A stream sediment geochemical survey of the Ganga River headwaters in the Garhwal Himalaya
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Geochemical Journal, Vol. 41, pp. 83 to 95, 2007
A stream sediment geochemical survey of the Ganga River headwaters
in the Garhwal Himalaya
P. K. M UKHERJEE,1* K. K. PUROHIT ,1 N. K. S AINI,1 P. P. KHANNA,1 M. S. RATHI 1 and A. E. G ROSZ2
1
Wadia Institute of Himalayan Geology, 33 GMS Road, Dehradun, India
2
U.S. Geological Survey, Reston, Virginia, U.S.A.
(Received June 24, 2006; Accepted October 31, 2006)
This study models geochemical and adjunct geologic data to define provinces that are favorable for radioactive-min-
eral exploration. A multi-element bed-sediment geochemical survey of streams was carried out in the headwaters region of
the Ganga River in northern India. Overall median values for uranium and thorium (3.6 and 13.8 ppm; maxima of 4.8 and
19.0 ppm and minima of 3.1 and 12.3 ppm respectively) exceed average upper crustal abundances (2.8 and 10.7 ppm) for
these radioactive elements. Anomalously high values reach up to 8.3 and 30.1 ppm in thrust zone rocks, and 11.4 and 22.5
ppm in porphyroids. At their maxima, these abundances are nearly four- and three-fold (respectively) enriched in com-
parison to average crustal abundances for these rock types. Deformed, metamorphosed and sheared rocks are characteris-
tic of the main central thrust zone (MCTZ). These intensively mylonitized rocks override and juxtapose porphyritic (PH)
and proterozoic metasedimentary rock sequences (PMS) to the south. Granitoid rocks, the major protoliths for mylonites,
as well as metamorphosed rocks in the MCT zone are naturally enriched in radioelements; high values associated with
sheared and mylonitized zones are coincident with reports of radioelement mineralization and with anomalous radon
concentrations in soils. The radioelement abundance as well as REE abundance shows a northward enrichment trend
consistent with increasing grade of metamorphism indicating deformation-induced remobilization of these elements. U
and Th illustrate good correlation with REEs but not with Zr. This implies that zircon is not a principal carrier of U and Th
within the granitoid-dominant thrust zone and that other radioelement-rich secondary minerals are present in considerable
amounts. Thus, the relatively flat, less fractionated, HREE trend is also not entirely controlled by zircon. The spatial
correlation of geologic boundary zones (faults, sheared zones) with geochemical and with geophysical (Rn) anomalies
infers ore mineralization by hydrothermal processes generated during multiple episodes of deformation and thrusting. The
geologic setting of the anomalies also suggests that crystalline rocks (MCT Zone) along the nearly 2500 km length of the
LesserHimalayan belt, where in the vicinity of thrust and fault zones, have potential for radioelement mineralization.
Zones of higher concentrations of radioelements delineated by this study and locations of anomalous radon discharge
determined by other investigations may indicate a potential health hazard over the long term. However, the low human
population density precludes direct manifestation of health effects attributable to chronic exposure to these radioelements;
however, the magnitude of natural concentrations suggests the need for more detailed studies and monitoring.
Keywords: geochemistry, radioelement, mineralization, uranium, thorium, radon, Himalayas, thrust zones
commonly by chemical analyses of stream-drainage
INTRODUCTION
sediments and of soil samples. Considering the terrain
Geochemical data, in combination with mineralogic characteristics in Himalayan region, sediments in a stream
and other adjunct data sets such as geologic maps, air- contain elements derived from the surrounding watershed
borne gamma-ray surveys, mineral deposit distribution, and their composition is more representative of the
among others, provides the foundation for classifying and geochemical characteristics of the area than other less
evaluating mineral-resource endowment and natural haz- easily available sampling media such as soil, plant and
ards. When exposed at, or near the surface of the earth, groundwater. Rainfall and weathering are more extensive
mineral resources produce diagnostic textural, geologic, and hence sediment yield is very high in streams of local
geophysical, and geochemical signatures. Geochemical extent. The Ganga river headwater region is a wide moun-
exploration is based on outlining such dispersion halos, tainous drainage network from which the vast downstream
floodplain (gangatic plains) receives input from a series
of variously-sized tributaries. The study area covers wa-
tersheds of its four main tributaries from west to east—
*Corresponding author (e-mail: mukherjee_pk@wihg.res.in)
Bhagirathi, Bhilangana, Mandakini and Alaknanda
Copyright © 2007 by The Geochemical Society of Japan. (Fig. 1).
83
Fig. 1. Map of the Ganga river headwaters region showing locations of stream sediment samples (open circles), localities
referred to in the text (filled circles). The dotted boundary delimits the area shown on the geochemical maps in Figs. 3–6.
The area of our study is remote and poorly accessi- cern when spatially associated with human community.
ble; therefore it has a poorly developed infrastructure. As Therefore concerns for the effect of these radioactive el-
this region is fast-growing in population and is part of a ements on the environment and human health have in-
newly created state in India, we think it important to as- creased in the last few decades (Lima et al., 2005).
sess the nature and extent of the zones that are potential Radioactive mineralization in the study area has been
at high risk from radioactive exposure. Such information reported by Negi (1967), Das et al. (1981), Nashine et al.
is needed for policy makers to provide sound basis for (1982) and Udas (1986). In Bhilangana valley near
addressing public concern regarding high natural radio- Budhakedar, uraninite, pitchblende, brannerite and flu-
activity in some specific areas. Anomalous radioelement orapatite have been identified and occur in lenticular
concentrations shown by geochemical data and by adjunct quartz veins containing radiometric assay values of
geophysical (Rn), geologic, and mineral occurrence data mylonitized granitic gneisses of the order of 380 to 6600
provide a regional structural and geologic context for the ppm U2O3 and about 50 ppm ThO2. The Atomic Mineral
nature and possible extent of mineralization. Division (Govt. of India) has also reported several oc-
Potassium (K), uranium (U), and thorium (Th) are the currences of pitchblende and uraninite as well as their
principal radioactive elements (henceforth, radioelements) secondary weathered products along the 50–80 km stretch
in terrestrial materials. These radioelements occur in a of the Thrust Zone between Uttarkashi and Chamoli
wide variety of minerals in various combinations, com- (Bhattacharya, 1989; Kaul et al., 1991). Boltwoodite, a
monly as phosphates (monazite), silicates (zircon), and hydrated alkali uranyl silicate, has also been identified
as oxides (uraninite). Daughter products of the U and Th by Singh et al. (1991) to occur as secondary precipitates
decay-series include radon (Rn) and radium (Ra) whose associated with uraninite-bearing quartz veinlets near
presence and relative abundance has implications for ex- Brijranigad in the Bhilangana valley. Thus, there are wide-
posure-related health hazards. Where host minerals oc- spread indications of radioactive mineralization all along
cur in unusually high concentration (mineralization; not the Thrust Zone. The mineralization is sporadically dis-
necessarily a mineral deposit), Rn may be of serious con- tributed and may not be commercially viable.
84 P. K. Mukherjee et al.
Unusually high discharge of radon was noted by The Lesser Himalayan terrain is simplified into three
Choubey and Ramola (1997) and Choubey et al. (1999) major litho-tectonic units in the study area. Each is
in soils and in spring waters in the study area. Radon bounded generally by northwest-southeast trending re-
emissions, varying from 1 to 57 KBq/M3 in soils and from gional tectonic contacts with a gentle northerly dip that
less than 5 to 887 Bq/L in spring water within the area of is locally variable. These are, from north to south: 1) the
our study confirm the high anomalies observed by Main Central Thrust Zone (MCTZ, Metcalfe, 1993) that
Choubey and Ramola (1997) that are described as con- includes Valdiya’s Munsiari, Baijnath, and Almora groups;
trolled by geological factors, especially around the thrust Fig. 2) the Porphyroids (PH) that include Valdiya’s
zone. The radon content of the Balganga (a tributary of Debguru formation of Ramgarh Group; and 3) a
Bhilangana) river water is also surprisingly high (26.2 Proterozoic metasedimentary sequence (PMS) that in-
Bq/l near Budhakadar to 0.1 Bq/L near Ghanshali; cludes Valdiya’s Gangolihat, Rautgara, and Berinag for-
Choubey et al., 2000). Moreover, radioactive minerali- mations (also referred to as Garhwal Group). The PMS
zation in this area has also been reported at some of the of the Lesser Himalayan terrain is overridden by the crys-
high Rn locations (Negi 1967; Nashine et al., 1982; Das talline nappes (MCTZ and PH) including higher
et al., 1981; Bhattacharya, 1989; Kaul et al., 1991). Himalayan crystallines (HHC) uprooted from the north.
Reports of base metal sulphide mineralizations have The rocks of the MCTZ are characterized by highly
also been reported from a number of locations in the stud- deformed, sheared, mylonitized and metamorphosed
ied area as well as in the adjacent regions (Kumar, 1970; schists, gneisses, mylonites and migmatites having mainly
Valdiya, 1980; Dutta and Ghose, 1970; Ghose et al., granitic parentage with minor imbricated foliated quartz-
1986). Moreover, the area has also witnessed substantial ite, calc-silicates and components of probable pelitic
mining activities in the past (Walton, 1910), but mostly sedimentaries. Below the MCTZ, multiple tectonic scales
for base metals only. Such evidence of extensive hydro- or schuppen structure is developed particularly between
thermal activity may or may not be related to Himalayan the Mandakini and Alaknanda rivers. PH is comprised of
orogeny. In spite of the fact that radioactive mineraliza- profoundly mylonitized and sheared suite of porphyritic
tion (as well as base metal sulphide mineralization) in granite-granodiorite-quartz porphyry intruded into the
this area has been reported from a number of locations phyllites interbedded with quartzite and minor carbon-
and radon emanations observed at places are abnormally ates. The PMS consists of a sequence of quartzites, car-
high, no comprehensive attempt has been made to assess bonate rocks and phyllites together with considerable
the mineral potential of the area. It is therefore important amount of pene-contemporaneous metavolcanics of the
to know the geochemical dispersion of the radioelements Lesser Himalaya (the Garhwal Group).
and the relationship of this distribution to the geology of The discontinuity and abrupt change between the crys-
the area to provide a useful guide for future exploration. talline rocks of Munsiari, Baijnath or Almora and under-
In this paper, we attempt to document the possible extent lying Proterozoic metasedimentary sequence was recog-
of radioelement mineralization through a stream sediment nized as the Main Central Thrust (MCT; Valdiya, 1980).
geochemical survey and resultant geochemical dispersion Recent workers propose that the MCT is a wide zone of
maps. high strain ductile shear corresponding to the entire thick-
ness of Munsiari/Baijnath/Almora crystalline rocks, as-
sociated with inverted metamorphism from south to north
GEOLOGIC SETTING
with increasing structural height rather than a single thrust
The area is situated in the Garhwal Himalaya region plane as perceived earlier (Valdiya et al., 1999, Metcalfe,
(Fig. 1) of India. It represents a boundary zone where 1993). We also prefer to refer to this as the Main Central
rocks of differing ages and compositions are juxtaposed Thrust Zone (MCTZ) for simplicity. The MCTZ thus sepa-
by intensive shearing and displacement associated with rates the high grade HHC rocks to the north by Vaikrita
structural thrusts. The area studied is drained by, the (roof) thrust (VT) and the low-grade Lesser Himalayan
Alaknanda, Mandakini, Bhilangana and Bhagirathi Riv- thrust sheets (PMS) by Munsiari (floor) thrust (MT) or
ers (Fig. 1). The structural and tectonic intricacy of its equivalents (Baijnath thrust—“BT” and Almora
Himalaya has been the subject of many studies notably thrust—“AT”; Fig. 2). The MCTZ at the base is under-
by Kumar and Agarwal (1975), Valdiya (1980) Thakur lain by PH with a thrust contact (MT, BT or AT) and at
and Rawat (1992), and Valdiya et al. (1999). It is beyond places thrust directly over the Proterozoic meta-sedimen-
the scope of this study to review and synthesize the geo- tary sequence (PMS). The PH in turn is thrust over the
logic mapping and structural interpretation for the area PMS to the south and is separated by “Ramgarh thrust”
at a large scale given the small size of the area. We present (RT). A simplified schematic N-S section of the area is
a simplified geologic base modified and adapted from shown in Fig. 2B for clarity.
Valdiya’s (1980) in Fig. 2. The grade of metamorphism in general increases with
Geochemical survey in Ganga headwaters 85
Fig. 2. [A] Simplified geologic map of the study area (after Valdiya, 1980). Lithotectonic units are separated by major thrusts. Almora thrust (AT) and Baijnath thrust (BT) is different local names for the Munsiari thrust (MT) used in literature. [B] A schematic north-south structural cross-section through the center of the area. 86 P. K. Mukherjee et al.
increasing structural height from south to north (Sachan BCS-267 (Govindaraju, 1994). Evaluation of reproduc- et al., 2001). Locally, however, there is retrogradation due ibility, accuracy and minimum detection limit were car- to shearing involving extensive fluid activity in the shear ried out in a similar way as outlined in Saini et al. (2002). zone. The sedimentary rocks (PMS) are metamorphosed The accuracy of measurements is better than 12% for U, to chlorite grade, whereas the PH demonstrate biotite Th, and Zr and
Table 1. Summary statistics of the abundance of U, Th, Zr and K 2O in the three
lithotectonic units and as a whole. The median value denotes the baseline concen-
tration. The ranges of concentration of the elements are represented by the 10th
and 90th percentile value. Standard deviation on average (Sd) are given in paren-
thesis.
Th U Zr K2 O
MCTZ (Crystalline) (N = 48)
Median 19.0 4.8 281 2.2
Average (Sd) 21.0 (10.1) 5.9 (5.3) 334 (163) 2.3 (1.18)
10th_Percentile 11.2 1.6 191 0.9
90th_Percentile 30.8 8.3 513 3.6
PH (Porphyroids) (N = 49)
Median 14.2 3.7 274 2.6
Average (Sd) 15.6 (6.4) 5.8 (4.0) 284 (89) 2.7 (1.09)
10th_Percentile 10.6 2.1 181 1.5
90th_Percentile 22.5 11.4 410 4.0
PMS (Proterozoic metasedimentary) (N = 85)
Median 12.3 3.1 294 2.2
Average (Sd) 12.7 (4.8) 3.3 (1.9) 300 (94) 2.2 (0.86)
10th_Percentile 8.2 1.3 186 1.2
90th_Percentile 16.3 5.2 398 3.4
All samples (N = 182)
Median 13.8 3.6 288 2.3
Average (Sd) 15.7 (7.7) 4.7 (3.9) 304 (116) 2.3 (1.03)
10th_Percentile 6.5 0.5 135 0.5
90th_Percentile 23.6 8.9 422 3.6
AUCA 10.7 2.8 190 3.4
U and 19 ppm Th and for PH; 3.7 and 14.2 ppm, respec- minor metasedimentary components, but the same unit
tively. PMS rocks are least enriched in U and Th (3.2 and 25 km to the west in the Bhagirathi valley consists mainly
12.4 ppm). Gradual southward decreases in the median of metasedimentary rocks and the granitic- and
values of the U and Th from the MCTZ through PH and granodioritic-rock component of PH in this part is present
PMS correspond to decreases in grade of metamorphism. to the northwest; outside of the sampling area of this study.
The inference is that elemental mobility and secondary The U and Th variation maps (Figs. 3 and 4) correlate
enrichment are largely driven and controlled by fluid-rock reasonably well with each other except for the fact that
interaction during deformation and metamorphism. This the dispersion of U is more extensive as compared to Th
trend is also consistent with the average REE abundance and the maxima for U and Th do not match exactly, indi-
(Fig. 8(b)). The range of concentration (as 10th and 90th cating decoupling of U and Th in their dispersion and
percentile values) for Th are consistent with the above differential mobility. This decoupling may be due to the
observation, but U reaches higher values in PH rocks, fact that U is readily soluble in its 6+ natural oxidizing
lower in MCTZ rocks, and least in PMS rocks (Table 1). state (forms uranyl complex) and is dispersed in aqueous
Baseline values are thus marginally higher in compari- solution quite easily. On the other hand, Th is sparingly
son to those of AUCA. Some samples from the MCTZ soluble in aqueous medium in its 6+ state, though Th4+ is
and the PH from the central and eastern parts show con- soluble to some extent but is not stable and precipitates
centrations up to 34 ppm U and 57 ppm Th. immediately. Thus, U shows more diffused aureoles
The spatial variations in the distribution of elements around the mineralized zones and also shows some sec-
shown in Figs. 3–6 reflect underlying geologic charac- ondary enrichment anomalies. Isolated patches of high U
teristics. It is important to consider that at the scale of and Th values are observed all along the MCTZ as well
our work we are using groupings of differing rock-types as part of PH in Bhilangana valley in the north and in
whose compositions vary spatially. For example, the PH eastern part with more intense maxima occurring close to
along the Bhilangana River (in the central part of the study thrust planes. The zirconium variation pattern (Fig. 6)
area) is composed of granitic or granodioritic rocks with shows more random dispersion with very little spatial
88 P. K. Mukherjee et al.Fig. 3. Geochemical map showing the distribution of uranium. The solid lines is the trace of the Bhatwari thrust (BT) demarcat-
ing PMS and PH; dashed lines represents the Munsiari thrust (MT) demarcating MCTZ and PH. Sampling points are shown as
open circles and major rivers are shown in blue lines.
Fig. 4. Geochemical map showing the distribution of thorium. For Legend explanation see Fig. 3 caption.
correlation with those of U and Th. The distribution of Zones of higher K2O concentrations correspond to the
potassium (Fig. 5), in contrast, shows high values mainly granitoid out crops within the PH and granitic gneisses
in PH and, less frequently, on MCTZ and PMS rocks ex- in the MCTZ. Relative abundances of granitoid versus
cept for the one near Tehri where phyllitic rocks prevail. metasedimentary components in PH are well illustrated
Geochemical survey in Ganga headwaters 89Fig. 5. Geochemical map showing the distribution of potassium (as wt% oxide). For Legend explanation see Fig. 3 caption.
Fig. 6. Geochemical map showing the distribution of zirconium. For Legend explanation see Fig. 3 caption.
by the K2O distribution pattern (Fig. 5). We, therefore, The host mineral of U and Th
infer that distribution patterns shown by U and Th are Many of the high-value samples cluster near MT and
neither fully controlled by the abundance of zircon nor BT thrust contacts; values reach up to 34 ppm U and 135
by the radiogenic granitoids; rather they seem to be con- ppm Th, indicating potential for mineralization. In most
trolled by secondary mineralization. This makes probable rock types where zircon occurs, it is a significant host for
the occurrence of ore-grade mineralization. rare-earth elements, Th, and U (Finch and Hanchar, 2003).
90 P. K. Mukherjee et al.Table 2. Average REE abundance (in ppm)
of the three Lithotectonic units (n = number
of samples averaged)
PMS PH MCTZ
(N = 10) (N = 5) (N = 13)
La 30.2 40.5 86.1
Ce 61.6 87.1 195.2
Nd 26.8 28.2 46.0
Sm 5.59 6.52 12.23
Eu 1.40 1.41 1.86
Gd 4.39 5.40 9.87
Tb 0.75 0.93 1.68
Dy 4.11 5.27 9.45
Ho 0.80 1.05 1.88
Er 2.32 3.07 5.77
Tm 0.32 0.42 0.85 Fig. 7. Binary plot of zirconium and sum of U and Th for all
Yb 1.84 2.38 5.05 the samples excluding outliers defined by 10th and 90th per-
Lu 0.27 0.34 0.77 centile values. The data from different lithotectonic unites are
Tot. REE 140.4 182.6 376.6 plotted with different symbols for clarity.
Zircon is a common accessory mineral in acid magmatic natures of MCTZ and PH in Ganga average bed-
rocks like granitoids and has very high partitioning coef- sediments. Thus the average Yamuna sediments are more
ficients for REEs, U and Th (Finch and Hanchar, 2003). enriched in REE abundances. The less fractionated flat
Since the MCTZ and PH are comprised primarily of meta- HREE pattern is typical of zircon, but some ores of U
morphosed and strongly sheared granitoids in this area, and Th (e.g., secondary oxides and phosphates like thorite,
the control of zircon on the abundance of high U, Th and uraninite, monazite, apatite, pitchblende etc.) can also
REEs needs to be ascertained. In a few well-sorted high- produce the same effect having high partition coefficient
order river bar sediments, abnormally high U (81 ppm) for REEs especially more for HREEs and MREEs. Oc-
and Th (135 ppm) were associated (high-order River data currence of these vein-hosted minerals in the study area
not included here) with high Zr (4413 ppm) in a sample has also been reported by, many workers (Bhattacharya,
from the Bhagirathi River. Another sample from the 1989; Kaul et al., 1991; Singh et al., 1991). Relatively
Alaknanda River having comparable Zr (4084 ppm) but high dissolved REE abundance observed in Ganga and
has lower U (32 ppm) and much higher Th (365 ppm). Yamuna river water samples (Rengarajan and Sarin, 2004)
There are several individual samples, both from high or- may also be due to partial contributions from dissolution
der rivers and low order stream sediment samples that of these secondary minerals that are relatively less resist-
show departure from the projected correlation of U and ant to weathering compared to zircon. The plot of U+Th
Th with Zr, if zircon were the principal radioelement car- versus Zr in MCTZ (Fig. 7) shows more scatter in com-
rier. A few sediment samples from all three lithotectonic parison to that of U+Th versus REEs (Fig. 8a). This clearly
units were also analyzed for their REE abundance (Table suggests less influence and control of zircon abundance
2) in order to compare the REE geochemistry of the in the source region. Notable mobility in REEs and prob-
lithotectonic units. The chondrite-normalized REE pat- ably U and Th as well, has been observed in tectono-ther-
terns (Fig. 8(b)) for the MCTZ samples are distinctly more mal processes such as shearing, where mechanical grind-
enriched than PMS samples with PH samples fall inter- ing and grain size reduction is accompanied under poten-
mediate between the two. Moreover, the MCTZ shows tially high fluid activity (Dostal et al., 1980; Winchester
more flat HREE trend than LREEs with prominent mag- and Max, 1984; Vocke et al., 1987; Grauch, 1989; Roland
nitude of Eu anomaly. The Eu anomaly in case of the et al., 2003 and others). This would mean that REEs, U,
stream sediment samples from the PMS is very feeble and and Th have been remobilized and concentrated into the
that of PH are intermediate. The REE trends of MCTZ fluid phase during the shearing and might have been em-
and PH are also more akin to the average Ganga and placed as veins at a shallower depth along the fluid chan-
Yamuna River bed sediments (Fig. 8(b)) as reported by nels (thrust contacts). Zones of intense deformation and
Rengarajan and Sarin (2004). Ganga catchment area be- shearing in the MCTZ and PH become more porous and
ing more laterally spread within PMS terrain compared provide pathways for fluid channeling (Selverstone et al.,
to narrow catchment of Yamuna, the influence of PMS 1991; Essaifi et al., 2004; Keller et al., 2004; and refer-
on Ganga sediments is more prevalent that dilutes the sig- ences therein) and their precipitation as ore minerals.
Geochemical survey in Ganga headwaters 91(b) (a) Fig. 8. (a) Binary plot of total REEs with U+Th using a limited number of representative samples from each lithotectonic unites. (b) Chondrite normalized REE plot of the average compositions of the each lithotectonic unit. Average Ganga and Yamuna sediments data are from Rengarajan and Sarin (2004). Fig. 9. Soil-gas radon concentration (in KBq/M3) at selected sites is shown as proportional plot (data after Choubey et al., 1999). The lithotectonic outlines are same as in Fig. 2. 92 P. K. Mukherjee et al.
Radioactive anomaly zones genesis to the presence of secondary U and Th rich ore
Several independent lines of evidence imply that zones minerals in MCTZ that are expectedly rich in REEs.
of U and Th ore mineralization are present in shear zones Anomalous radon values reported by others are consist-
within and near crystalline rocks of MCTZ and PH. In ent with, and predicted by our geochemical study. The
areas bounded by crystalline rocks to the north, the MCTZ, and to a lesser extent PH are prospective for
geochemical maps for U (Fig. 3) and Th (Fig. 4) show radioelement mineralization and geochemical maps are a
isolated patches of enrichment and correspond well with powerful guide for future exploration. Because of the
Rn anomalies (Fig. 9). Considering areas with >5 ppm U structural controls on the anomalies and related tectonic
and >15 ppm Th as threshold (Ewers, 1991), more than processes, the crystalline rocks along the entire length
60% of the MCTZ and PH terrain are favorable zones for (~2500 km) of the Lesser Himalayan belt probably have
exploration. These are located within the MCTZ (N of some potential for radioelement mineralization.
Nandprayag, E of Ukhimath, near Ghuttu and Budhakedar
and E-NE of Sainj) and within PH in Bhilangna valley. Acknowledgments—This work was carried out under the thrust
The rocks are extensively mylonitized, and complexly area projects of the Wadia Institute of Himalayan Geology,
thrust. We conclude that mineralization in this area is Dehradun. B. R. Arora is thankfully acknowledged for encour-
linked to deformation-induced radioelement agement and support. We thank Joseph S. Duval (USGS, Reston)
and C. Reimann for comments on an earlier draft of this manu-
remobilization and subsequent emplacement as veins. We
script. The work benefited from discussions with the members
model potential for uranium in vein and disseminated
of the FOREGS and IUGS group on global geochemical base-
mineralization in lower Himalaya crystalline rocks lines.
(MCTZ and PH) and predominantly occurring within the
hanging wall rocks immediately overlying the thrusts
planes. We speculate that the areas of relatively high REFERENCES
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Table A1. Assessment of accuracy (Mean % deviation) and precision (RSD) of the determination based
on repeated measurement of reference standards SGR-1 (shale, USGS) in case of measurement of REEs
by ICP-MS and GSS-4 (Soil, IGGE, China) for XRF analyses of K, Th, U and Zr
Element Reported value* Mean analyzed value Mean % deviation RSD
Elements analyzed by ICP-MS
Reference standard used: SGR-1 (Shale; USGS)
La 20.3 18.9 6.8 3.0
Ce 36 35 3 2
Pr 3.9 3.7 6.1 2.8
Nd 15.5 14.6 5.7 3.9
Sm 2.7 2.8 2.2 4.3
Eu 0.56 0.61 8.68 2.79
Gd 2 2.0 2.0 3.3
Tb 0.36 0.34 6.23 2.86
Dy 1.9 1.9 2.5 2.8
Ho 0.38 0.38 0.97 2.21
Er 1.11 1.17 5.82 5.28
Tm 0.17 0.17 1.13 4.09
Yb 0.94 1.07 14.29 4.63
Lu 0.14 0.16 16.61 4.41
Elements Analyzed by WD- XRF
Reference standard used: GSS-4 (Soil; IGGE, China)
K2 O 1.03 1.08 4.85 0.6
Th 27 28.8 6.5 1.2
U 6.7 7.5 11.2 1.8
Zr 500 509 1.7 1
*Reported values are from Govindaraju (1994).
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