Download 12 ABSTRACT Uranium is one of the most abundant element found

ABSTRACT
Uranium is one of the most abundant element found in the Earth's crust. It can be found
almost everywhere in rock and soil, in rivers and oceans. Traces of uranium are even
found in food and human tissue (IAEA, 1996). Uranium is naturally present in all
environmental media at very low concentrations (a few parts per million). Higher levels
are present in certain areas, including those with natural uranium ores. In its natural state,
uranium occurs as an oxide ore, U3O8. Additional compounds that may be present
include other oxides (UO2, UO3) as well as fluorides, carbides or carbonates, silicates,
vanadates, and phosphates. The environmental transport of uranium is strongly
influenced by its chemical form. It is generally one of the more mobile radioactive
metals and can move down through soil with percolating water to underlying
groundwater. Uranium preferentially adheres to soil particles, with a soil concentration
typically about 35 times higher than that in the interstitial water (the water between the
soil particles); concentration ratios are usually much higher for clay soils (e.g., 1,600).
Uranium can bio-concentrates in certain food crops and in terrestrial and aquatic
organisms. However, data do not indicate that it biomagnifies in terrestrial or aquatic
food chains. The U.S. Environmental Protection Agency (EPA) established a maximum
contaminant level (MCL) for uranium in drinking water of 0.030 milligram per liter
(mg/L).
The International Atomic Energy Agency (IAEA, 1996) assigns uranium deposits to 15
main categories of deposit types, according to their geological setting and genesis of
mineralization, arranged according to their approximate economic significance.
1. Unconformity-related deposits
6. Intrusive deposits (Alaskites)
2. Sandstone deposits
7. Phosphorite deposits
3. Quartz-pebble
conglomerate
8. Collapse breccia pipe deposits
deposits
9. Volcanic deposits
4. Breccia complex deposits
10. Surficial deposits
5. Vein type deposits
11. Metasomatite deposits
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12. Metamorphic deposits
14. Black shale deposits
13. Lignite
15. Other deposits
UNCONFORMITY RELATED URANIUM DEPOSITS
Mid-Proterozoic – Archean basement unconformity is proved all over the world as the most
potential zone hosting some of the world’s largest uranium deposits. The Srisailam sub basin is
geologically mid to late Proterozoic in age and it is unconformably overlying the Archean granite
basement. At present deposits of this type, spatially related to the Lowe-Middle
Proterozoic unconformity are known only from Australia and Canada (Hoeve et al.,
2005). The ore zones occur above, along and below the unconformity in Canadian
deposits (Athabasca) or mainly found in the Lower Proterozoic rocks below the
unconformity as in Australian deposits (Pine Creek Geosynclines). Uranium
metallogeny for this group of deposits, as inferred from the case studies of deposits
envisages a sequence of events that ultimately led to their formation often with high
grades and large tonnage forming giant deposits.
In Indian scenario the unconformity related uranium deposits, the first unconformity
deposit was established in the intra – cratonic proterozoic Cuddapah basin at Lambapur –
Peddagattu, Nalgonda district in Andhra Pradesh (Sinha et al., 1995) and then after works
at Koppunuru, Guntur District, (Jeyagopal, 1996) at the proximity contact of Meso –
Proterozoic Srisailam quartzite/ Neo – Proterozoic Banganapalle quartzite and the
basement granite respectively. Unconformity uranium type deposits are divided into
some outliers, like Chitrial, Lambapur- Peddagattu, Koppunuru, Amrabad outlier etc.
The Geochemical Investigations for Uranium Mineralization in the outliers, NNW of
Srisailam sub basin of Cuddapah Basin (Fig 1) has been carried out in the parts of
Nalgonda and Mahaboob Nagar districts, Andhra Pradesh.
Chitrial and Amrabad areas were selected for the Geochemical investigations.
To
accomplish the aims of this thesis the Geochemical investigations were carried in two
phases in Chitrial and Amrabad areas of Nalgonda district and Mahaboobnagar districts
respectively.
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First Phase: Geochemical Reconnaissance Survey
Second Phase: Detailed Geochemical Survey
In Chitrial around 45 sq.km and in Amrabad around 20 sq.km area has been covered for
Geochemical investigations.
The Chitrial area falls into the toposheet No. 56L/13,
56L/14 and is located between , latitude and longitudes are N 160 29’ 42.3” and E 780 56’
28.3” to N 160 34’ 45” and E 790 04’ 55.2. Amrabad belongs to toposheet No. 56L/15
and is located between latitudes and longitudes are N 160 25’ 15” to E 780 50’ 10” and N
160 27’ 15.5” to E 780 54’ 25”.
Amraba
d
Fig 1 Location of Chitrial and Amrabad in Srisailam Basin belonging to Cuddapah
formation (AMD, 1996)
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GEOLOGICAL MAP OF SRISAILAM SUB BASIN
Amrabad
Uranium Deposit
Fig 2 Location of Chitrial and Amrabad in the north eastern fringes of
Srisailam sub-basin (AMD, 1996).
OBJECTIVES:
The following objectives are set for the Geochemical Investigations for Uranium
Mineralization in the outliers – NW of Cuddapah Basin in the parts of Nalgonda and
Mahaboob Nagar, Andhra Pradesh.
1. To understand the geology and geochemistry of the Srisailam quartzite outlier
with reference to U- mineralization.
2. To establish geochemical signatures.
3. To study geochemical dispersions and mobility of U & its associated elements
4. The pH & EC environment around in unconformity zone.
5.
To study the geochemical behaviour of U & its associated elements in primary
and secondary environment.
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6. Study of alteration effects and controls of mineralization.
7. Correlation of anomalies in rocks & soils.
8. A comparative study of U behaviour in Chitrial, and Amrabad.
9. Establishing pathfinders for U mineralization.
METHODOLOGY (for accomplishing objectives):
1. Reconnaissance and detailed survey according to grid pattern
2. Litho, Pedogeochemical sampling and gamma ray survey.
3. Petrographic studies - Detailed Petro - mineralogical studies.
4. Geochemical analysis of samples for Rocks & Soils
5. Determination of pH and EC for soil samples
6. Kankar (Calcrete) formation and U mineralization.
7.
Geochemical analytical data generation
8. Data processing and preparation of geochemical maps.
9. Statistical Analysis and. Data interpretation.
10. Correlation between U & its associated elements.
Geology
The major rock types are a) basement granites with cross cutting dykes and pegmatites,
and b) quartzites around the Chitrial & Amrabad outliers.
However thin and
discontinuous shales and clays were present along the unconformity between granites and
quartzites.
Geological set - up: Chitrial and Amrabad outliers are located at NNW of Srisailam sub
basin (Fig 2). There is a major Dindi River flowing between the two faults with strike
direction as NW to SE separating Chitrial and Akkavaram. The Cuddapah Basin is
situated in the eastern part of the Dharwar Craton and is one of the largest Proterozoic,
intra-cratonic, sedimentary basins in India. It is crescent shaped and covers an area of
around 44 500 km2 with a maximum length and breadth of 440 km and 145 km,
respectively. The basin is in filled by a >10 km thick succession of igneous and
sedimentary rocks of the Cuddapah and Kurnool Groups. This basin comprises five sub-
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basins VIZ. Chitravathi, Nallamalai, Krishna, Srisailam, Kurnool and Palnad (Table 1).
The western part of the basin has been relatively unaffected by tectonic activity;
sedimentary rocks dip gently (10–15°) to the east. In contrast, the eastern part was
severely folded and highly metamorphosed during the Middle to Late Proterozoic (∼1·3–
1·6 Ga).
Eastern Ghat Orogeny Extrusive and intrusive mafic volcanic rocks are
exposed at lower stratigraphic horizons in the Cuddapah Basin and are mostly sub aerial
basaltic lavas and sills, occurring an arcuate pattern, parallel to the margin of the basin.
There are fourteen major types of basins in India; among these Cuddapah Basin is the one
of the biggest and most important for Economic geology. The geological succession of
the Cuddapah and Kurnool are as follows.
Table.1 Geological succession of the area (after Saha and Ttripathy, GSI, 2012)
Nandyal Shale
Koilkunta Limestone
Paniam Group
Owk Shale
Narji Limestone
Banganapalli quartzite
KURNOOL GROUP
Nallamalai Group
----------Unconformity-------SrisailamFormation
---------Tectonic Contact-----Cumbum Slate
Bairenkonda Quartzite
(=Nagari Quartzite)
CUDDAPAH SUPER GROUP
---------Tectonic Contact-------
ChitravathiGroup
Papaghni Group
Gandikota Quartzite
Tadpatri Shale
Pulivendla Quartzite
Vempalle Slate
Gulcheru Quartzite
---- ------- Unconformity---------
Archean Granite & gneisses
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Cuddapah Basin: Salient Features
Area: 44,500 sq km
Age:
Proterozoic
Sub-basinsKurnool,
Palnad
Papaghni,
Nallamalai, Srisailam
Lithology: 12 km thick volcano-sedimentary pile consisting of Arenaceous,
Argillaceous, Carbonates, and Volcanic (basic and acidic)
Structure: Western part is flat lying and Eastern part is folded, faulted and thrusted
Intrusives: Gabbro, Dolerite, Basalt, Kimberlite and Lamproite, and Younger granites,
syenite
Mineralization:
Uranium, Base metals, Asbestos, Barytes, Diamond, Phosphorite,
Limestone
Three genetic types of U-mineralization
1. Stratabound:
Impure
dolostone
hosted
syngenetic
stratabound
uranium
mineralization in the Vempalle Formation in the SW part.
2. Unconformity Associated: Uranium mineralization at the base of the Srisailam
and the Banganapalle Formations in the N part of the basin.
3. Vein Type:
(a) Uranium mineralization localized along fractures/shears in the basement
crystallines in the southwestern part.
(b) Uranium mineralization localized along shears in the basement schists in the E
margin.
(c) Uranium mineralization hosted in the Gulcheru Formation in the SW part
Petrography and Mineralogy of the host rocks: The host rock for uranium
mineralization at Chitrial & Amrabad outlier is mainly granite, which is medium to
coarse-grained and composed with phenocrysts of microcline, orthoclase - and quartz.
Microcline-microperthite shows post-crystalline deformation with fractures hosting
clusters of chlorite, epidote etc. and uraninite with secondary development of
uranophane. The host Srisailam arenite varies from feldspathic sandstone to arkose.
Uraninite and secondary uranophane are hosted by fractures within the granite. The host
dolerite dykes are highly altered, consist of plagioclase and chlorite (altered from
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pyroxene/amphiboles) with minor calcite, epidote, apatite, biotite and some opaque
minerals.
Mineralization:
Basement granite and quartzite are the host rocks for uranium mineralization in the
unconformity area and is akin to high-grade and large-tonnage unconformity-related
uranium deposits in Canada and Australia. Uranium mineralization is confined mostly to
the joints trending NS, NNE, and SSW direction.
The mineralized zones contain
Uraninite, pitchblende in addition of pyrite, hematite and secondary silica. The Verma
etal (2009) states that several uranium occurrences reported from Chitrial and adjoining
areas. In the entire Chitrial and adjoin areas, Uranium mineralization of 0.130% U3O8 x
7.20 m intercepted along the boreholes in the western sector with rich radioactive band.
The thickness of orebody varies from 1.0 to 7.20 m with an average value of 2.45 m.
Secondary Uranium minerals are identified in Chitrial and Amrabad in following forms.
 Secondary Uranium minerals are present as micro fracture fillings in Sericite.
 Secondary uranium minerals observed in Veins
 Radioactive Allanite and Zircon are also observed associated with Epidote,
Chlorite, Sericite and Biotite.
Uraninite occurs as inclusion in biotite and feldspar. Where as, pitchblende of later
generation, lower temperature, hydrothermal type occurs as fracture filling and veins
shows epigenetic nature. Uranophane is present as secondary uranium minerals close to
the fracture zone basement granitoid. Large scale alteration illitization of feldspar and
chloritization of biotite is noted in the ore zone granitoids.
Chitrial granites are considerably rich in chlorite, which aids in the mineralization. Large
scale intergranular fracturing, recrystellization of quartz, granulation of quartz and
feldspar might have further necessitated formation of richer concentration close to the
unconformity contact. It aided by the presence of suitable reductants in the form of grey
to black coloured, thinly laminated shale and pyrite. Hydrothermal signatures in the form
of bleeding pyrite in granite and also predominately seen.
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Based on the surface radioactivity survey, lithogeochemical and pedogeochemical
analysis results, primary and secondary dispersion patterns, petrographic investigations
are indicating the occurrence of U mineralization in Chitrial and Amrabad along the
unconformity contact between basement biotite granitoid and the Srisailam Formation.
The most favorable trend of the ore body is NE-SW (major fracture trend). This feature
supports the role of fractures in controlling U-mineralization, besides non-conformity
contact with basement granitoid.
Surface Radioactivity:
The surface radioactivity has been carried-out only in Amrabad but not in Chitrial. The
vein-like uranium mineralization along the fractures in the Lower Proterozoic pelitic
rocks close to the unconformity,
Basement granite of Amrabad outlier belongs to the Middle - Upper Proterozoic
Cuddapah of Super group. Based on the surface radioactivity investigations the secondary
uranium mineralization was observed, in the basement granite and the overlying
Srisailam pebbly arenite and basic dykes and vein quartz within the basement granite
close to the unconformity.. The radiometric surveys were conducted on basement granite
near Chennakeshavulu Gutta and near the village of the Padhra, the location point is N
160 25’ 55” and E 780 50’ 40.2” at Amrabad outlier. The radiometric counts are shows
195 and 202 ppm measured by the differential spectrometer. The good amount of the
secondary uranium may occur in granite at Padhra.
Mineralization appears to be controlled by NNE-trending vertical fracture in the
basement granite, filled with quartz associated with Chlorite and galena. Such an
association clearly points to open-space filling and hydrothermal nature of mineralization
at Amrabad. Thus, it is evident from the field and geochemical analysis data, prominent
sets of fractures/faults in the basement granite, trending NNE-SSW and NW-SE, have
proved the concentrating of secondary uranium mineralization at Amrabad.
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Kankar (Calcium Carbonate Precipitate- (Calcrete)
Formation of Calcium Carbonate (CaCO3) is a characteristic feature of semi-arid and arid
regions of the world, resulting from a displacive and/or replacive introduction of vadose
carbonates in greater or lesser quantities in the weathering profile. The breakdown of
feldspars as kaolinite during rock-water interaction, releases Ca2+. Soils/weathered
products contribute high CO2 under the open system. The Ca2+ and CO2 are added to the
groundwater through the infiltrating recharge water. They subsequently precipitate as
fine-grained carbonates in the weathering profile due to evapotranspiration under a
freshwater environment (Subba Rao et al, 2009)
According to Netterberg (1969), calcrete can be regarded as “a material formed by the in
situ cementation and/or replacement of almost any pre-existing soil by calcium carbonate
deposited from the soil or ground water”. Thus, although calcrete contains a high
proportion of calcium carbonate, it is not a sedimentary rock like limestone which also
contains a high proportion of Calcium Carbonate (CaCO3) but which has a quite different
origin. Instead, calcrete is a secondary product formed within or on top of an existing soil
and is a member of the useful group of road building materials known as pedogenic
materials, of which ferricrete (laterite) and silcrete are prominent members.
In Chitrial, and Amrabad we find Honeycomb and Nodular type Calcrete.
Kankar
generally forms when minerals are leached from the upper layer of the soil (the A
horizon) and accumulate in the next layer (the B horizon), at depths of approximately
three to 10 feet under the surface. It generally consists of carbonates in semiarid regions,
while in arid regions, less-soluble minerals will form kankar layers after all the
carbonates have been leached from the soil. The calcium carbonate precipitate first and
accumulates in the form of small lumps, nodules, then forms a discernible layer, and
finally, results in thick solid bed.
In Chitrial area kankar is found near the unconformity zone where Uranium
mineralization reported by AMD. In Amrabad the kankar formation is observed about 10
meters thick (Fig 3). The observed surface radio activity is high in Amrabad area
compared to that as Chitrial. The high surface radioactivity is due to the presence of
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secondary uranium minerals in granite (Uranophane and Uranyl Carbonate).
The
Leached Uranium Carbonate form the primary Uranium minerals are trapped in kankar
zone.
The kankar zone scavenges the further mobility of Uranium resulting in the
accumulation of Uranyl Carbonate in calcrete.
Hence the high surface radioactivity observed in kankar zone.
So kankar formation is
play major role in exploration of Uranium mineralization.
Quartzite Boulders
Kankar
Weathered Granite
Fig 3 Kankar (Calcrete) formation between quartzite and weathered granite
Geochemical Sampling:
The geochemical sampling has been carried-out in two stages. 1. Reconnaissance and 2.
Detailed Survey.
Reconnaissance Survey: The sampling grid of 1 x 1 Sq.Km was prepared and rocks &
soil samples were collected with the help of GPS from Chitrial and Amrabad are
tabulated. One sample per one square kilometer has been collected (Fig 4). A total of 64
lithogeochemical and 65 pedogeochemical in Chitrial, 20 lithogeochemical and 20
pedogeochemical in Amrabad (Table 2) samples were collected during geochemical
reconnaissance survey.
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Detailed Survey: The target area has been narrowed down based on the dispersion
patterns observed in the reconnaissance survey.
The sampling grid of 0.25 X 0.25 Sq.
Km (Table 2) was planned on narrowed target and carried out in detailed survey in
Chitrial and the same was not carried out for Amrabad area (Fig 5), but Gamma ray
survey was conducted and secondary Radiogenic minerals of Uranium on basement
granite were observed. About 44 lithogeochemical and 44 pedogeochemical samples
were collected at Chitrial.
Table 2 Geochemical sampling of Reconnaissance and Detailed surveys
Chitrial
Amrabad
Rock
Soil
Rock
Soil
Reconnaissance Survey
44
45
20
20
Detailed Survey
44
44
nil
Nil
Total
88
89
20
20
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CHITRIAL
NARAYANPUR
UDIMILLA
Amrabad
Fig 4 Litho & Pedogeochemical sampling at Chitrial & Amrabad of reconnaissance survey
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16.59313
16.58411
CTR/S-16 CTR/S-21
CTR/S-31CTR/S-36CTR/S-41
CTR/S-6 CTR/S-11
CTR/S-1
CTR/S-26
CTR/S-27CTR/S-32
CTR/S-2 CTR/S-7 CTR/S-12CTR/S-17CTR/S-22
CTR/S-3
CTR/S-13 CTR/S-18CTR/S-23
CTR/S-8
PEDDAMULA
16.57523
CTR/S-37
CTR/S-42
CTR/S-33
CTR/S-38
CTR/S-28
16.56622
16.55734
CTR/S-43
MADHAVARAM
CTR/S-24 CTR/S-29
CTR/S-39
CTR/S-34
CTR/S-44
CTR/S-9 CTR/S-14CTR/S-19
CHITRIAL
CHITRIAL BLOCK CTR/S-4
16.54832
CTR/S-45
CHITRAL
CTR/S-10 CTR/S-15CTR/S-20CTR/S-25
CTR/S-40
CTR/S-30CTR/S-35
CTR/S-5
16.53944
VENKATGHANI TANDA
16.53043
BUDDONI TANDA
DASARIPALLI
NP/S-1
NP/S-2
GHANPUR
16.52155
NP/S-5
NP/S-9 NP/S-13 NP/S-17 NP/S-21
NP/S-6NP/S-10
16.50308
NP/S-14 NP/S-18NP/S-22
NP/S-3 NP/S-7 NP/S-11 NP/S-15NP/S-19
NP/S-4 NP/S-8
16.51196
NP/S-12
NP/S-16 NP/S-20
REKALAGADDA
16.49406
NP/S-23
NARAYANPUR BLOCK
16.48519
NP/S-24
16.47617
UD/S-1AKKAVARAM
UD/S-5 UD/S-9
UD/S-2 UD/S-6
UD/S-3
UD/S-21
UD/S-13UD/S-17
UD/S-14
UD/S-10
UD/S-7 UD/S-11
UD/S-15
UD/S-16
UD/S-4 UD/S-8 UD/S-12
16.46729
UD/S-18UD/S-22
UD/S-23
UD/S-19
16.45827
16.44939
UDIMILLA BLOCK
UD/S-20 UD/S-24
16.44038
Fig 5 Grid pattern lay out - Rock and Soil samples locations and their coordinates at
Chitial area of Detailed Survey.
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79.11711
79.10799
79.09901
79.08989
79.08092
79.07179
79.06267
79.05355
79.04473
79.03546
79.02648
79.01737
79.00839
78.99942
78.99030
78.98133
78.97221
78.96265
78.95354
78.94456
78.93544
78.92647
78.91734
78.90837
78.89925
78.89028
16.43159