IAPRS & SIS, Vol.34, Part 7, “Resource and Environmental Monitoring”, Hyderabad, India, 2002 
  
The third patch exposed on the eastern bank of Kynshiang river, 
north of its confluence with Wah Blei river, which is continuing 
further south of the confluence had so far remained 
radiometrically unchecked. During the course of ground truth 
collection on this channel-filled sedimentary domain in the early 
months of 1992, the authors have located significant uranium 
occurrences south of the confluence of Wah Blei and Kynshiang 
rivers (91?06'34"E-25?18'38"N). These uranium anomalies 
range from 0.022% to 0.704% of uranium associated with 
carbonaceous shale, feldspathic sandstone and coal band. This 
newly discovered uranium occurrence in the channel-filled 
sedimentary domain of Mahadek formation has geared up the 
uranium exploration activities in this part of the sedimentary 
basin. 
2. DISCOVERY OF ALKALINE-CARBONATITE 
COMPLEXES 
Nearly 50% of the carbonatite complexes in North and South 
America were discovered by amateur explorers by the study of 
aerial photographs. Perhaps, this is one area where remote 
sensing can play a direct role in the exploration of atomic 
minerals. Alkaline carbonatite complexes, barring exceptional 
cases, generally occupy small areas of 2 to 40 sq.km and 
geomorphologically exhibit saucer shaped circular depressions. 
In a vast homogeneous country rock, a small circular feature of 
heterogeneous exotic rock assemblage makes a tremendous 
contrast in terms of tone, texture and geomorphology. Apatite, 
being a major accessory mineral in almost all the rock units of 
alkaline carbonatite complexes, makes the insitu soil cover rich 
in phosphorous, an essential nutrient for the healthy vegetation. 
Thus, a conspicuous contrast in vegetation could be observed in 
the alkaline complexes which is highlighted in NIR bands of 
satellite images. Of the five known alkaline carbonatite 
complexes in the state of Assam and Meghalaya three viz., 
Samchampi, Jasra and Barpung complexes have been 
discovered with the help of aerial photographs, satellite and 
aeromagnetic data sets. 
2.1. Samchampi alkaline carbonatite complex, Mikir Hills, 
Assam, India 
The Samchampi Alkaline Complex is a roughly circular (4 km 
diameter), sub volcanic and stock like body emplaced in the 
Archean gneisses of the Mikir Hills massif Syenitic fenites, 
comprising potassic, sodic and , and sodic-potassic types, 
constitute the dominant rock types, followed in abundance by 
magnetite-perovskite + apatite + phlogopite rock, ijolite- 
melteigite suite, carbonatite, pyroxenite, and syenites. Besides 
these, significant quantities of phosphatic and tuffaceous (?) 
rocks also occur. Carbonatites, occurring as dykes and veins, 
are essentially soviets, olivine-phlogopite soviets, and biotite 
soviets, with minor beforsitic types, typified by minor minerals, 
such as radioactive pyrochlore, apatite, magnetite, monazite and 
zircon (fig.3). 
Phospatic breccia, exposed on the eastern part of the complex 
contains uranium oxide to the tune of 0.068%. But the mineral 
  
  
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Fig.3. Geological map of Samchampi Alkaline- Carbonatite 
complex, Mikir Hills, Assam 
beneficiation studies indicate that it is not workable 
economically 
at present. Rare-earth and rare-metal-bearing minerals 
associated with the SAC include monazite, pyrochlore, 
perovskite, zircon, rutile, and thorite. Magnetite-perovskite 
rock, one of the most abundant rock types of the complex 
contains upto 0.27% Nb, 0.049% U3;0g and 0.26% ThO,, 
whereas, the magnetite-phlogopite rock contains upto 0.48% 
Nb, 0.041% U3Og and 0.36% ThO, Rare earth element 
concentration in the complex is generally associated with fenites 
especially the granitic type which contain upto 2.24% of total 
REE, especially the LREE group. The soil cover especially over 
the magnetite rock is rich in pyrochlore, a niobium rich mineral, 
and a substantial reserve of niobium has already been proved by 
AMD. 
2.2. Jasara Alkaline complex, Assam 
The Jasara alkaline complex is located on the eastern fringe of 
Shillong Plateau in Hamren subdivision Karbi Anglong district, 
Assam, NE India (92° 30” 00” - 92° 31’ 47” and 26° 00’ 00” - 
26° 01’ 47”) (fig.4). This complex was discovered on the basis 
of clues provided by aeromagnetic data (NGRI, 1980) and 
LANDSAT TM imagery. This complex is nestled within three 
prominent fracture systems viz. Barapani — Tyrsad Shear zone 
in the north, Kopilli fault in the east and Borpani fracture zone 
in the south. It covers an area of 2.5 km” (Figure 1) intruding 
the Shillong Group of metasedimentary rocks comprising 
quartzites and phyllites along the southern and western margins 
and by granitoids along the northern and eastern peripheries. 
536