Vanadium bearing titaniferous magnetite ore bodies of Ganjang, Karbi-Anglong District, Northeastern India

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

26 ABHISHEK SAHA AND OTHERS

Vanadium Bearing Titaniferous Magnetite Ore Bodies of Ganjang,Karbi-Anglong District, Northeastern India

ABHISHEK SAHA1, SOHINI GANGULY1, JYOTISANKAR RAY1 andAVIK DHANG2

1Department of Geology, University of Calcutta, 35, Ballygunge Circular Road, Kolkata 700 019, India2Aurum S.P.R.L., 59, Avenue Colnol Muzemba, Lubumbashi, Democratic Republic of Congo

Email: [email protected]

Abstract: A new occurrence of (syenite-hosted) Vanadium bearing titaniferous magnetite ore body has been reportedfrom Ganjang (26°09'35" N: 93°20' E), Karbi-Anglong, Northeastern India. The magnetite ore bodies have lumpy andsporadic occurrences within the host syenite pluton intrusive into gneissic country rocks. Ore microscopic studies revealthat magnetite is often associated with haematite and ilmenite depicting different textural patterns. Critical considerationof several elemental patterns suggests magmatic differentiation to be main ore-forming process. The ore body is suggestedto have been formed as late stage segregation from a differentiating alkaline magma in a fluid enriched milieu.

Keywords: Vanadium bearing titaniferous magnetite, Karbi-Anglong, Widmanstatten texture, Magmatic differentiation,Northeastern India.

bearing titaniferous magnetite ore body from Ganjang (26°09'35"N: 93°20'E), Karbi-Anglong, Northeastern India,supported by petrograhic and geochemical data. Availableliteratures (Kumar et al. 1989; Hoda et al. 1997) on this bodyare preliminary in nature and describe it as apatite-magnetite-perovskite (AMP) rock.

GEOLOGICAL SET UP AND MODE OFOCCURRENCE

The presently investigated vanadium bearingtitaniferous magnetite ore bodies occur within theSamchampi-Samteran ultramafic-mafic-alkaline-carbonatitecomplex of Northeastern India (Kumar et al. 1989; Nag et al.1999). The Samchampi-Samteran complex occurs as a nearcircular, stock like intrusion emplaced into the Precambriangneissic rocks of Mikir Hills, in the Karbi-Anglong districtofAssam (Kumar et al. 1989; Nag et al.1999; Srivastava andSinha, 2004; Srivastava and Sinha, 2007). This lineamentcontrolled emplacement is a part of ultramafic-mafic-alkaline-carbonatite magmatism of Shillong Plateau, representinglatest differentiation phases of Sylhet Trap basalts inNortheastern India (Coffin et al. 2002; Kent et al. 2002). Theoval shaped syenite body with arcuate ijolite-melteigite suiteof rocks occurs as a discrete plug like pluton within thePrecambrian basement gneisses. The ijolite-melteigite suiteof rocks also shows occasional presence of inliers of alkali

INTRODUCTION

The emplacement of alkaline-carbonatite magmas inrelatively stable, intracratonic platforms is facilitated bylithospheric uparching, crustal thinning followed byfracturing and rifting caused by the impact of an incubatingmantle plume onto the base of continental lithosphere(Woolley, 1989). A wide range of ore-forming processes areknown to be related to the mechanism of intracontinentalrifting and the resulting alkaline-carbonatite magmatism(Piranjo, 2007).The various processes of magmaticdifferentiation operating in a fluid enriched environment,sometimes aided by metasomatic effects on the parent melt,favour intrusions of alkaline-mafic-ultramafic rocks andcarbonatites. This is accompanied by late stage enrichmentof elements like Ti, V, Fe, Mn, Zr, Ni, Co, Cr, Cu etc. in theresidual or immiscible liquid fraction (Krishnamurthy et al.2000; Krishnamurthy, 2007). Economic minerals are knownto occur in alkaline igneous rocks and associatedcarbonatites as they are enriched in elements like Ti, V, Fe,Mn, Zr, Pb, Ni, Mo, Co, Cr, Cu, Th,Au,Ag and PGE. Titanium,Vanadium and Fe oxides are generally derived from magmasthat are richer in Fe, Ca and alkali. Economically important,orthomagmatic, vanadium bearing titaniferous magnetiteores are formed by late stage segregation from volatile rich,differentiated alkaline magmas triggered by episodicincreases in fO2 (Piranjo, 2007). The present article reportsfor the first time the occurrence of orthomagmatic vanadium

JOURNAL GEOLOGICAL SOCIETY OF INDIAVol.76, July 2010, pp.26-32

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VANADIUM BEARING TITANIFEROUS MAGNETITE ORE BODIES OF GANJANG, NE INDIA 27

pyroxenite and alkali gabbro. Younger intrusives marked bycarbonatite and nepheline syenite traverse the pluton (Fig.1).The vanadium bearing titaniferous magnetite ore bodieshave lumpy and sporadic occurrences and are distributedat and around Ganjang (26°09'35"N: 93°20' E) being hostedin syenite pluton (Fig.1). The vanadium bearing titaniferousmagnetite ore is hard, massive, deep brown in colour with a

very high specific gravity. Ore microscopic study of thepolished sections of the representative samples reveals thatthese rocks are dominantly composed of magnetite withsubordinate amount of haematite and ilmenite. Pronouncedeffect of martitization is also evident in magnetite (Fig.2).Ilmenite occurs as exsolution lenses in close associationwith haematite (Fig.3). Widmanstatten (Box-work type)

Fig.1. Geological map of the study area. Inset map shows the location of study area in the map of India.

Fig.2. Photomicrograph showing pronounced effects ofmartitization (Mar) in Magnetite (M).

Fig.3. Photomicrograph depicting exsolution lenses of ilmenite (I)occuring in close association with haematite (H).

Mar

M



textural pattern has also been observed in martitized grains(Fig.4).

CHEMISTRY

In order to decipher the pattern of elemental zonationand chemical variations within vanadium bearing titaniferous

magnetite ore bodies, several constituent elements wereanalysed from representative grid samples using hand-heldXRF XLt Niton (Model No. XLt 592 KVw). The analyseswere performed at Aurum S.P.R.L. Laboratory, Lubumbashi,Democratic Republic of Congo. The details of analyticalprocedure and accuracy are given in Acharya et al.(2006).

The analytical data (Table 1) reveal that this ore body ispredominantly composed of FeO (FeO(t) content rangingfrom 82.97 to 94.94 wt. %), followed by TiO2 (4.38 to 13.73wt. %) and V2O5 (0.07 to 2.14 wt. %) which justifies itsvanadium bearing titaniferous nature. Among traceelements, the vanadium bearing titaniferous magnetite orebody is characterized by consistent and appreciableconcentrations of Co (264-1765 ppm), Cr (86-1546 ppm), Ni(68-238 ppm), Cu (164-629 ppm), Zn (373-1161 ppm) and Zr(337-4542 ppm) with lesser amounts of As, Pt, Nb, Pd andAg. The Zr concentrations of the vanadium bearingtitaniferous magnetite ore body are found to vary from 337ppm. (in the margin) to 4542 ppm (in the core). Thecombination of high charge and comparatively high radius(0.79 Å) compels Zr not to enter into the common rockforming minerals to any degree but helps Zr to be enrichedinto later differentiates (Mason and Moore, 1985). This

Fig.4. Photomicrograph depicting Widmanstatten (Box-worktype) textural pattern in martitized magnetite.

Table 1. Chemical analysis of Vanadium bearing titaniferous magnetite ore body

Major oxides (wt %)

Specimen no. SAJ 75 SAJ 72 SAJ 77 SAJ 70 SAJ 61 SAJ 65 SAJ 67

FeO(t) 94.73 94.66 82.97 89.82 89.94 93.11 94.94TiO2 4.38 4.43 13.73 9.24 8.75 6.36 4.59V2O5* 0.61 0.58 2.14 0.67 0.90 0.30 0.07MnO 0.29 0.34 1.17 0.38 0.41 0.24 0.40FeO** 60.95 60.91 53.38 57.80 57.87 59.91 61.09Fe2O3** 37.53 37.50 32.87 35.59 35.63 36.89 37.62

Trace elements (ppm)Specimen no. SAJ 75 SAJ 72 SAJ 77 SAJ 70 SAJ 61 SAJ 65 SAJ 67Location of samples Margin Core Marginin the ore body

Pd 35 0 18 19 0 12 11Ag 47 96 0 68 99 0 22Mo 0 0 9 48 9 0 0Nb 12 0 712 1101 838 12 68Zr 381 337 - 4125 4542 423 362Bi 0 0 0 125 164 0 0Au 0 0 18 0 0 25 0P t 36 0 27 0 0 59 0As 36 96 36 29 58 0 34W 60 217 91 164 0 0 137Zn 570 482 1161 561 769 373 713Cu 617 361 244 164 239 629 271Ni 238 169 100 68 103 194 -Co 1119 1614 264 - 922 1048 1765Cr 216 - 173 1546 532 86 485V 3420 3252 11989 3736 5056 1675 375

*V2O5 recalculated from V content in ppm; ** FeO/Fe2O3 recalculated values



Fig.5. Contour maps showing (a) variation of Zr concentration in Vanadium bearing Titaniferous Magnetite ore body (from Ganjang).Bolder dotted line represents the margin of the investigated body. Figs.5 (b), (c) and (d) denotes contour-patterns for Ni, Co andV respectively in the ore body.

(a) (b)

(c) (d)



feature of progressive enhancement of Zr from margin tocore has been nicely depicted in Fig.5a. This behaviourclearly suggests that Zr gets enriched from margin to coreof the Vanadium bearing titaniferous magnetite ore bodyconcomitant to the advent of differentiation. Among theMg, Fe and coherent heavy trace elements, the sequence ofentry into crystal lattice is as follows: Mg, Ni, Co, Fe2+ onthe basis of ionic charges, radii and electronegativityprinciples (Ringwood, 1955; Taylor, 1965). The Ni contentof the Vanadium bearing titaniferous magnetite ore body isfound to range from 68 ppm to 238 ppm against 110 ppm ofthe world average of ultramafic rocks (Goles, 1967). Figure5b shows that Ni content of the Vanadium bearingtitaniferous magnetite ore body gradually falls from 238 ppm(in the margin) to 68 ppm (in the core) again attesting tonormal differentiation of the parent melt. Figure 5c showsthat Co depicts systematic fall from 1765 ppm in the marginto 264 ppm in the core. The elemental variation pattern forcobalt is therefore found to be similar to that observed fornickel. Since Co proxies for Mg during magmaticfractionation (Mason, 1966, p.136), the fall of cobaltconcentration from margin to core of the ore body suggestsprogressive magmatic differentiation. The V concentrationin the vanadium bearing titaniferous magnetite ore bodyhas been depicted in Fig.5d which clearly shows extremevanadium enrichment (11989 ppm) towards the core part ofthe ore body while in the marginal part vanadium contentfalls down to 325 ppm which again suggests normal magmaticdifferentiation trend. Logarithmic elemental concentrationpatterns of Zr, Ni, Co and V within the investigated orebody (margin-core-margin) have been shown in Fig.6 todepict the spatial variation of these elements.

DISCUSSION

Alkaline-carbonatite magmatism and associatedVanadium bearing titaniferous magnetite mineralization canbe attributed to a complex interplay of several tectono-magmatic processes (Gaspar and Wyllie, 1983; Piranjo, 2007;Reguir et al. 2008). The occurrence and geologicalrelationships of Ganjang vanadium bearing titaniferousmagnetite ores indicate that their genesis is intimatelyrelated to fractional crystallization processes that wereresponsible for the formation of their silicate host rocks as ithas been documented from Bushveld Complex (Reynolds,1985). The elemental concentration patterns and overallchemical features suggest that the Ganjang Vanadium-titanium-magnetite mineralization has resulted due to latestage segregations from a differentiating alkaline magma ina fluid enriched milieu controlled by metasomatism and

varying degrees of oxygen fugacity as documented bypresence of carbonatite with variable proportions of apatiteand opaque minerals. Vanadium bearing titaniferousmagnetite ore bodies have been described from differentparts of the Indian shield viz. Kumhardubi, Singhbhum(Banerjee, 1984), Nausahi, Orissa (Chakraborty et al. 1988),Masanikere, Shimoga, Karnataka (Govindaiah et al.1989) andKurihundi, Sargur, Karnataka (Vidyashankar and Govindaiah,2009). In most of the cases, such ore bodies are related toprimary magmatic crystallization involving cumulus,adcumulus and postcumulus mechanisms. Nevertheless,report on syenite-hosted Vanadium bearing titaniferous

10

100

1000

10000

100000

V

Ni

Co

Zr

log o

f el

emen

tal

con

cen

trati

on

inp

pm

Margin of theinvestigated body

Core of the investigated body Margin of theinvestigated body

NiVCoZr

Fig.6. Logarithmic elemental concentrations for Ni, V, Co and Zrin the Ganjang ore body (margin – core – margin).

Fig.7. Plots of investigated samples (open square) from Ganjangin FeO(t)-TiO2-MnO triangular diagram. Shaded areademarcates field for vanadium bearing titaniferous magnetiteore body from Singbhum region, Eastern India (Banerjee,1984; Saha, 1994)

FeO(t)

TiO2 MnO



magnetite ore body from Indian shield is rather rare. AsFeO(t),TiO2 and MnO are dominant constituents of vanadiumbearing titaniferous magnetite ore bodies of Ganjang, anattempt has been made to compare its chemistry with that ofvanadium bearing titaniferous magnetite ore body ofKumhardubi, Singhbhum (Banerjee, 1984; Saha, 1994, pp.219-221) on compositional-basis (Table 2). The data plots forGanjang clearly occupy the field demarcated by vanadiumbearing titaniferous magnetite body of Singhbhum in FeO(t)

- TiO2 – MnO diagram (Fig.7). The vanadium and titaniumconcentrations of the investigated magnetite ore body (V2O5:0.07-2.14 wt. % and TiO2: 4.38-13.73 wt%) seem to be quiteencouraging considering the economic prospects (seeMohanty et al. 1999; Devaraju et al. 2009) and hence, thisore body may be explored by suitable organizations at anearly date.

Acknowledgements: The authors thank Dr. M.Angamuthu (IAS), Mr. Pradip Singner and Mr. Har SinghKro for providing ample administrative and logistic supportfor carrying out the present field investigation in the remotepart of Karbi-Anglong. The authors are also thankful to Dr.Shyamal Sengupta for some stimulating discussion ongeology of Samchampi-Samteran Complex. JR thanks theUniversity Grants Commission, New Delhi for financialsupport in form of a major research project {Sanction No:34-51/2008(SR)}. The Head, Department of Geology,University of Calcutta and authorities of Aurum, S.R.P.L.,Lubumbashi, DRC provided necessary laboratory facilities.The authors gratefully acknowledge an anonymous reviewerfor constructive comments and suggestions.

Table 2. Electron probe analysis of magnetite (major), ilmenite(minor) phases of Kumhardubi ore, Singhbhum (afterBanerjee, 1984)

Sample no. 53 54 50

Phase M t M t Il M t Il

MgO 0.24 0.4 0.19 0.41 0.86Al2O3 2.62 3.75 1.63 1.6 1.43TiO2 5.76 10.26 25.72 12.85 28.48V2O5 1.54 1.18 1.31 1.71 1.81MnO 0.007 0.12 0.12 0.13 0.11FeO(t) 90.21 80.85 67.85 80.13 63.7Total 100.38 96.56 96.82 96.83 96.39

Mt: Magnetite, Il: Ilmenite

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(Received: 20 July 2009; Revised form accepted: 22 December 2009)

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Vanadium bearing titaniferous magnetite ore bodies of Ganjang, Karbi-Anglong District, Northeastern India