A reconnaissance survey of the distribution of some trace elements in Indian bauxite

Mineral. Deposita (Berl.) 10, 177--188 (1975) © by Springer-Verlag 1975

A Reconnaissance Survey of the Distribution of Some Trace Elements in Indian Bauxite

P. K. BANERJEE

Calcutta, India

The results of spectrographic analysis of 500 bauxite samples from 25 deposits show that the distribution of Cr, V, Zr and Ga is completely randomised in accordance with the model of complex, polycyclic sequence of bauxite genesis, deduced by other workers on the basis of mineralogical and major element studies. The same process of residual weathering, which generates a systematic enrichment and fractionation of major insoluble elements causes a random dispersion, notwithstanding the overall enrichment, of the insoluble trace elements due to seasonaI variations in pH and in direction of movement of the pore water.

The object of this communicat ion is to present a preliminary idea of the nature and variation of Cr, V, Zr, Pb, Ga and Sn in 25 bauxite deposits of India on the basis of 500 sets of analysis.

Geolog ic Set up of Indian Bauxite

Bauxite deposits in India are believed to be products of residual weathering in sub-tropical, humid environment (Fox 1923; RoY CHOWD- HUP~Y 1958). Generally, they occur as flat to undulating, lenticular to tabular bodies within a carapace of ferruginous laterite. The underlying bedrock is either a Deccan basaltic flow of pyroclastic bed, or an Archaean alumina-rich khondalite (garnet-sillimanite-quartz schist with graphite). Rarely, bauxite bearing laterite cappings are noted over Archaean charnockites (sensu lato), Upper Proterozoic granite gneisses, Infra-Cambrian (Vindhyan) sandstones and shales and even over (?) Permo-Carboniferous dolomites. The bauxite-bearing cappings range f rom 3 to 50 metres in thickness, and are underlain by a clay-rich, mottled, pallid zone (lithomarge) ranging f rom 1.5 to 34 metres in thickness. Cappings over Deccan basaltic flows and char-

nockites are strongly differentiated into a succession of ferruginous and aluminous layers. Cappings over khondalites are comparatively uniform (Table 1). The bauxite deposits lie at ground elevations, varying f rom 40 metres (in the western coast) to 1250 metres above the sea level. The deposits at plate autops are generally known as high level types. Most of the important deposits of this type are confined within q-1400 m m isohyetal zone possibly along some palaeo- drainage borders, as conceived by VAL~TON (1966) (Fig. 1) Since these isohyetal zones are post-pleistocene, it is possible, though by no means proved (cf. GouDm 1973, p. 96--110), that the high level bauxite deposits (as distinct f rom alumina-bearing (350,/0 A12Oa) laterites are also Holocene to recent in age. VALETON (1967) believes that the bauxite bearing laterites originated on a low relief during F~arly Ter- tiary times and that in tectonically low areas, the mineral paragenesis of the lateritic bands was preserved, but in uplifted blocks, the pr im- ary pattern changed continuously under the influence of later weathering processes. Critical evidences of an Early Tertiary cycle of bauxitisation are present in the Gujerat and J a m m u deposits. The Gujerat bauxite is overlain by

178 P.K. BANERJEE

Table 1. Some representa/ive bauxite-]aterite profiles in India

Type I bauxite Type IV bauxite Type III bauxite Type II bauxite (Loc: Dhangerwadi, (Loc: Amarkantak, (Galikonda, A.P.) (Salal, Jammu) Maharashtra) M.P.)

1. Vesicular, ferruginous Pisolitic ~erruginous - - laterite (0.3--2.5 m) laterite (0--5 m)

2. Grey, massiveandpisolitic, Aluminous laterite dense bauxite (1--2.5 m) (0--3 m) laterally (A120 a : 54%) grading into pisolitic

to massive bauxite (0--6 m) (A12Oa: 50%)

3. Laterite parting with bauxite pisolites (0--0.6 m) (A120 a :35%)

4. Ferruginous bauxite with angular patches of massive bauxite (Al=Oa :45%)

5. Laterite (0--6 m)

6. Lithomargic (Pallid zone) clay (16--40 m)

(A12Oa: 20--23%) Deccan Trap

(A120 a : 13-- 14%)

Lower aluminous laterite (A120 a : 40%)

Ferruginous laterite (4--15 m) (A120 a:36%)

Lithomargic clay (1--22.6 m)

Deccan Trap (AI2Oa: 13--14%)

Aluminous laterite (upto 22 m) (A120 a :46%)

Pisolitic bauxite (1--3 m) (A12Oa:75 %)

Laterite (up to 9 m) (A12Oa:35%)

Aluminous laterite (upto 2 m) (AlzOa:44%)

Lithomargic clay (6--12 m) (A12Oa:40%)

Khondalite (Kaolinised) (A120 a :20--35%)

Aluminous clay (A12Oa: 45%)

Orthoquartzite and Dolomite

N. t3. : The average alumina content is given, not the range.

the Upper Miocene Gaj sedimentaries and shows compelling evidences (given later) of partial degradation into clay. The Jammu bauxite, now sited at around 2130 metres, is overlain by the Eocene Nummulitic limestone and had participated in the Himalayan orogenic movements, as revealed by significant flattening of its pisolites in the ab plane (a: c = 1.2--2.0). I t would be clear from the foregoing summary that within the general framework of residual enrichment, the Indian bauxite deposits dis- play considerable diversity. Vertical as well as horizontal facies contrasts are common. This leads to diverse shapes and sizes of bauxite deposits.

Objective of the Work

Consequent upon this wide diversity, it has been found in India that no uniform norm of exploration is applicable to different bauxite

deposits. There are cases where a continuous bauxite bed as judged from scarp sections dis- appears abruptly towards the centre of the plateau (e. g. Phutka Pahar). As a result, considerable time and money is wasted in "trial and error" to fix up appropriate norms of exploration. Faced with this problem of deciding from surface studies how a bauxite bed is likely to behave below the laterite blanket, the appli- cability of trace elements as geochemical dis- criminators between major and minor deposits was examined. The programme was prompted by the finding of many previous workers [with the exception of K~ALmHI (1968)] that in the process of selective leaching and residual enrichment, leading to the development of bauxite deposits, there is a sympathetic geochemical behaviour between the major and trace elements, particularly those which are comparatively immobile and get enriched in bauxite e.g. Cr, Cu, Ga, Nb, Mo, Zr, Ti, Sc, V, Be,

A Reconnaissance Survey of Some Trace Elements in Indian Bauxite 179

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Mn, Y and Pb (VALETON 1972; Table-34, p. 191). If this geochemical similarity holds in detail. it would be logical to expect that in a locality where fractionation of alumina has advanced to the stage of development of a large bauxite bed, the associated trace elements of the enriched group should also show a better regular- ity and a lower standard deviation than in another locality where alumina concentrations are impersistent and pockety. If this contrast is established on a statistically valid programme, the extent of a bauxite deposit could be anticipated from the degree of variance of trace elements. In order to reduce the geochemical "noise", normally generated in com- paring between trace element concentrations in iron-rich and alumina-rich assemblages, and to obtain as direct a correlation as possible, it was decided that the trace element contents in the alumina-rich phase only among a sufficient number of bauxite deposits of different types would be compared to determine if there is any correlation between ore body dimension and trace element variability. This paper is based on the finding from 23 bauxite deposits.

Methods Adopted

The bauxite deposits were so selected as to represent the full range of basement types and of ore body dimensions. An arbitrary division of the second parameter was done as follows:

Type I: Ore body continuous over more than 1 km ~

Type II: Ore body continuous over 0.5--1 km ~

Type III : Ore body continuous over 0.25-- 0.49 km z

Type IV: Ore body extremely lenticular and erratic.

Twenty to thirty representative bauxite samples were obtained from each deposit through the kind courtsey of officers of the GS1 and a number of Public and Private Sector agencies. The trace element analyses were undertaken by the Central Headquarters Chemical Labor- atory of the GSI in their Hilger Quartz prism Spectrograph. The analytical precision is around ±10% and reproducibility is high.

General Considerat ions in the Select ion ot Trace E l e m e n t s

In order to reduce the analytical workload during this reconnaissance study, the follow- ing considerations were taken into account in selecting representative trace elements:

(a) elements with low solubility products;

(b) elements reflecting different patterns of migrational ability; and

(c) elements reflecting different order of concentration in the basement.

Under conditions of selective leaching of all alkali and alkaline earth elements as well as of silica, leading to a residual concentration of hydrated aluminium and iron oxides, it is expected that such elements whose solubility products of hydroxides at room P, T are close to or less than those of Fe(OH)a and AI(OH)a would be concentrated in the laterite-bauxite profile. To this category belong Sn, Zr, Th, Co, Sb, Ga, In, Cr, Ti and Bi (Peered'MaN 1967, Table 7). The weight clarkes of Sn in the various rock types are similar to those of Sb, Bi and In (TuREKIAN and WEDEPOHL 1961) and are quite low. The weight clarkes of Ga are similar to those of Th and are higher than the former group by one order of magnitude. Besides, Sn and Ga represent two extremes in their preference for the alumino-silicate lattice (CHowDVlUe, Yet aL 1965). These two elements were selected on that basis. Cr and Zr were selected on the reasoning that they have closely similar weight clarkes in basaltic rocks. However the solubility product of Cr(OH)a is much higher than that of Zr(OH)4. Hence intense, unidirectional leaching would cause fractionation of these two elements in a residual profile. The behaviour of trace elements of slightly higher solubility was studied by logging the dispersion of Pb and V. It is welt known that bivalent Pb and trivalent V remain dissolved in significant amounts in natural water. Under oxidising conditions of laterite-bauxite formation, only minerals of pentavalent V are stable, while fixation of elements like Pb, Ni, Cu, Zn, etc. is achieved through sorption or formation of insoluble compounds.

184 P . K . BA:N~RJEE

Table 3. Overlapping patterns of trace elements concentration in bauxite deposits of different dimensions and parentage ( Values in parts per million)

Element Deccan Basalt Deccan Pyroclastics

Type of deposit I II III .IV .I HI

No. of samples 80 43 40 79 15 30 No. of deposits 4 2 2 5 1 1

R 80--800 150--800 40--250 40--1000 100--G. 400 100--450 Cr M 188--385 255--390 144--200 114-460 220 250

S 39--163 63--154 33--49 47--235 !47 86

R 60--G. 200 120--G.200 120--G. 200 40--G. 200 10--G. 200 60--200 V M 125--G.200 185--G.200 n.d. 120--G.200 80 136

S 37 (in 1 n.d. n.d. 25--32 n.d. 34 deposit)

R 60--500 50--400 60--400 10--500 80--160 30--100 Zr M 85--360 168--280 107--250 45--355 120 54

S 25--45 59--70 24--69 24--66 25 20

Pb R L 20--G. 1000a L 20--150 L 20--100 L 20--100 L 10-20 L •0--20

Ga R 10--40 10-25 15--80 10--80 L 10--30 L 10--20

Sn R L 10--30a L 10--20 L 10--20 L. 10 L 10 L 10

a 1000 ppm Pb q- 30 ppm Sn in a brick red to pink bauxite of Rakti Dadar. Whether these basalts could locally carry tin and lead mineralisation is a moot point.

b Reflects the presence of galena pockets in the underlying Great limestone at Sersandu.

e The parentage of the bauxite profile at Bagru from granite gneiss is controversial, some authorities holding that the bauxite at Bagru is derived from a completely lateritised trap flow over the gneiss.

Fixa t ion of E l e m e n t s in the B a s e m e n t

T h e e lements under s tudy are usually sited wi th in

Element Basalt Charnockite

the basement as fo l lows :

Khondalite Granite

Cr pyroxenes, magnetite.

V magnetite ilmenite

Zr z i r c o n i u m

Pb p o t a s s i u m

Ga plagioclase

Sn not

pyroxenes, amphiboles, magnetite and other spine!s

magnetite ilmenite

plagioclase

known

Garnet, amphibole magnetite biotite

magnetite

magnetite magnetite ilmenite ilmenite

s i l i c a t e

m i n e r a l s

garnet plagioclase sillimanite

cassiterite


R = Range o£ values M = Average value in each deposit S = Standard deviat ion

G = Greater than L = Less than

n.d. = No t determined

Great V indhyan sandstone Grani te

l imestone gneiss o

Khondal i te Charnocki te

IV II I I I IV II I I I IV

27 21 20 20 21 42 20 1 1 1 1 1 2 1

100--400 100--300 150--G.400 120--350 120--G.400 10--250 60--150 180 150 ~ 3 7 0 225 270 87--100 118

59 48 n.d . 62 97 48--63 22

60--200 200--G.400 120--G.200 80--150 40--G.200 30--180 120--150 126 n .d . 230 126 210 114--123 147

30 n.d . n .d . 20 n .d . 28--43 9

20--80 150--500 100--180 120--300 100--300 30--350 40--200 45 340 140 226 150 106--187 75 16 91 24 53 47 57--74 40

L. 20 L 20--G. 1000 b 10--50 L 20--20 L 20--100 L 10--40 L 10

L 10--20 50--70 10--50 10--25 15--50 L 1 0 ~ 0 10--20

L 10 L 10 L 10 L 10 L 10 L 10 L 10

Table 4. Trace elemenl content of bauxite (a) and its daughter Kaolin (b) in veinlets and caverns (values in ppm) (G = Greater than, L = Less than, n .d . = not detected)

S1. No. Locality Cr V Z r Pb Ga Li

1 2 3 4 5 6 7 8

1. Bagru, Bihar (a) G 400 G 200 140 20 45 n.d . (b) 250 40 130 20 20 n .d .

2. Jamira Pat, Bihar (a) 400 G 200 300 20 60 n.d . (b) 400 G 200 200 30 70 n .d .

3. Amarkantak , M . P . (a) 160 150 80 30 20 n.d . (b) 160 130 100 30 20 L 20

4. Ringewadi, Maharashtra. (a) 250 G 200 220 L 20 20 n.d . (b) 150 160 180 L 20 10 20

5. Palakhada, Gujerat (a) 300 140 60 L 20 20 n .d . (b) 450 120 80 20 15 60 (a) 300 120 80 L 10 L 10 n.d . (b) 400 200 80 10 L 10 20

6. Chotilibil, Gujerat (a) 150 120 60 L 10 L 10 n.d . (b) 200 140 60 L 10 L 10 L 20

7. Bakharia, Gujerat (a) 250 180 40 L 10 L 10 n.d . (b) 300 140 100 10 15 60

186 P.K. BANERJEE

Most of the above minerals break down under prolonged and intense tropical weathering, although under identical conditions, the break- down of basalt would be more advanced than that of khondalites, acid charnockites and granites.

Sequence of Break-Down: Stage I

During the initial stages of weathering the medium is alkaline and contains the most mobile elements (Na, K, Mg, Ca), most of which are removed, together with SiO2 from the rock forming minerals. Under such conditions, small percentages of Cr and V are also leached out of the system in the form of hexa- valent Cr and trivalent or pentavalent V. After most of the alkali and alkaline earth elements together with silica are removed from the crust, the medium becomes neutral to feebly acidic. In sub-tropical climate zones, the monsoonic drainage, buffered by carbonic acid from rain water, introduces intense oxidation of the residual mineral phases, resulting in concentration of iron and aluminium oxides, together with such refractory elements like Zr, Cr, etc. The path of this leaching is however season- ally inverted by upward movement of ground- water from the pallid zone underlying the laterite carapace. The pallid zone is comparatively richer in alkaline earth elements. This leads to alkalinity of pore water during the spells of dry winter and summer. As a result of this duality, it is expected that a simple, vertical fractionation of all 'immobile' elements in a succession of enriched zones, in accordance with their solubility products and weight clarkes and in response to heavy mon- soons, will not be attained. While the leaching cycle of major elements like Fe, A1 etc will be dominantly controlled by the large volume of monsoonic drainage seeping through the laterite carapace, movement of the trace elements will be reversible during the dry and the wet spells. This point may be illustrated by a simple mathematical calculation. In one gram of rock, containing 30% A1 and 400 p.p.m. Cr, complete leaching of A1 from the system at pH 6 would require 6 × 106 lits. of water. On the other hand, complete leaching of Cr at pH 6

could be effected by only a little more than 10 lits. of water. In other words, the small volume of porewater during the dry spells would be sufficient to re-mobilise the trace elements to a large extent, although major elements will be only marginally modified. This migrational lag between major and trace elements is further overprinted by mechanical disintegration of the carapace during its development and subsequent chemical degradation.

Mechanical Disintegration of the Crust during Bauxitisation: Stage II

Textural studies of the different bauxite deposits reveal that except for the bauxite-laterite cappings over khondalites, the bauxites are polycyclic in development (c. f. VALETON 1967). Some of the important textural evidences are cited below: (a) In many fields, e.g. Udgiri, Amarkantak, etc, angular fragments of bauxite of one colour (cream or pink or cement grey) are embedded in bauxite cement of a different shade (dirty grey, red, etc);

(b) In the Gujerat orebodies, sub-rounded peb- bles of white bauxite are set in a grey bauxite cement;

(c) Aluminous pisolites of contrasting colour zonation are juxtaposed frequently, even on the scale of a hand specimen. Thus, in some Jamira Pat (Bihar) deposits, pisolites with a cream to ash grey kernel and a deep brown outer shell are seen side by side with pisolites having a brown kernel and an ash grey outer shell.

These are compelling evidences in support of mechanical admixture during the long spell of bauxitisation.

Alteration of Bauxite to Kaolin: Stage III

Evidences of silication of bauxite into clay are abundantly present in Gujerat deposits. Such evidences, albeit on a restricted scale, are also seen in the bauxite deposits of Eastern, Central and Western (Maharashtra) India. The evidences are:

(a) abundant veinlets and veins of kaolin across massive bauxite;


(b) four to five cm long angular fragments carrying incipient, polycentric growth of pisolites of white bauxite embedded in kaolin; (c) bauxite fragments embedded in 1 cm thick layers of crystalline silica.

The net result of Stage I, I I and I I I processes would be a randomisation of trace element dispersions. This is borne out by Tables 2, 3 and 4 where the analytical data are summa- rised.

Discussion of the Analytical Results

The data presented in Table 2 clearly illustrate opposing trends of fractionation. The follow- ing are illustrative: (a) Cr uptake higher in the alumina-rich fractions vide localities 3, 4, 5, 6 and 16 and lower in the alumina-rich fractions vide localities 2, 10, 12, 13 and 15.

(b) Ga higher in alumina-rich fractions vide localities 7, 10, 11, 12 and 13 and lower in alumina-rich fractions in locality No. 2. (c) Zr uptake higher in alumina-rich zones in localities 6, 12, 13, 15 and 16 and lower in alumina-rich fractions of localities 1, 2 and 14. (d) No systematic trace element fractionation trend discernible in locality No. 8, notwithstanding a three-stage development. I t confirms the expectation of randomisation of trace elements. This is further corroborated by the data presented in Table 3, where bauxite deposits of different dimensions are seen to have overlapping fields of trace element dispersion (average and standard deviation). Al though bauxite deposits over khondalites and charnockites have a recognisably Iower concentration of Cr, V and Zr there appears to be no scope for utilising the trace elements as a discriminator between major and minor deposits. Two other features of Table 3 are noteworthy: (a) The association of high Pb--Sn values in a brick red aluminous Iaterite f rom Rakti Dadar (M. P.) suggests, on analogy with the high Pb value in a bauxite sample over the galena bearing Salal-Sersandu basement (Jam- mu), that Deccan traps may locally host Pb-Sn mineralisation. In case corroborative evidences are found later, the geochemical utility of laterite-bauxite profiles for regional search of chaIcophile elements will increase. (b) The con-

centration of V and Zr in Gujerat bauxite is low notwithstanding a basic voIcanoclastic parent. This could not have been caused by silication of the ore into kaolin on an extensive scale and consequent reduction in all trace element concentrations. This will be apparent f rom Table 4, which illustrates that while trace element contents in kaolin are equal or lower than those in parent bauxite in the bauxite deposits of Eastern and Central India, the Gujerat trend is usually the reverse with higher contents of trace elements in daughter kaolin. The exact source and mechanism of this enrichment are not clear.

Acknowledgement

The author is deeply indebted to Dr. M. K. RoY CHOWDHURY, who had approved of this study in his capacity as Director General, Geological Survey of India in 1973 and extended continuous help in course of this work. The author is also grateful to Director General, Geological Survey of India for allowing the publication of this paper.

References

CHOWDHURSY, A. N., CHAKRAVORTY, S. C., BosE, B. B.: Geochemistry of Gallium in bauxite from India. Econ. Geol. 60, 1.052--1058 (1965)

Fox, C. S.: The bauxite and aluminous laterite occurrences of India. Mere. Geol. Surv. Ind. 49, 287 (1923)

GOUDIB, A.: Duricrusts in tropical and sub- tropical landscapes, 174 p. Oxford: Clarendon Press 1973

I~HALIGHI, M. : Zur Untersuchung der Spuren- elemente in den Indischen Bauxiten, lateriten und deren Ausgangsgesteinen Basalt und Char- nockit. Dipl. Arbeit, Hamburg, 76 p. (un- published). In: Valeton, I-Bauxites, 1972, p. 190, Elsevier

PEREL'MAN, A. I.: Geochemistry of epigenesis, 266 p. New York: Plenum Press 1967

RoY CHOWDHURY, M. K. : Bauxite in Bihar, Mad- hya Pradesh, Vindhya Pradesh, ?¢Iadhya Bharat and Bhopal. Mem. Geol. Surv. Ind. 85, 227 (1958)

TUREKIAN, K. K., WeDE~OHL, K. H.: Distribu- tion of the elements in some major units of the Earth's Crust. Bull. Geol. Soc. Am. 72, 175--192 (1961)

VALErOX, I. : Laterale Faziesdifferenzierung Late- rit-bauxit und deren Beziehung zum Palfio- relief in Gujerat, Indien. Tray. Comm. Intern.

188 P.K. BANeRJEE: A Reconnaissance Survey of Some Trace Elements in Indian Bauxite

Etude: Bauxite, Oxides, Hydroxides, Alumi- nium 1966 (2) pp. 50--82

- - Bauxitfiihrende Laterite auf dem Trappbasalt Indiens als Fossile, polygenetisch ver~inderte Bodenbildung. Sed. Geol. 1, 7--56 (1967)

• - - Bauxites. Develop. Soil Sci. 1, 226 (1972)

Received October 15, 1974

P. K. BANERJEE Director Division of Regional Int. Surveys, Eastern Region Geological Survey of India, 12 A @ B Russell Street, Calcutta -- 16, 700016, India

Documents

A reconnaissance survey of the distribution of some trace elements in Indian bauxite