Figure 1.
Geographic location of the study area.
Figure 2.
A: Simplified geological map of the Jebel Dhyr syncline; B: Lithostratigraphic log of Jebel Dhyr. [Legend of the geological map: 1= Holocene: Current and recent alluvium, scree slopes, piedmont accumulation, molasses. 2= Plio-Quaternary: Pebbles (sandstone and conglomerates) and marls. 3= Upper Lutetian: Marls, clays and conglomerates. 4= Ypresian, Lower Lutetian: Limestone with flint and marl-limestone, sometimes with gypsum. 5= Paleocene-Maastrichtian: Marl and marl-limestone. 6= Campanian, Maastrichtian: Marly at the base and varied limestone (oolitic, organogenic, flint) at the top. 7= Coniacian and Santonian: Limestones. 8= Turonian: Limestones and marls. 9= Cenomanian: Yellow limestone, marl and gypsum and dolomites. 10= Samples. 11= Streams. 12= Faults].
Figure 3.
Panoramic view of the flanks of the Jebel Dhyr syncline; A: extreme southeast flank, B: southwest flank; C: The outcrops of the ten phosphate levels (Phosphorites and Marly limestone phosphates) sampled from Jebel Dhyr Syncline.
Figure 4.
Photographs of the main allochems of Jebel Dhyr phosphorites illustrating A- Coprolith, B- Pellets, and C- Selachians Teeth.
Figure 5.
Texture of the phosphate samples: A- Bio-pellet phosphorite with a grainstone texture, featuring allochems represented by pellets, intraclasts, and bioclasts (bivalve arc and calcitic bone fragment), [200μm]. B- Bioclasts (vertebra and fish spine) within anisotropic granular phosphorite, [100μm]. C- Phosphatized blunt-edged intraclast (granule) surrounded by pellets and glauconite, [50μm]. D- Cryptocrystalline dolomite rhombohedron with an apatitic rim surrounded by grainstone pellets of various shapes, [50μm]. E- Cylindrical-shaped coprolite and brown-colored intraclast in grainstone textured phosphorite, [100μm]. F- Detrital quartz grains and quartz rim within the calcite-filled crack, [100μm]. G- Dispersed organic matter punctuates within pellets (concentric, non-nucleated, and oval) in a calcitic matrix, [50μm]. H- Globigerina acting as nuclei for a phosphatic ooid, surrounded by non-nucleated, organic-rich oval pellets, [50μm].
Table 1.
The concentration of Geochemical elements (wt%) in phosphorites (bulk rock) samples from the Jebel Dhyr syncline, Eastern Algerian Atlas.
| Sample ID | P2O5 | CO2 | MgO | Na2O | K2O | CaO | SiO2 | Fe2O3 | H2O | Al2O3 | SO3 | F | Tot. % |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| D1-I | 23.17 | 10.7 | 1.84 | 0.71 | 0.13 | 35.1 | 9.7 | 0.66 | 1.62 | 0.77 | 11.85 | 2.6 | 98.85 |
| D1-II | 22.86 | 10.75 | 1.86 | 0.6 | 0.13 | 34.8 | 9.2 | 0.7 | 1.54 | 0.78 | 12.2 | 2.8 | 98.22 |
| D1’-I | 24.6 | 10.68 | 1.78 | 0.79 | 0.16 | 35.6 | 10.3 | 0.92 | 1.65 | 0.83 | 10.1 | 2.3 | 99.71 |
| D2-II | 23.4 | 10.65 | 1.8 | 0.7 | 0.15 | 35 | 9.5 | 0.91 | 1.62 | 0.81 | 11.1 | 3.7 | 99.34 |
| D2-I | 20.6 | 12.21 | 3 | 0.51 | 0.21 | 32 | 9.63 | 0.85 | 1.4 | 0.95 | 10.5 | 6.2 | 98.06 |
| D3-II | 20.2 | 11.8 | 2.7 | 0.55 | 0.21 | 34.2 | 9.05 | 0.82 | 1.5 | 0.93 | 10.6 | 5.9 | 98.46 |
| D4-I | 22.53 | 10.53 | 2.45 | 0.58 | 0.14 | 34.1 | 9.15 | 0.65 | 1.65 | 0.79 | 11.8 | 4.9 | 99.27 |
| D4-II | 20.8 | 11.6 | 2.5 | 0.59 | 0.12 | 33.9 | 9.1 | 0.6 | 1.7 | 0.74 | 11.9 | 4.6 | 98.15 |
| D4’-I | 21.9 | 11.7 | 2.9 | 0.6 | 0.11 | 34.1 | 9.1 | 0.55 | 1.75 | 0.72 | 11.95 | 3.2 | 98.58 |
| D5-II | 23.8 | 10.9 | 2.7 | 0.61 | 0.1 | 33.01 | 9.8 | 0.5 | 1.92 | 0.7 | 12.4 | 3.2 | 99.64 |
| D6-I | 24.6 | 12.6 | 2.35 | 0.52 | 0.12 | 32.2 | 9.1 | 0.85 | 1.58 | 0.74 | 10.8 | 3.2 | 98.66 |
| D6-II | 25.8 | 12.6 | 2.32 | 0.53 | 0.12 | 32.1 | 9.2 | 0.82 | 1.56 | 0.74 | 10.9 | 2.4 | 99.09 |
| D8-I | 21.8 | 11.33 | 2.69 | 0.6 | 0.17 | 32.7 | 10.6 | 1 | 1.63 | 0.86 | 12.1 | 4.4 | 99.88 |
| D7-II | 22.2 | 12.1 | 2.8 | 0.61 | 0.1 | 32.1 | 9.4 | 0.85 | 1.62 | 0.7 | 12.15 | 4.2 | 98.83 |
Table 2.
Crystallographic parameters of the crystalline unit cell of apatite group in phosphorites from the Jebel Dhyr syncline, Eastern Algerian Atlas.
| Mineral | a or b (Å) | C (Å) | c/a | Vol. of unit cell | Chemical formula |
|---|---|---|---|---|---|
| fluorapatite | 9.371 | 6.885 | 0.734 | 523.12 | Ca5(PO4)3F |
| hydroxylapatite | 9.352 | 6.882 | 0.735 | 521.26 | Ca5(PO4)3(OH) |
| francolite | 9.340 | 6.880 | 0.736 | 519.77 | (Ca,Mg,Sr,Na)10(PO4,SO4,CO3)6F2-3 |
| dahllite | 9.450 | 6.885 | 0.725 | 532.09 | Ca5(PO4,CO3)3(OH,O) |
Figure 6.
Examples of X-ray diagram for phosphorite sample show the apatitic different component with carbonates and siliceous gangue of Jebel Dhyr syncline. Abbreviations after Warr (2021; IMA–CNMNC).
Table 3.
X-ray diffraction parameters of carbonate group in phosphorites from Djebel Dhyr syncline, Eastern Algerian Atlas.
| Mineral | hkl | d (Å) | 2Θ [deg] | Geochemical formula |
|---|---|---|---|---|
| calcite | 104 | 3.0360 | 29.395 | CaCO3 |
| magnesian calcite | 104 | 3.0254 | 29.500 | (CaMg)CO3 |
| dolomite | 104 | 2.8893 | 30.815 | CaMg(CO3)2 |
| ankerite | 104 | 2.8890 | 30.918 | Ca(Fe,Mg) |
| (CO3)2 |
Figure 7.
Examples of X-ray patterns showing the presence of sulphides and sulphates in phosphorites samples from Jebel Dhyr syncline.
Figure 8.
XRD diffractograms of fine fraction phosphorite samples from Jebel Dhyr syncline showing zeolites, feldspars and clays.
Table 4.
Recapitulation of mineral phases identified by light microscopy, X-ray diffraction and macroscopics observations, in phosphorites from the Jebel Dhyr syncline, Eastern Algerian Atlas.
| Mineral groups encountered | Sampling type | |
|---|---|---|
| Bulk rock | Phosphatic allochems grains | |
| apatite (hydroxylapatite, fluorapatite, francolite, dahllite*) | ++ | ++ |
| Carbonates (calcite, dolomite, magnesian calcite*, ankerite*, dawsonite*) | ++ | -- |
| Sulfates (gypsum) | + | -- |
| Sulfides (pyrite*-cinnabar*-covellite*) | + | -- |
| Tectosilicates (quartz) | ++ | + |
| Tectosilicates (feldspar, zeolite*) | + | -- |
| Clays (palygorskite*) | ++ | -- |
| Native element (graphite) | + | -- |
Figure 9.
Diffractogram of a phosphate granule sample from the Jebel Dhyr syncline.
Figure 10.
Left: Diffractogram of isolated pellets, Right: Diffractogram of isolated coprolites from the Jebel Dhyr syncline.
Table 5.
Comparative X-ray diffraction parameters (dhkl) of apatite group from phosphorites deposits in North Africa.
| (hkl) (Miller index) | dhklof peaks (Å) | |||
|---|---|---|---|---|
| J. Jebs, Tunisia (Beji-Sassi 1984) | Foum Selja,Tunisia (Chaabani 1978) | Morocco (El Haddi 2014) | Dhyr, Algeria (this study) | |
| 100 | 8.164 | 8.15 | 8.074 | 8.099 |
| 101 | 5.281 | 5.29 | 5.250 | 5.244 |
| 200 | 4.052 | 4.04 | 4.041 | 4.049 |
| 111 | 3.873 | 3.87 | 3.862 | 3.867 |
| 002 | 3.456 | 3.45 | 3.444 | 3.441 |
| 102 | 3.183 | 3.17 | 3.170 | 3.167 |
| 120 | 3.062 | 3.05 | 3.051 | 3.061 |
| 211 | 2.792 | 2.79 | 2.792 | 2.796 |
| 112 | --- | 2.78 | 2.771 | 2.771 |
| 300 | 2.695 | 2.69 | 2.693 | 2.699 |
| 202 | 2.627 | 2.62 | 2.622 | 2.622 |
| 301 | 2.507 | 2.51 | 2.510 | 2.513 |
| 122 | 2.284 | 2.28 | 2.282’ | 2.287 |
| 310 | 2.240 | 2.24 | 2.240 | 2.240 |
| 131 | 2.130 | 2.13 | 2.131 | 2.135 |
| 113 | 2.062 | 2.07 | 2.061 | 2.059 |
| 203 | 1.997 | --- | 1.996 | 1.995 |
| 222 | 1.931 | 1.93 | 1.930 | 1.933 |
| 132 | 1.879 | 1.87 | 1.880 | 1.880 |
| 123 | 1.836 | 1.84 | 1.836 | --- |
| 231 | 1.788 | 1.77 | 1.790 | 1.790 |
| 410 | 1.762 | 1.76 | 1.765 | 1.766 |
| 303 | 1.741 | 1.73 | 1.743 | --- |
| 004 | 1.722 | 1.71 | 1.723 | 1.720 |
| 322 | --- | --- | 1.632 | 1.634 |