Marfil and 2 co-authors reported in 2013 on their mineralogical and chemical study of an aluminum–phosphate–sulphate (APS) mineralization that occurs in a clastic sequence from the Triassic deposit is constituted by sandstones, mudstones, and conglomerates with arenaceous matrix, which were deposited in fluvial to shallow-marine environments. In addition to APS minerals, the following diagenetic minerals are present in the clastic sequence: quartz, K-feldspar, kaolinite group minerals, illite, Fe-oxides and hydroxides, APS minerals were identified and characterized by optical microscopy, X-ray diffraction, scanning electron microscopy, and electron microprobe.
Microcrystalline APS crystals occur replacing uraniferous minerals, associated with kaolinite, mica and filling pores, in distal fluvial-to-tidal arkoses subarkoses. Given their Ca, Sr, and Ba contents, the Sr and 0.01 Ba). The chemical composition, low LREE concentration and Sr > S suggest that the
APS minerals were formed during the supergene alteration of the Buntsandstein sandstones as indicated by the presence of the mineralizing processes which typically responsible for the development of U-bearing sandstones in a distal alteration area associated with APS minerals indicating that they were precipitated at diagenetic temperatures (higher than 80ºC), related to the uplifting that occurred during the late Cretaceous post-rift thermal stage.
They concluded that Triassic sequence, several units of Buntsandstein sandstones contain important concentrations of APS minerals deposited in secondary
framework minerals. APS minerals were precipitated under diagenetic conditions related to the uplifting occurred during the late Cretaceous post-rift thermal stage at high diagenetic temperatures, suggested by the presence of dickite in the studied samples of APS minerals that occurred in barren sandstones of the distal zones of alteration with low LREE contents, and related to some tectonic event responsible for the introduction of mineralizing ground water into the buried sediments.
The intergranular clay matrix composed of kaolinite, illite and the feldspars constituted the main Al source, whereas secondary uranium minerals and apatite were the most probable P sources. Fluids migrating from the Permian evaporitic formations, or, more probably, from the overlying Keuper evaporitic facies can account for the Ca, S and Sr contents.
Based on their chemical composition, the APS minerals have been defined as a solid solution of crandallite-goyacite-gorceixite
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