The carbonate-dominated Mesozoic sequence of the Transdanubian Mountain Range contains Triassic, uranium-enriched phosphorite layers and Cretaceous, REE-enriched nodular phosphorite. Detailed investigation of these deposits may have an economic benefit because of their large U and REE contents. The dominant minerals in the Triassic phosphorite are carbonate-bearing fluorapatite (CFA) and calcite. According to the electron-probe microanalysis (EPMA) the U is mainly associated with the CFA crystals. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) measurement shows that CFA contains 137–612 ppm U and 113–261 ppm total REE + Y. The LA-ICP-MS U-Pb age of the uppermost phosphorite horizon is 237 ± 11 Ma, which conforms with the stratigraphic age of the host limestone.The Cretaceous nodular phosphorite occurs on the base of an Aptian crinoid-bearing limestone mostly in the form of encrustations around bio- and silicic-clasts, but the clasts also contain phosphorite. The main minerals in these crusts are CFA, calcite, quartz, glauconite and Fe-oxide-hydroxides. Based on EPMA the REE enrichment is related to CFA and LA-ICP-MS measurements show that it contains 748–2953 ppm total REE + Y.The redox-sensitive proxies and the shape of NASC normalized REE patterns indicate that both phosphorites formed in anoxic environments. There are significant differences between these deposits such as appearance, rock-forming minerals, and U and REE contents which indicate differences in their sedimentary environments. The present results suggest that the Triassic phosphorite was formed by inorganic precipitation in a reducing environment close to sea-mounts. The Cretaceous occurrence resulted from a concentric growth mechanism in cold, ascending seawater at the continental margin environment during the anoxic Selli Event (OAE 1a) and/or Paquier Episode (OAE 1b). The critical raw material contents were derived from other sources.

western Neotethys margin, regional factors such as the establishment of an extensional tectonic regime and related marginal basin formation, monsoon-driven upwelling, and related high surface water productivity seem to be of critical importance in controlling the depositional conditions.

The middle Anisian extensional tectonics of the Neotethyan realm developed a small, isolated carbonate platform in the middle part of the Balaton Highland (western Hungary), resulted in the deposition of uranium-bearing seamount phosphorite on the top of the drowned platform and produced some epigenetic fluorite veins in the Middle Triassic sequence. The stable C-O isotope data of carbonates are shifted from the typical Triassic carbonate ranges, confirming the epigenetic-hydrothermal origin of veining. Primary fluid inclusions in fluorite indicate that these veins were formed from low temperature (85–169 °C) and high salinity NaCl + CaCl2 + H2O type (apparent total salinity: 15.91–22.46 NaCl wt%) hydrothermal fluids, similar to parent fluids of the Alpine-type Pb-Zn deposits. These findings indicate that the Triassic regional fluid circulation systems in the Alpine platform carbonates also affected the area of the Balaton Highland. This is also in agreement with the previously established palinspatic tectonic reconstructions indicating that the Triassic carbonate and basement units in the Balaton Highland area were a part of the Southern Alpine. Similar fluorite veining in phosphorite deposits is also known in the Southern Alpine areas (e.g., Monte San Giorgi, Italy). Raman spectroscopic analyses detected H2 gas in the vapor phase of the fluid inclusions and a defect-rich fluorite structure in violet to black colored growth zones. This unique phenomenon is assumed to be the result of interaction between the uranium-rich phosphorite and the parent fluids of the epigenetic fluorite veins.