Radiation Measurements 40 (2005) 491495www.elsevier.com/locate/radmeas

Search forUraniumSource inWarcha Sandstone, Salt Range,Pakistan, using SSNTDTechnique

K. Ullaha,, N.U. Khattaka, A.A. Qureshia, M.Akrama, H.A. Khanb,A. NisarcaPhysics Research Division, PINSTECH, P. O. Nilore, Islamabad, Pakistan

bCOMSATS Headquarters 4th Floor Shahrah-e-Jamhuriat, G-5/2 Islamabad-44000, PakistancRadiation and Isotope Application Division, PINSTECH, P. O. Nilore, Islamabad, Pakistan

Received 27 August 2004; accepted 19 January 2005

Abstract

The similarity in sedimentary depositional characteristics of the Warcha Sandstone of Nilawahan Group in the Salt Rangeto the uranium bearing sandstones of Siwalik Group in the foot hills of Himalaya and Sulaiman Ranges, Pakistan, temptedgeologists to investigate the former group for the occurrence of uranium deposits in it. Like volcanic ash beds in Siwaliks,phosphatic nodules may be a possible source of uranium mineralization in Warcha Sandstone. Samples of phosphatic nodulesoccurring in the Warcha sandstone near Chakwal were collected and subjected to the solid state nuclear track detectiontechnique for the determination of their uranium concentration. The uranium concentration in these samples ranges from(434 32) to (964 74) with an average of (699 16) ppm. The high uranium content indicates that the phosphatic nodulesmay be the possible source of uranium mineralization in Warcha Sandstone. These results are quite encouraging and favor theidea of exploring the area in detail for any possible occurrence of uranium deposits. 2005 Published by Elsevier Ltd.

Keywords: Uranium; Phosphatic nodules; Sandstone; SSNTD technique

1. Introduction

Sandstone uranium deposits occur in medium- to coarse-grained sandstones deposited in a continental uvial ormarginal marine sedimentary environment. Impermeableshale/mudstone units are interbedded in the sedimentarysequence and often occur immediately above and belowthe mineralized sandstone. Uranium precipitated under re-ducing conditions caused by a variety of reducing agentswithin the sandstone including: carbonaceous material,suldes, hydrocarbons and interbedded basic volcanics

Corresponding author. Tel.: +92 51 2207269;fax: +92 51 9290275.

E-mail address: kafayat@pinstech.org.pk (K. Ullah).

1350-4487/$ - see front matter 2005 Published by Elsevier Ltd.doi:10.1016/j.radmeas.2005.01.011

with abundant ferro-magnesian minerals. Ore bodies of thistype are commonly low to medium grade (0.050.4% U3O8)and individual ore bodies are small to medium in size (rang-ing up to a maximum of 50 000 t U3O8). Depositional en-vironments of these deposits may include continental-basinmargins, uvial channels, braided stream deposits and sta-ble coastal plains.The Siwalik Group of sedimentary rocks is the major

source of uranium deposits in Pakistan. The Siwalik rocksoccur along the southern anks of the Himalayas and con-sist predominantly of molasse sediments comprising sand-stones, siltstones, mudstones and conglomerates. The char-acteristic sedimentary features of the Siwalik rocks such asfrequent occurrence of cross-bedding, ripple marks, verte-brate fossils and wood logs, and the association of pebbleand cobble-sized fragments with sand size detritus are sug-gestive of shallow water deposition for these rocks. These

492 K. Ullah et al. / Radiation Measurements 40 (2005) 491495

Fig. 1. Map showing locations of samples collected from the Chakwal district. These locations include the areas of Nawabi Kas, Nurpur,Matin, Gahi, Simbal, Karuli, Malot and Warala in the south and south west of Chakwal district.

lithological characteristics favor braided stream depositionunder swampy conditions (Abid et al., 1983).Pakistan produces about 2000MW of electricity but that

demand has increased many folds due to industrializationand population growth. Our hydroelectric sources are lim-ited and thermal power production is beyond our reach dueto the high import bill for oil. As a result the best alter-native to generate electricity is by using nuclear fuel, ura-nium. Our uranium deposits in the Siwalik System of rockare being depleted. To cope with our future requirements ofpower generation, we need to search for new uranium de-posits. The best alternative for this purpose is to search foruranium deposits in the Warcha Sandstones of NilawahanGroup exposed extensively in the Salt Range.

Having sedimentary features and lithological characteris-tics nearly similar to the Siwalik Group, theWarcha Sand-stone of Nilawahan Group, Salt Range provides idealconditions for occurrence of potential uranium deposits.The presence of uranium mineralization in the Nilawa-

han Group, Eastern Salt Range has been reported in acouple of recently unpublished reports (Azizullah et al.,2003; Nisar, 2003). TheWarcha Sandstone of the Nilawa-han Group is of special interest containing phosphaticnodules, and is composed of sandstone, shale, conglom-eratic beds and some carbonaceous shale in the East-ern Salt Range. The presence of phosphatic nodules inthe Warcha Sandstone, Eastern Salt Range supports theidea and requires detailed study of any uranium mineral-ization associated with these nodules. These phosphaticnodules are scavengers of heavy metals, particularly, rareearth elements and uranium. Furthermore, the geologyof the eastern part of the Salt Range is also favorable forconcentrating uranium to form deposits. Several uraniumand thorium anomalies in the eastern part of the SaltRange have been discovered in geological and radiomet-ric surveys carried out during 19921993. More promis-ing areas for hosting signicant uranium resources in theEastern Salt Range have also been delineated (Azizullahet al., 2003).

K. Ullah et al. / Radiation Measurements 40 (2005) 491495 493

The development of the earths crust and creation of con-tinents were not uniform processes all over the globe, whichis why uranium ore deposit formation started at differenttimes in various geostructural units. The transition of theearths crust evolution from sea to continental conditionsof sedimentation took place in six denite geological peri-ods during which extensive uranium deposits were gener-ated all over the globe. One such period is the Permian time(250190my) during which 16 uranium deposits in Asia(India), Africa, South America and Australia were formed.Thus, the search for a uranium deposit in Warcha Sandstoneof Nilawahan Group, Salt Range seems to be a justied pro-posal.The solid state nuclear track detection technique (SSNTD)

is being used for measuring the concentration and spatialdistribution of certain elements which emit heavy nuclearparticles either directly or as a result of a specic nuclearreaction (Fleischer and Price, 1964). This technique is asuitable choice and is selected to observe the uranium dis-tribution pattern in the phosphatic nodules and other phos-phatic materials (Qureshi et al., 1997). Samples of phos-phatic nodules associated with the Warcha Sandstone of theNilawahan Group have been collected from Nawabi Kas,Nurpur, Matin, Gahi, Simbal, Karuli, Malot andWarala areas(Fig. 1). The technique has been used for determination ofuranium concentration in samples of phosphatic nodules us-ing 235U(n, f) nuclear reaction under thermal neutrons in

Table 1Lower Permian succession (Nilawahan Group) of the Salt Range (Shah, 1980)

Formation Description Environment Stage

Sardhai Shale and clays of lavendercolor, with interbedded sand-stone of greenish color wellbedded and cross bedded; car-bonaceous in part with copperminerals, jasper and gypsum

The formation was mostly de-posited in the lacustrine butlaterally marine reducing en-vironment has also been noted

Sakmarian (288283Ma)

Warcha Sandstone Sandstone, shale, conglomer-ates and some carbonaceousshale; the facies changes fromsandstone in the Western SaltRange to alternation of sandand shale in the Eastern SaltRange. Thin coal seams andcopper minerals are locallypresent

Mostly uvial with localizedlagoonal conditions

Sakmarian (288283Ma)

Dandot Olive grayish green shale andcoarse sandstone with local-ized carbonaceous shale

Marine in the Eastern andWestern Salt Range

Asselian (291288Ma)

Tobra Boulder with claystone, sand-stone and siltstone

Glacial, glacio-uviatile anduviatile environment

Asselian (291288Ma)

order to search for any possibility of uranium sources inWarcha Sandstone.

2. Geology of the area

The Permian sequence of the Salt Range is composed oftwo groups: (i) the Nilawahan and (ii) the Zaluch groups.The Nilawahan Group is well developed in the Salt Rangeand represents mostly non-marine rocks with only a smalltransitory marine transgression during Asselian. The Groupincludes Tobra Formation, Dandot Formation,Warcha Sand-stone and Sardhai Formation (Table 1). Lithologically thisgroup consists of boulders, conglomerates, sandstones, silt-stones and shales (Shah, 1977, 1980; Kadri, 1995).The Warcha Sandstone of Nilawahan Group is widely

distributed and well preserved all over the Salt Range. Thesandstone is red, purple or is of lighter shades of pink. It ismedium to thick bedded, ne to coarse grained, with gravelsand pebbles of granite at places. Sedimentary features likecrossbedding in the sandstone are suggestive of a uvialdepositional environment. Shale is thin bedded and darkbrown in color. Phosphatic nodules are associated with shalebeds in the upper part of the formation. The thickness of theformation varies from 70 to 165m in the Salt Range. Theformation was deposited probably in the near shore/uviatileenvironments (Shah, 1977, 1980; Kadri, 1995).

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Fig. 2. Diagrammatic sketch showing packing arrangement forirradiation of phosphatic nodules in the research reactor PARR-1,at PINSTECH, Islamabad.

3. Experimental procedure

Twelve samples of phosphatic nodules taken from thestudied area were cut into rectangular pieces and polishedwith an automatic lapping and polishing machine to obtainsmooth surfaces. Lexan detectors were placed in contactwith all samples and Standard Reference Material (SRM-612) of known uranium content as shown in Fig. 2. Boththe samples and Standard Reference Material were irradi-ated with thermal neutrons in the Pakistan Research Reactor-1 (PARR-1). After irradiation the lexan detectors were re-moved from samples and standard and etched in a 6.5MNaOH solution at 50 C for 45min. The ssion tracks reg-istered in the lexan detectors were counted using a Zeissbinocular microscope at an overall magnication of 400.The uranium content in the phosphatic nodules was deter-mined by comparing the track density of unknown sampleswith the standard samples using the following relation ofFleischer et al. (1975):

Cux = TxTs

Is

Ix

Rs

RxCus, (1)

where Cux and Cus are the uranium content in the unknownand standard samples, Tx and Ts are the ssion track den-sities in lexan detectors for the unknown and standard sam-ples, Ix and Is are the isotopic abundance ratios of U235to U238 in the unknown and standard samples and Rx andRs are the average etchable ranges of ssion fragments inthe unknown and standard samples, respectively. The ratioRs/Rx is assumed to be unity, because the average ranges ofssion fragments in the SRM-612 and phosphatic materialare approximately the same.

4. Result and discussion

Twelve samples of pinkish brown to dark brown phos-phatic nodules were collected from Nawabi Kas, Nurpur,Matin, Gahi, Simbal, Karuli, Malot and Warala areas ofChakwal district, Punjab, Pakistan (Fig. 1). These noduleshave a high specic gravity and range in size from 1 to15mm. These nodules are mainly restricted to the shale in

Table 2Uranium concentration in samples of phosphatic nodules of WarchaSandstone, Nilawahan Group, Salt Range

S. no. Sample no. Induced tracks in Lexan U Content (ppm)Total tracks Track density(Ni) (i ) (104)

1 WS-2 12 711 76.69 711552 WS-3(a) 112 399 74.81 694533 WS-3(b) 9969 60.15 558434 WS-4(a) 14 706 88.73 823635 WS-4(b) 16 566 99.95 927716 WS-5(a) 11 352 68.49 635497 WS-5(b) 10 878 65.63 609478 WS-6(a) 7752 46.77 434329 WS-6(b) 9195 55.48 5154010 WS-7 10 956 71.53 6645111 WS-8(a) 19 220 103.89 9647412 WS-8(b) 15 240 91.95 85365

Mean 69916

the upper part and are characteristic of the Warcha Sand-stone. They are present throughout along the strike in a stripof 25 km length.The uranium content in this study has been found to range

from 434 32 to 964 74 ppm with an average value of699 16 ppm. The average uranium concentration in eachnodule has also been given in Table 2. It was observed thatsome irregular patterns of calcite lled veins on the pol-ished surfaces of the samples had negligible uranium con-tent. Some clusters of ssion tracks have also been noted asshowing a relatively high content of uranium at a few placesin these nodules. Generally, uranium distribution is uniformand no preferred control of increasing uranium content fromthe core to the periphery or vice versa has been noted inthese phosphatic nodules.The results of this study can be compared with the ura-

nium concentration in these phosphatic nodules determinedby Nisar (2003), ranging from 47020 to 78625 ppm us-ing gamma spectrometry (unpublished M.Sc. Thesis). Theresults of uranium concentration in phosphatic nodules de-termined with the SSNTD technique are in good agreementwith the uranium concentration determined with gammaspectrometry.Strong bleaching and uraniferous solution movements are

also present in Simbal and Matin areas, in the Eastern SaltRange. The presence of color bandings and bleaching withinthe sandstones strata due to uraniferous solution movementsindicates that some uranium deposit was formed in the vicin-ity of Matin area, but has possibly been disturbed due toblock faulting associated with Salt Range Thrust. Therefore,areas with high radioactivity, bleaching, color bandings andrelatively higher values of uranium, both within the sand-stone as well as in phosphatic nodules need attention forfurther exploration (Azizullah et al., 2004).

K. Ullah et al. / Radiation Measurements 40 (2005) 491495 495

5. Conclusion

(1) Like volcanic ash beds in Siwaliks, phosphatic nod-ules may be a possible source of uranium mineraliza-tion from where uranium has been leached out and dis-tributed in the Warcha Sandstone of Nilawahan Group,Eastern Salt Range.

(2) The presence of color bandings and bleaching within thesandstones strata due to uraniferous solution movementsalso supports the idea that uranium has been leachedfrom these nodules and possibly precipitated where thegeological conditions were favorable.

(3) Keeping in view these encouraging results, it is sug-gested to carry out a comprehensive exploratory workin all other extensions of the Warcha Sandstone, es-pecially in areas having phosphatic nodule beds. It ishoped that these studies would lead to the discovery ofnew uranium deposits in the Nilawahan Group, EasternSalt Range.

References

Abid, I.A., Abbasi, I.A., Khan, M.A., Shah, M.T., 1983.Petrography and geochemistry of the Siwalik Sandstone andits relationship to the Himalayan Orogeny. Geol. Bull. Univ.Peshawar. 16, 6583.

Azizullah, Butt, M.J., Rehman, A., 2003. Signicance of phosphaticnodules within the Warcha Sandstone, Nilawahan Group (LowerPermian) of Salt Range area. Internal Report, Atomic EnergyMineral Center Lahore.

Azizullah, Butt, M.J., Rehman, A., 2004. Possibility of uraniumdeposits within theWarcha Sandstone, Nilawahan Group (LowerPermian) of Salt Range area, Pakistan. (Abstract) NationalConference on Economic and Environmental Sustainability ofMineral Resources of Pakistan at Baragali Summer Campus,University of Peshawar, 2022 July, 2004, p. 13.

Fleischer, R.L., Price, B.P., 1964. Track registration in various solidstate nuclear track detectors. Phys. Rev. 133A, 14431449.

Fleischer, R.L., Price, B.W., Walker, R.M., 1975. Nuclear Tracksin Solids Principles and Applications. University of CaliforniaPress, Berkeley, USA.

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Nisar, A., 2003. Application of analytical techniques forcharacterization of uranium bearing phosphate nodules fromEastern Salt Range. M.Sc. Thesis (Unpub.), Pakistan Instituteof Engineering and Applied Sciences, Islamabad, Pakistan.

Qureshi, A.A., Khattak, N.U., Akram, M., Mehmood, K., Majid,C.A., Durrani, S.A., Haleem, A., Qureshi, I.E., Khan, H.A.,1997. Application of SSNTD technique in the study of fossilbones. Radiat. Meas. 28 (16), 571574.

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Search for Uranium Source in Warcha Sandstone, Salt Range, Pakistan, using SSNTD TechniqueIntroductionGeology of the areaExperimental procedureResult and discussionConclusionReferences