Introduction

The phosphorite at Duwi Formation around the area of Quseir–Safaga in Eastern Desert, Egypt attracted the attention of previous authors, e.g., Youssef (1957); Baioumy and Tada (2005); Abou El-Anwar et al. (2017, 2019a), Abou El-Anwar et al. (2022). The model of quadratic regression theoretically was used in multiple practices (Narula and Wellington 2007). The phosphatic rocks contain a lot of million tons of U. It can be extracted as a product of manufactured fertilizers (Abou El-Anwar et al. 2019b). Generally, the occurrence of U in marine phosphorus illustrates either by replacement Ca in the constitution of apatite mineral or the incorporation under mixed set apatite and organic matter (Peter et al. 1986).

Phosphate is one of the most important strategic raw materials, since it is involved in many vital industries, the most important of which is the fertilizer industry. Phosphate is one of the raw materials rich in trace and rare earth elements that are used in many modern technological industries (Abou El-Anwar et al. 2022). Researchers in Egypt have been interested in evaluating phosphate deposits from an economic point of view for the production of phosphoric acid and its derivatives, without addressing the phosphate content of these elements and their environmental and economic importance (El-Kammar et al. 1990; Abou El-Anwar et al. 2017, 2022). Generally, apatite was accumulated in euxinic condition at calm environment where anaerobic microbes attack the organic matter and release PO4 3−. So, this acid medium dissolved the enclosing sediments and released some soluble cations such as Ca2+, Mg2+, etc. Thus, PO3− can react with Ca2+ and Mg2+ to form the transitional mineral “ Struvite (PO4 (Mg) NH4”. This mineral is unbalanced, can be re-precipitated in stable forms (Abou El-Anwar 2019a; Abou El-Anwar, et al. 2019c, 2020).

Potentially toxic elements (PTEs) (e.g., As, Cd, Cr, Pb, Hg, and Ni) are enriched in some natural geological materials such as black shales and phosphatic rocks (Nganje et al. 2020). Phosphatic rocks are the main source for the P-fertilizers production worldwide to improve the fertility and yield of agriculture soil. Salman et al. (2017) concluded that the P-fertilizers are the main source of some PTEs in the agriculture soil of Sohag, Egypt. In some cases, the concentrations of some PTEs are such that economic extraction is viable (Abou El-Anwar et al. 2021). REEs are subjected to enrichment during the authigenesis processes of phosphatic ores, and hence can be used to estimate the paleo-environment (McMurtry 2019).

Thus, the main target of the present article is to give detailed petrographical and geochemical remarks on the diagenesis of the dolomitic phosphates that represented the main phosphatic rocks of Queih Mine (Duwi Formation) at Quseir province, in a try to identify its environmental condition and the economic evolution. Also, to discuss some aspects regarding the environmental conditions through the deposition of the Upper Member of Duwi Formation in Quseir region in its type locality at the Queih Mine.

Materials and methods

Geology of the area

Late Cretaceous phosphorites in Egypt, which make up part of the Middle East to North Africa phosphogenic province with more than 3 billion tons of reserves, are widely distributed in the Eastern Desert, Western Desert, and Nile Valley (Baioumy and Tada 2005). The Duwi Formation, phosphorites bearing, is conformable overlaid by the Quseir variegated shales and underlaid by the Dakhla shales in the Quseir–Safaga zone (Fig. 1a). According to Baioumy and Tada (2005), the Duwi Formation is subdivided into four members—the lower member is composed of quartzose sandstone and siliceous shale; the middle one consists of soft laminated organic-rich black shale; the upper one is composed of phosphatic sandstone and oyster calcarenite in the Red Sea area; the uppermost member is composed of hard massive grayish brown to gray shale, that is mined (underground) in the study area. The thickness of the productive phosphorites bed is about 80 cm. The chosen area is represented by Queih Mine (Fig. 1a, b). It is located at longitudes 34° 05′ 00″ E and latitudes 26° 19′ 60″ N. It is located 5 km north of Al-Hamrawin area and at 25 km north of El-El-Quseir.

Fig. 1
figure 1

a Location and geologic map of the study area (modified after Conoco 1987; Mahfouz et al. 2021). b Photograph showing the entrance of the sampling tunnel

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Sampling and analyses

The field trip was done to study the geological setting and collect the rock samples of the phosphorites from Queih Mine. The mine is ceased for technical problems, such as many mines in the study area. Eleven samples were collected from the carbonate phosphorites in the horizontal direction of Queih Mine. The petrographic investigations of the 11 dolomitic phosphates samples were done by advanced research microscope. The mineralogical composition of two bulk samples (No. 1 and 9) was studied by the X-ray diffraction (XRD) analyses ((Philips type’PanALytica’ equipment model’X-Pert-PRO’ with’Ni-filter), a Cu-radiation (ƛ = 1.542 Å) of 45 kV, 35 mA, and a normal scanning speed of 0.03◦/sec, the diffractograms were obtained using a range of 2–60◦) at the Egyptian Mineral Resources Authority (Dokki, Egypt).

The chemical composition of the collected 11 bulk samples was performed using XRF (X-ray fluorescence—Axios, Sequential WD- XRF, PANalytical 2005) with reference to the ASTM-E1621 standard. Microstructure characterization or surface morphology was performed using SEM/EDX (scan electron microscope/energy dispersive X-ray—Quanta FEG 250, 30 kV, 14x-350x). All these measurements have been carried out at the laboratories of the NRC (National Research Center).

The Index of Compositional Variability (ICV) values were determined using the concentrations of major oxides as wt. % following Cox et al. (1995) equation:

$${\text{ICV}}\, = \,{{(Fe_{2} {\text{O}}_{3} \, + \,{\text{K}}_{2} {\text{O}}\,{ + }\,{\text{Na}}_{{2}} {\text{O}}\,{ + }\;{\text{CaO}}\,{ + }\,{\text{MgO}}\,{\text{ + MnO)}}} \mathord{\left/ {\vphantom {{(Fe_{2} {\text{O}}_{3} \, + \,{\text{K}}_{2} {\text{O}}\,{ + }\,{\text{Na}}_{{2}} {\text{O}}\,{ + }\;{\text{CaO}}\,{ + }\,{\text{MgO}}\,{\text{ + MnO)}}} {{\text{Al}}_{{2}} {\text{O}}}}} \right. \kern-0pt} {{\text{Al}}_{{2}} {\text{O}}}}_{3}$$

The Chemical Index of Alteration (CIA) and the Chemical Index of Weathering (CIW) that provide information about the intensity of sediments chemical were calculated using Nesbitt and Young (1982) equations:

$${\text{CIA }} = \, \left[ {{\text{Al}}_{{2}} {\text{O}}_{{3}} /\left( {{\text{ Al}}_{{2}} {\text{O}}_{{3}} + {\text{CaO}}* + {\text{Na}}_{{2}} {\text{O}} + {\text{K}}_{{2}} {\text{O}}} \right)} \right]{\text{ x 1}}00)$$
$${\text{CIW}} = \, \left[ {{\text{Al}}_{{2}} {\text{O}}_{{3}} /\left( {{\text{Al}}_{{2}} {\text{O}}_{{3}} + {\text{CaO}}* + {\text{Na}}_{{2}} {\text{O}}} \right)} \right]{\text{ x 1}}00)$$

Pollution indices were determined using the following equations:

The contamination factor (CF) (Hakanson 1980);

$${\text{CF }} = {\text{ C}}_{{\text{m}}} /{\text{B}}_{{\text{m}}}$$

The enrichment factor (EF) (Buat-Menard and Chesselet 1979);

$${\text{EF }} = \, \left( {{\text{C}}_{{\text{m}}} /{\text{B}}_{{\text{m}}} } \right) \, / \, \left( {{\text{R}}_{{\text{s}}} /{\text{R}}_{{\text{c}}} } \right)$$

Index of Geoaccumulation (Igeo) (Muller 1979);

$${\text{I}}_{{{\text{geo}}}} = {\text{ Log}}_{{2}} \left( {{\text{C}}_{{\text{m}}} /{1}.{5}*{\text{B}}_{{\text{m}}} } \right)$$

where Cm represents the content of the examined element in the phosphate samples, Bm represents the content of the inspected element in the upper continental crust (UCC) (Rudnick and Gao 2014), Rs represents the content of the reference element in the phosphatic ore, and Rc represents the content of the reference element in the UCC. In the current study, Zr had been used to represent the conventional traces that distinguish the natural from anthropogenic components. Generally, Zr is represented as mostly originating from natural origin and have no considerable anthropogenic source (Bam, et al. 2011).

Results and discussion

Petrographical and mineralogical study

Microscopically, the phosphorite at Um Queih area is mainly constituting of collophane, fluorapatite (phosphatic phase), pyrite, and quartz grains embedded in a cryptocrystalline phosphatic matrix according to their decreasing order of abundance (Fig. 2A–D). Dolomite, calcite, gypsum, pyrite, and quartz grains (non-phosphatic phase) occurred in the studied samples in association with the phosphatic phase as identified by the XRD (Fig. 3a). The occurrence of framboidal pyrite indicated the deposition of these sediments in dyoxic marine condition under the effect of microbial activity (Boulemia et al. 2021; Ciobota et al. 2014). The paragenetic sequence of the studied phosphorite is fluorapatite followed by collophane.

Fig. 2
figure 2

Microscopical investigations of Um Queih phosphorite (in PPL. X40): A fluorapatite (colorless subhedral rectangular crystals), collophane (brown grains, pellets, spheroids, ovoids), and dolomite as well as calcite (colorless anhedral grains and rhombohedral crystals) embedded in a cryptocrystalline phosphatic matrix. Collophane is replaced by the phosphatic matrix. B Fluorapatite, collophane, coprolite (brown cylindrical form), and dolomite as well as calcite (colorless anhedral grains and rhombohedral crystals) embedded in a cryptocrystalline phosphatic matrix. C Fluorapatite, collophane, and dolomite as well as calcite (colorless anhedral grains and rhombohedral crystals) embedded in a cryptocrystalline phosphatic matrix. Framboidal pyrite (opaque) scattered in the collophane. D Fluorapatite, collophane, and dolomite as well as calcite (colorless anhedral grains and rhombohedral crystals) embedded in a cryptocrystalline phosphatic matrix

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Fig. 3
figure 3

a XRD for the phosphatic rocks of the studied mine. b BSE image and EDX analysis data viewing a domination of the bone remains, halite crystals, dolomite and phosphatic grains scattered in the matrix, EDX recorded P2O5 (10.52%), Ca (30.75%), and Na (3.11%). c BSE image and EDX analysis data viewing an elongated bone fragments and quartz grains scattered in the matrix, P2O5 (18.03%), SiO2 (46.7%). and SO3 (3.82%)

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Based on the XRD, the analyzed samples are characterized by two dominant mineral phases; the prominence phosphatic phase, fluorapatite (Fig. 3a). In contrast, the non-phosphatic phase encloses carbonate minerals (mostly dolomite and calcite), evaporated minerals (gypsum), sulphide minerals (pyrite), as well as silicates, expressed as a quartz mineral which was approved by the petrographic study.

SEM and EDX-ray investigation of the dolomitic phosphates was exhibiting the prominence of bone fragmentations, crystalline halite, and quartz grains disassembled in the phosphatic matrix and within phosphatic grains (Fig. 3b and c). EDX recorded P (10.52%), Mg (6.22%), Ca (30.75%), and Na (3.11%), (Fig. 3b). Elongated bone fragment and quartz granules are sprinkled in the phosphatic matrix (Fig. 3c), EDX got P (18.03%), Si (48.71%), and Mg (9.38%).

Generally, Phosphorites, the most important sources of phosphate rock in the Middle East and North Africa, is mineralogically monotonous; composed of carbonate-fluorapatite (called collophane or francolite) (Dar et al. 2017; Howari et al. 2022). Usually, during authigenesis processes, admixtures of detrital impurities from hosting rocks are associated with the carbonate-fluorapatite. Also, this deposit usually contains 5% to 28% P2O5 with some element enrichment such as Sr and Y (McMurtry 2019).

Geochemical characterization

Major oxides features

The studied samples’ geochemical content of the major oxides, traces, REEs and their ratios are recorded in Table 1, and inter-correlation among them is present in Table 2.

Table 1 Major oxides (%), traces and REEs (ppm) contents, elemental ratios CIA, CIW, and ICV of the studied phosphorites rocks of Um Queih Mine
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Table 2 Correlation matrix of the studied parameters in the phosphatic rocks of Um Queih Mine
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Generally, CaO is the main constituent (30.24–38.93%) of the studied dolomitic phosphates followed by P2O5 in the studied phosphatic samples that vary from 16.7 to 20.85% and averaging 19.33%, (Table 1). The strong significant positive relation (r = 0.89) between CaO and P2O5 (Table 2) indicated the presence of apatite, while the high concentration of CaO indicated the presence of other Ca-bearing minerals, gypsum, calcite, and dolomite as confirmed by petrography, XRD, and EDX (Figs. 2 and 3). MgO is the third in the abundance, ranges from 7.01 to 10.01% with an average of 8.42%, and its positive correlation (r = 0.60) with CaO (Table 2) indicted their association in the dolomite mineral, which was verified by petrographic, XRD, SEM, and EDX techniques (Figs. 2 and 3). SiO2 ranges from 6.17 to 8.1% averaging 7.41, revealed the presence of quartz grains which detected with XRD (Fig. 3a). Its strong positive correlation with Fe2O3 (r = 0.8) and weak to moderate with other major elements (Table 2) indicated its presence as detrital grains stained with iron oxides.

The content of Fe2O3 is generally low, averaging 1.96% compared with the matching value for UCC, 4.5% (Taylor and McLennan 1985) and Post-Archean Australian Shale (PAAS), 6.5% (Rudnick and Gao 2014). The high content of Fe2O3 in the studied samples indicates the occurrence of free hydrate iron oxides and iron minerals (pyrite, Figs. 2 and 3a). Thus, iron oxides may be present as authigenic in origin. Al, Na, K, Ti, and F are documented in small percentage ratios. The weak and moderate positive linkage among Al2O3 with both SiO2 and NaO (r = 0.34 and 0.5; respectively), point out their association in aluminosilicate minerals. A positive relationship (r = 0.57) among Na and Cl revealed the existence of halite, which was confirmed with SEM and XRD investigations.

Trace and rare earth elements

The traces and rare earths enrichment in sediments perhaps are coming from seawater, hydrothermal, or diagenesis processing. The moderate traces and rare earths content in Queih phosphatic ores are excess enrichments rather than those in the UCC and PAAS countable (Table 3 and Fig. 4a). Commonly, the examined Queih phosphatic ores are enriched in all most traces, and Y (as REE) except Cr, Ba, Ce, La, and Ga more than those in the UCC and PAAS countable.

Table 3 The trace, rare earths composition, P2O5 and CIA of the studied phosphorites in comparison with published average phosphates in different localities
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Fig. 4
figure 4

a Distribution of trace elements in the studied phosphorites in comparison with other locations. b 3D pyramids plotting showing the distribution of Um, Uc, F, and P2O5 in the studied phosphorites. c Relationship between U and P2O5. d Element ratio paleo-environment classes, star is the current results (Yan et al. 2018), e V/Ni vs. Co/Ni (Galarraga et al. 2008)

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Accordingly, REEs conjoined with ore of phosphate can be ascribed to either exchange process through diagenesis or adsorption (McLennan 1989; Kohn and Moses 2013) and/or exposed to the demanding chemical weathering (El-Kammar et al. 1979; Abou El-Anwar et al. 2019b,c).

P2O5 has very intensive positive association with the trace elements; Cr, Cu, Co, Ni, V, Zn, Zr, and Cd, (r = 0.84, 0.43, 0.63, 0.62, 0.81, 0.51, 0.24, and 0.46, respectively, (Table 2), and SiO2 has positive association with some trace metal elements; Cr, Ni, Zr, and V (r = 0.34, 0.14, 0.29, and 0.41, respectively). Thus, traces are mostly associated with phosphatic rocks and/or detrital quartz. La, Ce, Nd, Sc, and Y are represented as the rare earth elements. La has recorded a positive correlation with Si, Mo, Cr, Zr, V, and Rb (r = 0.34, 0.49, 0.44, 0.49, 0.51, and 0.37; respectively) indicating the incorporation of these elements in silicates. Ce has moderate positive correlation with Na, K, and Ni (r = 0.26, 0.30, 0.36, respectively), Ce associated with clay minerals and/or heavy metals. Nd has weak to moderate positive correlation with P, Ca, K, Cr, Cu, Ni, Zn, Cd, and As (r = 0.38, 0.41, 0.34, 0.27, 0.31, 0.49, 0.36, 0.59, and 0.15, respectively, Table 2). Thus, Nd may be coupled with phosphate, clay minerals, and heavy metals. Sc positively correlated with Al, Ti, and Ni (r = 0.28, 0.69, and 0.34, respectively), so it associated with clay minerals and heavy metals. Finley, Y was positively correlated with Zr and Rb (r = 0.28 and 0.65, respectively), so it accumulated in heavy and trace metals.

Some heavy metal elements (such as Cr, Ni, V, As, and Cd) and rare earth elements, Sc are positively linked to Fe2O3, TiO2, and each other, which indicated that these components may be connected with TiO2, or the heavy mineral elements (Table 2), (Abou El-Anwar 2019a).

Dolomitization processes

The positive linkage (r = 0.51) among MgO and P2O5 indicated that the dolomite mineral was associated with the studied phosphatic ores. The dolomite rhombs occur in the thin sections (Fig. 2), SEM (Fig. 3b and c) and XRD indicated the studied phosphatic rocks subjected to the dolomitization effect. The dolomitization process must be attributed to the presence of magnesium (Abou El-Anwar 2019b). Thus, the studied samples represented the first occasion of the dolomite mineral was associated with phosphate rocks. The source of MgO is probable to be the presence of ultramafic rocks in the area. Hence, under the suitably conditions, the magnesium element replaces calcium in calcite and led to the precipitation of dolomite.

There are strong to medium positive relation (r = 0.25, 0.66, 0.48, 0.40, 0.32, and 0.28, respectively) for the heavy metals Co, Zn, Cu, Cr, V, and Ni, respectively, with MgO (Table 2). Also, there is positive correlation between MgO and some toxic and rare earth elements; Cd, Ga, Nd, As, Sc, and U (r = 0.42, 0.41, 0.13, 0.20, 0.20, and 0.15, respectively).

Thus, dolomite mineral can play role in scavenge and absorbing (Abou El-Anwar 2014 and 2019a) some heavy and rare elements and increasing their concentration in phosphate rocks. Consequently, this study is adding an important role for dolomite to increase the concentration of the heavy and rare elements in phosphates, and not only leached it from the black shales which spread in the region.

Mobilization of rare earth elements

Generally, concentrations of REEs logically present in sediments related to the parent rocks. They are mostly initiated from rock, chemical weathering, erosion, and soil.

Table 1 reveals LREEs (average 35.58 ppm) enrichment and HREEs (average 26.27 ppm) depletion. LREEs and HREEs are representing 57.5 and 42.5%, respectively, from the total content of the REEs which is a result of the weathering effect. The ratio LREE/HREE is 1.36 indicating the prevailing of LREEs, and hence the role of weathering processes on the fractionation of REEs in the studied area and also the metaluminous granites source rock of these sediments (Yusoff, et al. 2013). Low mobility, during weathering process, of LREEs compared with HREEs led to the LREEs enhancement (Yusoff et al. 2013 and Gao et al. 2016).

Concentration of U

The concentration of U in the studied phosphatic samples varies from 33 to 45 ppm with an average of 37.33 ppm (Table 1), which is higher than U content within the UCC and PAAS content (2.5 and 2.7 ppm, respectively).

U has strong positive relationship with P2O5 (r = 0.76) and CaO (r = 0.68), indicating the incorporation of U within the apatite minerals (Fig. 4b and Table 2). This relationship, also, pointed out the significant function of phosphate in deposition of U as secondary uranium mineral; phosphuranylite during weathering. So, phosphuranylite may be deposited in Queih phosphatic rocks as secondary mineral which agree with Abou El-Anwar et al. (2019b). In addition, U recorded strong to moderate positive correlation with Cr, Zr, Co, V, Zn, As, and La (r = 0.79, 0.60, 0.66, 0.53, 0.44, 0.49, and 0.45, respectively) indicating their geochemical association. Moderate positive correlation between U and SO3 (r = 0.55) may not be possibly present only in fluorapatite but also associated with other apatite group. Therefore, U may be out through the weathering and act as immobile and it may be transformed to a new phase (Venter and Boylett 2009). U was negatively correlated with HREE and weakly to moderately correlated with some LREE. The anoxic sediments are more enriched in U than oxic ones (Abou El-Anwar et al. 2019b, c).

Phosphatic rocks are considered as an important source of U worldwide (Gabriel, et al. 2013). The relationship between P2O5, F, and U can be deduced from the linear regression Eq. (1) based on the obtained results of the current study.

$${\text{U}}_{{\text{c}}} = { 2}.{195}*{\text{P}}_{{2}} {\text{O}}_{{5}} - { 2}.0{15}*{\text{F }}{-} \, 0.{4}0{7}$$
(1)

where P2O5 in %, U and F in ppm.

It was found that the calculated U (Uc) and measured U (Um) are nearly identical. Figure 4c shows the 3D pyramids plotting of Um and Uc. This model can be used to expect the U concentration in the phosphatic rocks.

Depositional environment

Deposition geochemical indices

The paleo-depositional environments can be identified using redox-sensitive elements; e.g., V, Ni, Mo, U, Cu, Cr, Re, Cd, Sb, and Tl (Adegoke, et al. 2015; Pattan and Pearce 2009; Pi, et al., 2014), as their concentration in the sediment increases in the anoxic environment.

The mean (in ppm), V = 1253.08, Ni = 208, Mo = 338.38, U = 39.74, Cu = 73.69, Cr = 27, Cd = 28.08, Co = 27.92, and Zn = 1062.85, in the studied phosphate rocks from Um Queih Mine is higher than the UCC (Rudnick and Gao 2014), Table 3 and Fig. 4a. Accordingly, those sediments are enriched with the oxidation-sensitive elements, indicating the deposition of phosphate rock in an anoxic environment (Adegoke et al. 2015 and Pi et al. 2014). It is also possible that the reason for the increase in the concentration of these elements in phosphates is due to their leaching from the above Dakhla Formation rocks in the study area. V is more stable and resistant to geochemical weathering than Ni, especially in the anoxic marine environments with bacterial activity, which led to an enrichment of V compared to Ni (Abou El-Anwar et al. 2019b; 2020).

The positive correlation between Cr and Ni (r = 0.47) have been used as a marker of mafic origin for the sedimentary source. The enrichment in Ni in the studied phosphatic rocks may indicate that they originated from mafic to ultramafic rocks (Graver and Royce 1993; Abou El-Anwar et al. 2020).

The average V/Mo for the studied phosphatic rocks is 3.9, which mentioned that the study phosphatic samples are formed in suboxic conditions (Gallego et al. 2010). V/Ni value ranges from 2.71 to 7.93 ratio and average is 6.29 (Table 1), which indicates that the study phosphatic rocks are deposited in marine reducing environments (Fig. 4d). This result was supported with the relationship between V/Ni and Co/Ni which indicated all the studied samples present in marine source organic matter field, except one sample (sample No. 3) in the field of mixed source organic matter due to the low content of V as shown in Fig. 4e (Galarraga et al. 2008).

The average (V/Cr) value was recorded as 47.63 (Table 1); thus, the study phosphatic samples are deposited in anoxic condition. The (Ni/Co) value varies from 5.13 to 12.11 and average is 7.77, which revealed the study phosphatic samples are deposited in anoxic condition (Jones and Manning 1994; Shi et al. 2015).

V/(V + Ni) and V/(V + Cr) ratios for the study phosphatic samples are recorded as 0.85 and 0.98, respectively; these indicate the study phosphatic rocks are deposited in strongly reducing conditions (Zho and Jiang 2009 and Pi et al. 2014).

The low U/Mo (average 0.10, Table 1) revealed that the studied phosphatic rocks in Queih Mine were deposited under sulfidic marine anoxic environment (Arning et al. 2009), within marine source organic matter (Abou El-Anwar et al. 2019b, c; 2021).

Weathering effects and paleosalinity

The Chemical Index of Alteration (CIA) is used to determine the degree of weathering of the parent rocks (Nesbitt and Young 1982). The average CIA (51.76) value for the studied phosphate samples, which is lower than the PAAS value “88.32”(Taylor and McLennan 1985), indicates that the studied samples have low chemical weathering at the source area (Fedo et al. 1995) (Table 1).

The Queih phosphatic rocks have ICV values in the range 7.12–10.13, with an average of 8.12% (Table 1). The ICV values are higher than the PAAS values (0.85) and those values of the UCC (1.2). Consequently, the Queih phosphatic rocks are geochemically more mature, and were derived from a low weathered source. On average, the CIA, CIW, and ICV average values of the studied samples are 51.76%, 56.41%, and 8.12%, respectively) (Table 1). These values suggest that the studied phosphatic samples were subjected to low weathering either of the novel source or during transportation before deposition.

The studied phosphate samples of Um Queih Mine recorded Rb/Sr ratio as average of 0.02 (Table 1). It is lower than that of the average UCC (0.33) and is comparatively equivalent to PAAS (0.08). It indicates that the rate of the chemical weathering of the study rocks was similar to the PAAS values (McLennan et al. 1993).

Consequently, the Duwi Formation can be significantly affected by the chemical weathering, which agrees with Abou El-Anwar et al. (2017; 2019b, c; 2022a).

The Sr/Ba ratio can used to conclude the dissimilarity in the salinity of water and climatic environment (Wang et al. 2005 and Shi et al. 2015). High Sr/Ba ratio is related to arid hot climate conditions and high salinity, whereas a low ratio is related to low salinity and warm climate (Wang et al. 2005). The Sr/Ba ratios for the studied phosphatic rocks are relatively high (13.89–32.42) with an average of 21.9, indicating a high salinity of water and a humid warm climate, which is in agreement with Abou El-Anwar and Abdel Rahim (2022); Boulemia et al. (2021); Mekky, et al. (2019). This is confirmed with the relation between Sr/Ba and V/Ni ratio plot (Adegoke et al. 2015), where the Um Queih samples plot in high salinity field (Fig. 5a).

Fig. 5
figure 5

a Sr/Ba vs. V/Ni (Adegoke et al. 2015). b Distribution of the Σtrace and ΣREE elements for the study area and others. c Distribution of the ΣLREE and ΣHREE elements for the study area and others

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Rare earths infer to the parent rocks

REEs in sediments can be indicating the origin rocks. Ce/La (> 2) is indicated of the hydrogenic and (< 2) reveals a hydrothermal impact on REEs accumulation in the marine sediments (Khadijeh, et al. 2009). The average ratio of Ce/La in the studied phosphate samples of Queih Mine is 0.70 which is less than 2, thus indicating the hydrothermal origin also, it is lower to those of the average PAAS (2.13). Resulting of REEs has low mobility within near-surface environments. Thus, these minerals were reflecting near sources.

Comparison of the chemical composition with those of others localities

Table 3 shows the concentrations of the traces, rare earths, Σ trace, ΣREEs, P2O5, and CIA for the studied phosphatic rocks and other locations; Um El-Huwtat (Safaga), Yunis, and Gebel Duwi mines (Quseir) and El-Sabiya, in the Nile Valley.

The studied phosphatic rocks in Queih Mine are enriched in Mn, Zr, Sr, and Br than all the other localities (Table 3). Um El-Huwtat (Safaga) phosphatic rocks are enriched in Pb, Ba, Ni, Co, Rb, Sc, Ce, Ga, and U than all the other mines (Table 3). Yunis phosphatic rocks had high contents of Mo, Cr, V, Cd, Y, As, and Se than the studied phosphatic rocks. In addition, phosphatic rocks from Gebel Duwi and El-Sabiya are only enriched in La and Nd (32.2 and 16 ppm, receptivity) as shown in Table 3.

The studied phosphatic rocks in Queih Mine are represented with the highest content of the total trace elements (Σtrace = 5613.5ppm) than other mines, while El-Sabiya phosphatic rocks recorded the lowest content (Σtrace = 479.5 ppm) (Table 3 and Fig. 5b). Um El-Huwtat phosphatic rocks represented the highest content of the total rare earth elements and light rear earth elements (ΣREEs and LREEs = 92 and 47 ppm, respectively), and El-Sabiya phosphatic rocks represented the lowest content (Table 3 and Fig. 5b). In contrast, the phosphatic rocks for Yunis Mine recorded the highest values for HREEs (70.25 ppm), although has the lowest content of P2O5 12.46% (Table 3 and Figs. 5c and 6a).

Fig. 6
figure 6

a Distribution of the P2O5 for the study area and others. b Distribution of the Zn for the study area and others. c Distribution of the Zr for the study area and others

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The studied phosphatic samples in Queih Mine represented the highest content of the heavy metals Zn and Zr (average value 1062.85 and 160.23 ppm, respectively) as shown in Fig. 6b, c); thus, these elements are enriched in Quseir than those for Safaga and Nile Valley.

Thus, the rare earths are generally decreasing from Safaga to Quseir, toward Nile Valley, while the traces are increasing. This finding is in agreement with Abou El-Anwar et al. (2019b, c); Abou El-Anwar et al. (2022).

Pollution indices of PTEs

The enrichment of the studied phosphatic rocks with some PTEs can be deduced from the CF, EF, and Igeo (Fig. 7).

Fig. 7
figure 7

Distribution of pollution indices, a CF, b EF, and c Igeo, in the studied shale and indices classes

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The CF is the simplest pollution indices used to express the extent to which the rock is enriched with the element. There is a large range in the recorded values of the CF, as the values ranged between 0.1 and 355.1 (Fig. 7a). The lowest values were recorded for Ba, Cr, Rb, Y, Ga, Ce, La, and Nd, and considered low contaminated with these elements. While, the highest values were recorded for Sr, Mo, V, Zn, Cd, As, Se, Br, and U, and classified as very high contaminated with these elements.

The EF gives a clear picture of the process of enriching the element in the rock, as it is compared with the CF of an element that is resistant to different weathering processes. The calculated EF values were ranged from 0.1 to 437.7 (Fig. 7b). The elements with EF < 2 indicating depletion or no enrichment in the studied rock are Ba, Cr, Co, Rb, Y, Ga, Ce, La, and Nd. The studied phosphate was extremely highly enriched with Mo, Cd, and Se.

Since it was introduced by Müller (1979), the Igeo was worldwide applied for determination of trace elements pollution evaluation (Mekky, et al. 2019). The Igeo calculated values varied from −3.1 to 7.8 (Fig. 7c). The studied phosphate was practically uncontaminated with Ba, Pb, Cr, Rb, Y, Sc, Ga, Ce, La, and Nd, while it was extremely contaminated with Mo, Cd, and Se.

It was observed that Ba showed the lowest CF, EF, and Igeo values; 0.1, 0.01, and −3.7, respectively, while the highest values were 355.1, 437.7, and 7.8, respectively, for Mo. The studied phosphatic rocks are extremely enriched with Mo, Cd, and Se, as well as relatively enriched with V, Zn, As, Br, and U. Although, Mo is essential for human, animal, and plant health and industrial applications, exposure to high doses of Mo can be detrimental to plant, animal, and human health (Smedley and Kinniburgh 2017). While Se is an essential micronutrient element considered also toxic to the living things, it is toxic for humans at > 400 μg /d (Gebreeyessus and Zewge 2019). Owing to the unique physical and chemical properties of Cd, it is widely used in many industrial processes. Among all the PTEs, it is known that Cd is harmful to almost all forms of life, as it has no benefit for the biofunctions processes in living organisms (Suhani, et al. 2021). The recorded REEs (Y, Sc, La, Ce, and Nd) are generally depleted in the studied samples with Cf < 1, EF < 2, and Igeo < 0. The study area at Queih is characterized by agricultural projects development. The weathering or excavation of phosphatic rocks can potentially be of environmental concern since this type of phosphate is enriched in PTEs.

Conclusion

The studied phosphorites from Queih Mine, Quseir Area, Duwi Formation are enriched in some trace and rare earth elements, which have an additional important role to the studied phosphatic rocks. Also, they are represented by an intermediate grade. They are deposited under anoxic reducing marine environment and are subjected to low chemical weathering in depositional environment. The petrographic studies show that the phosphorites at Queih Mine are composed of phosphatic lithoclasts, bioclasts, pyrite, and quartz grains enclosed in a cryptocrystalline phosphatic matrix. Mineralogically, the phosphorites are consisting of two main mineral phases. Phosphatic phase is represented by apatite (fluorapatite). Non-phosphatic phase is represented by calcite, dolomite, gypsum, pyrite, and quartz. The heavy and rare earth elements are associated with apatite, quartz grains, and titanium-iron oxides minerals; thus, there are many sources for these elements. The measurement U is relatively higher than calculated U values; this is credited to the post-depositional enrichment of U under the chemical weathering in Quseir area. Petrographic studies and geochemical analysis indicated that the studied phosphorites deposited in a high salinity marine anoxic condition. The pollution indices for the ore were considered low contaminated for Ba, Cr, Rb, Y, Ga, Ce, La, and Nd with low CF, while the EF indicates extremely highly enriched with Mo, Cd, and Se.