Carbonate Fluorapatite Research Articles

Electron microscopy study on the formation of ferromanganese crusts, western Pacific Magellan Seamounts

Variations in mineralogy and chemical composition, layer structures, redox states of Fe and Mn, and microbial diversity are closely linked to the biogeochemical process when a ferromanganese crust layer forms. A sample collected from the Magellan Seamount (OSM11), in the western Pacific, was characterized in five well-defined layers, top to bottom (L1–5). Fe-vernadite occurs in all layers, compared to detritus quartz, feldspar, goethite, and hematite in L1 and L3, and carbonate fluorapatite (CFA) in L4–5. The relatively high concentrations of Ca and P in L4–5, and Fe, Co, and Si in L1 and L3 correspond to the mineralogical variations in the crust layer. Disappearance of elongated voids along the convex growth line is likely due to void filling precipitation of CFA in L4–5, resulting in the void reduction (31.6 to 6.0%). The oxidation states of Fe in Fe-vernadite measured by electron energy loss spectroscopy (EELS) ranges from 36 to 63% of Fe3+/Fetot, and a layer where CFA appeared (L4) contains a more reductive form of Fe (Fe3+/Fetot = 36–48%). Presence of Fe- (coxC) and Mn-oxidizing gene (cumA), particularly displaying a strong PCR band of coxC in L2–3, indicates a dominant oxidizing condition. Direct evidence of microbial activity in Fe - and Mn-oxide precipitation with various redox conditions was identified in the focused ion beam-sectioned microfossil. Particularly, a spectrum image displaying a more reducing form of Fe around the voids previously occupied by microorganisms, strongly supports that microorganisms play an important role in the redox reaction in the growth of a crust.

Efficient removal of Sr ions from water utilizing a novel Ni-/Fe-doped spongy apatite through fixed bed column system: optimization and realistic application

The removal of strontium metal ions from aqueous solutions and raw groundwater using synthetic spongy apatite was studied based on the experimental parameters of the continuous fixed bed column system. Novel Ni-/Fe-doped spongy apatite of carbonate fluorapatite composition was synthesized as an effective adsorbent and ion exchanger bed of high adsorption capacity for strontium ions in water. Based on the mathematical parameters, the best removal percentage of strontium (83.7%) from aqueous solutions was obtained after treatment of 6.6 L at optimum conditions of pH6, 3 cm bed height, 5 mL/min flow rate and 15 mg/L initial concentration. Under the previous conditions, the breakthrough time was attained after 1200 min. The total amount of adsorbed strontium in the column system is about 1446 mg, and the equilibration uptake capacity of spongy apatite is about 347.8 mg/g within the limitations of the studied parameters. The regeneration studies reflected the suitability of spongy Ni-/Fe-doped carbonate fluorapatite to be used effectively for five cycles in the removal of strontium contaminants. The operating adsorption mechanisms and the column performance were addressed based on Thomas, Adams–Bohart and Yoon–Nelson mathematical kinetic models. Ni-/Fe-doped spongy apatite column system was applied in a realistic purification of groundwater samples from strontium pollutants in Quseir area, Egypt (Wadi El Nakheil well and Wadi El Ambagi spring). The obtained results reflected the efficiency of the synthetic material in the decontamination of strontium ions and other metal ions from raw water.

Microbial communities associated with phosphogenic sediments and phosphoclast‐associated DNA of the Benguela upwelling system

The processes that lead to the precipitation of authigenic calcium phosphate minerals in certain marine pore waters remain poorly understood. Phosphogenesis occurs in sediments beneath some oceanic upwelling zones that harbor polyphosphate-accumulating bacteria. These bacteria are believed to concentrate phosphate in sediment pore waters, creating supersaturated conditions with respect to apatite precursors. However, the relationship between microbes and phosphorite formation is not fully resolved. To further study this association, we examined microbial community data generated from two sources: sediment cores recovered from the shelf of the Benguela upwelling region where phosphorites are currently forming, and DNA preserved within phosphoclasts recovered from a phosphorite deposit along the Benguela shelf. iTag and clone library sequencing of the 16S rRNA gene showed that many of our sediment-hosted communities shared large numbers of phylotypes with one another, and that the same metabolic guilds were represented at localities across the shelf. Sulfate-reducing bacteria and sulfur-oxidizing bacteria were particularly abundant in our datasets, as were phylotypes that are known to carry out nitrification and the anaerobic oxidation of ammonium. The DNA extracted from phosphoclasts contained the signature of a distinct microbial community from those observed in the modern sediments. While some aspects of the modern and phosphoclast communities were similar, we observed both an enrichment of certain common microbial classes found in the modern phosphogenic sediments and a relative depletion of others. The phosphoclast-associated DNA could represent a relict signature of one or more microbial assemblages that were present when the apatite or its precursors precipitated. While these taxa may or may not have contributed to the precipitation of the apatite that now hosts their genetic remains, several groups represented in the phosphoclast extract dataset have the genetic potential to metabolize polyphosphate, and perhaps modulate phosphate concentrations in pore waters where carbonate fluorapatite (or its precursors) are known to be precipitating.

Phosphatized tungsten-metabolizing coccoid microbes interpreted from oil shale of an Eocene lake, Green River Formation, Utah, USA.

Microscopic globular structures have been observed in some beds of oil shale from eastern Utah. These beds comprise carbonate-dominated mud that is interlaminated with variably thick and continuous organic-rich layers. Collectively they are enriched in phosphorus, REEs, and actinides. The beds are considered of lacustrine origin and assigned to the Eocene Green River Formation. The globules themselves are of microcrystalline carbonate fluorapatite (μCFA), often contain concentric internal structures, and usually group together in clusters of up to 80, possibly more. Detailed SEM and microprobe analyses have revealed tungsten (W) to be almost exclusively associated with the globular clusters found within the more organic-rich laminae, often at concentrations of over 200ppm, two orders of magnitude above shale standards. The globular structures are present in freshly cut sections where they occasionally grade into a μCFA matrix cement. This, together with the draping of the clusters by stringers of organic matter that would have accumulated in the Eocene lake, confirms that the structures are not a contaminant. The limited range of sizes and globular shapes is consistent with the morphology of coccoidal bacteria: Concentric internal structures may represent remnants of the nucleoid and cell wall. Paired concentric structures may indicate cell division (reproduction) processes were occurring until mineralization. The phosphate mineralization itself may have been promoted by release of phosphate from the stressed cells, bringing porewaters to supersaturation, or by the cells acting as nucleation sites. The recording of trace amounts of W almost exclusively in globular clusters preserved in the most organic-rich stringers (anoxia prone) further suggests facultative use of W-enzymes in a microbial metabolism. Combined, their context, morphology, and indication of biogenic process are strong evidence that the structures are fossilized (phosphatized) microbes, possibly sulfate-reducing bacteria, or methanogenic archaea.

Diagenetic evolution of the upper Devonian phosphorites, Alborz Mountain Range, northern Iran

The upper Devonian, mixed siliciclastic‑carbonate stratigraphic succession of the Geirud Formation in the Alborz Mountain Range, north of Iran, hosts numerous phosphorites and phosphatic rocks. These phosphorites, which represent one of the most globally important deposits in the Devonian, have gained little attention regarding their genesis and diagenetic evolution. This study focuses mainly on the post-depositional changes that occurred during shallow to deep burial diagenetic evolution and subaerial weathering of the Geirud phosphorites. The phosphorites consist of phosphatic massive mudclasts, detritus-rich lithoclasts, bioclasts and bones formed by several stages of phosphogenesis and erosion, reworking, winnowing and condensation associated with Famennian sea level changes. The phosphatic clasts consist of early diagenetic, poorly crystalline, carbonate fluorapatite (CFA) and pyrite cementing detrital quartz, illite, muscovite, rutile and zircon. Phosphatic clasts are intensely compacted with sutured grain contacts, along which dissolution and reprecipitation of chemically-refined, well crystalline CFA with a bright blue cathodoluminescence and illite occurred during deep burial diagenesis. Similarly, quartz shows deformation planar features; overgrowth cement was developed as a result of pressure dissolution in phosphatic sandstones, followed by precipitation of ferroan dolomite, ankerite and chlorite in secondary porosity. Subaerial weathering led to oxidation of pyrite and generation of acidic pH condition, under which Ca and P from phosphates, Fe and S from pyrite, Fe, Ca, Mg and Mn from ferroan carbonates and Al and Si from aluminosilicates were released to form goethite, psilomelane, calcite, gypsum and crandallite.The PAAS-normalized rare earth elements (REEs) show bell-shaped patterns with middle (REEs) enrichment, positive Eu anomaly and a weak negative Ce anomaly. This implies recrystallization of CFA in phosphorites and phosphatic rocks during deep burial diagenesis, deviating from the modern seawater-like REE patterns. In this regard, deep burial diagenesis affecting the upper Devonian Geirud phosphorites is possibly a common process in the Proterozoic-Paleozoic phosphorites in northern Iran and elsewhere in the world.

Authigenesis of biomorphic apatite particles from Benguela upwelling zone sediments off Namibia: The role of organic matter in sedimentary apatite nucleation and growth.

Sedimentary phosphorites comprise a major phosphorus (P) ore, yet their formation remains poorly understood. Extant polyphosphate-metabolizing bacterial communities are known to act as bacterial phosphate-pumps, leading to episodically high dissolved phosphate concentrations in pore waters of organic-rich sediment. These conditions can promote the precipitation of amorphous precursor phases that are quickly converted to apatite-usually in carbonate fluorapatite form [Ca10 (PO4 ,CO3 )6 F2-3 ]. To assess the mechanisms underpinning the nucleation and growth of sedimentary apatite, we sampled P-rich sediments from the Namibian shelf, a modern environment where phosphogenesis presently occurs. The P-rich fraction of the topmost centimetres of sediment mainly consists of pellets about 50-400μm in size, which in turn are comprised of micron-sized apatite particles that are often arranged into radial structures with diameters ranging from 2 to 4μm, and morphologies that range from rod-shapes to dumbbells to spheres that resemble laboratory-grown fluorapatite-gelatin nanocomposites known from double-diffusion experiments in organic matrices. The nucleation and growth of authigenic apatite on the Namibian shelf is likely analogous to these laboratory-produced precipitates, where organic macromolecules play a central role in apatite nucleation and growth. The high density of apatite nucleation sites within the pellets (>109 particles per cm3 ) suggests precipitation at high pore water phosphate concentrations that have been reported from the Namibian shelf and may be attributed to microbial phosphate pumping. The intimate association of organic material with the apatite could suggest a possible role of biological substrata, such as exopolymeric substances (EPS), in the nucleation of apatite precursors. Importantly, we do not observe any evidence that the apatite particles are actual phosphatized microbes, contradicting some earlier studies. Nevertheless, these results further evidence the potential importance of microbially derived (extracellular) organic matter as a template for phosphatic mineral nucleation in both recent and ancient phosphorites.

Phosphorus dynamics around the sulphate-methane transition in continental margin sediments: Authigenic apatite and Fe(II) phosphates

The formation of authigenic phosphate minerals in marine sediments is an important process for the burial and long-term storage of the bio-essential nutrient phosphorus (P). In this context, we report the composition of pore waters, bulk sediments, and the speciation of P in four sediment cores recovered on the continental margins off the Amazon, Rio de la Plata and Zambezi rivers. Here, pronounced sulphate-methane transitions (SMTs) occur between 4.5 and 6.5 m sediment depth where sulphate is consumed by the anaerobic oxidation of methane and free hydrogen sulphide builds up in the pore waters. This leads to the reductive dissolution of primary Fe (oxyhydr)oxides (FeOx) by hydrogen sulphide, and the subsequent liberation of FeOx-adsorbed phosphate into pore waters at the SMT. The released phosphate builds up to significant concentrations, making it available for the precipitation of authigenic minerals within and below the SMT. Using a sequential P extraction, we find consistently high contributions of carbonate fluorapatite (CFA) to the total P pool within the SMT, where it likely precipitates due to high local phosphate concentrations, high alkalinity and abundant dissolved Ca in the pore waters. PHREEQC calculations confirm these results, with highest saturation states with respect to authigenic apatite calculated at all SMTs. CFA authigenesis, however, is insufficient to completely consume pore water phosphate, leading to diffusive loss of phosphate from the SMT. While the upward decrease in phosphate above the SMT is relatively gentle, the significantly steeper phosphate gradient into underlying sediments suggests the formation of another authigenic mineral phase. Sequential P extraction and PHREEQC results clearly show that the dominant authigenic phase below the SMT is not CFA. Instead, geochemical conditions below the sulphidic zone at all four sites are favourable for the precipitation of Fe(II) phosphate minerals (e.g., vivianite). These conditions are summarized as the absence of sulphate and free hydrogen sulphide, but the presence of Fe2+ and phosphate in pore waters, and low calcium carbonate contents in the sediment. While we did not directly detect or quantify Fe(II) phosphate minerals, Fe-bound P clearly increases in the sediments below the sulphidic zones at all studied sites, and this is where highest pore water saturation states with respect to vivianite are calculated with PHREEQC. In addition, geochemical inverse models performed in PHREEQC show that vivianite formation is an important geochemical process controlling the observed patterns of dissolved P and Fe, pH and redox potential of the pore waters analysed below the SMT. We therefore argue that Fe(II) phosphate minerals are formed in these ocean margin sediments on a large scale, and pore water and sediment data indicate that this Fe-bound P largely originates from FeOx-adsorbed phosphate liberated within the sulphidic SMT. This study suggests that under specific but not unusual depositional conditions, SMTs are hotspots for biogeochemical P cycling in marginal marine sediments worldwide, with CFA precipitating within the SMT, and Fe(II) phosphates forming below it. It also adds to the growing evidence that Fe(II) phosphates may contribute significantly to the long-term burial of reactive P phases in Fe-rich, methanic marine sediments, and thus act as a previously underestimated sedimentary P sink.

A geochemical approach to fossilization processes in Miocene vertebrate bones from Sahabi, NE Libya

In the present paper a multi-technique approach was followed in order to study the diagenetic alterations of fifteen fossil bones derived from the Miocene site of Sahabi in NE Libya. Specifically, X-ray Diffraction (XRD) supplemented by the Rietveld method, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDS), Electron Probe Microanalysis (EPMA) and Fourier Transform Infrared Spectroscopy in the Mid-IR (FTIR, Mid-IR), were performed on fossilized bone fragments belonging mainly to artiodactyl mammals. From the qualitative observation of bone histology by means of SEM, a moderate preservation of the internal bone morphology and limited microbial attack were inferred. The high percentage (wt.%) of F concentration that the EPMA analyses yielded, combined: (a) with the absorbance bands of carbonate anions in the FTIR spectra and (b) the structural parameters calculated by the Rietveld method, revealed the partial substitution of F− for OH− and CO32− for PO43− in the apatite structure. As a result, one of the basic diagenetic trends was the preservation of the inorganic part of the studied samples as carbonate fluorapatite. Additionally, according to our infrared spectra, CO32− substituted for OH− and a carbonate species known to be labile was also present. Apart from F, EPMA also detected S and Fe. Sulfur speciation was studied by micro-XANES, that confirmed the presence of S6+ (sulfates). Iron speciation was investigated with Mössbauer spectroscopy, which indicated the possible presence of goethite-type (FeOOH) submicroscopic inclusions. In nearly all specimens, quartz and gypsum were identified as the main secondary phases.

REEs and U distribution in P-rich nodules from Gelasian Apulian Tethyan carbonate: A genetic record

In the Tethyan realm the carbonate-dominated Meso-Cenozoic South Tethyan Phosphogenic Province is of considerable economic importance since it represents the greatest accumulation of sedimentary phosphorites. In southern Italy, in the Salentine peninsula (the southern part of the Apulian Carbonate Platform, ACP), is well documented the occurrence of Cenozoic P-rich levels consisting of nodules and pebbles and showing a large P2O5 fluctuation (4.07–22.07 wt%), due to variable calcite abundance. The mainly observed P-bearing minerals are hydroxyapatite and carbonate fluorapatite and U, together with Sr and Pb, preferentially acts as Ca substitutes in both lattices. Minor authigenic monazite (LREE-bearing phosphate) and xenotime (HREE+Y-bearing phosphate), likely formed during sediment burial compaction and diagenesis. The total REEs' abundances and the shape of the shale-normalized REE-patterns in the P-rich nodules are in the range of those typically observed in Paleocene-Eocene through Pleistocene-Recent P-rich sediments, supporting the idea of a broadly consistent ocean chemistry in this span of geological time. The (La/Yb)N proxy is within the modern seawater range, signifying early diagenetic adsorption played only a minor role in affecting the REEs' distribution. The Ce and Pr anomalies suggest some P-rich nodules experienced very localized hypoxic to anoxic conditions promoting Ce/Ce* spurious results in a generally oxic to hypoxic environment causing real negative Ce anomaly. This scenario is reinforced by the lack of the coupled uranium-vanadium enrichment typically observed in an anoxic environment. Since the Pliocene the eastern Mediterranean was variously affected by oxygenation and productivity and it is likely the ACP phosphate-rich sediments formed under low sedimentation rates and authigenesis in a bottom current-dominated regime, as also indicated by the glauconite occurrence. Transgressions and sea levels rising following major glaciations may have favored the deposition of phosphate sediments by creating new restricted basin configurations and increased nutrient input promoted by upwelling processes.

High-Resolution Analysis of Critical Minerals and Elements in Fe–Mn Crusts from the Canary Island Seamount Province (Atlantic Ocean)

Two Fe–Mn crusts among 35 samples, from six seamounts in the Canary Island Seamount Province, were selected as representatives of the endpoint members of two distinct types of genetic processes, i.e., mixed diagenetic/hydrogenetic and purely hydrogenetic. High-resolution analyses pursued the main aim of distinguishing the critical elements and their association with mineral phases and genetic processes forming a long-lived Fe–Mn crust. The Fe–Mn crust collected on the Tropic Seamount is composed of dense laminations of Fe-vernadite (>90%) and goethite group minerals, reflecting the predominance of the hydrogenetic process during their formation. Based on high-resolution age calculation, this purely hydrogenetic crust yielded an age of 99 Ma. The Fe–Mn crust collected on the Paps Seamount shows a typical botryoidal surface yielding an age of 30 Ma. electron probe microanalyzer (EPMA) spot analyses show two main types of manganese oxides, indicating their origin: (i) hydrogenetic Fe-vernadite, the main Mn oxide, and (ii) laminations of interlayered buserite and asbolane. Additionally, the occurrence of calcite, authigenic carbonate fluor-apatite (CFA) and palygorskite suggests early diagenesis and pervasive phosphatization events. Sequential leaching analysis indicated that Co, Ni, Cu, Ba and Ce are linked to Mn minerals. Therefore, Mn-oxides are enriched in Ni and Cu by diagenetic processes or in Co and Ce by hydrogenetic processes. On the other hand, Fe-oxides concentrate V, Zn, As and Pb. Moreover, the evidence of HREE enrichment related to Fe-hydroxides is confirmed in the mixed hydrogenetic/diagenetic crust.

Volcanic and hydrothermal activities recorded in phosphate nodules from the Lower Cambrian Niutitang Formation black shales in South China

Deposition of black shale of the Lower Cambrian Niutitang Formation (NTT) of the Yangtze Block, South China, in association with the Ediacaran-Cambrian (E-C) transition was accompanied by widespread formation of phosphate nodules. Petrological and geochemical studies of the nodules and host sedimentary rocks were carried out to elucidate hydrographic conditions of the Early Cambrian ocean. Our results reveal that NTT phosphate nodules are composed principally of concentrically banded carbonate fluorapatite (CFA) that likely reflects changing Eh and pH conditions contemporaneous with diagenetic nodule growth. Accumulation of organic-rich sediment and nodule growth may have been induced and sustained by contemporaneous volcanic and hydrothermal activities on the Yangtze Block. The introduction of voluminous nutrients with volcanic ash, including phosphate and aqueous Fe and Si, promoted the bloom of plankton, including sponges and lower algae leading to organic matter enrichment. Productivity may have been further enhanced by upwelling of phosphate-rich bottom water that resulted in widespread phosphogenesis and formation of phosphate nodules. The hyalophane-quartz association documented from phosphate nodules suggests the possible interaction of K-feldspar-rich volcanic ash and Ba-rich hydrothermal fluids at lower pH levels in association with nodule growth. The formation of phosphate nodules of the Niutitang Formation, then, reflects the complex interaction among primary productivity, volcanic and hydrothermal activity, and the accumulation of organic matter at a critical period of Earth history.

The Contribution of Opal-Associated Phosphorus to Bioavailable Phosphorus in Surface and Core Sediments in the East China Sea

To improve the burial flux calculations of bioavailable phosphorus (P) and study opal-associated P (Opal-P) in the East China Sea (ECS), surface and core sediments were collected in the Changjiang Estuary (CE) and the south of the Cheju Island. In this study, sedimentary P was operationally divided into seven different forms using modified sedimentary extraction (SEDEX) technique: LSor-P (exchangeable or loosely sorbed P), Fe-P (easily reducible or reactive ferric Fe-bound P), CFA-P (authigenic carbonate fluorapatite and biogenic apatite and CaCO3-bound P), Detr-P (detrital apatite), Org-P (organic P), Opal-P and Ref-P (refractory P). The data revealed that the concentrations of the seven different P forms rank as Detr-P > CFA-P > Org-P > Ref-P > Opal-P > Fe-P > LSor-P in surface sediments and CFA-P > Detr-P > Org-P > Ref-P > Fe-P > Opal-P > LSor-P in core sediments. The distributions of the total phosphorus (TP), TIP, CFA-P, Detr-P are similar and decrease from the CE to the south of the Cheju Island. Meanwhile, Org-P and Opal-P exhibit different distribution trends; this may be affected by the grain size and TOM. The concentrations of potentially bioavailable P are 9.6-13.0 μmol g−1 and 10.0-13.6 μmol g−1, representing 61%-70% and 41%-64% of the TP in surface and core sediments, respectively. The concentrations of Opal-P are 0.6-2.3 μmol g−1 and 0.6-1.4 μmol g−1 in surface and core sediments, accounting for 5.3%-19.8% and 4.2%-10.6% of bioavailable P, respectively. The total burial fluxes of Opal-P and bioavailable P are 1.4×109 mol yr−1 and 1.1×1010 mol yr−1 in the ECS, respectively. Opal-P represents about 12.7% of potentially bioavailable P, which should be recognized when studying P cycling in marine ecosystems.

Superior removal of Co2+, Cu2+ and Zn2+ contaminants from water utilizing spongy Ni/Fe carbonate–fluorapatite; preparation, application and mechanism

Spongy Ni/Fe carbonate - fluorapatite was synthesized from natural phosphorite enriched with iron impurities. The morphological, chemical and structural features of the product were estimated using several techniques as XRD, SEM, EDX, and FT-IR. It exhibits spongy structure of nano and micro-pores. The average crystallite size is about 8.27 nm. The suitability of the product for considerable decontamination of Zn2+, Co2+, and Cu2+, ions from water was studied based on several reacting parameters. The equilibrium was attained after 240 min for Zn2+ and Co2+ ions while the adsorption equilibrium of Cu2+ reached after 120 min. The adsorption data for the selected metals was represented well by a pseudo-second-order model which revealed chemisorption uptake. The equilibrium studies were appraised based on traditional models and two advanced models were designed according to the statistical physical theories. The adsorption results highly fitted with Langmuir model followed rather than the other models. This indicated a monolayer adsorption for the metal ions by spongy Ni/Fe carbonate - fluorapatite. The estimated qmax values are 149.25 mg/g, 106.4 mg/g and 147.5 mg/g for the uptake of Zn2+, Co2+, and Cu2+, respectively. Based on monolayer models of one energy and two energies, the number of receptor adsorption sites, number of adsorbed metal ions per active site, the average number of sites which occupied by ions, mono layer adsorption quantity and the adsorption quantity after total saturation were calculated for the first time for such materials.

Characterization of phosphate rock and phosphogypsum from Gabes phosphate fertilizer factories (SE Tunisia): high mining potential and implications for environmental protection.

Since the establishment of the coastal industrial complex in Gabes city (Gulf of Gabes, SE Tunisia), hundred million tons of untreated phosphogypsum have been discharged in the open sea causing serious environmental problems. To better understand the dynamic and behavior of phosphate/phosphogypsum contaminants from raw ores to marine environment, a chemical, organic, mineralogical, and morphological characterization of phosphate rock and phosphogypsum was conducted using several sophisticated techniques. The chemical analysis showed that phosphate and phosphogypsum contain high loads of trace elements and that the transfer factors of pollutants varied from 5.83% (U) to 140% (Hg). Estimated annual flows of phosphogypsum contaminants into the marine environment ranged between 0.05 (Re) and 87,249.60 (F) tons. The phosphate rock was found to be formed by carbonate fluorapatite, calcite, dolomite, natural gypsum, quartz, calcite-Mg, apatite, pyrite, fluorite, and sphalerite-Cd and phosphogypsum by synthetic gypsum and sphalerite-Cd. The phosphate was found to be richer in organic compounds compared to phosphogypsum. Based on this work, the Tunisian phosphogypsum has a high mining potential and encourages the development of an economically beneficial and environmentally friendly phosphogypsum-treating industry.

Halogen chemistry and hydrogen isotopes of apatite from the >3.7 Ga Isua supracrustal belt, SW Greenland

The origin and evolution of volatiles, particularly water, in the abiotic early Earth environment have been intensively studied, and this is a topic of high relevance when considering the timing and conditions of life’s emergence. Investigation of hydrogen isotopes in the oldest crystals of minerals from the apatite group Ca10(PO4)6(F,Cl,OH)2 should bring new insight to this topic as the D/H ratio of apatite has proved useful for establishing the evolution of volatiles in other solar system bodies. Apatite crystals from metasedimentary and metavolcanic rocks collected from a low-strain domain of the Eoarchean Isua supracrustal belt have been investigated for their D/H signatures using secondary ion mass spectrometry and for major and trace element abundances using EPMA and laser ablation ICP-MS. Apatite crystals from Isua have a broad range in volatile compositions, both within samples from the same lithology (e.g., banded iron formation; BIF) and between different lithologies (BIF, metacarbonate, mafic dyke). Most of the crystals are chlorine-rich, which is in contrast to typical modern sedimentary apatite that is predominantly carbonate fluorapatite. We have used the REE distribution patterns from Isua apatite to distinguish those crystals having sedimentary, metasomatic and magmatic origins. The D/H ratios for all samples were determined to be very low with δDVSMOW values falling within the range from −93 to −56‰. δD values of Isua apatite do not correlate with REE signatures of crystals nor could we relate δD to the host lithologies. We conclude that this geochemical system has been reset during long and multi-phase geologic history, making it difficult, if not impossible, to use hydrogen isotopes for assessment of the primary signatures of the Archean hydrosphere.

Polarized IR and Raman spectra of (H2O)n clusters (n = 2–5) in the c-channels of apatite single crystals

The infrared (IR) and Raman spectra of three samples of fluorapatite single crystals and carbonate fluorapatite single crystal in the region of 7000–400 cm–1 were studied. It has been shown that isomorphic substitution of the Ca2+ cation and the PO43- anion leads to an increase in the size of the c-channels in the apatite crystal, which is accompanied by the formation of water clusters of the (H2O) n and H3O+ · (H2O) n (n = 2–5) types as a result of the diffusion processes in these local sections of the c-channels.

Geochemistry and depositional environments of Paleocene–Eocene phosphorites: Metlaoui Group, Tunisia

The Late Paleocene–Early Eocene phosphorites of the Metlaoui Group in Tunisia are a world-class phosphate resource. We review the characteristics of phosphorites deposited in three areas: the Northern Basins; Eastern Basins; and Gafsa-Metlaoui Basin. Comprehensive new bulk rock elemental data are presented, together with complementary mineralogical and mineral chemical results. Carbonate fluorapatite (francolite) constitutes the dominant mineral phase in the deposits. Phosphorite samples are enriched in Cd, Sr, U, rare-earth elements and Y, together with environmentally diagnostic trace elements that provide detrital (Cr, Zr), productivity (Cu, Ni, Zn) and redox (Mo, V) proxies. Suboxic bottom-water conditions predominated, with suboxic to anoxic porewaters accompanying francolite precipitation. Phosphorite deposition occurred under increasingly arid climate conditions, accompanying global Paleocene–Eocene warming. The Northern Basins show the strongest Tethys Ocean influence, with surface seawater rare-earth element signatures consistently developed in the phosphorites. Bed-scale compositional variation indicates relatively unstable environmental conditions and episodes of sediment redeposition, with varying detrital supply and a relatively wet local climate. Glauconitic facies in the Northern Basins and the more isolated evaporite-associated phosphorites in the dryer Eastern Basins display the greatest diagenetic influences. The phosphorite – organic-rich marl – diatom-bearing porcelanite facies association in the Gafsa-Metlaoui Basin represents the classic coastal upwelling trinity. Modified Tethyan waters occurred within the Basin during phosphorite deposition, with decreasing marine productivity from NW to SE evidenced by systematically falling enrichment factors for Cu, Ni, Cd and Zn in the phosphorites. Productivity declined in concert with increasing basin isolation during the deposition of the commercial phosphorite beds in the latest Paleocene to earliest Eocene. This isolation trend was temporarily reversed during an episode of maximum flooding associated with the earliest Eocene Paleocene–Eocene Thermal Maximum (PETM).

Controls on rare earth element distributions in ancient organic-rich sedimentary sequences: Role of post-depositional diagenesis of phosphorus phases

The processes that dictate the formation and preservation of rare earth element (REE) signatures in ancient marine black shales are incompletely understood, thus potentially limiting the utility of the REEs as geochemical tracers. Here, we report on whole-rock REE analyses of six black shale formations from different ages and depositional settings, which fall within three general groupings: Group 1 is characterized by low whole-rock REE content (ΣREE) (<250μg/g) and middle- and heavy-REE-enriched patterns (GdN/LaN<2, YbN/LaN<2.5); Group 2 is characterized by low ΣREE (<250μg/g) but greater middle-REE-enriched patterns (GdN/LaN>2, YbN/LaN<3); and Group 3 is characterized by high ΣREE (>250μg/g) and moderately middle-REE-enriched patterns (GdN/LaN~1.5–2.5, YbN/LaN~1). Representative samples from these groups were selected from the Marcellus and Hushpuckney shales and subjected to a multi-step leaching procedure, to isolate four extractable P-phases (reducible, authigenic carbonate-associated, detrital apatite, organic). In Group 1 samples with low carbonate content (<4% CaCO3), REEs were hosted mainly in the organic (50% of ΣREE) and siliciclastic fractions (37%); whereas in samples with greater carbonate content (>25% CaCO3), REEs were hosted mainly in carbonate-associated phases (53%). In Group 2, REEs were hosted mainly in the carbonate-associated (64%) and organic fractions (30%), and in Group 3, REEs were hosted mainly in the carbonate-associated (60%), detrital apatite (23%), and siliciclastic fractions (16%). Authigenic phases include minerals such as carbonate fluorapatite and authigenic calcite that, if present, tend to dominate the whole-rock REE inventory. In the absence of carbonate, whole-rock REE content depends on the relative REE contributions of the organic and siliciclastic fractions.

Physico-chemical characterization of Ogun and Sokoto phosphate rocks

There is a need to identify potential phosphate rock sources to supply phosphorus (P) for crop growth and sustain food production. Physico-chemical characteristics of phosphate rocks from two Nigerian deposits were evaluated to determine their suitability for processing or direct application as P fertilizer. Physical properties such as textural forms, hardness, specific gravity, shrinkage, water absorption capacity and firing color were determined. Ogun rock phosphate (ORP) and Sokoto rock phosphate (SRP) were also subjected to chemical and mineralogical analysis. Solubility tests were conducted at two different particle sizes in 2% citric acid. ORP had a higher water absorption capacity and shrinkage than SRP while specific gravity of ORP was lower. Total P 2 O 5 of SRP and ORP were 36.1% and 31% respectively, which is greater than P 2 O 5 content of Morocco rock phosphate. Both ORP and SRP contained carbonate fluorapatite and chlorapatite minerals. Gypsum, calcite and lime were associated with both rock phosphates indicating their liming potential in the soil. ORP was more soluble in water, probably because it has a lower pH (5.0) than SRP (7.8). Higher solubility of SRP in 2% citric acid may be caused by its high carbonate content. Solubility of both rocks in 2% citric acid increased with decreasing particle size. Solubility of both rocks in 2% citric acid was greater than 30% indicating that they are reactive rocks. The agronomic effectiveness of these rocks has been validated in several on farm trials. We recommend these phosphate rocks for production of P fertilizers and direct application in crop production.

Phosphorus Sequestration in Sediments Along the Salinity Gradients of Chesapeake Bay Subestuaries

We used a sequential extraction technique to compare the forms and amounts of particulate phosphorus (PP) deposited in the top meter of sediment spanning salinities from 0 to 10 in three Chesapeake Bay subestuaries: the Potomac, Choptank, and Bush Rivers. Fe-bound P (i.e., citrate-bicarbonate-dithionite (CDB)-extractable P) was the most dynamic fraction of PP, dominating oligohaline (salinity <3) sediments, but declining to near zero with depth in the most saline sediments of all three subestuaries. In contrast, we previously found Fe-P dominating the sediment PP at salinities ranging 0–11 in the Patuxent subestuary. Particulate organic P was relatively constant with depth and salinity and became the dominant form of PP in the most saline sediments. Fe-P was not replaced with diagenetic authigenic carbonate fluorapatite. In all the subestuaries, Fe-P generally persisted in the oligohaline sediments to 1 m depth, where sediment ages ranged from 60 to 200 years, based on 210Pb dating. At one site, PP burial reflected changing P loads from a nearby wastewater treatment plant. About 67% of the PP discharged from the Potomac watershed at the head of tide was buried in the sediments in the upper reaches of that subestuary. The form and amount of PP buried depended on the amount of CDB-extractable Fe in the sediments and on the distribution of sediment deposition along the salinity gradient. Even though CDB targets iron oxides, the predominant form of Fe in the sediments was ferrous iron suggesting that the predominant form of PP in oligohaline sediments may be ferrous phosphate.