Petrological and PGE Mineralisation Study of the Channagiri Mafic- Ultramafic Complex, Shimoga...

0016-7622/2007-70-4-535/$ 1.00 © GEOL. SOC. INDIA

JOURNAL GEOLOGICAL SOCIETY OF INDIAVol.70, October 2007, pp.535-556

Petrological and PGE Mineralisation Study of the Channagiri Mafic-Ultramafic Complex, Shimoga Supracrustal Belt, Karnataka

T. C. DEVARAJU1, T. T. ALAPIETI

2, R. J. KAUKONEN2 and T. L. SUDHAKARA

3

1‘Rajamangala’, Saptapur, Haliyal Road, Dharwad – 580 0012Institute of Geosciences, University of Oulu, P.O. Box 3000, FIN-90014, Oulu, Finland

3MSPL Limited, Nehru Co-Operative Colony, Hospet – 583 2033Department of Applied Geology, Kuvempu University, Jnanasahyadri, Shankaraghatta - 577 451

Email: [email protected]

Abstract: The Channagiri mafic-ultramafic complex constitutes the main lithounit of Hegdale Gudda Formationof the Shimoga Supracrustal Belt. Mapping at a scale of 1:2000 coupled with detailed petrological examination of thePlatinum Group Element (PGE) mineralized 3.5 km x 0.3 km Hanumalapur segment of the complex has revealed thatit is composed of outer gabbroic zone and central 100-150 m ultramafic zone. While V-Ti magnetite seams occupy theouter boundary of the ultramafic zone, several small isolated lenses/pods of anorthositic variation occur within theultramafic zone itself. The complex is affected by penetrative deformation, hydrothermal alteration and low-grademetamorphism, which together have caused complete replacement of olivine and pyroxenes by chlorite, amphibole,epidote and carbonate. The gabbro forming outer zone is in the range of quartz gabbro-melagabbro and is stronglybanded/foliated. The ultramafite in the central zone is a complex mix of the dominant fine (chromite-chlorite schist)and subordinate coarse grained units. The magnetite occupying the western interface zone is the typically coarse grainedV-Ti variety whereas that on the eastern side includes narrow chromiferous lenses. PGE data obtained for the differentunits of Hanumalapur segment has revealed that only the central fine-grained ultramafite and the chromiferouslenses in the eastern magnetite seam host PGE mineralization of commercial interest with Pt+Pd values ranging from1.5 to 6 ppm; the other lithologies of the segment as well as those constituting the remaining segments of Channagiriultramafic complex and Hegdale Gudda Formation have not yielded positive anomalies of PGEmineralization. Thegoverning control of chromite over the separation of PGE in the very early stages of magmatic crystallization isinferred taking into account the close association of PGE with the chromite-bearing units. The recorded texturalrelationships suggest that the PGEs remained virtually immobile during later penetrative alterations of the host rock.

Geochemically, the PGE mineralized ultramafic units of Hanumalapur segment carry signatures of basaltic komatiiteto Fe-rich tholeiite and in terms of Pd/Ir : Ni/Cu, Pd/Pt : Ni/Cu and Ni/Pd : Cu/Pt ratios they compare with layeredintrusions.

The chromite controlled PGE mineralization of Hanumalapura roughly resembles the UG2 of the Bushveld complexand a part of the SJ reef of the Penikat. Detailed logging of a 252 m deep drill core has revealed the existence of three orereefs of 20, 30 and 35cm thickness, analyzing 3.7, 5.0 and 4.0 ppm Pt+Pd respectively, located within a 5 m zone, and5 lower grade reefs of 0.35 m to 1.0 m thickness analyzing 1.3 to 1.8 ppm Pt+Pd (and 0.7 to 1.8% Cu), located in a50 m wide zone, just above the main ore zone. The PGE reefs of Hanumalapur segment include both Pt- and Pd-richones but the latter dominate.

Keywords: Channagiri mafic-ultramafic complex, PGE distribution, Chromite-controlled, Hanumalapur segment,Shimoga belt, Karnataka.

INTRODUCTION

The Channagiri mafic-ultramafic complex hosting thewell known V-Ti magnetite ore seams of Ubrani, Tavarekereand Masanikere (Slater, 1905, 1912; Jayaram, 1915;

Channappa and Subramanya, 1973; 1979; Ramiengar andChayapathi, 1977; Ramiengar et al. 1978; Vasudev andSrinivasan, 1979, Jayaraj et al. 1995, 1996) constitutes oneof the major lithologies of the Hegdale Gudda Formation

We dedicate this publication to Prof. Tuomo T. Alapieti who was instrumental in the discovery of this PGE deposit in Karnataka, but, did notlive long to realize his dream of establishing its viability for commercial exploitation. Prof. Alapieti suddenly passed away on 6th August 2007

JOUR.GEOL.SOC.INDIA, VOL.70, OCT. 2007

536 T. C. DEVARAJU AND OTHERS

(Chadwick et al. 1988) located in the southeastern part ofthe Shimoga Supracrustal Belt.

A careful examination of the Channagiri complex in theearly nineties by Devaraju, Alapieti and their co-workers(e.g. Devaraju et al. 1994; Alapieti et al. 1994) revealed notonly the existence of a chromite-bearing ultramafite but alsothe associated PGE mineralization in the Hanumalapursegment of the complex. Subsequently, (i) in a researchreport submitted to Department of Science & Technology,Govt. of India, Devaraju (2000) presented a comprehensiveaccount of PGE mineralization in the Channagiri and otherultramafic bodies in the SE of Shimoga Suprcrustal Belt,(ii) Devaraju et al. (2002), Alapieti et al. (2002) andKaukonen et al. (2002) summarized the results of their jointoutcrop as well as drill core based geochemical andmineralogical investigations of the PGE mineralizedHanumalapura segment at the 9th International PlatinumSymposium held in Montana, USA, and (iii) very recentlyDevaraju et al. (2005) have presented an account ofSEM-EDS based study of platinum-group minerals in theoutcrop samples of the PGE mineralized Hanumalapursegment.

In the light of confirmed evidence of ore level PGEmineralization in the Hanumalapur segment, an overallexploratory study of the Channagiri ultramafic complex andthe Hegdale Gudda Formation has been carried out with thepresumption of finding more zones of PGE mineralizationin other parts of the Formation. However, the exercise hasnot yielded so far any positive results.

This publication is aimed at highlighting the pattern ofdistribution of PGE, petrological features and the observedcontrols of ore level PGE mineralization in the Hanumalapursegment. It also presents data on PGE distribution in theChannagiri complex and other litho units of Hegdale GuddaFormation as a whole. Based on outcrop, trench and corelog data, an attempt is also made to give an approximateestimation of the reserves of Pt and Pd held in the mainore zones of the Hanumalapur segment.

GENERAL GEOLOGY

The area investigated forms a part of Archaean WesternDharwar Craton and contains essentially ~3 Ga. oldbasement granitoids and Late Archaean cover rocks ofDharwar Super Group (Fig.1). It stretches between thelongitudes 75°50'-76°10' and latitudes13°45'-13°50' andoccupies a total area of 700 km2. While the western about20 km area comprises a portion of the southeastern part ofthe Shimoga basin (Fig.1b), the eastern more than about17 km of the area is occupied predominantly by (Peninsular)

gneissic terrain. The western and eastern parts of thearea are separated from each other by northeasterlytrending fault plane, which is designated by Chadwicket al. (1988) as ‘Main Eastern Boundary Fault’. More thanabout 50 per cent of the western part of the area is composedof the Dharwar Supracrustals coming largely underHegdale Gudda and Kur Gudda Formations of Chadwicket al. (1988). The younger Tuppadahalli Formation appearsonly at the northeastern border of the western block of thearea (Fig.1b). The youngest rocks of the area are theoccasionally noted mafic dykes (quartz dolerite to olivinemeladolerite), which intrude both basement granitoids andsupracrustal sequences.

The contacts between the cover and basement rocks arebroadly concordant. There are no signs of contactmetamorphism in the cover rocks to suggest that theunderlying granitoids are younger and intrusive. It isregarded here that the granitoids of the area are a part of themultiphase Peninsular Gneissic Complex.

The overall synclinal fold structure identified in thecover rocks includes much of the Kur Gudda Formation(Fig.1b). The strongly marked fabrics in the cover rocksinclude bedding parallel-preferred orientation ofphyllosilicates in all the lithologies. This is related to primarydeposition and compaction phenomenon. Preferred linearand planar orientation of detrital grains and clasts are normalstructural features. Rotation of clasts and modificationof grain shapes by pressure action has given rise to LSfabrics of cover rocks.

Prolific flushing of fluids, including water and carbondioxide, through the basement and cover rocks duringdeformation is indicated by profound retrogression ofboth basement and cover rocks to assemblages rich inchlorite and carbonate. The centrally located Main EasternBoundary Fault of the area has been identified on the basisof termination of Dharwar Super Group comprising ofHegdale Gudda, Kur Gudda and Tuppadahalli Formationsand to some extent by the presence of a well markedshear zone.

The Hegdale Gudda Formation occupies lower part ofthe supracrustal succession and constitutes the oldest cycleof volcano-sedimentary sequence of Dharwar Supergrouprecognized in the area. The dominant mafic compositionsof the main lithologies of Kur Gudda Formation viz.,polymict conglomerate and phyllites suggest its derivationfrom predominantly mafic provenance. While slumpstructures in the phyllites of the Formation suggest depositionin deeper fan environments and in unstable subsiding basin,periods of stability and deposition of the Formation in clearerwater in later stages are indicated by the occurrence of inter-


PETROLOGICAL AND PGE MINERALIZATION STUDY OF CHANNAGIRI ULTRAMAFIC COMPLEX, KARNATAKA 537

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Fig.1. (a) Generalized Geological map of the area south of Channagiri. (b) Geological map of Hanumalapur area showing HegdaleGudda Formation and Channagiri ultramafic complex (after Chadwick et al. 1987).



bands of cherty limestone such as those near Bhadigund.The Tuppadahalli Formation is similar in several respectsto Kur Gudda Formation but contains more frequent inter-bands of cross-bedded quartzites. This Formation bearsevidence of having deposited in a littoral environment(Chadwick et al. 1988).

No isotopic age data is available for any of the rockformations of the study area. However, extending theinformation obtained for the adjoining Chikmagalurgranodiorite and Bababudan-Chitradurga Supracrustals(Taylor et al. 1984), it is presumed that the basementgranitoids are around 3.0 Ga. old and the supracrustals areyounger and the dyke intrusions are still younger. Thetectonic movements and metamorphism that have affectedthe basement rocks and supracrustals predate intrusion ofmafic dykes.

Lithostratigraphic sequence in the area inferredessentially on the basis of field relationships is given inTable 1.

THE HEGDALE GUDDA FORMATION AND THECHANNAGIRI UL TRAMAFIC COMPLEX

Field Occurrence

Named after the prominent hill (1,074 m) to the southof Ubrani (Fig. 1b), the Hegdale Gudda Formation(Chadwick et al. 1988) is predominantly composed of amafic-ultramafic complex (to which we have proposed thename Channagiri Ultramafic Complex). It hosts the wellknown V-Ti magnetite deposits of Masanikere, Tavarekere,

Ubrani, Gaurapura and Devaranarsipura. The otherlithologies of the Formation are broadly classified asmetabasite, phyllite, chlorite schist, quartz-sericite schist,quartzite and carbonates, which are well exposed in theBukkambudi hill and on the eastern slopes of Masanikerehill. In the map presented here (Fig. 1b), however, onlymagnetite, chromitite, carbonate and quartzite are shownseparately; all other rocks are shown in the same grey color.This is mainly because the other rocks are not readilyseparable from the mafic-ultramafic units of Channagiriultramafic complex. The Channagiri ultramafic complex inparticular measures over 40 km in the NE-SW direction andhas a maximum width of about 12 km (NW-SE). It istectonically segmented, but, generally maintains aconformable relation with the adjoining tonalite andSupracrustal belt rocks. In fuller details, the complexencompasses a sequence of mafic-ultramafic rocks, but isgreatly dominated by completely altered sequence ofultramafic rocks.

The prominent outcrops of Channagiri ultramaficcomplex in the vicinity of Ubrani, Gourapura, Chickmalali,Hanumalapur, Tavarekere, Masanikere are typicallydominated by V-Ti magnetite seams. The ultramafic-maficrocks noted at these locations look very weathered and aremostly covered by blocks of abundant V-Ti magnetitefloat.

Salient Petrological Features

The Channagiri mafic-ultramafic complex, althoughinterpreted as representing dunite-peridotite-pyroxenite-

Table 1. Generalized Lithostratigraphic sequence of the area south of Channagiri (refer to Fig. 1b for the spatial distributionof the rock formations)

Mafic dykes Range from quartz dolerite to olivine meladolerite. Postdate both basement granitoidsand Supracrustals, unaffected by metamorphism and deformation.

Tuppadahalli Formation Mainly a suite of phyllites/argillites interstratified with a large number of ortho-quartzite bands.

Kur Gudda Formation Dominated by phyllite and quartzo-feldspathic wackes and includes themetasedimentory sequence of polymict conglomerate – quartzite – phyllite –chlorite schist – dolomitic limestone.

Hegdale Gudda Formation Predominantly a metamorphosed sequence of gabbro - pyroxenite - peridotite withseveral prominent seams of V-Ti-magnetite, localized pods of anorthositic variationsand very restricted chromite-bearing ultramafite. Also includes smaller proportionof metavolcanic-sedimentory sequence of metabasites-phyllite-chlorite schist-quartzo-feldspathic wackes-quartzites- Cr-Ni- enriched silicious Mg-carbonates.

The Eastern Ultramafic Mostly ultramafic constituting peridotite-chromite banded peridotite-duniteBodies chromitite sequence with local pods and gabbroic variations. Typically include

isolated patches of fine grained chlorite-enriched aluminous ultramafic rock

Basement Granitoids Homogeneous tonalite-quartz-tonalite-traondhjemite on the west and multiphasebanded quartzofeldspathic ortho gneiss- granodiorite on the east



metagabbro-gabbro sequence with several isolated seams/lenses of V-Ti magnetite and localized lenses of anorthositicvariations, because of very penetrative hydrothermaland low grade (green schist-low-amphibolite facies)metamorphic alterations coupled with strong shearing, theoriginal structures, textures and mineralogy of the complexesare completely altered. Relics of original dunite/peridotite/gabbro are not found anywhere. Even in the 252 m longdrill core of Hanumalapur segment examined no relics ofeither olivine and/or pyroxenes are picked up. The only relicoriginal rock units that could be recognized are those madeup essentially of V-Ti magnetite and chromite. Even thoseunits do not contain olivine or pyroxenes; those arecompletely replaced by chlorite and minor amphibole andepidote. Besides, magnetite and chromite too are very muchaffected by oxidation. The ultramafic rocks of the complexare composed mainly of variable proportions of chlorite andamphibole; epidote, carbonate and talc are generally presentin minor amounts and assume importance only locally. Nofresh plagioclase is retained in the mafic gabbroic units andanorthositic variations; it is largely replaced by sasusserite,in which epidote often dominates and patches ofrecrystalized albitic feldspar occur. Disseminations andmicrobands of Fe-Ti oxides, and sporadic crystals ofsulphides and carbonates related to hydrothermal alterationare common but there is no uniform distribution of these.Absence of relic minerals, obliteration of original texturesand reduction of mineralogy into assemblages containingmostly variable proportion of chlorite and amphibole donot permit a precise reconstruction of precursor mineralogyand original rock sequence.

Modal mineralogical data and chemical analysesobtained for representative lithologies of Hegdale GuddaFormation and Channagiri ultramafic complex are given inTables 2 and 3.

PGE Distribution in the Hegdale Gudda Formation

Analysis of relatively large number of samples collectedfrom various litho units of Channagiri ultramafic complexand Hegdale Gudda Formation, lying outside Hanumalapursegment, has been prompted by the fact that theHanumalapur segment, hosting confirmed evidence ofPGE mineralization is an integral part of the saidstratigraphic Formation. High Cr, Ni and sulphide contentsof some of the lithologies of those units has been anotherencouraging factor. And, our decision to analyse a goodnumber of samples from magnetite seams lying outside thelimits of Hanumalapur segment derived support from thefollowing: (i) assumed presence of Cr-magnetite lenses(i.e. as in the eastern magnetite seams of Hanumalapur) inother magnetite seam of Channagiri complex, (ii) presenceof sulphide as one of the important components inparts of Masanikere magnetite seam and (iii) reportedassociation of PGE mineralization with magnetites in Russia(Begiznov, 1975), Ethiopia (Cabri et al. 1981), Canada(Tucker Barrie et al. 2002) and Australia (Johan,2002). However, disappointingly no important evidence ofPGE mineralization has been picked up so far outsideHanumalapur segment. Absence of chromite-bearing unitsoutside Hanumalapur segment possibly explains thesituation.

With the exception of schistose ultramafite containingchlorite and magnetite (M110), collected from northernfringes of the Tavarekere segment and a sample of chlorite-rich magnetite (M72) from the Chikkamalali segment of theChannagiri ultramafic complex, which analyse 131 ppb and54 ppb of Pt+Pd respectively, the remaining 30 samplescollected over widely separated locations representingmagnetites, a range of ultramafites, metagabbro/amphibolites and meta-anorthositic variations of the

Table 2. Modal analyses of selected rocks of Channagiri ultramafic complex and Hegdale Gudda Formation

Sl.No. 1 2 3 4 5 6 7 8* 9 10 11Sample M-13 M-20 M-35 M-17 M-33 M-112 M-54 M-50 M-21 M-51A M-55

Quartz — — — — — — — 14.2 27.1 8.3 17.3

K-Feldspar — — — — — — — 0.6 0.9 — —

Plagioclase — — — 3.8 12.2 28.5 26.3 — 25.3 — —

Amphibole — — — 94.6 — — — — — — —

Chlorite — 0.3 16.0 1.4 38.2 33.6 26.8 38.2 34.4 2.7 39.0

Epidote — — — 0.2 8.6 30.2 7.8 8.6 — —

Carbonate — — — — 30.5 7.7 32.0 30.4 7.7 77.9 37.4

Muscovite — — — — — — 5.4 — — — 1.0

Fe-Ti oxides 89.6 89.7 78.3 — 9.7 — 1.7 9.7 4.6 11.1 5.3

Hogbomite 10.4 10.0 3.6 — — — — — — — —

Sl. No: 1-3: Magnetite; 4: Meta-ultramafite; 5-7: Metabasites; 8: Phyllite; 9: Quartzo-feldspathicwacke; 10-11: Crabonates1-7 Channagiri ultramafic complex; 7-11 Hegdale Gudda Formation. * contains 0.8 % sphene



Channagiri mafic-ultramafic complex and phyllites andcarbonates (the last two lithologies were analysed forPGE taking into account their high Ni and Cr contents) ofHegdale Gudda Formation are found to be distinctly low inPGE, with Pt and Pd values being equally low togetheraccounting for 2.8 and 20.3 ppb (Table 4). Even in the fourmagnetite samples, including the one from Masanikere withsulphide as one of the major minerals, which are analysedfor all the six PGE, the total PGE content is in the rangeof <16 to <32.5 ppb (Table 4a). Further, Au values obtainedfor these lithologies are also low viz., <1 to 10 ppb; theexception to this generalization being phyllite fromBukkambudi hill (44 ppb) and schisted metagabbro fromTavarekere (24 ppb).

THE HANUMALAPUR SEGMENT

Field Occurrence

The Hanumalapur segment of the Channagiri mafic-ultramafic complex is a tabular body with a maximumthickness of 300 m. It strikes N to NNW and dips east atangles of 55° to 70°. It has a maximum strike length of about7.5 km, but only the northern about 3.5 km portion of thesegment with chromitite association hosts PGEmineralization of commercial value. The segment is

surrounded by tonalite gneiss, but, the contacts are notexposed for direct observation. While the eastern contactexposes a 10-15 m wide shear zone in which both ultramafiteand tonalite are involved, the western contact is concealedunderneath ½ to ¾ km wide stretch of thick soil cover. Thereis no obvious observed field relationship which would enableus to interpret whether the complex is younger or older thanthe adjoining tonalite. The segment also does not includeany of the other lithologies (viz., metabasalt, phyllite,quartzite, carbonates, etc) of the Hegdale Gudda Formationor pegmatite/aplite permeations; there are however,occasional quartz veins unrelated to surrounding tonalite.Further, it is significant to note that chromitite andanorthositic variations are recorded only in the Hanumalapursegment (Fig.2) of Channagiri ultramafic complex; thisfactor possibly explains the restriction of PGE mineralizationonly to the Hanumalapura Segment of the complex.

Petrological Features

The Hanumalapur segment of the Channagiri mafic-ultramafic complex is a tabular easterly dipping body inwhich the outer 15-130 m of border zones of the body aregabbroic whereas the central 150-250 m zone is ultramaficrock. Marking the western and eastern boundary of thecentral unltramafic zone there are 10-35 m thick discontinues

Table 3. Chemical analyses of representative rocks of Channagiri mafic-ultramafic complex and Hegdale Gudda Formation

1 2 3 4 5 6 7 8M13:96 M35:96 M17:96 M114:97 M54:96 M50:96 M28:96 M51A:96

SiO2

0.57 4.56 48.64 50.35 48.79 45.94 61.67 14.82

TiO2

12.87 10.80 0.21 0.06 0.57 0.98 0.73 0.08

Al2O

33.96 3.58 12.39 5.35 11.65 23.78 17.66 2.05

Fe2O

380.14 75.99 9.70 9.23 10.44 10.07 9.46 12.86

MnO 0.17 0.11 0.18 0.14 0.14 0.09 0.03 0.26

MgO 1.76 3.30 15.29 23.89 6.54 9.04 2.45 16.23

CaO 0.02 0.01 9.57 5.80 7.73 0.57 0.03 19.08

Na2O 0.05 0.00 0.60 bld 2.36 0.27 0.16 0.00

K2O 0.01 0.02 0.67 0.02 0.80 2.33 4.18 0.01

P2O

50.01 0.02 0.02 0.02 0.08 0.13 0.02 0.01

LOI 0.15 1.74 2.24 4.24 10.14 6.32 3.55 32.66

Total 99.71 100.13 99.51 99.10 99.24 99.52 99.94 98.06

Cr 2463 5679 1415 5734 360 624 348 4927

Ni 415 463 384 1120 85 1165 128 2099

V 4011 3671 193 78 245 199 140 83

Cu 44 133 8 9 287 19 25 30

Zn 510 185 79 108 70 652 57 153

Rb bld 2 23 2 36 79 142

Sr 4 3 50 9 128 135 31 209

Zr 3 6 20 3 127 334 168 34

1-2: Magnetite; 3-4: Metaultramafite; 5: Metabasite; 6: Phyllite; 7: Quartzo-feldspathic wacke; 8: Carbonate.1 to 4: Channagiri ultramafic complex; 5 to 8: Hegdale Gudda Formation



Table 4. Pd, Pt, Au, Cr, Ni and Cu analyses of magnetites and other rocks of Channagiri mafic-ultramafic complex and Hegdale Gudda Formation lyingoutside Hanumalapur segment (values in ppb)

Sl.No. Sample Rock Description Location Pd Pt Au Cr Ni Cu

V-Ti Magnetites

1 M:13 Coarse-grained with considerable hogbomite Ubrani 14 15 8 2462 450 44

2 M:15 Coarse-grained with thin sulphide bands Ubrani 14 12 7 1094 295 97

3 M:32 Granular with considerable chlorite Masanikere 3.4 1.3 2 8618 681 97

4 M:35 Granular with some hogbomite & chlorite Masanikere 3.5 2.1 5 5677 463 133

5 20A Fine-grained, sulphide bearing - drill core Masanikere 3 5 10

6 M:80A Fine-grained with more hogbomite than chlorite Bukkambudi 26 8.1 6 503 136

7 M:65 Coarse granular with ~ 80% magnetite & ~ 20% chl. Chikkamalali 11 6 5 684 523 345

8 M:72 Fine-grained with considerable chlorite Chikkamalali 34 20 9 3557 385 101

9 M:20 Fine-grained with 80% magnetite & 20% hog. + Chl. Gaurapur 1.9 0.7 8 1231 793 78

Mafic-Ultramafic Rocks

10 M:112 Chlorite-epidote schist with sporadic carbonate Tavarekere 10 12 4

11 M:17 Schisted amphibolite with ~ 85% Hbl & ~ 15 % plg Ubrani 4 8.4 2 1415 384 8

12 M:58 Coarse-grained amphibolite enclave in tonalite Ubrani 5.4 1.5 3 122 177 176

13 M:113 Trimolite-actinolite schist with some chlorite Tavarekere 3.1 3.9 24

14 M:110 Fine-grained chlorite schist with some Chr & Carb. Tavarekere 104 27 10

15 M:207A Coarse-grained, massive looking with abundant talc Masanikere <4 <5 3

16 M:19 Fine-grained qtz.-chl-ser-mt schist with epi. & plg. Basavanahalli 1.7 0.8 297

Metabasite/Phyllites

17 M:36 Sericite-quartzite 30 % ser., 70% qtz. Tavarekere 2.7 2 5 220 105 136

18 M:28 Qtz.-chl. schist ~ 70% chlorite & much Fe-Ti oxide Masanikere 3.1 2.8 4 348 128 25

19 M:77 Qtz-chl.-carb schist Bukkambudi 7.5 5.6 44 377 75 369

20 M:78 Qtz-chl.-carb schist with less carb. than M.77 Bukkambudi 5.6 5.7 7 61 74 168

21 M:66 Qtz.-plg-chl.-bio. schist with Fe-Ti oxide Chikkamalali 7 8.1 8 232 130 246

22 M:66A Chlorite schist with quartzo-feldspathic bands Chikkamalali 2.1 0.7 10 45 20 632

23 M:54 Qtz-plg-chl-epi-carb schist Chikkamalali 9.2 6.2 8 360 85 287

24 M:50 Chl. schist with qtz-interbands & some musc-car-rut. Bukkambudi 2.3 2.1 4 624 1165 19

Carbonates

25 M:49A Dolomite with talc, sericite and Fe-Cr oxide Bukkambudi 3.7 7.5 3 3557 1624 31

26 M:51 Dolomite with chl. and Fe-Ti oxide Bukkambudi 5.7 5.7 4 4036 2344 32

27 M:51A Dolomite with some qtz.-chl. and Fe-oxide Bukkambudi 4.3 16 4 4925 2099 30

28 M:52 Magnesite with good amount of talc Bukkambudi 3.5 8.6 3 4036 2294 13

Table 4a. PGE, Au and Re analyses of magnetites of Channagiri mafic-ultramafic complex andHegdale Gudda Formation lying outside Hanumalapur segment (values in ppb)

Sl.No. Sample Os Ir Ru Rh Pt Pd Au Re

Masanikere1 12-IND-93 <2 0.3 16 0.5 <5 8 0.7 <52 20B-IND-93 <2 0.3 <5 <0.2 <5 <2 1.1 <5

Tavarekere3 10-IND-93 <2 0.1 7 <0.2 <5 <2 <0.5 <54 11-IND-93 <2 0.1 <5 <0.2 <5 <2 1.5 <5

1.Sulphide bearing weathered magnetite; 2. Drill core sample of coarse grained magnetite withconsiderable sulphide; 3. Magnetite containing considerable chlorite, 4. Compact magnetite



ð

ð

ð

ð

ð

ð

ðY

Y

Y

Y

Y

Y

Y

604

000

603

500

603

000

1536500

1536000

1535500

1534500

1534000

1533500

Nellihankalu

Hanumalapur

M3

M1

M5

M93

M98

M11

M104

BH-1

BH-3

BH-4

BH-5

BH-6

BH-7

BH-8

850800

750

700

850

800

750

700

B'B'B

A A'

A'A

B

35

60

45

40

71

45

38

40

64 40

56

45

60

60

31

55

4565

1535000

0 0.2 0.4 Kilometers

N

Tonalite

Metagabbro (Amphibolite)

Finegrained metaultramafite(Chlorite-chromite rock)

Coarse grained metaultramafite(Hornblende-chlorite-talc rock)

V-Ti magnetite

Meta-anorthosite pods

ð Sample location

Y Drillhole locationRoad

Strike-dip of schistosity/foliation

M5

BH-3

40

Trench

Fig.2. Geological map of the northern 3.5 km of PGE mineralized Hanumalapura segment. Locations of the samples studied are showntogether with the 8 exploratory drill holes. The drill holes are sunk at angles of 55° to 60° towards west. Persistence of PGEmineralization is recorded in all the 8 drill holes but the concentrations vary.



seams of V-Ti magnetite. Several small isolated anorthositiclenses measuring less than a meter in width and 10 m inlength occur scattered within the ultramafic zone, but,more frequently in the vicinity of V-Ti magnetiteseams (Fig.2). Salient petrographic, mineralogical andgeochemical characteristic of the main petrologicalunits of the Hanumalapur segment are described in thefollowing.

Metagabbro is a fine grained, moderate to stronglybanded and foliated rock. It has an overall light to dark greencolour and forms a part of intensely deformed marginalportion of the complex. In thin section, the rock showsbanding and mineral lineation. Feldspar is largely replacedby epidote, recrystallized and untwinned. Theferromagnesian silicate is predominantly uralite (weaklypleochroic, light green tremolite-actinolite), which in turnis unevenly altered to chlorite and epidote, often enclosingoriented schiller inclusion patches.

Metaultramafic rocks forming the center ofHanumalapur segment include fine and coarse grainedunits, of which the former greatly dominates.

Fine-grained ultramafite (metadunite with variableproportions of chromite) is moderate to strikingly schistose,greenish to greenish black rock, generally soft and easy tobreak. Extreme variations of the rock correspond tochromitite and chlorite schist. Closer examination of the rockhas revealed that it includes variable proportions of smallchromitite lenses/pods/bands, varying in thickness from lessthan a cm to a few cms and showing preferred orientationparallel to the schistosity of the rock. In thin section, it showsembedding of subhedral to nearly euhedral chromite grainsin chlorite matrix (Figs.3a and b). Chlorite occurs asinterlocking scales and is often present in two different grainsizes. Coarse chlorite has higher birefringence and looksmore greenish and pleochroic than finer variety. The mineralalso occurs as oriented scaly intergrowths, fracture fillingsand coarse impregnations in chromite (Figs.3a and b).Chromite has undergone variable degree of peripheraloxidation and occasionally shows concentric compositionalzoning (Fig.3c).

Coarse-grained ultramafite (metapyroxenite withvariable proportions of Fe-Ti oxides) has dark green colourand shows variable degree of mineral lineation withreference to megacrysts of hornblende, which typically showdiffused outlines. It is not uniformly coarse pegmatitic. It isgenerally a composite mixture of fine and coarse-grainedunits. It is dominated by amphibole and is devoid ofchromite; instead it contains V-Ti oxides and abundantmalachite patches. In thin section, the rock shows coarseinterlocking elongated prisms of amphibole, which are

commonly chloritized along the grain boundaries and carryunevenly distributed fine oriented ferriferous schillerinclusions (Fig. 3d).

Magnetite: The magnetite seam on the western side ofthe segment is coarse grained and moderately foliated. Itincludes isolated small patches showing distinctconcentrations of chlorite. In thin section, the rock displaysinterlocking grains of magnetite and ilmenite (these twogenerally account for more than 85% of the modalmineralogy (Table 5), which show variable degrees ofoxidation, and unevenly distributed patches of högbomite(<5 to 25 %) (see also Jayaraj et al. 1995) and aggregates ofchlorite. As compared to entirely V-Ti magnetite on the west,the magnetite seam on the eastern side of the segmentincludes both the normal V-Ti magnetite and narrowdisconnected lenses/bands of Cr-magnetite. It has an overallgranular appearance and tends to contain more chlorite. Inthin section, it resembles chromitite and containschromiferous magnetite in association with magnetite andilmenite. Högbomite, which is usually present in minoramounts in V-Ti magnetite portions, is nearly absent in thechromiferous magnetite lenses.

Meta-anorthositic variations show up in the fieldwith their whitish to light grey colour. These are medium tocoarse grained and weak to strongly foliated with linearorientation and flattening of feldspar crystals parallel tofoliation. The boundaries of the individual anorthositiclenses tend to be diffused and a narrow transition zoneexists between these and the surrounding ultrabasic-melabasic rocks. In thin section, the rock shows evidenceof cataclasis and recrystalization. Original hypidiomorphicto xenomorphic textures of the rock look almost completelyaltered with the superimposition of replacement textures.Plagioclase of the rock is replaced by a mixture of chlorite,epidote, glass clear recrystallized and poorly twinned albiticfeldspar, carbonate, small patches of released quartz andscales of sericite/muscovite. Opaque Fe-Ti oxides andsulphide grains may assume importance at places.

Late intrusive phases include ultramafic dykes. Threeseparate intrusions measuring 1 to 3 m in width and 5 to15 m length have been recorded in the northern hilly portionof the segment. These are fine-grained, massive, granularand composed of variable proportion of Fe-Ti oxide andamphibole.

A few representative modal analyses of the mainlithounits of Hanumalapur segment are given in Table 5.Presence of only chlorite and near absence of amphibole inthe fine-grained ultramafite, chromiferous magnetite andV-Ti magnetite, existence of both amphibole and chloriteas major minerals but virtual absence of chromite in the

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Fig.3. (a and b) Photomicrograph of the main host rock of PGE mineralization, viz., fine-grained ultramafite in the Hanumalapur segment of Channagiri Ultramafic Complex.(a) represents ore sample M 5, which is Pd dominated with 3.38 ppm Pd and 1.2 ppm Pt while (b) represents ore sample M 11 in which Pt dominates with 1.78 ppm Pt and 0.72ppm Pd. Note the overwhelming abundance of Fe-Cr oxide (Fe-Cr) over chlorite (Chl) in M11 as compared to M 5. Also note the presence of oriented fracture fillings of chloritein Fe-Cr-oxide. Polarized light. The width of the photo in both sections covers 2.8 mm of the slide. (c) Fe-Cr-oxide grains of fine-grained ultramafite (8IND-93) showing theconcentric compositional zoning. The cores (grey area) analyse distinctly less Fe but more Al and Mg as compared to rims (light outer area). The outer areas of the zoned crystalsare oxidized, enriched in Fe and show abundant microfractures which are filled with Fe oxide and chlorite (Chl). Incident light. Width of the photo represents 2.8 mm of the slidearea. (d) Photomicrograph of coarse pegmatitic hornblendite (metapyroxenite) (M181) showing large relics of hornblende plates (Hbl) which are considerably altered to chlorite(Chl) and fine grained second generation amphibole. The black opaque mineral is Fe-Ti oxide. Crossed nicols. Width of the photograph represents 10 mm of the slide area.



coarse grained ultramafite and metagabbroic variations maybe noted.

Representative electron probe microanalyses of the mainrock-forming minerals of the PGE mineralized fine-grainedultramafite are given in Table 6. The data has indicated thatwhile chlorite is nearly always ripidolite with Si ionsconstituting 5.26 to 5.23 ions per formula unit and Fe/Fe+Mgratio of 0.24 to 0.41, chromite is iron-rich (FeOt 40.5 to45.6%), depleted in Cr (Cr2O3 29.2-34.7 wt%), greatlyimpoverished in Mg (0.01-0.37 wt %), with Cr# 0.533 -0.645, Fe# 0.044 - 0.215 and Mg# 0.01- 0.02,.

Selected major element analyses of the PGE mineralizedand the associated lithologies of Hanumalapur segment aregiven in Table 7. Averages of all the analyses obtained fordifferent lithounits of the segment are given in Table 8 toenable ready comparison of the units both in terms of majoras well as minor/trace elements and PGE contents. Attentionis specially drawn to: (i) low silica (6-18%), high iron, Cr,alumina and magnesia, near absence to very low lime, andmarked abundance of Ni, Zn and Cu of the fine-grainedultramafite; (ii) very high iron content, about the same levelof alumina, magnesia and vanadium but typically higherCr2O3 and Ni and lower titania of the chromiferous magnetiteas compared to V-Ti magnetite; (iii) variable chemistry, beinghigh or low in magnesia, alumina, iron, titania and lime andcontrastingly low Cr2O3 of coarse grained ultramafite ascompared to fine-grained ultramafite; (iv) considerablevariation in major element chemistry, but, generally highCu and V of the metagabbroic units; and (v) significantlyhigh Mg, Cr and Sr of anorthositic units.

Distribution of PGE in the Hanumalapur Segment

Samples and Analytical Methods

Full (i.e., all 6 elements of the platinum-group togetherwith Au and Re) and partial (viz., only Pt, Pd and Au) PGEanalyses of samples have been obtained. The analyses werecarried out at the Activation Lab, Ancaster, Canada, whichhas an international reputation for precise and reliable PGEanalysis. The lab has employed a combination of methodsfor the analyses. For partial analysis, 15 gm and for fullanalysis, 30-35 gm of the sample were used. For partialanalysis, a combination of Ni-sulphide fusion and ICPMStechniques were employed while for full analysis,Ni-sulphide fusion was coupled with INAA. The detectionlimits of the methods adopted by the lab were as follows(values in ppb): Os 2.0, Ir 0.1, Ru 5.0, Rh 1.0, Pt 5.0, Pd2.0, and Au 0.5.

29 of the 58 outcrop samples collected (each weighing2 to 6 Kgs) from the mineralized 3.5 km x 0.3 kmHanumalapur Segment have been analysed for all the sixPGE, Au and Re. The remaining 29 samples were analysedonly for Pt, Pd and Au. 26 of these samples representedfine-grained ultramafite, 8 each of coarse grained ultramafiteand chromiferous magnetite, 3 each of gabbro and metabasicdykes and 2 anorthosites. The following salient featuresmay be noted in respect of the distribution of PGE in theHanumalapur segment (Tables 9 and 9a).

Localization of PGE Mineralization

On the whole, PGE mineralization in the Hanumalapura

Table 5. Modal analyses of representative petrological units of Hanumalapur segment

Sl. No. 1 2 3 4 5 6 7 8 9 10 11Sample M-1 M-7 M-2 M-11 M-91 M-5 M-87 M-99 M-10 M-105 M-104

Fe-Cr oxide 62.8 60.0 58.5 57.3 51.3 43.1 42.8 40.4 40.1 38.6 27.2

Chlorite 37.2 40.0 41.5 42.7 48.7 56.9 57.2 59.6 59.9 61.4 72.8

Sl. No. 12 13 14 15 16 17q 18* 19 20q 21 22+

Sample M-92 M-93 M-4 M-3 M-100 M-76 M-104A M-96 M-9 M-102 M-88

Ti-Fe-Cr oxide 75.0 66.3 — — — — — — — — —

Fe-Ti Oxide — — 77.6 93.2 92.4 13.3 2.7 0.3 — 0.6 0.2

Hogbomite 25.0 — — 5.8 6.2 — — — — — —

Chlorite — 33.7 — — — 23.7 1.9 7.1 44.2 — 1.9

Amphibole — 22.4 1.0 1.4 62.1 71.7 74.8 4.4 — —

Epidote — — — — 0.6 — 5.4 49.9 71.8 56.4

Plagioclase — — — — — 16.9 11.6 — 27.6 37.7

Carbonate — — — — — 3.3 0.8 — — 1.8

Contains *: 3.5 % Sphene, q: 0.3 and 1.5 % Quartz; +: 4 % Muscovite

1-5: Chromite-rich lenses in fine-grained ultramafite; 6-11: Fine-grained ultramafite; 12-13: Chromiferrous magnetite forming a partof eastern magnetite seam; 14-16: V-Ti magnetite; 17: Coarse-grained ultramafite; 18-20: Melabasic units; 21-22: Meta-anorthosites

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STable 6. Representative chemical analyses of rock-forming minerals of PGE mineralized fine-grained ultramafite of Hanumalapur segment

Chlorites Amphibole Fe-Cr-Ti oxides Alteration related zoned chromite

BH-1 JS-29 3-IND-93 JS-159C BH-1 BH-1 5-IND-93 3-IND-93 3-IND-93 2-IND-93 JS-159 Core Inner Outerrim rim

SiO2

23.95 26.62 26.93 28.80 45.49 52.61 SiO2

0.34 0.03 0.04 0.11 SiO2

0.09 0.06 0.1TiO

20.04 0.08 0.02 0.03 0.28 0.01 TiO

20.06 0.67 50.89 0.83 TiO

20.41 0.59 0.35

Al2O

322.69 19.30 20.24 20.63 9.9 5.5 Al

2O

30.25 0.4 0.02 0.54 Al

2O

315.26 6.27 1.92

FeO 26.19 21.91 17.10 13.41 19.3 8.63 Cr2O

30.13 19.56 0.13 23.16 Cr

2O

330.82 30.02 30.33

MnO 0.23 0.02 0.05 0.09 0.24 0.12 V2O

30.75 0.83 0.17 V

2O

30.5 0.46 0.4

MgO 13.96 18.95 22.43 24.32 9.22 17.06 Fe2O

365.23 43.61 41.87 FeO 49.73 57.79 61.87

Cr2O

30.05 0.63 0.73 1.31 FeO 30.93 35.25 44.27 31.56 MnO 0.76 0.82 0.87

Na2O n.d. 0.00 0.02 0.00 1.15 0.85 MnO 0 0.28 1.25 0.41 MgO 0.69 0.24 0.15

K2O n.d. 0.02 0.16 0.02 0.23 0.01 MgO 0.02 0.06 0.24 0.07 ZnO 1.15 0.56 0.39

CaO n.d. 0.00 0.02 0.02 11.29 11.69 ZnO 0.07 0.15 0.04 0.05 NiO 0.15 0.13 0.08NiO 0.02 0.06 0.21 0.02 0.09 NiO 0.07 0 0.14 Sum 99.56 96.94 96.46ZnO 0.12 0.03 0.08 CaO 0.04 0.02 0.04BaO 0.04 0.02 0.08 Total 91.38 96.6 97.21 98.60 Fe

2O

319.44 29.29 34.56

V2O

30.21 n.d. FeO 32.24 31.45 30.8

H2O 11.55 Si 0.108 0.009 0.012 0.0339 Total 101.52 99.89 99.94

F 0.29 0.28 Ti 0.015 0.154 10.592 0.1900Total 87.25 99.13 88.13 87.10 Al 0.094 0.143 0.006 0.1933 Number of ions on the basis of 32(O)

Cr 0.34 4.707 0.028 5.5979 [Fe2O

3/FeO from ulvospinel basis]

Number of ions on the basis of 28 (O) V 0.189 0.201 0.039Fe2+ 8.116 8.972 10.248 8.0700 Si 0.025 0.018 0.030

Si 5.123 5.5273 5.438 5.382 6.86 7.51 Fe3+ 15.403 9.988 9.6320 Al 4.941 2.166 0.679Ti 0.004 0.0128 0.002 0.004 0.036 Mn 0 0.071 0.293 0.1058 Cr 6.694 6.957 7.196Al4 5.726 2.4727 2.562 2.618 1.758 0.926 Mg 0.009 0.027 0.101 0.0330 Fe3+ 4.020 6.460 7.803Al6 2.2506 2.556 2.265 Zn 0.017 0.033 0.007 0.0121 Ti 0.085 0.130 0.079Fe 4.673 3.8047 2.888 2.252 2.438 1.029 Ni 0.017 0 0.032 V 0.110 0.108 0.096Mn 0.039 0.0036 0.008 0.016 0.027 0.017 Ca 0.013 0.007 0.002 Mg 0.283 0.105 0.067Mg 4.442 5.8650 6.753 7.28 2.075 3.626 Ni 0.033 0.031 0.019Cr 0.1032 0.117 0.208 Fe2+ 7.408 7.709 7.728Na 0.0000 0.006 0 0.326 0.24

Plagioclase BH-1Zn 0.233 0.121 0.086

K 0.0064 0.042 0.005 0.036 SiO2

67.44 Si 2.947 Mn 0.177 0.204 0.221Ca 0.0000 0.004 0.005 1.822 1.783 Al

2O

320.5 Al 1.056 Mol.%

Ba 0.0036 0.002 CaO 0.88 Ca 0.042 RCr2O

40.43 0.45 0.46

Ni 0.009 0.033 0.009 FeO 0.07 Fe 0.003 RAl2O

40.31 0.14 0.04

V 0.018 Na2O 11.3 Na 0.956 Fe

3O

40.26 0.41 0.5

Zn 0.013 0.009 Total 100.19 An 4.20%OH 16.000 Ab 95.60%

H2O - calculated



segment is localized to chromite-bearing fine-grainedultramafite in the centre and chromiferous magnetite lenseswithin the eastern magnetite seam. The said localization isso well defined that it could very well be used as petrologicalguide to the location of PGE mineralization in the segment.The other lithologies of the segment viz., metagabbro/amphibolite, V-Ti magnetite, meta-anorthosite and mafic-ultramafic dykes have similar low PGE contents of <8 to 50ppb; even in the samples of V-Ti magnetite, which areanalysed for all the 6 PGE, the total remains below 59 ppb.The coarse grained ultramafic rock generally analysesrelatively more PGE (viz., Pt+Pd: up to 128 ppb; all 6 PGE:<112 to 150 ppb) than the lithounits mentioned in thepreceding, but, looks contrastingly low as compared to theadjoining and closely associated PGE mineralized fine-grained ultramafite.

It may be noted that the well known base metal sulphideassociation of PGE mineralization is missing in theHanumalapur segment. Evidence of Cu sulphidemineralization is recorded in the coarse grained ultramafiteof the segment, but, there is no PGE mineralizationassociated with this unit.

Pattern of PGE Distribution in the Fine-grained Ultramafite

The analytical data obtained has indicated thenormal inhomogeneity in the distribution of PGE and alsoexistence of separate ore reefs enriched in Pt or Pd.Generally, samples analysing high Pt also contain high Pdand vice versa (Tables 8 and 8a). The ratios of Pt:Pd varyfrom 0.24 to 4.21. There appears to be a negative correlationbetween silicate enrichment and PGE contents; samples of

fine-grained ultramafite collected from silicate enrichedportions with very little chromite (e.g., M1A, M3, M84,M90, M104A) have yielded lowest PGE values. Likewise,in the chromite-enriched samples that contain Ru as the mostdominant PGE, Pt and Pd are subordinate to distinctly lowand in such samples the relative abundance follows thepattern Ru>Os>Rh (e.g., 7/IND93, M10, M87, JS159). Inaddition, it is noted that the samples collected fromthe southern about 2 km of the mineralized segment haveyielded consistently high values of PGE and six of them(viz. M11, M5, 3/IND/93, 2/IND/93, M104 and M105) inthe range of 2500 to 6250 ppb i.e. economically interestingconcentrations.

PGE Distribution in the Chromiferous Magnetite

The PGE mineralized chromiferous magnetite occursforming narrow bands/pods/lenses within the easternV-Ti magnetite seam. In the outcrops, chromiferousmagnetite is not readily distinguishable from the V-Timagnetite and for the same reason an assessment of theproportion of chromiferous magnetite has not beenpossible. Generally the chromiferous magnetite is Pddominant (only one viz., M93, out of the 8 samples hasanalysed more Pt than Pd) and up to 4851 ppb of PGE isrecorded in this; average of 8 samples being 2000 ppb(Tables 9 and 9a).

PGE Distribution Recorded in the Trench Samples

Pt, Pd and Au data obtained for 23 serial samplescollected from a 50.6 m long trench cut across central PGEmineralized zone of Hanumalapura segment, about 250 m

Table 7. Chemical analyses of representative petrological units of PGE mineralized Hanumalapur segment

Sl.No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Sp.No. M M M M M M M M M M M M M M M M M M M83:97 98:97 11:96 5:96 104:97 99:97 92:97 93:97 4:96 100:97 3:96 86:97 89:97 181:97 97:97 76:96 96:97102:97 88:97

SiO2

6.35 9.56 10.51 14.93 15.63 17.83 6.63 8.20 5.39 0.00 0.61 27.49 34.98 38.29 45.34 40.90 49.39 44.40 45.20

TiO2 4.26 2.86 3.49 1.55 2.23 2.86 4.35 2.50 9.5512.09 12.12 0.16 0.12 3.51 0.23 3.86 0.23 0.35 0.13

Al2O

310.48 11.33 12.27 11.84 12.09 11.82 6.24 5.55 9.92 4.36 4.33 18.29 14.03 3.63 5.72 6.36 13.03 21.10 27.23

Cr2O3 17.03 18.29 14.23 11.52 11.05 13.45 10.52 5.90 0.57 0.19 0.29 0.00 0.02 0.57 0.30 0.11 0.18 0.13 0.28

Fe2O

353.96 46.46 46.64 40.05 39.31 35.26 66.37 70.18 67.21 81.24 82.27 14.58 18.80 28.41 14.81 23.509.60 7.18 4.28

MnO 0.46 0.35 0.32 0.29 0.37 0.29 0.33 0.17 0.23 0.20 0.19 0.14 0.13 0.17 0.19 0.18 0.16 0.08 0.05

MgO 6.25 10.04 9.07 14.42 15.73 13.64 4.31 5.17 6.05 1.32 0.80 26.70 21.75 13.35 20.46 11.59 12.80 5.62 5.50

CaO 0.03 0.05 0.00 0.01 bld 0.03 0.04 0.05 0.00 0.04 0.03 0.00 4.45 9.70 8.5610.05 8.67 12.18 12.03

Na2O 0.00 0.02 0.00 0.01 0.01 0.02 0.03 bld 0.00 0.00 0.00 0.01 0.23 0.21 0.08 0.54 1.34 2.98 2.08

K2O 0.01 0.01 0.00 0.01 0.00 0.00 0.01 0.01 0.01 0.01 0.01 0.00bld 0.04 0.01 0.08 0.63 0.17 0.91

P2O

50.01 0.00 0.01 0.01 0.01 0.01 0.00 0.00 0.01 0.01 0.01 0.02 0.02 0.01 0.01 0.01 0.04 0.01 0.01

V2O3 0.56 0.49 0.41 0.31 0.34 0.27 0.72 0.89 0.75 0.75 0.62 0.02 0.02 0.20 0.03 0.24 0.03 0.03 0.01

LOI 0.56 1.92 2.53 4.47 4.47 4.74 0.52 1.81 2.12 0.20 0.5011.12 6.88 1.54 3.44 1.05 2.23 3.00 3.24

Total 99.96 101.38 99.48 99.42 101.24 100.22 100.07 100.43 101.81 100.41 101.7898.53 101.43 99.63 99.18 98.47 98.33 97.22100.95

Sl.No: 1-6 : Fine-grained ultramafite; 7-8 : Chromiferrous magnetite; 9-11: Magnetite; 12-14: Coarse grained ultramafite; 16-17: Metagabbro ;17-19: AnorthositeNote : Refer Tables 8 and 8A for PGE, Ni and Cu contents of these samples



south of Hanumalapur-Nellihankalu road (Fig. 4), hasindicated that (i) with the exception of those portions of thetrench where anorthositic and silicate enriched litho unitsexist, the rest of the trench has anomalously high Pd and Ptvalues, the highest Pt+Pd value of 1384 ppb having beenobtained from a 3.2 m wide zone at the eastern end of thetrench (see Fig. 4). The trench sample results have furtherindicated that almost over the entire 50.6 m wide zone ofthe trench there is diffused PGE mineralization. Further,except for a narrow zone, represented by sample 8 (Fig. 4),in the rest of the trench zone Pd dominates over Pt withPd:Pt ratios mostly ranging between 0.7 and 3.

Inferences on PGE Mineralization Based on Drill CoreLogging

Lithogeochemical analysis including PGE distributiondata obtained by systematic logging of 252 m drill corecolumn (BH1), which represents a cross section of the bestportion of the PGE mineralized Hanumalapur segment isgraphically presented in Fig.5. Although data has beenobtained for all major and a range of almost 40 differentminor/trace elements, in the presentation given hereconcentrations of only Pt, Pd, Cu, Ni and Cr are selectivelyhighlighted. A special focus is also made on the PGE orezones of commercial value identified in the drill core sectionlying between 30 and 120 m, using a close-up of graphicalpresentation (Fig. 5a). Attention is particularly drawnto the 3 main ore reefs analysing 3.8, 5.0 and 4.0 ppmPt+Pd intersected at depths of 97.23, 101.05 and 101.6 mand also to the 3 leaner reefs analysing 1.6, 1.7 and 1.8 ppmPt+Pd , intersected at depths of 89.5, 93.0 and 94.8 m(Fig. 5a). These reefs are located in (metamorphosed)clinopyroxenite with picrite and websterite inter-bands andentirely picrite layer, but, closely associated with chromitebands, which lie adjoining the PGE reefs and form inter-bands in the host rocks. The three additional leaner reefsintersected at depths of 35.95, 45.6 and 75.7 m, analysing1.3, 1.5 and 1.4 ppm Pt+Pd respectively, show an overallCu-Ni sulphide association (values of Cu and Ni may be ashigh as 0.8 and 0.2 wt % respectively), but, some Crassociation is still recognized. On the whole it is noted thateven in the drill core data, although the mineralization itselfis in the silicate assemblage there are chromite bandsadjoining the PGE reefs, emphasizing the interlinking ofPGE mineralization with chromite distribution.

Distribution of Au and Re

On an average, the PGE mineralized fine-grainedultramafite and chromiferous magnetite analyse 41 ppb Au,which is distinctly more than the values recorded in theassociated lithologies viz., V-Ti magnetite, anorthosite,gabbro-amphibolite and mafic-ultramafic dyke phases.Coarse grained ultramafite, however, usually analyses onan average more Au viz., 36 ppb, which is more than whatwe have in other associated lithologies (Table 9). Re isusually below detection limits both in PGE mineralized andnon-PGE mineralized lithologies of the segment; exceptionsare the samples of fine-grained ultramafites 1/IND93 andM104 which analyse 57 and 7 ppb Re respectively.

Comments on Layering and Genesis of PGE Mineralization

The layering displayed by Hanumalapur segment,

Table 8. Average chemical compositions of the main lithounits ofHanumalapur segment

1 2 3 4 5 6Samples (16) (3) (5) (9) (6) (4)

SiO2

13.22 7.78 3.88 37.26 43.85 42.03

TiO2

2.84 3.49 10.64 1.10 1.71 0.19

Al2O

311.55 6.48 6.78 9.59 9.02 22.34

Cr2O

313.40 9.60 0.27 0.21 0.30 0.15

Fe2O

342.82 65.44 73.41 20.73 17.07 7.50

MnO 0.35 0.28 0.19 0.16 0.17 0.10

MgO 11.99 4.62 3.71 19.55 12.85 7.18

CaO 0.02 0.07 0.17 5.04 10.18 12.56

Na2O 0.01 0.03 0.05 0.10 0.50 1.68

K2O 0.02 0.01 0.01 0.02 0.14 0.28

P2O

50.01 0.00 0.01 0.03 0.04 0.01

V2O

30.39 0.78 0.70 0.06 0.10 0.01

LOI 3.36 1.25 1.42 5.33 3.18 4.12

Ni 1290 1037 523 762 518 199

Cu 402 213 212 1348 1168 54

Zn 812 610 505 105 101 46

Cl 49 22 9 55 51 12

Rb 3 1 3 6 11

Sr 3 4 10 12 57 390

Ba 1 3

Nb 2 5 4 4 4 1

Ta 1 1 6 5 1

Hf 0 0 0 3 1 0

Zr 1 2 4 25 32 45

U 2 3 4

Th 3 0 9 5 10

Ga 49 47 54 15 15 20

Y 0 1 7 9 4Sc 12 21 18 29 47 12

Values in ppb

Pt 776 386 6 31 19 7

Pd 1243 351 8 19 19 8

Au 32 3 10 16 15 3

1- Fine grained ultramafite; 2 - Chromiferrous magnetite; 3 - V-TiMagnetite; 4 - Coarse grained ultramafite; 5 -Metagabbro; 6 - Meta-anorthosite



Ass

ay (

valu

es

in p

pb)

Au

Pt

Pd

Wid

th(m

ts)

5519

11

0.7

1454

102

358

277

470.

5

1.7

4226

74

28

63

21

220.

7

1.2

6.8

159

174

0.4 Scree

Metagabbro

Meta-anothosite

Coarse grained ultramafite

- - - - do - - - - schistose

Fine grained ultramafite

45

78

70

58

55

o

o

o

o

o

21

1423

1.0

2.0

33

562

59 793

81

53

.0

3.0

16

55

68 864

78

3.5

2.0

142

45

0 77

42

104

.0

4.0

97

94

209

236

166

262.

7

3.2

3819

82

37

285

135

623.

0

2.0

5210

91

92

127

5134

3.0

2.5

261

662

13

95

19

242.

3

1.0

3317

71

45

130

084

116

3.2

ScaleBoth Vertical & Horizantal

0 1

Mts

987

654321

1514

131211

10

23222120

191817

16 EW

although similar to the layering noted in some of theunmetamorphosed differentiated mafic dyke intrusions (e.g.Devaraju et al. 1995), has several important differences.One of the major differences noted in the Hanumalapursegment is the presence of silica deficient ultramafite in thecenter and more silicic gabbroic units at the border ascompared to differentiated dyke intrusions, which arecharacterized by more mafic borders and silicic/fractionatedcentral zones.

Layering and zonary arrangement of lithologies ofHanumalapur segment bear conformable relationship withthe tabular form of the segment. Temperature gradient setupbetween (the colder) contacts and (hotter) center duringcooling of the tabular intrusion is thought to explain thelayered character as well as zonary arrangement of thelithologies parallel to the contacts of the steep dippingtabular intrusion. It is not a saucer/funnel-shapedintrusion like Bushveld or Skaergaard or Stillwater wherelayering is related to downward gravity settling fromcolder roof of the intrusion to produce vertical sequentialvariation.

Taking into account the available petrological andgeochemical data, it is proposed that the central fine-grained ultramafite and the eastern chromiferousmagnetite were the first pulses to intrude. Those were closelyfollowed by emplacement of V-Ti magnetite along thewestern and eastern contacts of the central zone. Theanorthosite developed as in-situ local segregations. Thegabbroic pulses emplaced later along the tectonically activecontacts. The coarse pegmatitic ultramafite has intruded inthe late stages, largely on the eastern hanging wall side ofthe central ultramafic zone. The contrasting composition ofcoarse grained ultramafite, specially the enrichment of

Fe-Ti oxides and Cu-sulphides, absence of chromite, highlime and sharply depleted PGE contents as compared tofine-grained ultramafite, do not permit interpretation ofcoarse grained ultramafite as being related to fine grainedultramafite through anatexis (Mutanen, 1989). We think thatthe coarse grained ultramafite represents permeations ofresidual ultramafic liquid along contraction openings andcrevasses emplaced in the late stages.

Genesis of PGE mineralization is a greatly debated issueand differing opinion are put forth regarding the source andnature of magma, mechanism of concentration PGE, etc.No attempt is made here to discuss the issue in fuller details.We have only highlighted in the following some of theobservations that have implications on the genesis ofHanumalapur PGE deposit.

Plotting of major element data in respect of cations ofAl, Fe+Ti and Mg in the Jensen (1976) ternary diagram(Fig. 6) and in the Al 2O3 vs MgO wt% binary discriminationdiagram of Viljoen et al. (1982) (Fig. 7) has indicated thatwith the exception of anorthositic and some gabbroicsamples, analyses of all other petrological units ofHanumalapur segment carry geochemical signatures ofkomatiitic basalt to high Fe-tholeiite basalt. Even morerevealing are the plots of Pd/Ir : Ni/Cu (Fig. 8a), Pd/Pt:Ni/Cu (Fig. 8b) and Ni/Pd : Cu/Pt (Fig. 8c) metal ratios inthe binary discrimination diagrams of Barnes et al. (1987).The close chemical similarity of the PGE mineralizedHanumalapur segment with the well known layeredintrusions and also some of ophiolites, High-Mg basaltsand PGE reefs is clearly brought out in terms of theseratios. We do not, however, intend to elaborate thesefindings any further. Whatever postulations are putforth for explaining the relation of these ratios to the PGE

Fig.4. Pt-Pd-Au data for the serial samples collected from the 50.6 m long trench cut across the PGE mineralized zone, about 250 msouth of Hanumalapur-Nellihankalu Road. Note the anomalously high PGE values recorded over the entire length and dominanceof Pd over Pt in all the samples analysed, except one.

JOU

R.G

EO

L.SO

C.IN

DIA

, VOL

.70,O

CT.2007

55

0T. C

. DE

VAR

AJU

AN

D O

TH

ER

S

Table 9. PGE, Au and Re analyses and ratios of PGE and base metals of Hanumalapur segment (PGE in ppb and base metals in ppm)

Sl.No. Sp.No. Os Ir Ru Rh Pt Pd Au Re Cu Ni Pd/Pt Pt/Pd Pd/Ir (Pt+Pd)/ Cu/Pt Cu/Pd Cu/Ir Ni/Pd Ni/Cu(Os+Ir+Ru)

V-Ti Magnetites

1 4/IND/93 <2 0.3 5 <0.2 14 13 1.7 <5 0.9 1.1 43.3

2 5/IND/93 <2 0.6 10 3.3 16 18 12 <5 1.1 0.9 30.0

3 6/IND/93 <2 0.8 20 4.7 18 13 1 <5 0.7 1.4 16.3

4 9/IND/93 <2 0.5 <5 <0.2 11 2 0.8 <5 0.2 5.5 4.0

5 M4:96 <2 0.5 <5 0.9 13 18 2.5 <5 384 626 1.4 0.7 36.0 29538 21333 768000 34778 1.6

Chromiferrous magnetite

5 M93:97 16 31 110 101 930 630 12 <5 254 925 0.7 1.5 20.3 9.9 273 403 8194 1468 3.6

6 M98:97 5 16 40 37 860 2080 370 <5 85 1087 2.4 0.4 130.0 48.2 99 41 5313 523 12.8

Coarse grained ultramafites

7 M6:96 <2 0.6 <5 1.4 55 48 28 <5 854 779 0.9 1.1 80.0 15527 17792 1423333 16229 0.9

8 M95:97 <2 1.3 13 43 53 39 17 <5 456 1274 0.7 1.4 30.0 8604 11692 350769 32667 2.8

Fine-grained ultramafites

9 1/IND/93 27 21 68 66 607 499 9.3 55 0.8 1.2 23.8 9.5

10 2/IND/93 13 19 30 56 1090 3050 49 <5 2.8 0.4 160.5 66.8

11 3/IND/93 43 84 40 385 4000 1700 29 <3 0.4 2.4 20.2 34.1

12 7/IND/93 100 52 275 24 131 127 5.5 <5 1.0 1.0 2.4 0.6

13 8/IND/93 82 58 280 36 33 36 2 <5 1.1 0.9 0.6 0.2

14 M1:96 38 29 120 24 196 260 14 <5 279 1342 1.3 0.8 9.0 2.4 1423 1073 9621 5162 4.8

15 M2:96 27 27 75 93 694 434 31 <5 333 1471 0.6 1.6 16.1 8.7 480 767 12333 3389 4.4

16 M5:96 15 22 41 71 1200 3380 82 <5 306 1511 2.8 0.4 153.6 58.7 255 91 13909 447 4.9

17 M7:96 96 56 230 38 54 48 8.8 <5 525 1476 0.9 1.1 0.9 0.3 9722 10938 9375 30750 2.8

18 M10:96 130 96 300 87 307 281 58 <5 0.9 1.1 2.9 1.1

19 M11:96 30 42 65 87 1780 715 20 <5 734 1416 0.4 2.5 17.0 18.2 412 1027 17476 1980 1.9

20 M84:97 18 19 66 28 101 24 5.3 <5 583 1253 0.2 4.2 1.3 1.2 5772 24292 30684 52208 2.1

21 M87:97 88 61 180 41 120 133 7 <5 34 755 1.1 0.9 2.2 0.8 283 256 557 5677 22.2

22 M91:97 35 39 83 154 1930 2610 18 <5 279 1342 1.4 0.7 66.9 28.9 145 107 7154 514 4.8

23 M92:97 14 12 110 46 100 230 10 <5 57 1053 2.3 0.4 19.2 2.4 570 248 4750 4578 18.5

24 M99:97 8 11 23 48 1000 2250 57 <5 249 1361 2.3 0.4 204.5 77.4 249 111 22636 605 5.5

25 M104:97 8 14 29 47 720 1750 15 7 401 1287 2.4 0.4 125.0 48.4 557 229 28643 735 3.2

26 M105:97 10 17 28 55 956 2180 74 <5 710 1744 2.3 0.4 128.2 57.0 743 326 41765 800 2.5

27 JS-159 61 48 220 23.9 29 19 7.2 <5 0.7 1.5 0.4 0.1

28 JS-29 4 3.9 10 14.1 43 61 3.8 <5 1.4 0.7 15.6 5.8

Primitive mantle

4.2 4.4 6 2 9.2 4.4 1.4 28 2000 0.48 2.09 1.0 0.93 3043 6364 6364 454545 71.4



deposits in the layered intrusions and other relatedrocks could as well be extended to Hanumalapur case.

It is not yet clear how the thick heterogeneous PGEmineralized zones in the Hanumalapur segment wereformed. But, the evidence gathered so far suggests something other than a traditional orthomagmatic model. Suchan opinion derives support by the general lack of base metalsulphide association in favor of chromite and silicates.Considering close association of PGE mineralization withthe chromite both in outcrops and drill core columns it isinferred that the precipitation of Cr had governing controlover PGE mineralization. It is also surmised that PGEmineralization in the Channagiri ultramafic complex tookplace in the very early stages of magmatic crystallization ofthe complex in which chromite got separated. Theassociation further suggests that no significant post-cumulus redistribution and/or overprint of the primary PGEmineralization has taken place. Nucleation of chromiteapparently changed the solubility of sulphur triggering

the deposition of PGE in its association (Naldrett andLahmann, 1998; Scoon and Teigler, 1994). In terms ofenrichment of Fe-Cr oxide in the host rock and lack ofNi-base metal sulphide association, the PGE mineralizationin the Hanumalapur segment compares with that reportedfrom Koitelainen, Keivitsa-Setavara and Penikat layeredintrusion in northern Finland (Alapieti, 1986; Mutanen,1984; Halkoaho, 1994).

The discrete PGM’s are certainly too small to accumulateto form economically viable reefs. Direct precipitation ofPGM from the magma relatively enriched in PGE, isproposed by Hiemstra (1985), Merkle (1992) and Tredouxet al. (1995). PGE entrapment from adherence to chromitegrains (Hiemstra, 1992) and encapsuling in silicates(Tredoux et al. 1995) are suggested mechanisms. Apparentlythe PGM inclusions have remained virtually immobile inspite of complete transformation of original silicates, olivineand pyroxenes, to chlorite, amphibole and epidote andoxidation of chromite in response to penetrative tectonic

Table 9a. Partial PGE, Au and base metal analyses of various lithounits of Hanumalapur segment

Sl. Sample Pd Pt Au Cu Ni Pt/Pd Cu/Ni Cu/Pt Cu/PdNo.

1 M11a 218 216 7 509 1445 0.99 0.35 2.36 2.33

2 M197 1355 593 36 0.44

3 M101 221 54 5 66 820 0.24 0.08 1.22 0.30

4 M90 <4 <5 94 366 27 13.56

5 M1a 15 30 <2 2.00

6 M104A <4 <5 6 539 745 0.72

7 M111 4 4.1 4 110 1147 1.03 0.10 26.83 27.50

8 M83 1690 1400 37 0.83

9 M94 100 41 <2 327 1132 0.41 0.29 7.98 3.27

10 M76 32 41 45 2189 460 1.28 4.76 53.39 68.41

11 M89 11 10 2 255 832 0.91 0.31 25.50 23.18

12 M97 <4 <5 <2 466 820 0.57

13 M181 103 25 57 9093 487 0.24 18.67 363.72 88.28

14 M85 <4 <5 <2

15 M86 <4 <5 <2 9 276 0.03

16 M85a 24 9.4 2 62 230 0.39 0.27 6.60 2.58

17 M3 13 6.2 12 97 654 0.48 0.15 15.65 7.46

18 M82 5.2 2.8 19 322 656 0.54 0.49 115.00 61.92

19 M103 <4 <5 5 115 338 0.34

20 M100 5.6 3.1 10 143 341 0.55 0.42 46.13 25.54

21 M96 <4 <5 <2 60 274 0.22

22 M102 11 9.5 4 107 172 0.86 0.62 11.26 9.73

23 M88 <4 <5 <2 22 192 0.11

24 M196 38 12 3 0.32

25 M198 <4 <5 2

26 M200 10 13 2 1.30

1-3: Fine-grained ultramafite; 4-7: Silicate enriched fine-grained ultramafite; 8-9: Chromiferrous magnetite;10-16: Coarse-grained ultramafite; 17-20: V-Ti magnetite; 21: Metagabbro (amphibolite); 22-23: Meta-anorthosite; 24-26: Ultramafic dykes intruding Hanumalpur segment


552 T. C. DEVARAJU AND OTHERS0 25 50 75 100

125

150

175

200

225

250

m

Ni

01

000

200

0

Cu

010

00

02

00

00

Cr

10

10

00

10

0000

Pd

01

50

03

00

0P

t0

20

00

40

00

Quartz-gabbro-quartz-dioriteGabbroMalagabbroChromititeMagnetite

WebsteritePicriteClinopyroxenite + PicriteClinopyroxenite + WebsteriteClinopyroxenite

0.01

0.1

10

%

Fig.5. Lithological details and distribution of Cr, Ni, Cu, Pt and Pd as recorded in drill core column of Borehole 1 representing a crosssection of the tabular Hanumalapur segment (see Fig.2 for location of the borehole). Attention is drawn to the following:(i) layering parallel to the contacts of the tabular body, (ii) presence of thinner gabbro rim on the eastern side and thicker rim ofthe rock on the western side (iii) about 130m zone of ultramafic rocks, lying between the gabbroic rims, which comprises oflayers of chromitite, magnetite, clinopyroxenite, websterite and picrite, (iv) localization of ore level PGE mineralization to 5 mcolumn consisting of clinopyroxene-websterite-picrite with thin cm scale layers of chromite, and (v) diffused leaner PGEmineralization in about 60 m column of ultramafic rock lying to the east of the main PGE zone.

movements, hydrothermal alteration and low-grademetamorphism.

Strong inhomogenity of the PGE mineralization togetherwith the paucity of Cu-Ni sulphides negates models basedon: (i) hydrothermal or late-stage magmatic fluids, and(ii) collection of immiscible sulphide droplets (Tredoux etal. 1995).

The PGM textures show little evidence of hydrothermalalteration and remobilization, but, as already mentioned, thePGE mineralogy itself bears certain characteristics of fluidaction as indicated by the rare occurrence of OH-bearingPt+Pd minerals (Devaraju et al. 2005).

Comparison with SJ Reef and UG2

Although lower in PGE content (see Table 10) the

Hanumalapur segment of Channagiri ultramafic complexresembles the Cr-controlled mineralization forming a partof the SJ reef of Penikat layered intrusion (Halkoaho, 1994)and UG2 of the Bushveld complex (McLaren and DcVilliers, 1982). The similarity among the three, althoughreflected in absolute values compiled in Table 10, looksmore impressive when their mantle normalized PGE patternsare compared (Fig.9). This similarity is thought to suggestnot only derivation from comparable source magma butalso analogous process of PGE mineralization. TheHanumalapur segment is of course a miniature example ascompared to Bushveld and even Penikat.

Comments on Commercial Potential

Platinum mineralization in the Hanumalapur segment



includes both Pt- and Pd-rich ore reefs, but, the latter greatlydominate over the former. Although evidence of persistenceof mineralization over the entire strike length of 3.5 km ofHanumalapur segment has been picked up, it is typicallyinhomogeneous varying both along and across the strike.Further, a perusal of graphical presentation (Fig. 5) given inrespect of Pt and Pd data obtained by systematic logging of252 m drill core column of Borehole 1 (refer Fig. 2 forborehole location) would indicate that while there are threereefs of 20 cm, 30 cm and 35 cm thickness, analyzing3.7 ppm, 5.0 ppm and 4.0 ppm of combined Pt+Pd, thereare at least five other lower grade reefs analyzing 1.3 to1.8 ppm of combined Pt+Pd, located in a 50 m thick zonelying stratigraphically above the main ore zones. The reefsshow strike persistence from 10’s of meters to a couple ofhundred meters. Interestingly the leaner ore reefs contain0.7 to 1.8 wt % Cu and 0.12 to 0.22 wt % Ni, which shouldadd to the commercial value of these reefs. Depth-wisepersistence of mineralization for more than 100 m has beenascertained by drill core data. Assuming a strike persistenceof 2.5 km and depth persistence down to 100m, anapproximate estimation of combined Pt+Pd contained in thethree main reefs located in the central fine-grainedultramafite analysing 3.7 gm, 5.0 gm and 4.0 gm/tonne ofore indicates the possible existence of 7,500 kg of combinedPt+Pd. It should, however, be stressed that the estimate isapproximate and is given here only to highlight the possiblecommercial value of the Hanumalapur deposit. Certainly alot more quantitative three dimensional estimation of assay

30

50

75

100

120

Dep

th in

dri

ll h

ole

(m)

0 1 2 3 4 5 6Pt+Pd+Au (ppm)

ChromititeMagnetiteWebsteritePicriteClinopyroxenite + PicriteClinopyroxenite + WebsteriteClinopyroxenite

35.95

45.6

75.7

89.5

93.094.8

97.23

101.6101.9101.05

5a

Fig.5a. Close-up of drill core column highlighting the PGEmineralization in the 70 m column of ultramafic rocks lyingon the eastern side of Hanumalapur segment.

Calc-Alkaline

Tholeiite

Komatiite

KomatiiticBasalt

High Mg – Tholeiitic Basalt

High Fe-Tholeiitic

Basalt

Al Mg

Fe+Ti

Fine-grained ultramafites

Meta-anorthosite

Chromiferous magnetiteV-Ti magnetiteCoarse grained ultramafiteMetagabbro

Fig.6. Al-Fe+Ti-Mg ternary discrimination diagram (after Jensen,1976). Predominantly komatiitic basalt affinity with bothV-Ti magnetites and chromiferous magnetite analysesbarely straying into high-Fe tholeiiteic filed and someanorthositic units displaying tholeiite-calc-alkaline affinitymay be noted.

0 10 20 30 40

5

10

15

20

25

MgO (%)

Al 2

O3

(%)

Komatiite field

Tholeiite field

Fig.7. Al 2O3-MgO binary discrimination diagram (after Viljoenet al., 1982) showing boundary limits of komatiite andtholeiite fields. Komatiitic affinity of all the petrologicalunits of Hanumalapur segment except anorthosite andanorthositic gabbro is indicated.



Komatiites

Mantle

Chromitiites

PGEReefs

FloodBasalts

10-2 10-1 100 101 102 103

10-2

10-1

100

101

102

103

LayeredIntrusions

Cu-richSulphide Veins

High MgO Basalts

Ophiolites

L.I.

Oph.

+OL

+CHR

Ni/Cu

Pd

/Pt

104

a

Table 10. Comparison of Cu, Ni, PGE and Au concentrations in selected samples from PGE mineralized portions of Hanumalapur segment withMerensky Reef, SJ Reef, UG2, Mantle and C1 Chondrite

No. of Cu Ni Os Ir Ru Rh Pt Pd Ausamples

HS Range 11Max 734 1744 43 84 110 385 4000 3380 370Min 249 925 5 11 23 37 607 499 9

HS Average 11 396 1321 19 29 51 101 1370 1895 67

Merensky Reef 63 74 430 240 3740 1530 310

SJ-sulphide type 3 600 1600 61 99 123 373 2667 2700 83

UG2 12 200 1300 53 60 1060 600 3200 1960 50

Mantle 28 2000 4.2 4.4 6 2 9.2 4.4 1.4

C1 Chondrite 514 540 690 200 1020 545 152

HS- Hanumalapur Segment (present study), Merensky Reef (Naldrett and Cabri, 1976), SJ Reef (sulphide type) (Halkoaho, 1994), UG2 Chromitite(Naldrett and Cabri 1976; McLaren and De Villiers, 1982), C1 Chondrite (Barnes et al. 1985) and Mantle (Sun 1982; Barnes et al. 1988)

+SU

L

or+PG

M

10-2 10-1 100 101 102 103

10-2

10-1

100

101

102

103

104

105

106

+CHRmss

Ni/Cu

Pd

/Ir

PGE Reefs

Cu-richsulphide veins

FloodBasalts

LayeredIntrusions

Chromitite L.I.

Mantle

Ophiolite

ChromititeOph.

Komatiites

High MgO Basalts

OL+

b

Mantle

OPH

Chr

omiti

tes

L.I.

PG

E -

Ree

fs

FloodBasalts

Cu-richsulphide vein

High MgO Basalts

Ophiolites

Komatiites

Laye

red

Intr

usio

ns

+SUL or

PGM

+ OL or+ CHR

107

106

105

104

103

102

101

100 101 102 103 104 105 106 107

Cu/Pt

Ni/P

d

c

Fig.8. Binary discrimination diagrams based on (a) Pd/Ir vs Ni/Cu, (b) Pd/Pt vs Ni/Cu and (c) Ni/Pd vs Cu/Pt metal ratios (fields afterBarnes et al. 1987). Plotting of most analyses of PGE mineralized Hanumalapur segment into the filed of layered intrusions(with which High-Mg basalt, PGE reef, ophiolite, Komatiite fields overlap partly to fully) is in keeping with the layeringdisplayed by the segment. The inset shows the displacement of vectors for olivine (Ol) addition, chromite (Chr) and monosulphidesolid solution (mss) addition or platinum-group element (PGE) addition during partial melting.



values are needed to asses the actual size of the deposit.Equally essential is the experimental data pertaining to theviability of Hanumalapur ore for concentration andextraction of PGE. Experiments are now under way, inassociation with the Geological Survey of Finland, to assessthe viability of the Hanumalapur ore for concentration,extraction and ultimate commercial exploitation.

CONCLUSIONS

The Hanumalapur segment of the Channagiri mafic-ultramafic complex in the Late Archaean Hegdale GuddaFormation, SE of Shimoga Supracrustal belt, hosts ratherunique PGE mineralization. It holds promise of a

commercially workable deposit with three closely spacedore reefs measuring 20, 30 and 35 cm in thickness andanalysing 3.7 ppm, 5 ppm and 4 ppm of Pt+Pd and anapproximate combined Pt+Pd reserves of 7500 kg. Genesisof this unusual chromite controlled silicate dominatedmineralization remains enigmatic and is open to speculation,but, it is hoped that further detailed examination wouldshed light on this aspect of the deposit. The HanumalapurPGE mineralization, like SJ-reef in the Penikat intrusion,Finland, is sulphide poor and it is expected to serves ashighly significant discovery in the formulation of futureexploration strategies.

Acknowledgements: This study has been accomplished by TCDunder the research project “Investigation of layered mafic-ultramafic complexes of the Shimoga schist belt of Karnataka withspecial reference to evidence of platinum mineralization”sponsored by Dept. of Science & Technology, Govt. of India. TTAand RJK have participated in the study as a part of their workunder the Finnish Academy grants, held by the former, to work inparts of Karnataka to locate signs of PGE mineralization. Weexpress our sincere thanks to both the funding authoritiesmentioned. Prof. K.S. Anantha Murthy, Dept. of AppliedGeology, Kuvempu University, has shown continued interest inthe progress of work and has always extended thoughtfulsupport and warm hospitality during our repeated visits toShimoga and Shankaraghatta for examination of field area.Dr. R.C. Nyamati, presently with Rolta’s Mumbai, during hisassociation with us in the final year of project implementation,has offered valuable assistance in the preparation of reportsubmitted by TCD to DST and also in the study of drill coresamples. Exploratory drilling support has been received fromDepartment of Mines and Geology, Govt. of Karnataka. Wegratefully acknowledge the keen interest and encouragementreceived from the then Additional Director (Minerals) of theDepartment, Sri. B.A. Lalgondar.

Fig.9. Comparison of mantle-normalized PGE, Au, Ni and Cudata for selected fine-grained ultramafite and chromiferousmagnetite samples of Hanumalapura segment with SJ Reef(data from Halkoaho, 1994) and UG2 (data from McLarenand De Villiers 1982, Naldrett and Cabri, 1976).

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0.2

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Ni Os Ir Ru Rh Pt Pd Au Cu

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ized

UG 2

Chromiferrous magnetite

Fine-grained ultramafite

SJ Reef



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(Received: 22 September, 2005; Revised form accepted: 16 August 2006)

Petrological and PGE Mineralisation Study of the Channagiri Mafic- Ultramafic Complex, Shimoga...

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