Shamim Ahmad Dar

The phosphate nodules are solely confined to the Green facies of late Paleocene–middle Eocene Subathu Formation in the Subathu Basin of Solan District, Himachal Pradesh, India. The phosphate nodules are hard and compact, elliptical, rounded to well rounded, usually dull earthy to dark grayish in color and break with sharp and conchoidal surfaces. The present study deals with the rare-earth elements (REE) geochemical characteristics viz. hat-shaped, enrichment of middle REE relative to light REE and heavy REE, negative Eu and weak negative to weak positive Ce anomalies and values of ratios such as Er/Nd (0.07–0.19), Y/Ho (32–48), La/Nd (0.46–0.90), (La/Sm)N (0.18–0.47) and (La/Yb)N (0.26–0.51). It appears that the seawater conditions or growth mechanisms were different at the time of formation of cores and rims of the nodules as indicated by the contrast REE concentrations, respectively. Although in both cases very similar REE spectra are observed, rims are much more likely to show a diagenetic alteration front than cores. The Y/Ho ratio (32–48) suggests that the principal source of REE was the terrigenous sediments followed by seawater in the rims and cores of these nodules. The results of this study suggest a dominant role of diagenetic processes in the REE concentration and distribution as well as possible suboxic to anoxic conditions during the formation of cores and rims of phosphate nodules, as also evident by the presence of pyritic nodules in the Subathu Basin of Solan District.

Newer Dolerite Dykes (NDD) traverses the Singhbhum Granitoid Complex (SGC) in distinct orientations viz., NNE-SSW, NNW-SSE and E-W, among which the NNE-SSW trend is the most dominant. These dykes are subalkaline in nature and show compositional variation from basalt through basaltic andesite to andesite. The relationship shown by various oxides against MgO is consistent with fractional crystallization of a mafic magma. Variations in major elements, particularly SiO2, Al2O3, CaO, TiO2 contents, and CaO/TiO2 and Al2O3/TiO2 ratios in the studied dykes indicates that their Ca and Al are held in the residual mantle phases such as clinopyroxene, plagioclase, spinel and garnet. Low Ni and highly variable Cr values suggest that olivine and clinopyroxene fractionation controlled the abundances of Ni and Cr in these rocks. The high (La/Yb)N and (Gd/Yb)N in combination with relatively low HREE abundance of the Newer Dolerites dykes suggest that they may have formed by low degrees of partial me...

The Late Paleocene–Middle Eocene phosphate nodules of Solan District of Himachal Pradesh belong to green facies of Subathu Formation of Sirmur group. Field observations indicate sporadic distribution of phosphatic nodules in the yellow brown to rusty brown, buff-colored bleach shales. Phosphatic nodules are dull earthy to dark grayish in color and break with sharp and conchoidal surfaces. Studies of phosphatic nodules using petrological microscope, X-ray diffractometry, and scanning electron microscopy (SEM) attached with energy dispersive X-ray (EDX) reveal that cryptocrystalline apatite (fluorapatite) is the dominant phosphate mineral. Silt sized silica is the dominant gangue, whereas pyrite and muscovite are present as minor gangue. The phosphate minerals occur as oolites, pellets, and cryptocrystalline apatite in the groundmass. Silica veins form a network replacing the original phosphatic matrix. Brown to brownish black color may be attributed by the organic matter in the phosphatic nodules. Completely phosphatized radiolaria and partially pyritized planktonic foraminifera are observed. There is corroboration of organic matter in the form of microbial filaments in the groundmass of apatite. The findings in the present investigation indicate that the different forms of the minerals, their texture, and distribution in the phosphatic nodules might be due to environmental vicissitudes in oxidizing to reducing conditions followed by replacement processes. Presence of microbial filaments may be due to the active role of microorganisms during the formation of these phosphatic nodules.

ABSTRACT The rare earth element (REE) data from the Paleoproterozoic Bijawar basin, Sonrai phosphorites were used to interpret the depositional conditions of the phosphorites. The post archean Australian shales (PAAS) normalized REE patterns of the Sonrai phosphorites were characterized by negative Ce and positive Eu anomalies. Middle rare earth elements (MREE)-enrichment was a characteristic feature. Phosphorites showing the diagenetic effects on the REE patterns were limited. The observed Eu anomaly was indicative of an anoxic (or sulphate reducing) diagenetic environment of phosphate formation. Mixing of sea water and upwelling during the Paleoproterozoic was responsible for the recording of positive Eu and negative Ce anomalies in the Sonrai phosphorites.

ABSTRACT The paper presents the uranium (U) concentration and distribution pattern in the Paleoproterozoic phosphorites of Lalitpur district of Uttar Pradesh. The study of thin sections, SEM and XRD reveal that apatite is the essential phosphate mineral while quartz and feldspars are the dominant gangue in the phosphorites of the investigated area. The collophane is observed to be mostly oolitic in form and microspherulitic in texture. The major element geochemistry indicated that the phosphorite samples are rich in P2O5, CaO, SiO2 and Fe2O3 whereas depletion of MgO, MnO, K2O and Al2O3 was observed. The CaO/P2O5 ratio ranges from 1.13 to 1.46 which is slightly lower than that of cations and anions substituted francolite (1.621) and close to that of carbonate-fluorapatite (1.318). The trace element geochemistry indicates that the phosphorites of Lalitpur have the significant range of U concentration (1.67 to 129.67 μg/g) which is more than that of Th (0.69 to 0.09 μg/g) among the analysed trace elements in the phosphorite samples of the area. The positive correlation of U with P2O5, CaO and U/P2O5 indicates a close association of U with phosphate minerals like collophane (apatite), whereas negative correlation of U with SiO2 and Fe2O3 may be due to mutual replacement. The antipathetic relationship of U with Ni may be an indication of high oxidizing conditions, whereas sympathetic relationship of U with K2O points towards higher alkaline conditions of the basin of deposition during phosphatization. The variable concentration of U and its relationship with significant major and trace elements in most of the phosphorite samples lead one to believe that the deposition of these phosphorites might have taken place in highly alkaline medium during fairly oxidizing to weakly reducing environmental conditions of geosynclinal basin.

ABSTRACT Major, trace and rare earth elements of phosphatic rocks around Sonrai block of Paleo-Mesoproterozoic age having phosphatic breccia, quartzite, shale, sandstone, limestone and ironstone, have been determined to evaluate their correlation, relationship with the phosphorus content, the nature of possible substitution of various elements and regional distribution pattern over the area. The study indicates that the number of elements is substituted in the apatite structures; few of them are associated with phosphate and carbonate minerals. The variable concentration of major, trace and rare earth elements in the phosphatic rocks has been influenced by various physico-chemical processes involved during weathering and leaching of the source rocks. The distribution of the major, trace and rare earth elements is controlled by the environmental variations in the sediment water interface. The majority of trace elements were mainly influenced by the principle adsorbents like the phosphate minerals in addition to clay, iron oxides and silicate minerals. The PAAS normalized REE patterns of Sonrai block of phosphorites are characterized by negative Ce anomalies and Positive Eu anomalies. It is inferred from the distribution and interrelationship of major, trace and rare earth elements that the deposition of phosphate minerals might have occurred in highly oxidizing to slightly reducing conditions in supratidal to intertidal continental margins and shallow marine environment. The deposition was controlled by marine upwelling leading to excess charge of phosphate in certain zones of phosphogenic basins, lithologic facies variations in restricted circulations of basinal waters and electrochemical factors such as negative Eh, pH and other factors, which influenced the deposition of phosphates. The replacement, precipitation in voids and fissures and diagenesis were also important mechanisms of phosphate generation in Sonrai basin. The main source for various elements may be the minerals of cratonic mass of Bundelkhand Granitic Complex, a basement of Bijawar Basin, which also provided land derived phosphorus through weathering of the terrestrial cover.

Newer Dolerite Dykes (NDD) traverses the Singhbhum Granitoid Complex (SGC) in distinct orientations viz., NNE-SSW, NNW-SSE and E-W, among which the NNE-SSW trend is the most dominant. These dykes are subalkaline in nature and show compositional variation from basalt through basaltic andesite to andesite. The relationship shown by various oxides against MgO is consistent with fractional crystallization of a mafic magma. Variations in major elements, particularly SiO2, Al2O3, CaO, TiO2 contents, and CaO/TiO2 and Al2O3/TiO2 ratios in the studied dykes indicates that their Ca and Al are held in the residual mantle phases such as clinopyroxene, plagioclase, spinel and garnet. Low Ni and highly variable Cr values suggest that olivine and clinopyroxene fractionation controlled the abundances of Ni and Cr in these rocks. The high (La/Yb)N and (Gd/Yb)N in combination with relatively low HREE abundance of the Newer Dolerites dykes suggest that they may have formed by low degrees of partial me...

The phosphate nodules are solely confined to the Green facies of late Paleocene-middle Eocene Subathu Formation in the Subathu Basin of Solan District, Himachal Pradesh, India. The phosphate nodules are hard and compact, elliptical, rounded to well rounded, usually dull earthy to dark grayish in color and break with sharp and conchoidal surfaces. The present study deals with the rare-earth elements (REE) geochemical characteristics viz. hat-shaped, enrichment of middle REE relative to light REE and heavy REE, negative Eu and weak negative to weak positive Ce anomalies and values of ratios such as Er/Nd (0.07-0.19), Y/Ho (32-48), La/Nd (0.46-0.90), (La/Sm) N (0.18-0.47) and (La/Yb) N (0.26-0.51). It appears that the seawater conditions or growth mechanisms were different at the time of formation of cores and rims of the nodules as indicated by the contrast REE concentrations, respectively. Although in both cases very similar REE spectra are observed, rims are much more likely to show a diagenetic alteration front than cores. The Y/Ho ratio (32-48) suggests that the principal source of REE was the terrigenous sediments followed by seawater in the rims and cores of these nodules. The results of this study suggest a dominant role of diagenetic processes in the REE concentration and distribution as well as possible suboxic to anoxic conditions during the formation of cores and rims of phosphate nodules, as also evident by the presence of pyritic nodules in the Subathu Basin of Solan District.

The rare earth element (REE) data from the Paleoproterozoic Bijawar basin, Sonrai phosphorites were used to interpret the depositional conditions of the phosphorites. The post archean Australian shales (PAAS) normalized REE patterns of the Sonrai phosphorites were characterized by negative Ce and positive Eu anomalies. Middle rare earth elements (MREE)-enrichment was a characteristic feature. Phosphorites showing the diagenetic effects on the REE patterns were limited. The observed Eu anomaly was indicative of an anoxic (or sulphate reducing) diagenetic environment of phosphate formation. Mixing of sea water and upwelling during the Paleoproterozoic was responsible for the recording of positive Eu and negative Ce anomalies in the Sonrai phosphorites.

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Newer Dolerite Dykes (NDD) traverses the Singhbhum Granitoid Complex (SGC) in distinct orientations viz., NNE-SSW, NNW-SSE and E-W, among which the NNE-SSW trend is the most dominant. These dykes are subalkaline in nature and show compositional variation from basalt through basaltic andesite to andesite. The relationship shown by various oxides against MgO is consistent with fractional crystallization of a mafic magma. Variations in major elements, particularly SiO 2 , Al 2 O 3 , CaO, TiO 2 contents, and CaO/TiO 2 and Al 2 O 3 /TiO 2 ratios in the studied dykes indicates that their Ca and Al are held in the residual mantle phases such as clinopyroxene, plagioclase, spinel and garnet. Low Ni and highly variable Cr values suggest that olivine and clinopyroxene fractionation controlled the abundances of Ni and Cr in these rocks. The high (La/Yb) N and (Gd/Yb) N in combination with relatively low HREE abundance of the Newer Dolerites dykes suggest that they may have formed by low degrees of partial melting of a garnet bearing source. The higher Th/Zr, Rb/Y, Ba/Nb and Ba/Th ratios of these dykes suggest that their mantle source was enriched/ metasomatised by slab derived fluids. Their geochemical characteristics particularly Ti/Y, Zr/Y, Th/Nb, Ba/Nb, La/Nb, (La/Sm) PM are similar to subduction zone basalts that occur along the plate margin. The enriched LREE-LILE and depletion of high-field strength elements (HFSE) especially Nb, P and Ti and detectable slab-derived components of the studied dykes are all features typical for subduction zone-related petrogenesis.