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IAPRS & SIS, Vol.34, Part 7, *Resource and Environmental Monitoring", Hyderabad, India, 2002
ROLE OF REMOTE SENSING FOR EXPLORATION OF ATOMIC MINERALS; FEW
CASE STUDIES FROM NORTHEAST INDIA.
R.Mamallan, S.N.Kak, A.K.Bagchi and R.K.Gupta
Atomic Minerals Directorate for Exploration and Research, Begumpet, Hyderabad-500 016. Telephone: 040-7767101 Fax: 040-
7162940, email: amdhyd G ap.nic.in
KEY WORDS: uranium, Meghalaya, cuesta, Cretaceous, Mahadek, Wahkyn, Samchampi, Jasara
ABSTRACT :
Satellite data products, aerial photographs and aeromagnetic data have proved extremely useful in the preliminary stages of
exploration for atomic minerals in many areas in India including the northeastern region. The inherent terrain constraints together
with thick forest cover inhibit accessibility in this region. Remotely sensed data products have became very handy in the selection of
target areas for further exploration. Thematic information with reference to uranium and niobium rich lithounits and major structures
in the states of Meghalaya, Arunachal Pradesh and Assam has been established by using these data products. The Cretaceous channel
filled sediments of Mahadek formation exposed on the southern flanks of Khasi Hills, Meghalaya are known to incorporate
favourable geochemical attributes to host uranium mineralization. The intrinsic geomorphological and photo elemental traits of the
channel fill and the adjoining overbank sediments in the environs of Domiasiat village have been characterized and thereby two
more domains of channel fill sediments have been demarcated using aerial photographs and satellite images. Ground follow-up
revealed rich uranium mineralisation in channel fill sediments around the junction of Wah Blei and Kynnshiang rivers, later named
as Wahkyn, where substantial reserves of Uranium oxide has already been proved. A very characteristic feature of Alkaline-
Carbonatite complexes is their circular configuration and a prominent magnetic signature. Study and interpretation of satellite
images and aero-magnetic data and ground follow-up investigation has brought to light three new alkaline carbonatite complexes
rich in Niobium and Light Rare Earth elements.
INTRODUCTION
With more than 70% of the hard rock area covered with a thick
forest cover and a very difficult terrain to negotiate, the
northeastern states of India pose severe constraints and
challenge to mineral explorers and earth scientists. Perhaps,
this is one terrain where Remote Sensing could play a
meaningful role in understanding the geological framework,
exploration of minerals and oil and to reconstruct the processes
that actually concentrated the minerals and oil. Atomic
Minerals Directorate for Exploration and Research (AMD), the
Government of India organization engaged in the exploration of
uranium and other atomic minerals used in the country's
indigenous Nuclear Power Programme, make use of Remotely
Sensed data products in a big way in the first stage of its
exploration programme. Needless to mention, Remote Sensing
and airborne geophysics have played important role in the
discovery and expansion of the major uranium deposits
discovered in India. In this regard, the importance of Remote
Sensing has been realized in (a) selection of the target area for
detailed exploration (b) to understand and explain the
mineralizing processes in an existing uranium deposits and (c)
having understood the processes, to search for similar
geological environments in the neighboring terrain. It has been
seen that the uranium mineralized areas may or may not have a
tell tale signatures but it largely depends on climate, weathering
processes, lithology, relief of terrain and a host of other
features. No two similar deposits can have the same signatures
and so every deposit has to be studied with reference to its
associated features.
Some of the cases where Remote Sensing and airborne
geophysics have played a major role in the discovery /
533
expansion of deposits of uranium and other atomic minerals are
discussed in the following pages:
1. WAHKYN AREA, MEGHALAYA
Meghalaya plateau is a horst-like feature bounded by
Brahmaputra graben, Dawki fault, Yamuna fault and Naga
thrust in the north, south, west and east, respectively (fig.1).
The plateau incorporates three major geological provinces, viz.
(i) The cratonic massif of Archaean gnessic rocks, (ii) tlie
Proterozoic Shillong group of metasediments with intrusive
mafic rocks and granite batholiths, and (iii) the rift-related
basalts and alkaline rocks of late Jurassic to early Cretaceous
age and a late Mesozoic to Tertiary sedimentary cover
occurring along the southern margin.
The deposition of Cretaceous sediments along the southern
fringe of the plateau began with the accumulation of alternate
sandstone-conglomerate beds. Conformably overlying these
beds in the south and unconformable resting over the
Precambrian crystalline in the north is a thick sequence of
Meade formation, which is characterized by the deposition of
both continental and marginal marine sediments.
In the region of present study the vast continental arkoses
sandstones are overlain by isolated exposures of marginal
marine purple sandstones. Two distinct sedimentary facies, viz.
channel-filled and floodplain sediments of the continental unit
have been identified. Channel-filled sandstones are flanked on
either side by floodplain sediments and both these units were
deposited during the upper Cretaceous period along the braided
river channels and the corresponding swampy floodplains,
respectively. Aerial photographs were extremely useful in
accurate delineation of these fancies.
