Available online at www.sciencedirect.com *- arsr

1 * 9

ill ScienceDirect JOURNAL OF

Mia M ? H S

JOURNAL OF RARE EARTHS 25 (2007) 749 - 758 www.elseviE.md&dre

Contmting REE Signatms on Manganese Oms of h n Om Gmup in North Orissa, India P. P. Mishra', B. K. Mohapatra' * , P. P. Singh2 ( I . Institute of Minerals and Mderials Technology, Bhubanesww 751013, India; 2. Post G r d u d e Department of Geology, Utkal University, Bhubanesww 751004, India)

Received 18 May 2007; revised 14 September 2007

Abstract: The distribution pattern of Rare Earth Elements (REE) in three categories of manganese ores viz. stratiform, stratabound-replacement, and detrital of Precambrian Iron Ore Group from north Orissa, India was reported. These cate- gories of Mn-ore differed in their major and trace chemistry and exhibited contrasting REE signature. The stratiform ores were relatively enriched in SREE content (697 pg - g-I ) and their normalized pattern showed both positive Ce and Eu anomalies, whereas the stratabound-replacement types were comparatively depleted in 1 REE content (21 1 pg - g- I ) and showed negative Ce and flat Eu signatures. The detrital categories showed mixed REE pattern. The data plotted in differ- ent discrimination diagrams revealed a mixed volcaniclastic and chemogenic source of material for stratiform categories, and LREE (Light Rare Earth Elements) and HREE (Heavy Rare Earth Elements) are contributed by such sources, respectively. In contrast, the stratabound ore bodies were developed during the remobilization of stratiform ores, and associated Mn- containing rocks under supergene condition followed by the redeposition of circulating mineralized colloidal solutions in structurally favorable zones. During this process, some of the constituents were found only in very low concentration within stratabound ores, and this is attributed to their poor leachability/mobility. The detrital ores did not exhibit any sig nificant characteristic in respect of REE as their development was via a complex combination of processes involving weathering fragmmtation, recementation, and burial under soil cover.

Key words: manganese ore; REE normalization; geochemistry; Bonai-Keonjhar belt; Orissa; rare earths cu3 number: TD861; 0614.3 Document code: A Atticle ID: 1002 - 072 1 (2007)06 - 0749 - 10

Tabular manganese ore bodies closely associated with iron ores occur in the Precambrian Iron Ore Group (IOG) of rocks in north Orissa, India. These ore bodies are distributed in a province known as Bo- nai-Keonjhar belt or Jamda-Koira valley. Several re- searchers" - 6 1 have earlier described the general geolo- gy, stratigraphy, mineralogy, and genesis of these ores. Mohapatra et al"' elsewhere described the chemistry of rare earth elements (REE) in a part of the western Koira valley of this belt.

Recently, Mishra et a1[*' have discussed the mode of occurrence and characteristics of Mn-ore bodies from Bonai-Keonjhar belt and its a part of s ig nificance in the evaluation of resource. In the present article, the authors gave a detailed description of the nature and distribution of rare earth elements in man- ganese ores of Iron Ore Group, highlighted the con- trasting chondrite-normalized REE patterns shown by different categories of ore bodies, and interpreted its genesis from REE signatures.

: Conesponding authoHE-mail: bk - mohapatra@yahoo.com) Foundation item: Project supported by the Department of Science and Technology, Government of India, New Delhi (ESSR3NESB43D9) Biofpphy: Patitapaban Mishra (1973-), Male, Research scholar

Copyright 02007, by Editorial Committee of Journal of the Chinese Rare Earths Society. Published by Elsevier B.V. AU rights reserved.

750

1 Geologicalsetting The Precambrian Iron Ore Group of rocks in

north Orissa, India is exposed in form of a ' U ' shaped pattern. Jones[g1 described the basin as a hor- seshoe-shaped synclinorium because of its geographic configuration (Fig. 1). The structure of this belt is considered to be a synclinorium plunging with low an- gle (8" - 12") towards NNE with an over-folded western limb. The basin consists of a large volume of volcano-sedimentary rocks. Volcanic rocks of acidic to basic varieties crop out in the outer fringe of the belt on all three sides except in the north. The litho assem- blages of Iron Ore Group are comprised of shale and

phyllites, BIF (Banded Iron Formation), and BMF (Banded Manganese Formation) along with iron and manganese ore deposits. Most of the ' shales ' in the basin are of tuffaceous nature"']. From the geological investimtion and deep borehole log, several iron and manganese ore bands are found to be interbedded with shalelchert and reported to be of syngenetic origin'"].

2 Materials and Methods Twenty-four representative samples from sepa-

rate operating manganese mines in the Bonai-Keonjhar belt along with six samples of the associated country rocks (shale) were collected and studied in detail in re- spect of their major, trace elements, and REE distribu-

I J I Attitude of bedding plane

Banded iron formation r-4 Mn ore sample locality

... r . . . a ....... Sandstone I . . . . . .

Fig. 1 Geological map of Precambrian iron ore group of rocks in horseshoe shaped synclinorium, north Orissa, India, showing Mn-ore sample localities (modified after Jones, 1934)

Mkhm P P et a! Contnsting REE Signdm on Manganese O m of Imn Om Gmrq, in North Oksa, India 75 1

tion. Trace elements and REE abundances were deter- mined using Inductively Coupled Plasma Mass Spec- trometer (ICP-MS)['*]. Sample solutions were pre- pared by HF-HNO, acid digestion with Indium (100 mg ml- ' ) as internal standard. To ensure preci- sion of the data, a set of International Standards of different compositions (USGS standards: NODA-1 and NODP-1) were analysed along with the samples. The relative standard deviation (RSD) was better than *3% for most of the elements. Mineralogy of the fer-

romanpese ores was identified by optical microscope O i t z make Orthoplan) and XRD (Philips automatic dif-lkctometer) techniques. Major elements (partial) in the samples fiom study area were analysed using Phil- lips X-Ray Fluorescence spectrometer (XRF ) with pressed powder pellet method. Both in house and in- ternational standards of appropriate composition (BCS-176) were employed for better precision.

3 N a t m of the Manganese om Body Mineralization of manganese ore in this region

can be divided into three major categories viz., strati- form, stratabound-replacement, and detrital. The strat- iform ores occur interbedded with variegated shales (Fig. 2(a)). Generally, the ore beds display structural concordance with the associatedlenclosing rock and are commonly co-folded (Fig. 2(b)). Locally, such ore bodies also occur as lenticular or irregular pockets. The individual mineralized bands are of limited thick- ness but continue to a great depth. The ore is usually

soft, laminated, and low to medium-grade in nature. Manganese ore body of the stratabound-replace-

ment category constitutes an important source of me- dium to high-grade ores. The ore bodies either show a crosscutting relationship with the enclosing shale units (Fig. 2(c)) or they are confined below a cherty hori- zon (Fig. 2(d)). They are formed by the dissolution and remobilization of Mn-oxides from the surrounding ore bodies and manganiferous shale followed by its re- precipitation along structurally favorable zones. Dif- ferent subtypes of stratabound deposits exhibit dis- tinctive characters and field dispositions. In the shear zone controlled sub-type, mineralization of manganese is usually confined to a narrow shear zone. Such sub- types may show brecciation and silicification because of intense shearing. In some places, the Mn-ore bands can be found below brecciated cherty rock bed, and it can be considered as another sub-type. In all such oc- currences, the ore is hard, massive, and high-grade in nature. However, in highly silicified zones, the ores are of low-grade type.

The detrital category shows limited depth per- sistency with extensive lateritisation (Fig. 2(e)). They mostly occur as fragmented boulders below a thin cover at plateau edges (Fig. 2(f)). Generally, the ore pockets are small in size, but ore bodies of 30 m x 50 m dimension are also presented. In this category, the nature and distribution of M n-ore is highly erratic both vertically and laterally. The ore zones, common- ly over 5 - 10 m in thickness , terminate against shale .

Fig, 2 Field photographs of different categories of Mn-ore bodies ((a) & (b) stratiform type; (c). (d) stratabound type; (e), ( f ) detrital

(a) Rhythmic layering of Mn-ore and cherty silica; @) A broad artiformal fold where both mangmese and shaly layers are co-folded; (c) A linear Mn-ore body (shown by dotted line) confmed within shale; (d) Mn-mineralisation confmed below a cherty zore; (e) Pano- ramic view of a detrital Mn-ore body and ( f ) Large boulders of Mn-ore, below 20 m depth, in a detrital type of deposit

type)

752 JOURNAL OF RARE EARTHS, Vo125, N0.6, Dec 2007

The occurrence of shale in the quarries generally marks the base of minable ore. The ore zone is mas- sive, cavernous, and non-uniform in quality. These Mn-ores are mostly of low-grade nature. Such ore bodies are formed by fi-agmentation and intensive lat- erit isat ion.

4 Minelrrlogical Chamctenstics The Mn-Fe oxide minerals are abundant in the

stratiform ore bodies. Besides iuanganese and iron minerals, it contains significant amounts of silicate/ gangue minerals (quartz, kaolinitelillite). Cryptomelane or romanechite is the main manganese mineral with occasional pyrolusite. Iron minerals are predominantly hematite, goethite, and limonite. The shaly Mn-ores and wad belong to this categry. Morphologically , the samples are spongy and soft in nature. The major Mn-phase of the stratabound category is pyrolusite, but it may also contain subordinate cryptomelane, ro- manechite, and lithiophorite. Some samples contain minor goethite. Generally these ore zones exhibit box- work, massive, botryoidal or nodular textures. The de- trital ores generally show two morphological varieties such as recemented and spheroidal type. The rece- mented type invariably contains hematite clasts en- closed within cryptomelane matrice. Cryptomelane is the major mineral in spheroidal variety, though minor pyrolusite is recorded some times.

Most of the above varieties of ore bodies are surfacially lateritised. The gossans/floats are mostly pisolitic or appear as spongy because of intense leac- hing.

5 Chemical Characteristics

5.1 Major and tmce elements Three major metal oxides, namely MnO,, Fe,O,,

and Al,O, control the overall chemistry of manganese ores in this belt. Manganese and alumina dominate in stratiform type, whereas stratabound type is fairly rich in manganese, and the detrital ores contain both manganese and iron. Thus, the stratiform types are usually low to medium-grade in nature with a typical average of 26% MnO, but may contain up to 35% (Table 1 ). Medium to high-grade M n-ores (average Mn > 35%) are characteristic of stratabound type. Some low-grade stratabound ores are rich in silica (SiO,: 20% to 35%). Detrital types of ores are gener- ally low-grade in nature, although some pockets of medium grade ores are locally observed.

Results of partial trace elements analysis are shown in Table 1. Trace constituents are mainly at- tributed to volcanic flux and partly to precipitating Mn-oxide from oceanic water. The stratiform ore bodies, BMF (Banded Manganese Formation) analo- gous to BIF (Banded Iron Formation), are character- ized by relatively lower abundance of trace (1500 to 2500 pg g-I) constituents. The interelemental rela- tionship in stratiform category ores reveals that Cu, Co, Ni, Pb, and Zn were absorbed on precipitating hydrous Mn-oxides, whereas some trace elements Li, Nb, Sc and Y were contributed by volcaniclastic rocks. The stratabound ore bodies are typically en- riched with trace metals (5000 to 8500 pg - s - ' ) ; Cu, Co, Ni, Pb, and Zn in particular. The detrital ore bodies usually show a low content of trace elements ( <2000 pg * g-l).

TaMe 1 Partial major and trace element abundance in diffenent categories of one types and associated country mck

Major oxidePh I 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5

M no, 11.55 522 12.7 6.4 927 16.93 54.43 40.9 50.9 5224 42.62 48.32 47.53 49.78 82.98

Fe20, 33.62 37.68 36.46 7.37 3924 24.91 6.66 20.31 23.97 6.18 31.42 10.85 10.74 13.85 027

' 412 0 3 20.48 19.37 16.85 33.36 14.49 16.58 10.79 12.83 829 13.42 6.12 5.92 11.32 9.69 0.68

SiO, 2224 23.4 21.88 38.81 21.92 28.97 15.67 14.49 4.45 17.96 11.16 22.71 17.85 1522 1.85

Trace element/lO - 6

co 87 6 84 18 6 230 1609 487 815 327 248 644 1207 1822 372

cu 59 15 5 33 8 144 857 210 690 53 236 287 183 335 497

Ni 95 31 93 142 19 16 301 64 350 404 208 306 381 198 291

Pb 9 6 86 88 119 90 67 64 108 113 116 168 32 116 109

Zn 198 64 108 140 47 56 1271 459 1101 454 123 215 675 135 394

Li 5.4 3.7 34.0 8.0 13.0 0.9 98.1 6.9 94.5 1.3 112.0 23.0 23.6 49.4 4.1

Nb 5 2 4.5 9.0 1 I .O 3.0 0.6 0 2 2.5 I .8 0.9 2.0 2.0 I .6 0.4 0.3

sc 23 8 21 14 12 38 58 107 61 17 44 9 14 52 14

Y 8 3 24 20 209 17 42 104 47 42 34 33 34 29 198

Mbhm P P pl d Contmthg REE Signdum on A4-e O m of Iron Ore Groy in NoHh Olissa, India 753

Table 1 Partial major and trace element abundance in Memnt catefprieS of om types and apsociated country mck (continued)

Major oxide& 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

78.38 72.89 77.36 65.82 62.6 61.13 62.12 64.63 58.02 86.41 63.35 43.93 42.15 34.02 18.31

1.38 2.04 2.32 13.61 15.1 21.46 12.86 11.73 11.02 2.16 528 425 24.71 44.37 51.36

2.73 3.23 2.29 4.07 4.95 3.66 5.91 322 525 1.01 9.81 825 8.77 6.13 10.68

3.02 6.4 4.54 6.62 2.43 6.5 327 8.94 10.34 1.03 329 31.07 13.37 1.83 10.43

Trace element/lO - 6

co cu Ni

Pb

Zn

Li

Nb

sc

Y

425 517

296 580

366 84

31 28

552 388

55.3 14.0

1.6 0.4

7 24

38 84

239

176

42

23

105

4 2

1 A

17

25

2899 459

1986 1191

3719 804

130 169

638 335

628.6 352.1

I 2 0.5

33 35

54 40

938

805

899

196

205

227 2

0 A

48

37

769 728

592 128

1071 160

36 116

584 86

266.3 34.0

4.7 1.0

15 9

45 56

53 F t a ~ earth element (REE) chemistry Together with major element chemistry, proper

understanding of the geochemistry of the REE (LREE & HREE) is helpful to interpret the depositional envi- ronment of any ore deposits. Dispersion pattern of REE in the representative materials (24 samples) se- lected from three categories of Mn-ores have been in- terpreted in terms of their genesis. Six samples from adjacent country rocks (shale) were also studied for comparison. Total LREE content in different types of Mn-ores varied between 53 and 455 pg g-' . 5.2.1 Averag, range, and ratios of REE The abundances of REE in different categories of manga- nese ores are presented in Table 2. Amonst the LREE, only the promethium content could not be de- termined because of instrumental limitations. The av- erage lanthanum content is recorded as 37 pg g-' and the maximum (160 pg g- ') was observed in a stratiform deposit. Cerium enrichment is observed in al- most all the samples irrespective of their occurrence and &. The a v w value of cerium is 78 pg g-', and the highest value (358 pg g- ' ) is recorded in a sam- ple from detrital deposit (sample 28). A lower level of praseodymium concentration (avg.: 11 pg g - ' ) is noted, though minor enrichment (45 pg g - ' ) is ob- served in a stratabound (shear zone controlled) ore body. Except for a few samples, the concentration level of Nd is high with respect to Pr. Neodymium shows an average concentration of 51 pg * g- ' , ran- ging between 13 and 111 pg * g- ' . The HREE con- centration in the study area is very low, average being <8 Fg g - ' , except for some stratabound ore sam-

ples (avg:15 pg g-').Total concentration of heavy

I698

2179

1455

105

381

360.0

1 .o 16

35 -

364 3433 444 347

237 776 397 275

29 530 532 269

45 162 136 37

164 1017 424 333

3.9 249.1 185.9 74.6

0.4 2.1 1.6 5.9

2 11 11 9

126 22 30 35

323 68

125 160

27 117

137 37

84

12.0 1.6

1.0 7.9

22 4

12 14

rare earth elements is low (46 pg g-') relative to C LREE (192 pg g-I).

The average values of 1 LREEIX HREE, Ce/La, M u , La/Yb, and NdrYb ratios of various categories of Mn-ore show contrasting results (Table 3). Ratios of 1 LREE/X HREE show that LREE were enriched before the formation process of manganese deposits. The highest value 22.3 pg g-' shown by stratiform ores reflect the inclusion of more LREE during its for- mation. This average value declines (2.4 pg * g e ' ) in stratabound process and thereby, indicating the poor leachiability and mobility of LREE. Dubinin and V~lkov"~] suggested that a low Ce/La ratio (0.12) in- dicated that a large part of the REE to be associated with hydrogenous mangmese-hydroxides which are absorbed from seawater. With the increase in the a- mount of carbonate, biogenic, and terrigenous compo- nents, the Ce/La ratio also increases. Therefore, the high average value of C e h ratio (4.5) in the strati- form ores indicates the inclusion of volcaniclastic components. With decrease in the volcaniclastic frac- tion, this average ratio decreases to 0.8 in stratabound ores. Weathering and lateritisation has further in- creased the average ratio to 4.0 in detrital ore. The La/ Lu and La/Yb ratios indicate the degree of fractiona- tion of light and heavy REE"']. Higher average ratios of M u and La/Yb in stratiform ores (76 and 11 re- spectively) indicate significant fractionation of light and heavy REE. In contrast, lower ratios (av. 31 and 5 ) in stratabound ores reveal that the fractionation of the light and heavy REE is relatively less. The detrital ores exhibit higher values of these ratios indicating the influence of secondary processes in the REE enrich- ment.

754 JOURNAL OFRARE EARTHS, VoL25, N0.6, Dee. 2007

Table 2 Rare earth elements distribution in diffemnt categories of Mn-ores and associated countty mck (10 -')

REE 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5

La 2.1 2 2 6.9 91 79.9 102 46.8 159.8 59.4 51.1 62 41.7 49.9 30.9 17.9 Ce 9.1 7.3 46.1 112 82.1 992 1992 332.3 209.8 282.5 165 156.5 211.0 245.5 1.5 Pr 0.9 0.7 2.4 I5 20.8 3.8 18.6 35.7 15.1 17.5 16 15.6 132 10.6 5.8 Nd 3 2 3.3 9.5 48 82.6 13.4 63.8 128.3 47.4 55.9 52 51.0 146.7 36.2 23.9 Sm 0.7 12 2.5 8 22.7 9.3 182 29.9 112 18.9 10 11.0 18.0 21.1 16.7

LREE 16 14.7 67.4 274 288.1 135.9 346.6 386 343 426 305 276 439 344.5 66.0 Eu 0 3 0.4 I 1 6 3.5 6.5 2.4 6.3 4 . 4 3 5 1.8 7.7 7 2 Gd 0.6 0.8 2.4 5 21 4.7 162 9.0 20.2 11.6 1 1 15 4.9 10.9 18.7 Tb 0.1 0.1 0.3 I 3 1.0 2 1.3 2.5 2 2 I 2 0.9 2.1 4.6

DY 12 1.9 2.9 2 122 5.7 11.7 6.7 12.4 12.1 9 12 5.1 11.1 292 Ho 0.1 0.3 0.4 1 1.6 1.3 2.1 1.3 2 2 3.0 2 2 12 2.4 8 2 Er 02 1.3 1.6 1 2.7 2.5 5.5 3.3 6.6 5.8 5 6 2.4 4.5 152 Tm 0.1 0.1 0.3 1 0 2 0.5 0.7 0.4 0.9 1.1 I 1 0.4 0.8 2.5 Yb 0.5 1.5 1.5 1 0.7 3 2 5 3 2.6 5.8 6 . 5 4 5 2.6 5.4 13.8 Lu 0.1 0.1 0.1 I 0.1 0.4 0.5 0.3 0.6 0.9 1 1 0.4 0.7 2.0 r HREE 3 2 6.5 10.5 14.0 47.5 22.8 50.5 27.3 57.5 35.6 37.0 49.0 29.7 45.6 101.4 - Y REE 192 212 77.9 288.0 335.6 158.7 397.1 413.3 400.5 461.6 342.0 325.0 468.7 390.1 167.4

Table 2 Ram earth elements distribution in diffemnt categories of Mn-om and associated countly mck (10 -')(continued)

REE 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

La 8.645 15.095 17239 39.705 18.478 12.468 39.608 54 104 83.7 28.6 36.3 30 28.4 64.8 Ce 8.431 19.115 32.547 22.037 11.715 15.136 35.094 5 118 24.9 159.4 142 125 358.1 33.3 Pr 2.481 5.713 5.725 10.446 6.122 3.662 7.161 7 27 15.4 8.9 9.8 10 13.4 15.9 Nd 28.76 74.177 59232 12.125 7.712 3.758 69.879 33 95 58.1 30.4 35 33 43.7 54.6 Sm 4.622 12.448 7.979 19.022 11.585 5.595 6.418 9 25 14.7 7.3 9.1 9 11.1 162 1 LREE 52.9 126.5 122.7 103.3 55.6 40.6 1582 108.0 169.0 196.8 234.6 2322 207.0 454.7 184.8 Eu 3.9 4.131 5.3 6.5634.114 1.98 1 . 9 4 7 2 2.1 6 2.7 3.5 3 4.4 3.9 Gd 6.8 11.178 10.3 15.871 8.022 4.557 6.569 9 5.6 26 9.4 13.4 7 19.3 10.4 Tb 1.5 2.72 2.0 3.017 1.615 0.962 1228 1 0.9 5 1.1 1.5 1 12 1.4 DY 9.8 17.456 9.7 16.021 8.864 5.359 6.866 8 5.3 25 7.9 8.2 6 6.1 8 Ho 2.8 4.979 2.1 3.518 2.097 1237 1.817 1 0.9 8.8 1.9 1.4 1 1 1 .I Er 5.6 10.379 3.7 6.102 3.884 2.337 3.742 5 2.7 15.3 5 3.9 3 2.7 3 Tm 1.0 1.951 0.7 1.06 0.68 0.421 0.677 I 0.3 2.5 0.8 0.5 1 0.3 0.4 Yb 5.8 12.067 4.0 6.526 4.138 2.467 4.114 4 , 3.0 13.1 4.5 3.7 2 2.9 2.6 Lu 0.9 1.755 0.6 0.927 0.594 0.351 0.635 I 0.3 2 0.6 0.3 I 0 2 0.3 1 HREE 38.1 66.6 38.4 59.6 34.0 19.7 27.6 32.0 21.1 103.7 33.9 36.4 25.0 38.1 31.1 z REE 91.0 1932 161.1 162.9 89.6 60.3 185.8 140.0 190.1 300.5 268.5 268.6 232.0 492.8 215.9

1 to 6: Country rocks (shale), 7 to 14: Stratiform ore, 15 to 24: Stratabound ore, 25 to 30: Detrital ore

5 2 2 Normalization of REE All the REE results obtained from different categories of Mn-ore, viz. stratiform, stratabound, detrital and country rock are normalized to chondritt: vaiues. Different normalized profile patterns are shown in F ig . 3(a), (b), (c), and

The most important feature for comparison is the Ce and Eu anomaly for different categories of Mn-ores. The calculated anomalies for Ce show the deviation of the respective elements from the intrapo- lated values between the adjacent elements, and the positive and negative results are indicated by + or - sign, respectively. The extent of Ce anomaly is gner-

( 4 .

ally defined by the ratio Ce/Ce' , where Ce is the ob- served chondrite-normalized Ce concentration and Ce' is the value obtained at cerium position by straight line intrapolation between the observed values for La and Pr. The magnitude of Ce anomaly is de- fined by Ce,,,/[ 2/3 La,,, + 1 /3 Prnom ] ' 1 4 ] . To differ- entiate among different types of Mn-ores and associ- ated rocks, Eu anomaly is a useful tool. The magni- tude of Eu anomaly is defined as Eu,,,/[ 2/3 Sm,,, + 1/3 Gdno,][141. The averag Ce/Ce* , EuEu' , and NdKb ratios for the above categories of ores show significant differences.

Mishm P P et d Contrrsting RhE Sip#um on M-e O m

Y) 1000.00, I 0 4- . -

2 10.00 c Y = 0.101 I 5 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

rA

Rare earth elements 2 1000.001 I . + 0 c c, 10.00 0 - 1 ' I Q 2 0.101 1

rA La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Rare earth elements

of Iron Ore Croq in NoHh Orissa, Indk 755

z 1000.00, .. .

g 0.10' I rA La Ce Pr Nd Sm EuGd Tb Dy Ho Er TmYbLu

Rare earth elements rn $ 1000.00

g 9 10.00 c

0 0.

v)

- : 0.10

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Rare earth elements

Fig 3 Chondrite normalized REE pattern of Mn-ores from different categories of deposit and associated country rock (shale) (a) Country rock; (b) Stratifom ore; (c) Stratabound ore; (d) Detrital ore

6 Discussion Geochemical signature in general and REE in par-

ticular are used to differentiate among various genetic types like hydrothermal, hydrogenous, and diagenetic Mn and Mn-Fe deposits. Recently, some research-

have reported the environment of deposition of manganese deposit from northern Alps, through REE interpretation. The absolute REE contents of IOG country rock (shale), stratiform Mn-ore, (which may be termed as Banded Manganese Formation, BMF- as for Banded Iron Formation, BIF), and stratabound-rep lacement ore show significant variation in abundance i.e. it varies from very low to apprecia- bly high to moderate value, respectively (Table 2).

Selected data relating to the two types of Mn- ores such as stratiform and stratabound types have been plotted in binary diagrams. The resulting pattern clearly reveals that different processes were effective in the formation of the stratiform and stratabound cat- egories of ore within IOG of rocks. The source of manganese in this area is attributed to hydrothermal volcanic exhalation, in which Mn-rich material is dis- solved in seawater and later precipitated. The inter- mittent deposition of volcanic ash is evident from the occurrence of significant amounts of tuffaceous sedi- ments either independently or interbedded with Mn- layer across the basin. Volcanic rocks of both basic and acidic composition also border the horse-shoe- shaped iron ore synclinorium.

6.1 Countly mck (tuffaceous shale) The country rock usually shows low absolute

REE content, positive Ce and Eu anomalies, and a sloping HREE pattern (Fig. 3 (a)). Average M n F e (<0.04) and MnO,/Al,O, ratios (<0.6) are low. The average Ce/Ce' and Eu/Eu* ratios of shale are 2.0 and

ers[ 15. 161

1 . l , respectively. The positive Ce anomaly shown by the country rock is attributed to the relatively easy oxidation of Ce to insoluble +4 state and its incorpo- ration into (volcaniclastic) sediments"'] (Fig. 3 (a)). The country rock also shows a weak positive Eu anomaly. Such positive Eu anomaly in the country rock could have been inherited from source rocks in which the Eu anomalies were produced by igneous process. Eu anomaly in igneous systems has been ex- plained in terms of the ease reduction of Eu3+ to Eu2+. The Eu2+ is then incorporated in the feldspar more easily['*'. But as the 2 REE increases from country rock to stratiform ores, the amplitude of the positive Eu anomaly gradually diminishes and become flat because of the mixing of Mn-enriched fluids with volcaniclasts.

62 Stratifonnones The stratiform ores usually show high absolute

REE abundances, positive Ce anomalies, and flat Eu signatures (Fig. 3(b)). Distinctive positive Ce anomaly indicates that the materials for manganese deposit were primarily derived from sub-marine volcanism. Average MnFe ratio (3 .9) and MnO,/Al,O, ratio ( 5 . 8 ) are moderate and show sloping normalized HREE pattern. The average Ce/Ce* and Eu/Eu' ratios of stratiform ores are 1.8 and 0.9, respectively. This indicates that the REE patterns and the Ce anomalies of Mn-ores in IOG are significantly influenced by the mixingof two components: Mn-Fe mineral rich sea- water and volcaniclasts. The REE patterns shown by stratiform ores represent the end product of a com- plex series of events that record the properties of the Mn-Fe rich solutions subsequently precipitated with volcaniclastic sediments. A contemporaneous input of volcaniclastic material appears to have significantly in- fluenced the absolute abundance of REE particularly

756 JOURNAL OFRARE U R T H S , VoL-25, N0.6, Dec. 2007

LREE in these rocks. Though the absolute REE abun- dance widely differs in the country rock, the overall shape of the normalized REE patterns (sloping HREE) of the stratiform samples (comprising Mn- minerals and volcaniclasts) is very similar to the pat- terns shown by the country rock except Eu (very weak positive anomaly or flat pattern).

6 3 Stlataboundones The stratabound ore usually shows moderate ab-

solute REE abundance, a negative Ce, and flat to very weak positive Eu anomaly (Fig. 3(c)). Its M n F e rati- o, MnO,/Al,O, ratio, and absolute REE abundance appreciably differ from that of stratiform ores. Aver- age MnFe ratio (41) and MnO,/Al,O, ratio (36) are high and displays a flat normalized HREE pattern. The average Ce/Ce' and EuEu' ratios of stratabound ores are 0.4 and 1 . 1 , respectively . This indicates that the REE patterns and Ce anomaly of stratabound Mn-ores of IOG are significantly influenced by disso- lution process under supergene condition"'] .

Remobilization of Mn-oxide and Fe-oxide is at- tributed to the release of varying amounts of REE. Precipitating supergene Mn-oxides may reflect this changing availability of LREE and HREE. The nega- tive Ce anomalies in stratabound ores support this in- terpretation. Ce and Eu are the most mobile members of the REE group and a general decrease of these ele- ments in stratabound ores may be linked to prolonged reaction times that result from the increased availabili- ty of ground water, which favors the redox reac- tions[201. The HREEs in stratabound ores show rela- tively higher values and show nearly horizontal pat- tern. The mobility of REE during weathering depends on the waterhock ratio and on the mineralogy of source rock, which decompose and produce secondary minerals. The mobility of REE also depends on the physico-chemical environment of alteration (for exam- p l e n , andfCO,) and composition of the alteration fluid (PH and availability of free ligands for REE com- plexation).

6.4 Detntal one The detrital ores are poor in REE content and do

not show any regular pattern. Some samples exhibit a positive Ce anomaly, whereas others show a negative anomaly (Fig. 3(d)).

6 5 SourreofREE Total REE vs MnO, and REE vs Al,O, have

been plotted for both stratiform and stratabound ores.

As one may notice from Fig . 4(a) & (b), both types of ore exhibit separate domain indicating the difference in their process of formation.

To ascertain whether the intake of LREE and HREE is by adsorption through Mn-oxide precipi- tates or through volcaniclastic fraction, LREE vs MnO,(Fig. 4(c)) & L E E vs AI,O,(Fig. 4(d)) and HREE vs MnO,(Fig. 4(e)) and HREE vs Al,O,(Fig. 4 (0) have been plotted. The positive relationship ( r = 88) between LREE and Al,O, in stratiform ores (Fig. 4(d)) is attributed to the contribution of LREE mostly by volcaniclasts. The intake of HREE in stratiform M n-ore is chiefly through chemognic precipitation of Mn-oxide which are least affected by volcaniclastic influx (Fig. 4(e)). Though the REE, particularly the HREE are relatively immobile, slight enrichment of CHREE in few stratabound ores and its positive cor- relation with MnO, shows that the HREE was dis- solved and carried in solution along with manganese under some extreme conditions.

The negative correlation ( r = - 0.67) between 1 LREE & I HREE in stratiform ore is indicative of the different operative mechanism for REE intake in the formation process of ore. The LREE is contribu- ted by volcaniclastics, whereas the HREE is attributed to MnO, that precipitates from marine water. When the clastic fraction in stratiform increases, the CLREE increases and inversely both Mn and IHREE depletes. Paucity of REE in associated rock (volcaniclastic shale) indicates that enrichment of REE in stratiform ore is because of the complex interplay of volcaniclastic and chemogenic sources.

7 Conclusions 1. On the basis of the mode of occurrence, the

ferromanganese oxide ores of Bonai-Keonjhar belt, Orissa, India could be grouped into: stratiform, stratabound-replacement, and detrital categories. Chemically, MnO,: Al,O, ratio increased from strati- form to stratabound because of depletion in volcani- clastics, whereas rich iron content in detrital ore body was because of intense lateritisation.

2. The Mn-ores in general exhibited similar min- eral assemblages but contrasting REE signatures. The higher absolute value of REE was observed in strati- form ore and moderate abundance in stratabound ores, whereas detrital category samples showed low CREE values. REE intake in stratiform ores from a volcanic source was suggested. Poor leachability and mobility of REE resulted in a decrease in their abundance in stratabound ores.

Mishm P P et a! Contmstitg REE Sigrutm on Mangutme Ores of Iron Ore Grorq, in Norih Olissa, India 757

k n .- C W W a!

5 rA

E n n .- C J W a! A

5 rA

.fi n

w

z Y

rA

+ Stratiform orc + + (a) 400 4 '

Stratabound orc

100

40 50 60 70 80 90

MnO,/(%, mass fraction)

40 50 60 70 80 90

MnO,/(%, mass fraction)

" 40 50 60 70 80 90

MnO,/(%, mass fraction)

O J 0 2 4 6 8 10 1 2 1 4 1

Al,O,/(%, mass fraction)

I I

A1,0,/(%, mass fraction)

1 O : 5 10 15

Al,O,i(%, mass fraction)

Fig 4 Plots of (a) I R E E vs MnO,, (b) IREE vs A1203; (c) CLREE vs MnO,; (d) I L R E E vs Al,O,; (e) XHREE vs MnO,; ( f ) XHREE vs Al,03 in stratiform and stratabound categories of Mn-ores

3. Two distinct normalized REE patterns were attributed to the bimodal origin of Mn-ores represen- ting the stratiform and stratabound category. The de- trital ores did not show any REE pattern having resul- ted from frapentation and lateritisation of other two ore types.

4. The REE chemistry of Mn-ores thus indicated that a complex interplay of primary and secondary processes was involved in the development of Mn- ore bodies in north Orissa, India.

Acknowledgments: The authors thank Prof. B.K.M ishra, Direc- tor, Institute of Minerals and Materials Technology, Bhu- baneswar, India, for his kind permission to publish this article. The authors are also thankful to the Department of Science & Technology, New Delhi, India, for their fmancial support in the form of a project (ESSD3NES/043/99)

Referrences :

[ 1 1 Murthy V N, Ghosh, B K. M a n p e s e ore deposit of the Bonai-Keonjhar belt, Orissa [ J 1. Indim Minerds, 1971, 25(3): 201.

[ 2 ] Murthy V N, Acharya S. Lithostratigraphy of pre- Cambrian rocks around Koira, Keonjhar Dist., Orissa [ J ] . Journd of Geologicd Society of India, 1975,16(1): 55.

Roy S. Syngenetic M a n p e s e Formation of India [ M I . Calcutta: Jadavpur University, 1966. Roy S. Mangnese Deposits [ M 1. London: Academic Press, 1981. Mohapatra B K. Paul A K, Sahoo R K. Characteriza- tion of manganese ores of a part of western Koira val- ley, Keonjhar district Orissa [ J ] . Joumd of Geological Society of India, 1989,34: 632. Mishra R N. Geological environment of manganese ores of north Orissa - an exercise in modelling of depos- its [ J 1. Indim Mining md Engineering Journd, 1994,

Mohapatra B K, Paul D, Sahoo R K. REE distribution in ferromanganese oxide ores from Iron Ore Group, Western Koira Valley, Orissa, India [ J ] . Joumd of Mineralogy, Petrology and Economic Geology (Japan), 1996,91: 266. Mishra P P, Mohapatra B K, Sm& P P. Mode of oc- currence and characteristics of Mn-ore bodies in Iron Ore Group of rocks, North Orissa, India and its signifi- cance in resource evaluation [ J 1. Resource Geology, 2006,56(1): 5 5 . Jones H C. The iron ore deposits of Bihar and Orissa [ J ] . Gwlogiccd Survey of India Memoir, 1934,63: 375. Mohapatra B K, Paul A K, Sahoo R K. Characteris- tics of shale units from Iron Ore Group of rocks, Orissa [ J ] . Indim Joumd of Geology, 1991,23: 220. Mishra P P. Mineralogical and geochemical studies of

10-11: 23.

JOURNAL OFRARE mRTHS, VoL25, N0.6, Dec. 2007

mangpnese ores fiom Roida region, Keonjhar district, Orissa with special reference to their optimum utiliza- tion [ D] . Utkal University, Bhubaneswar, India. 2005. B a l m V, Manikyamba C, Ramesh S L, Saxena V C. Determination of rare earth elements in Japanese rock standards by Inductively coupled Plasma Mass Spec- trometry [ J ] . Atomic Spectroscopy, 1989,2(1): 19. Dubinin A V, Volkov I I. Rare earth elements in met- alliferous sediments of the East Pacific rise [ J ] . GeokhimQa, 1986,s: 645. Grasselly Gy, Panto Gy. Rare earth elements in the mangpnese deposit of Urkut (Bakony Mts Hungary) [ J ] . Ore Geology Review. 1988,4(1R): 115. Rantitsch G, Melcher F, Meisel Th, Rainer Th. Rare earth, Major and trace elements in Jurassic mangpnese shales of the northern calcareous Alps: hydrothermal versus hydrognous origin of stratiform manganese ore deposits [ J] . M i n d o g y md Petrology, 2003,77(1-2): 109.

[ 161 Xie Jiancheng, Yang Xiaoyong, Du Jianguo, Xu Wei. Geochemical characteristics of sedimentary mangdnese deposit of Guichi, Anhui Province, China [ J 3 . Joumd of R m Emths, 2006,24: 374. Goldberg E D, Koide M Schmitt R A, Smith R H. Rare earth distribution in the marine environment [ J ] . Joumd of Gwphysicd. Resecrch, 1963,68: 4209. Haskin L A, Helmke P A, Paster T P, Allen R 0. Rare earths in Meteoritic, Terrestrial and Lunar Matter [ M 1 . Brunfelt A 0, Steirnest E. Activation analysis in Geochemistry and Cosmochemistry Universitetsforlaget, Oslo. 1970. 201. Brookms G D. Aqueous gochemistry of rare earth el- ements [ J ] . Reviews in M i n d o g y md Geochemistry, 1989,21: 201. Pracejus B, Bolton B R, Frakes L A, Abbot M . Rare earth element geochemistry of supergme manppese de- posits from Groote Eylandt, N T, Australia [ J ] . Ore Geology Review, 1990,5: 293.