Multi analytical approach to the study of Albanian phosphorite deposits in Jurassic and Cretaceous marine carbonate successions

The Mediterranean Phosphogenic Province includes numerous phosphorite deposits within sedimentary successions in North Africa, Southern Europe and the Middle East. (Notholt, 1985). This study investigates three uranium-bearing phosphorite deposits, occurring in the Jurassic to Cretaceous marine carbonate rock succession of Southern Albania, through petrographic, scanning electron microscope (SEM) and X-Ray powder Diffraction (XRD), and EMPA analyses. At Bogaz, uranium-rich phosphorites occur as authigenic fluorapatite cement in the interparticle space of hydraulic or tectonic breccia with clasts of Lower Jurassic (Sinemurian-Pliensbachian) shallow-water peritidal platform carbonates, containing Siphovalvulina foraminifers and Palaeodasycladus mediterraneous dasyclad algae. In Fushëbardha, the lower Toarcian (Lower Jurassic), carbonate facies rich in Bositra-like thin-shelled pelagic bivalves corresponding to the organic matter-rich “Posidonia” Shales of Austria and Germany, alternate with tabular phosphorite deposits. Gusmar deposit consists of pelagic calci-mudstone/wackestone with globotruncarid planktonic foraminifers indicative of Late Cretaceous (probably Coniacian) age, alternating with a few millimeters-thick layers of phosphates. SEM analysis was pivotal in identifying the euhedral morphology of calcium phosphate minerals with hexagonal basal section, often organized in radial spherulites and in confirming the presence of microbial organic remains, such as biofilm extracellular polymeric substances (EPS) and filaments. The formation of phosphorite deposits within pelagic carbonates requires up-welling currents that contribute to increasing primary productivity, organic matter accumulation and expansion of the oxygen minimum zone. This allows the concentration of calcium phosphate associated with organic-rich sediments. Phosphorous and uranium migrate in the first few meters of sediments, from organic matter to pore fluids that precipitate apatite in suboxic conditions. The process described above is valid for the Toarcian Fushëbardha and the Coniacian Gusmar pelagic carbonate deposits both linked to global Oceanic Anoxic Event (OAE). As for the Bogaz fluorapatite in brecciated shallow, platform-interior carbonates, it was determined that a Toarcian or later hydraulic brecciation of the older and underlying Sinemurian-Pliensbachian carbonates was responsible for the formation of this secondary phosphorite deposit. Hydrothermal fluids percolating downwards into the carbonate sequence re-mobilized phosphates higher up in the stratigraphy and re-deposited them while brecciating the host carbonates. This study is one of the first comprehensive investigations of primary sedimentary and secondary diagenetic phosphorites in Southern Albania. References 0 Notholt A.J.G. (1985) – Phosphorite resources in the Mediterranean (Tethyan) phosphogenic province: a progress report. . In: Phosphorites. Sixth International Field-Workshop and Seminar on Phosphorites. I.G.C.P. 156. Maroc-Sénégal, oct.-nov. 1983. Strasbourg : Institut de Géologie – Université Louis-Pasteur, 1985. pp. 9-17. (Sciences Géologiques. Mémoire, 77)