Provenance studies on the heavy mineral placers along the coastal deposits of Odisha,eastern India

Shyntni Ghosl ,Sudh Agrhri ,Debshish Sengupt

a Department of Geology and Geophysics, Indian Institute of Technology Kharagpur, West Bengal, India

b Department of Applied Geology,Indian Institute of Technology(Indian School of Mines)Dhanbad,Jharkhand,India

Abstract The coastal deposits along the eastern part of the Indian Peninsula are known for the high abundance of heavy minerals. The present study, as discussed here, has been undertaken along the southwestern coastal part of Odisha, India, adjoining the charnockite—migmatite zone of the Eastern Ghat Mobile Belt (EGMB). The composition of the placers along the study area is primarily controlled by the detritus from the proximal hinterland rock type(s). The weathering index has been established based on the grain morphology, major element concentration and radioelement ratios. Petrological characteristics and grain morphology of monazite, zircon,ilmenite and rutile have been presented respectively, and their implications are discussed.The provenance study of these coastal placers is based on the abundance of rare earth elements(REE) and radioactive elements in the placer sands and the rock types in the study area. The tectonic implications are based on the major element abundance of the beach sands.

Keywords Monazite placers, High background radiation area (HBRA), Eastern Ghat Mobile Belt (EGMB),Weathering, Zircon, Rare earth elements (REE), East coast of India

1. Introduction

Geochemical study of the bulk sediments in any given study area provide useful proxy data for understanding the palaeo-weathering, provenance and tectonic history (Armstrong-Altrin et al., 2012, 2016;Madhavaraju et al., 2016, 2017). Varying behaviour of elements during various sedimentary processes preserves the source rock characteristics(Nagarajan et al.,2015; Ramirez-Montoya et al., 2021). Contrasting geochemical behaviour of sediments can provide useful information about provenance and nature of the weathering, thus providing a connection between source and sink obtained through geochemical data.The presence of certain elements resistant to erosion and weathering during the transportation and/or deposition processes is beneficial to preserve the source rock signature (Weltje and von Eynatten, 2004;Madhavaraju et al., 2021). The actinides, trace elements and REE are all suitable for the same as they are more resistant to weathering and erosion processes and hence provide a consistent result as far as the provenance of a sedimentary terrain is concerned.

Fig.1 Lithological variations along the vicinity of the study area(modified after Ramakrishnan et al.,1998).The location of the study area is marked by a solid red square.The various megalineaments are:MSZ—Mahanadi Shear Zone;SSZ—Sileru Shear Zone;KSZ—Koraput—Sonapur Shear Zone; VSZ — Vamsadhara Shear Zone; NSZ — Naggavalli Shear Zone.

The study area of the present work is located alongside the south-western beach area of the coast of Odisha in India. The beach sands have an abundance of heavy minerals like garnet, sphene/titanite, sillimanite,monazite, zircon, rutile, ilmenite and magnetite(Behera,2003).The occurrence of radioactive minerals like zircon and monazite results in an elevated background radiation and hence the area is termed as a high background radiation area (HBRA) (UNSCEAR, 2000;Mohanty et al., 2004; Ghosal et al., 2021). The beach placerslayadjoiningthehigh-grademetamorphicterrain of Eastern Ghat Mobile Belt (EGMB). The charnockite—migmatite zone as proposed by Ramakrishnanetal.(1998)andtheEasternGhatProvince as proposed by Dobmeier and Raith(2003)is a part of the EGMBthat lays immediatelyadjacent to thebeach placer depositsinthestudyarea.TheEasternGhatisconsidered as a mobile belt and has a high geothermal gradient(Baranwal et al.,2006).It has a highly complicated tectonic history which is reflected in the petrology of the variousrocktypespresentwithintheterrain.Considering the importance of the heavy mineral coastal placer deposits oftheeastcoastofIndia,limitedstudies havebeen conducted to assess the specific provenance of these deposits. Provenance studies based on the ilmenite grains from the red sediments of the Bhimlipatnam Coast showed a charnockite provenance(Rao et al.,2019).The provenance and distribution studies of the heavy mineral placers along Tamil Nadu shoreline showed a granulite gneiss, charnockite, migmatite and basic dyke provenance(Kumari et al.,2020).

The present study primarily aims to estimate the weathering index and the provenance of the beach placer deposits along the south western coastal area of Odisha,India.It is apparent that the mineralogy of the placer deposits is influenced by the mineralogy of various rocks of EGMB.But it is to be examined whether the provenance of the placer deposits is linked to the specific terrain, the EGMB, lying adjacent to the study area. Geochemical analyses of these minerals are essential to get an idea about the provenance of such deposits. This includes the study of the petrological characteristics of the heavy mineral beach sands and the study of the grain morphology and its implication of possible weathering intensities. It also includes the tectonic inspection of the source area based on the geochemical nature of the major element oxides.

2. Geological setting

The beach area in the present study lay alongside the charnockite—migmatite zone as proposed by Ramakrishnan et al. (1998)and the Eastern Ghat Province as proposed by Dobmeier and Raith(2003)(Fig.1).Both these geologic zonesofthe EGMB occupyalmost the same area and have similar lithology broadly comprising of charnockite,khondalite,granite and migmatite.The charnockite—migmatite zone comprises an assemblage of acutely migmatised granulites intruded by massiftype anorthosites and porphyritic granitoids(Ramakrishnan et al.,1998).The Eastern Ghat Province consists of the majority of charnockite—migmatite zone as proposed by Ramakrishnan et al. (1998). It mostly comprises assemblages of basic and massif-type anorthosites, garnetiferous gneiss, enderbitic granulites,khondalite gneiss and granite—charnockite complexes(Sengupta et al., 1999; Dasgupta and Sengupta, 2003;Dobmeier and Raith,2003).The beach area of Odisha is bordered by the Singhbhum shear zone to the north,the Bay of Bengal to the east,the EGMB to the west and the Markandi canal to the southwest. The proposed study area lay alongside the south-western beach front of Odisha,extendingfromtheGarampetabeachareatothe north east up to the Markandi beach to the south west.

Studies show that the Eastern Ghat Mobile Belt has a complicated tectonic history, which dates back to the formation of the supercontinent Columbia, its disintegration and later formation of the continent Rodinia.This cratonic block took part in the conjoining of the Indian and the East Antarctica Plate during the formation of both the Columbia and Rodinia supercontinents(Dasgupta and Sengupta,2003;Bose et al.,2011; Henderson et al., 2014; Morrissey et al., 2015;Dasgupta et al., 2017). The age of the Columbia emergence is 2.1—1.8 Ga,and the Rodinia emergence is 1.0—0.9 Ga (Li et al.,2008;Dasgupta et al., 2017).

The Eastern Ghat Province is divided into two regions. The southern region extends from the Vamsadhara-Naggavalli Shear Zones in the northeast to the Godavari Rift in the south, and extends up to the Sileru Shear Zone in the west (Fig. 1; Rickers et al.,2001).Granitic magmatism at a global scale was taking place in the time span of 1.76—1.70 Ga,which was also theperiodfortheaccretionarygrowthofColumbia(Zhao et al., 2002, 2004; Condie et al., 2009). This thermal pulse initiated the rifting within Columbia followed by subduction where the subduction polarity is towards the Indian side(Naganjaneyulu and Santosh,2012).

The geological history belonging to the northern region of the Eastern Ghat Province does not have a clear picture and produces a lot of ambiguity. A multistage tectonic history of this particular region has been deduced by Bose et al. (2016). An ultra-high temperature metamorphism occurred at around 0.98 Ga, which was followed by three tectonometamorphic events at ages of 0.78 Ga,0.75 Ga and 0.52 Ga(Bose et al., 2016; Bose and Dasgupta, 2018). According to Dasgupta et al.(2017),the northern region of EGMB was originally a part of the East Antarctica.The East Antarctic block got separated from the Indian block around 0.78 Ga due to the formation of a rift system(Bose et al.,2016).The blocks again conjoined together during the time of the Pan-African Orogeny around 0.55—0.50 Ga. The subduction polarity of this time was towards the Antarctic Plate as proven from the presence of high pressure mafic granulites along the Grove Mountains, Prydz Bay region of East Antarctica (Liu et al., 2009). The evidence of closure of the ocean is possibly present under the East Antarctic ice sheets and the Indo-Gangetic alluvium(Harley et al., 2013).

3. Methodology

Ten beach sand samples were collected along the coastal area of southern Odisha, typical rock samples of charnockite, migmatite, granite and khondalite from the adjoining areas were also collected. The beach sand samples were then dried in an oven at 60°C for 8 h,and sieved through mesh of various sizes. The samples used for the petrographic analysis belong to the size range between 180 micron and 250 micron(0.18—0.25 mm).The sand samples are then separated with the help of an Isodynamic Separator (Frantz Magnetic Barrier Laboratory Separator, Model LB-1,Serial No. 508) at the Eastern Region, Geological Survey of India, Salt Lake, Kolkata, India. The separator has a side tilt angle of 15°.The current setting used for the separation of each mineral is: 0.1 amp — magnetite; 0.2 amp — magnetite; 0.35 amp — garnet; 0.5 amp — xenotime; 0.76 amp — monazite; 1.5 amp and 1.7 amp — garnet and xenotime; 1.8 amp — zircon.Followed by the separation of the minerals by the Isodynamic Separator, the minerals were also separated with the help of bromoform.Thin sections were made out of these separated samples and were used for petrological and mineralogical studies.

For mineral identification and petrological study of the sand grains, they were observed under optical microscope. Certain minerals like ilmenite and magnetite appeared as opaque minerals under optical microscope. In order to study these opaque minerals and also to study the morphological characteristics of the grains, the thin sections were investigated with the help of a scanning electron microscope with energy dispersive X-ray spectrometer (SEM—EDS, JEOL JSM 6490) at the Department of Geology and Geophysics,Indian Institute of Technology Kharagpur.

The study is based on pertinent geochemical parameters related to the heavy mineral placers. The major element concentration of the samples were undertaken by inductively coupled plasma atomic emission spectrometer (ICP-AES). Instrumental neutron activation analysis (INAA) was carried out for the trace and rare earth element analysis,and the REE concentration was also obtained from the inductively coupled plasma mass spectrometry (ICP-MS) analysis.The details of the sample preparation methods, the equipment used and calibrations were discussed in Khan et al. (2019) and Ghosal et al. (2020). The radioelement concentration was studied using a high purity germanium detector (HPGe) in procedures discussed earlier by Ghosal et al. (2017, 2021).

4. Results

4.1. Petrological study

Fig.2 A)and C)Monazite and zircon grains(marked by yellow arrow)under plain polarized light;B)and D)Backscattered electron images of monazite and zircon grains (marked also by yellow arrow) of the sand samples from the beach placer deposits.

The thin sections of the sand samples collected along the coastal area of southern Odisha contain both opaque and non-opaque mineral percentages. Special emphasis has been given to the study of monazite grains(Fig.2A,B),which are the principal thorium ore within the Indian subcontinent. Monazite grains have also been studied to get an idea of the rare earth elements (REE) concentration. The monazite grains as observed under microscope are mainly elongated in shape and rounded at the edges (Fig. 2A). There are certain monazite grains that are rounded to subrounded in shape, but they are very low in comparison to the elongated monazite grains.

4.2. Geochemical study

The detailed concentration variations of the individual major, trace, rare earth elements and radioelements of the beach sands have been discussed in Khan et al. (2019) and Ghosal et al. (2020). The average SiO2content of the beach sands is roughly 68% which indicates an acidic source rock.The average K2O,Na2O and CaO content is about 1.5%, 0.3% and 0.6% respectively. The beach sands show a high TiO2content with an average value of 8%,and their average Al2O3content is 9%. The trace element concentration has been measured by INAA and exhibits high vanadium(average of ～260 ppm) and zinc (average of ～136 ppm) concentration. The concentration of barium varies between 281 ppm and 10,893 ppm; and the scandium concentration has a range of 7.12—34 ppm. The REE concentrations obtained from the ICP-MS analysis show an average ∑REE of 650 ppm. The concentration of light rare earth elements(LREE)is elevated compared to the heavy rare earth elements (HREE), and a negative europium anomaly with an average value of ～0.3 exists prominently. The average concentration of each individual rare earth element is in the order from high to low as Ce ＞La ＞Nd ＞Pr ＞Sm ＞Gd ＞Dy ＞Er ＞Yb ＞Tb(Ghosal et al.,2020).The REE concentration(∑REE)of the surrounding charnockite rocks is 743 ppm exhibiting the LREE concentration of 729 ppm and HREE concentration of 14 ppm (Ghosal et al., 2020). In the surrounding khondalite rocks, the ∑REE concentration is 38 ppm, and their LREE and HREE concentration are 29 ppm and 9 ppm respectively(Ghosal et al.,2020).

Furthermore, the radioelement concentration of the surrounding rock types shows that the charnockite rocks have a higher uranium and thorium concentration than the khondalite and granite. However, granites show a comparatively high potassium concentration(Ghosal et al., 2021). The beach sands collected from the study area show a high concentration of thorium compared to the uranium and potassium. The average232Th,238U,and40K activity concentration of the beach sands are 2489 Bq/kg, 274 Bq/kg, and 683 Bq/kg respectively(Ghosal et al.,2017).

In monazite,the composition of phosphorus is ＞10%and of thorium is ＞5%; and among REE's the concentration of cerium is ＞20% followed by the lanthanum concentration of ＞10%and the neodymium of＞6%is measured with the SEM—EDS.The monazite grains also consist of elements like Fe,Ni,Cr,Ag,Si,Ca in very small quantities. The thorium concentration of the monazite grains exhibits a wide variation between 4%to 14%,with some grains showing total absence of thorium altogether. The zircon grains obtained from the study area have been studied with SEM(Fig.2D).It exhibits a low concentration of uranium and REE,which is below the detection level of the SEM—EDS instrument.

5. Discussion

5.1. Textural and compositional study of heavy mineral grains

The elongated shape of the monazite grains as observed under microscope suggests that the source of the monazite grains is nearby and the rounded edge shows that the grains have experienced some sort of abrasion activity during the transport process. The backscattered electron image of the monazite grains(Fig. 2B) shows no striation which is indicative of the high durability of the monazite and also points to the smaller transportation distance of the grains.

The zircon grains are elongated in shape with rounded edges(Fig.2C).The composition of the zircon grains is constant with the zirconium concentration equal to almost 50% in all grains. There is minor concentration of chromium found in certain zircon grains.Zircon is the primary source of uranium in the placer deposits. However, none of the zircon grains in the SEM—EDS shows any trace of the presence of uranium.The concentration of uranium in the zircon grains is below the detection limit of the instrument. The detection limit of an instrument is the lowest quantity of an element detected that can be distinguished from the absence, and the lowest detection limit is 1500—2000 ppm for an element within the SEM, JEOL JSM 6490. The present study area is noted for its high thorium and low uranium concentration (Mohanty et al., 2004; Rao et al., 2009; Ghosal et al., 2017,2021;Khan et al.,2019).The low232U concentration in the placer deposits is a direct consequence of the low uranium concentration in the zircon grains.

Fig. 3 A) Backscattered electron image of ilmenite and rutile grains (marked by arrow); B) Rutile crystal showing striations and pits. Note that the chromium deposit (marked by arrow) is found in the grooves of the pit structure.

The ilmenite grains in these placer deposits show an elongated shape with rounded edges(Fig.3A). Most of thegrainshave a titaniumconcentrationbetween30%to 35%and iron concentration between 30%to 33%.This is in contrast to the ilmenite grains along the Vishakhapatnam—Bhimlipatnam Coast in Andhra Pradesh where the titanium concentration is lower than the iron concentration (Jagannadha Rao et al., 2005).Certain ilmenite grains consistof chromium(Cr ＞2%)and magnesium(Mg ＞2%)which again is a common feature found in ilmenite grains along the coastal areas(Jagannadha Rao et al.,2005).The elongated shape and rounded edges of the ilmenite grains suggest a smaller transportation distance from the source. Altered ilmenite grains show a higher Ti concentration and a lower Fe concentration, but ilmenite grains from the placerdeposits ofthestudyareado not showsuchkindof a compositional variation. The concentration of impurities like chromium,which increases with the increase in degree of alteration,also shows a low concentration.Considering the above aspects,it can be concluded that the ilmenite grains in the beach sands of the study area have a low degree of weathering and alteration.

In the study area the rutile grains are angular to sub-rounded in shape. The titanium concentration in the rutile grains varies between 50% to 60%. The roundness of the grains does not imply a high degree of weathering and transportation, however in quite a number of grains, the grain surface consists of striations and pits. In Fig. 3B, the rutile grain shows multiple striations and pits as well. The grooves formed because the pits showed a secondary deposit of Cr.

5.2. Weathering condition

The study of Chemical Index of Alteration (CIA),Plagioclase Index of Alteration (PIA) coupled with the Th/U ratio has been used to comprehend the intensity of weathering in the study area.

The estimation of the CIA values of the placer deposits is based on the following equation (Nesbitt and Young, 1982):

here,CaO＊corresponds to the CaO incorporated in the silicate minerals.

The CIA value lies between 71 to 86 and it suggests a high to moderate intensity of weathering (Ghosal et al., 2020).

The Plagioclase Index of Alteration values are calculated by the following equation:

The degree of chemical alteration for a sedimentary deposit can be estimated by the PIA (Nesbitt and Young, 1984). This value basically calculates the degree to which plagioclase feldspars have been eroded.During the weathering of a source rock, calcium is leached comparatively faster than Na and K from feldspars. Also, plagioclase feldspar is broken and removed faster than the K-feldspar in the course of weathering and transportation (Nesbitt and Young,1984). A high PIA value (＞80) designates a higher degree of chemical weathering. Considering the study area shows PIA values ranging between 86 to 92,it can be concluded that the study area faces a high degree of chemical weathering. The heavy mineral beach placer deposits exhibit a higher degree of chemical weathering along with the elimination of plagioclase feldspar, which is a fact substantiated by the consistent negative europium anomaly of the samples(Fig. 4A; Ghosal et al., 2020).

The beach sand samples show an average Th/U ratio of ～29(Ghosal et al.,2020),which is quite high as compared to the crustal ratio of 3.8(Rudnick and Gao,2003).A high-intensity weathering of the source rocks can be interpreted from the elevated value of the Th/U ratio. Hexavalent uranium tends to go into the solution that results in leaching, hence extreme weathering of the source rocks results in the removal of uranium which thereby increases the Th/U ratio. The presence of these placer deposits alongside water bodies also results in the further leaching of uranium.Therefore, a high Th/U ratio value of the coastal placers can be implicated to a high degree of weathering (Armstrong-Altrin et al., 2014).

Fig.4 A)The chondrite-normalized REE pattern diagram of the beach placers and the surrounding rocks(the chondrite REE values obtained from Taylor and McLennan(1985);and the migmatite REE data are from Bhadra et al.(2007));B)The La—Th-Sc ternary diagram depicts the felsic nature of the beach placers as the sample cluster lies along the La—Th joining line which are two elements both enriched in felsic rocks(Taylor and McLennan,1985).The sample cluster also shows a granite gneiss provenance when compared to Taylor and McLennan(1985)which can be explained by the presence of charnockite rock bodies adjacent to the study area.

5.3. Provenance

The study area is located adjacent to the EGMB containing rock types of granite,migmatite,khondalite and charnockite (Ramakrishnan et al., 1998). Therefore, the compositional characteristics of the beach sands should be similar to these mentioned rocks,which have a felsic composition. The REE and radioelement concentration ratios in the beach sands like the La/Sc and Th/Sc ratios were used to provide a reliable indication about the felsic composition of the placers. For felsic rocks,the La/Sc and Th/Sc ratios range between 2.5 to 16.3 and 0.84 to 20.5 respectively(Cullers et al.,1988; Cullers, 1994, 2000; Cullers and Podkovyrov,2000; Nagarajan et al., 2007). The La/Sc ratio of the beach sands ranges between 6.29 to 57.59 and the Th/Sc ratio ranges between 3.82 to 42.06.In addition,the mafic rocks usually show a low LREE/HREE value and a dearth of europium anomaly,while the felsic rocks are observed as high LREE/HREE values with the negative europium anomaly (Cullers and Graf, 1984; Taylor and McLennan, 1985; Kasanzu et al., 2008). The LREE/HREE ratio of beach sands varies from 3.3 to 30 with negative europium anomaly values ranging between 0.06 to 0.7 (Ghosal et al., 2020). Fig. 4A shows the chondrite-normalized REE pattern of the beach sand samples and specific source rock types present along the surrounding areas.The figure exhibits the LREE and HREE pattern as well as the negative europium anomaly of the specific source rock types as well. The concentration variation among elements La, Th and Sc has been utilized to discern between felsic and mafic sources (Cullers, 2002). The high concentration of La and Th is symptomatic of a felsic source and the high concentration of Sc is indicative of a mafic source. A La—Th-Sc ternary diagram presented in Fig. 4B shows that the sample cluster was plotted along the La—Th line, indicating a felsic affinity instead of a mafic affinity (close to Sc). This would suggest that the beach placer deposits belongs to a felsic source (McLennan et al.,1980;Kasanzu et al.,2008).

The La—Th-Sc ternary diagram provides information not only about the felsic or mafic affinity of the placer deposits but also about the probable provenance of these deposits (McLennan and Taylor, 1991;Babu, 2017). The La, Th and Sc compositions of the beach sand samples were plotted in the La—Th-Sc ternary diagram as proposed by Taylor and McLennan(1985) and fell into the field of granite and gneiss sources (Fig. 4B). Considering charnockite belongs to the granite groups of rocks or more evidently it is considered as the‘pyroxene-bearing granite’,hence it can be said that the beach sand samples have been sourced from the charnockite group of rocks present adjacent to the study area. As the charnockite—migmatite zone is the main lithologic unit adjoining the study area (Fig. 1), this conclusion is in accordance with the present scenario.The high barium concentration as mentioned in the Result section also indicates the proximity of the source area. The concentration of barite gives us an idea of the distance between the source and the sink area. The mineral barite is brittle and metastable hence,its presence in secondary deposits,which is situated at a considerable distance from its source area, is extremely rare (El-Kammar et al., 2011). Also, the entire catchment of the Rushikulya River, which is the major supplier of sediments to the study area, lies within the charnockite—migmatite zone(Fig.1).Hence,it can be inferred that the main source of the beach placers is charnockitic in nature.

The rare earth element pattern and its concentration variation have been used to identify the possible source rock of the beach placer deposits.The Gd/Yb ratio is an indication of the HREE concentration of the source rock in a deposit.A value greater than 2 indicates an HREE-depleted source and an HREEenriched source is indicated by a value less than 2.The average Gd/Yb ratio of the beach sands is ～4 which indicates that these beach sands have been derived from a HREE-depleted source. A cross plot of Gd/Yb ratio versus Eu/Eu＊ ratio of the beach sands and the hinterland rocks is provided in Fig. 5A. It shows that the REE composition of the beach sands is similar to the charnockite and migmatite composition (Ghosal et al., 2020). Considering that the beach area derived most of its detritus from the adjacent charnockite—migmatite zone, the beach placers indicate a charnockite provenance.

5.4. Tectonic implications

Tectonic setting of the source rock region can be identified from the major and trace element concentration of a sedimentary deposit (Bhatia, 1983;Armstrong-Altrin and Verma, 2005). A multidimensional discriminant—function diagram had been put forward by Verma and Armstrong-Altrin (2013)based on the major element concentration of siliciclastic sediments to discriminating a study area among three types of tectonic setting (Fig. 5B): the continental or island arc, the continental rift, and the collision.The two discriminant functions(DF1 and DF2)involved in the diagram are calculated as the following equations (3) and (4) (Verma and Armstrong-Altrin,2013, their Table 8):

This discriminant—function diagram has been validated in a number of studies such as Armstrong-Altrin et al. (2014), Zaid and Gahtani (2014) and Nagarajan et al. (2015). From Fig. 5B it is observed that the composition of the sand samples fall in the ‘collision’field, providing an idea about the collisional tectonic history of the source region. However, the EGMB does not represent a collisional setting,it rather represents an accretionary tectonic setting (Dasgupta et al.,2013, 2017; Bose and Dasgupta, 2018). According to Dasgupta et al. (2017), the charnockite emplacement along EGMB occurred during 0.98 Ga, which was followed by three episodes of tectonometamorphic events (as discussed in section 2). As observed earlier the REE geochemistry of the beach sands shows a charnockite—migmatite provenance.Hence, it can be said that the tectonic implication is a manifestation of the earlier formed charnockite lithology of the area.The geochemical data of the detritus sourced from the early formed charnockite, is the reason behind the incorrect tectonic setting identification.

Acknowledgements

The authors express their gratitude to Dr. Mandakini Maharana, Geologist, Eastern Region, Geological Survey of India, Salt Lake, Kolkata, India, for her constant support.

6. Conclusions

The beach placer deposit along the coastal area of Odisha,eastern India has a moderate degree of weathering as indicated by the grain morphology of most of the heavy minerals. The weathering index of the studied deposits based on the CIA,PIA and the Th/U ratio values indicates that this area has experienced a moderate to a high degree of chemical weathering. The monazite grains consist of high thorium and LREE concentrations.The ilmenite grains show a high titanium concentration(30%—35%), which causes a major economic deposit in the study area. The REE and radioelement concentrations indicate that the beach placer deposits have a felsic composition with a charnockite provenance.

Availability of data and materials

The datasets used during the current study are available from the corresponding author on reasonable request.

Funding

Financial assistance for the completion of this work has been received from the Science and Engineering Research Board (SERB), DST, Government of India,under the Project Code: YSS/2015/000979.

Authors' contributions

All the authors have actively participated in the preparation of the manuscript. All authors read and approved the final proof.

Declaration of competing interest

There are no conflicting interests between the authors and institutions involved.