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JOURNAL GEOLOGICAL SOCIETY OF INDIA 

Vol.76, December 2010, pp.589-606 

Komatiite within Chhotanagpur Gneissic Complex at Semra, Palamau 

District, Jharkhand: Petrological and Geochemical Fingerprints 

D. K. BHATTACHARYA 1 , D. MUKHERJEE 2# and V. C. BARLA 3 

1 Post Graduate Department of Geology, Ranchi University, Ranchi – 834 008 

2 202, Manna Surti Complex, Lohianagar, Kankarbagh, Patna – 800 020 

# Present Address: Geological Survey of India, Operation: Bihar, Patna – 800 020 

3 P.G. Department of Geology, Vinoba Bhave University, Hazaribag – 821 305 

Email: dkbprofru78@gmail.com; dmukherjeegsi@gmail.com 

Abstract: Komatiite near Semra village, southwest of Daltonganj in Palamau District of Jharkhand, occurs within 

tremolite actinolite schist of ultramafic parentage. The fragmented olivine phenocrysts show mutually parallel as well as 

angular alignment, representing relict spinifex texture. Mineralogically the Semra ultramafic is lehrzolite in composition. 

The cumulates lack visible deformation suggesting original magmatic crystallization of these ultramafic rocks. The 

present occurrence of Spinifex Textured Peridotitic Komatiite (STPK) in Chhotanagpur Gneissic Complex (CGC) at 

northwestern part of Eastern Indian Shield is of great significance as it opens up a possibility of the presence of Archaean 

rock in CGC, which is yet to be established. 

These ultramafics are geochemically characterised by distinctive high MgO, Ni, Cr and poor in alkali, TiO 2 

, Ba, Cs, 

Rb, Nb, Hf and Y contents. It has low abundance of incompatible elements and is LREE depleted [(La/Yb) n 

= 0.74 – 

1.07] with enriched flat HREE profile, representing chondrite like composition. This shows diagnostic convex upward 

REE profile. All these together with relict but distinct spinifex texture confirm the komatiitic character of Semra ultramafic. 

The chemical data plots for ultramafics confine to komatiite field in discriminate diagrams. The Mg# (>74) of the Semra 

ultramafics are comparable to primitive upper mantle Mg# (89.8) and high enough for rocks derived from ultramagnesian 

liquid of the mantle derived source. Considerably high Zr concentration in Semra ultramafic is attributed to Zr-enriched 

mantle source. Geochemically Semra ultramafics is comparable with “Al-undepleted” Munro type komatiites. Depleted 

incompatible trace elements also point towards Al-undepleted nature for the investigated ultramafics, which are 

characterised by distinctive low SiO 2 

content in comparison to many well known komatiites of the world. The low K 2 

O 

content indicate plume related magmatism for its generation. Tectonic setting of this STPK with distinctive cumulus 

nature is suggestive of its emplacement in an extensional tectonic regime. 

Keywords: Komatiite, Plume magmatism, Extensional Regime, Chhotanagpur Gneissic Complex, Semra, Palamau, 

Jharkhand. 

INTRODUCTION 

Komatiite represents an important group of igneous rock 

(Nesbitt et al. 1979). The term “Spinifex texture” was coined 

by Nesbitt (1971) referring to large, skeletal, platy, bladed 

or acicular grains of olivine, initially called “crystalline 

quench texture” of Komatiites in the Barberton greenstone 

belt, South Africa (Viljoen and Viljoen, 1969). Komatiite 

was defined by Arndt and Nesbitt (1982) as ultramafic 

mantle-derived volcanic rock having spinifex texture (Arndt 

and Lesher, 1992). Subsequently as per IUGS classification, 

komatiites were defined as containing >18 wt% MgO with 

590 D. K. BHATTACHARYA AND OTHERS 

magmatism, spanning over a prolong period (Mukherjee and 

Ghose, 1999). The earliest magmatism recorded in CGC is 

represented by the highly altered mafic-ultramafic suite, 

considered as late Archaean or Early Palaeo-Proterozoic in 

age (Mukherjee and Ghose, 1992). The ultramafics of CGC 

are well differentiated, ranging in composition from 

peridotite to pyroxenite and metamorphosed to serpentinite 

or talc tremolite or chlorite schist (Ghose and Mukherjee, 

2000). Large clusters of these rocks are known from 

Daltonganj, Dumka, Parasnath Hill to Mathurapur, Hura- 

Puncha areas and also along North Purulia Shear Zone 

(NPSZ) in Purulia district of West Bengal (Mahadevan, 

2002; Mandal et al., 2007, Mandal and Ray, 2009). The 

ultramafic enclaves are also reported from the granulite 

belts of Adra in Purulia district (Mahadevan, 1992) and 

Dumka area (Bhattacharya, 1975). Mahadevan (2002) 

suggested possible linkage with sub-crustal peridotitic 

layers. Most of the mafic rocks of CGC including those of 

Palamau Districts (Ghose et al. 1983, Srivastava et al. 1984) 

and also the ultramafics within the CGC (Mandal and Ray, 

2009) have been assigned tholeiitic parentage.In marked 

contrast, the presently investigated Semra ultramafic at 

northwestern sector of CGC is representing Komatiitic 

characters. 

Komatiites are rare and exotic rocks serving as windows 

to the earth’s mantle. Its potentiality as host of Cu-Ni-Fe 

sulfides and PGE make the study of Semra Komatiite 

extremely important and rewarding both from academic as 

well as economic points of view. The present occurrence of 

Komatiite within CGC probably represents only one of its 

kind, thereby bears great significance to elucidate early 

magmatic history of this vast mobile belt. The nearest 

known occurrence of Komatiite is reported from Kunchia 

belonging to Proterozoic volcanosedimentary sequence 

north of Dalma (Das et al. 2001), occurring just south of 

southern margin of CGC. The present work primarily 

focused to evaluate komatiitic character of Semra ultramafic 

by evaluating its petrological and chemical attributes. This 

will be helpful in understanding nature of mantle in this 

part of CGC. 

GEOLOGICAL SETTING 

Geological map of Eastern Indian Shield (northern part, 

Fig.1) depicts the regional geological and tectonic setting 

of the study area within CGC. The spatial disposition of 

Chhotanagpur Gneissic Complex (CGC) with respect to 

different cratonic blocks of Indian shield is shown in Fig.1 

(Inset A). The episodic igneous activity within the CGC was 

spanning about two billion years over an ensialic basement 

(Mukherjee and Ghose, 1999; Ghose and Mukherjee, 2000; 

Ghose et al. 2005; Ghose and Chatterjee, 2008). The study 

area comprises mainly of granite gneisses that contain 

enclaves of older supracrustals of varying dimensions 

oriented parallel to NNW-SSE to NW-SE regional trend. 

These supracrustals comprise of metabasics, metapelites and 

metapsammites (Lahiri and Das, 1984; Srivastava et al. 

1984). There are several lenses of mafic/ultramafic rocks 

within the granite gneiss/migmatite gneiss country rock. The 

later is mainly represented by diorite, granodiorite, tonalite 

and leucogranite, which are the result of late- to post-tectonic 

large scale granitic activities and pegmatite intrusions. 

Numerous small size ultramafic bodies of different 

geological ages within CGC have been classified into three 

categories: (i) Pre-tectonic Ultramafics, (ii) Syn-tectonic 

Ultramafics and (iii) Post-tectonic Ultramafics (Mishra 

et al. 2004; Ghose and Chatterjee, 2008). The ultramafic 

clusters along the Auranga-Koel valley at south and 

southwest of Daltonganj (viz. Sua (23°59'35":84°06'12", 

73A/1), Kauria (23°58'45":84°06'34", 73A/1), Semra 

(24°00'02":83 o 59'40", 63P/16), Salatua (24°02'45": 

83°57'10", 63P/16), Datam (23°56'’50":84°02’33", 73A/1), 

Biwabathan (23°54'59":84°02'50", 73A/1), Gore (23°58' 

13":83°58'33", 64M/13), Nawadih (23°57'31":83°59'07", 

64M/13) and Mahawat-Murie (23°55'45":84°04', 73A/1)), 

have been considered as Pre-tectonic ultramafics (Ghose 

and Chatterjee, op.cit). These represent the oldest magmatic 

rock in the CGC (Ghose, 1983, 1992; Mukherjee and Ghose, 

1992; Ghose and Mukherjee, 2000). The earliest ultramafic 

magmatism appears to be contemporaneous with early 

depositional history predating folding and metamorphism. 

Basic intrusives (accompanying second generation of 

folding) are now represented by amphibolites and 

metagabbros which occur mostly as concordant bodies cofolded 

with gneisses and migmatites. The basic magmatism 

was succeeded by large scale granitic activities and 

pegmatite intrusions which are syn- to post-tectonic 

(Mukherjee and Ghose, 1999; Ghose and Mukherjee, 2000). 

The presently investigated ultramafic rocks in the 

Auranga-Koel valley occurring at the northwestern part of 

the CGC is located near Semra (24°00'02"N; 83°59'40"E) 

village, about 8.5 km SW of Daltonganj town (Fig.1) in 

Palamau District of Jharkhand. Semra-Salatua area of 

Palamau district is well known for numerous bands of 

tremolite-actinolite-magnetite schists in places with 

cummingtonite-grunerite schists and amphibolites 

(Mahadevan, 2002, p.275), which have been assigned 

magmatic origin by Das Gupta et al. (1994) and Sinha and 

Bhattacharya (1995). The petrology of different rock types 

occurring southeast of the present area has been studied by 

JOUR.GEOL.SOC.INDIA, VOL.76,DEC.2010

KOMATIITE WITHIN CHHOTANAGPUR GNEISSIC COMPLEX AT SEMRA, JHARKHAND 591 

Fig.1. Geological map of Eastern Indian Shield (modified after Acharyya, 2003), showing the regional geological and tectonic setting 

of the study area within CGC. 1 – Singhbhum and other Granites, 2 – Iron Ore Group, 3 – Unclassified metamorphics, 

4 – Dhanjori Volcanosediments, 5 – Dalma Volcanics, 6 – Older Metasediments, 7 – Granulites, 8 – Chhotanagpur Gneiss and 

Granites including Bihar Mica Belt, 9 – Bengal Anorthosite, 10 – Mahakoshal–Rajgir–Munger–Metasediments, 11 – Vindhayan 

Supergroup, 12 – Gondwana Supergroup, 13 – Rajmahal Volcanics, 14 – Indogangetic Alluvium, 15 – Major Lineament/Shear 

Zone/Fault. AKGB – Auranga-Koel Gondwana Basin; GDGB – Garhwa-Daltonganj Gondwana Basin; SNNF – Son Narmada 

Northern Fault. SNSF - Son Narmada Southern Fault, BTF – Balarampur Tatapani Fault, NPSZ – North Purulia Shear Zone, 

SPSZ – South Purulia Shear Zone, SSZ – Singhbhum Shear Zone. DM – Dumka, DL – Daltonganj, DU – Dudhi, MU – Munger, 

PR – Purulia, RN – Ranchi. Inset: Spatial disposition of Chhotanagpur Gneissic Complex (CGC) at Eastern Indian Shield in 

relation to Eastern Ghats Mobile Belt (EGMB), Central Indian Tectonic Zone (CITZ), Shillong-Meghalaya Gneissic Complex 

(SMGC) and Singhbhum Mobile Belt (SMB), SC – Singhbhum Craton, BC – Bastar Craton, BuC – Bundelkhand and 

KC – Karnataka Craton (modified after Acharyya et al. 1998). 

Lahiri and Das (1984), Srivastava et al. (1984), and Ghose 

and Srivastava (2001), and east of present area by Kar and 

Sarkar (1989). In the northwestern part of CGC, ultramafic 

rocks are rare and post-tectonic intrusion of ultramafic rocks 

(two hornblende peridotite dykes) have also been reported 

from the southern margin of Gondwana Basin at Richughuta 

(Ghose, 1970). 

TECTONIC SETTING 

The tectonic framework surrounding the study area is 

shown in geological map of Eastern Indian shield (northern 

part) (Fig.1).Spatial disposition of Chhotanagpur Gneissic 

Complex (CGC) in relation to other major lithotectonic 

provinces are shown in Fig.1 (Inset A). The proximity of 

the study area to Son-Narmada South Fault (SNSF) at north 



and Balarampur-Tattapani Fault (BTF) to the south (Fig.1; 

cf. Fig.2 of Acharyya and Roy, 2000; Mukherjee, 1998) is a 

significant spatial aspect of its tectonic setting. The SNSF 

is an ENE-WSW brittle-ductile shear zone marked by 

discontinuous fault breccia and mylonite separating the 

Mahakoshal belt from the CGC (Mazumdar, 1988; Roy et 

al. 2002; Mohan et al. 2007). The eastern continuation of 

SNSF is also locally referred as Nagar Untari (68P/7) - 

Chhatarpur (72D/3) Shear zone, which is located 38 Kms 

north of study area. In addition to these, immediately 

adjoining Semra, the Garhwa-Daltonganj Gondwana basin 

(GDGB) at north and Auranga-Koel Gondwana basin 

(AKGB) at south (Fig.1) are located, which are characterised 

by number of basin margin faults and transverse faults. The 

easterly strikes of the basin boundary fault (Fig.1) coincide 

with the general strike trends of the Precambrian basement. 

Such parallelism with the strikes of basement rocks lends 

credence to the possibility that the Gondwana formations 

have responded to tectonic forces along pre-existing lines 

of least resistance (Pascoe, 1959). Some of these basin 

boundary faults continue for more than 80 km across the 

intervening Precambrian basement (Chatterjee and Ghosh, 

1970), signifying that these major faults are pre-Gondwana 

precursor faults (Dutta and Mitra, 1984; quoted by Sarkar, 

1988, p.132). Precambrian ancestry may have provided 

broad tectonised basement framework for Gondwana basins 

(Mahadevan, 2002, p.374). 

The pattern of the intrabasinal faults and basin-bounding 

faults represent both extensional and strike-slip regimes in 

the Precambrian basement leading to the development of 

Gondwana basins along the E-W direction (Mukherjee and 

Ghose, 1999; Chakraborty et al. 2003; Srivasatava et al. 

2009). The tectonics of Gondwana basins formation 

have been linked largely to distensional stress fields 

(Mahdevan, 2002) and their development is often attributed 

to epiorogenic processes and to deep crust-mantle 

interactions (Chatterjee and Ghose, 1970; Niyogi, 1987). 

Lamprophyric/lamproite within the Gondawana basins 

are essentially fault controlled (Mukherjee and Ghose, 

1999) which are the manifestation of plume generated 

magmatism. 

Five major intra-continental rift/shear zones largely 

controlled magmatism in the CGC (Ghose and Chatterjee, 

2008). These intra-continental rift/shear zones (Fig.1) 

represent major extensional zone of tectonism. The 

widespread mafic-ultramafic magmatism in the CGC 

mostly occurs in proximity to these major intra-continental 

rift/shear zones, suggesting their emplacement under 

extensional tectonism (Mukherjee and Ghose, 1999). Such 

widespread occurrence of intrusive and extrusive magmatic 

rocks ranging from Late Palaeoproterozoic to Early Tertiary 

signifies reactivation of the intra-continental rift/shear zones 

time and again (Mukherjee and Ghose, op.cit.; Ghose and 

Chatterjee, 2008.). The origin of Son-Narmada Graben has 

also been attributed to an intracratonic rift related to mantle 

upwelling (Das and Patel, 1984; Shankar, 1991) or a backarc 

rift basin during the northward subduction (Roy and 

Prasad, 2003). Proterozoic rifting in the CGC marks the 

earliest major extensional tectonism. Thus the occurrences 

of the mafic-ultramafic suites of rock in proximity to the 

palaeo-suture was induced by thinning and fracturing of the 

crust as a result of extensional tectonism involving shallower 

depths of the mantle probably not exceeding 250-300 kms. 

(Ghose and Chatterjee, 2008). 

NATURE OF OCCURRENCE 

The Semra ultramafics at northwestern part of CGC 

(Fig.1) occur as two isolated NNW–SSE trending lensoidal 

massive bodies within tremolite actinolite schist of ultramafic 

parentage in a predominantly granite gneiss and migmatite 

gneiss country. Concordant relationship of these bodies with 

reference to the dominant structural grain such as foliation/ 

gneissosity in the country rocks has been observed. These 

rocks are dark greyish black in colour when fresh and pale 

to dark brown on weathered surface. 

The presence of spinifex texture has been recognised as 

a diagnostic feature of komatiite flows (Nisbet, 1982; 

Donaldson, 1982; Arndt and Nesbitt, 1984). This spinifex 

texture is present in many, but not in all komatiite flows 

(Nesbitt, 1971). According to Hanski and Smolkin, (1995), 

Spinifex textures are, however, not a diagnostic feature of 

komatiites, as some picritic rocks also show this texture. 

Spinifex is textural term to describe an array of criss-cross 

sheafs or booklets characterised by numerous closely 

spaced and parallel blade or plate-like crystals of olivine 

(Pyke et al. 1973). Thus the spinifex texture of komatiite 

is characterised by the presence of large skeletal long 

acicular phenocrysts of olivine (or pseudomorphs after 

olivine), giving rise to a bladed appearance especially on a 

weathered surface. The spinifex texture in the investigated 

rocks is not very convincing on the surface outcrop, 

which is generally manifested as either parallel or 

mutually at low acute angle linear fracture-like growth. 

However, the criss-cross relationship between elongated 

crystals of olivine (Fig.2A) is very much conspicuous on 

polished rock slab viewed under microscopes. The plate 

like or bladed crystals of olivine in Semra ultramafic rock 

varies in length from 50 mm to 2 cm and 0.5 mm to 5 mm 

in thickness. 



PETROGRAPHY 

Semra ultramafics are medium to coarse grained massive 

rocks. The variation in texture and structure of these rocks 

are primarily due to presence or absence of oriented bladed 

or acicular mafic phenocrysts embedded in a granular mafic 

groundmass. This has given rise to two megascopically 

distinguishable varieties of ultramafic rocks. The most 

commonly occurring one is massive ultramafic and other 

occasionally recorded one is spinifex (relict) textured 

ultramafic. Mineralogically these are composed of olivine 

(29-51 vol%), clinopyroxene (30-37 vol%), orthopyroxene 

(12-21 vol%) with magnetite ±spinel ± serpentine ± 

phlogopite ± sphene (Fig.2C and Fig.3C). The relative 

proportion of olivine and pyroxene varies widely giving rise 

to dominance of olivine over pyroxene at one place and the 

reverse relation at other place. Thus, mineralogically Semra 

ultramafic is lherzolite. At places spinel has also become an 

essential constituent. Presence of appreciable amount of 

sulphide minerals are noteworthy feature recorded at places, 

which are represented by pyrrhotite, pentlandite, 

chalcopyrite, pyrite and arsenopyrite. 

Spinifex texture on a polished rock slab (under the 

microscope) is defined by criss-cross fragmented olivine 

shelfs (Fig.2A, marked by two lines). The intersection of 

two elongated skeletal serpentinised olivine (black) defining 

microspinifex texture is reasonably perceptible in the 

microphotograph (Fig.2B) as a relict feature. In contrast, 

parallely aligned bladed / acicular fragmented skeletal 

olivine phenocrysts within an equigranular mosaic of augite 

and olivine with spinel and magnetite also defines microflow 

layer / line (Fig.3A). Occasionally near parallel 

orientation of euhedral clinopyroxene and orthopyroxene 

under the microscope also defines micro-flow layer / line 

Fig.2. (A) Polished rock slab image of Semra komatiite under the microscope showing crisscrossed relationship between elongated 

crystal of olivine defining the relict nature of spinifex texture, (B) Microphotograph of Semra komatiite exhibiting relict microspinifex 

texture defined by elongated skeletal serpentinised olivine (black), (C) Microphotograph documenting mineral composition 

and granular texture of Semra Komatiite defined by anhedral to subhedral olivine (OL), clinopyroxene (CPX) and spinel (SP) 

grains. Note the anhedral nature of olivine, and (D) Microphotograph of Semra komatiite exhibiting flow layer defined by 

euhedral prismatic olivine and pyroxene crystals under the microscope. 



Fig.3. (A) Microphotograph of Semra komatiite showing parallely oriented platy olivine defining micro-flow layer/line within olivineclinopyroxene-orthopyroxene-spinel 

ground mass, (B) Concentration of cumulates at places (left lower part) defines 

glomeroporphyritic texture in Semra komatiite under the microscope. Note the grain size differences. (C) Microphotograph 

exhibiting random orientation of euhedral clinopyroxene (CPX). Note orthopyroxene (OPX) is marginally encircled by spinel 

and opaque ores. (D) Anhedral olivine (OL) with typical reticulated cracks is being marginally penetrated by later growing 

clinopyroxene (CPX). Note the occasional presence of phlogopite (PH). 

(Fig.2D) .However mostly anhedral near equant crystal of 

olivine and augite defines intergranular texture (Fig.2C). 

Locally there is a development of glomeroporphyritic texture 

defined by subhedral olivine or pyroxene cumulates 

(Fig.3B). The euhedral to subhedral clinopyroxene grains 

at other places are randomly oriented (Fig.3C). 

Both olivine and pyroxene occur as phenocrysts as well 

as equigranular groundmass. Olivine crystals (altered to 

serpentine/antigorite in varying degree) are of various shapes 

and sizes. Olivine phenocrysts occur either as fragmented 

bladed / acicular skeletal olivine (Fig.3A) or as anhedral 

olivine phenocrysts (Fig.3D). However the olivine grains 

forming groundmass are mostly of anhedral habit (Fig.2C). 

Prominent serpentinisation along reticulated cracks of 

skeletal primary olivine (Fig.3D) within the granular mass 

of pyroxene and tremolite is an ubiquitous feature. Though 

pyroxene is represented by both clinopyroxene and 

orthopyroxene, the dominance of former one over the other 

is noticed. Spinel mostly occurs as subhedral to anhedral 

grains along intergranular space. The complete lack of 

plagioclase grains is a noticeable feature, denoting its 

formation beyond the stability field of this mineral. Presence 

of euhedral crystals of green spinel (pleonaste?) support 

this contention. Small grains of devitrified glass preferably 

occur along intergranular space. The orthopyroxene is 

marginally encircled by spinel and magnetite (Fig.3C). 

Anhedral olivine with reticulated cracks is marginally 

penetrated by lately grown clinopyroxene (Fig.3D). This 

interpenetrative relationship suggests that anhedral olivine 

started crystallizing prior to pyroxene. Again anhedral 

olivine is also found to be interpenetrating along cleavage 

traces of pyroxene (Fig.3D). These two divergent mutual 

relationships among olivine and pyroxene are possible 

only when crystallization of olivine continued even after 

pyroxene crystallization. This is further being corroborated 

by the presence of pyroxene inclusions in olivine. 



Pyroxene inclusion in spinel, clinopyroxene surrounded by 

spinel and occurrence of spinel and magnetite along 

intergranular spaces of pyroxene suggest that pyroxene has 

crystallised prior to spinel and magnetite. Thus the 

paragenetic sequence of crystallisation of Semra ultramafic 

is olivine- pyroxene spinel-magnetite (Fig.3C) with 

partial overlapping in crystallization history of constituent 

minerals. 

less magnesian volcanic rocks (Cattell and Taylor, 1990; 

Arndt et al. 2008). Such a high concentration of MgO and 

their variation of about 5 wt% in a restricted area are possibly 

attributable to different degree of olivine cumulate 

fractionation, which is very conspicuous even in thin section 

(Fig.3B). The investigated samples confine to Komatiite 

field in TAS diagram of Le Maitre et al. (1989, Fig.4A) and 

also in Na 2 

O + K 2 

O vs MgO diagram (Le Bas, 2000; 

Fig. 4B). Numbers of samples show distinctly higher MgO 

GEOCHEMISTRY 

Present work mainly deals with major and trace elements 

geochemistry of Semra ultramafic occurring within 

Chhotanagpur Gneissic Complex. Rare earth elements of 

three representative samples selected on basis of 

preservation of original texture and mineralogy, have also 

been taken into consideration for geochemical 

characterisation of Semra ultramafic rocks. Due care have 

been taken in selecting least altered samples for chemical 

analysis by detailed petrographic examination. Whole rock 

analyses of five representative samples were carried out by 

Philips-PW 1450/20 Sequential Automatic X-ray 

Fluorescence Spectrophotometer at Chemical Division, 

Eastern Region, Geological Survey of India, Kolkata. Three 

other samples were analysed at Research and Development 

Centre for Iron and Steel, Ranchi by Perkin Elmer model 

ELAN ICP-MS. Trace elements analyses of first five 

samples were carried out by AAS (Varian model 1475) 

installed at Institute of Minerals and Materials Technology, 

Bhubaneswar. Values of Fe 2 

O 3 

(total) obtained from XRF 

have been cross checked by determining the amount of Fe 2 

O 3 

and FeO by classical methods. LOI was determined by 

heating powdered sample for 2 hours at 900°C. Precisions 

of analyses of major, trace and REE from all the laboratories 

are of comparable accuracy as checked by running 

international standard samples and these are within the error 

limit of ±5% in all cases. Normative composition (Table 1) 

was calculated by using SINCLAS software (Verma et al. 

2002). The analytical data are presented in Tables 1-3. 

These also includes data of known komatiitic ultramafic 

of Eastern Indian Shield along with other well known 

Komatiites of Indian, Canadian, Australian and 

African Shield areas for a comparative evaluation and 

characterisation of Semra ultramafic rocks. 

Semra ultramafics are typically characterised by high 

MgO content ranging from 24.48 to 29.90 wt% (Table 1) 

with an average of 26.90 wt% (n=8). All the samples 

(excepting one with 24.48 wt%) contain more than 25 wt% 

MgO. This is characteristically much above the limit of 

18 wt% MgO at which komatiites are distinguished from 

Fig.4. (A) Semra ultramafic (open square) plotted in TAS diagram 

(after Le Maitre et al. 1989) which are compared with 

average komatiite (open triangle) (after Cattle and Taylor, 

1990) and Kunchia ultrabasics (open circle) of Singhbhum 

(Das et al. 2001). (B) Plot of spinifex texture Semra 

ultramafic (Open square) in total alkalis vs MgO diagram 

showing the classification fields proposed for high-Mg 

rocks by the IUGS sub commission (Le Bas, 2000, Kerr 

and Arndt, 2001). Spinifex-textured komatiites from 

Gorgona (filled rectangle) are plotted for a comparison. 

(Data sources: Echeverria (1980); Kerr et al. (1996); Arndt 

et al. (1997). 



Table 1. Major oxide and normative composition of Semra ultramafic from Chhotanagpur Gneiss Granulite Complex and other occurrences of Komatiite 

Averages of STPK from Different Shields # 

Sample No. DB 10 

DB 3 

DB 12 

DB 15 

DB 18 

DB 8 

DB 6 

DB 5 

Av. Km 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 

SiO 2 

35.84 34.87 40.65 37.1 35.6 30.2 27.5 28.2 43.56 47.4 49.2 45.6 46.8 45.9 47.2 45.2 47.17 

TiO 2 

0.40 0.41 0.45 0.39 0.32 0.37 0.48 0.33 0.69 0.46 0.43 0.4 0.33 0.41 0.38 0.28 0.5 

Al 2 

O 3 

7.98 7.67 8.58 7.05 6.68 8.4 7.94 8.04 8.17 6.76 3.76 7.95 3.42 7.97 4.09 5.7 7.58 

Fe 2 

O 3 

(T) 13.06 13.07 11.2 9.9 12.66 18 17.3 20.5 11.53 12.2 11 14.07* 12.51* 12.30* 13.35* 11.7 12.78* 

MnO 0.27 0.23 0.14 0.16 0.18 0.24 0.15 0.17 0.17 0.19 0.17 0.2 0.19 0.21 0.2 0.21 0.25 

MgO 25.56 27.72 24.48 25.4 29.9 25.1 28 29.1 21.85 20.4 20 25 31.5 26.4 28 30.9 21.70 

CaO 10.77 9.50 7.19 9.3 6.6 5.95 8.68 5.88 7.46 8.31 9.31 7.6 5.67 7.74 6.61 5.6 9.22 

Na 2 

O 0.32 0.09 0.13 0.07 0.14 0.32 0.27 0.21 0.61 0.39 0.1 0.01 0.12 0.43 0.37 0.43 0.19 

K 2 

O 0.01 0.52 0.02 0.03 0.02 0.23 0.11 0.17 0.08 0.06 0.02 0.02 0.08 0.09 0.04 0.02 0.14 

P 2 

O 5 

0.07 0.06 0.02 0.08 0.05 0.36 0.21 0.22 0.10 0.02 0.03 

LOI 6.02 6.70 7.04 9.4 8.22 10 9.02 8.04 5.71 6.38 

Total 100.30 100.84 99.90 98.8 100.4 99.2 99.7 101 99.93 96.1 94 86.8 88.1 89.1 86.8 106 86.78 

Orthoclase — — 0.13 — — — — — 

Albite — — 1.19 — — — — — 

Anorthite 21.78 20.40 24.75 21.26 19.35 23.73 22.56 22.47 

Leucite 0.05 — — 0.16 0.10 — — — 

Nepheline 1.57 0.45 — 0.36 0.61 1.67 1.39 1.05 

Diopside 2.02 — 11.01 18.37 2.27 — — — 

Hypersthene — — 18.59 — — — — — 

Olivine 59.27 63.98 39.38 53.23 68.62 68.47 72.43 76.47 

Ilmenite 0.82 0.87 0.93 0.84 0.67 0.82 1.02 0.69 

Magnetite 4.25 4.31 3.97 3.40 4.13 5.72 5.01 5.91 

Apatite 0.17 0.15 0.05 0.21 0.13 0.95 0.54 0.56 

Sum 89.94 90.11 100 97.82 95.86 101.36 102.95 107.15 

* = Total iron converted as Fe 2 

O 3 

(T) 

Present Data:1 to 8 for Ultramafics of Semra, Palamau District, # 9 = Kunchia 

Ultrabasics, East Singhbhum District. (Das et al. 2001), 10 = Average Highalumina 

Geluk type komatiite. (Gupta et al. 1980), 11 = Average low-alumina 

Geluk type komatiite. (Viljoen and Viljoen, 1969), 12 = Al-undepleted komatiite 

from Munro Township, Ontario. (Arndt and Nesbitt, 1984), 13 = Al-depleted 

komatiite from Barberton, South Africa. (Smith and Erlank, 1982), 14 = Average 

of 22 Al-undepleted komatiites. (Nesbitt et al. 1979; Arndt and Nesbitt, 1984; 

Cattell and Arndt, 1987; Nisbet et al. 1987), 15 = Average of 18 Al-depleted 

komatiites. (Nesbitt et al. 1979; Smith and Erlank, 1982), 16 = Average of 7 

STP from Yilgarn Block, Australia. (Nesbitt and Sun, 1976), 17 = Komatiite 

(2.7 Ga), Newton township, Canada (Cattell and Taylor, 1990). 

Table 2. Trace element composition and ratios of Semra ultramafic from Chhotanagpur Gneissic Complex and other occurrences of Komatiite 

Sample No. DB 10 

DB 3 

DB 12 

DB 15 

DB 18 

DB 8 

DB 6 

DB 5 

Averages of STPK from Different Shields# Av.Km CI 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Chondrite 

Cr 3000 2800 3300 3400 3195 3364 3192 3092 2075 

Ni 1650 1520 850 750 1725 1810 1625 1587 1406 

V 120 115 167 181 135 210 200 230 186 

Sc 21.9 24.6 21.6 24.7 21.9 23.08 22.1 24.8 

Sr 10 16 12 9 30 12.2 7.19 13.1 29 7.26 

Ba 2 3 4 3 5 4.5 2.9 3.84 1 2.41 

Rb 3 4 1 2 5 3.79 2.45 3.6 4 2.32 

Cs 0.279 0.36 0.365 0.281 0.275 0.372 0.37 0.36 

Zr 31.5 35.2 34.8 36.4 33.3 37.2 33.1 36.5 28 3.87 

Hf 0.749 0.73 0.735 0.739 0.75 0.73 0.73 0.75 0.107 

Nb 1 3 2 1 1 0.425 0.42 0.41 2 0.246 

Y 9 11 10 12 14 9.95 12 12.1 10 1.57 

P 30.55 26.2 8.73 34.91 21.82 157.1 91.6 96 43.6 445 

Ti 239.8 246 269.78 233.8 191.8 221.8 288 198 414 276 258 239.8 197.8 245.8 228 167.86 299.75 

RATIOS 

CaO/Al 2 

O 3 

1.35 1.24 0.84 1.32 0.99 0.71 1.09 0.73 0.91 1.23 2.48 0.96 1.66 0.97 1.62 0.98 1.22 0.79 

CaO/TiO 2 

26.93 23.2 15.98 23.85 20.63 16.08 18.1 17.8 10.8 18.1 21.7 19 17.18 18.88 17.4 20 18.44 17.45 

Al 2 

O 3 

/TiO 2 

19.95 18.7 19.07 18.08 20.88 22.7 22.7 22.7 11.8 14.7 8.74 19.88 10.36 19.43 10.8 20.36 15.16 22 

MgO/TiO 2 

63.9 67.6 54.4 65 93.44 67.78 58.3 88.2 31.7 44.3 46.6 62.5 95.48 64.34 73.6 110.5 43.4 220.27 

MgO/Al 2 

O 3 

3.2 3.61 2.85 3.6 4.48 2.99 3.52 3.62 2.67 3.02 5.33 3.14 9.21 3.31 6.84 5.43 2.86 10.01 

Fe 2 

O 3 

T/TiO 2 

32.65 31.9 24.88 25.38 39.56 48.73 36.1 62.2 16.7 26.4 25.6 35.18 37.91 30 35.1 41.71 25.56 365.73 

Ti/Zr 7.61 6.98 7.75 6.42 5.76 5.96 8.7 5.42 110 100 114.99 

V/Zr 3.81 3.27 4.8 4.97 4.05 5.65 6.05 6.3 

Zr/Y 3.5 3.2 3.48 3.03 2.38 3.74 2.77 3.03 2.5 2.8 to 2.47 

4.6 

Ti/Y 26.64 22.4 26.98 19.48 13.7 22.29 24.1 16.4 283.44 

Zr/Nb 31.5 11.7 17.4 36.4 33.3 87.53 78 89.9 0.44 

Zr/Sm 25.66 24.5 26.3 

Hf/Nd 0.218 0.21 0.2 

(La/Yb) n 

0.822 0.74 1.07 

(La/Sm) n 

0.525 0.41 0.56 

(Gd/Yb) 

n 

1.542 1.74 1.96 

(Nd/Sm) n 

0.757 0.85 0.87 

Mg. No. 82.02 83.2 83.59 85.65 84.63 76.43 79 76.8 77.9 83.3 80.9 80.6 75.3 

Mg# = (MgO/40.13)/(MgO/40.13)+Fe 2 

O 3 

T*0.8998/71.85*(1-0.15)*100 (After Zhou & Li, 2006) . # Samples and other details as in Table 1 



Table 3. Rare earth element concentration of Semra ultramafics from 

Chhotanagpur gneissic complex 

Sample No. DB8 DB6 DB5 Chondrite* 

La 1.18 0.855 1.2 0.237 

Ce 3.2 2.17 3.17 0.613 

Pr 0.629 0.54 0.601 0.093 

Nd 3.35 3.52 3.71 0.457 

Sm 1.45 1.35 1.39 0.148 

Eu 0.469 0.461 0.532 0.056 

Gd 1.92 1.75 1.9 0.199 

Tb 0.415 0.321 0.327 0.036 

Dy 1.89 1.86 1.93 0.246 

Ho 0.388 0.365 0.381 0.055 

Er 1.15 1.01 1.07 0.160 

Tm 0.161 0.128 0.125 0.025 

Yb 1.03 0.83 0.802 0.161 

Lu 0.122 0.115 0.157 0.025 

ΣREE 17.354 15.275 17.295 2.511 

ΣLREE 8.359 7.085 8.681 1.411 

ΣHREE 2.463 2.083 2.154 0.3864 

*McDonough, W.F. and Sun, S.S. (1995) 

concentration at the same level of Na 2 

O + K 2 

O. The Semra 

ultramafics plots exclusively in komatiite field in Jensen’s 

(1976) Al–(Fe+Ti)–Mg cation discrimination diagram 

(Fig.5A) and also in Kulikov’s TiO 2 

*10-Al 2 

O 3 

-MgO 

discriminate diagram (Fig.5B) for classification of ultramafic 

series of rocks. In the CaO–MgO–Al 2 

O 3 

ternary diagram 

(Fig.5C), the Semra ultramafics fall in the peridotitic 

komatiite field (after Arndt et al. 1977). When these samples 

are compared with Barbarton (BR) type, Geluk (GL) type 

and Badplass (BD) type komatiites (all fields after Viljoen 

and Viljoen, 1969), the samples mostly show resemblance 

with Geluk komatiite (Fig.5C). With respect to average 

komatiite (Cattle and Taylor, 1990) and Kunchia ultrabasics 

of Singhbhum (Das et al. 2001), the Semra ultramafic is 

very much distinctive by their lower SiO 2 

content (Fig.4A). 

The Semra ultramafics are distinctly characterised by higher 

MgO (Fig.4B) with respect to Spinifex-textured Cretaceous 

komatiites from Gorgona (Echeverria, 1980; Kerr et al. 

1996; Arndt et al. 1997). 

Petrologically most important element in komatiites is 

aluminum and variations of Al 2 

O 3 

/TiO 2 

or CaO/Al 2 

O 3 

form 

important factors of all komatiite classifications (Arndt et 

al. 2008). Al 2 

O 3 

content of Semra ultramafics vary between 

6.68 to 8.58 wt% (Table 1, Av. 7.79 wt%). The Al 2 

O 3 

/TiO 2 

ratio of Semra ultramafics varies from 16.54 to 24.36 wt% 

(Table 2, Av.20.04 wt %) showing similarity with accepted 

chondritic value (Al 2 

O 3 

/TiO 2 

= 20.4 Schmus and Hayes, 

1974); with “Munro type” Komatiites (Fan and Kerrich, 

1997) and also with Al-undepleted komatiites of late- 

Fig.5. (A) Jensen’s (1976) (Fe+Ti)-Mg-Al cation discriminate plot 

of Semra ultramafics (Open square). (B) Semra ultramafics 

(Open square) plotted in TiO 2 

*10- Al 2 

O 3 

–MgO 

discriminate diagram (after Kulikov) for classifying 

Ultramafic rocks. (C) CaO–MgO–Al 2 

O 3 

diagram (after 

Arndt, Naldrett and Pyke, 1977) for Semra ultramafic (Open 

Square) showing fields of Barbarton (BR) type, Geluk (GL) 

type and Badplass (BD) type komatiites (after Viljoen and 

Viljoen, 1969) and peridotitic (I), pyroxenitic (II), basaltic 

(III) komatiite and tholeiites (IV) (after Arndt et al. 1977) 

are shown. 



Archaean (~2.7 Ga) Abitibi greenstone belt (Fan and 

Kerrich, op. cit.). This is in marked contrast with Barberton 

komatiite having Al 2 

O 3 

/TiO 2 

ratios of about 11 (Nesbitt et 

al 1979). Most other komatiites are characterised by Al 2 

O 3 

/ 

TiO 2 

ratio around 20 (a value close to the chondrite value). 

Al 2 

O 3 

vs TiO 2 

binary plot (Fig,6A) shows that Semra 

ultramafics generally scatter about the chondritic line and 

show resemblance with Archaean Al-undepleted ultramafic 

of Sandur greenstone belt of Karnataka (Naqvi et al. 2002) 

and distinct from Al-depleted ultramafic (Naqvi et al. op. 

cit.). Semra ultramafics show a distinct similarity with 

Al-undepleted ultramafic of Sandur greenstone belt of 

Karnataka (Naqvi et al. Op.cit.), particularly in terms of 

MgO vs Al 2 

O 3 

plot (Fig.6E). Similar behaviour is also 

shown by the mobile CaO (Fig.6C) and immobile TiO 2 

(Fig.6F). 

According to Brooks and Hart (1974), the komatiites 

must have CaO/Al 2 

O 3 

ratios greater than one and that the 

low TiO 2 

content be emphasised. But Nesbitt et al (1979) is 

of the opinion that parameters such as Ca/Al and TiO 2 

content should not be the prime factors used in the 

identification of peridotitic komatiite (PK), rather the high 

ratio should be close to or greater than one (Arndt et al, 

1977; Nesbitt et al, 1979).The CaO/Al 2 

O 3 

ratio of Semra 

ultramafics varies from 0.71 to 1.35 wt% (Table 2, Av.1.03 

wt%), which is comparable with average Munro Township 

spinifex textured komatiite (Arndt et al. 1977), average 

Komatiite (2.7 Ga) of Newton Township, Canada (Cattle 

and Taylor, 1990), and also average High-alumina Geluk 

type komatiite (Gupta et al. 1980). In terms of CaO/Al 2 

O 3 

ratio, the Semra ultramafic shows similarity only with 

Kunchia ultrabasic of Singhbhum district (Das et al. 2001), 

whereas most of the komatiite of Singhbhum (Ray, 1984; 

Bhattacharya et al. 1996) and Mayurbhanj (Sahu and 

Mukherjee, 2001) districts of Eastern India Shield distinctly 

show higher CaO/Al 2 

O 3 

ratio in comparison to Semra 

ultramafic. The CaO/TiO 2 

ratio ranging from 15.98 to 26.93 

wt% (Table 2, Av. 20.32,) of these rocks is well comparable 

with the chondritic value. In the CaO vs TiO 2 

diagram, Semra 

ultramafics (Fig.6B), plot mostly along chondrite line with 

variation in their ratio and it shows resemblance with Munro 

and Geluk komatiite. 

All the investigated samples fall close to the olivine 

fractionation line as defined in MgO vs Al 2 

O 3 

plot (Fig.6E) 

indicating their komatiitic affinities and also shows their 

similarities with Archaean Alumina-undepleted Komatiite 

(AUDK) of Sandur Schist Belt (cf. Naqvi et al. 2002) and 

also with Munro komatiite (Nesbitt et al. 1979). MgO vs 

Fe 2 

O 3 

binary plot of Semra ultramafic (Fig.6D) shows wide 

variation of Fe 2 

O 3 

in the same range of MgO. MgO vs Fe 2 

O 3 

and MgO vs TiO 2 

binary plot of Semra ultramafic (Fig.6D 

and 6F) do not show any distinctive relationship with 

Archaean komatiite of Greenstone belt of Karnataka (Naqvi 

et al. 2002). 

These rocks display high Mg# varying from 76.43 to 

85.65 (Table 1), comparable to primitive upper mantle Mg# 

(89.8), suggesting their mantle derived source. This high 

Mg# suggests the rock to be of Archaean komatiite in 

composition (Glikson, 1983). High normative olivine (Avg. 

62.73, ranging from 39.38 to 76.47, Table 1) indicate that 

these rocks have experienced crystal fractionation as 

reflected by the presence of olivine cumulates at places 

(Fig.3C). 

The extremely low K 2 

O content (0.01 to 0.17 wt% with 

one exotic value of 0.52 wt %) of these ultramafics appear 

to be of primary nature (Das et al. 2001). The rock has 

distinctly low value of SiO 2 

in comparison to many well 

known komatiites of the world and may represent plume 

related magmatism for its generation (Parman, 2001). 

Majority of the samples are characterised by typically high 

LOI values, possibly attributable to alteration/hydration of 

olivine and clinopyroxene into hydrous secondary phases 

viz serpentine and also due to presence of amphiboles. 

In terms of Al 2 

O 3 

/TiO 2 

ratio vs CaO/Al 2 

O 3 

ratio (Fig.7A), 

the Semra ultramafics are comparable to well known 

komatiites from different shields (Nesbitt et al. 1979) like 

Munro, Geluk and Scotia, Yakabindie, Burges komatiite. 

However these are distinctly differentiable from Barberton 

komatiite (Nesbitt et al. op.cit.) and Cretaceous komatiite 

of Gorgona Island, Colombia (Echeverria, 1980; Fig.7A). 

In the same variation diagram, the Semra ultramafics plots 

near the estimated source composition for Early Archaean 

to Late Archaean Komatiites (cf. Fig.6 of Walter, 1998) 

illustrating that this komatiite is akin to the estimated source 

composition for Early Archaean to Late Archaean Komatiites 

and distinctly different chemical signature with respect to 

the estimated source composition for Cretaceous Komatiites 

(Walter, 1998.).The CaO/TiO 2 

vs Al 2 

O 3 

/TiO 2 

variation 

diagrams of Semra ultramafic (Fig.7B) illustrates its 

similarities with Munro komatiite (Arndt et al. 1977; Nesbitt 

et al. 1979). The intersection of chondrite values for these 

element pairs are marked by the cross at centre (Fig.7B). 

The major oxide ratios like MgO/TiO 2 

, MgO/Al 2 

O 3 

and 

Fe 2 

O 3 

/TiO 2 

(Table 2) show near similarity with Munro type 

Komatiite. 

The Semra ultramafics are characterised by very high 

values of Ni (750 – 1810 ppm) and Cr (2800-3400 ppm) 

within the same level of MgO as in Sandur Komatiite of 

Karnataka, reflecting olivine + pyroxene fractionation. This 

is also being reflected in MgO vs Al 2 

O 3 

and TiO 2 

variation 



Fig.6. (A) Al 2 

O 3 

vs TiO 2 

variation diagram illustrating the position of Semra ultramafic (open square) relative to chondrite line, 

Archaean Al-depleted ultramafic (open circle) and Al-undepleted ultramafic (open triangle) of Sandur greenstone belt of Karnataka 

(Naqvi et al. 2002), Munro (inverted triangle) and Geluk (closed circle) komatiite (after Nesbitt et al. 1979). (B) CaO vs TiO 2 

variation diagram demonstrates the position of Semra ultramafic (open square) in relation to chondrite line and Munro (inverted 

triangle) and Geluk (open circle) komatiite. (C) MgO vs CaO variation diagram showing the variation of Cao at same level of 

MgO in Semra ultramafic (open square) (D) MgO vs Fe 2 

O 3 

variation diagram exhibiting the position of Semra ultramafic (open 

square) relative to Archaean Al-depleted ultramafic (open circle) and Al-undepleted ultramafic (closed triangle) of Sandur greenstone 

belt of Karnataka (Naqvi et al. 2002). (E) MgO vs Al 2 

O 3 

variation diagram illustrating the position of Semra ultramafic (open 

square) in relation to olivine fractionation line (dotted line) and their relationship with typical Archaean Al-depleted (open 

circle) and Al-undepleted (closed triangle) komatiitic ultramafic schist of Sandur Greenstone belt (Naqvi et al. 2002). Munro and 

Barbarton lines are after Nesbitt, Sun and Purvis (1979). (F) MgO vs TiO 2 

variation diagram demonstrating the position of 

Semra ultramafic (open square) in relation to typical Archaean Al-depleted (open circle) and Al-undepleted (closed triangle) 

komatiitic ultramafic schist of Sandur Greenstone belt (Naqvi et al. 2002). 



Fig.7. (A) Al 2 

O 3 

/TiO 2 

vs CaO/Al 2 

O 3 

variation diagram of Semra ultramafics (open square) with respect to other well known komatiites 

of different shields (after Nesbitt et al.1979). The position of Semra ultramafics are examined with reference to the estimated 

source composition for Early Archaean, Late Archaean and Cretaceous Komatiites (Walter, 1998). (B) CaO/TiO 2 

vs Al 2 

O 3 

/TiO 2 

variation diagrams indicates the position of Semra ultramafic (open square) in relation to Munro komatiite after Arndt et al. 

(1977) (open circle) and after Nesbitt et al. (1979) (closed circle). The cross represents the intersection of chondrite values for 

these element pairs. (C) MgO vs. Zr variation diagrams illustrates the distinctly high and uniform Zr concentration in the Semra 

ultramafic (open square) relative to typical Archaean Al-depleted (open circle) and Al-undepleted (closed triangle) komatiitic 

ultramafic schist of Sandur Greenstone belt (Naqvi et al. 2002). (D) MgO vs. Ni variation diagram exhibits the spread of Ni 

(shown by dashed line) in the same range of MgO. (E) MgO vs Nb variation diagrams shows the Nb concentration in the Semra 

ultramafic (open square) is well comparable to typical Archaean Al-undepleted (closed triangle) komatiitic ultramafic schist and 

not Al-depleted (open circle) one of Sandur Greenstone belt (Naqvi et al. 2002). (F) Chondrite normalized REE profile for Semra 

STPK (Normalisation factor after McDoungh and Sun,1995). 



diagrams (Fig.6E, 6F). Ni concentrations is one of the factors 

attributed to the magmatic processes related with the mantle 

plumes (Condie, 1997a,b; Kerrich et al. 1999a, b) due to 

their immobile nature. The spread of Ni in the same range 

of MgO is demonstrated in MgO vs. Ni variation diagrams 

(Fig.7D). Enrichment of Ni and Cr may have resulted in 

liquidus phases during magmatic evolution. 

Zr concentration is an important indicator of magmatic 

processes, which is fairly correlatable with immobile 

elements such as Al 2 

O 3, 

TiO 2 

, Ni and Cr. Irrespective of their 

MgO content, Zr in Semra ultramafic remains considerably 

high (31.5 – 37.2 ppm, Table 2, Fig.7C) relative to typical 

Archaean Al-depleted and Al-undepleted komatiitic 

ultramafic schist of Sandur Greenstone belt (Naqvi et al. 

2002) and also in comparison to Munro komatiite and 

Western Australia komatiite (Nesbitt et al. 1979). The Ti/Zr 

(average 6.79, ranging 5.42 to 8.7, Table 2) and Ti/Y 

(average 20.98, ranging 13.7 to 26.98, with Table 2) of Semra 

ultramafics are abnormally low to very low in comparisons 

to Chondrite ratios (Ti/Zr=100-110 and Ti/Y~ 256, Wänke 

et al. 1974). The “primitive” liquid generated by extensive 

melting of the mantle is likely to have a Ti/Zr ratio close to 

100-110. The Ti/Zr ratio is a valuable indicator ranging from 

122 to 97 for the Spinifex Texture Peridotitic Komatiite 

(STPK). In this respect, the Semra ultramafic shows a 

pronounced deviation and such high Zr concentration and 

abnormally low Ti/Zr is possibly attributable Zr-enriched 

mantle source with very little Ti content. Low concentration 

of Ba and Sr suggest that these rocks were not affected by 

crustal contamination The variation of Nb with respect to 

MgO (Fig.7E) in the Semra ultramafic is also comparable 

to typical Archaean Al-undepleted komatiitic ultramafic 

schist of Sandur Greenstone belt (Naqvi et al., 2002). These 

ultramafic rocks are depleted in Cs, Rb, Ba, Sr, Nb, Hf and 

Y. Depleted incompatible trace elements point towards Alundepleted 

nature for the komatiites of the study area (Nna 

Mvondo and Frias, 2005). 

Komatiites of the present area are characterised by a 

diagnostic convex upward REE profile (Fig.7F) in chondrite 

normalized diagram (normalization factor after McDonough 

and Sun, 1995). The chondrite normalized REE pattern 

display LREE depletion compared to HREE, which is similar 

to most of the other Arachean komatiites (Mitra and Bose, 

2007). Depleted LREE signifies least crustal contamination 

(Gupta, 2007).The unfractionated HREE ranging from 2.083 

to 2.463 exhibits flat HREE pattern. HREE is at 5.39 to 

6.37 times chondritic abundances. Total REEs ranging from 

15.275 to 17.354 (Table 2), is 5.96 to 6.77 times the 

chondrite. LREE contents (7.085 to 8.681, Table 3) are 

seven to eight times more than chondrite. Zr/Sm (25.5) and 

Hf/Nd (0.21) ratios (Table 2) are comparable to primitive 

mantle (25 and 0.23 respectively, Sun and McDonough, 

1989). The chondrite normalized value of (La/Yb) n 

( 0.74 

to 1.07, Table 2)) is in conformity with other komatiites 

including Barberton. Lower values of interelemental ratios 

like V/Zr (Avg. 4.88), Ti/Y (Avg. 20.98) and Zr/Nb (Avg. 

30.02) and higher Zr/Y (Avg. 3.09) in comparison to 

chondrite (Table 2), rules out the possibility of greater degree 

of partial melting (Smith and Erlank, 1982).There is a 

positive correlation of MgO with (Gd/Yb)n (1.75±0.21) 

ranging from 1.54 to 1.96 (Table 2). Such increase in 

(Gd/Yb) n 

(>1) is similar to Palaeoproterozoic Jeesiörova 

komatiites of Kittilä greenstone belt (Gangopadhyay 

et al. 2006) and also to Archaean Sandur greenstone belt 

(Naqvi et al. 2002). 

CONCLUSION 

Semra Komatiite is spatially located in proximity to Son- 

Narmada South Fault (SNSF) at north and Balarampur- 

Tattapani Fault (BTF) to the south (Fig.1; cf. Fig.2 of 

Acharyya and Roy, 2000; Mukherjee, 1998). Regionally the 

eastern continuation of SNSF is locally referred as Nagar 

Untari (68P/7) - Chhatarpur (72D/3) Shear zone, which is 

exactly 38 Kms north of the study area. Furthermore, the 

Garhwa-Daltonganj Gondwana basin (GDGB) and Auranga- 

Koel Gondwana basin (AKGB) (Fig.1) are located 

immediately adjoining north and south of Semra respectively 

and these are characterised by number of basin margin faults 

and transverse faults. The easterly strikes of the basin 

boundary fault (Fig.1) coincide with the general strike of 

the Precambrian basement rock. Some of these basin 

boundary faults continue for more than 80 km across the 

intervening Precambrian basement (Chatterjee and Ghosh, 

1970), signifying that these major faults are pre-Gondwana 

precursor faults (Dutta and Mitra, 1984; quoted by 

Sarkar, 1988, p.132). Precambrian ancestry of these faults 

may have provided broad tectonised basement framework 

(Mahadevan, 2002, p.374).The pattern of the intrabasinal 

faults and basin-bounding faults represent both 

extensional and strike-slip regimes in the Precambrian 

basement leading to the development of Gondwana basins 

along the E-W direction (Mukherjee and Ghose, 1999; 

Chakraborty et al. 2003, Srivasatava et al. 2009). The role 

of extensional tectonics in the development of Gondwana 

basins formation is often attributed to epiorogenic procesess 

and to deep crust-mantle interactions (Chatterjee and 

Ghose, 1970; Niyogi, 1987). Lamprophyric/lamproite within 

the Gondwana basins are essentially fault controlled 

(Mukherjee and Ghose, 1999) which are the manifestation 



of plume generated magmatism. This together with 

intracratonic rift related origin of Son-Narmada Graben 

witnessing mantle upwelling (Das and Patel, 1984; Shankar, 

1991) mark major extensional tectonic regime. The 

widespread mafic-ultramafic magmatism in the CGC mostly 

occurs in proximity to number of major intra-continental 

rift/shear zones, suggesting their emplacement under 

extensional tectonism witnessed by this part of CGC 

(Mukherjee and Ghose, 1999). The spatial disposition of 

Semra ultramafics with reference to regional tectonic 

setting and the distinctive cumulus nature suggest their 

emplacement in an extensional phase, thereby playing 

an important role in crustal growth and evolution of 

CGC. 

Semra Komatiite is the only of its kind in CGC, though 

there are a few known occurrences of komatiite in 

Singhbhum Group of rocks at south of CGC (Das et al. 2001; 

Roy et al. 2002; Mitra and Bose, 2007). The elongated 

lensoid bodies of peridotitic Komatiite of Semra occur within 

tremolite actinolite schist of ultramafic parentage and are 

composed of olivine, clinopyroxene, orthopyroxene with 

magnetite ± spinel ± serpentine ± phlogopite ± sphene. 

Mineralogically Semra ultramafic is lehrzolite in 

composition and the paragenetic sequence of crystallization 

of Semra ultramafic is olivine-pyroxene-spinel-magnetite. 

Prominent serpentinisation along reticulated cracks of 

skeletal primary olivine within the granular mass of pyroxene 

is an ubiquitous feature. Criss-cross fragmented olivine 

shelves (Fig.2A) on a polished rock slab (under the 

microscope) and the microphotograph showing intersection 

of two skeletal acicular olivine grains (Fig.2B) defining the 

microspinifex texture is recognized as relict feature. This 

spinifex texture is being interpreted as indicative of in situ 

rapid cooling of a crystal-free ultramafic liquid. Locally 

accumulation of cumulates has given rise to glomeroporphyritic 

texture. The characteristic petrographic 

features, like cumuluse texture and lack of visible 

deformation suggest original magmatic crystallization of 

these ultramafic rocks. 

Chemically, the Semra ultramafics are characterised by 

distinctly high MgO, Ni, Cr and poor in alkali, TiO 2 

, Ba, 

Cs, Rb, Nb, Hf and Y contents. Based on MgO content, the 

rock is peridotitic komatiite as per the three fold 

classification of Arndt et al. (1977). High normative olivine 

(42.56 to 75.91, Table 2) indicate that these rocks have 

experienced crystal fractionation which is evident from the 

presence of olivine cumulates at places (Fig.3B). The 

relatively high Mg# (76.43 to 85.65), Cr and Ni (Table 2), 

also suggest that the Semra ultramafics are of cumulate 

origin. Hence the high concentration of MgO and their 

variation of about 5 wt% in a restricted area may be attributed 

to different degree of olivine cumulate fractionation. Low 

abundance of incompatible elements, depleted LREE 

[(La/Yb) n 

= 0.74 – 1.07] and enriched HREE with flat profile 

represent chondrite like compositional characteristics. All 

these together with relict, but distinct spinifex texture 

confirm the komatiitic character of Semra ultramafic. The 

Semra ultramafic do plots exclusively in komatiite field of 

various discriminate diagrams using various geochemical 

parameters (Fig: 4a, 4b, 5a, 5b and 5c). Immobile elements 

plot on olivine control lines in variation diagrams (Arndt, 

1994) indicate their komatiitic affinities. Thus Semra 

ultramafic satisfies all the IUGS chemical and textural 

criteria to qualify as Komatiites. The CaO/TiO 2 

ratio ranging 

from 15.98 to 26.93 wt% (Av. 20.32, Table 3) of these rocks 

is well comparable with the chondrite value. All the 

investigated samples fall close to the olivine fractionation 

line as defined in Al 2 

O 3 

– MgO plot (Fig.i) indicating their 

komatiitic affinities. The extremely low K 2 

O content (0.01 

to 0.17 Wt % with one exotic value of 0.52 wt%) of these 

ultramafics appear to be a primary feature. These ultramafics 

has distinctly low SiO 2 

content in comparison to many well 

known komatiites of the world and may represent plume 

related magmatism for its generation (Parman, 2001). Low 

SiO 2 

content of the sample match with the plume scenario 

as SiO 2 

content of the magma generally decrease as the 

pressure of melting increases (Nna-Mvondo and Frias, 

2005). The high MgO and low TiO 2 

and SiO 2 

contents in 

the Semra ultramafics are regarded as the result of primary 

partial melting of the mantle (Nesbitt and Sun, 1976). 

The Al 2 

O 3 

/TiO 2 

ratio of Semra ultramafics (Av. 

20.04 wt%).) show similarity with “Munro type” komatiites 

characterised by Al 2 

O 3 

/TiO 2 

ratio around 20, which is 

consistent with most other komatiites having the ratio 

close to chondrite (about 20) (Nesbitt et al. 1979). The 

CaO/Al 2 

O 3 

ratio variying from 0.71 to 1.35 wt% (Table 2, 

Av.1.03 wt%), is well comparable with Munro type 

komatiites (~1.1 to 1.6), average Komatiite (2.7 Ga) of 

Newton Township, Canada (Cattle and Taylor, 1990) and 

average High-alumina Geluk type komatiite (Gupta et al. 

1980). In terms of CaO/Al 2 

O 3 

ratio, the Semra ultramafic 

shows similarity only with Kunchia ultrabasic of 

Singhbhum district (Das et al., 2001). 

Enrichment of Ni and Cr may have resulted in liquidus 

phases during magmatic evolution. The Mg # (>74) of the 

Semra ultramafics are comparable to primitive upper mantle 

Mg# (89.8) and high enough for rocks derived from ultramagnesian 

liquid of the mantle derived source. Considerably 

high Zr concentration in Semra ultramafic is attributed to 

Zr-enriched mantle source and not due to crustal 



contamination. Depleted incompatible trace elements point 

towards Al-undepleted nature for the komatiites of the study 

area (Nna-Mvondo and Martinez-Frias, 2005). 

Different geochemical types of komatiites can be 

distinguished using Al 2 

O 3 

/TiO 2 

and rare earth elements (Jahn 

et al. 1982; Nesbitt et al. 1982; Sun and Nesbitt, 1978). 

Nesbitt and Sun (1976), Sun and Nesbitt (1978) and Nesbitt 

et al. (1979) classified the komatiites into two groups: Aldepleted 

(Barberton type) komatiites with relatively low 

Al 2 

O 3 

/TiO 2 

ratio and depleted HREE and Al-undepleted 

(Munro type) komatiites with near chondritic Al 2 

O 3 

/TiO 2 

ratio, Gd/Yb ratio and flat HREE. Jahn et al. (1982) 

recognised a third types a complement of the Al-depleted 

komatiites with high Al 2 

O 3 

/TiO 2 

ratio and relatively enriched 

HREE. With reference to these criteria, the Semra komatiite 

shows their similarities with Archaean Alumina-undepleted 

Komatiite (AUDK), as it is characterised by Al 2 

O 3 

content 

(6.68 to 8.58 wt% with Av. 7.79 wt% Table 1), near Al 2 

O 3 

/ 

TiO 2 

(Semra=Avg. 20.60, accepted chondritic value =20.4 

Schmus and Hayes, 1974) and flat unfractionated HREEs 

pattern. The diagnostic convex upward REE profile exhibits 

LREE depletion compared to HREE, which is similar to 

most of the other Archaean komatiites (Mitra and Bose, 

2007). Depleted LREE signifies least crustal contamination 

(Gupta, 2007). HREE is at 5.39 to 6.37 times more than 

chondritic abundances. Such enrichment in HREE and 

increase in (Gd/Yb)n (1.54 to 1.96, Table 2) represents 

garnet signature (Arndt, 1994; Naqvi et al., 2002). LREE 

contents are seven to eight times greater than chondrite. The 

Ti/Zr ratio (Avg.6.825) is very low in comparison to 

chondrite (114.99), which can be attributed to Zr-enriched 

mantle source. Semra komatiite shows similarities with 

“Munro type” Komatiites (Arndt et al., 1977; Nesbit et al. 

1979; Fan and Kerrich, 1997) and also with late-Archean 

(~2.7 Ga) Al-undepleted komatiites of Western Abitibi 

greenstone belt (Fan and Kerrich, op. cit.) in terms of Al 2 

O 3 

/ 

TiO 2 

, Zr/Y, La/Sm n, 

Gd/Yb n 

(Table 2) and total REE 

(Table 3) may indicate that Semra ultramafic represent an 

Archaean component in CGC. The Semra ultramafics also 

show similarity with Archaean Sandur schist belt of 

Karnataka (Naqvi et al. 2002). 

The petrographic and geochemical fingerprints of Semra 

ultramafic together with its regional tectonic setting point 

towards komatiitic characters which was derived by eruption 

of essentially unmodified primary magma (Nisbet and 

Chinner, 1981) from mantle source under extensional 

tectonic setup. Deep fracturing and rifting (Gondwana) of 

the protocontinental crust with local upwelling of upper 

mantle (along specific tectonic domain) due to uprising 

mantle plume giving rise to direct effusion of mantle material 

of komatiitic affinity. Komatiites are generally found in 

Archaean greenstone belt but are rare in Proterozoic 

sequences and Cretaceous (Arndt and Lesher, 1992). The 

Semra ultramafics plots near the estimated source 

composition for Early Archaean to Late Archaean Komatiites 

(cf.Fig.6 of Walter, 1998) in the variation diagram between 

Al 2 

O 3 

/TiO 2 

ratio vs CaO/Al 2 

O 3 

ratio (Fig. 7A). In the light 

of this observation, the occurrence of komatiite within CGC 

at the northwestern part of Eastern Indian Shield is of 

paramount significance, as it suggests a possibility of 

the presence of Archaean component in CGC. So far the 

presence of late Archaean rock in CGC had remained to be 

conjectural. 

Acknowledgement: The authors are thankful to Prof. R.K. 

Srivastava, BHU, Varanasi and Prof. S. Das, IIT Kharagpur 

for their critical comments and suggestions on the initial 

manuscript. Constructive comments and thoughtful 

suggestions of the anonymous reviewers of the journal are 

of immense help in improving the earlier version of the 

manuscript. Financial assistance rendered by University 

Grants Commission, New Delhi to DKB for the sponsored 

project [FNo.34-50/2008(SR)] is highly acknowledged. The 

assistance of Dr. D. Mishra during the field work and that 

of Miss Jugnu Prasad in drafting of chemical diagrams are 

thankfully acknowledged. 

ACHARYYA, S.K., DASGUPTA, A. and CHAKRAVORTY, K. (1998) 

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ACHARYYA, S.K. (2003) The nature of Mesoproterozoic Central 

Indian Tectonic Zone with exhumed and reworked older 

granulites. Gondwana Res., v.6(2), pp.197-214. 

JOUR.GEOL.SOC.INDIA, VOL.76,DEC.2010 

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(Received: 18 November 2009; Revised form accepted: 2 June 2010)

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