REE mineralization in the carbonatites of the Sung Valley Ultramafic-Alkaline-Carbonatite Complex, Meghalaya, India

Abstract

The Early Cretaceous Sung Valley Ultramafic-Alkaline-Carbonatite (SUAC) complex intruded the Proterozoic Shillong Group of rocks and located in the East Khasi Hills and West Jaintia Hills districts of Meghalaya. The SUAC complex is a bowl-shaped depression covering an area of about 26 km2 and is comprised serpentinised peridotite forming the core of the complex with pyroxenite rim. Alkaline rocks are dominantly ijolite and nepheline syenite, occur as ring-shaped bodies as well as dykes. Carbonatites are, the youngest intrusive phase in the complex, where they form oval-shaped bodies, small dykes and veins. During the course of large scale mapping in parts of the Sung Valley complex, eleven carbonatite bodies were delineated. These isolated carbonatite bodies have a general NW-SE and E-W trend and vary from 20–125 m long and 10–40 m wide. Calcite carbonatite is the dominant variety and comprises minor dolomite and apatite and accessory olivine, magnetite, pyrochlore and phlogopite. The REE-bearing minerals identified in the Sung Valley carbonatites are bastnäsite-(Ce), ancylite-(Ce), belovite-(Ce), britholite-(Ce) and pyrochlore that are associated with calcite and apatite. The presence of REE carbonates and phosphates associated with REE-Nb bearing pyrochlore enhances the economic potential of the Sung Valley carbonatites. Trace-element geochemistry also reveals an enrichment of LREEs in the carbonatites and average ΣREE value of 0.102% in 26 bed rock samples. Channel samples shows average ΣREE values of 0.103 wt%. Moreover, few samples from carbonatite bodies has indicated relatively higher values for Sn, Hf, Ta and U. Since the present study focuses surface evaluation of REE, therefore, detailed subsurface exploration will be of immense help to determine the REE and other associated mineralization of the Sung Valley carbonatite prospect.

Full text

Cent. Eur. J. Geosci. • 6(4) • 2014 • 457-475
DOI: 10.2478/s13533-012-0191-y
Central European Journal of Geosciences
REE Mineralization in the Carbonatites of the Sung
Valley Ultramafic-Alkaline-Carbonatite Complex,
Meghalaya, India
Topical issue
Mohd. Sadiq∗, Ranjith A., Ravi Kumar Umrao
Geological Survey of India, North Eastern Region, Shillong-793003, India
Received 31 January 2014; accepted 22 May 2014
Abstract:
The Early Cretaceous Sung Valley Ultramafic-Alkaline-Carbonatite (SUAC) complex intruded the Proterozoic
Shillong Group of rocks and located in the East Khasi Hills and West Jaintia Hills districts of Meghalaya. The
SUAC complex is a bowl-shaped depression covering an area of about 26 km
2
and is comprised serpentinised
peridotite forming the core of the complex with pyroxenite rim. Alkaline rocks are dominantly ijolite and nepheline
syenite, occur as ring-shaped bodies as well as dykes. Carbonatites are, the youngest intrusive phase in the
complex, where they form oval-shaped bodies, small dykes and veins. During the course of large scale mapping
in parts of the Sung Valley complex, eleven carbonatite bodies were delineated. These isolated carbonatite bodies
have a general NW-SE and E-W trend and vary from 20–125 m long and 10–40 m wide. Calcite carbonatite is
the dominant variety and comprises minor dolomite and apatite and accessory olivine, magnetite, pyrochlore and
phlogopite. The REE-bearing minerals identified in the Sung Valley carbonatites are bastnäsite-(Ce), ancylite-(Ce),
belovite-(Ce), britholite-(Ce) and pyrochlore that are associated with calcite and apatite. The presence of REE
carbonates and phosphates associated with REE-Nb bearing pyrochlore enhances the economic potential of the
Sung Valley carbonatites. Trace-element geochemistry also reveals an enrichment of LREEs in the carbonatites
and average
P
REE value of 0.102% in 26 bed rock samples. Channel samples shows average
P
REE values of
0.103 wt%. Moreover, few samples from carbonatite bodies has indicated relatively higher values for Sn, Hf, Ta
and U. Since the present study focuses surface evaluation of REE, therefore, detailed subsurface exploration will
be of immense help to determine the REE and other associated mineralization of the Sung Valley carbonatite
prospect.
Keywords: Carbonatite • REE • bastnäsite-(Ce) • ancylite-(Ce) • Sung Valley • Meghalaya • India
©Versita sp. z o.o.
1. Introduction
Carbonatites are known to host high concentrations of rare
earth elements (REE) [
1
]. Moreover, syenites, phonolites,
alkali granite, pegmatite and secondary or supergene en-
∗E-mail: mohd.sadiq.gsi@gov.in
richment in some bauxite, laterite, phosphorites, placers
and beach sands are also potential hosts for REE’s. Rare
Earth Metals are becoming a critical strategic resource
with an increase in demand mainly from scientific and
military applications. About 95% of the REE export mar-
ket is dominated by China who is a leading producer of
REEs. In China, production is mainly from the Bayan
Obo REE-iron ore deposits and clay deposits in southern
457

REE Mineralization in the Carbonatites of the Sung Valley Ultramafic-Alkaline-Carbonatite Complex, Meghalaya, India
China, and rest of the world has comparatively limited
production [
2
]. Prior to the rise of Chinese REE produc-
tion, monazite and xenotime-beach placer deposits in India,
Brazil and Australia had been the main source for REEs.
With the discovery of carbonatite-hosted REE deposits
(mainly bastnäsite-(Ce)), carbonatite has become a primary
resource of world REE production e.g. Mountain Pass,
USA. In India, the first carbonatite-hosted REE deposit
has been discovered at Kamthai, Barmer district, Rajasthan
and contains a highest LREE grade of 17.31 wt% and a
weighted average grade is 2.97 wt% LREO with a total
volume of 1,38,428 tonnes [
2
]. The Shillong Plateau of
northeastern India hosts four intrusive alkaline-carbonatite
complexes, the Samchampi, Sung Valley, Jasra-Barpung
and Swangkre complexes [
3
,
4
]. Sung Valley was the
first carbonatite complex reported from north east India
[
5
]. These complexes, especially the Sung Valley complex,
has drawn attention of many researchers mainly for two
reasons. Firstly, its petrogenesis, emplacement age and
relationship with associated silicate rocks and secondly
to assess mineral potential of the alkaline-carbonatite
complex [
3
,
4
,
6
–
13
]. The Shillong plateau complexes are
known for their appreciable potential of apatite, pyrochlore
and magnetite [
6
,
14
] but REE’s are almost unexplored,
and they may have significant REE potential.
This work focuses on the systematic study of carbonatites
of Sung Valley ultramafic-alkaline-carbonatite complex
(SUAC) to evaluate their REE potential. Large scale map-
ping on 1:12,500 scale was carried out in parts of the Sung
Valley complex to demarcate carbonatite bodies, which in
turn were mapped in detail on the 1:5000 scale. Detailed
petrographic study followed by evaluation of mineral chem-
istry resulted in identification of REE-bearing phases, their
relationships with coexisting minerals, their mode of oc-
currence and REE potential. Whole rock analysis was
performed to chemically classify the carbonatites and to
assess their REE potential.
2. Geological Background
The area was mapped during the 1970s and this estab-
lished the identity of the Sung Valley intrusive as a major
ultramafic-alkaline-carbonatite complex that opened up
scope for the search for niobium (Nb), tantalum (Ta), rare
earth elements (REE), phosphate and associated elements
within the SUAC complex [
5
,
6
,
15
,
16
]. Subsequently, the
presence of significant concentrations of apatite, pyrochlore
(Nb-Ta phases) was also reported by Geological Survey of
India and others [
5
,
6
,
16
–
18
]. A total resource of 4.56 m.t.
of ore with 11.05% P
2
O
5
under the ‘probable category’
was indicated in the carbonatites and associated apatite-
magnetite rocks around Sung village [
18
]. Several workers
have presented the geology of the Sung Valley complex and
discussed the magmatic source of the carbonatites and as-
sociated silicate rocks [
6
,
7
,
9
,
19
–
22
]. Viladkar et al. [
19
]
suggested that a carbonated nephelinite-derived magma
was the source of the carbonatites and associated silicate
rocks in the SUAC complex. Veena et al. [
9
] and Ray et al.
[
20
,
21
] correlated the source of the magma with mantle
plume activity. Veena et al. [
9
] suggested the involvement
of sub-continental lithosphere that had been metasoma-
tised by fluids derived from an upwelling mantle plume and
subsequent partial melting of this mantle source. Ray et
al. [
21
] presented evidence for liquid immiscibility, crustal
contamination and an Rb/Sr-enriched mantle source for
the SUAC complex. Sen [
22
] suggested derivation from
a melilitic parental magma. Srivastava and Sinha [
4
,
11
]
ruled out liquid immiscibility and fractional crystallization
models for the genesis of the rocks of the Sung Valley com-
plex and recommended that the primary carbonate magma
originated from a metasomatized mantle peridotite by low
degree partial melting at a pressure greater than 25 kbar.
Melluso et al. [
12
] carried out mineral composition studies
and suggested that these rocks are either the products
of immiscibility between magnesian silicate and carbon-
ate melts or the direct product of mantle melting. Ray &
Pande (2001) dated the carbonatite of this complex by the
40
Ar–
39
Ar method and placed it at 107.2
±
0.8 Ma [
10
].
Later, Srivastava et al. (2005) provided a U–Pb perovskite
age of 115.1
±
5.1 Ma for the ijolite and correlated the
SUAC complex with the Kerguelen plume [
11
]. The age of
the Sung Valley ultramafic-alkaline-carbonatite complex
as dated by various methods on different minerals and rocks
of the complex ranges between 90 Ma and 150 Ma [4].
3. Geology of Sung Valley Ultra-
mafic-Alkaline-Carbonatite Complex
The Sung Valley ultramafic-alkaline–carbonatite (SUAC)
complex is an oval-shaped body covering an area of about
26 km
2
in the Survey of India toposheet no. 83C/2 in
the West Jaintia Hills and East Khasi Hills districts of
Meghalaya, India (Figure 1). The SUAC complex is em-
placed within the Shillong Plateau, an uplifted horst-like
structure in the Meghalaya state of Northeast India. A
remote sensing study revealed that the complex is situ-
ated at the intersection of three major lineaments trend-
ing E-W, NE-SW and NNW-SSE. The SUAC complex
consists of peridotite/serpentinised peridotite, pyroxen-
ite, melilitolite, ijolite, nepheline syenite, carbonatite and
apatite-magnetite rocks (Table 1).
Pyroxenite is the dominant lithology and encloses ser-
pentinised peridotite. Serpentinised peridotite forms the
458

Mohd. Sadiq, Ranjith A., Ravi Kumar Umrao
Figure 1. Location map of Sung Valley complex, West Jaintia Hills and East Khasi Hills districts, Meghalaya.
Table 1. Generalised stratigraphic succession of the Sung Valley area [6,17].
Recent/Tertiary Soil, laterite/bauxite
Sylhet Sandstone
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Unconformity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Early Cretaceous
Younger Intrusives
(Sung Valley ultramafic-
alkaline-carbonatite
complex)
Apatite-magnetite rocks
Carbonatite
Nepheline syenite
Ijolite
Pyroxenite
Serpentinised peridotite
Peridotite
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Unconformity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Precambrian
Older Intrusives/ Khasi
Metabasic Rocks Amphibolite/Epidiorite
Shillong Group Quartzite with phyllite with local
intraformational conglomerate
core of the complex. Ijolite forms a ring structure. These
three rock types cover the major portion of the complex.
Apatite-magnetite rock, melilitolite, nepheline syenite and
carbonatite occur as oval shaped bodies, small dykes and
veins within pyroxenite and peridotite/serpentinised peri-
dotite (Figure 2).
Peridotite/serpentinised peridotite is an important member
of the SUAC complex and is well exposed in Sung nala,
where it is traversed by numerous criss-cross veins of
pyroxenite and carbonatite (Figure 3a). It is a greenish
black coarse-grained rock characterized by the dominant
presence of olivine, partly or totally serpentinised and
by variable amounts of magnetite and perovskite. Relict
clinopyroxenes are present among grains of serpentinised
olivine.
Pyroxenite is the dominant rock type in the complex and
mostly occurs in the marginal part of the complex generally
in direct contact with quartzite of Shillong Group. The
pyroxenite body also outcrops in the central part of the com-
plex where it is intruded by all the other rock types of the
complex and encloses serpentinised peridotite. Texturally,
the pyroxenite varies in grain size from fine grained in the
marginal part to coarse grained in the central part of the
complex. The pyroxenite is generally dark, greenish black
to black and massive, consisting dominantly of diopsidic
augite cumulate. The pyroxenite is nearly monomineralic
with more than 95% clinopyroxene and rare orthopyroxene.
Pyroxene occurs as discrete, short, prismatic and euhedral
grains showing a cumulate texture. The interstitial spaces
are occupied by feldspar which appears to have crystal-
459

REE Mineralization in the Carbonatites of the Sung Valley Ultramafic-Alkaline-Carbonatite Complex, Meghalaya, India
Figure 2. Geological map (1:12,500) in par ts of Sung Valley ultramafic-alkaline–carbonatite complex.
lized later from residual liquid. Pyroxene also contains
inclusions of euhedral apatite. Hornblende and biotite oc-
cur as secondary minerals whereas titanite and magnetite
as accessory minerals. Magnetite-rich granular pyroxenite
occurs towards eastern side of Sung village.
Ijolite is the third most abundant rock type emplaced within
the SUAC complex. It is medium to very coarse grained and
shows a wide variation in texture. It consists of nepheline,
pyroxene, apatite and accessory titanite, calcite and mag-
netite. Nepheline occurs as coarse, pinkish, smoky black,
subhedral to anhedral grains. Bluish-green clinopyrox-
ene is euhedral. These prismatic pyroxene grains and
nepheline sometimes show a "comb structure" which is a
characteristic feature of ijolite.
Syenite occurs as veins, lenses and small dykes of variable
dimensions and intruded pyroxenite and ijolite around
Maskut, Sung and northwest of Byrthap villages.
Coarse-grained apatite-magnetite rock occurs as veins,
lenses and fracture-fillings within the pyroxenites and
consists mainly of apatite and magnetite with a significant
quantity of calcite along with minor olivine, phlogopite,
perovskite, pyrochlore and minor spinels.
Melilitolite is exposed mainly at the northern part of the
complex and occurs as large oval-shaped bodies as well
as small dykes within pyroxenite.
4. Analytical Techniques and
Methodology
Major and trace-element (Ba, Ga, Sc, V, Th, Pb, Ni, Co,
Rb, Sr, Y, Zr, Nb, Cr, Cu and Zn) whole rock analysis of
14 representative samples from different carbonatite bod-
ies were analyzed by fully automated X-ray fluorescence
(XRF), PANalytical model MagiX-2424 using end window
X-ray tube at the Chemical Division, Geological Survey
of India, North Eastern Region, Shillong. The REE and
other trace elements were analysed by Inductively Cou-
460

Mohd. Sadiq, Ranjith A., Ravi Kumar Umrao
Figure 3.
(a) Veins of pyroxenite disrupted by carbonatite veins within peridotite along Sung Nala, Sung Village (b) Medium to coarse grained
carbonatite with caught-up patch of pyroxenite, NE of Byrthap village.
pled Plasma Emission Mass Spectrometer (ICP-MS) in
the Central Chemical Laboratory, Geological Survey of
India, Kolkata, India. The details of techniques, procedure,
precision and accuracy of these analyses are described in
SOP (http://www.portal.gsi.gov.in/, GSI, 2010). Twenty-six
samples were analysed for 22 trace elements (REE, Sn,
Hf, Ta, Mo, W, Ge, Be and U).
A total of 14 channel samples were collected from two
isolated carbonatite bodies (C2 & C4). To ensure the uni-
form quality of material over the entire body and to have
representative samples for assessing REE concentrations
in carbonatite, 10
×
2.5
×
100 cm
3
channels were made
across the strike of the carbonatite bodies. A fixed width
of 10 cm along the sample line was first cleaned so that
the surface undulations were removed as far as possible
and for bringing the surface of the sample to a uniform
level. After cleaning the surface confined to this width,
samples were collected at every meter across the strike
of the body. Mineral composition study of ten polished
thin sections of carbonatite was carried out by Electron
Microprobe Analyzer (EPMA) CAMECA SX-100 at the
Petrology, Petrochemistry and Ore Dressing (PPOD) Divi-
sion, Geological Survey of India, Bengaluru to classify the
rock-forming minerals and identify the rare earth-bearing
minerals in the Sung Valley carbonatites. Silicate, car-
bonate and REE phases were analysed at an accelerating
potential of 20 kV and 20 nA and beam size of 0.5
µ
m
for silicates and 1.0
µ
m for REE analysis. Data were
processed in Minpet 2.02 and SX-100 softwares.
5. Carbonatites of the Sung Valley
Complex
Carbonatite bodies intruded mainly in the southern part
with few in the central part of the Sung Valley complex
(Figure 2). The eleven (C1 to C11) circular to semi-circular
carbonatite bodies were mapped at 1:5,000 scale in and
around Maskut and Sung villages. These isolated car-
bonatite bodies have a general NW-SE and E-W trend
and vary from 20–125 m long and 10–40 m wide. The
coarse-grained calcite carbonatite is the most dominant va-
riety exposed in the SUAC complex, though fine to medium
grained calcite carbonatites do occur as late dykes and
veins. Calcite carbonatites contain minor dolomite, apatite
and olivine with rare occurrence of pyroxene. Magnetite,
ilmenite, phlogopite, chalcopyrite, pyrrhotite and pyrite
are accessory minerals. Coarse grained, subhedral to an-
hedral calcite grains often form interlocking mosaic texture
with nests and disseminations of prismatic needle-shaped
apatite and large magnetite grains. Some of the calcite
grains are euhedral, possibly indicating primary magmatic
crystallization. Magnetite veins up to 6 cm thick occur
in the carbonatites. Veins of carbonatite are common in
the pyroxenite and serpentinized peridotite. Enclaves and
xenoliths of pyroxenite within the carbonatite suggest car-
bonatite emplacement at a later stage (Figure 3a).
5.1. Petrography
The carbonatites are fine to coarse grained rocks dom-
inantly comprises of carbonate minerals (85–98%) (Fig-
ure 3b and 4c). Calcite is the major mineral constituent
with minor dolomite and apatite. The accessory minerals
are olivine with serpentine rims, phlogopite, pyrochlore,
magnetite, barite, baddeleyite and perovskite (Figure 4a,
4b, 4c, 5a, 5b). Subhedral to euhedral magnetite grains
are the main opaque mineral with a few grains of ilmenite
occurring in clusters. Intergrowth between magnetite and
ilmenite is a common feature represented by a few laths
of ilmenite within magnetite. Subhedral to subrounded,
elongated grains of apatite occur in clusters. The dis-
seminated sulfides are chalcopyrite, pyrrhotite, pyrite and
461

REE Mineralization in the Carbonatites of the Sung Valley Ultramafic-Alkaline-Carbonatite Complex, Meghalaya, India
Figure 4.
Photomicrographs of thin polished sections of carbonatites
(a) Oriented grains of carbonates showing flow textures and
euhedral apatite towards southwest corner, (b) Pyrochlores
with inclusions of perovskite and apatite, (c) Coarse grained
crystalline texture in the carbonates with well-defined triple
points, (d) Acicular crystals of apatite and associated sul-
fide grains within calcite, (e) Green mica (phlogopite) in
carbonatites, (f) Highly resorbed crystals of pyrochlore and
pleochroic halo around a sulfide grain, (g) Disseminated
minute grains of perovskite included within calcite, (h) Car-
bonate grains with inclusions zoned xenotime.
arsenopyrite. Perovskite and pyrochlore are the main hosts
of REEs. Sovite is the dominant variety of carbonatite
with alvikite occurring at few places in SUAC complex.
Texturally, there are three variants of carbonatites, (1)
The fine grained variety of carbonatite comprises 90–95%
carbonates with calcite as major mineral that occurs as
small, sub rounded to prismatic crystals showing distinct
orientation, possibly a flow feature (Figure 4a). The sup-
posed flow layers are displaced around larger oxide grains.
The second most abundant mineral is apatite which oc-
curs in two distinct modes; smaller acicular needles dis-
tributed throughout the rock and as larger euhedral grains.
The larger crystals of apatite often enclose smaller nee-
dles. Carbonatite also shows the presence of subhedral
and colourless to pale greenish minerals identified as
pyrochlore with abundant opaque inclusions (Figure 4b,
4f, 6b).
(2) The medium to coarse grained variety of carbonatite
comprises about 98% carbonate minerals (major calcite
with minor dolomite). The medium-sized carbonate grains
form polycrystalline aggregates with well-defined crystal-
lization boundaries (Figure 4c). Carbonates are fractured
and dusted with numerous opaque minerals. The other min-
erals observed are occasional grains of euhedral prismatic
apatite (Figure 4d) and micron-sized sulfide grains. (3) In
coarse-grained carbonatites, calcite grains are fractured
and well-defined triple points and strain lamellae occur.
Carbonates are dusted and turbid and constitute about
85–90% of the rock. Large prismatic grains of green mica
occurring in clusters show distinct pleochroism from colour-
less to green (Figure 4e). Highly resorbed grains of py-
rochlore and occasionally perovskite also occur (Figure 4f,
4g). The sulfide minerals are bismuthinite, pyrrhotite, chal-
copyrite, pyrite and arsenopyrite. Disseminated grains of
maghemite, euhedral crystals of xenotime (Figure 4h) are
present.
5.2. Mineral Chemistry of Carbonatites
REE-bearing phases identified by EPMA study include
bastnäsite-(Ce), ancylite-(Ce), belovite-(Ce) and britholite-
(Ce) that are associated with calcite and apatite. Appre-
ciable amount of REEs also occur in pyrochlore grains
associated with magnetite. Moreover, tiny native grains
of Sn (~10
µ
m) and Au (~5
µ
m) (Figure 8b) were also
encountered during probe analysis.
Calcite and Dolomite
Calcite is the major carbonate phase occuring with minor
dolomite in the selected samples of Sung Valley carbon-
atites (Table 2). Both phases contain substantial amounts
of Sr. Sr is higher in calcite than in coexisting dolomite
(0.28–0.81 wt% SrO in calcite versus 0.09–0.33 wt% SrO
in dolomite). In, Calcite, Mn, Fe and Mg are invariably
very low (Figure 5a, 6b).
Apatite
Chemical analysis of apatite were obtained in section no.
EPMA-01, 02, 05, 06, 08, 09 &10 (Table 3). In apatite CaO
ranges from 53.71–56.08 wt%, P
2
O
5
from 39.93–42.6 wt%
with very low contents of total REO (Rare Earth Oxide)
(0.07–0.26 wt%), U and Th (Figure 5a, 5b, 6a, 6b).
Monazite
Minor grains of monazite occur in carbonatite sample
no. EPMA-02. Total REO in monazite ranges from
462

Mohd. Sadiq, Ranjith A., Ravi Kumar Umrao
Figure 5.
(a) FCC-BSE image show calcite-dolomite-apatite-mica-pyrrhotite-magnetite-pyrochlore association of carbonatite (sample
no. EPMA-01), (b) FCC-BSE image of monazite between cluster of apatite (EPMA-02).
Figure 6.
(a) FCC-BSE image of olivine grains with serpentine rim in EPMA-04, (b) FCC-BSE image of pyrochlore grains in EPMA-01.
64.4–67.44 wt% and P
2
O
5
ranges between 29.42–30.66 wt%
(Table 4; Figure 5b).
Olivine
Olivine, analysed in sample no. EPMA-04 & 09, has a
narrow range of compositions, but markedly high forsterite
contents (almost pure forsterite) and with low CaO contents
(Table 5), which is generally, unexpected for a mineral in
equilibrium with such Ca-rich rocks and minerals [
12
].
Olivine has a core slightly more Fe-rich than the rim, a
feature much more evident in the coexisting phlogopite
(Figure 6a; Table 6).
Mica
The carbonatites of Sung Valley contain minor phlogopite
(Figure 6b) and Ba-mica. Mica has high Al
2
O
3
(15.58–
23.08%) and MgO (23.51–26.73%), low FeO (1.38–2.78%)
and TiO
2
(0–0.36%). The mica phases contain higher BaO
(0.57–10.98%) Na
2
O (0.86–2.98%) and K
2
O (2.91–9.02%).
BaO is high in mica in sample no. EPMA-10 (Table 6).
Pyrochlore
Pyrochlore was identified in carbonatite sample no.
EPMA-01, 05, 07 & 08 (Table 7). Pyrochlore con-
tains 30.93–56.93 wt% Nb
2
O
5
, 7.30–31.35 wt% Ta
2
O
5
,
0.06–18.79 wt% UO
2
and 0.8–12.32 wt% total REO (Fig-
ure 6b).
REE phases
REE phases occur in traces and identified in carbonatite
samples include ancylite-(Ce), belovite-(Ce), britholite-
(Ce) and bastnäsite-(Ce) in decreasing abundance (Fig-
ure 10a,b).
Ancylite-(Ce)
Ancylite is a strontium-rich REE-carbonate with high con-
centrations of REEs and can be processed easily for ex-
463

REE Mineralization in the Carbonatites of the Sung Valley Ultramafic-Alkaline-Carbonatite Complex, Meghalaya, India
Figure 7.
(a) FCC-BSE image showing REE phases (1 to 7) in sample no. EPMA-05, (b) BSE image showing Sr- rich REE phase in
carbonatite (circled bright spots) sample no. EPMA-08.
Table 2. Representative composition of calcite and dolomite.
Sample No. Point No. CaO MgO MnO FeO SrO Total
EPMA-01
1 32.94 22.73 0.35 0.43 0.33 56.78
6 32.53 21.11 0.30 0.56 0.32 54.82
9 61.96 1.23 0.29 0.02 0.81 64.31
10 59.48 0.27 0.18 0.13 0.27 60.33
16 63.11 0.13 0.09 0.00 0.43 63.76
21 33.35 22.06 0.35 0.38 0.30 56.44
22 32.2 22.58 0.23 0.42 0.32 55.75
EPMA-02
1 32.56 22.75 0.23 0.73 0.16 56.43
2 29.06 19.87 0.35 1.16 0.09 50.53
3 63.72 0.08 0.15 0.11 0.18 64.24
10 62.00 0.16 0.18 0.03 0.49 62.86
13 35.23 20.57 0.19 0.74 0.28 57.01
14 61.67 0.18 0.10 0.01 0.54 62.50
EPMA-03
1 56.66 0.41 0.11 0.04 0.28 57.50
3 60.01 0.48 0.12 0.45 0.57 61.63
7 52.67 2.21 0.09 0.32 0.44 55.73
8 53.23 2.22 0.02 0.13 0.46 56.06
9 50.61 2.14 0.09 0.49 0.53 53.86
EPMA-05 10 32.74 24.67 0.24 0.39 0.21 58.25
11 59.82 0.51 0.19 0.05 0.53 61.10
21 51.93 0.35 0.14 0.07 0.34 52.83
EPMA-07 31 33.24 25.14 0.25 0.25 0.21 59.09
46 31.86 23.67 0.14 0.21 0.24 56.12
EPMA-08 32 59.07 0.83 0.12 0.07 0.40 60.49
45 59.29 0.97 0.13 0.05 0.57 61.01
EPMA-09 10 32.35 24.89 0.21 0.14 0.29 57.88
traction of rare earths. Ancylite is an exploration target
at Prairie Lake carbonatite complex [
23
]. Ancylite is the
major REE bearing mineral at the Bear Lodge carbonatite
(Wyoming), where a measured and indicated resource of
6.8 million tonnes grading 3.75 wt% REO has been es-
tablished by Rare Element Resources Ltd [
23
]. Ancylite
is the main REE phase in Sung Valley carbonatites and
identified in carbonatite sections no. EPMA-07 and 08
with total REO ranges from 22.22–56.86 wt% (Figure 7b,
8a). SrO ranges from 9.01–23.42 wt%. CaO is variable
and ranges from 1.18–20.83 wt%; there are minor amount
of P2O5and BaO (Table 8).
Belovite-(Ce)
Belovite was identified in EPMA/07, 08, 09 and 10
(Figure 7b). Total REO in this mineral ranges from
25.12–49.13 wt%. CaO ranges from 4.32–11.25 wt%, P
2
O
5
from 3.34–21.31 wt%, and SrO ranges from 8.17%–42.27 wt%
with minor amounts of MgO, BaO and SiO2(Table 9).
Britholite-(Ce)
Britholite grains were analyzed in section no. EPMA-
07, 08 and 09. Total REO in this phase ranges from
43.71–54.06 wt%. P
2
O
5
ranges from 14.66–33.32 wt% and
CaO ranges from 1.27–13.77 wt% (Table 10).
Bastnäsite-(Ce)
Bastnäsite-(Ce) is the most productive global mineral
source for rare earth elements. At Mountain Pass,
bastnäsite-(Ce) is the leading ore mineral where it is being
separated by means of grounding and floatation from the
accompanying barite, calcite and dolomite [
24
]. Bastnäsite-
(Ce), identified in section no. EPMA-05, contains total
REO ranges from 58.25–74.23% (Table 11).
5.3. Geochemistry of Sung Valley Carbon-
atites
The major and trace-element chemistry of 14 carbonatite
whole rock samples is presented in Table 12. Woolley and
Kempe [
25
] classified carbonatites as calcio- magnesio-
or ferro-carbonatites based on CaO-MgO-Fe
2
O
3
+MnO
triangular diagram. The SUAC carbonatite samples anal-
yses indicate a variation from 46.58–52.21 wt% CaO and
464

Mohd. Sadiq, Ranjith A., Ravi Kumar Umrao
Table 3. Representative composition of apatite.
Sample. No. Point No. SiO2FeO CaO Na2O MgO P2O5SrO La2O3Ce2O3ThO2UO2SO2Total
EPMA-01*
5 0.47 53.71 0.16 0.10 41.24 0.42 96.1
17 0.01 0.04 54.5 0.37 0.17 39.93 0.49 95.51
24 0.03 0.02 54.38 0.20 0.06 40.99 0.43 96.11
33 0.05 54.65 0.21 0.07 41.30 0.39 96.67
34 0.04 55.21 0.22 0.12 41.40 0.53 97.52
35 0.02 0.1 55.54 0.15 0.09 41.62 0.41 97.93
EPMA-02*
6 0.11 55.59 0.20 0.09 41.86 0.24 98.09
7 0.07 0.02 54.7 0.16 0.08 41.65 0.27 96.95
11 0.04 55.78 0.15 0.04 41.67 0.30 97.98
12 0.05 0.01 56.08 0.22 0.08 41.68 0.26 98.38
EPMA-05 5 0.05 0.05 55.64 0.22 41.83 0.2 0.02 0.05 0.01 0.03 98.10
9 0.09 0.03 55.49 0.24 0.12 42.01 0.28 0.04 0.08 0.06 98.44
EPMA-06 9 0.19 0.09 54.78 0.28 0.16 40.46 0.25 0.01 0.07 0.01 0.03 0.09 96.42
EPMA-08 33 0.07 0.07 55.62 0.25 0.15 41.42 0.27 0.02 0.1 0.09 98.06
44 0.02 0.03 55.62 0.19 0.08 41.80 0.31 0.02 0.12 0.03 0.05 98.27
EPMA-09 24 0.04 0.01 55.38 0.08 0.06 42.13 0.28 0.04 0.07 0.01 0.04 98.14
25 0.03 54.75 0.12 0.09 42.60 0.37 0.09 0.17 0.07 98.29
EPMA-10 6 0.04 0.02 55.55 0.22 0.08 42.34 0.35 0.08 0.14 0.01 0.08 98.91
*Rare earth oxides are not analysed
Table 4. Representative composition of Monazite in carbonatite.
Point No. CaO SmO PbO Y2O3La2O3Ce2O3Pr2O3Nd2O3Gd2O3SiO2ThO2UO2P2O5Total
1 0.48 0.61 18.56 34.01 3.13 8.85 2.89 0.06 0.01 0.01 30.66 99.25
2 0.63 0.51 20.64 33.44 2.89 7.42 2.82 0.04 0.01 30.61 99.02
3 0.57 1.09 0.03 16.33 32.94 3.39 10.64 3.03 0.03 30.67 98.72
4 0.33 1.58 0.11 14.23 32.35 3.67 12.47 3.27 0.05 30.41 98.49
5 0.8 1.17 0.02 14.84 32.79 3.60 11.77 3.04 0.04 0.01 29.96 98.03
6 0.75 1.23 0.03 15.3 32.54 3.59 11.67 3.07 0.07 0.01 29.9 98.18
7 1.18 0.56 18.31 33.98 3.07 8.27 2.90 0.02 29.58 97.86
8 1.65 1.71 0.03 11.83 31.68 3.89 13.94 3.06 0.06 0.03 0.03 29.42 97.35
Table 5. Representative composition of olivine.
Sample EPMA-04 EPMA-09
Point/Analysis 10 11 12 13 14 16 19 cr 20 rm 5 7 1 cr 2 rm
SiO242.00 42.00 42.00 38.00 40.00 39.00 42.00 42.00 42.00 42.00 39.00 39.00
TiO2- - - 0.03 - - - 0.03 - - 0.26 0.15
FeO 3.00 3.00 3.00 2.00 2.00 2.00 4.00 3.00 3.00 3.00 2.00 1.00
MnO 0.31 0.41 0.39 0.26 0.30 0.37 0.45 0.44 0.35 0.45 0.31 0.28
MgO 54.00 55.00 54.00 50.00 53.00 52.00 54.00 54.00 54.00 54.00 56.00 57.00
CaO 0.08 0.07 0.06 0.05 0.06 0.05 0.08 0.13 0.04 0.06 0.02 0.02
Na2O 0.03 0.01 0.01 0.02 0.02 0.03 0.01 0.03 0.02 0.04 0.01 –
Total 99.42 100.49 99.46 90.36 95.38 93.45 100.54 99.63 99.41 99.55 97.60 97.45
On the basis of 4O
Si 1.00 0.99 1.00 1.00 0.99 0.99 1.00 1.00 1.00 1.00 0.95 0.95
Ti 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00
Fe2 0.06 0.06 0.06 0.04 0.04 0.04 0.08 0.06 0.06 0.06 0.04 0.02
Mn 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01
Mg 1.92 1.94 1.92 1.95 1.96 1.97 1.91 1.92 1.92 1.92 2.04 2.07
Ca 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Na 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Total 3.00 3.00 3.00 3.00 3.01 3.01 3.00 3.00 3.00 3.00 3.04 3.05
Mg# 97 97 97 98 98 98 96 97 97 97 98 99
cr – core, rm – rim of the grains. Mg# = 100 Mg2+/(Mg2+ + Fe2+)
465

REE Mineralization in the Carbonatites of the Sung Valley Ultramafic-Alkaline-Carbonatite Complex, Meghalaya, India
Figure 8.
(a) FCC-BSE image showing ancylite (Sr-REE phases) in sample no. EPMA-07, (b) FCC-BSE image showing a small
Au-grain in carbonatite sample no. EPMA-10.
Figure 9.
CaO-MgO-Fe
2
O
3
+ MnO triangular diagram for classification
of Sung Valley carbonatites [25].
Figure 10. Chondrite-normalized rare earth element spidergrams for carbonatite samples of Sung Valley, normalization values [26].
466

Mohd. Sadiq, Ranjith A., Ravi Kumar Umrao
Table 6. Representative composition of mica.
Sample EPMA-01 EPMA-03
Analysis 10 rm 11 cr 12 rm 13 cr 14 rm 25 27 31 9 cr 1 cr 2 rm 3 cr 4 rm
SiO239.59 39.49 39.89 38.5 39.24 38.74 38.56 38.93 39.15 38.58 38.51 38.81 38.4
TiO20.27 0.19 0.2 0.16 0.16 0.18 0.19 0.2 0.18 0.3 0.28 0.32 0.36
Al2O315.82 15.95 15.58 17.29 15.97 15.99 15.82 15.76 16.39 18.2 18.36 18.87 18.44
FeO 2.05 1.93 1.81 2.21 2.05 1.95 2.23 2.02 2.26 2.68 2.68 2.7 2.59
MnO 0.03 0.03 0.04 0.04 0.08 0.05 0.07 0.07
MgO 25.84 26.02 25.82 25.08 25.66 25.84 25.82 25.83 25.75 24.38 24.82 25 24.63
CaO 0.03 0.05 0.04 0 0.07 0.04 0.03 0.04 0.01 0 0 0 0.03
BaO 0.85 0.57 0.72 1.94 1.21 1.23 1.32 1.27 1.32 0.93 1 1.33 1.62
Na2O 1.27 0.86 1.23 1.46 1.32 1.22 1.29 1.37 1.38 2.49 2.72 2.71 2.67
K2O 8.74 9.02 8.86 8.19 8.56 8.54 8.3 8.27 8.42 6.7 6.64 6.46 6.39
Total 94.49 94.11 94.15 94.87 94.28 93.73 93.56 93.77 94.91 94.26 95.08 96.27 95.13
On the basis of 11O
Si 2.299 2.296 2.319 2.243 2.29 2.274 2.271 2.283 2.272 2.234 2.215 2.206 2.213
Ti 0.012 0.008 0.009 0.007 0.007 0.008 0.008 0.009 0.008 0.013 0.012 0.014 0.016
Al 1.082 1.092 1.067 1.186 1.097 1.105 1.097 1.089 1.12 1.241 1.244 1.263 1.252
Fe2 0.1 0.094 0.088 0.108 0.1 0.096 0.11 0.099 0.11 0.13 0.129 0.128 0.125
Mn 0.001 0.001 0 0.002 0.002 0 0 0.004 0.002 0 0.003 0.003 0
Mg 2.237 2.256 2.238 2.178 2.232 2.261 2.267 2.259 2.227 2.104 2.128 2.119 2.116
Ca 0.002 0.003 0.002 0 0.004 0.003 0.002 0.003 0.001 0 0 0 0.002
Ba 0.019 0.013 0.016 0.044 0.028 0.028 0.03 0.029 0.03 0.021 0.023 0.03 0.037
Na 0.143 0.097 0.139 0.165 0.149 0.139 0.147 0.156 0.155 0.28 0.303 0.299 0.298
K 0.647 0.669 0.657 0.609 0.637 0.639 0.624 0.619 0.623 0.495 0.487 0.468 0.47
Total 6.542 6.529 6.535 6.542 6.546 6.553 6.556 6.55 6.548 6.518 6.544 6.53 6.529
Mg# 96 96 96 95 96 96 95 96 95 94 94 94 94
Sample EPMA-03 EPMA-10
Analysis 5 cr 6 rm 7 cr 8 rm 1 18 19 2 20 21 22 3 4
SiO238.13 38.69 38.47 38.4 38.23 37.62 34.34 31.83 31.4 32.39 39.44 38.74 32.67
TiO20.27 0.29 0.22 0.34 0.03 0.04 0.01 0.02 0.03 0.02
Al2O318.49 18.55 19.1 18.45 18.86 18.59 20.39 22.84 23.08 21.99 17.91 18.59 22.22
FeO 2.59 2.78 2.43 2.49 1.85 1.64 1.44 1.47 1.38 1.5 1.7 1.83 1.47
MnO 0.04 0.04 0.01 0.03 0.02 0.02 0.05 0.02 0.04 0.05 0.03
MgO 24.93 24.82 24.75 24.95 26.13 25.94 24.64 23.63 23.51 23.91 26.73 26.18 23.8
CaO 0.01 0.05 0 0.09 0.08 0.02 0.1 0.05 0.13 0.19 0.13 0.04 0.04
BaO 1.39 1.42 1.49 1.81 3.45 3.83 8.24 10.66 10.98 9.62 2.87 2.88 9.77
Na2O 2.62 2.68 2.79 2.61 2.98 2.51 2.25 2.76 2.74 2.47 1.95 2.63 2.45
K2O 6.44 6.37 6.32 6.45 5.49 5.46 4.64 3.26 2.91 3.65 6.11 5.71 3.92
Total 94.87 95.69 95.61 95.6 97.1 95.63 96.09 96.59 96.14 95.76 96.88 96.68 96.39
On the basis of 11O
Si 2.201 2.214 2.201 2.206 2.175 2.176 2.044 1.915 1.899 1.952 2.234 2.202 1.958
Ti 0.012 0.012 0.009 0.015 0 0 0.001 0.002 0 0.001 0 0.001 0.001
Al 1.257 1.25 1.287 1.248 1.264 1.266 1.429 1.618 1.644 1.561 1.195 1.244 1.569
Fe2 0.125 0.133 0.116 0.12 0.088 0.079 0.072 0.074 0.07 0.076 0.081 0.087 0.074
Mn 0 0.002 0.002 0 0.001 0.001 0.001 0.003 0 0.001 0.002 0.002 0.002
Mg 2.146 2.118 2.111 2.137 2.217 2.237 2.186 2.119 2.12 2.149 2.257 2.218 2.127
Ca 0.001 0.003 0 0.006 0.005 0.001 0.006 0.003 0.008 0.012 0.008 0.002 0.003
Ba 0.031 0.032 0.033 0.041 0.077 0.087 0.192 0.251 0.26 0.227 0.064 0.064 0.229
Na 0.293 0.297 0.309 0.291 0.329 0.281 0.26 0.322 0.321 0.289 0.214 0.29 0.285
K 0.474 0.465 0.461 0.473 0.399 0.403 0.352 0.25 0.225 0.281 0.441 0.414 0.3
Total 6.54 6.526 6.529 6.537 6.555 6.531 6.543 6.557 6.547 6.549 6.496 6.524 6.548
Mg# 94 94 95 95 96 97 97 97 97 97 97 96 97
cr – core, rm – rim of the grains. Mg# = 100 Mg2+/(Mg2++Fe2+)
42.35–46.69 wt% LOI. Therefore, chemically these can be
classified as calico-carbonatite (Figure 9) which confirms
its modal classification as calcite carbonatite. Analysis
indicates low MgO (1.55–2.64 wt%), Fe
2
O
3
(0.15–3.2 wt%)
and very low MnO (0.05–0.1 wt%) in carbonatites. The
higher values of Fe
2
O
3
in a few samples correspond to
disseminated grains of magnetite in the carbonatites. Also
most carbonatite samples contain negligible amounts of
467

REE Mineralization in the Carbonatites of the Sung Valley Ultramafic-Alkaline-Carbonatite Complex, Meghalaya, India
Table 7. Representative composition of pyrochlore.
Formula Na2O MgO CaO MnO FeO BaO PbO La2O3Ce2O3Nd2O3Tm2O3TiO2ZrO2ThO2UO2Nb2O5Ta2O5Total
EPMA-01
1 cr 0.61 0.72 11.89 0.5 1.83 2.18 0.09 0 0.74 0 0.25 1.03 0.66 2.13 15.04 48.04 9.29 95.00
2 rm 0.09 1.03 11.53 0.39 1.8 1.08 0.17 0.04 0.97 0.38 0.16 1.63 0.53 6.49 6.92 56.93 7.52 97.66
3 cr 0.09 0.76 10.5 0.28 3.76 1.41 0.08 0.16 1.07 0.24 0.37 1.48 0.52 5.83 8.75 54.99 7.43 97.72
4 rm 0.08 0.74 10.82 0.22 3.61 1.17 0 0.16 1.15 0.24 0.14 1.48 0.47 5.84 7.91 54.73 7.4 96.16
5 cr 1.21 0.51 10.94 0.58 2.24 1.01 0.45 0.09 0.73 0.24 0.29 1.33 0.57 4.23 11.7 53.17 8.16 97.45
6 rim 0.09 0.93 10.95 0.4 2.77 1.15 0.2 0.14 1.22 0.29 0.34 1.66 0.48 6.44 7.32 55.09 7.3 96.77
7 cr 0.14 0.7 8.94 0.45 2.63 2.02 0.1 0.28 1.86 0.4 0.23 1.68 0.74 4.29 11.26 51.6 7.62 94.94
8 rm 2.37 0.08 12.65 0.57 4.13 0.73 0.04 0.13 1.2 0.43 0.11 1.79 0.78 6.94 7.13 49.77 8.28 97.13
EPMA-05 10 2.36 0.05 10.45 0.43 3.2 2.07 0.09 0.35 2.65 0.66 0.07 3.16 0.33 7.3 0.98 40.17 12.88 87.20
14 6.5 0.01 15.5 0.06 1.5 0.05 0 0.37 2.7 0.55 0.28 3.51 0 0 0 52.36 8.91 92.30
EPMA-07
13 6.97 0.02 14.72 0.06 3.8 0.02 0 0.15 1.1 0.07 0.45 0.73 -0.04 0.09 0.04 50.63 14.07 92.88
16 4.48 0 5.72 0.23 3.4 4.69 0.25 0.02 1.36 0.09 0.4 0.8 1.12 5.02 10.51 36.26 18.71 93.06
17 0.95 0.02 8.95 0.88 4.32 2.4 0.06 0.04 0.88 0 0.5 0.9 0.86 3.14 11.64 32.33 19.17 87.04
18 4.89 0.13 14.38 0.22 5.27 -0.06 0.46 0.11 1.07 0.38 0.6 0.4 1.53 6.04 1.84 30.93 31.35 99.54
26. 3.91 0.03 13.96 0.08 1.02 0.22 0.04 0.77 8.75 2.5 0.3 10.01 -0.19 3.78 0.06 38.16 10.89 94.29
EPMA-08 16 4.78 0.43 7.62 0.35 1.39 0.99 0.68 0 0.48 0.17 0.17 0.52 1.7 3.67 18.79 46.3 11.76 99.80
Table 8. Composition of ancylite.
Sample No. Point Na2O K2O MgO CaO SrO BaO SiO2TiO2ThO2UO2P2O5Nb2O5Ta2O5La2O3Ce2O3Pr2O3Nd2O3EuO Gd2O3Tb2O3Dy2O3Ho2O3Er2O3Tm2O3Yb2O3Lu2O3Total REO%
EPMA-08
28 5.56 22.38 0.74 0.05 0.05 0.53 0.01 11.37 21.31 1.9 7.65 0.17 2.11 0.36 0.09 0.12 74.4 45.08
29 3.44 0.02 0.02 15.37 23.42 1.54 0.03 0.03 0.01 4.95 10.62 1.16 4.06 0.02 1.12 0.12 0.03 0.12 0 66.08 22.20
31 0.12 0.05 0.21 3.45 21.48 0.31 0.73 0.03 0.82 0.14 12.84 21.06 1.88 6.61 1.85 0.04 0.05 0.02 71.69 44.35
39 0.11 0.03 0.13 4.11 18.37 0.14 0.2 0.09 0.01 1.85 0.07 14.13 23.2 1.79 6.26 2.39 0.1 0.24 0.01 73.23 48.12
40 5.36 18.65 0.41 0.08 0.05 0.08 13.4 21.42 2.14 7.23 2.03 0.03 70.88 46.25
42 0.77 0.03 14.76 17.84 0.78 0.03 0.03 0.01 0.08 0.05 9.42 15.26 1.36 4.83 1.5 0.09 0.04 66.88 32.50
45 0 0.01 0.1 5.01 13.35 0.22 0.01 0.05 1.66 0.1 14.85 24.99 2.65 7.61 2.21 0.04 0.07 0.06 72.99 52.48
47 0.01 1.8 21.17 0.06 0.01 0.03 0.04 1.14 11.78 21.86 2.58 9.44 0.34 2.21 0.1 0.13 0.17 0.07 72.94 48.68
48 2.74 20.83 13.16 0.02 0.02 0.06 0 0.06 7.36 11.85 0.81 3.33 1.17 0.4 0.05 61.86 24.97
49 0.04 2.22 16.57 0.18 0.21 0.02 0.02 0.03 14.81 24.84 2.48 7.59 2.12 0.2 0.14 0.09 71.56 52.27
50 0.03 0 4.46 20.69 0.63 0.01 0.06 0.03 0.02 0.03 0.18 12.61 21.12 1.92 7.25 1.84 0.28 0.04 0.01 0.02 71.23 45.09
51 4.38 21.22 0.77 0.04 0.03 0.03 0.04 13.65 20.7 1.9 5.47 1.97 0.1 0.04 70.34 43.83
52 3.47 0.01 0.01 17.89 9.01 0.74 0.05 0.09 0.01 0.04 7.67 12.51 0.82 2.42 1.04 0.04 -0.05 0.05 0.03 55.85 24.53
53 7.98 17.6 0.1 0.03 0.04 0.01 0.03 0.03 0 9.81 18.71 2.09 8.32 0.08 2.43 0.02 0.09 0.23 0.08 67.68 41.86
54 0.02 4.57 19.41 0.62 0.1 0.04 0.04 0.15 0.03 12.7 20.55 1.92 7.06 2.03 0.19 0.01 69.44 44.46
55 2.79 19.97 0.49 0.03 0.01 0.01 0.11 0.2 12.79 22.56 1.95 7.54 2.14 0.01 0.1 0.08 0.1 70.88 47.27
56 0.04 2.26 21.64 0.46 0.02 0.09 0.03 0.03 0.01 12.74 21.98 1.83 7.27 2.13 0.08 0.13 70.74 46.16
57 0.02 4.28 16.77 0.28 0.06 0 12.53 23.39 2.47 8.33 2.1 0.14 0.38 0.1 0.03 0.09 0.04 71.01 49.6
58 0.02 0.02 5 18.88 0.26 0.03 0.03 0.05 0.01 12.64 22.58 2.2 7.57 2.26 0.06 0.05 0.25 0 71.91 47.61
EPMA-05
11.18 18.94 0.21 0.17 0.02 0.18 12.77 24.31 2.88 9.66 2.18 0.19 0.17 0.14 73 52.30
8 0.02 0.02 1.59 17.28 0.04 0.25 0.07 0.15 0.2 16.12 27.05 2.63 8.34 2.35 0.01 0.26 0.05 0.01 0.04 76.48 56.86
13 0.06 0.01 2.38 19.29 0.07 0.17 0.03 0.01 1.05 13.97 23.97 2.14 8.62 2 0.03 0.23 0.16 0.07 0.04 74.3 51.23
11 0.07 1.67 19.23 0.05 0.36 0.09 0.09 0.03 0.03 16.94 27.49 2.85 7.59 2.32 0.05 0.12 0.04 79.02 57.40
7 0.04 7.96 16.08 0.14 0.07 0.03 0.06 10.64 27.92 3.64 11.05 0.3 2.33 0.05 0.39 0.14 0.06 0.03 80.93 56.55
9 0.07 0.08 2.97 18.03 0.19 0.11 0 0.01 0.03 0.01 0.01 11.52 26.2 3.46 10.66 0.16 2.11 0.07 0.18 0.05 0.04 0.17 76.13 54.62
468

Mohd. Sadiq, Ranjith A., Ravi Kumar Umrao
Table 9. Composition of belovite.
Sample No. Point Na2O MgO CaO SrO BaO SiO2TiO2ThO2UO2P2O5La2O3Ce2O3Pr2O3Nd2O3EuO Gd2O3Tb2O3Dy2O3Ho2O3Er2O3Tm2O3Yb2O3Lu2O3Total REO%
EPMA-07 40. 1.91 6.17 16.78 0.1 1.69 0.04 0.01 3.74 11.34 15.66 1.08 4.69 1.29 0.34 0.04 64.88 34.44
EPMA-08
36. 0.05 0.05 5.53 12.71 0.8 0.22 0.04 0.03 0.05 6.79 13.67 23.62 2.09 7.3 2.22 0.08 0.05 0.03 0.07 75.32 49.13
38. 0.13 0.14 8.64 10.93 0.24 0.21 0.04 8.56 10.61 23.97 2.37 8.07 0.01 2.26 0.24 0.07 0.01 0.11 0.03 76.64 47.75
41. 0.59 0.14 11.25 8.17 0.38 0.24 0.05 19.52 10.13 21.99 2.96 9 0.4 2.19 0.46 0.21 0.02 0.22 87.92 47.58
35. 0.04 0.08 9.7 10.11 0.53 0.09 0.04 0.1 0.03 21.31 15.94 22.62 2.07 5.34 2.07 0.5 0.01 0.16 90.74 48.71
44. 0.22 5.1 13.92 0.59 0.06 0.04 4.28 15.3 24.07 2.03 6.56 2.12 0.04 0.08 0.01 74.42 50.21
43. 0.13 0.02 4.48 42.27 0.25 1.31 0.01 0.1 0.07 12.87 8.08 10.99 1.2 3.31 1.02 0.26 0.1 0.07 0.09 86.63 25.12
EPMA-09 15. 0.04 4.32 18.41 0.1 0.15 0.03 0.42 4.01 14.74 22.92 2.17 6.82 2.09 0.11 0.02 0.04 76.39 48.91
EPMA-10 17. 0.19 0.01 7.93 20.97 0.2 0.28 0.02 0.02 0.03 7.67 12.04 17.95 1.82 5.03 1.88 0.17 76.21 38.89
Table 10. Composition of britholite.
Sample No. Point Na2O K2O MgO CaO MnO FeO SrO BaO PbO Al2O3La2O3Ce2O3Pr2O3Nd2O3Gd2O3Tb2O3Dy2O3Ho2O3Er2O3Tm2O3Yb2O3Lu2O3SiO2SO2TiO2UO2P2O5Total REO%
EPMA-08
27 0.22 0.37 0.22 13.24 0.76 0.38 0.28 0.07 11.77 21.3 1.88 6.75 1.85 0.04 0.1 0.02 0.64 0.24 0.06 0.21 27.28 87.68 43.71
30 0.7 0.23 0.36 6.05 0.17 0.12 3.61 0.36 0.17 0.24 12.21 25.83 2.92 9.09 2.39 0.07 0.15 0.06 0.06 1.39 0.23 0.1 0.04 23.63 90.18 52.78
32 0.07 0.28 0.19 13.54 0.02 0.04 1.13 0.56 0.19 0.01 13.54 21.6 2.28 6.69 1.87 0.19 0.13 0.09 0.11 0.02 0.01 0.27 0.32 0.04 0.07 30.9 94.16 46.53
33 0.14 0.25 0.16 15.21 0.32 1.29 0.48 0.05 13.38 23.76 2.09 6.16 2.23 0.05 0.05 0.23 0.26 0.33 0.05 0.11 31.25 97.85 47.95
34 0.11 0.13 0.11 13.77 1.29 0.47 0.14 13.54 24.17 2.14 8.08 2.27 0.14 0.01 0.04 0.06 0.08 0.12 0.25 0.03 0.07 33.32 100.34 50.53
37 0.14 0.29 0.28 12.23 0.04 0.09 1.01 0.4 0.73 0.07 12.09 21.17 1.9 7.29 1.84 0.14 0.05 0.05 0.03 0.03 0.54 0.16 0.01 0.11 14.66 75.29 44.53
EPMA-09 23 0.03 0.2 11.75 0.38 0.69 0.16 0.06 0.04 15.02 25.32 3.08 7.9 2.24 0.36 0.06 0.01 0.07 0.28 0.26 0.03 0.01 27.69 95.64 54.06
EPMA-07 27 0.04 10.03 1.27 0.05 3.15 0.57 0.14 0.24 16.85 23.13 1.78 3.89 1.94 0.21 0.08 14.51 0.04 0.04 20.21 98.07 47.88
Table 11. Composition of bastnasite.
Sample No. Point MgO CaO SrO BaO SiO2PbO Al2O3Y2O3TiO2ThO2UO2P2O5Ta2O5La2O3Ce2O3Pr2O3Nd2O3Gd2O3Tb2O3Dy2O3Ho2O3Tm2O3Yb2O3Lu2O3Total REO%
EPMA-05
20.03 1.51 0.49 0.11 0.23 0.05 0.01 0.3 0.03 0.02 0.03 0.06 23.01 34.13 3.3 10.09 2.86 0.16 0.25 0.1 0.19 0.14 77.1 74.23
3 1.05 2.89 0.34 0.13 2.56 0.28 0.06 0.07 0.05 0.26 19.09 32.35 3.78 10.72 3.21 0.24 0.16 0.07 0.04 77.35 69.66
4 1.54 3.88 0.98 0.12 0.71 0.15 0.04 0.05 0.04 1.85 0.09 17.67 27.03 2.55 8.27 2.54 0.19 67.7 58.25
5 1.05 3.23 0.43 0.18 0.21 0.12 0.03 0.38 0.08 0.01 0.5 0.15 18.4 30.9 3.24 11.02 2.67 0.31 0.08 0.18 0.07 0.03 73.27 66.90
469

REE Mineralization in the Carbonatites of the Sung Valley Ultramafic-Alkaline-Carbonatite Complex, Meghalaya, India
Table 12. Whole rock XRF analysis of Sung Valley carbonatite samples, major oxides (wt.%) and trace elements (ppm).
S. No. SV/XRF-02 SV/XRF-03 SV/XRF-07 SV/XRF-08 SV/XRF-09 SV/XRF-10 SV/XRF-13 SV/XRF-14 SV/XRF-17 SV/XRF-18 SV/XRF-19 SV/XRF-20 SV/XRF-21 SV/XRF-22
SiO20.02 0.50 0.82 1.35 0.18 0.28 1.33 0.63 1.09 0.06 0.2 0.32 0.24 0.13
Al2O3- 0.23 0.47 0.18 0.07 0.03 0.75 0.42 0.54 0.11 0.07 0.11 0.08 0.06
Fe2O3(T) 0.17 0.25 0.34 0.42 0.04 0.29 1.14 1.19 0.15 0.05 2.13 3.10 3.20 2.31
MnO 0.05 0.06 0.05 0.08 0.05 0.05 0.09 0.09 0.05 0.05 0.09 0.10 0.09 0.09
MgO 2.03 2.06 1.82 2.64 1.55 1.78 2.35 2.36 1.84 1.56 2.53 2.54 2.53 2.47
CaO 52.21 50.35 50.13 48.50 51.16 49.24 48.74 48.19 49.67 50.32 47.89 46.61 46.58 48.80
Na2O - 0.01 0.08 0.02 0.03 - 0.01 - 0.07 0.01 0.05 0.06 0.06 0.06
K2O - 0.14 0.03 - - 0.02 0.04 0.04 0.03 0.00 - - - 0.01
TiO20.02 0.03 0.03 0.03 0.03 0.03 0.05 0.04 0.03 0.02 0.03 0.03 0.04 0.04
P2O50.12 0.59 1.10 2.79 1.78 2.32 2.79 3.53 0.64 0.54 3.40 4.78 3.84 2.23
LOI 45.42 45.01 44.75 43.48 45.06 44.86 42.55 42.65 44.95 46.69 42.76 42.35 42.87 42.48
Total 100.04 99.23 99.62 99.49 99.95 98.9 99.84 99.14 99.06 99.41 99.15 100 99.53 98.68
Ba - 76 - - - - 52 53 - - - - - -
Ga 18 17 19 13 17 24 14 22 18 19 19 11 14 18
Sc 26 27 29 24 24 27 23 31 28 25 30 27 31 29
V - - - 20 - - 115 117 - - 47 85 56 42
Th 5 - 9 8 10 14 12 13 6 9 8 10 14 6
Pb 3 - 3 - 9 3 2 4 - - - - 4 -
Ni 5 8 2 6 - 13 - 2 7 4 7 - - 4
Co - 9 13 16 - 12 - 15 2 - 10 13 19 6
Rb --------------
Sr 1840 1904 1802 1741 1876 1853 2118 2096 1867 1858 1845 1826 1679 1717
Y 47 49 46 47 48 49 42 43 51 49 39 39 37 39
Zr 295 442 285 257 325 372 301 334 311 302 353 365 518 258
Nb - - - - - - 59 39 - - - 5 - -
Cr --------------
Cu 1 9 1 1 1 8 - - - - - - - -
Zn 24 28 40 36 34 39 77 75 44 31 51 66 59 44
(“–” below detection limit)
470

Mohd. Sadiq, Ranjith A., Ravi Kumar Umrao
Table 13. Rare earth elements concentration in bed rock samples of Sung Valley carbonatite bodies (C1-C11) by ICP-MS analysis (rare earth elements in ppm).
Carb. Body Sample No. La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu PREE Sn Hf Ta Mo W Ge Be U
C1 BRS-23 286.61 514.77 65.56 189.29 43.23 7.72 33.90 3.68 15.19 2.23 4.99 0.64 3.24 - 1171.05 1.49 - 1.13 - 0.74 0.25 - -
BRS-24 273.14 470.80 62.75 181.56 41.89 7.62 32.51 3.58 14.58 2.14 4.72 0.58 3.01 - 1098.88 - - 1.96 - 0.58 0.25 - -
C2
BRS-54 244.73 434.30 55.88 190.89 39.03 6.95 29.44 3.12 13.18 1.95 4.26 0.53 2.78 - 1027.04 - - - - - - - -
BRS-55 212.21 376.19 47.94 165.53 34.01 6.05 25.19 2.74 11.44 1.68 3.70 - 2.38 - 889.06 - - - - - - - -
BRS-56 214.72 382.73 49.35 167.48 34.16 6.14 26.74 2.84 11.99 1.77 3.77 - 2.44 - 904.13 - - - - - - - -
BRS-57 188.92 338.26 42.87 147.36 30.22 5.34 23.19 2.51 10.78 1.63 3.65 - 2.46 - 797.19 - - - - - - - -
BRS-58 242.74 429.91 54.13 189.34 37.71 6.65 28.88 3.13 13.24 2.00 4.39 0.57 2.99 - 1015.68 - - - - - - - -
C3 BRS-25 267.92 483.97 60.75 174.48 41.17 7.31 32.32 3.56 14.92 2.22 5.06 0.65 3.43 - 1097.76 - 2.76 3.62 - 0.62 0.28 - -
BRS-26 243.57 437.09 55.58 154.74 38.01 6.83 30.06 3.22 13.27 1.90 4.27 0.54 2.81 - 991.89 - - 9.19 - - 0.21 - -
C4 BRS-30 326.92 595.00 75.52 217.34 50.07 8.98 39.09 4.19 17.51 2.52 5.43 0.71 3.48 - 1346.76 1.09 6.52 4.77 - 0.72 0.34 - 1.07
C5 BRS-43 253.10 451.79 57.34 131.15 40.53 7.40 30.62 3.22 3.26 1.91 4.20 - 2.54 - 987.06 3.31 - 1.48 - - 0.23 - 0.70
BRS-44 269.00 479.13 59.87 138.27 42.41 7.82 32.03 3.37 3.87 2.01 4.27 0.53 2.63 - 1045.21 6.30 1.73 0.33 - - 0.34 - 0.63
BRS-45 285.96 514.25 64.86 147.80 45.71 8.43 34.73 3.63 5.20 2.20 4.82 0.59 3.05 - 1121.23 4.52 1.73 0.95 - - 0.29 - 1.01
C6
BRS-39 170.90 312.10 40.20 109.20 27.60 5.40 22.00 2.40 10.00 1.50 3.30 - 2.20 - 706.80 2.70 0.70 28.8 - - 1.20 - 4.20
BRS-40 262.30 473.20 59.10 162.50 40.60 7.80 31.80 3.40 14.4 2.10 4.8 0.60 3.10 - 1065.70 2.70 - 1.10 - - 0.30 - 0.70
BRS-41 221.50 402.40 50.80 137.40 34.80 6.70 27.00 2.90 11.9 1.70 3.8 - 2.40 - 903.30 3.60 1.10 1.10 - - 0.30 - 2.40
BRS-42 231.29 412.81 52.21 119.08 37.12 6.98 23.85 3.15 3.48 2.00 4.35 0.55 2.77 - 899.64 4.20 1.15 1.86 - - 0.25 - 26.88
C7 BRS-46 262.98 477.15 59.35 137.17 41.97 7.64 31.22 3.38 3.85 2.05 4.50 0.56 2.84 - 1034.66 5.02 4.16 0.34 - - 0.26 - 0.75
C8 BRS-01 274.42 488.20 62.30 206.64 40.38 7.68 31.96 3.63 15.1 2.23 5.16 0.66 3.36 - 1141.72 1.54 - 2.08 0.58 0.96 0.24 - -
BRS-02 297.40 531.26 67.99 215.44 43.73 8.15 34.44 3.90 16.29 2.39 5.58 0.70 3.62 - 1230.89 - 0.54 0.85 0.70 1.10 0.25 - -
BRS-03 274.86 494.54 63.88 202.27 42.08 7.88 33.12 3.63 14.79 2.14 4.78 0.61 3.06 - 1147.64 1.90 1.08 5.22 0.67 1.13 0.35 - -
C9 BRS-06 232.66 416.34 54.19 155.55 36.43 6.78 28.34 3.15 13.06 1.96 4.56 0.59 3.12 - 956.73 3.57 4.37 4.43 0.77 1.67 0.56 - 0.76
C10 BRS-48 244.30 440.63 58.50 129.69 39.92 7.38 30.30 3.27 3.63 2.01 4.45 0.54 2.79 - 967.41 3.44 0.88 2.22 - - 0.18 - 18.97
BRS-49 238.41 427.96 54.94 129.15 39.05 7.18 29.21 3.12 3.05 1.87 4.05 - 2.57 - 940.56 4.99 1.00 1.31 - - 0.19 - 5.32
C11 BRS-28 251.89 452.85 58.18 164.80 39.47 7.19 31.48 3.40 13.78 2.00 4.48 0.56 2.85 - 1032.93 - - 1.53 0.52 0.78 0.26 - -
BRS-29 254.96 455.62 59.54 172.01 39.76 7.19 30.63 3.29 12.99 1.87 3.93 - 2.42 - 1044.21 2.60 0.57
10.69
0.61 0.91 0.38 0.3 -
(“-” below detection limit)
471

REE Mineralization in the Carbonatites of the Sung Valley Ultramafic-Alkaline-Carbonatite Complex, Meghalaya, India
Table 14. Correlation matrix of Rare earth elements and Sn, Hf, Ta, Mo, W, Ge, Be, U from Sung Valley carbonatites.
La Ce Pr Nd Eu Sm Gd Tb Dy Ho Er Tm Yb Lu REE Sn Hf Ta Mo W Ge Be U
La 1.0000
Ce 0.9963 1.0000
Pr 0.9928 0.9913 1.0000
Nd 0.6308 0.6104 0.6302 1.0000
Eu 0.9624 0.9658 0.9608 0.4490 1.0000
Sm 0.9799 0.9793 0.9747 0.5101 0.9753 1.0000
Gd 0.9670 0.9691 0.9718 0.6165 0.9317 0.9555 1.0000
Tb 0.9861 0.9841 0.9889 0.6364 0.9492 0.9540 0.9487 1.0000
Dy 0.2678 0.2595 0.2816 0.8058 0.0820 0.1130 0.3015 0.3122 1.0000
Ho 0.9522 0.9493 0.9465 0.6567 0.9022 0.9128 0.8934 0.9728 0.3230 1.0000
Er 0.8979 0.8955 0.8924 0.6676 0.8408 0.8341 0.8419 0.9354 0.3910 0.9770 1.0000
Tm 0.7885 0.7889 0.7811 0.6374 0.7231 0.7157 0.7298 0.8413 0.4456 0.9120 0.9436 1.0000
Yb 0.8012 0.7993 0.7936 0.6967 0.7142 0.7184 0.7502 0.8510 0.4905 0.9251 0.9737 0.9606 1.0000
Lu 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 1.0000
REE 0.9809 0.9767 0.9775 0.7644 0.9072 0.9346 0.9566 0.9735 0.4320 0.9490 0.9087 0.8139 0.8381 0.0000 1.0000
Sn -0.2962 -0.2851 -0.3385 -0.6927 -0.0925 -0.1425 -0.3330 -0.4014 -0.8448 -0.3807 -0.4603 -0.4709 -0.5189 0.0000 -0.4269 1.0000
Hf 0.3212 0.3643 0.3306 0.1544 0.3342 0.3731 0.3237 0.3223 0.0618 0.3604 0.2934 0.3524 0.3244 0.0000 0.3132 0.1319 1.0000
Ta -0.5891 -0.5706 -0.5503 -0.2385 -0.6501 -0.6306 -0.5017 -0.5601 0.1310 -0.5503 -0.5369 -0.3653 -0.4321 0.0000 -0.5050 -0.1633 -0.0739 1.0000
Mo 0.1068 0.0946 0.1486 0.4750 0.0348 -0.0090 0.0901 0.1810 0.4225 0.1626 0.2652 0.2535 0.3140 0.0000 0.2087 -0.2359 0.0412 0.0158 1.0000
W 0.2215 0.2104 0.2678 0.5867 0.1063 0.0974 0.2112 0.3046 0.5604 0.3027 0.3959 0.4100 0.4696 0.0000 0.3319 -0.3514 0.2274 -0.0182 0.9307 1.0000
Ge -0.5871 -0.5669 -0.5657 -0.2801 -0.6045 -0.6295 -0.5125 -0.5677 0.0836 -0.5160 -0.4818 -0.2864 -0.3678 0.0000 -0.5151 0.0348 0.0859 0.8834 0.1035 0.1045 1.0000
Be -0.0241 -0.0316 0.0107 0.0803 -0.0764 -0.0273 -0.0219 -0.0587 0.1014 -0.1779 -0.2589 -0.3488 -0.2985 0.0000 0.0002 -0.0191 -0.1267 0.2414 0.2679 0.1747 0.0542 1.0000
U -0.3295 -0.3281 -0.3072 -0.4732 -0.2198 -0.2449 -0.4890 -0.2749 -0.5072 -0.1668 -0.2027 -0.1351 -0.2194 0.0000 -0.3909 0.2979 -0.0941 -0.0258 -0.2384 -0.2965 -0.0780 -0.0939 1.0000
472

Mohd. Sadiq, Ranjith A., Ravi Kumar Umrao
Table 15. REE concentration in eleven carbonatite bodies of SUAC complex.
Carbonatite
Body Sample No. PLREE PHREE PLREE/
PHREE %PLREE %PHREE %PREE
C1 BRS-23 1099.45 71.59 17.33 0.1099 0.0072 0.1171
BRS-24 1030.14 68.74 16.98 0.1030 0.0069 0.1099
C2
BRS-54 964.83 62.21 17.59 0.0965 0.0062 0.1027
BRS-55 835.88 53.18 17.86 0.0836 0.0053 0.0889
BRS-56 848.44 55.69 17.25 0.0848 0.0056 0.0904
BRS-57 747.63 49.56 17.03 0.0748 0.0050 0.0798
BRS-58 953.83 61.85 17.40 0.0954 0.0062 0.1016
C3 BRS-25 1028.28 69.47 16.66 0.1028 0.0069 0.1097
BRS-26 928.99 62.90 16.69 0.0929 0.0063 0.0992
C4 BRS-30 1264.85 81.92 17.47 0.1265 0.0082 0.1347
C5 BRS-43 933.91 53.15 20.58 0.0934 0.0053 0.0987
BRS-44 988.68 56.53 20.46 0.0989 0.0057 0.1046
BRS-45 1058.58 62.65 19.68 0.1059 0.0063 0.1122
C6
BRS-39 660.00 46.80 16.07 0.0660 0.0047 0.0707
BRS-40 997.70 68.00 16.70 0.0998 0.0068 0.1066
BRS-41 846.90 56.40 17.18 0.0847 0.0056 0.0903
BRS-42 852.51 47.13 21.41 0.0853 0.0047 0.0900
C7 BRS-46 978.62 56.04 20.38 0.0979 0.0056 0.1035
C8 BRS-01 1071.93 69.78 17.39 0.1072 0.0070 0.1142
BRS-02 1155.82 75.07 17.39 0.1156 0.0075 0.1231
BRS-03 1077.62 70.00 17.47 0.1078 0.0070 0.1148
C9 BRS-06 895.17 60.98 16.46 0.0900 0.0060 0.0960
C10 BRS-48 913.04 54.37 19.59 0.0913 0.0054 0.0967
BRS-49 889.51 51.05 20.44 0.0890 0.0051 0.0941
C11 BRS-28 967.19 65.73 16.64 0.0967 0.0066 0.1033
BRS-29 981.89 62.31 17.94 0.0982 0.0062 0.1044
SiO
2
and TiO
2
. The enrichment in P
2
O
5
indicates the
presence of apatite in the carbonatites.
The REE data of 26 selected samples of the Sung Valley
carbonatites are shown in Table 13. The data show poor
association of trace elements (Sn, Hf, Ta, Mo, W, Ge, Be
and U) in carbonatite except in a few samples. The highest
values of Sn, Hf, Ta and U are 6.30, 6.52, 28.80, and 26.88
ppm respectively. The two samples showing the higher U
contents (18.97 and 26.88 ppm), are characterised by the
presence of uraninite. The concentration average values
of 26 samples for La, Ce, Pr, and Nd are 251 (
σ
= 33.5),
450 (
σ
= 60.3), 57 (
σ
= 7.6) and 163 (
σ
= 30.0) ppm
respectively. In the unit correlation matrix, La with Ce show
99.6% positive correlation suggesting these two elements
are always enriched together in the carbonatite. There is
strong positive correlation among other LREEs (Table 15).
Sn, Ta, Ge, Be and U have negative correlations with rare
earth elements (Table 14).
The normalised REE patterns of Sung Valley carbonatite
samples show enrichment of light rare earth elements
(LREE) relatively to the heavy rare earth elements (HREE)
(Figure 10). The total LREE concentration in the eleven
carbonatite bodies varies from 660 to 1265 ppm while
the HREE varies from 47 to 82 ppm (Figure 2; Table 15).
The total REE varies from 707 ppm to 1347 ppm with an
average value of 1022 ppm (0.1022%). The LREE is higher
than HREE by a factor 18.0 (LREE/HREE=18.0). The
channel sampling has been carried out from C2 body and
13 samples yield average
P
REE value 1025 ppm similar
to the value of one sample from C4 body that has
P
REE
value of 1026 ppm (Table 16). The carbonatites of SUAC
complex have a significant amount of REEs along with
pyrochlore and phosphate.
6. Conclusion
Carbonatites are well-known for their economic or anoma-
lous concentrations of rare earth elements, phosphorous,
niobium - tantalum, uranium, thorium, copper, iron and
other rare elements. The Early Cretaceous Sung Valley
complex of northeastern India covers about 26 km
2
. Car-
bonatites are intruded in different members of Sung Valley
complex and occur as small dykes, veins and oval shaped
bodies. Calcite carbonatite is dominant in the SUAC
complex. Chemically, being Mg-poor, carbonatites are
classified as calcio-carbonatite. The calcite carbonatite of
the Sung Valley hosts REE-bearing carbonate and phos-
473

REE Mineralization in the Carbonatites of the Sung Valley Ultramafic-Alkaline-Carbonatite Complex, Meghalaya, India
Table 16. REE analysis of channel samples from C2 and C4 carbonatite bodies.
Carbo-natite Body Sample No La Ce Pr Nd Sm PLREE Eu Gd Tb Dy Ho Er Tm Yb Lu PHREE
C2
CS-01 270.40 450.23 62.30 220.12 42.03 1045.08 7.12 32.14 3.62 15.64 2.50 6.02 0.74 3.68 0.61 64.95
CS-02 298.24 445.69 70.23 220.56 45.69 782.17 7.50 33.68 3.98 16.25 2.58 5.98 0.68 3.19 0.64 66.98
CS-03 320.75 562.03 72.45 257.14 52.40 1264.77 7.94 40.56 3.44 16.27 2.76 5.85 0.71 3.54 0.56 73.69
CS-04 267.75 481.91 62.47 211.73 40.79 1064.65 6.57 30.83 3.41 14.22 2.06 4.89 0.54 2.75 0.00 58.72
CS-05 256.20 454.23 60.12 205.70 39.99 1016.24 6.46 30.69 3.27 13.30 1.87 4.40 0.00 2.54 0.00 56.07
CS-06 207.85 358.49 48.47 163.16 32.55 810.52 5.00 24.05 2.70 11.24 1.63 3.93 0.00 2.28 0.00 45.83
CS-07 239.44 407.46 55.09 181.72 36.36 920.07 5.71 27.82 3.10 12.97 1.89 4.47 0.00 2.55 0.00 52.79
CS-08 194.32 352.24 45.70 146.00 31.31 769.57 4.98 23.05 2.61 10.51 1.65 3.49 0.00 2.14 0.00 43.45
CS-09 215.50 376.84 52.01 189.50 33.39 867.23 6.05 26.85 2.92 12.36 1.84 4.28 0.00 2.57 0.00 50.83
CS-10 256.32 424.35 62.77 233.11 39.65 1016.19 7.55 31.02 3.54 15.13 2.24 5.23 0.61 3.15 0.00 60.91
CS-11 244.38 407.67 58.86 214.43 37.14 962.48 7.46 29.45 3.25 13.59 2.03 4.77 0.52 2.89 0.00 56.50
CS-12 225.47 379.71 53.83 201.86 33.49 894.35 6.66 26.65 2.98 12.54 1.84 4.30 0.00 2.51 0.00 50.82
CS-13 202.77 342.27 47.89 179.43 29.65 802.01 6.00 23.87 2.73 11.69 1.75 4.17 0.00 2.49 0.00 46.70
C4 CS-14 252.19 388.91 59.52 225.39 36.26 962.27 7.41 28.15 3.35 14.30 2.19 5.22 0.00 3.20 0.00 56.42
phate minerals, bastnäsite-(Ce), ancylite-(Ce), belovite-
(Ce) and britholite-(Ce), associated with calcite and apatite,
that contain total REO in a range from 58.25–74.23 wt%,
43.71–54.06 wt%, 22.22–56.86 wt% and 25.12–49.13 wt%
respectively. Britholite also contains P
2
O
5
in the range
between 14.66–33.32 wt%. Ancylite and belovite contain
SrO ranging from 9.01–23.42 wt% and 8.17–42.27 wt% re-
spectively. Apart from these REE phases, pyrochlore, a
host for 30.93–56.93 wt% Nb
2
O
5
, 7.30–31.35 wt% Ta
2
O
5
,
0.06–18.79 wt% UO
2
, also contains 0.8–12.32 wt% total
REO. The eleven isolated carbonatite bodies show average
P
REE value of 0.102 wt% in 26 bed rock samples. Thir-
teen channel samples of C2 body show average
P
REE
0.103 wt% and one channel sample from C4 body yield
P
REE value 0.103 wt%. The REEs are enriched in LREE
by a factor of 18.0 (LREE/HREE=18.0). This study indi-
cated that SUAC carbonatite hosts noteworthy amount of
REEs along with apatite (phosphate) and pyrochlore (Nb-
Ta) mineralisation. Moreover, tiny grains of Sn (~10
µ
m)
and Au (~5
µ
m) were also identified. Finding REE car-
bonates and phosphates that can be easily processed and
extracted, in combination with the reported occurrence of
phosphorus-bearing apatite and REE bearing pyrochlore
enhances the possibilities with regard to Sung Carbon-
atites economic viability. Moreover, because of the resid-
ual soil cover (1–2 m thick) that has developed, different
carbonatite bodies can be explored for secondary REE
mineralization by detail sampling. Therefore, the present
study opens the scope for detailed investigation to assess
the REE potential and associated mineralisation in the
Sung Valley prospect.
Acknowledgments
The authors express their gratitude towards Director Gen-
eral, Geological Survey of India, Kolkata and Additional
Director General and Head of Department, Geological
Survey of India, North Eastern Region, Shillong for his
continuous support and permission to publish the work.
Sincere thanks to Dr. T. Kannadasan and J.C. Dutta for
technical guidance and supervision during the field and
laboratory studies and Dr. Fareeduddin, M. Korakoppam,
PPOD, GSI, Bangalore for Petrography and EPMA study.
Dr. S. Chakraborti, B.B. Sharma„ Dr. M.L. Dora, Dr. Sudip
Bhattacharyya, Ms S. Sujata and Ms Imlishila Imchen GSI,
Shillong and Prof. K. Randive, RTM University Nagpur for
discussions, suggestions and comments on the manuscript.
Authors also express their gratitude towards editor’s and
anonymous reviewer’s scrutiny that helped in improving
the manuscript substantially.
474

Mohd. Sadiq, Ranjith A., Ravi Kumar Umrao
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