); ErLα, ErPO4 (PET); EuLβ, (LLIF); FKα, topaz (PC1); FeKα, almandine (LLIF); GdLβ, GdPO4 (LLIF); HfMα, Hf (TAP); KKα, sanidine (TAP); LaLα, LaPO4 (PET); MgKα, Mg2SiO4 (TAP); MnKα, spessartine (LLIF); NaKα, albite (PET); NbLα, columbite, Ivigtut (LPET); NdLβ, NdPO4 (LLIF); PKα, fluorapatite (PET); PbMα, vanadinite (PET); PrLβ, PrPO4 (LLIF); RbLα, RbCl (LTAP); SKα, SrSO4 (LPET); ScKα, ScP5O14 (PET); SiKα, sanidine (TAP); SmLβ, SmPO4 (LLIF); SrLα, SrSO4 (TAP); TaMα, CrTa2O6 (TAP); TbLα, TbPO4 (LLIF); ThMα, CaTh(PO4)2 (PET); TiKα, anatase (PET); UMβ, metallic U (PET); VKβ, vanadinite (LPET); YLα, YPO4 (PET); YbLα, YbPO4 (LLIF); and ZrLα, zircon (TAP). The raw data were corrected using the PAP matrix corrections [6]. The detections limits were approximately 400–500 ppm for Y, 600 ppm for Zr, 500–800 ppm for REE, and 600–700 ppm for U and Th.

Apatite structural formula was calculated on the basis of 13 oxygen. The calculation of mineral formulas for end-member F-, Cl, and OH-apatites was performed according to Piccoli and Candela [7]. The formula of titanite was calculated on the basis of 1 Si as suggested by Harlov et al. [8]. Allanite formula was calculated on the basis of 12.5 oxygen and eight cations per formula using WinEpclas software developed by Yavuz and Yildirim [9].
