Quantitative Mineralogical Analysis and Study of Morphology and Thermal Characteristics of Rock Samples of Dudhi Nala and Bokaro River.

Introduction

Damodar Valley Basin, an important storehouse of indian  coal,  is part of the Gondwana Systems. The beds of Talchir   formation are well exposed in the western part of the Bokaro basin, ( Dudhi Nala) which comprises tillite, conglomerates, sandstones, with dropstones and turbidite sequences comprising siltstones and shales. The lower part of the  Talchir formation is believed to be of glacial origin. On the other hand  the environment of deposition of the upper part is still not clear and the observed sedimentary features can be explained by sedimentation in a sea or a big lake ¹. The polyplacophoran fossils reported from upper Talchir sediments of Dudhi Nala area reveal a marine link of the west Bokaro basin during the Upper Talchir times ². However, absence of marine fossils and presence of cross- bedded sandstone and conglomerate in overlying unit ( along with a few fish  bones and reptile fossils) which are common in most of the Talchir basins are indicative of glaciofluvial- glaciolacustrine freshwater regime³.  Stable isotope analysis  was carried out ⁴, suggests that precipitation of the Talchir carbonates took place in a fresh water environment, and the water was suppplied by melting of glacier formed in nearby hills ⁵. In this work, chemical composition, morphological and thermal characteristics of the sediments of the Talchir deposits of Dudhi Nala has been studied to understand the   environment of the sediments . We also focused on some part of Bokaro river to study the variation.

Geologic Overview

Dudhi Nala is located in the western part of the Bokaro Coalfields,  near  the Mandu block of  Ramgarh  district. An excellent exposure of the Talchir sediments of the Damodar valley basin was found³  near the confluence of Dudhi Nala, Dube Nala and Silahi Nala about 0.5 km south of the village Jarwa (lat. 85^◦27’ and long. 23^◦ 49’ ) at the western part of the Bokaro sub-basin. The sediments here rest unconformably on the Archaean basement and comprise conglomerate, sandstone and siltstone⁶. Here, bluish-grey siltstones, yellow coloured sandstone bed with hummocky cross stratification, greenish-grey siltstones, bluish- green rhythmite   bed is very well exposed. Sediments of Bokaro river are different in colour and texture.

Figure 1: Showing Gondwana basins and the study areas: Dudhinala, Silahi Nala, and Bokaro river7. Click here to View Figure

Methods

Damoder valley basin contains  a sub chain of stratigraphic  sequences of Talcher deposits.  An interesting deposit appears near the village Jarawara dudhinala, Dubey nala and Silainala. Large number of samples were collected from Dudhi Nala and Bokaro river⁸, out of which 8 samples of geological significance  based on petrography were subjected  for the analysis.  Rock samples were powdered using  mortar and pestle and sieved to very fine powdered form. Samples were dried in a hot air oven to remove the moisture content in the samples, then different analysis were carried out. Majority of the analysis, FESEM/EDX, TGA, DSC and XRD were carried out  in  the Central Instrumentation Facility, Birla Institute of Technology Mesra, Ranchi. Major and trace elements were analysed at the XRF-IRMS lab, Department of Earth Sciences, Indian Institute of Technology, Kanpur.

Petrography

A typical petrography photograph is shown in figure 2.

Figure 2: Typical photographs  of rock outcrops on (A) Dudhi Nala and (B) Bokaro river. Click here to View Figure

FESEM and EDX Study: FESEM ans EDX studies were conducted by taking eight samples. A typical FESEM and EDX analysis of sample S2 from Dudhinala  and sample S6 from Bokaro river are shown in the figure 3 to  figure 6 respectively. 

Figure 3: FESEM micrograph of sample S2 collected from Dudhi Nala. Click here to View Figure

Figure 4: EDX peaks of sample S2 collected from Dudhi Nala. Click here to View Figure

Figure 5: FESEM micrograph of sample S6 collected from Bokaro  river. Click here to View Figure

Figure 6: EDX peaks of sample S6 collected from Bokaro  river. Click here to View Figure

The  rock outcrops consist of the Dropstones, Potholes, Concretions, and Hummocky cross stratification. The difference in morphology in the samples collected from both the study areas is clearly evident from the FESEM images and EDX data, Si is dominant in the samples collected from the Dudhi Nala section  with lower  concentrations of Ca,  Na, K.  Fe is dominant in the  samples collected from Bokaro river, with lower concentrations of Si, Mn, Al and K. Quartz grains can be easily observed in the FESEM image of sample S1 and sample S2 of Dudhi Nala.

Thermal Analysis (Tga & Dta)

Figures 7: Showing TGA & DTA analysis of sample S2 collected from Dudhinala. Click here to View Figure

The TGA and DTA analysis of sample S2 and S6  are shown in figure7 and figure 8 shows multi stage decomposition in both the samples⁹.  Total weight loss in sample S2 collected from Dudhi Nala was observed to be -11.660 %, within the temperature range of 30-1000^◦ C. While, in the same temperature range, total weight loss was observed to be -18.467%. Also the DTA curve vary in both the samples.

Figure 8: Showing  TGA  & DSC curve of sample S6 collected from and S6 of Bokaro river. Click here to View Figure

The DSC analysis  of sample S6  shows an endothermic peak, with Peak temperature of 273.43^◦ C. Onset was observed at 227.42^◦ C. Enthalpy normalised was found to be: 37.222 J/g. The endothermic peak, hints about the presence of Clay minerals in the sample. The sample S8 shows three peaks. Peak temperature for the first peak is observed at 39.13^◦ C. Enathalpy normalised is 6.8964 J/g, and Onset is observed at 31.81^◦ C. Peak temperature for the 2nd peak is 147.11^◦ C. Enthalpy normalised is 1.0004 J/g, and onset is observed at 125.69^◦ C. Peaks hint about the presence of clay minerals.

X – RAY DIFFRACTION STUDY : A typical X-ray photographs  of sample S2 is shown  in figure 9 and that of sample S6 is shown in figure 10.

Figure 9: showing XRD peaks of Sample 2 collected from Dudhi Nala. Click here to View  Figure

Figure 10: showing XRD peaks of sample S6 collected from Bokaro river. Click here to View Figure

From XRD Analysis it is clear that the samples collected from Dudhi Nala are dominant with Quartz with minor amount of Feldspar, Calcite and Zircon. And in the case of Bokaro river samples, Magnetite and Quartz are the major minerals with minor amount of feldspar and Zircon.

X-Ray Fluorescence

X-ray fluorescence analysis data is shown in table 1. It is clear from the table 1  that

Table 1: XRF data of major oxides and Trace elements. Dashes means that the elements were not analysed.

Major oxides and Trace elements	Sl	S2	S3	S4	S5	S6	S7	S8
AI203	12.68	11.77	12.82	12.11	9.62	10.60	16.56	19.45
CaO	0.59	0.72	1.33	0.74	0.42	0.17	1.04	0.11
Fe203	1.73	1.18	4.99	56.63	61.50	68.08	5.76	3.22
K2o	4.99	6.39	2.65	0.88	0.91	0.59	2.95	2.76
MgO	1.01	0.13	3.28	0.35	0.52	0.24	2.03	0.53
Na20	3.65	3.09	2.31	0.87	0.00	0.88	2.19	0.74
P205	0.06	0.00	0.17	0.00	0.00	0.04	0.12	0.08
Si02	67.68	68.75	66.98	25.34	24.11	18.42	68.15	60.99
Ti02	0.43	0.11	0.65	0.65	0.34	0.29	0.71	0.45
NiO	0.001	0.000	0.002	0.003	0.00	0.006	0.003	0.003
MnO	0.05	0.05	0.09	1.12	1.67	1.46	0.07	0.05
Total	92.85	92.19	95.27	98.70	99.09	100.77	99.57	88.36
Ba	921	1047	748	287	386	198	930	301
Ce	74	–	92	31	30	41	59	67
Cr	106	81	81	58	36	43	78	140
La	46	–	53	18	14	26	50	44
Rb	219	210	93	28	31	22	93	54
Sc	–	–	10	38	35	39	12	12
Sr	225	312	104	–	9	–	69	–
Th	22	3	16	7	3	6	14	6
V	39	–	90	95	70	68	94	117
Y	37	36	34	–	5	–	28	15
Zr	151	54	256	71	41	–	144	66
Zn	26	21	55	70	59	90	74	41
Pb	41	65	25	16	19	11	20	8

SiO₂ is the dominant oxide present in the Dudhi Nala Samples, and Fe₂O₃ is the major oxide, present in the samples of Bokaro  river.  Al₂O₃  is the common major oxide present in the samples of both the study areas.   From the XRF Data it was evident that many  trace elements, and Rare Earth Elements are present in the samples of both the study areas. A comparison of rare earth trace element  of Dudhinala and Bokaroriver  is shown in figure 11.  Concentration of Ba (1047 ppm),  Ce (92 ppm), La(53 ppm),  Rb(219 ppm),  Sr(312 ppm), Th(22 ppm), Y(37 ppm),  Zr(256 ppm) and Pb(65 ppm) is higher in the Quartz dominated, samples of Dudhinala. Concentration of trace elements like Cr(140 ppm),  Sc(39 ppm), V(117 ppm), Zn(90 ppm), is higher in the samples of Bokaro  river.

Figure 11: Comparison of the concentration (ppm) of Trace Elements in both the study areas: Dudhi Nala and Bokaro  river. Click here to View Figure

Figure 12: Comparison of the Rare Earth Elements concentration in the samples of Dudhi Nala and Bokaro  river . Click here to View Figure

The comparision of rare earth element  concentration in Dudhinala  and Bokaro river  sample is shown in figure 12.  It is evident from the graph that the concentration of Ce, La, Y is higher in the samples of Dudhi Nala. While, Sc concentration is higher in the Bokaro river sample.

Results and Discussions

There is a clear difference in the morphological characteristics^10-12 and thermal characteristics of the permo- carnboniferous Talchir sediments collected from  the  Dudhi  Nala section and sediments of Bokaro river^13-16, which is evident from the Petrographic investigations and through TGA/ DSC studies. FESEM images reveals fine grains of Quartz in the Dudhi Nala samples, with rounded to sub rounded grains of Zircon. The nodules of Dudhi Nala are composed of   quartz, feldspar  and heavy minerals with minor amount of clay minerals.  Biotite, Aragonite and zircon could be identified by the XRD analysis. SiO₂ is the dominant oxide found in the nodules of Dudhi Nala while, Fe₂O₃ is the major oxide present in the nodules of Bokaro river.  The  EDX  analysis indicate  a significance  presence of iron in S6 while the  XRD analysis of the same sample shows  prominent quartz peak indicating substantial amount silica  may be attributed  to  the multicomponent  mixture usually  contain  overlapping peaks,  crystal size and  scan duration.

Al₂O₃  concentration is  similar in the samples of both  the study areas. SEMEDX analysis shows significant presence of iron in sample S6 while XRD analysis  shows prominent peak of silica, which may be attributed to  the  intensity of X-Ray diffraction line  depends on minerals  composition , nature of samples and  scan duration.  The  rock samples  contains a mixture of different compositions of iron contents  therefore  diffraction peaks of these minerals shows overlapping  and  favours XRD peaks of lower intensity. 

High silica source rocks ^19-20[  ] tend to contain higher concentrations of REE, Th, Hf and Ba, lower concentration of Co, Fe, Sc and Cr, and more negative Eu anomalies than the low silica source rocks (17-18)High SiO₂ containing rock samples of Dudhi Nala has higher concentration of Ba (1047 ppm), Th(22 ppm), Zr(256 ppm), Sr(312 ppm) and Pb(65 ppm). And High Fe₂O₃ containing rock samples of Bokaro river has higher concentration of Sc(39 ppm)  and  Zn(90 ppm).  Concentration   of  Rare Earth Elements, Ce(92 ppm), La(53 ppm), Y (37 ppm) is higher in the nodules of Dudhi Nala and  concentration of Sc(39 ppm) is higher in the nodules of Bokaro river. Therefore, REE concentration and their pattern in the sediments are very useful for identification of source rock types.

Conclusion

This study of  glacigenic  Talchir sediments of  the Bokaro district  Dudhi Nala section  shows  morphology variations , major oxides, trace elements and Rare Earth elements  are of great geological importance. The samples collected from Dudhi Nala are enriched in SiO₂ (66-68  wt % compared  to 25-60 wt % in the samples of Bokaro river). In contrast to SiO₂, Fe₂O₃  is dominant in the Bokaro river samples. Dudhi Nala samples are rich in trace elements like Ba (1047 ppm),  Rb ( 219 ppm),  Sr (312 ppm),  Zr ( 256 ppm),  Pb (65 ppm), while Cr (140 ppm), Sc (39 ppm), V (117 ppm), Zn (90 ppm) concentration is found to be more in the Bokaro river samples. It was  confirmed that Calcite and feldspar are the common minerals present in  the samples of the both the study areas.

Acknowledgement

We thank Central Instrumentation Facility (CIF) BIT Mesra, for help in the analysis, Professor Debajyoti Paul, Department of Earth Sciences, IIT Kanpur, for the XRF analysis, and Dr. MK Saini, Principal Scientist, CIMFR, Namkum, Ranchi for his valuable feedbacks.

Conflict of Interest

The authors declare that there is no conflict of interest to be reported.

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