Geochemical diagenetic trends during phosphorite formation – economic implications: The case of the Negev Campanian phosphorites, Southern Israel

Abstract

Research on the Upper Campanian (Upper Cretaceous) Negev phosphorites (Mishash Formation), based on microprobe analyses, Fourier Transform Infrared spectroscopy, wet chemistry, microtextural (Scanning Electron Microscopy) studies and mineralogical analyses, together with quantified rates of sedimentation and P accumulation, enables the chemistry of these rocks to be better constrained across the Negev area and allows their suitability for the manufacture of P fertilizers to be better determined. Two phosphorite facies are differentiated: (i) a pristine phosphorite facies of low P content, more typical of basinal sections and (ii) a reworked, granular phosphorite facies commonly enriched in P, found predominantly near palaeo‐highs and forming most of the economic phosphates. The distribution of F/P2O5, CO2/F, U(IV), Cd, Zn and other trace metals (Mo, Ni, Cr, Cu, V and Y), rare‐earth elements concentration, Ce and Eu anomalies and heavy rare earth elements enrichment, are controlled by these two facies. F/P2O5 in carbonate‐fluorapatite is much lower (0·090 to 0·107) in the pristine than in the reworked facies (0·107 to 0·120); in addition, the lower F/P2O5 in the pristine facies is coupled with: (i) higher Cd, Zn, Mo, Ni, Cr, Cu and V concentrations; (ii) a considerably reduced (< 10%) U(IV) fraction of total U; (iii) lower rare earth elements/P2O5 and Y/P2O5 ratios; (iv) less negative Ce and Eu anomalies and lower heavy rare earth elements (Lu/La) enrichment; (v) an increase in Fe‐rich smectites in the clay fraction; and (vi) presence of OH in the carbonate‐fluorapatite structure. Sedimentary reworking of previously formed pristine phosphate, together with its redeposition near structural highs in more oxic bottom conditions, results in considerable diagenetic changes in the chemistry of the phosphorites, making them more suitable for economic exploitation. The results presented here provide geochemical criteria for identifying pristine phosphate in other phosphorite sequences and may help to better locate phosphate strata chemically suitable for the phosphate industry elsewhere.

The Moroccan High Atlas phosphate-rich sediments: Unraveling the accumulation and differentiation processes

“…The presence of phosphate peloids and the scarcity of detrital particles suggest the formation in relatively distal parts of the platform away from terrigenous inputs. Hence, we interpret these phosphatic marls to have formed pristinely in the outer platform, below the storm wavebase, where phosphatic peloids were precipitated authigenically in pore water microsystems at the water-sediment interface (Föllmi, 1996;Glenn et al, 1994;Pufahl and Groat, 2017;Soudry et al, 2013;Zhang et al, 2019). This phosphogenesis process requires the conjunction of many biochemical conditions to occur, including: i) the availability of phosphorus and its release from the organic matter to pore water by bacterial mediation (Diaz et al, 2008;Krajewski et al, 1994), ii) the availability of fluorine (F), and iii) the pumping of Mg from pore water in order to precipitate the francolite by supersaturation of P (Jarvis et al, 1994, Glenn 1994).…”

“…Despite their critical role in the phosphate accumulation, these post-phosphogenesis agents remained understudied. Phosphate-rich sediments are traditionally subdivided into primary and reworked facies (e.g., Trappe, 1998, Follmi 1996, 2016Glenn et al, 1994;Soudry et al, 2013;Pufahl and Groat 2017). Primary or pristine phosphate refers to phosphatic fine sediments preserved in their initial state without undergoing transport or reworking.…”

Phosphorus resources, their depletion and conservation, a review

“…In recent decades the average P content of mined phosphate resources has shown a declining trend (Abouzeid, 2008;Ford and O'Connor, 2009;Dawson and Hilton, 2011;Cooper et al, 2011;Filippelli, 2011). Given current ways of phosphoric acid production, high levels of CaO, carbonate, organic matter, Mg, S, F, lanthanides, heavy metals and radionuclides (such as uranium and thorium) are considered to negatively affect resource quality (Abdel-Khalek et al, 2008;Mar and Okazaki, 2012;Soudry et al, 2013).…”

“…Casanova, 1995). Regarding more than 95% of fossil P use, which is mainly as fertilizer but also in other applications, industrial treatments with acid are applied to de-sequester phosphate from phosphate ore (Van Kauwenberg, 2010;Childers et al, 2011;Soudry et al, 2013), though it is also conceivable to desequester phosphate by the use of micro-organisms, which excrete organic acids or chelators (Vassilev et al, 2001;Hamdali et al, 2008) or make use of reductive dissolution (Jaisi et al, 2011).…”

Sedimentology and stratigraphy sequence of the north of Saudi Arabia: Implications for the evolution of the Neo‐Tethys in the Late Cretaceous

“…The transgression proved to be vigorous in the Late Cretaceous in the north of AP (Robertson et al, 2016; Simmons et al, 2007), and created a wide phosphorite province (Figure 1). Jordan and Israel to the north of the Saudi Arabia are the depositional centre, where accumulated a large thickness of phosphorite (e.g., Abed & Amireh, 1999; Pufahl, Grimm, Abed, & Sadaqah, 2003; Soudry, Nathan, & Ehrlich, 2013; Figure 1). The research area in the north of Saudi Arabia is located in the southern margin of the phosphorite province (Figure 2a).…”