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Uranium series disequilibrium studies in Chenchu colony area, Guntur district, Andhra Pradesh, India
Author’s Accepted Manuscript Uranium Series Disequilibrium Studies In Chenchu Colony Area, Guntur District, Andhra Pradesh, India H.B. Shrivastava, V. Koteswara Rao, R.V. Singh, M. Rahman, G.B. Rout, Rahul Banerjee, B.K. Pandey, M.B. Verma www.elsevier.com/locate/apradiso
PII: DOI: Reference:
S0969-8043(15)30135-4 http://dx.doi.org/10.1016/j.apradiso.2015.07.055 ARI7084
To appear in: Applied Radiation and Isotopes Received date: 17 December 2014 Revised date: 25 July 2015 Accepted date: 29 July 2015 Cite this article as: H.B. Shrivastava, V. Koteswara Rao, R.V. Singh, M. Rahman, G.B. Rout, Rahul Banerjee, B.K. Pandey and M.B. Verma, Uranium Series Disequilibrium Studies In Chenchu Colony Area, Guntur District, Andhra Pradesh, India, Applied Radiation and Isotopes, http://dx.doi.org/10.1016/j.apradiso.2015.07.055 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Uranium series disequilibrium studies in Chenchu colony area, Guntur District, Andhra Pradesh, India H. B. Shrivastava, V. Koteswara Rao, R. V. Singh, M. Rahman, G. B. Rout, Rahul Banerjee, B. K. Pandey and M.B.Verma Atomic Minerals Directorate for Exploration and Research, Begumpet, Hyderabad Email: [email protected]
Abstract An attempt is made to understand uranium series disequilibrium in unconformity proximal related uranium mineralisation in Chenchu colony area, Guntur District, Andhra Pradesh, India. The uranium mineralization in Chenchu colony is the western continuity of the Koppunuru uranium deposit and predominantly hosted by gritty quartzite/conglomerate, which occasionally transgresses to underlying basement granite/basic rock. Disequilibrium studies are based on borehole core samples (35 boreholes, No. of samples =634) broadly divided in two groups of cover rocks of Banganapalle formation (above unconformity) and basement granites (below unconformity). Linear regression coefficient between uranium and radium is 0.95, which reflects excellent correlation and significant enrichment of parent uranium. Disequilibrium studies have indicated predominant disequilibrium in favour of parent uranium (35%), which is probably due to the weathering process causing migration of some of the radionuclides while dissolution of minerals due to groundwater action might have also played a significant role. Further, escape of radon might have accentuated the disequilibrium factor resulting in an increase in the grade of the mineralization. This is well corroborated by the presence of fractures and faults in the study area providing channels for radon migration/ escape. Key words: Uranium, Disequilibrium factor, Beta gamma method, Gamma Ray Spectrometry, Guntur district, Andhra Pradesh
Introduction For the growth and development of any country, energy is the prime requirement and hence sustainable energy resources are essential. With the fast depletion of fossil fuel reserves and pollution related issues associated with thermal energy, attention is being given to green and high density energy sources such as nuclear energy. Uranium is one of the main nuclear fuels, which needs to be developed to sustain the growth of nuclear energy. In India, an extensive exploration programme is being carried out in different geological domains to establish new uranium resources and reserves. In most of the cases, disequilibrium in radioactive ore has presented a difficult problem for proper assessment of the resources. However, it is observed that the magnitude and frequency of radioactivity disequilibria is generally ignored leading to underestimation or overestimation of the deposit. In recent years the significance of disequilibrium studies is being given importance both in field and 1
laboratory counting measurements to overcome uranium ore deposit evaluation related constraints. In a radioactive series, equilibrium is attained when all the daughter products decay at the same rate that they are produced from the parent isotope (Hay et al., 1972). Thus, at equilibrium each of these daughter products would be present in a constant proportion to its parent isotope. The loss or gain of any important isotopes, by different geological and physicochemical processes, during the more recent part of the existence of a mineral, causes disequilibrium in the proportions of the parent isotope to its daughter products (Rosholt, 1958). The importance of these aspects is being evaluated for unconformity proximal and fracture controlled types of uranium mineralisation in Chenchu colony area, which falls in the Northern part of Cuddapah basin. U-series disequilibrium study of subsurface core samples of Chenchu colony area has been done by using the beta gamma method and gamma ray spectrometry. The present paper deals with results of disequilibrium studies and its implication on uranium distribution pattern/mineralisation. Geological Setting Uranium mineralization in the northern part of Cuddapah basin has been explored by the Atomic Minerals Directorate for Exploration and Research (AMD) over two decades and the established unconformity proximal uranium deposit in Srisailam and Palnad sub-basins (Sinha et al., 1995; Sinha et al., 1996; Jeyagopal et al., 1996). Koppunuru uranium deposit is mainly hosted in cover rocks of Banganapalle formation (85%) and occasionally transgresses in to basement granites (15%) along well defined fractures across the unconformity contact (Verma et al., 2011). Chenchu Colony area is located in the south-western marginal part of Palnad Subbasin and is being explored for uranium mineralization to check the western continuity of the Koppunuru uranium deposit. Palnad sub basin exposes Kurnool Group of sediments which are deposited over basement granites, exposed along the up-thrown block of the WNW–ESE trending Kandlagunta fault and as inliers in the southern and western parts (Fig. 1). The basement rocks are mainly represented by medium to coarse grained pink and pinkish grey granites. These granites are highly sheared, fractured and traversed at places by dolerite dykes and quartz veins signifying basement reactivation. Kurnool Group is represented by a thick column of sediments belonging to the quartzite-limestone-shale cycle. This group is classified into six formations viz., 2
Banganapalle, Narji, Auk (Owk), Paniam, Koilkuntla and Nandyal formations (Nagaraja Rao et al., 1987). Among these, the first four formations are well developed in the study area. The lowermost unit, Banganapalle Formation is represented by a 10-173 m thick column of quartz arenite and intercalated grey shale sequence with basal conglomerate/gritty quartzite (Gupta et al., 2010; Banerjee et al., 2012). This is overlain by the Narji Formation comprising white to grey coloured massive limestones and an intercalated calcareous shale sequence. The Auk Formation consists of 2–10 m thick ferruginous ochreous calc-shale while an outlier of younger Paniam quartzite (10–20 m thick quartz arenite) occurs at ridge tops. The overall thickness of the Kurnool sediments in this part varies from 10 m to 205 m with gentle dips (350), mostly following the basement topography. In Chenchu colony area, Banganapalle Formation is hosting uranium mineralisation proximal
to
basement
unconformity
and
mainly
associated
with
a
gritty
quartzite/conglomerate unit. At places, uranium mineralisation partly transgresses below the unconformity contact in basement granitoids along the fracture planes (Gupta et al., 2010, 2012; Ramesh Babu et al., 2012). It is observed that the mineralisation follows a predominant N-S to NNE – SSW trend in this area which is sympathetic to post – depositional (Banganapalle sediments) younger faults and fractures. Besides, the basement granites in the vicinity show substantial reactivation as evidenced by the presence of basic dykes, profuse quartz veins and WNW-ESE trending fractures sub-parallel to the Kandlagunta fault (Ramesh Babu et al., 2012; Thomas et al., 2014). Sampling and Analytical techniques A total of 634 mineralised core samples from 35 boreholes of Chenchu colony area were collected for the disequilibrium studies. In these boreholes uranium mineralisation was intercepted between 75 to 170 m depth and mineralised bands have thicknesses between 0.6 m to 6.8 m and average grade is between 0.01 % to 0.094 % of eU3O8. Details of mineralized intercepts, lithounit, depth of unconformity and number of samples collected are shown in Table 1. Out of 634 samples, 216 samples are from basement granite below the unconformity contact. These core samples were crushed to -200 mesh to maintain homogeneity. Subsequently, samples were studied for equilibrium/disequilibrium state using High Energy Gamma Ray Spectrometry (HEGS) along with physical assay of U3O8(%) by β/γ–method (Acharyulu et al., 2004; Bhaumik et al., 2004). Further, these samples were analyzed for equivalent U3O8 (%eU3O8), radium equivalent U3O8 (%RaeU3O8), %ThO2 and %K.
3
U3O8 content in the sample was estimated by simultaneous measurement of total beta and total gamma radiations using a LND 73201 beta tube and
a 1¾″ x 2″ NaI(Tl)
scintillation detector, respectively (Eichholz et al., 1953; Ghosh, 1972). The U3O8 estimation was determined by the following equation:U3O8 = (1+C)Uβ – C Uγ Where:
(1)
Uβ = beta activity of uranium Uγ = gamma activity of uranium C = ratio of Ra beta to U beta
Estimation of Uranium: The concentration of uranium in the sample was estimated by beta gamma method using equation (1). Detection limit is 90 ppm with ±10% error. IAEA uranium reference standard RGU-1(U3O8 = 460 ppm & Ra (eU3O8) =470 ppm) was also analysed to validate the technique. The value obtained for RGU-1 by this technique was 453 ppm ± 24 ppm. Ra (eU3O8), ThO2 and %K concentrations in the sample were estimated by using gamma ray spectrometry. For the estimation of Ra (eU3O8), the 1.76 MeV of gamma ray energy was measured from the Bi-214 (t1/2 = 19.7 min) which is one of the daughters of the radium series and always in equilibrium with radium. The estimation of ThO2 was done by measuring the 2.62 MeV of gamma ray energy from Tl-208 (t1/2 = 3.1 min) and the 1.46 MeV of gamma ray energy was measured for the estimation of %K. The detector used for the analysis was 5” x 4” NaI (Tl) scintillation detector. A detector is coupled to a dMCA-prodigital-Multi-Channel-Analyser (Target, Germany) which directly digitizes signals from the radiation detectors and stores them in the format desired by the inbuilt software (winTMCA32). Standard gamma ray sources
137
Cs (662 keV) and 60Co (1173 keV and 1332
keV) are used for energy calibration. Sensitivity is calculated using an equilibrium U3O8 standard developed in-house (Atomic Minerals Directorate for Exploration and Research, Hyderabad). The samples and standard are taken in the plastic container of the same volume and size to maintain a similar geometry. The counting of samples was carried out in a Low Back Ground room which is ~4 ft below the ground level and walls of the room are made up of quartz, with a thickness of 0.9 m. The samples were placed on the top of the detector and the spectra from each sample were obtained. The concentration of the Ra (eU3O8) is calculated by dividing the net peak area of the characteristic gamma ray energies of 1.76 MeV to the sensitivity of radium 4
(Grasty, 1979), ThO2 concentration is calculated by dividing the net peak area of the characteristic gamma ray energies of 2.62 MeV to the sensitivity of thorium and similarly the concentration of %K is calculated by dividing the net peak area of the characteristic gamma ray energies of 1.46 MeV to the sensitivity of potassium. Net peak area of the gamma ray was calculated by subtracting background counts and stripping of the higher energy contribution. Results and Discussion Estimation of Uranium: The concentration of uranium in the sample was estimated by the beta gamma method using equation (1). Detection limit is 90 ppm with ±10% error. Estimation of Ra(eU3O8): Sensitivity of Ra(eU3O8) SRa using NaI (Tl) detector was estimated by using the following equation :SRa = Nstd / Con.std
(2)
Where S Ra = Sensitivity of Ra(eU3O8), Nstd = Net counts under the peak (1.76MeV) in the standard Con.std = Concentration of standard Using the spectra collected for each of the samples from the NaI(Tl) detector, the concentration of Ra (eU3O8) is obtained by a comparative technique as follows: Ra (eU3O8) [sample] = N[sample] / S Ra
(3)
Where Ra (eU3O8) [sample] = Concentration of radium in the sample N[sample]= Net counts under the peak(1.76MeV) in the sample Sensitivity of Ra (eU3O8) with a counting time of 200 s is 5 counts/ppm for 140g of sample weight and detection limit is 2 ppm (error <10%). Uranium concentration of 634 samples has been estimated by beta gamma method and radium concentration by gamma ray spectrometry. Minimum, maximum and average values of U3O8 and Ra (eU3O8) of borehole core samples are given in Table 2. The linear regression equation between radium concentration and uranium concentration has been found from the regression plot is: Y(U3O8 ) = 1.352 X (Ra(eU3O8) ) + 7.072 with R2 = 0.9557
(4)
The linear regression plot of studied samples from 35 boreholes has indicated a correlation coefficient of 0.9557 (Fig. 2). This plot indicates the association of daughter product with significant enrichment of parent and good correlation among them. 5
For the calculation of disequilibrium factor in the sample the following formula is applied DF = U3O8 in the sample/ Ra (eU3O8) in the sample
(5)
If the value of DF is more than one (DF > 1), then disequilibrium is considered to be towards the parent uranium and this is the favorable condition for the prospector as it shows enrichment of uranium resulting in positive corrections in final ore reserve estimation based on total gamma ray logging data. In contrast, if the value of DF is less than one (DF < 1), then disequilibrium is towards the daughter radium and is a non-desirable condition for uranium prospecting as it signifies partial removal of uranium from the system leading to a lowering of final ore reserve estimates based on total gamma ray logging data. Out of 35 boreholes studied for disequilibrium, 32 boreholes have shown average DF significantly greater than 1 and 3 boreholes have average DF values close to unity. Disequilibrium factor for 634 boreholes core samples is listed in Table 2, which shows an average value of 1.35. This suggests, enrichment of uranium is either due to remobilization of uranium and deposition at the present locale or leaching of daughter products of the uranium series leading to an increase in concentration of parent uranium. These features are further supported by the presence of fractures, faults, felsic and matic intrusive signifying pre- and post- depositional reactivation in the area providing a hydrothermal gradient for remobilization (Ramesh Babu et al., 2012; Thomas et al., 2014). In addition, the presence of higher hydrouranium content (<10 ppb) away from the ore deposit suggests a possible role of groundwater in radioelement migration and fixation at suitable locales (Banerjee et al., 2014). Hence, the setup is favourable for uranium mineralisation in the study area. Core samples of mineralised zones are broadly classified in two groups i.e. granite (below the unconformity) and cover rock of Banganapalle quartzite/grit (above the unconformity). Out of 634 core samples, 216 samples are granite hosted samples and 418 samples are from the Banganapalle quartzite/grit. The disequilibrium factor is separately calculated for both types of samples. Average disequilibrium factor for the granite samples is 1.36 as shown in Table 3 and the average disequilibrium factor for quartzite/grit samples obtained is 1.357 as shown in Table 4. Thus, the studies clearly indicate that disequilibrium factor is same for the samples above and below the unconformity contact, irrespective of the different lithic compositions.
6
Impact on Ore Reserve Assessment: The presence of disequilibrium in uranium series between parent uranium and daughter Radium-226 implies that ore grades of mineralized zones based on total gamma ray logging results which gives eU3O8 values of mineralized rocks needs to be corrected. The disequilibrium correction factor calculated for core samples of different ranges of eU3O8 are given in Table 5 and vary from 1.14 to 1.42. Conclusion The disequilibrium analysis of the radiometric data on samples from boreholes of Chenchu colony area of uranium mineralization has indicated: 1) Presences of strong disequilibrium in favour of parent uranium, with average DF value of 1.35. 2) DF has been found to be the same in the mineralization hosted by basement granite as well as quartzite cover rock above the unconformity. 3) Presence of disequilibrium in mineralized zone implies an upward correction in the ore grades based on total gamma log by a factor of 1.35. Thus, an additional increase in grade and tonnage of the total proved resources. Acknowledgment The authors express sincere thanks to Shri P.S. Parihar, Director, AMD, Hyderabad for giving permission to publish this Paper. They also extend their sincere thanks to Dr. A. K. Chaturvedi, Additional Director (R & D), AMD, Hyderabad for his suggestion and encouragement. References Acharyulu, A.A.P.S.R., Sreenivasa Murthy, B., Bhaumik, B.K., 2004. Enrichment characteristics of radioelements in various types of rock from Sambalpur district, Orissa, India. Proc. Ind. Acad. Sci. (Earth and Planet. Sci.), 113(3), 321-352. Banerjee, R., Bahukhandi, N.K., Rahman, M., Achar, K.K., Ramesh Babu, P.V., Umamaheshwar, K., Pariahr, P.S., 2012. Lithostratigraphic and radiometric appraisal of deeper parts of Srisailam and Palnad Sub-basins in Kottapullareddipuram Achchammagunta–Rachchamallepadu area, Guntur district, Andhra Pradesh. Expl. Res. Atm. Miner., 22, 55–69. Banerjee, R., Singh, R.V., Vimal, R., Paneerselvam, A., Verma, M.B. and Nanda, L.K., 2014. Environmental baseline data of Koppunuru Uranium deposit and its environs, Guntur district, Andhra Pradesh. In: Annual Conf. Vol. of : INSAC-2014: Technological Advances in Exploration, Mining and Manufacturing of Nuclear Materials”, 113-116. Bhaumik, B.K., Bhattacharya, T., Acharyulu, A.A.P.S.R., Srinivas, D., Shandilya, M.K., 2004. Principles of radiometry in radioactive metal exploration (First Edition). Physics Lab., Eastern Region, AMD, Jamshedpur, India. 7
Eichholz, G.G., Hilborn, J.W., McMohan, C., 1953. The Determination of Uranium and Thorium in Ores. Can. Jour. Phy. 31, 613–628. Ghosh, P.C., 1972. Some studies of the Radioactivity in minerals, ores and soil, with special reference to Radon. Unpub. Ph.D. Thesis, IIT, Delhi. Grasty, R.L.,1979. Gamma Ray Spectrometric Methods in Uranium Exploration - theory and Operational Procedures; in Geophysics and Geochemistry in the Search for Metallic Ores. Geol. Sur. Canada, Econ. Geol. Rep. 31, 147–161. Gupta, S., Vimal, R., Banerjee, R., Ramesh Babu, P.V., Maithani, P.B., 2010. Sedimentation pattern and depositional environment of Banganapalle formation in southwestern part of Palnad Sub-basin, Guntur District Andhra Pradesh. Gond. Geol. Mag. Spl. Vol. 12,59-70. Gupta, S., Vimal, R., Banerjee, R., Ramesh Babu, P.V., Parihar, P.S., Maithani, P.B., 2012. Geochemistry of uraniferous Banganapalle sediments in the Western part of Palnad Subbasin, Andhra Pradesh: Implications on provenance and palaeo-weathering. Gond. Geol. Magz. Spl. Vol., 13, 1-14. Hay, S., Bowie, U., Davis, M., Ostle, D., 1972. Uranium prospecting handbook: Proceedings of a NATO-sponsored Advanced Study Institute on methods of prospecting for Uranium minerals, London. Inst. Min. Metal. 1-346. Jeyagopal, A.V., Kumar, P. and Sinha, R. M., 1996. Uranium mineralisation in the Palnad sub-basin, Andhra Pradesh, Curr. Sci. Vol., 71, 957-959. Nagaraja Rao, B. K. Rajurkar, S. T. Ramalinga Swamy, G. and Ravindar Babu, B., 1987. Startigraphy, structure and evolution of the Cuddapah Basin. Mem. Geol. Soc. India. 6, 33-86. Ramesh Babu, P.V., Banerjee, R., Achar, K.K., 2012. Srisailam and Palnad Sub-basins: Potential geological domains for unconformity – related uranium mineralisation in India. Expl. Res. Atm. Miner. 22, 21–42. Rosholt, J. N., Jr., 1958. Radioactive disequilibrium studies as an aid in understanding the natural migration of uranium and its decay products. In: Proc. of UN Int. Conf. “The Peaceful Uses of Atomic Energy”, Pap. QIC 183, U. N. 772. Sinha, R.M., Parthasarathy, T.N. and Dwivedy, K.K., 1996. On the possibility of identifying low cost, medium grade uranium deposits close to the Proterozoic unconformity in Cuddapah Basin, Andhra Pradesh, India. IAEA – TECDOC-868, 35-55. Sinha, R.M., Srivastava, V.K., Sarma, G.V.G. and Parthasarthy, T.N., 1995. Geological favourability for unconformity related uranium deposits in the northern parts of the Cuddapah Basin: Evidences from Lambapur uranium occurrences, Andhra Pradesh. Expl. Res.Atm.Miner. 8, 111-126. Thomas, P.K., Thomas, T., Tomas, J., Pandian, M.S., Banerjee, R., Ramesh Babu, P.V., Gupta, S. and Vimal, R., 2014. Role of hydrothermal activity in uranium mineralisation in Palnad Sub-basin, Cuddapah Basin, India. Jour. Asian Earth Sci., 91, 280-288. Verma, M.B., Gupta, Shekhar, Singh, R.V., Latha, A., Maithani, P.B. and Chaki, A., 2011. Ore body characterization of Koppunuru uranium deposit in Palnad sub-basin, Guntur District, Andhra Pradesh. The Indian Mineralogist: Jour. Mineral. Soc. India, 45, 51-61.
8
Fig. 1. Geological map of Chenchu colony area, Guntur district, Andhra Pradesh along with studied borehole locations
9
1400
y = 1.352x + 7.0727 R2 = 0.9557
1200
1000
U 3 O8
800
600
400
200
0 0
100
200
300
400 500 Ra(eU3O8)
600
700
800
900
Fig. 2. Linear regression plot between Ra(eU3O8) and U3O8 of borehole core samples(n =634)
10
Table 1. Detail of mineralised intercepts in boreholes and host rock of Chenchu colony area, Guntur district S No
BH No.
1 2
KPU-210C KPU-214C
3
KPU-219C
4 5
KPU-221C KPU-224C
6
KPU-229C
7
KPU-236C
8
KPU-244C
9 10
KPU-248C KPU-249C
11
KPU-256C
12
KPU-278C
13
KPU-281C
14
KPU-284C
15
KPU-287C
16 17 18 19
KPU-295C KPU-297C KPU-300C KPU-302C
20 21
KPU-310C KPU-313C
Mineralised zone From (m)
To (m)
88.35 - 90.15 106.75 - 107.75 109.25 - 112.25 120.85 - 122.05 134.85 - 135.45 145.95 - 148.05 122.65 - 123.25 125.65 - 127.95 173.85 - 177.45 198.55 -199.95 205.45 -207.25 110.85 - 112.05 150.15 - 152.95 120.65 - 122.25 136.25 - 137.35 136.55 – 142.15 116.35 – 120.75 136.15 – 137.75 78.75 – 79.45 92.75 – 94.45 95.65 – 96.45 121.85 – 123.45 124.35 – 124.85 125.35 – 129.65 72.35 - 74.05 74.75 - 75.55 77.65 - 79.95 81.95 - 89.25 95.95 - 96.85 72.55 – 74.35 88.25 – 90.55 93.25 – 96.55 98.65 – 100.05 111.05 – 113.35 114.35 – 115.35 117.25 – 119.15 171.85 – 173.95 163.75 – 165.65 82.95 – 84.05 96.15 – 99.15 114.65 – 115.05 119.65 – 120.15 124.45 – 125.25 130.65 – 131.25 174.25 – 175.95 81.55 - 83.25 98.05 - 99.65 100.45 - 101.05 103.55 -104.15 117.95 - 118.55
Rock Type
Thickness X Avg. Grade (%eU3O8)
0.8m of 0.046 1.0m of 0.022 3.0m of 0.09 1.2m of 0.013 0.6m of 0.014 2.9m of 0.017 0.6m of 0.014 2.3m of 0.010 3.6m of 0.014 1.4m of 0.010 1.8m of 0.020 1.2m of 0.075 2.8m of 0.017 1.6m of 0.058 1.1m of 0.014 5.6m of 0.02 4.4m of 0.019 1.6m of 0.049 0.7m of 0.010 1.7m of 0.094 0.8m of 0.013 1.6m of 0.011 0.5m of 0.013 4.3m of 0.011 1.7m of 0.016 0.8m of 0.026 2.3m of 0.077 7.3m of 0.050 0.9m of 0.013 1.8m of 0.013 2.3m of 0.023 3.3m of 0.017 1.4m of 0.015 2.3m of 0.010 1.0m of 0.014 1.9m of 0.015 2.1m of 0.034 1.9m of 0.012 1.1m of 0.018 3.0m of 0.067 0.4m of 0.021 0.5m of 0.013 0.8m of 0.035 0.6m of 0.013 1.7m of 0.027 1.7m of 0.051 1.6m of 0.025 0.6m of 0.017 0.6m of 0.041 0.6m of 0.013
11
Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Granite Granite Granite Gritty Quartzite Granite Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Conglomerate Gritty Conglomerate Gritty Conglomerate Gritty Conglomerate Gritty Conglomerate Gritty Conglomerate Gritty Conglomerate Granite Gritty Quartzite Granite Granite Gritty Conglomerate Gritty Conglomerate Gritty Conglomerate Gritty Quartzite Granite Gritty Quartzite Quartzite Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Granite Gritty Quartzite Granite Granite Granite Granite
Depth Of unconformity (m) 91.70 132.30
No of sample (n) 8 42
144.80
23
155.05 129.85
8 11
163.45
32
117.10 148.45
7 12 8
143.65 148.15
10 29
102.30
10
129.85
14
89.40
48
88.50
10 4 12
115.30
11
121.90 166.30 167.75 143.05
9 9 8 14
173.95 87.95
9 2 9
S No
BH No.
22
KPU-314C
23
KPU-316C
24
KPU-317C
25
KPU-323C
26
KPU-324C
27 28
KPU-330C KPU-331C
29 30 31 32
KPU-332C KPU-335C KPU-337C KPU-339C
33
KPU-350C
34 35
KPU-357C KPU-375C
Mineralised zone From (m)
To (m)
Rock Type
Thickness X Avg. Grade (%eU3O8)
108.05 -110.55 118.25 - 118.65 86.85 – 88.15 101.15 - 103.15 103.45 -110.25 81.95 – 82.95 93.35 – 98.15 94.75 – 96.35 107.65 – 108.25 72.95 – 76.15 78.95 – 79.75 110.65 – 113.05 169.55 – 173.45
2.5m of 0.023 0.4m of 0.020 1.3m of 0.042 2.0m of 0.015 6.8m of 0.047 1.0m of 0.011 4.8m of 0.049 1.6m of 0.013 0.6m of 0.018 3.2m of 0.023 0.8m of 0.045 2.4m of 0.023 3.9m of 0.015
103.65 – 110.65 163.55 – 167.05 113.85 – 116.85 137.95 – 139.05 142.85 – 146.75 148.95 – 150.45 152.15 -154.75 158.85 - 159.45 85.55 – 87.45 94.55 – 95.55 98.35 – 99.05 130.15 – 132.65 119.55 – 122.65
6.4m of 0.016 3.4m of 0.023 3.0m of 0.018 1.1m of 0.018 3.9m of 0.015 1.5m of 0.010 2.6m of 0.013 0.6m of 0.016 1.9m of 0.044 1.0m of 0.017 0.7m of 0.033 2.5m of 0.018 3.1m of 0.013
12
Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Granite Granite Granite Granite Gritty Quartzite Granite Granite Gritty Quartzite Basic Gritty Quartzite Gritty Quartzite Gritty Quartzite Granite Granite Granite Granite Granite Gritty Conglomerate Gritty Conglomerate Gritty Conglomerate Dolerite Dolerite
Depth Of unconformity (m) 119.50
No of sample (n) 12
113.50
58
76.60
19
90.05
8
76.60
110.30 168.30 122.25 123.45
9 7 14 8 9 27 11 8 40
105.40
19
130.70 120.05
12 14
111.05 172.20
Table 2. Details of U3O8, Ra (eU3O8) and disequilibrium factor (DF) of borehole core samples, Chenchu colony area, Guntur district No of sample S. No.
BH No.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35
KPU-210C KPU-214C KPU-219C KPU-221C KPU-224C KPU-229C KPU-236C KPU-244C KPU-248C KPU-249C KPU-256C KPU-278C KPU-281C KPU-284C KPU-287C KPU-295C KPU-297C KPU-300C KPU-302C KPU-310C KPU-313C KPU-314C KPU-316C KPU-317C KPU-323C KPU-324C KPU-330C KPU-331C KPU-332C KPU-335C KPU-337C KPU-339C KPU-350C KPU-357C KPU-375C
U3O8 (ppm)
Ra (e U3O8 ) ppm DF
Above u/c 8 42 23 8 11 0 7 8 10 29 10 14 48 4 11 9 0 8 14 0 2 12 58 0 0 9 0 8 27 11 8 0 19 0 0
Below u/c 0 0 0 0 0 32 12 0 0 0 0 0 10 12 0 0 9 0 0 9 9 0 0 19 8 7 14 9 0 0 0 40 0 12 14 Average
Min
Max
Av.
Min.
Max.
Av.
112 96 100 126 90 90 91 125 98 90 171 96 95 103 97 105 122 92 90 103 90 107 90 90 98 90 91 101 96 92 104 90 93 90 98 100
309 7243 921 886 179 447 7393 3670 1149 3860 5095 278 5340 1360 209 233 781 251 1918 327 4196 1239 1832 3122 254 2324 293 847 908 2168 603 299 3560 488 303 1837
198 509 316 328 125 220 632 942 371 876 1151 135 678 408 143 144 287 136 382 208 825 327 325 412 171 393 186 206 238 398 271 140 514 173 178 370
75 68 77 88 67 62 71 91 70 69 118 65 73 76 77 70 126 69 72 109 65 76 73 68 72 72 70 71 61 76 114 67 95 99 89 79
414 4757 566 437 148 480 3566 3458 911 2358 2738 300 4252 568 142 151 667 191 1392 415 3481 508 1226 1639 199 1497 263 521 432 1475 443 240 2259 308 232 1218
159 369 216 197 90 158 414 701 297 720 770 106 607 203 103 110 277 101 302 211 583 192 250 280 121 263 128 152 156 304 224 118 403 164 133 274
Note: - u/c- unconformity
13
1.51 1.43 1.49 1.58 1.45 1.50 1.28 1.4 1.27 1.19 1.35 1.37 1.25 1.96 1.39 1.22 1.00 1.36 1.34 1.02 1.61 1.59 1.25 1.11 1.48 1.48 1.48 1.32 1.48 1.22 1.14 1.20 1.19 0.97 1.33 1.35
Table 3. Disequilibrium factor of Granites boreholes core samples (below unconformity), Chenchu colony area, Guntur district S No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
BH No. KPU-229C KPU-236C KPU-281C KPU-284C KPU-297C KPU-310C KPU-313C KPU-317C KPU-323C KPU-324C KPU-330C KPU-331C KPU-339C KPU-357C KPU-375C
No of Samples 32 12 10 12 9 9 9 19 8 7 14 9 40 12 14 Total sample: 216
DF 1.5 1.3 1.27 2.08 1 1.02 1.76 1.11 1.48 1.62 1.48 1.31 1.2 0.97 1.33 Average: 1.36
Table 4. Disequilibrium factor of Banganapalle quartzite /grit boreholes core samples (above unconformity ), Chenchu colony area, Guntur district S No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
BH No. KPU-210C KPU-214C KPU-219C KPU-221C KPU-224C KPU-236C KPU-244C KPU-248C KPU-249C KPU-256C KPU-278C KPU-281C KPU-284C KPU-287C KPU-295C KPU-300C KPU-302C KPU-313C KPU-314C KPU-316C KPU-324C KPU-331C KPU-332C KPU-335C KPU-337C KPU-350C
No of Samples 8 42 23 8 11 7 8 10 29 10 14 48 4 11 9 8 14 2 12 58 9 8 27 11 8 19 Total sample: 418
14
DF 1.51 1.43 1.49 1.58 1.45 1.24 1.40 1.27 1.19 1.35 1.37 1.25 1.96 1.39 1.22 1.36 1.34 0.92 1.59 1.25 1.37 1.33 1.48 1.22 1.14 1.19 Average: 1.357
Table 5. Disequilibrium factor of core samples with different eU3O8 ranges of Chenchu colony area, Guntur district
Range (ppm) (eU3O8)
No of Sample
Avg U3O8
DF = U/Ra
90-200 200-400 400-600 600-800 800-1000 1000-1500 1500-3000 More than 3000
405 126 46 12 8 14 15 8
150 335 588 750 1028 1685 2637 4870
1.36 1.34 1.26 1.17 1.14 1.42 1.37 1.29
Highlight
Chenchu colony area of Guntur District, Andhra Pradesh of India is a part of Koppunuru uranium deposit with an established tonnage of 3000 tons. A disequlibrium study has been carried out in the Chenchu Colony area to know the presence of disequilibrium in uranium series between parent uranium and daughter Radium-226 . The ore grades of mineralized zones obtained based on total gamma ray logging results gives eU3O8 values of mineralized rocks which needs to be corrected due to disequlibrium in the Uranium series. For this study, 634 numbers of subsurface samples collected from 35 boreholes of the Chenchu colony area and Uranium and Ra( eU3O8) concentration estimated to find out the disequilibrium factor by using Beta Gamma Method and Gamma Ray Spectrometry respectively.
15
PII: DOI: Reference:
S0969-8043(15)30135-4 http://dx.doi.org/10.1016/j.apradiso.2015.07.055 ARI7084
To appear in: Applied Radiation and Isotopes Received date: 17 December 2014 Revised date: 25 July 2015 Accepted date: 29 July 2015 Cite this article as: H.B. Shrivastava, V. Koteswara Rao, R.V. Singh, M. Rahman, G.B. Rout, Rahul Banerjee, B.K. Pandey and M.B. Verma, Uranium Series Disequilibrium Studies In Chenchu Colony Area, Guntur District, Andhra Pradesh, India, Applied Radiation and Isotopes, http://dx.doi.org/10.1016/j.apradiso.2015.07.055 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Uranium series disequilibrium studies in Chenchu colony area, Guntur District, Andhra Pradesh, India H. B. Shrivastava, V. Koteswara Rao, R. V. Singh, M. Rahman, G. B. Rout, Rahul Banerjee, B. K. Pandey and M.B.Verma Atomic Minerals Directorate for Exploration and Research, Begumpet, Hyderabad Email: [email protected]
Abstract An attempt is made to understand uranium series disequilibrium in unconformity proximal related uranium mineralisation in Chenchu colony area, Guntur District, Andhra Pradesh, India. The uranium mineralization in Chenchu colony is the western continuity of the Koppunuru uranium deposit and predominantly hosted by gritty quartzite/conglomerate, which occasionally transgresses to underlying basement granite/basic rock. Disequilibrium studies are based on borehole core samples (35 boreholes, No. of samples =634) broadly divided in two groups of cover rocks of Banganapalle formation (above unconformity) and basement granites (below unconformity). Linear regression coefficient between uranium and radium is 0.95, which reflects excellent correlation and significant enrichment of parent uranium. Disequilibrium studies have indicated predominant disequilibrium in favour of parent uranium (35%), which is probably due to the weathering process causing migration of some of the radionuclides while dissolution of minerals due to groundwater action might have also played a significant role. Further, escape of radon might have accentuated the disequilibrium factor resulting in an increase in the grade of the mineralization. This is well corroborated by the presence of fractures and faults in the study area providing channels for radon migration/ escape. Key words: Uranium, Disequilibrium factor, Beta gamma method, Gamma Ray Spectrometry, Guntur district, Andhra Pradesh
Introduction For the growth and development of any country, energy is the prime requirement and hence sustainable energy resources are essential. With the fast depletion of fossil fuel reserves and pollution related issues associated with thermal energy, attention is being given to green and high density energy sources such as nuclear energy. Uranium is one of the main nuclear fuels, which needs to be developed to sustain the growth of nuclear energy. In India, an extensive exploration programme is being carried out in different geological domains to establish new uranium resources and reserves. In most of the cases, disequilibrium in radioactive ore has presented a difficult problem for proper assessment of the resources. However, it is observed that the magnitude and frequency of radioactivity disequilibria is generally ignored leading to underestimation or overestimation of the deposit. In recent years the significance of disequilibrium studies is being given importance both in field and 1
laboratory counting measurements to overcome uranium ore deposit evaluation related constraints. In a radioactive series, equilibrium is attained when all the daughter products decay at the same rate that they are produced from the parent isotope (Hay et al., 1972). Thus, at equilibrium each of these daughter products would be present in a constant proportion to its parent isotope. The loss or gain of any important isotopes, by different geological and physicochemical processes, during the more recent part of the existence of a mineral, causes disequilibrium in the proportions of the parent isotope to its daughter products (Rosholt, 1958). The importance of these aspects is being evaluated for unconformity proximal and fracture controlled types of uranium mineralisation in Chenchu colony area, which falls in the Northern part of Cuddapah basin. U-series disequilibrium study of subsurface core samples of Chenchu colony area has been done by using the beta gamma method and gamma ray spectrometry. The present paper deals with results of disequilibrium studies and its implication on uranium distribution pattern/mineralisation. Geological Setting Uranium mineralization in the northern part of Cuddapah basin has been explored by the Atomic Minerals Directorate for Exploration and Research (AMD) over two decades and the established unconformity proximal uranium deposit in Srisailam and Palnad sub-basins (Sinha et al., 1995; Sinha et al., 1996; Jeyagopal et al., 1996). Koppunuru uranium deposit is mainly hosted in cover rocks of Banganapalle formation (85%) and occasionally transgresses in to basement granites (15%) along well defined fractures across the unconformity contact (Verma et al., 2011). Chenchu Colony area is located in the south-western marginal part of Palnad Subbasin and is being explored for uranium mineralization to check the western continuity of the Koppunuru uranium deposit. Palnad sub basin exposes Kurnool Group of sediments which are deposited over basement granites, exposed along the up-thrown block of the WNW–ESE trending Kandlagunta fault and as inliers in the southern and western parts (Fig. 1). The basement rocks are mainly represented by medium to coarse grained pink and pinkish grey granites. These granites are highly sheared, fractured and traversed at places by dolerite dykes and quartz veins signifying basement reactivation. Kurnool Group is represented by a thick column of sediments belonging to the quartzite-limestone-shale cycle. This group is classified into six formations viz., 2
Banganapalle, Narji, Auk (Owk), Paniam, Koilkuntla and Nandyal formations (Nagaraja Rao et al., 1987). Among these, the first four formations are well developed in the study area. The lowermost unit, Banganapalle Formation is represented by a 10-173 m thick column of quartz arenite and intercalated grey shale sequence with basal conglomerate/gritty quartzite (Gupta et al., 2010; Banerjee et al., 2012). This is overlain by the Narji Formation comprising white to grey coloured massive limestones and an intercalated calcareous shale sequence. The Auk Formation consists of 2–10 m thick ferruginous ochreous calc-shale while an outlier of younger Paniam quartzite (10–20 m thick quartz arenite) occurs at ridge tops. The overall thickness of the Kurnool sediments in this part varies from 10 m to 205 m with gentle dips (350), mostly following the basement topography. In Chenchu colony area, Banganapalle Formation is hosting uranium mineralisation proximal
to
basement
unconformity
and
mainly
associated
with
a
gritty
quartzite/conglomerate unit. At places, uranium mineralisation partly transgresses below the unconformity contact in basement granitoids along the fracture planes (Gupta et al., 2010, 2012; Ramesh Babu et al., 2012). It is observed that the mineralisation follows a predominant N-S to NNE – SSW trend in this area which is sympathetic to post – depositional (Banganapalle sediments) younger faults and fractures. Besides, the basement granites in the vicinity show substantial reactivation as evidenced by the presence of basic dykes, profuse quartz veins and WNW-ESE trending fractures sub-parallel to the Kandlagunta fault (Ramesh Babu et al., 2012; Thomas et al., 2014). Sampling and Analytical techniques A total of 634 mineralised core samples from 35 boreholes of Chenchu colony area were collected for the disequilibrium studies. In these boreholes uranium mineralisation was intercepted between 75 to 170 m depth and mineralised bands have thicknesses between 0.6 m to 6.8 m and average grade is between 0.01 % to 0.094 % of eU3O8. Details of mineralized intercepts, lithounit, depth of unconformity and number of samples collected are shown in Table 1. Out of 634 samples, 216 samples are from basement granite below the unconformity contact. These core samples were crushed to -200 mesh to maintain homogeneity. Subsequently, samples were studied for equilibrium/disequilibrium state using High Energy Gamma Ray Spectrometry (HEGS) along with physical assay of U3O8(%) by β/γ–method (Acharyulu et al., 2004; Bhaumik et al., 2004). Further, these samples were analyzed for equivalent U3O8 (%eU3O8), radium equivalent U3O8 (%RaeU3O8), %ThO2 and %K.
3
U3O8 content in the sample was estimated by simultaneous measurement of total beta and total gamma radiations using a LND 73201 beta tube and
a 1¾″ x 2″ NaI(Tl)
scintillation detector, respectively (Eichholz et al., 1953; Ghosh, 1972). The U3O8 estimation was determined by the following equation:U3O8 = (1+C)Uβ – C Uγ Where:
(1)
Uβ = beta activity of uranium Uγ = gamma activity of uranium C = ratio of Ra beta to U beta
Estimation of Uranium: The concentration of uranium in the sample was estimated by beta gamma method using equation (1). Detection limit is 90 ppm with ±10% error. IAEA uranium reference standard RGU-1(U3O8 = 460 ppm & Ra (eU3O8) =470 ppm) was also analysed to validate the technique. The value obtained for RGU-1 by this technique was 453 ppm ± 24 ppm. Ra (eU3O8), ThO2 and %K concentrations in the sample were estimated by using gamma ray spectrometry. For the estimation of Ra (eU3O8), the 1.76 MeV of gamma ray energy was measured from the Bi-214 (t1/2 = 19.7 min) which is one of the daughters of the radium series and always in equilibrium with radium. The estimation of ThO2 was done by measuring the 2.62 MeV of gamma ray energy from Tl-208 (t1/2 = 3.1 min) and the 1.46 MeV of gamma ray energy was measured for the estimation of %K. The detector used for the analysis was 5” x 4” NaI (Tl) scintillation detector. A detector is coupled to a dMCA-prodigital-Multi-Channel-Analyser (Target, Germany) which directly digitizes signals from the radiation detectors and stores them in the format desired by the inbuilt software (winTMCA32). Standard gamma ray sources
137
Cs (662 keV) and 60Co (1173 keV and 1332
keV) are used for energy calibration. Sensitivity is calculated using an equilibrium U3O8 standard developed in-house (Atomic Minerals Directorate for Exploration and Research, Hyderabad). The samples and standard are taken in the plastic container of the same volume and size to maintain a similar geometry. The counting of samples was carried out in a Low Back Ground room which is ~4 ft below the ground level and walls of the room are made up of quartz, with a thickness of 0.9 m. The samples were placed on the top of the detector and the spectra from each sample were obtained. The concentration of the Ra (eU3O8) is calculated by dividing the net peak area of the characteristic gamma ray energies of 1.76 MeV to the sensitivity of radium 4
(Grasty, 1979), ThO2 concentration is calculated by dividing the net peak area of the characteristic gamma ray energies of 2.62 MeV to the sensitivity of thorium and similarly the concentration of %K is calculated by dividing the net peak area of the characteristic gamma ray energies of 1.46 MeV to the sensitivity of potassium. Net peak area of the gamma ray was calculated by subtracting background counts and stripping of the higher energy contribution. Results and Discussion Estimation of Uranium: The concentration of uranium in the sample was estimated by the beta gamma method using equation (1). Detection limit is 90 ppm with ±10% error. Estimation of Ra(eU3O8): Sensitivity of Ra(eU3O8) SRa using NaI (Tl) detector was estimated by using the following equation :SRa = Nstd / Con.std
(2)
Where S Ra = Sensitivity of Ra(eU3O8), Nstd = Net counts under the peak (1.76MeV) in the standard Con.std = Concentration of standard Using the spectra collected for each of the samples from the NaI(Tl) detector, the concentration of Ra (eU3O8) is obtained by a comparative technique as follows: Ra (eU3O8) [sample] = N[sample] / S Ra
(3)
Where Ra (eU3O8) [sample] = Concentration of radium in the sample N[sample]= Net counts under the peak(1.76MeV) in the sample Sensitivity of Ra (eU3O8) with a counting time of 200 s is 5 counts/ppm for 140g of sample weight and detection limit is 2 ppm (error <10%). Uranium concentration of 634 samples has been estimated by beta gamma method and radium concentration by gamma ray spectrometry. Minimum, maximum and average values of U3O8 and Ra (eU3O8) of borehole core samples are given in Table 2. The linear regression equation between radium concentration and uranium concentration has been found from the regression plot is: Y(U3O8 ) = 1.352 X (Ra(eU3O8) ) + 7.072 with R2 = 0.9557
(4)
The linear regression plot of studied samples from 35 boreholes has indicated a correlation coefficient of 0.9557 (Fig. 2). This plot indicates the association of daughter product with significant enrichment of parent and good correlation among them. 5
For the calculation of disequilibrium factor in the sample the following formula is applied DF = U3O8 in the sample/ Ra (eU3O8) in the sample
(5)
If the value of DF is more than one (DF > 1), then disequilibrium is considered to be towards the parent uranium and this is the favorable condition for the prospector as it shows enrichment of uranium resulting in positive corrections in final ore reserve estimation based on total gamma ray logging data. In contrast, if the value of DF is less than one (DF < 1), then disequilibrium is towards the daughter radium and is a non-desirable condition for uranium prospecting as it signifies partial removal of uranium from the system leading to a lowering of final ore reserve estimates based on total gamma ray logging data. Out of 35 boreholes studied for disequilibrium, 32 boreholes have shown average DF significantly greater than 1 and 3 boreholes have average DF values close to unity. Disequilibrium factor for 634 boreholes core samples is listed in Table 2, which shows an average value of 1.35. This suggests, enrichment of uranium is either due to remobilization of uranium and deposition at the present locale or leaching of daughter products of the uranium series leading to an increase in concentration of parent uranium. These features are further supported by the presence of fractures, faults, felsic and matic intrusive signifying pre- and post- depositional reactivation in the area providing a hydrothermal gradient for remobilization (Ramesh Babu et al., 2012; Thomas et al., 2014). In addition, the presence of higher hydrouranium content (<10 ppb) away from the ore deposit suggests a possible role of groundwater in radioelement migration and fixation at suitable locales (Banerjee et al., 2014). Hence, the setup is favourable for uranium mineralisation in the study area. Core samples of mineralised zones are broadly classified in two groups i.e. granite (below the unconformity) and cover rock of Banganapalle quartzite/grit (above the unconformity). Out of 634 core samples, 216 samples are granite hosted samples and 418 samples are from the Banganapalle quartzite/grit. The disequilibrium factor is separately calculated for both types of samples. Average disequilibrium factor for the granite samples is 1.36 as shown in Table 3 and the average disequilibrium factor for quartzite/grit samples obtained is 1.357 as shown in Table 4. Thus, the studies clearly indicate that disequilibrium factor is same for the samples above and below the unconformity contact, irrespective of the different lithic compositions.
6
Impact on Ore Reserve Assessment: The presence of disequilibrium in uranium series between parent uranium and daughter Radium-226 implies that ore grades of mineralized zones based on total gamma ray logging results which gives eU3O8 values of mineralized rocks needs to be corrected. The disequilibrium correction factor calculated for core samples of different ranges of eU3O8 are given in Table 5 and vary from 1.14 to 1.42. Conclusion The disequilibrium analysis of the radiometric data on samples from boreholes of Chenchu colony area of uranium mineralization has indicated: 1) Presences of strong disequilibrium in favour of parent uranium, with average DF value of 1.35. 2) DF has been found to be the same in the mineralization hosted by basement granite as well as quartzite cover rock above the unconformity. 3) Presence of disequilibrium in mineralized zone implies an upward correction in the ore grades based on total gamma log by a factor of 1.35. Thus, an additional increase in grade and tonnage of the total proved resources. Acknowledgment The authors express sincere thanks to Shri P.S. Parihar, Director, AMD, Hyderabad for giving permission to publish this Paper. They also extend their sincere thanks to Dr. A. K. Chaturvedi, Additional Director (R & D), AMD, Hyderabad for his suggestion and encouragement. References Acharyulu, A.A.P.S.R., Sreenivasa Murthy, B., Bhaumik, B.K., 2004. Enrichment characteristics of radioelements in various types of rock from Sambalpur district, Orissa, India. Proc. Ind. Acad. Sci. (Earth and Planet. Sci.), 113(3), 321-352. Banerjee, R., Bahukhandi, N.K., Rahman, M., Achar, K.K., Ramesh Babu, P.V., Umamaheshwar, K., Pariahr, P.S., 2012. Lithostratigraphic and radiometric appraisal of deeper parts of Srisailam and Palnad Sub-basins in Kottapullareddipuram Achchammagunta–Rachchamallepadu area, Guntur district, Andhra Pradesh. Expl. Res. Atm. Miner., 22, 55–69. Banerjee, R., Singh, R.V., Vimal, R., Paneerselvam, A., Verma, M.B. and Nanda, L.K., 2014. Environmental baseline data of Koppunuru Uranium deposit and its environs, Guntur district, Andhra Pradesh. In: Annual Conf. Vol. of : INSAC-2014: Technological Advances in Exploration, Mining and Manufacturing of Nuclear Materials”, 113-116. Bhaumik, B.K., Bhattacharya, T., Acharyulu, A.A.P.S.R., Srinivas, D., Shandilya, M.K., 2004. Principles of radiometry in radioactive metal exploration (First Edition). Physics Lab., Eastern Region, AMD, Jamshedpur, India. 7
Eichholz, G.G., Hilborn, J.W., McMohan, C., 1953. The Determination of Uranium and Thorium in Ores. Can. Jour. Phy. 31, 613–628. Ghosh, P.C., 1972. Some studies of the Radioactivity in minerals, ores and soil, with special reference to Radon. Unpub. Ph.D. Thesis, IIT, Delhi. Grasty, R.L.,1979. Gamma Ray Spectrometric Methods in Uranium Exploration - theory and Operational Procedures; in Geophysics and Geochemistry in the Search for Metallic Ores. Geol. Sur. Canada, Econ. Geol. Rep. 31, 147–161. Gupta, S., Vimal, R., Banerjee, R., Ramesh Babu, P.V., Maithani, P.B., 2010. Sedimentation pattern and depositional environment of Banganapalle formation in southwestern part of Palnad Sub-basin, Guntur District Andhra Pradesh. Gond. Geol. Mag. Spl. Vol. 12,59-70. Gupta, S., Vimal, R., Banerjee, R., Ramesh Babu, P.V., Parihar, P.S., Maithani, P.B., 2012. Geochemistry of uraniferous Banganapalle sediments in the Western part of Palnad Subbasin, Andhra Pradesh: Implications on provenance and palaeo-weathering. Gond. Geol. Magz. Spl. Vol., 13, 1-14. Hay, S., Bowie, U., Davis, M., Ostle, D., 1972. Uranium prospecting handbook: Proceedings of a NATO-sponsored Advanced Study Institute on methods of prospecting for Uranium minerals, London. Inst. Min. Metal. 1-346. Jeyagopal, A.V., Kumar, P. and Sinha, R. M., 1996. Uranium mineralisation in the Palnad sub-basin, Andhra Pradesh, Curr. Sci. Vol., 71, 957-959. Nagaraja Rao, B. K. Rajurkar, S. T. Ramalinga Swamy, G. and Ravindar Babu, B., 1987. Startigraphy, structure and evolution of the Cuddapah Basin. Mem. Geol. Soc. India. 6, 33-86. Ramesh Babu, P.V., Banerjee, R., Achar, K.K., 2012. Srisailam and Palnad Sub-basins: Potential geological domains for unconformity – related uranium mineralisation in India. Expl. Res. Atm. Miner. 22, 21–42. Rosholt, J. N., Jr., 1958. Radioactive disequilibrium studies as an aid in understanding the natural migration of uranium and its decay products. In: Proc. of UN Int. Conf. “The Peaceful Uses of Atomic Energy”, Pap. QIC 183, U. N. 772. Sinha, R.M., Parthasarathy, T.N. and Dwivedy, K.K., 1996. On the possibility of identifying low cost, medium grade uranium deposits close to the Proterozoic unconformity in Cuddapah Basin, Andhra Pradesh, India. IAEA – TECDOC-868, 35-55. Sinha, R.M., Srivastava, V.K., Sarma, G.V.G. and Parthasarthy, T.N., 1995. Geological favourability for unconformity related uranium deposits in the northern parts of the Cuddapah Basin: Evidences from Lambapur uranium occurrences, Andhra Pradesh. Expl. Res.Atm.Miner. 8, 111-126. Thomas, P.K., Thomas, T., Tomas, J., Pandian, M.S., Banerjee, R., Ramesh Babu, P.V., Gupta, S. and Vimal, R., 2014. Role of hydrothermal activity in uranium mineralisation in Palnad Sub-basin, Cuddapah Basin, India. Jour. Asian Earth Sci., 91, 280-288. Verma, M.B., Gupta, Shekhar, Singh, R.V., Latha, A., Maithani, P.B. and Chaki, A., 2011. Ore body characterization of Koppunuru uranium deposit in Palnad sub-basin, Guntur District, Andhra Pradesh. The Indian Mineralogist: Jour. Mineral. Soc. India, 45, 51-61.
8
Fig. 1. Geological map of Chenchu colony area, Guntur district, Andhra Pradesh along with studied borehole locations
9
1400
y = 1.352x + 7.0727 R2 = 0.9557
1200
1000
U 3 O8
800
600
400
200
0 0
100
200
300
400 500 Ra(eU3O8)
600
700
800
900
Fig. 2. Linear regression plot between Ra(eU3O8) and U3O8 of borehole core samples(n =634)
10
Table 1. Detail of mineralised intercepts in boreholes and host rock of Chenchu colony area, Guntur district S No
BH No.
1 2
KPU-210C KPU-214C
3
KPU-219C
4 5
KPU-221C KPU-224C
6
KPU-229C
7
KPU-236C
8
KPU-244C
9 10
KPU-248C KPU-249C
11
KPU-256C
12
KPU-278C
13
KPU-281C
14
KPU-284C
15
KPU-287C
16 17 18 19
KPU-295C KPU-297C KPU-300C KPU-302C
20 21
KPU-310C KPU-313C
Mineralised zone From (m)
To (m)
88.35 - 90.15 106.75 - 107.75 109.25 - 112.25 120.85 - 122.05 134.85 - 135.45 145.95 - 148.05 122.65 - 123.25 125.65 - 127.95 173.85 - 177.45 198.55 -199.95 205.45 -207.25 110.85 - 112.05 150.15 - 152.95 120.65 - 122.25 136.25 - 137.35 136.55 – 142.15 116.35 – 120.75 136.15 – 137.75 78.75 – 79.45 92.75 – 94.45 95.65 – 96.45 121.85 – 123.45 124.35 – 124.85 125.35 – 129.65 72.35 - 74.05 74.75 - 75.55 77.65 - 79.95 81.95 - 89.25 95.95 - 96.85 72.55 – 74.35 88.25 – 90.55 93.25 – 96.55 98.65 – 100.05 111.05 – 113.35 114.35 – 115.35 117.25 – 119.15 171.85 – 173.95 163.75 – 165.65 82.95 – 84.05 96.15 – 99.15 114.65 – 115.05 119.65 – 120.15 124.45 – 125.25 130.65 – 131.25 174.25 – 175.95 81.55 - 83.25 98.05 - 99.65 100.45 - 101.05 103.55 -104.15 117.95 - 118.55
Rock Type
Thickness X Avg. Grade (%eU3O8)
0.8m of 0.046 1.0m of 0.022 3.0m of 0.09 1.2m of 0.013 0.6m of 0.014 2.9m of 0.017 0.6m of 0.014 2.3m of 0.010 3.6m of 0.014 1.4m of 0.010 1.8m of 0.020 1.2m of 0.075 2.8m of 0.017 1.6m of 0.058 1.1m of 0.014 5.6m of 0.02 4.4m of 0.019 1.6m of 0.049 0.7m of 0.010 1.7m of 0.094 0.8m of 0.013 1.6m of 0.011 0.5m of 0.013 4.3m of 0.011 1.7m of 0.016 0.8m of 0.026 2.3m of 0.077 7.3m of 0.050 0.9m of 0.013 1.8m of 0.013 2.3m of 0.023 3.3m of 0.017 1.4m of 0.015 2.3m of 0.010 1.0m of 0.014 1.9m of 0.015 2.1m of 0.034 1.9m of 0.012 1.1m of 0.018 3.0m of 0.067 0.4m of 0.021 0.5m of 0.013 0.8m of 0.035 0.6m of 0.013 1.7m of 0.027 1.7m of 0.051 1.6m of 0.025 0.6m of 0.017 0.6m of 0.041 0.6m of 0.013
11
Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Granite Granite Granite Gritty Quartzite Granite Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Conglomerate Gritty Conglomerate Gritty Conglomerate Gritty Conglomerate Gritty Conglomerate Gritty Conglomerate Gritty Conglomerate Granite Gritty Quartzite Granite Granite Gritty Conglomerate Gritty Conglomerate Gritty Conglomerate Gritty Quartzite Granite Gritty Quartzite Quartzite Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Granite Gritty Quartzite Granite Granite Granite Granite
Depth Of unconformity (m) 91.70 132.30
No of sample (n) 8 42
144.80
23
155.05 129.85
8 11
163.45
32
117.10 148.45
7 12 8
143.65 148.15
10 29
102.30
10
129.85
14
89.40
48
88.50
10 4 12
115.30
11
121.90 166.30 167.75 143.05
9 9 8 14
173.95 87.95
9 2 9
S No
BH No.
22
KPU-314C
23
KPU-316C
24
KPU-317C
25
KPU-323C
26
KPU-324C
27 28
KPU-330C KPU-331C
29 30 31 32
KPU-332C KPU-335C KPU-337C KPU-339C
33
KPU-350C
34 35
KPU-357C KPU-375C
Mineralised zone From (m)
To (m)
Rock Type
Thickness X Avg. Grade (%eU3O8)
108.05 -110.55 118.25 - 118.65 86.85 – 88.15 101.15 - 103.15 103.45 -110.25 81.95 – 82.95 93.35 – 98.15 94.75 – 96.35 107.65 – 108.25 72.95 – 76.15 78.95 – 79.75 110.65 – 113.05 169.55 – 173.45
2.5m of 0.023 0.4m of 0.020 1.3m of 0.042 2.0m of 0.015 6.8m of 0.047 1.0m of 0.011 4.8m of 0.049 1.6m of 0.013 0.6m of 0.018 3.2m of 0.023 0.8m of 0.045 2.4m of 0.023 3.9m of 0.015
103.65 – 110.65 163.55 – 167.05 113.85 – 116.85 137.95 – 139.05 142.85 – 146.75 148.95 – 150.45 152.15 -154.75 158.85 - 159.45 85.55 – 87.45 94.55 – 95.55 98.35 – 99.05 130.15 – 132.65 119.55 – 122.65
6.4m of 0.016 3.4m of 0.023 3.0m of 0.018 1.1m of 0.018 3.9m of 0.015 1.5m of 0.010 2.6m of 0.013 0.6m of 0.016 1.9m of 0.044 1.0m of 0.017 0.7m of 0.033 2.5m of 0.018 3.1m of 0.013
12
Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Gritty Quartzite Granite Granite Granite Granite Gritty Quartzite Granite Granite Gritty Quartzite Basic Gritty Quartzite Gritty Quartzite Gritty Quartzite Granite Granite Granite Granite Granite Gritty Conglomerate Gritty Conglomerate Gritty Conglomerate Dolerite Dolerite
Depth Of unconformity (m) 119.50
No of sample (n) 12
113.50
58
76.60
19
90.05
8
76.60
110.30 168.30 122.25 123.45
9 7 14 8 9 27 11 8 40
105.40
19
130.70 120.05
12 14
111.05 172.20
Table 2. Details of U3O8, Ra (eU3O8) and disequilibrium factor (DF) of borehole core samples, Chenchu colony area, Guntur district No of sample S. No.
BH No.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35
KPU-210C KPU-214C KPU-219C KPU-221C KPU-224C KPU-229C KPU-236C KPU-244C KPU-248C KPU-249C KPU-256C KPU-278C KPU-281C KPU-284C KPU-287C KPU-295C KPU-297C KPU-300C KPU-302C KPU-310C KPU-313C KPU-314C KPU-316C KPU-317C KPU-323C KPU-324C KPU-330C KPU-331C KPU-332C KPU-335C KPU-337C KPU-339C KPU-350C KPU-357C KPU-375C
U3O8 (ppm)
Ra (e U3O8 ) ppm DF
Above u/c 8 42 23 8 11 0 7 8 10 29 10 14 48 4 11 9 0 8 14 0 2 12 58 0 0 9 0 8 27 11 8 0 19 0 0
Below u/c 0 0 0 0 0 32 12 0 0 0 0 0 10 12 0 0 9 0 0 9 9 0 0 19 8 7 14 9 0 0 0 40 0 12 14 Average
Min
Max
Av.
Min.
Max.
Av.
112 96 100 126 90 90 91 125 98 90 171 96 95 103 97 105 122 92 90 103 90 107 90 90 98 90 91 101 96 92 104 90 93 90 98 100
309 7243 921 886 179 447 7393 3670 1149 3860 5095 278 5340 1360 209 233 781 251 1918 327 4196 1239 1832 3122 254 2324 293 847 908 2168 603 299 3560 488 303 1837
198 509 316 328 125 220 632 942 371 876 1151 135 678 408 143 144 287 136 382 208 825 327 325 412 171 393 186 206 238 398 271 140 514 173 178 370
75 68 77 88 67 62 71 91 70 69 118 65 73 76 77 70 126 69 72 109 65 76 73 68 72 72 70 71 61 76 114 67 95 99 89 79
414 4757 566 437 148 480 3566 3458 911 2358 2738 300 4252 568 142 151 667 191 1392 415 3481 508 1226 1639 199 1497 263 521 432 1475 443 240 2259 308 232 1218
159 369 216 197 90 158 414 701 297 720 770 106 607 203 103 110 277 101 302 211 583 192 250 280 121 263 128 152 156 304 224 118 403 164 133 274
Note: - u/c- unconformity
13
1.51 1.43 1.49 1.58 1.45 1.50 1.28 1.4 1.27 1.19 1.35 1.37 1.25 1.96 1.39 1.22 1.00 1.36 1.34 1.02 1.61 1.59 1.25 1.11 1.48 1.48 1.48 1.32 1.48 1.22 1.14 1.20 1.19 0.97 1.33 1.35
Table 3. Disequilibrium factor of Granites boreholes core samples (below unconformity), Chenchu colony area, Guntur district S No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
BH No. KPU-229C KPU-236C KPU-281C KPU-284C KPU-297C KPU-310C KPU-313C KPU-317C KPU-323C KPU-324C KPU-330C KPU-331C KPU-339C KPU-357C KPU-375C
No of Samples 32 12 10 12 9 9 9 19 8 7 14 9 40 12 14 Total sample: 216
DF 1.5 1.3 1.27 2.08 1 1.02 1.76 1.11 1.48 1.62 1.48 1.31 1.2 0.97 1.33 Average: 1.36
Table 4. Disequilibrium factor of Banganapalle quartzite /grit boreholes core samples (above unconformity ), Chenchu colony area, Guntur district S No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
BH No. KPU-210C KPU-214C KPU-219C KPU-221C KPU-224C KPU-236C KPU-244C KPU-248C KPU-249C KPU-256C KPU-278C KPU-281C KPU-284C KPU-287C KPU-295C KPU-300C KPU-302C KPU-313C KPU-314C KPU-316C KPU-324C KPU-331C KPU-332C KPU-335C KPU-337C KPU-350C
No of Samples 8 42 23 8 11 7 8 10 29 10 14 48 4 11 9 8 14 2 12 58 9 8 27 11 8 19 Total sample: 418
14
DF 1.51 1.43 1.49 1.58 1.45 1.24 1.40 1.27 1.19 1.35 1.37 1.25 1.96 1.39 1.22 1.36 1.34 0.92 1.59 1.25 1.37 1.33 1.48 1.22 1.14 1.19 Average: 1.357
Table 5. Disequilibrium factor of core samples with different eU3O8 ranges of Chenchu colony area, Guntur district
Range (ppm) (eU3O8)
No of Sample
Avg U3O8
DF = U/Ra
90-200 200-400 400-600 600-800 800-1000 1000-1500 1500-3000 More than 3000
405 126 46 12 8 14 15 8
150 335 588 750 1028 1685 2637 4870
1.36 1.34 1.26 1.17 1.14 1.42 1.37 1.29
Highlight
Chenchu colony area of Guntur District, Andhra Pradesh of India is a part of Koppunuru uranium deposit with an established tonnage of 3000 tons. A disequlibrium study has been carried out in the Chenchu Colony area to know the presence of disequilibrium in uranium series between parent uranium and daughter Radium-226 . The ore grades of mineralized zones obtained based on total gamma ray logging results gives eU3O8 values of mineralized rocks which needs to be corrected due to disequlibrium in the Uranium series. For this study, 634 numbers of subsurface samples collected from 35 boreholes of the Chenchu colony area and Uranium and Ra( eU3O8) concentration estimated to find out the disequilibrium factor by using Beta Gamma Method and Gamma Ray Spectrometry respectively.
15