Hydrogeochemical study in Palnad sub-basin of Cuddapah Basin, India

Hydrogeochemical exploration for unconformity-related uranium

mineralization: example from Palnadu sub-basin, Cuddapah Basin,

Andhra Pradesh, India

R.V. Singh, R.M. Sinha *, B.S. Bisht, D.C. Banerjee

Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, AMD Complex, Begumpet,

Hyderabad 500 016, India

Received 6 June 2000; accepted 17 April 2002

Abstract

Hydrogeochemical exploration was undertaken over an area of 3100 km2 in the northeastern part of Cuddapah Basin to

identify target areas for exploring the unconformity-related U-mineralization. Water samples from 626 borewells drilled in the

Kurnool Group of the Palnadu sub-basin, Nallamalai Group and basement rocks were collected. For the individual lithological

domain, univariate and multivariate statistical techniques were applied to the analytical data on 20 variables, i.e. U, Na, K, Ca,

Mg, Cl, SO4, HCO3, CO3, Si, Fe, Cu, Ba, Zn, F, Mn, conductivity, total dissolved salts (TDS), Eh and pH. The R-mode factor

analysis establishes geochemical association between U, Na, K, Cl, SO4, HCO3, TDS and conductivity. Another important

association is between Fe, Mn and Zn. Maps of factor-1 scores (with high loadings on U) and U-contours, clearly delineate the

well-established U-mineralization at Koppunuru–Dwarkapuri in the Palnadu sub-basin. Interestingly, the same maps also

display another prominent north–south trending anomaly zone extending over a linear stretch of 45 km, commencing in the

basement, passing through the Nallamalai Group and continuing into the younger Kurnool Basin in the eastern part. The

hydrogeochemical anomaly around Julakallu is significant for targeting unconformity-related U-mineralization as, in this area,

the Kurnool Group sediments unconformably overly the most promising Cumbum Formation comprising low-grade

metamorphosed carbonaceous pelites. D 2002 Elsevier Science B.V. All rights reserved.

Keywords: Uranium; Unconformity; Kurnool; Nallamalai; Basement; Contour map; Correlation coefficient; Factor analysis

1. Introduction

Unconformity-related deposits constitute 33% of

the world’s U-reserves, outside centrally planned

economic areas (WOCAs). These include some of

the largest and richest deposits of Canada and Aus-

tralia (Lambert et al., 1996). In India, exploration

efforts for locating similar deposits have resulted in

the discovery of the Lambapur U-deposit in the north-

ern part of the Proterozoic Cuddapah Basin (Sinha et

al., 1995). At Lambapur, U-mineralization is located

adjacent to the unconformity between the Neo-Arch-

aean basement granite (caf2500 Ma) and the Middle

Proterozoic Srisailam Formation. Further southeast,

similar mineralization has also been established at

Koppunuru–Dwarkapuri in the Palnadu sub-basin,

0375-6742/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved.

PII: S0375 -6742 (02 )00218 -2

* Corresponding author.

E-mail address: [email protected] (R.M. Sinha).

www.elsevier.com/locate/jgeoexp

Journal of Geochemical Exploration 76 (2002) 71–92

occurring adjacent to the unconformity between the

Neo-Archaean basement granite and Middle–Upper

Proterozoic Banganapalle Formation of the Kurnool

Group. In both the areas, the basement granite adja-

cent to the unconformity host major part (more than

90%) of the U-ore bodies. The rest of the U-ore occur

in the gritty-pebbly quartzites lying immediately

above the unconformity. Occurrence of U-mineraliza-

tion at Kuchanapalle, Cu–Pb mineralization at Band-

lamottu within the Cumbum Formation (Viswanath et

al., 1990; Roy et al., 2000) and U-occurrences in

Koppunuru–Dwarkapuri within Kurnool Group

(Jeyagopal et al., 1996) are well established in the

vicinity of Palnadu sub-basin. These deposits have

many features similar to the classical ‘unconformity-

type U-deposits’ except that the host is granite rather

than pelitic rocks and the grades are considerably

lower.

Encouraging results in the Srisailam and Palnadu

sub-basins (Fig. 1) prompted more intense search for

U-mineralization at the unconformity between the

Nallamalai and Kurnool Groups in the Palnadu sub-

Fig. 1. Geological map of the northern part of Cuddapah Basin.

R.V. Singh et al. / Journal of Geochemical Exploration 76 (2002) 71–9272

basin. In the southern margin of the Palnadu sub-

basin, the Cumbum Formation of the Nallamalai

Group extends below the cover of the Kurnool Group.

The Cumbum Formation, comprising carbonaceous

pelites, has suffered low-grade metamorphism and

deformation and could be a suitable host for uncon-

formity related U-mineralization with the cover of

Srisailam and/or Kurnool Group. Doming up of

Cumbum Formation by younger/reactivated granite

in northeastern part of the Cuddapah Basin make the

geological setting favorable for the U-mineralization.

The study area has scanty outcrops and the uncon-

formity separating the Nallamalai and the Kurnool

Group is concealed. Therefore, hydrogeochemical

exploration has been sought to delineate favorable

targets as the ground water samples, drawn from

considerable depths, have remained in contact with

large volumes of rocks. In the present work, the

chemical composition of ground water that could be

in contact with hidden U-ore has been used as a guide

(Runnels and Lindberg, 1981) for delineation of new

U exploration targets.

2. Geography

Major portion of the area is nearly flat, with

altitudes of about 100 m. In upland areas, the altitude

rises to about 600 m above MSL. The forest cover is

thin to moderate. The folded Nallamalai hill ranges

trend NNE–SSW and form hogbacks and cuestas.

The climate is semi-arid with temperatures from 17.2

to 45.1 jC and average rainfall of about 850 mm. The

potential evapotranspiration ranges from 145 mm in

winter (November–December) to 350 mm in summer

(May–June).

As per the 1991 census, the population in the area

was 361 persons per km2. About 50% of the land is

used for agricultural purpose, 18% is covered by

forest and 20% is barren.

3. Regional geology

The crescent-shaped, intra-cratonic Cuddapah

Basin comprise the Cuddapah Supergroup andKurnool

Group of sediments lying unconformably above the

Archaean basement. The sedimentary setting in the

Cuddapah Basin accounts for both the siliciclastics and

carbonates. While the Cuddapah Supergroup is com-

posed dominantly of arenaceous and argillaceous

sequences with subordinate calcareous sediments, the

Kurnool Group is composed mainly of calcareous

strata with minor arenaceous and argillaceous sedi-

ments. Lithology and sedimentary structures of indi-

vidual horizons in the Cuddapah Basin are indicative of

complex beach, littoral, tidal flat, lagoonal and carbo-

nate shelf environment pointing to an overall shallow

marine shelf environment (Ramam and Murty, 1997).

The structures in the basement and the cover sediments

allow to reconstruct the different stages of basin evo-

lution. In the western part, the sediments are devoid of

any major folding but in the eastern part they exhibit

relatively complex structures comprising tight isoclinal

folds and overthrust. Detailed geological aspects of

Cuddapah Basin, its basement rocks and younger

Kurnool Group have been reported by several workers,

the most recent and significant ones being Nagaraja

Rao et al. (1987) and Ramam and Murty (1997).

4. Geology of the area

The study area comprises basement, Cuddapah and

Kurnool Group of rocks (Fig. 1). The geological

succession along with major geomorphic features in

the area is given in Table 1.

The granite, granite–gneisses and greenschist

forming the basement constitute the pediplained coun-

try north of the Kurnool Group and southeast of the

Nallamalai Group. Granite–gneisses are light gray,

coarse-grained, in places porphyritic, and consist of

quartz, orthoclase, microcline, hornblende, biotite and

magnetite. The hornblende schist, quartz feldspar

schist and mica schist represent the pelitic rocks.

Cuddapah Supergroup rocks consist of the Cum-

bum Formation and Bairenkonda quartzites of the

Nallamalai Group and the Srisailam quartzites (Table

1). The Cumbum Formation is dominantly argilla-

ceous with the carbonaceous shale and phyllites

making the bulk and is intensely folded with major

NNE–SSW axial trends. The Bairenkonda quartzites

form the high relief areas and phyllites of the Cum-

bum Formation occupy the valleys and plains. Phyl-

lites are gray, sometimes yellow to purple and also

grade into slates. The foliation planes of phyllites strike

R.V. Singh et al. / Journal of Geochemical Exploration 76 (2002) 71–92 73

N10jE–S10jWwith an easterly dip varying from 20jto 30j. Large exposures of granite in the form of

Nekarikallu, Ipuru and Vellaturu domes are present

within the Nallamalai fold belt in the eastern margin.

These granites are considered either as intrusive into

the Nallamalai Group rocks or as reactivated basement.

The doming up of the Cumbum shales and the Bair-

enkonda quartzites around these granite bodies resulted

in quaquaversal dips (dips away from the dome axis in

all the directions) of the sediments. From the model

Rb–Sr age of domal granites, it is apparent that the

Cumbum Formation is older than 1575F20Ma (Craw-

ford and Compston, 1973). However, the unpublished

age data (AMD geochronology report no. 94/8, 1994)

on the granite samples (n=11) from these domes giving

Rb/Sr age of 2398F55 Ma, suggest reactivation of the

older basement granite, doming the Cumbum Forma-

tion, around 1575F20 Ma.

Srisailam quartzites unconformably overly the

basement granite and gneisses. They are exposed in

the northwestern part. To the northeast, the Bangana-

palli and Narjee Formations represent the Kurnool

Group of the Palnadu sub-basin. The Banganapalli

Formation comprising conglomerate, quartzite and

shale forms dissected plateaus and structural hills

whereas the Narjee Formation comprising limestone,

shale and siltstone forming pediplains.

5. Mineralization

At Lambapur–Peddagattu and Chitrial in the Sri-

sailam sub-basin (Fig. 1), the well-established uncon-

formity-related U-deposit is located adjacent to the

unconformity surface between the chloritised biotite

granite and the gritty-pebbly quartzite. The U-ore

bodies are confined to definite fracture trends in the

basement granite. Higher U-values in the gritty-pebbly

quartzite lying immediately above the unconformity is

controlled by the presence of carbonaceous matter. The

characteristic U-minerals in Lambapur–Peddagattu

deposit are uraninite, pitchblende, kasolite and urano-

phane with minor galena, chalcopyrite and pyrite

association. The primary uranium mineralization is

epigenetic hydrothermal in nature. In the adjoining

younger Palnadu sub-basin at Koppunuru–Dwarka-

puri, the U-ore bodies occur both in the Banganapalli

quartzite of the Kurnool Group (Jeyagopal et al., 1996)

and along the unconformity between basement granite

and the Banganapalle quartzite. The U-minerals in this

Table 1

Geological succession along with major geomorphic features in the northern part of the Cuddapah Basin

Age Group Formation Geomorphic unit

Middle–Upper Kurnool Group Nandyal shale Pediplain

Proterozoic Koilkuntla limestone Pediplain

Panian quartzite Mesa and butte

Owk shale Pediplain

Narjee limestone Pediplain

Banganapalli quartzite Dissected plateau

and structural hills

Unconformity

Lower–Middle

Proterozoic

Cuddapah Supergroup Srisailam quartzite Dissected plateau


Unconformity

Nallamalai Group Cumbum Formation Pediplain and

structural hills

Bairenkonda quartzite Dissected plateau


Unconformity

Archaean Basement complex Granite–gneisses,

basic dykes, amphibolites

and mica schist

Denudational and

residual hill,

pedimont inselberg

with pediplain


deposit are pitchblende, coffinite, phosphuranylite and

metazeunerite associated with the sulfides of Cu, Pb

and Fe. Besides uranium and basemetals, high-grade

limestone is widely exposed in the Palnadu sub-basin.

In the Cumbum Formation, U-mineralization is

associated with the NNE–SSW trending ferruginous

fault breccia developed within the Ipuru granitic dome

at Kuchanapalli (Roy et al., 2000). Within the Cum-

bum Formation, over 30 basemetal sulfide occurren-

ces, spread over a 50-m-long ENE–WSW trending

belt, are known around Agnigundla. Of these, Band-

lamottu, Nallakonda and Dhukonda constitute the

main deposits. The Agnigundla Pb–Cu-mineraliza-

tion (Fig. 1), hosted by the dolomite and dolomitic

limestone interbedded with the chloritic and carbona-

ceous phyllites of the Cumbum Formation, occurs

along the closure of Vellaturu granite dome (Viswa-

nath et al., 1990). The sulfide mineralization occurs as

disseminations, stringers and veinlets confined to

brecciated dolomites and carbonaceous phyllite. Apart

from Cu and Pb, minor amounts of Zn, Co, Ni, As,

Mo, W and Ag are found.

6. Hydrogeology

In the southeastern part of the area, the granite

gneisses and the schistose rocks of the basement form

the predominant water-bearing formations. These for-

mations developed secondary porosity through frac-

turing and deep weathering over the ages and become

water bearing. The movement of ground water is

controlled by the degree of interconnections of sec-

ondary pores and voids. The depth of weathering

ranges from 8 to 15 m below the ground level (bgl).

The weathered zone contains lime-rich clayey con-

cretionery materials. The depth of water level ranges

from less than 1 to 12 m bgl.

In the Cuddapah Supergroup, ground water occurs

in the slates, phyllites, quartzites and limestones along

joints, bedding planes and the soil zones. The depth of

water level generally ranges from 0.4 to over 7.0 m bgl,

but in phyllites and slates it varies from 4 to 15 m bgl.

In the Kurnool Group, ground water occurs along

the bedding planes, joints and fissures in the Narjee

limestone and Banganapalli quartzite. The water table

Fig. 2. Location map of hydrogeochemical samples, Koppunuru–Dwarkapuri– Julakallu–Agnigundla area, Andhra Pradesh.


Table 2

Summary statistics of raw and normalized data

(A) Kurnool Group

U

(ppb)

pHa Eha

(mV)

Cond

(AV cm�1)

Na

(ppm)

K

(ppm)

Ca

(ppm)

Mg

(ppm)

Cl

(ppm)

SO4

(ppm)

N 389 369 367 371 389 389 389 389 384 383

Min 0.5 7.6 39 86 2.5 0.09 7 1 10 5

Max 100 8.9 388 14180 1813 1058 553 267 4500 2500

Mean 9 8.0 109 1491 160.6 36.3 96 38 272 140

SD 13 0.5 37 1354 176.8 101.3 73 35 367 214

N (normalized data) 280 280 280 280 280 280 280 280 280 280

Geometric mean 4.4 8.1 101 1067 100.2 6.2 70 25 139 65.7

Antilog (log x̄�1SD) 1.6 7.7 69 587 45.3 1.2 38 10 54 23.3

Antilog (log x̄+1SD) 12.1 8.4 138 1937 221.7 31.7 127 61 359 185.4

Antilog (log x̄+2SD) 33.5 8.8 181 3518 490.2 163.5 232 152 929 523.3

HCO3

(ppm)

CO3

(ppm)

Si

(ppm)

Fe

(ppb)

TDS

(ppm)

Cu

(ppb)

Ba

(ppb)

Zn

(ppb)

F

(ppm)

Mn

(ppb)

N 371 329 386 388 375 388 388 388 386 388

Min 5 0.5 4 10 74 2 5 1 0.05 1

Max 1168 87 117 74720 14180 170 900 10200 4 1666

Mean 259 14.8 29 1759 1000 12.5 153 412 0.94 73.5

SD 144 15.4 16 4924 1084 15.8 110 927 0.69 190


Geometric mean 226 8.2 26 565 721 8 121 89 0.73 14

Antilog (log x̄�1SD) 140 2.3 16 158 387 3.8 61 17 0.34 3.6

Antilog (log x̄+1SD) 365 29.4 43 2017 1344 16 243 467 1.53 56

Antilg (log x̄+2SD) 590 – 72 7199 2502 34 487 2442 3.24 223

(B) Nallamalai Group

U

(ppb)

pH Eh

(mV)

Cond

(AV cm�1)

Na

(ppm)

K

(ppm)

Ca

(ppm)

Mg

(ppm)

Cl

(ppm)

SO4

(ppm)

N 135 109 110 110 135 135 135 133 135 135

Min 0.5 7.2 35 305 18 0.5 4 1 29 5

Max 82 8.9 131 6000 980 405 690 168 1650 950

Mean 14 8.0 93 1413 164 28.2 65 44 248 76.6

SD 16 0.4 18 958 140 65.1 68 33 258 103


Geometric mean 8.0 8.0 92 1142 115 4.8 47 31 160 42.8

Antilog (log x̄�1SD) 3.5 7.6 75.7 65.8 55 1.0 21 12 68 17.8

Antilog (log x̄+1SD) 18.5 8.4 112 1982 242 23.4 98 78 378 102.8

Antilog (log x̄+2SD) 42.7 8.8 – 3439 508 114.6 203 – 890 246.8

HCO3

(ppm)

CO3

(ppm)

Si

(ppm)

Fe

(ppb)

TDS

(ppm)

Cu

(ppb)

Ba

(ppb)

Zn

(ppb)

F

(ppm)

Mn

(ppb)

N 110 83 135 135 110 135 135 135 135 135

Min 117 1.5 13 9 180 1.5 5 1 0.1 1

Max 689 78 99 9610 5520 32 665 3500 5.6 250

Mean 322 21.2 46 791 975 9.2 142 281 1.2 18

SD 114 14.4 20 1388 754 5.6 134 633 0.9 33


Geometric mean 298 16.3 43 373 780 7.3 63 77 0.9 8

Antilog (log x̄�1SD) 209 8.6 27 107 464 3.9 19 17 0.6 1

Antilog (log x̄+1SD) 423 31.0 69 1293 1312 13.7 211 344 1.8 22

Antilog (log x̄+2SD) 601 58.9 – 4485 2207 25.5 – 1541 3.4 61


in the Narjee limestone varies from 1.5 to 10.0 m bgl.

The upland pedimont area, especially occupied by

quartzites, phyllites and slates along the Krishna

River, has deeper water levels.

7. Study area, sampling and analytical procedure

The hydrogeochemical sampling in the study area

was carried out in three distinct geological domains,

comprising the Kurnool Group, the Nallamalai Group

and the basement. The location map of samples in these

domains is presented in Fig. 2. Results of the study are

presented separately for these domains in the paper.

The ground water sampling was carried out over an

area of 3100 km2. Two sampling grids, a first involv-

ing a grid of one sample per 5 km2, followed by a

closer grid of one sample per 1 km2 for the areas

delineated based on encouraging U-results, were used.

Depth of water sampled from borewells ranged from

12 to 80 m. During water sampling, geological and

radiometric information were recorded at each loca-

tion. Samples were collected in duplicate. To one

sample, HNO3 and 1 ml of chloroform were added

to prevent adsorption of U and other cations by the

container walls (pH of samples maintained below 2)

whereas the other sample was left untreated. The

procedure adopted to avoid any contamination of

samples involved use of thoroughly cleaned, high

density polythene bottles of 1-l capacity that were

rinsed at least thrice with the water to be sampled. The

water was flushed from hand pump for 2–3 min at

each location and samples without any visible insolu-

ble particles or growth of water plant and algae were

collected.

Scintrex UA3 nitrogen laser fluorometer was used

for U estimation (Robbins, 1978). Na and K were

analyzed by flame photometer; Ca, Mg, HCO3 and

CO3 by volumetric and Cl and F by ion-selective/

volumetric methods using ORION ion selective elec-

trodes of chloride (model 94-17B) and fluoride (model

94-09). Si was analyzed by spectrometry; SO4 by

turbidimetry; pH by a pH-meter, conductivity by con-

ductometer and total dissolved salt by gravimetry. The

(C) Basement

U

(ppb)

pH Eh

(mV)

Cond

(AV cm�1)

Na

(ppm)

K

(ppm)

Ca

(ppm)

Mg

(ppm)

Cl

(ppm)

SO4

(ppm)

N 102 88 88 88 101 101 101 101 101 101

Min 1 7.0 25 380 32 0.3 2.5 2.4 28 5

Max 410 9.1 120 8520 2083 573 189 143 3000 1200

Mean 27 8.3 79 2042 323 60 40.1 31.1 394 158

SD 47 0.3 21 1665 303 114 36.8 24.7 542 195


Geometric Mean 2.6 8.3 75 1709 268 14.1 24.8 2.9 5 103.3

Antilog (log x̄�1SD) 1.8 8.1 57 890 129 2.7 9.8 2.1 4 41.2

Antilog (log x̄+1SD) 3.7 8.6 97 3279 557 74.8 63.0 4.1 7 258.5

Antilog (log x̄+2SD) 5.3 8.8 – 6291 1157 396.6 159.6 5.7 8 647.1

HCO3

(ppm)

CO3

(ppm)

Si

(ppm)

Fe

(ppb)

TDS

(ppm)

Cu

(ppb)

Ba

(ppb)

Zn

(ppb)

F

(ppm)

Mn

(ppb)

N 88 86 100 101 88 101 101 101 101 101

Min 191 2.5 16 38 314 2 21 4 0.1 1

Max 949 202 100 4200 5891 22 625 880 8.3 140

Mean 474 42.4 47 413 1422 7.6 173 86 2.2 14

SD 169 30.0 20 629 1167 4.9 113 142 1.5 26


Geometric mean 459 35.3 42 232 1181 7 134 38 1.9 6

Antilog (log x̄�1SD) 326 17.6 28 94 611 3.6 66 11 1.1 2

Antilog (log x̄+1SD) 646 70.5 63 570 2282 12 270 129 3.7 22

Antilog (log x̄+2SD) 909 140.8 95 1403 4412 22 546 441 7.0 79

a Square root transform.

Table 2 (continued)


total Fe, Cu, Ba, Zn and Mn were determined by flame

atomic absorption/emission spectrometer (AAS/AES)

using varian spectrophotometer AA-20B, after appro-

priate pre-concentration methods to bring the analytes

to determinable level.

The lower (MIN) values presented in Table 2A–C

refer to the determination limits of the elements by the

estimation methods considered. The determination li-

mits of the elements depended on the instrumental pa-

rameters, the analytical mode and the degree of pre-

concentration of elements by taking the large initial

volumes of the sample for analysis. The detection limits

for the elements are about 10 times less than the

determination limits.


For trace elements, the instrument calibrations

were made using SY-2, SY-3 and MRG-1 interna-

tional standards (Govindaraju, 1989).

8. Hydrogeochemistry

The aspect of hydrogeochemistry is covered

under two sections namely: (i) Spatial distribution

of U and (ii) Element correlations and factor

analysis.

8.1. Spatial distribution of U

The U-contents in ground water samples

(n=626) draining through the Kurnool, Cuddapah

and basement rocks, are highly variable with a

range from <1 to 410 ppb, and a mean and


standard deviation of 13 and 24 ppb, respectively

(sample with <1 ppb U taken as 0.5 ppb for

computational purposes). The maximum U-content

(410 ppb) in ground water sample was obtained

from the basement at Tummalakunta (79j48V43WE:16j08’20WN).

Fig. 3. (a) Histograms of normalized data (in ppm if not mentioned)—hydrogeochemical samples from the Kurnool Group. (b) Histograms of

normalized data (in ppm if not mentioned)—hydrogeochemical samples from the Nallamalai Group. (c) Histograms of normalized data (in ppm

if not mentioned)—hydrogeochemical samples from the basement rocks.

Fig. 4. (A) Hydrogeochemical contour map of U (ppb), Koppunuru–Dwarkapuri– Julakallu–Agnigundla area, Andhra Pradesh. Contour maps

prepared independently for the Kurnool Group (K), the Nallamalai Group (N) and the basement (B) and then superimposed. (B)

Hydrogeochemical contour map of U (ppb), Koppunuru–Dwarkapuri– Julakallu–Agnigundla area, Andhra Pradesh. Contour maps prepared

using combined data for the Kurnool Group, the Nallamalai Group and the basement.


Table 3

Correlation coefficient matrix for normalized data of hydrogeochemical samples (log-transformed variables)

U pH Eh Cond Na K Ca Mg Cl SO4 HCO3 CO3 Si Fe TDS Cu Ba Zn F

(A) Kurnool Group (N=280)

pH

Eh ** **

Cond *

Na * *

K * *

Ca ** * * *

Mg * * * * *

Cl * * * * * *

SO4 * * * * * * *

HCO3 * + *

CO3 + * ** * *

Si * * ** * + + * + * *

Fe + + + * *

TDS * * * * * * * * + * +

Cu * * * + * * * * * *

Ba + + * + +

Zn + * + * *

F * + ++ * ++ * * +

Mn + * + ++ * * * **

(B) Nallamalai group (N=94)

pH

Eh **

Cond * ** *

Na * *

K +

Ca ++ *

Mg * * *

Cl + * * + * *

SO4 * ++ * * * * * *

HCO3 * * * ++ + * +

CO3

Si * * + + *

Fe *

TDS * * * + * * * * * * +

Cu * * * * *

Ba * ** + ++ **

Zn + ** * *

F * * + * * +

Mn ++ + * + * *

(C) Basement rocks (N=81)

pH

Eh **

Cond *

Na * *

K + * *

Ca + * *

Mg + * * *

Cl * * * * * *

SO4 * * * * * * *

HCO3 * + * * + * *


Notable differences exist in the lithological assem-

blages of the three groups. Accordingly, for the sta-

tistical work, the hydrogeochemical data were divided

into three lithology-based domains, comprising the

basement, the Nallamalai and the Kurnool Group for

identifying the elemental associations of U and delin-

eating U-anomaly zones.

The U-content of samples from the Kurnool Group

(n=389 taken over 1900 km2) ranges from <1 to 100

ppb with a mean of 9 ppb and standard deviation of 13

ppb. In the Nallamalai Group (n=135 taken over 700

km2) the U-content of ground water ranges from <1 to

82 ppb with a mean of 14 ppb and standard deviation

of 16 ppb. Ground water samples from the basement

(n=102 taken over 500 km2) show higher U-contents

than the other two groups, with a range from 1 to 410

ppb, a mean of 27 ppb and standard deviation of 47

ppb. Summary statistics of raw as well as normalized

data for U and other elements in these groups is

presented in Table 2A–C.

The frequency distributions of raw (untransformed)

data for all the elements exhibit positive skewness. To

provide normally distributed data, the U and other

trace element data were log transformed, after remov-

ing the extreme outlier values. Square root trans-

formation was applied to some of the variables. The

number of normalized data along with the geometrical

mean (GM), and antilog values of logarithmic

mean�1SD, logarithmic mean+1SD and mean+2SD

are given in Table 2A–C. The distribution of normal-

ized data for 20 elements each from the three groups is

presented in the form of histograms (Fig. 3a–c). The

elements such as Ni and Sr, which did not show

normality after any transformation, were not consid-

ered.

Prior to factor analysis, contour maps of the U-

distribution were prepared for the three geology-

determined regions, however, they are represented in

one figure, i.e. Fig. 4A. Noteworthy is that the

mean+2SD values were higher than the average U

content in ground waters of the Kurnool and Nalla-

malai regions. The contours with values higher than

mean+2SD value cannot appropriately outline the

well-established Koppunuru–Dwarkapuri mineralized

area. Therefore, the antilog value (log mean+1SD of

log-transformed data) was considered as a relevant

threshold (Rose et al., 1979; Hoffman, 1988, Dekkers

et al., 1989). For the basement rocks, a threshold of

antilog (log mean+3SD of log-transformed data)

appears appropriate to delineate anomalous values.

The contours above threshold values led to the iden-

tification of new hydro-uranium anomalies besides the

known areas of mineralization. The response of the

anomalies in the vicinity of known U-occurrences

supports the choice of thresholds appropriate for the

area.

Another contour map was prepared using U-values

of samples for the three geological regions (Fig. 4B).

A remarkably similar outline of higher value contours

has been found in both the maps. One of the E–W

trending anomalous zones in the western part of the

study area corresponds fairly well with the established

Table 3 (continued)

U pH Eh Cond Na K Ca Mg Cl SO4 HCO3 CO3 Si Fe TDS Cu Ba Zn F

(C) Basement rocks (N=81)

CO3 + * * * + *

Si + + + **

Fe +

TDS * * * * * * * * * *

Cu * * * * * * * * + *

Ba + + * * +

Zn + *

F * * * * * ** ++ + * * * ** * **

Mn + * + + * * + * *

*=Significant (+ve) at 99% confidence limit.

**=Significant (�ve) at 99% confidence limit.

+=Significant (+ve) at 95% confidence limit.

++=Significant (�ve) at 95% confidence limit.

Blank: no significant correlation.


Table 4

Rotated factor matrix

(A) Kurnool Group (log-transformed variables, n=280)

Variable Communality Factor-1 Factor-2 Factor-3 Factor-4 Factor-5 Factor-6

U 0.584 0.624 �0.011 0.186 0.360 0.006 �0.174

pH 0.741 0.011 �0.046 0.592 �0.076 �0.423 �0.452

Eh 0.817 �0.009 �0.037 �0.199 �0.087 �0.073 0.874

Cond 0.937 0.951 �0.058 0.027 �0.041 0.158 0.042

Na 0.875 0.913 �0.067 0.061 0.099 �0.137 0.071

K 0.558 0.454 �0.086 0.193 �0.527 0.169 0.015

Ca 0.703 0.413 �0.184 �0.234 �0.196 0.602 �0.205

Mg 0.538 0.571 �0.054 0.356 0.227 0.168 0.055

Cl 0.907 0.920 �0.137 �0.019 �0.091 0.159 �0.083

SO4 0.808 0.862 �0.052 �0.149 �0.081 �0.180 �0.041

HCO3 0.725 0.044 0.010 0.338 0.666 0.348 0.208

CO3 0.666 �0.015 �0.138 0.778 0.113 �0.115 �0.120

Si 0.565 0.181 0.232 0.674 �0.012 0.145 �0.047

Fe 0.767 0.077 �0.859 0.000 �0.035 �0.024 0.144

TDS 0.896 0.919 �0.077 0.100 �0.026 0.189 �0.009

Cu 0.654 0.318 �0.677 �0.184 0.076 0.016 �0.232

Ba 0.494 0.014 �0.058 0.031 �0.036 0.699 0.007

Zn 0.595 0.053 �0.758 �0.014 0.107 0.062 �0.040

F 0.649 0.147 0.015 0.012 0.736 �0.224 �0.186

Mn 0.595 �0.023 �0.716 0.102 �0.230 0.116 0.062

Eigenvalue 5.777 2.536 2.036 1.409 1.315 1.000

Variance 28.89 12.68 10.18 7.05 6.58 5.00

Cumulative variance 28.89 41.57 51.75 58.80 65.38 70.38

(B) Nallamalai Group (log-transformed variables, n=94)

Variable Communality Factor-1 Factor-2 Factor-3 Factor-4 Factor-5 Factor-6

U 0.700 0.669 0.344 0.280 0.170 �0.161 0.027

pH 0.771 �0.045 �0.076 0.108 0.849 �0.172 �0.017

Eh 0.552 0.150 �0.120 �0.034 �0.693 �0.112 �0.144

Cond 0.948 0.838 �0.140 �0.240 �0.336 0.015 0.234

Na 0.767 0.792 �0.172 0.087 0.117 �0.079 0.289

K 0.746 0.194 0.131 �0.733 0.159 �0.356 0.044

Ca 0.629 0.146 �0.162 �0.686 �0.189 0.260 �0.082

Mg 0.643 0.689 0.068 0.087 �0.076 0.221 �0.319

Cl 0.889 0.771 �0.353 �0.304 �0.071 0.149 0.222

SO4 0.649 0.707 0.004 �0.343 �0.160 0.064 �0.042

HCO3 0.682 0.569 0.078 0.389 0.004 �0.211 0.396

CO3 0.815 �0.105 �0.042 0.018 0.033 �0.895 �0.006

Si 0.678 0.243 0.295 �0.122 0.024 0.076 0.715

Fe 0.741 0.082 �0.843 �0.060 0.134 0.032 0.010

TDS 0.933 0.868 �0.226 �0.258 �0.126 0.073 0.200

Cu 0.606 0.198 �0.646 0.040 �0.361 �0.113 �0.073

Ba 0.731 0.018 0.225 �0.218 0.579 �0.076 �0.540

Zn 0.699 0.043 �0.720 0.127 �0.208 �0.234 �0.256

F 0.609 0.296 �0.103 0.343 0.298 �0.163 0.526

Mn 0.589 �0.001 �0.744 �0.092 0.032 0.137 0.081

Eigenvalue 5.368 2.942 2.073 1.679 1.195 1.120

Variance 26.85 14.71 10.37 8.40 5.98 5.60

Cumulative variance 26.85 41.56 51.93 60.33 66.31 71.91


Koppunuru–Dwarkapuri U-deposit. An other N–S

trending anomalous zone commences in the basement,

subsequently passes through the Nallamalai and con-

tinues into the Kurnool Group in the eastern part

where no potential U-mineralization surface manifes-

tations exist.

8.2. Element correlations and factor analysis

Uranium distribution in ground water, apart from

the proximity to mineralization, is influenced by the

presence of other dissolved ions and their interrela-

tionship. Therefore, the correlations between meas-

u red va r i ab l e s were per fo rmed af t e r l og

transformation of the data. The 20�20-correlation

matrices computed from the log-transformed normal-

ized variables for the three groups is presented in

Table 3A–C. The most striking feature observed from

these matrices is a significant positive correlation, at

99% confidence limits, between U, conductivity, Na,

Mg, Cl, SO4, HCO3, TDS and F in all the groups. The

pH shows significant negative correlation with Eh.

The conductivity, Na, K, Ca, Mg, Cl, SO4, HCO3,

CO3, Si, TDS and F show positive correlations with

each other. Fe, Cu, Zn and Mn are also positively

correlated. The Cu in the Kurnool Group and base-

ment shows significant positive correlation with U.

Subsequently, R-mode factor analysis with vari-

max rotation (Kaiser, 1958; Davis, 1986) was per-

formed on data for the individual geological regions.

Only the factors with eigenvalue of more than 1 were

extracted. Varimax rotation of the extracted factors

was performed to simplify patterns of factor loading.

The factor loadings along with eigenvalues, percent of

trace (variance) and total percent of trace (cumulative

variance) for the Kurnool Group, Nallamalai Group

and basement rocks are presented in Table 4A–C. In

the Kurnool Group, six factors account for about 70%

of the variance, in the Nallamalai Group the same

number of factors account for about 72%, while in the

basement five factors account for about 74% variance.

The extraction of a limited number of factors results in

the lower values of communalities (less than 1.00).

For certain elements such as U in the Kurnool Group,

the communality is lower than the other variables. On

extraction of larger number of factors, it was seen that

Table 4 (continued)

(C) Basement rocks (log-transformed variables, n=81)

Variable Communality Factor-1 Factor-2 Factor-3 Factor-4 Factor-5

U 0.589 0.735 0.048 0.017 �0.207 0.056

pH 0.623 0.074 0.027 �0.031 �0.751 0.227

Eh 0.766 �0.019 �0.154 0.038 0.849 0.139

Cond 0.973 0.973 �0.152 0.008 0.032 0.050

Na 0.881 0.890 0.137 0.015 �0.149 0.218

K 0.623 0.601 �0.486 �0.100 0.039 �0.118

Ca 0.821 0.354 �0.649 0.323 0.227 �0.344

Mg 0.812 0.332 �0.741 0.169 0.037 �0.350

Cl 0.870 0.900 �0.243 0.017 �0.004 0.008

SO4 0.768 0.862 �0.065 0.128 0.061 0.003

HCO3 0.693 0.676 0.074 �0.143 �0.047 0.457

CO3 0.872 0.344 0.008 �0.041 �0.002 0.867

Si 0.560 0.084 �0.178 �0.294 0.106 �0.651

Fe 0.758 �0.105 �0.159 0.843 0.006 0.108

TDS 0.957 0.965 �0.150 0.047 �0.009 0.044

Cu 0.455 0.523 �0.227 0.353 �0.066 0.008

Ba 0.802 �0.086 �0.876 0.048 0.139 0.077

Zn 0.706 0.023 0.122 0.824 0.030 �0.102

F 0.713 0.423 0.346 �0.084 �0.470 0.432

Mn 0.582 0.208 �0.288 0.646 0.097 0.168

Eigenvalue 6.883 3.570 2.064 1.312 0.994

Variance 34.42 17.85 10.32 6.56 4.97

Cumulative variance 34.42 52.27 62.59 69.15 74.12


Fig. 5. (A) Map of factor-1 scores, Kurnool Group. (B) Map of factor-2 scores, Kurnool Group.


the remaining part of the variance of U is weakly

related to the other elements with a very small eigen-

value for the corresponding factors, and are not inter-

preted easily.

The scores for each factor, with eigenvalues of

more than 1, were computed using the rotated factor

loadings (Davis, 1986). In subsequent sections of the

paper, positive scores are indicated by (+ve) and

negative scores by (�ve) signs. The calculated scores

corresponding to the two factors that explain highest

variances and exhibit spatial distribution of elemental

associations of U and basemetals in each geological

domain were plotted. The contours in the score plots

clearly outline the trends of correlated variables.

Interpretations of factor analysis result for individual

geological regions are discussed in the following

sections.

9. Kurnool Group

In the Kurnool Group, the first rotated factor

explaining 28.89% of the total variance has high

loadings on U (+ve), conductivity (+ve), Na (+ve),

Cl (+ve), SO4 (+ve), TDS (+ve), moderate on K (+ve),

Ca (+ve), Mg (+ve), Cu (+ve) and low on Si (+ve) and

F (+ve). High loadings on Na, K, Cl, SO4, TDS and

conductivity are interpreted in terms of evapotranspi-

ration (cf. Dekkers et al., 1989). Moderate loadings on

Ca and Mg are related to the weathering of the Narjee

limestone. The evapotranspiration may also be

responsible for high loading on U. High loadings on

U and Cu represent contribution in ground water

composition due to the weathering of mineralized

areas. Higher value contours in the map of factor�1

scores (Fig. 5A) clearly demarcate an E–W trending

U+Cu mineralized area at Koppunuru–Dwarkapuri in

the western part of the Kurnool Group. The same map

displays a roughly N–S trend of high value contours

near Julakallu in the eastern part.

The second rotated factor, contributing 12.68% of

the variance, has high loadings on Fe (�ve), Cu

(�ve), Zn (�ve), Mn (�ve) and small on Si (+ve)

and other variables. This is an iron axis and repre-

sents derivation of metal ions from the ferruginous

(�hematitic) Banganapalle quartzites. Iron is also

present as pyrites in the calcareous strata of the Narjee

Limestone that overly the Banganapalle Quartzite.

However, the loading on SO4 in this factor is near

zero, and therefore the contribution of Fe from pyrites

may be insignificant. Map of factor�2 scores (Fig.

5B) shows widespread distribution of higher value

contours owing to extensive ferruginous character of

the quartzites. The most conspicuous zone is located

between long. 79j30VE and 79j48VE, near the south-ern contact of the Kurnool Group with the Nallamalai

Group.

The third rotated factor contributing 10.18% of the

variance shows moderate to high loadings on pH

(+ve), CO3(+ve), Si (+ve). This is a CO3axis and

indicates the increasing alkalinity of ground water

samples and the increasing solubility of Si with higher

dissolved CO2.

The fourth rotated factor contributing 7.05% of the

variance has high loadings on F (+ve), moderate on K

(�ve), HCO3 (+ve), and low on U (+ve). This shows

local association of U with HCO3and F, and suggests

the possibility of some mixing of ground waters

draining felsic rocks, which form the basement of

the Kurnool Group, and rocks of the Kurnool Group.

At the pH range (7.6–8.9) however the fluoride

complexes appear unimportant as the uranyl fluoride

complexes predominate at pH below 5.0 (Langmuir,

1978). Carbonate rocks produce alkaline ground

waters and carbonate complexes tend to facilitate the

transport of U (Boyle, 1982).

The fifth factor contributing 6.58% variance shows

high loadings on Ca (+ve) and Ba (+ve) and low on

HCO3 (+ve) and pH (�ve). This factor could be

related to weathering of feldspars in quartzite. The

sixth factor contributing 5.00% variance has high

loadings on Eh (+ve) and moderate on pH (�ve),

relating to the redox chemical reactions in the water

(Garrels, 1960).

10. Nallamalai group

In the Nallamalai Group the first rotated factor,

explaining 26.85% of the total variance, has high

loadings on U (+ve), conductivity (+ve), Na (+ve),

Mg (+ve), Cl (+ve), SO4 (+ve), TDS (+ve), moderate

on HCO3 (+ve), and low on K (+ve), Ca (+ve), Si

(+ve), Cu (+ve) and F (+ve). The loadings of this

factor are similar to factor-1 of the Kurnool Group,

indicating similar processes. Map of the factor�1


scores (Fig. 6A) interestingly exhibit roughly a N–S

trend of higher value contours forming the southern

continuity of the N–S trending contours of factor�1

in the eastern part of the Kurnool Group (Fig. 5A).

The patterns of higher value contours of factor�1

scores resemble the U-contours (Fig. 4A–B).

The second rotated factor contributing 14.71% of

the variance has high loadings on Fe (�ve), Cu (�ve),

Zn (�ve) and Mn (�ve), like factor�2 of the Kurnool

Group. However, it also has moderate loadings on U

(+ve) and Cl (�ve) and weak loadings on Si (+ve) and

Ba (+ve). This factor represents derivation of ground

water from the hydrothermal Pb–Cu–Zn (FU) min-

eralization found in these rocks. The (+ve) U and

(�ve) Fe–Cu–Zn–Mn loadings indicate different

mobility of U in comparison with the other elements

in ground waters. The map of factor�2 scores (Fig.

6B) indicate higher value contours commencing from

Fig. 6. (A) Map of factor-1 scores, Nallamalai Group. (B) Map of factor-2 scores, Nallamalai Group.


SW of the Agnigundla Pb–Cu-deposit and follows a

NE–SW trend in the eastern part of the Nallamalai

Group.

Factor�3, contributing 10.37% of the variance,

shows high loadings on K (�ve) and Ca (�ve) and

low loadings on Cl (�ve), SO4 (�ve), HCO3 (+ve)

and F (+ve). This is a K-axis and reflects the composi-

tional controls of the pelitic and carbonate host rocks

on the ground water chemistry.

Factor�4, contributing 8.40% of the variance, is

similar to factor�6 of the Kurnool Group with high

loadings on pH (+ve) and Eh (�ve), moderate on Ba

(+ve) and low on F (+ve). The fifth factor contributing

5.98% variance has high loading on CO3 (�ve) and

low on K (�ve). As in the pH range of samples (7.2–

8.9) the CO3 concentration is small as compared to the

HCO3, this factor is not significant. Factor�6 contri-

buting 5.60% variance, is essentially an Si axis with

Fig. 7. (A) Map of factor-1 scores, basement rocks. (B) Map of factor-3 scores, basement rocks.


high loadings on Si (+ve), Ba (�ve) and F (+ve), and

indicates more dissolution of Si from the siliceous

rocks with increasing F.

11. Basement

In the basement, the first rotated factor explaining

34.42% of the total variance has high loadings on U

(+ve), conductivity (+ve), Na (+ve), K (+ve), Cl (+ve),

SO4 (+ve), HCO3 (+ve), TDS (+ve), Cu (+ve) and

moderate loadings on Ca (+ve), Mg (+ve), CO3 (+ve),

and F (+ve). This factor is similar to the factor�1 of

other two groups. Higher loadings on U and F together

with higher concentrations are unique to the Basement.

High levels of U and F are commonly reported in

ground waters draining felsic igneous rocks (Giblin,

1994). However, at the pH range of ground waters in

the basement (7.0–9.1) the formation of uranyl carbo-

nate and hydroxide complexes is more likely than the

fluorides (Langmuir, 1978). The map of factor�1

scores (Fig. 7A) show isolated clusters of higher value

contours located east and northeast of Agnigundla and

southwest of Venukonda. The most prominent outline

defined by contours with highest scores is located to the

south of the N–S trending contours of factor�1 scores

in the eastern part of the Kurnool Group and the

Nallamalai Group (Figs. 5A and 6A). Again the corre-

spondence between the U and factor�1 contours is

striking (Fig. 4A and 4B).

Factor�2, contributing 17.85% of the variance has

high loadings on Ca (�ve), Mg (�ve), Ba (�ve),

moderate on K (�ve), F (+ve) and small on Cl (�ve),

Cu (�ve) and Mn (�ve). This is mainly a Ba axis, and

reflects the rock factor in ground water composition

with elements derived by the weathering of micas and

feldspars of the chloritised granitic basement.

Factor�3, contributing 10.32% of the variance has

high loadings on Fe(+ve), Zn(+ve), Mn (+ve) and

small on Ca (+ve) and Cu (+ve). This is the Fe axis

similar to factor�2 of the Kurnool and Nallamalai

Groups. The map of factor�3 scores (Fig. 7B) shows

higher value contours to the southeast of the Agni-

gundla Pb–Cu-deposit. Possibility of derivation of

ground water composition in the basement rocks from

the adjoining mineralized area of Nallamalai Group

appears to be responsible for the higher scores of

factor�3.

The fourth rotated factor contributing 6.56% var-

iance has high loadings on pH (�ve), Eh (+ve) and F

(�ve). This is similar to factor�6 of the Kurnool

Group. The fifth factor contributing 4.97% of total

variance has high loadings on CO3 (+ve), Si (�ve)

and moderate on Ca (�ve), Mg (�ve), HCO3 (+ve)

and F (+ve). This factor is due to the balancing of

build up of HCO3� produced due to rock alteration by

cations such as Ca, Mg, Si and K in ground water

solutions.

12. Discussion and conclusion

The geologically favorable set-up of the northern

part of the Cuddapah Basin for hosting the uncon-

formity-related U-mineralization is well known by the

presence of well-established U-deposits at Lamba-

pur–Peddagattu and Koppunuru–Dwarkapuri. The

low U-grades of these deposits are due to the granitic

host rock, providing limited fluid–rock interaction

and the reductants that could result in substantial

uranium precipitation. The host rock age, structure

and shape of the ore bodies, physico–chemical envi-

ronment of mineralization, host rock alterations and

nearness to Archaean gneissic domes of these deposits

are similar to the unconformity-related U-deposits of

Canada and Australia (Sinha et al., 1995, 1996; Bisht

et al., 2001). The Canadian and Australian deposits

are typified by higher ore grades, as these are asso-

ciated with pelitic carbonaceous sediments (Needham

and Roarty, 1980; Fogwill, 1981; Sibbald, 1986,

1988; Needham et al., 1988). Association of Ni, Cu,

Pb, Zn and Ag with U is known in some of these

deposits as in the Rum Jungle U field (Needham and

Roarty, 1980).

Statistical analysis of the hydrogeochemical data

on different lithological domains resulted in five to six

factors accounting for major part of the variance with

similar associations and loadings of variables. The

first of these factors, accounting for the maximum

variance, is important from the viewpoint of U-min-

eralization and is discussed here. Interpretation of

other factors is discussed in the main text for individ-

ual lithological domains.

High loadings for Na, Cl, SO4, TDS and conduc-

tivity and moderate loadings for K, Mg, Cu and

HCO3 characterize factor�1. High total dissolved salt


(TDS), with values higher than 950 ppb, reflect low

annual ground water recharge from the low seasonal

rainfall. As the content of Cl is higher than Na+K

combined, it is argued that the ground water compo-

sition is influenced by the contribution of seawater

trapped during sedimentation. Factor�1 also shows

significant loading on U, which reflect the association

of soluble U-complexes with the ground water. In arid

regions, evaporation and transpiration of plants are

considered important processes controlling the back-

ground U-content of the natural waters (Benson and

Leach, 1979; Dekkers et al., 1989; Rose, 1994).

However, in the study area the map of factor�1

scores and the U-contours closely resemble in each

geological domain, define continuous trends, and

clearly demarcate the well-established U-mineraliza-

tion at Koppunuru–Dwarkapuri. The uneven distri-

bution of U along with distinct patterns of higher

values along well-defined trends reflects U-enrich-

ment in the ground water due to its derivation from

the ore bodies. In all the domains, U and Cu have

positive loadings and bring out their common asso-

ciation, as known at Dwarkapuri. Similar anomalous

U-contents in ground waters near or in the ore are

reported from essentially all the significant uncon-

formity-type deposits of the Pine Creek Geosyncline,

Australia and the Athabasca basins, Canada (Earle

and Drever, 1983; Giblin and Snelling, 1983). At the

pH range of 7.1–8.9 in ground waters of all the three

geological domains of the study area, the average Eh

values are lower than 100 mV. These Eh values are

mildly reducing, being slightly above the redox

potential for the oxidation of U4+ to U6+. This

possibly explains the relatively lower levels of U in

the ground waters. Reducing conditions in the ore

zone prevent U solubility and mobility in the ground

waters, resulting in lower concentration levels, as has

also been reported from the Jabiluka deposit of

Australia (Deutscher et al., 1980) and the Key Lake

deposit of Canada (Maurice et al., 1981).

It is pertinent to note that at Koppunuru–Dwarka-

puri the cover sequence of the Kurnool Group is

mainly represented by its lowermost unit, i.e., the

Banganapalle quartzite. The prominent hydro-ura-

nium anomalies and the map of factor�1 scores

clearly demarcate the well-established U-mineraliza-

tion in the area. The same maps also delineate a new

area in the east, near Julakallu, both in the hydro-

uranium contour maps as well as in the maps of

factor�1 scores. This area, with the absence of out-

cropping U-mineralization, probably involved miner-

alizing processes similar to that at Koppunuru–

Dwarkapuri, as evidenced by the score maps. Detailed

information on the hydrology of this region is not

available, but a general northward flow and down-

ward flow are visualized on the basis of drainage

patterns and the topographic relief. Therefore the

hydro-uranium anomaly in the Kurnool Group near

Julakallu appears most interesting, as here the carbo-

naceous Cumbum Formation rocks unconformably

underlie the Kurnool Group rocks. The unconformity

plane provides a reducible zone, where the ore body

could be expected to occur. The occurrences of U–

Cu–Pb mineralization in the Cumbum Formation

furthermore supports its suitability for hosting the

unconformity type U-deposit.

The area outlined by the prominent N–S trending

hydro-uranium anomaly zone and the factor-1 scores,

where the carbonaceous pelites of the Cumbum

Formation are overlain by the Kurnool Group rocks

holds significant promise for unconformity-related

U-mineralization. This study allowed to define a

25-km2 area around Julakallu and a 36-km2 area

around Koppunuru–Dwarkapuri where the geochem-

ical patterns defined regions of potential targets for

concealed U-mineralization. The area (around Jula-

kallu) with the cover of the Kurnool Group rocks

over the Cumbum shale/phyllites of Nallamalai

Group has been selected for ground geophysical

gravity, magnetic and EM surveys, to test the hydro-

geochemical U-anomalies identified and further nar-

row down the target for exploration (research in

progress).

Acknowledgements

The manuscript has significantly improved by the

critical reviews of Prof. Rudy Swennen, Dr. David R.

Cohen and Dr. Simon P. Vriend. The authors are

grateful to the scientists of chemical laboratory, AMD

Hyderabad, for providing excellent analytical support

and discussions from time to time. The scientists of

the geochronology laboratory, AMD Hyderabad are

sincerely acknowledged for providing Rb/Sr dates of

Ipuru and Velturu granites.


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Hydrogeochemical study in Palnad sub-basin of Cuddapah Basin, India

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