GEOCHEMISTRY AND GENESIS OF BIF OF KUDREMUKH SCHIST BELT. KARNATAKA NUCLEUS, INDIA
DISSERTATION; Submitted in partial fulfilment of the requiremer.! For the Award of the Degree of ^^astcr of pi:|tJogo|3l|| IN GEOLOGY
BY R!YAZ MD. KAMARUDDIN KHAN
FACULTY OF SCIENCE DEPARTMENT OF GEOLOGY ALIGARH MUSLIM UNIVERSITY ALiGARH
1 9 f 1 D^ 2- IZ^
DS2125 CERTIFICATE
We certify that this work is the original research work carried out by Mr. Ri\az Md. Kamaruddin Khan under our joint supervision at National Geophysical Research Institute, Hyderabad. It has not been submitted before either in parts or in full, to any University for the award of any degree.
Supervisor Supervisor
Dr. S. M. Zainuddin, /i, FN A. Reader, Scieptim, Department of Geology, National Geophysical Aligarh Muslim University Research Institute, A L I G A R H HYDERABAD ., , \x ^-^^W^ \ CXX C-t^L- Prof. D. Gupta Sarma, FNA, Director, National Geophysical Research Institute. HYDERABAD CONTENTS LIST OF FIGURES " III LIST OF PLATES V LIST OF TABLES VI ACKNOWLEDGEMENTS VII CHAPTER I INTRODUCTION 1.1 A General Perspective 1 1.2 Significance, Importance and Objective of the Problem 10 1.3 Methodology 11 1.4 Organization of the Dissertation 13 CHAPTER II SUMMARY OF THE ARCHAEAN GEOLOGY OF THE KARNATAKA NUCLEUS WITH SPECIAL REFERENCE TO KUDREMUKH SCHIST BELT 2.1 Archaean Rocks of India-Distribution in Space 14 2.2 A Brief Review of Archaean Geology of the Karnataka Nucleus 17 2.3 Structure of Karnataka Nucleus 25 2.4 Biological Activity in Karnataka Nucleus 26 2.5 Geological Setting of the Kudremukh Schist Belt 27 2.6 Age of Kudremukh Schist Belt 29 2.7 Previous Geological Investigation in the Area Under Study 29 CHAPTER III PETROLOGY AND MINERALOGY 3.1 General Statement 31 3.2 Mineral Composition 31 II 3.3 Magnetite 34 3.4 Chert 4 0 3.5 Amphiboles 40 3.6 Carbonates 42 3.7 Biotite 42 CHAPTER IV ANALYTICAL TECHNIQUES AND DATA PRESENTATION 4.1 Sampling and Sample Selection 43 4.2 Sample Preparation and Analytical Techniques 43 4.3 X-ray Fluorescence Analysis (XRF) 44 4.4 Atomic Absorption Spectrometer (AAS) 45 4.5 Inductively Coupled Plasma Mass Spectrometer (ICP-MS) 45 4.6 Tabulation of Analytical Data 46 CHAPTER V GEOCHEMISTRY 5.1 General Statement 51 5.2 Major Elements 51 5.3 Trace Elements 55 5.4 Rare Earth Elements 72 5.5 Enrichment of XREE, EU Anomaly and Anomalous Behaviour of La 83 CHAPTER VI DISCUSSION AND CONCLUSION 94 REFERENCES 103 III FIGURES Tectonic map of India Generalized geological map of Peninsular India 16 Generalized geological map of Karnataka Nucleus 18 Geological map of Kudremukh Schist Belt 28 5 Major element variation diagram, 52 6 Al203-Ti02 variation diagram 54 7 AI2O3-K2O variation diagram 56 8 Trace element variation diagram 57 9 Rb-K20 variation diagram 59 10 Sr-CaO variation diagram 60 11 Rb-Sr variation diagram 61 12 SC-AI2O3 variation diagram 62 13 Zr-Sc variation diagram 63 14 Zr-Y variation diagram 64 15 Zr-Hf variation diagram 66 16 Cr-MgO variation diagram 67 17 Cr-Ni variation diagram 68 18 Cr-Co variation diagram 69 19 Ni-Co variation diagram 70 20 Cr-Zr variation diagram 71 21 Zr vs. Cr+Co+Ni variation diagram 73 22 Zr/Y/Zr variation diagram 74 23 REE patterns of CBIF 75 24 REE patterns.of CBIF 76 25 REE patterns of CBIF 77 IV 26 REE patterns of CBIF 79 27 REE patterns of CBIF 80 28 REE patterns of SBIF 81 29 REE patterns of SBIF 82 30 j^REE-Al203 variation diagram 84 31 LREE-HREE variation diagram 85 32 Zr- REE variation diagram 86 33 Nd-Yb variation diagram 87 34 La-Lu variation diagram 88 35 La-Sc variation diagram 89 36 Ce-Fe203 variation diagram 90 37 Plot of Cu+Co+Ni against IREE for their source 98 PLATES 1 a Bore hole core of BIF 12 1 b Bore hole cores of BIF 12 2 a Alternating light and dark bands in BIF 32 2 b Chert and magnetite 32 3 a Magnetite and pyrite 3 3 3 b Amphiboles of CBIF 3 3 4 a Carbonates of CBIF 35 4 b Contact between magnetite and silicate rich layer 35 5 a Magnetite band surrounded by nonferrous layer 36 5 b Calcite/dolomite and biotite in SBIF 36 6 a Fibrous amphiboles along with magnetite 37 6 b Fibrous amphiboles along with magnetite 37 7 a Disseminated granules of magnetite 38 7 b Disseminated granules of magnetite 38 8 a Granular magnetite 39 8 b Granular magnetite 39 9 a Recrystallized magnetite 41 9 b Recrystallized magnetite 41 UI TABLES 1 GeneraTized chronology of the Karnataka Nucleus 20 2 Generalized succession of the Supracrustal rocks in the early Precarabrian schist belts of South India 21 3 Stratigraphic order of Dharwar Supergroup 24 4 Major and trace element composition of the Kudremukh cherty banded iron formation 47 5 Major and trace element composition of the Kudremukh shaly banded iron formation and interlayered amphibolite 48 6 Rare earth element abundances in the Kudremukh cherty banded iron formation 49 7 Rare earth element abundances in the Kudremukh shaly banded iron formation and interlayered amphibolite 50 UII ACKNOWLEDGEMENTS I thank Dr. S.M. Naqvi, FNA, National Geophysical Research Institute,, Hyderabad and Dr. S.M. Zainuddin, Department of Geology, Aligarh Muslim University, Aligarh for their supervision, inspiration and help. I am greatly indebted to Prof. D. Gupta Sarma, FNA, the Director, National Geophysical Research Institute, Hyderabad for his valuable guidance and encouragement, for providing all the facilities for successful completion of this work. I am extremely grateful to Dr. P.K. Govil for training and guiding me for different geochemical and analytical techniques during last few years. It is with pleasure that I express my grateful thanks to Padma Shri Dr. Hari Narain, FNA, Prof. K. Gopalan, FNA, Prof. S.N. Bhalla, Chairman, Department of Geology, Aligarh Muslim University, Aligarh, Prof. S.M. Casshyap, Dr. V. Divakara Rao, Dr. R. Srinivasan, Dr. R.N. Singh, FNA, Dr. U. Raval and Dr. D.C. Mishra for help, encouragement and affection. I sincerely thank Shri R. Natarajan and Dr. S. Nirmal Charan for their help in EPMA analysis. Dr. V. Balaram, Smt. C. Manikyamba, Shri S.L. Ramesh and-Shri K.V. Anjaiah for their help in AAS and ICP-MS and Shri T. Gnaneswar Rao for his help in XRF analysis. \illl The cooperation and help received from all ray colleagues in the Geochemistry Division, NGRI, particularly Dr. D.V. Subba Rao, Dr. B. Uday Raj, Dr. Y.J. Bhaskar Rao, Dr. P. Rama Rao, Dr. B.L. Narayana, Dr. S.M. Hussain, Dr. T.V. Sivaraman, Shri N.N. Murthy and Shri R. Murari have been invaluable to me. My special thanks are due to Shri Mukesh Arora, SRF, for constructive and helpful criticism of the manuscript despite his busy schedule he has helped me in innumerable ways. I am extremely grateful to the authorities of Kudremukh iron ore mines to allowing to collect samples from their core library. I am very grateful to Shri Achutam for his kind help at the time of sampling. I acknowledge the help rendered by Shri P.N. Sharma for drawings, Shri Chandra Pal Singh for photographic work, Shri A. Rahim for making the thin sections, Shri K. Nageswara Rao and Smt. Nancy Rajan for flawless typing of the manuscript. This work has been carried out under the DST grant on evolution of life (Grant No. SP/12/PC2/86) to Dr. S.M. Naqvi and CSIR Fellowship as JRF-CSIR and SRF(NET) (Fellowship No. 31/23/18)/88-EMR-I). My thanks are also due to Smt. Indira Saxena and Dr. E.R. Saxena (Retd. Deputy Director, Indian Institute of Chemical Technology, Hyderabad) for their parental love, affection, encouragement and advice. CHAPTER 1 INTRODUCTION 1.1 A general perspective : The present state of our knowledge in Geology, may be likened to our knowledge of terrestrial Geography during the period of the great voyages of exploration. The early earth is very much like Salome and her seven veils: we essentially are trying to get back to the naked truth, but one is still caught up in the first veil. One momentous event in evolution of earth was the deposition of "BANDED IRON FORMATION". Because of their obvious and overwhelming economic significance, the Banded Iron Formations (BIFs) have been the subject of intensive and long continued investigations. Several authors have coined definitions for iron formations (see for example, James, 1954; Gross, 1959; Trendall and Blockley, 1970; Brandt et al., 1972; James and Sims, 1973; Trendall, 1983). The following definition for BIF is generally agreed among the contemporaneous workers for the iron-rich sedimentary rock (after Gross, 1959; James and Sims, 1973). "Banded Iron Formation is a chemically precipited sedimentary rock in which iron rich bands or laminae alternate with iron poor ones containing 15% or more iron and the banded structure of the ferruginous rocks conform in pattern and attitude with the banded structure of the adjacent sedimen tary, volcanic and metasedimentary rocks". BIFs have been classified variously. In 1954, James published his classic paper on the facies of iron-formations. In this paper he proposed four-fold subdivision of the BIFs of the Lake Superior area into four "facies" on the basis of the dominant original iron-mineral: oxide, carbonate, sulphide and silicate. The relationship of the first three facies was shown to be gradational deposited simultaneously in the shallow, intermediate and deep parts of the basin respectively. The different iron minerals characteristic of deposition at these different depths were related to parallel depth-related variation in Eh and pH. The silicate facies was believed to have a more complex, and less precisely depth related control (Trendall, 1983). Trendall (1983) has suggested the use of the term facies to indicate the dominant iron bearing mineral present in particular BIF without relating it to any stratigraphic or intergradational relationship between various BIFs. Gnaneswar Rao (1991) has given a very comprehensive account of facies variation within the BIFs of Chitradurga schist belt. In another classification, known as type classification, the term Lake Superior and Algoma types were introduced to differentiate between the kinds of associated rock in the depositional environment and geological settings for the various occurrences of BIFs (Gross, 1965). These two types, widely used in literature, do not have any time connotation. Lake Superior type BIFs are associated with dolomite, quartzite, black shale and minor am"ounts of tuff or other volcanic rocks, thereby indicating deposition near shore on continental 2 shelves. Algoma type BIFs are formed at or relatively close to volcanic centres and are associated with shale, graywacke, turbidites and volcanic rocks (Gross, 1983). Oxide, carbonate, sulphide or silicate facies, common constituents in both the types of BIF, reflect the different environmental conditions of their deposition (Gross, 1983). The development and distribution of sedimentary facies was controlled by the complex interplay of chemical, biogenic, sedimentological and other geological factors that prevailed in the basin environment (Gross, 1986). A third type of Precambrian iron formation has been suggested by Prasad et al. (1982), this type is known as Tamil Nadu type. These BIFs occur as narrow, highly deformed and metamorphosed belts within Archaean granulite and gneisses; they represent the formations of an older age group (>3000 Ma), formed in distinct tectonic environment and later incorporated within high grade mobile belts (Radhakrishna et al., 1986). Recent studies, however, have exposed the difficulties in grouping iron formations into one or the other type. Gross (1973; 1980) classified the Hamersley Group BIFs as Superior type, where as Dimroth (1975) regarded them as one of the best described examples of Algoma type. The late Archaean BIFs of India posses the characteristics of both Algoma and Superior type but are characteristically akin to Algoma type, therefore they have been considered as Algoma type (Radhakrishna et al., 1986). The general opinion now seems to be that the use of type names may prove to be misleading and, therefore, be best abandoned (Kimberley, 1978 ,• Trendall ,1983) , especially in the case of BIF exposed in Archaean 3 schist belt (Radhakrishna et al., 1986). The BIF deposition is restricted in time and space. Inspite of the rarity of radiometric dates on BIFs, James (1983) has grouped the world's iron-formation into four general age groups; they are mid-Archaean (3500 - 3000 Ma), late Archaean (2900 - 2600 Ma) , early Proterozoic (2500 - 1900 Ma) and late-Proterozoic-early Phanerozoic. Late Archaean and early Proterozoic are two major peak periods for the deposition of BIF. In Isua, Greenland the oldest know iron formation occur interbedded with quartzite, one of the oldest rock of supracrustal origin (Allaart, 1976). The oldest preserved rock on Earth is the Acasta gneiss, 3,960 Ma old, in the Slave province of northwest Canada (Bowring et al., 1989) . The youngest BIF deposit is of the Altai region of western Siberia and eastern Kazakhstan, U.S.S.R., with an assigned age of about 380 Ma (Kalugin, 1973). Banded iron formation of early Palaeozoic age has also been reported from Nepal and elswhere (O'Rourke, 1961) . BIFs are one of the most important and enegmatic rock in Earth's geological past (Cloud, 1973; Nealson and Myers, 1990). They form an important component of Archaean schist belts all over the world and occupy an unique position in Archaean sedimentation history, as they have no modern analogue (Cloud, 1983; Dymek and Klein, 1988). Their virtual confinement in space and time with two major peaks occurring at late Archaean and early Proterozoic (James, 1983) have made them extremely useful for the understanding of the exogenic processes operating during early history of the earth. They have been extensively used in support 4 of models of atmospheric and hydrospheric evolution (Cloud, 1973, 1983; Nagy et al., 1983; Towe, 1983, 1990; Walker et al.,1983; Holland, 1984; Derry and Jacobsen, 1990). Cloud (1983) has q proposed that about 2 x 10 years ago atmosphere became oxidizing. This he concluded on the basis of absence of terrestrial red beds in the rocks older than 2 x 10^ years and the presence of enormous amount of BIFs and detrital uraninite and pyrite in late Archaean and early Proterozoic. The conversion of ferrous iron to ferric and ferro-ferric oxides acted as a sink for free O2. However, Walker et al., (1983) have suggested 1.7 Ga ago as the time at which the atmosphere became oxidizing.In the absence of aerobic consumption of oxygen produced by photosynthesis in the ocean, the major sink for this oxygen would have been oxidation of dissolved Fe'^ and oxidation of biogenic methane for removal of atmospheric methane. Very low estimates of global primary productivity, obtained from the amounts of organic carbon preserved in Archaean rocks (now present as kerogen), seem to require the sedimentation of an enormous amount of iron and oxidation of a large quantity of methane to maintain global anoxia. Towe (1990) suggested that aerobic respiration must have developed early in the Archaean to prevent a build-up of atmospheric oxygen before the Proterozoic. With the passage of time the earth acquired a stable condition from an unstable regime. These tectonic changes lowered volcanic activity and the input of iron and reduced gases into the ocean. During the period of basinal stability (in between'the unstable period of opening and closing of the basin), most of the BIFs were deposited with 5 declining hydrothermal input. Arora (1991) has shown that the BiFs of Bababudan schist belt were deposited at the peak of basin opening and just after the deposition of BIFs, basin started closing down. During the deposition of BIFs O2 added to the atmosphere through carbon burial was no longer absorbed by reduced volcanic gases. This resulted in the development of an effective ozone screen, eventually leading to the origin of metaphytes and metazoans (Towe, 1990). There is no method for direct study of composition and evolution of seawater through time as the samples of ancient seawater is not preserved. Chemical sediments (e.g., limestones, BIFs, phosphorites) precipitated from seawater record some of the trace element and isotopic characteristics of the water mass from which they form (Derry and Jacobsen, 1990). Though extensive work has been carried out on BIFs of Australia (Trendall, 1983), Canada (Gross and Zajac, 1983), S. Africa (Beukes, 1983; Wilson and Nutt, 1990), China (Zhai and Windley, 1990) and Greenland (Moorbath et al., 1973; Appel, 1980; Dymek and Klein, 1988) but still their origin remains highly controversial and debated (Trendall and Morris,1983; Simonsen, 1985; Klein and Beukes, 1989; Beukes and Klein, 1990) . Studies in India have mainly centred around the economic aspect of the iron ores, while geochemical and genetic aspects are seldom attempted. "A number of partial major element analysis of iron formation are available but no systematic comparative geochemical study of the different facies iron-formations of India has yet been attempted. Information on trace element and REE is scanty" (Radhakrishna et al., 1986). The 6 geochemistry and related information of Indian BIF are only sporadic in nature (Majumder et al., 1982; Subba Reddy and Prasad, 1982; Majumder et al., 1984; Chakraborty and Majumder, 1986; Devaraju and Laajoki, 1986; Appel and Mahabaleswar, 1988; Basavanna and Mahabaleswar, 1988; Manikyamba et al., 1991; Khan et al., 1991; Gnaneswar Rao, 1991). There are several major aspects of BIF for which no satisfactory and generally agreed explanation is available and have been the subject of considerable debate and speculation. How the rhythemic banding and lamination that occurs and commonly prevails in all true BIF, are formed ? What was the source of Fe and SiOn ? How was iron transported to the sites of deposition ? Why BIFs are mainly confined to the rocks older than 2.9 Ga ? Why some anomalous occurrences of deposits younger than 2.9 Ga are found (Cloud, 1983)? Are some bacteria involved in producing rhythemic bands (La Berge, 1986; Nealson and Myers, 1990)? Despite the realization of their significance, and consequent world wide effort, understanding of major problems regarding the genesis of BIF remains extremely limited. The existing data base is not adequate to arrive at a satisfactory explanation for BIF genesis. The exhalative model (Gross, 1986; Simonsen, 1985), the biological model (Cloud, 1973; La Berge, 1973, 1986; Nealson and Myers, 1990), the continental weathering and leaching model (Cullen, 1963; Mel'nik, 1982), the ocean upwelling model (Holland, 1973; Morris, 1986), the evaporation model (Trendall and Blockley, 1970; Trendall, 1973; Garrels, 1987), dust storm model (Carey, 1986) and geochemical model (Drever, 1974); all of them require 7 reexamining the field association, minera-logy, chemistry and lithology. Some of these controversies stem from a poor understanding of the sedimentological environments in which they were deposited. Most of the time extremely "Pure" samples made up of only chert and iron minerals are chosen for geochemical studies and associated elastics, regarded as "contaminants" are ignored. Pure chert and iron minerals have chemical and crystal characters due to which not much of the REEs and other trace elements are accumulated in these minerals (Taylor and McLennan, 1985). Therefore if an imprint of a genetic process has to be lifted it can be preserved in the so called contaminants, which are more than often an integral part of most of the BIF sequences, atleast in the BIFs of the Greenstone Belts of Dharwar craton (Manikyamba et al., 1991). One of the important aspects to be taken note of in considering the origin of BIFs is the character of the late Archaean-early Proterozoic atmosphere. The atmosphere at that time was different from the present day atmosphere. Presence of detrital uraninite and pyrite in 2.3 Ga old rocks (Roscoe, 1969), absence of terrestrial red beds, deficiency of iron near the top of palesois of Archaean and early Proterozoic age (Walker et al., 1983) and the presence of procaryotic organism equipped with ultraviolet damage repair mechanisms than advanced forms (Cloud, 1973) indicates that atmosphere at that time was rich in CO2 and N2 and deficient in O2. The strongest development of iron-formation in India is restricted to the Archaean (Pichamuthu, 1974; Radhakrishna and 8 Naqvi, 1986; Naqvi and Rogers, 1987). The older of these (3500-3000 Ma) are represented by the minor bands of complexly folded and metamorphosed iron-rich beds confined to high grade regions like those of'Tamil Nadu, Kerala and South Karnataka. They occur as remnants of an older group of sediments and volcanics (Sargur Supracrustals) engulfed in a sea of tonalitic gneisses dated at 3305 + 54 Ma (Beckinsale et al., 1980). These are known as Tamil Nadu type (Prasad et al., 1982) and are also found in Bihar, Madhya Pradesh and Rajasthan (Sahoo and Mathur, 1991). The bulk of the iron-formation of India, however, are confined to the Archaean cratonic nucleii (2900-2600 Ma) forming part of the greenstone sequence (Sarkar et al., 1969; Sarkar and Saha, 1977) and are found in Bihar and Orissa (Gurumahisani, Badampahar, Tomka-Daiteri, Jamda-Koira), Karnataka (Bababudan, Kudremukh, Bellary-Hospet, Sandur, Chitradurga, Kushtagi), Maharashtra (Ratnagiri), Madhya Pradesh (Bailadilla, Rowghat, Dalli, Rajhara) and Goa. These BIFs are akin to the Algoma type of Gross (1965). Mishra (1990) has given a beautiful account of the distribution of Precambrian BIFs of Karnataka in space and time. In India development of Early Proterozoic basins has not taken place. The Middle Proterozoic bains like Cuddapah are devoid of BIF and its sedimentation is confined to Archaean schist belts and are most developed in 3.0 to 2.8 Ga old Bababudan Group. Therefore, these BIFs have a special significance in the history of continental evolution and probably represent a much more evolved stage of evolution of Dharwar craton and related biosphere 9 as such thick BIF development has not taken place in the other Archaean Greenstone belts of other shield areas. 1.2 Significancey Importance and Objective of the Problem ; As it has already been discussed that the origin of BIFs of the Precambrian is an enigma. Continued research has only increased the number of hypothesis of their origin. One should keep in mind that the climatic condition during the history of early earth was entirely different of that from today. It is likely to have affected the origin and evolution of life, the composition and mineralogy and stable isotopic ratio of sedimentary rocks. The factors that must have affected the Precambrian climate include enhanced rotation rate of the earth, reduced solar luminosity, decreased land area, presence of enormous amount of CO2 / absence of UV radiation protectine covering, high rate of heat flow from earth, absence of vegetation on earth's surface and the biological evolution. Cloud cover is a major uncertainty. For a detailed discussion on Precambrian climatic evolution please see Walker (1990). Majority opinion indicates that BIFs are of marine origin, but still some workers opt for a freshwater origin. For some, they are related to an Earth hotter than that of today; for others, they indicate an Earth colder than today. Some believe their deposition in restricted environments, while others in the open sea. In general it is assumed that they formed under anoxic or very low oxygen conditions in a basin which had an enormous amount of soluble Fe^'^, but the source of soluble Fe^"^ — may be 10 weathering, volcanic activity, hydrotherraal vents or a combination of such mechanism, is highly debated. Kudremukh schist belt is one of the younger schist belts of Karnataka nucleus and is metamorphosed to amphibolite facies. The BIF of this belt overlie current bedded and rippled marked quartzites. The BIF investigated is mined for iron and contains around 33% of Fe. Due to mining activity bore hole samples of BIF and interlayered amphibolites were available. These samples were absolutely fresh and were collected from the bore hole cores penetrating upto 60 and 70 mts. (Pi. la & lb). In present study an attempt has been made to provide new information in terms of major, trace and rare earth composition and interpret these data for possible origin of the BIF of the Kudremukh region. 1.3 Methodology ; Methods adopted in the present work are : (1) 50 representative samples of Cherty Banded Iron Formation (CBIF), Shaly Banded Iron Formation (SBIF) and interlayered amphibolites were collected from the bore hole samples; (2) 40 thin section were studied for petrography; (3) 41 samples were analysed for their major, trace and rare earth elements; (4) Microprobe analyses of coexisting minerals in 10 CBIF, SBIF and amphibolite layer have been carried out to distinguish between various type of silicates present in the rock. The Data obtained is finally used to interpret for the possible origin of the BIF of the Kudremukh schist belt. 11 PLATE I a. Core of the BIF from Kudremukh schist belt b. Cores of the BIF from Kudremukh schist belt from different bore holes. 12 1.4 Organization of the Dissertation ; The contents of the dissertation are organized as follows : In Chapter II, a general review of the Archaean geology of the Karnataka nucleus, with special reference to Kudremukh schist belt has been summarised. In Chapter III, detailed petrography and mineralogical description of CBIF, SBIF and amphibolite layer are given. In Chapter IV, the analytical techniques and procedure fol lowed for chemical analysis and the analytical data thus obtained are presented. Chapter V, presents geochemistry of each rock type incorporating the variation in major, trace and rare earth element abundances. Different geochemical diagram have been used to highlight the genetic aspects of BIF. Chapter VI, sums up the conclusions arrived at, after the detailed study of BIF of Kudremukh schist belt. 13 CHAPTER II SUMMARY OF THE ARCHAEAN GEOLOGY OF THE KARNATAKA NUCLEUS WITH SPECIAL REFERENCE TO KUDREMUKH SCHIST BELT 2.1 Archaean Rocks of India - Distribution in Space; The Archaean rocks of India are mainly distributed in three protocontinents (Naqvi et al., 1974), namely Aravalli Craton of Northwestern India, Singhbhum Craton of Eastern India and Dharwar Craton of Southern India (Fig. 1). There is no doubt about the existence of Archaean rocks in Singhbhum and Dharwar region. Recently, Choudhary et al. (1984) and Gopalan et al. (1990) have reported the presence of rocks of Archaean age in Aravalli craton. The Archaean rocks are well exposed in Rajasthan, Bihar, Madhya Pradesh and Karnataka. Radhakrishna and Naqvi (1986) have proposed three early Precambrian (Archaean) nucleii, namely Karnataka Nucleus (KN), Jeypore-Bastar Nucleus (JBN) and Singhbhum Nucleus (SN) (Fig. 2). The Karnataka and Singhbhum Nucleii of the Dharwar-Singhbhum Protocontinent are fairly well established and appear to have survived in the craton; they are characterized by low-grade supra crustals and tonalitic trondhjemitic-gneisses, formed 3800-2600 Ma ago. A possibly similar Jeypore-Bastar nucleus is not yet established as there are no radiometric age data available (Radhakrishna and Naqvi, 1986). These appear to have survived in the craton and are characterized by low-grade supracrustals and tonalitic trondhjemitic-gneisses, formed 3800-2600 Ma ago. 14 GEOLOGICAL AND STRUCTu^lkL TREND MAP OF INDIA ^^•« M *• c M •or ;•»«.«< S / -•;' '• PROTOCONTmtNT . •vf I' - liC ft«i 0* »l*lCAk StNGHBHUM 'pftOTOCONTiNENT i I & C 10 o It' \V.- \ \ • la'. / •r Figure 1. Tectonic map of India. Shows the separa tion of Indian Shield into three protocon- tinents that had evolved about individual Archaean nuclei! (From Naqvi et al., 1974). 15 25' 20 15 - 10 Figure 2. Generalized geological map of Peninsular India. KN-Karnataka Nucleus, SN-Singhbhura Nucleus, EPMB-Early Proterozoic Mobile Belt, MPMB-Middle Proterozoic Mobile Belt; 1-schist belts within nucleii, 2-tonalitic gneisses, 3-granodiorites (From Radhakrishna and Naqvi, 1986). 16 2.2 A brief review of Archaean geology of the Karnataka Nucleus ; Karnataka nucleus (Dharwar Craton) (Fig. 3) is a well studied region. It's geology has been summarised by several workers (Swami Nath and Ramakrishnan, 1981; Naqvi, 1981; Divakara Rao and Rama Rao, 1982; Pichamuthu and Srinivasan, 1983; Ramakrishnan and Viswanatha, 1983; Radhakrishna and Naqvi, 1986; Naqvi and Rogers, 1987). It is an elliptical area west of the Closepet Granite with a garland of K-rich granite plutons on at least two sides. The eastern margin of KN is uncertain; apart from Closepet Granite forming its eastern margin, another possible margin is a major shear zone slightly west of the Closepet outcrop which has been recognized by Kaila et al. (1979), Drury and Holt (1980), Drury et al. (1984) and Naqvi and Rogers (1987). The northern extension of this nucleus is covered by Deccan Traps, whereas the western part is terminated at a passive continental margin developed at the time of the split of the Gondwana continent which resulted in the formation of Arabian Sea. Towards south, it is transitional into granulite facies assemblages. The early Precambrian terrane of Dharwar craton, like many other shields, is composed of schist belts (referred to as greenstone belts in other region), gneisses and granitoids. Radhakrishna and Naqvi (1986) have suggested that the term "schist belt" should be used in place of greenstone belts for the Archaean volcano-sedimentary sequences of India, as it emphasizes the unique schistose character of these belts, whereas the terms like greenstone belt, supracrustal association and supracrustals are inadequate in characterizing the essential schistose and metamorphic status of the supracrustal rocks of the 17 Figure 3. Schist belts of Karnataka nucleus. High grade schist belts are in black; low grade belts in lined pattern. Schist belts are Sh, Shiraoga; G, Gadag; S, Sandur; Ga, Ghatti-Hosahalli; J, Javanahalli; Ch, Chitradurga; W, Western Ghats; B, Bababudan; K, Kibbenhalli; Ku, Kudremukh; Si, Sigegudda; C, Chiknayakanhalli; Ho, Holenarasipur; N, Nuggihalli, Kr, Krishnarajpet; H, Hadnur; Kh , Kunigal-Hulliyurdurga- (From Naqvi and Rogers, 1987). Indian Archaean. The schist belts of this craton, in spite of- scanty radiometric data are suitably divided into older and younger belts ranging in age from 3.5 to 2.5 Ga, these belts are separated by a widespread continental crust forming event at or around 3.0 Ga represented by Peninsular Gneisses of tonalitic and trondhjemitic composition (Naqvi and Rogers, 1987). The sediments of older schist belt (3.5 to 3.0 Ga) are mainly chemogenic and fine grained argillaceous sediments including thin bands of recrystallized garnet bearing BIFs (Naqvi, 1981; Naqvi et al., 1983; Hussain and Naqvi, 1983). These belts are exposed at Holenarasipur, Nuggihalli, Krishnarajpet, Hadnur and several other places and have been metamorphosed to amphibolite facies (Naqvi and Rogers, 1983). The sedimentary component of the younger schist belts (3.0-2.6 Ga) is mainly made up of shales/phyllites, quartzites, carbonates, BIFs, conglomerates and graywackes (Naqvi et al. , 1988). The basal portions of the younger schist belts are designated as Bababudan group which is followed by Chitradurga group. A generalized chornology of the Karnataka nucleus, based on available radiometric age data, lithology and sedimentological evidence (after Radhakrishna and Naqvi, 1986) is given in Table 1. Another generalized chronology (after Srinivasan and Naqvi, 1990) of KN is given in Table 2. A comparative study of both the tables gives a clear picture of the distribution of rock types of KN in space and time. 19 TABLE 1. Generalized chronology of the Karnataka Nucleus (Adopted from Radhakrishna and Naqvi, 1986). Date (M.Y.) Event Late Archaean Invasion of younger granites (K-rich) bordering the nucleus. 2600 Granulite transformation of older crust along the margins of the nucleus. Deposition of younger schist belts (Shimoga, Chitradurga, Sandur). 3000-2600 Conglomerates, orthoquartzites, mafic and felsic volcanic sequences, banded iron formation, greywackes. Early Archaean 3 000 Main development of migmatitic gneisses Emplacement of oldest tonalite- trondhjemite gneisses with enclaves 3400 of ancient supracrustal sequences. Deposition of ancient supracrustal >3400 sequences, mafic-ultramafic volcanics and chemical sediments. Basement predominantly mafic crust. 20 TABLE 2. Generalized succession of the Supracrustal rocks in the early Precambrian schist belts of South India (Adopted from Srinivasan and Naqvi, 1990). Age (in B.Y.) Event Belt/Area 2.5 Polymictic conglomerates and Chitradurga and Greywackes; Metabasalts, Andesites, Gadag areas of Dacites and rhyolites; Banded Chitradurga Iron Formation schist belt; 2.6 Parts of Central portion of Dhar- war Shimoga belt 2.7 Quartz-Arenite/Arkose, Metapelite, Western Margin carbonate (Limestone and dolomite), of Chitradurga Banded Manganese and Iron Formation schist belt(low- 2.8 with some mafic sills grade metamor phosed) southern and western part of Dharwar Shimoga schist belt 2.9 Quartz pebble conglomerates, Bababudan schist Quartz Arenites, Metabsaltic and belt; Kudremukh- Rhyodacitic Lava flows. Graphitic Kodachari area 3.0 Schists and Banded Iron Formation of Western Ghat schist belt 3.1 Layered Ultramafic-mafic complexes Nuggihalli and (deformed) associated with minor Holenarasipur amounts of quartzites (detrital as schist belts well as chemogenic), highest Al-Mg 3.2 schists 3.3 3.4 21 The entire succession of the Dharwar schist belt shows interfingering stratigraphy with polyphase gneisses; it is not exposed at any one locality. This aspect has given rise to many controversies about the structure and stratigraphy of the schist belt. There is no unanimity of opinion, several conflicting models of stratigraphy are proposed. Three views are prevalent : (1) The schist belts represent a group of rocks younger than the Peninsular Gneisses and there exists an older Sargur Group which is older than the gneisses (Swami Nath and Ramakrishnan, 1981). (2) Together the Dharwar supracrustals and the Sargurs represent one Supergroup older than the Pninsular gneisses {Pichamuthu and Sr inivasan, 1984) . (3) The Archaean supracrustals represent belts formed at different periods covering a span of at least 1000 Ma (3500-2500 Ma), some of which are older and some younger than the gneisses, which are themselves polyphase and polymetamorphic (Naqvi, 1981; Radhakrishna, 1983; Naqvi and Rogers, 1983). The primary sedimentary features in older schist belts are obliterated by deformation and metamorphism. As such, in absence of reliable radiometric dates, it is difficult to determine the internal primary stratigraphy for these belts. Based on tectonic and other considerations, Naqvi (1976) suggested that the mafic-ultramafic volcanic rocks are the basal members of this group and are overlain by sediments. In contrast, Swami Nath and Ramakrishnan (1981) considered the mafic-ultramafic rocks to be intrusive. 22 According to Radhakrishna and Naqvi (1986), the younger schist belts of KN, deposited over a clearly recognizable sialic basement, were formed in fault-bounded ensialic intracratonic basins. The belt contains ultramafic to mafic volcanic rocks at the base, which is succeeded by thick accumulation of clastic sediments. However, Naqvi (1985) and Rajamani et al. (1985) have argued in favour of a plate tectonic model for the evolution of Chitradurga and Kolar schist belts respectively. Arora (1991) has demonstrated that the Bababudan schist belt was formed in a very short period of time by opening and closing of the basin. The younger schist belts, termed as Dharwar Supergroup (Swami Nath et al., 1976) overlie the regional basal unconformity marked by the uraniferous and pyritiferous orthoquartzite-conglomerate (oligomict) exposed in Bababudan, Western Ghat, Chitradurga and Sigegudda belts. The Dharwar Supergroup is overlain unconformably by the flat-bedded unmetamorphosed rocks of the Kaladgi Group in northern Karnataka (Swami Nath and Ramakrishnan, 1981). The classification of Dharwar Supergroup is given in Table 3 (after Swami Nath and Ramakrishnan, 1981). The Bababudan Group represents platform facies characterised by oligomictic conglomerates, orthoquartzites and banded iron formation, whereas the Chitradurga Group represents rocks deposited in deeper parts of the basin (Radhakrishna and Naqvi, 1986). BIFs are one of the most important rock of these schist belts. 23 TABLE 3. Stratigraphic order of Dharwar Supergroup (Adopted from Swami Nath and Ramakrishnan 1981). Middle to late Kaladgi, Badami and Bhima Groups Proterozoic Unconformity Late Archaean to Early Dharwar Chitradurga Group Proterozoic Supergroup Unconformity— (2400-2600 MY) Bababudan Group -Unconformity- Middle Archaean Peninsular (2900-3000 MY) Gneiss 24 Most extensive deposition of BIF had taken place in the Bababudan Group around 3.0-2.8 Ga. The BIF of this group consists of magnetite and/or hematite, quartz, cummingtonite, grunerite, magnesio-riebeckite and acmite. The oxide facies BIFs of Chitradurga Group in the regions of amphibolite facies metamorphism consist of rhythemic layers of magnetite and quartz, whereas in low grade regions, chlorite, and other silicates are formed with hematite-chert or hematite-jasper (Radhakrishna and Naqvi, 1986). According to Manikyamba et al., (1991) the BIFs of Dharwar Supergroup (Swami Nath et al., 1976) can be subdivided into two groups: (1) predominantly oxide facies BIFs of Bababudan belt proper, Kudremukh and Kushtagi belts; they are not associated with stromatolites, Mn formations and widespread carbon phyllites (2) the BIFs of the Chitradurga, Shimoga and Sandur schist belts associated with stromatolites (Murthy and Reddy, 1984; Srinivasan et al., 1989, 1990; Vasudev et al., 1989; Venkatachala et al., 1989), Mn formations and extensive carbon phyllites. The BIF present in younger schist belts of Kudremukh region are very conspicuous and are used in the present study to formulate a model for their genesis and tectonic setting. 2.3 Structure of Karnataka Nucleus: Naha and Mukhopadhyay (1990) have summarised the structural styles of the Archaean rocks of KN. Structures of three generations in hand specimen and outcrop are common in all supracrustal rocks. The first generation structures comprise of isoclinal folds on stratification (DhF^) having long limbs and 25 thickened hinges, with an axial planar cleavage. At a number of places these folds are recumbent to reclined, with fold axes plunging gently westward. The DhF-]^ folds have been affected locally by near-coaxial upright folding (DhF^^) during the second phase; these two sets of folds may represent structures formed at different stages of progressive deformation. Structures of the third generation (DhF2) consist of upright folds with varying tightness with the strike of axial planes varying between NNW and NNE. Superposition of folds of three generations has resulted in fold interference on different scales. 2.4 Biological activity in Karnataka Nucleus; The Archaean schist belts of KN, composed of extensive deposits of carbonate rocks and banded iron formation and banded manganese formation, have the potential to preserve evidence of a large magnitude of biological activity (Srinivasan et al., 1989). These rocks are considered to act as a sink for oxygen produced during the early part of the Earth's history (Cloud, 1976). Although Pichamuthu (1945) recorded the presence of cyanobacterial filaments in cherts of the Dodguni area in Chitradurga schist belt, the evidence for its syngenecity and biogenecity was provided by Suresh (1982). Naqvi et al. (1987) have recorded unambiguous syngenetic silicified cyanobacteria like microfossils in the black cherts of Donimalai in Sandur schist belt. From carbon-isotopic data, Kumar et al. (1983) have suggested the presence of life during the formation of younger schist belts of KN. Murthy and Reddy (1984), Baral (1986), Mallikarjuna et al. 26 (1987), Srinivasan et al. (1989; 1990), Vasudev et . al. (1989), Venkatachala et al. (1989) have recorded the occurrence of stromatolites in the carbonate rocks of the lower part of the Dharwar sequence. 2.5 Geological setting of the Kudremukh schist belt ; Kudremukh schist belt (Fig. 4) is one of the belts of the Western Ghat region. The other belts of this region are Agumbe and Kodachadri belts (Ramakrishnan and Harinadha Babu, 1981). Kudremukh schist belt has an average width of 25 km and length of about 60 kras. It is a very complexly folded belt and has been metamorphosed upto amphibolite facies. Swami Nath et al. (1976) assigned the sequence to the Bababudan Group in their stratigraphic model for Archaean supracrustal in the Karnataka nucleus. It starts with the oligomictic conglomerate near Walkunje which is followed by an identical Bababudan succession. Radhakrishna (1983) proposed subdivision of the low grade schist belts into three basins: Shimoga, Chitradurga and Sandur. Kudremukh belt is a part of Shimoga basin apart from Bababudan, North and South Kanara. The outcrop of rocks is generally poor because of deep lateritic weathering. Although the contact between the schist belt and the underlying gneisses around Kudremukh is not exposed, but are believed to ovelie them. Near Kudremukh, the lower part of the belt consists of komatiitic to tholeiitic lava flows (Drury, 1981) with interlayered chlorite and mica schists, 27 75*10- 10 KILOMETERS INDEX \^\ Basic Dykes Ulframafites (Unclassified) \H I Ironstone IV I Meta-Volcanis;Acid [j'/Zyj Meta-Volcanics:Basic m auarzife LYVS Older Granite anara Battiolithf 13; t^"*| Migmatites 0' 13° Figure 4. Geological map of Kudremukh schist belt, (after Sampat Iyengar, 1910) showing location of mine area from where samples have been collected. 28 quartzites and sills. The upper part of the belt consists of iron-rich schists, banded iron formations, graywacke, carbonates and mafic to acid volcanic assemblages (Krishna Rao et al., 1977; Drury, 1981; Ramakrishnan and Harinada Babu, 1981; Naqvi and Rogers, 19 87) . 2.6 Age of Kudremukh schist belt : None of the Indian schist belt has been dated directly; only relevant available age is either from later granitoid intrusion (minimum age) or from underlying gneisses (maximum age). In Kudremukh region, the underlying granitoid gneisses have yielded a Rb-Sr age of about 3280 +^ 230 Ma and the basal metavolcanics have yielded a Sm-Nd whole rock isochron age of about 3020 + 230 Ma (Drury et al., 1983). These ages indicate that the filling of an ensialic basin with volcanic and sedimentary rocks began at around 3000 Ma. Thus the age of the belt can reasonable be estimated to be late Archaean. 2.7 Previous geological investigation in the area under study : The area was first studied by Bruce Foote (1900) who recorded the presence of mica schist, garnetiferous mica schist, contemporaneous metavolcanics/trap, quartzite and hematite-magnetite quartzite, resting on uneven Archaean granitoid gneiss. Later on, the traps described by him were considered to be hornblende gneiss. Subsequently, Sampat Iyengar (1912) prepared the first geological map of the area which is the only published available base map even today. The gneissic complex was 29 considered by him to be intrusive into the schists. Smeeth (1912) postulated that present position of the schist belt on the ghats was due to folding. Rama Rao (1962) reported a complex series of quartzitesir grits, ferruginous quartzites, acid volcanics and granites present in the area. Rammohan Rao (1968) and Venkataraman (1968) mapped parts of Kudremukh greenstone belt and proposed that the gneissic complex with remnant metamorphites formed the basement to the Dharwars. In late sixties National Mineral Development Corporation carried out detailed exploration for iron ore in this area. Ramakrishnan (1973) investigated the Kudremukh area for locating asbestos deposits. Inspite of its economic importance still the study of this belt is in nascent stage and no unequivocal stratigraphic sequence is available.. 30 CHAPTER III PETROLOGY AND MINERALOGY 3.1 General Statement; Forty polished thin sections were used for detailed petrographic study of the mineral assemblages and their textural relations, prior to electron problem analysis. BIFs of Kudremukh schist belt are having relatively simple mineralogy; the meso-bands and micro-bands of the BIF are mainly composed of magnetite and chert. The mineralogy of Cherty Banded Iron Formation (CBIF) is very simple, whereas the same of the Shaly Banded Iron Formation (SBIF) and interlayered amphibolite is slightly complex. Mineralogy of BIF together with that of interlayered metasediments indicates that most of the BIF in this schist belt have been metamorphosed to grades between those of the upper greenschist and the upper amphibolite facies. Bhaskar Rao (1980) has suggested epidote-amphibolite facies of metamorphism for the BIFs of Kudremukh region. These BIFs have also undergone considerable post-depositional recrystallization and alteration, which has obscured primary textural-mineraiogical relations. 3.2 Mineral Compositions; CBIF consist of micro-crystalline chert, magnetite (Pl. 2a & 2b), few specks of pyrite (Pl. 3a) with minor cummingtonite, grunerite and actinolite (Pl. 3b). However, in several samples 31 PLATE II Photomicrograph showing the well developed magnetite and chert rich bands in CBIF (X 125). Photomicrograph showing the presence of dis seminated magnetite within the chert rich layer (X 350) . 32 PLATE III a. Photomicrograph (reflected light) showing the presence of a few specks of pyrite in Kudremukh BIF (X 350). Photomicrograph showing all the minerals of amphibole family present in CBIF (X 125). 33 thin layers of carbonate and interstitial development of calcite/dolomite have been found (Pi. 4a). SBIFs consist of layers of chert and iron minerals and also the layers of shaly material. In addition to chert and magnetite and few specks of pyrite, they contain layers of several kind of amphiboles like actinolite, cummingtonite, grunerite, riebeckite and aegerine (Pi. 4b & 5a). These minerals are also found in the BiFs of Bababudan schist belt (Chadwick et al., 1986). In this type also minor carbonate and a few biotite crystals are present (Pi. 5b). In addition to iron and quartz rich bands, thin bands rich in silicates are also found in several bore holes at varying depths, alternating with Fe- rhythmites. The amphibolitic layers are made up of actinolite, cummingtonite, grunerite, magnetite, quartz and other accessory and secondary minerals (Pi. 6a & b). A brief description of the mineral present in the rock under study is given as follows: 3.3 Magnetite; Magnetite is normally subhedral to euhedral and relatively coarse grained. It may occur as granule, as lenses or as evenly disseminated bands in a cherty matrix (Pi. lb, 2a & 7a). A few individual granules of magnetite surrounded by amphiboles, quartz and calcite/dolomite are also observed (Pi. 7b, 8a and 8b). It appears as a contribution from continental source. Magnetite with an octahedral form is the dominant iron oxide throughout the horizon. Disseminated magnetite is widespread in SBIF but is relatively rare in CBIF. Sharp octahedral grain boundaries often 34 PLATE IV a. Photomicrograph showing development of calcite/dolomite in CBIF (X 350). b. Photomicrograph showing the contact between magnetite and silicate rich layer in SBIF (X 125) . 35 PLATE V a. Photomicrograph showing cummingtonite- grunerite and minor amount of carbonates along with magnetite rich band (X 125). b. Photomicrograph showing calcite/dolomite and amphiboles and biotite in one field in SBIF (X 350). 36 PLATE VI a. photomicrograph of fibrous amphiboles along with few specks of magnetite (cross nicols) (X 350) . b. Photomicrograph of fibrous amphiboles along with few specks of magnetite (X 350). 37 PLATE VII a. Photomicrograph (reflected light) showing irregular distribution of magnetite in cherts and silicates (X 125). b. Photomicrograph (reflected light) showing granular magnetite in the recrystallized form with irregular boundaries (X 125). 38 PLATE VIII a. Photomicrograph of granular magnetite within amphibole, calcite/dolomite and quartz bear ing band (cross nicols) (X 125). b. photomicrograph of granular magnetite within amphibole, calcite/dolomite and quartz bear ing band (X 125). 39 appear to cut across other minerals and have been concluded by some authors (Dimroth and Chauvel, 1973; French, (1973) as evidence for replacement of the other iron oxides by magnetite (Pi. 9a and b) . Klein (1974) points out that a strong force of recrystallization would produce an euhedral outline against a coexisting mineral and that such textures are not unambiguous evidence for replacement. The textures of magnetite as granules, relict granule, original sedimentary laminae indicate that much of the magnetite of Kudremukh schist belt is of primary origin and may have precipitated as mixtures of ferrous and ferric hydroxides (Fe (OH)2 and Fe(0H)2 ) as suggested by Eugster and Chou (1973), or perhaps as Fe^O^ directly. 3.4 Chert: Chert and fine grained equigranular quartz are the most abundant phases in the iron formation of Kudremukh schist belt. They usually occur in thin bands or lenses in which the grains are anhadral and interlocking and frequently display parallel optical orientation. Nearly all the quartz is considered to be the recrystallized product of original chert. 3.5 Amphiboles: Both one and two amphibole assemblages are found. Coexisting amphiboies occur in several textural modes: (1) as independent grain, (2) as intergrowths of two amphiboies within a single grain separated by an optically sharp boundary. Members of thecummingtonite-grunerite series are the most common amphiboies 40 PLATE IX Photomicrograph showing recrystallized magnetite within silicate rich layer of SBIF (cross nicols) (X 125) . b. Photomicrograph showing recrystallized magnetite within silicate rich layer of SBIF (X 125) . 41 with some actinolite and minor amount of riebeckite. In general, the amphiboles are interpreted to be part of the high temp-pressure equilibrium assemblage, with temperature of metamor- phism at 650°-750°C and 4-6 Kbar pressure. The distribution of amphiboles in BIF is dependent on the amount of clastic input into the BIF during its chemical precipitation. The CBIF have negligible or no amphiboles at all whereas SBlFs have appreciable amount of amphiboles, the amphibolite layer is entirely made up of the amphiboles. They are commonly present as randomly distributed aggregates, may be in the form of laths. 3.5 Carbonates: Carbonates (calcite/dolomite) occur as granules, as cement or as disseminated grains in a chert matrix. They are subhedral to euhedral in outline and range from fine to coarse grained. 3.7 Biotite: Biotite occurs as traces in some bands. The biotite is very fine grained hence is very difficult to identify within the chert-magnetite layers. It may have formed at the expenses of chlorite during metamorphism. 42 CHAPTER IV ANALYTICAL TECHNIQUE AND DATA PRESENTATION 4.1 Sampling and Sample Selection ; Selection of proper analytical material for geochemical interpretation is not, by any means, an easy task. It follows from theoretical premises that the most valuable material in this context are those collected at random but according to a systematic pattern, which of course depends on the objectives of sampling. Since no detailed account of the geochemical features of the rocks under study are documented in previous literature, this work had to be of reconnaissance nature and sampling was therefore, regretably not random and was entirely dependent on the available bore hole cores, provided by Kudremukh Iron Ore Company. 50 samples of the CBIF, SBIF and interlayered amphibolite were collected from the bore hole samples. These samples were absolutely fresh and were collected from the cores penetrating upto 60 and 70 mts in different bore holes. Special care was taken in the selection of these samples, those affected by alteration were avoided. 4.2 Sample Preparation and Analytical techniques : Sample preparation and geochemical analysis of the samples were carried out at the Geochemical Laboratories of the National Geophysical Research Institute, Hyderabad. Samples were powdered to -250 mesh using a Herzog Swing-Grinding Mill with grinding 43 tools made up of tungsten carbide for SBIF and amphibolite and of stainless steel for CBIF. The Major element were estimated by X-ray Fluorescence Spectrometer (XRF). The trace element analysis was carried out on Atomic Absorption Spectrometer (AAS) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The rare earths concentrations were determined by ICP-MS. Mineral composition of coexisting phases were determined by Electron Probe Micro Analyser (EPMA). 4.3 X-ray Fluorescence Analysis (XRF); For determination of major elements, samples were fused with lithium tetra borate, lithium metaborate and lanthanum oxide to remove the ground effect and to bring down the melting point of the elements. Samples were fused in 5% gold-platinum crucibles in a 'HERZOG' automatic fusion machine at 1200°C. Sample to flux (including lanthanum oxide) ratio was kept at 1:5. Melt was shaked well before it was allowed to be cooled down in the form of fused pellets of 40 mm in diameter. These pellets were analysed by using a Philips PW 1400 model, microprocessor controlled, sequential X-ray fluorescence spectrometer with 100 KvA X-ray generator. A Philips model P851, on line, dedicated computer was used to prepare calibration curves using Geological Survey of Canada (GSC) reference standard rock samples. For detailed analytical proceedure, precision, accuracy and standard errors of the analytical procedure used, please refer Govil (1985). 44 4.4 Atomic Absorption Spectrometer (AAS) : 2 gm. of sample was digested with HF and a few drops of HCl in platinum crucibles and evaporated on water baths. The residue was then dissolved on a minimum quantity of 1:1 HNOT• Cu, Zn, Cr, Co and Ni were determined directly from this solution using air/ acetylene mixtures. For the determination of Rb, potassium chloride solution was added. The AAS consists mainly of a hollow cathode lamp for obtaining radiation of suitable frequency which is characteristic of the element to be estimated, and a burner assembly where the sample solution is aspirated through a nebuliser resulting in atoraization of the sample. The emergent flame in the burner assembly enters a monochromator where the isolation of the required spectral line is achieved. A photo-multiplier is used to amplify and convert the signal to a digital read out of the absorbance. Absorbance is measured in a series of natural rock and synthetic internal standard solutions along with the unknown sample solutions. The concentration in the unknown solutions is then measured in comparison with the standards. For a detailed procedure please refer Shapiro (1975). 4.5 Inductively Coupled Plasma Mass Spectrometer (ICP-MS) : Trace elements and rare earth elements were analysed by ICP-MS (VG Plasma Quad) For ICP-MS, 0.1 gm of the sample powder were weighed accurately and placed in Teflon beakers with tight lids. To each sample, 3 ml concentrated nitric acid (HNO3) and 7 ml hydrofluoric acid (HF) were added. The teflon beaker were placed on hot plate (110 degrees centigrade) till the solutions 45 evaporated to dryness. The lids from Teflon beakers were removed after one hour. The residue was dissolved in 10 ml of nitric acid and double distilled water (1:1). Then, 0.1% rock solutions were prepared with an overall concentration of 100 gm/ml. of indium, as an internal standard. Calibration curve was prepared by using Geological Survey of Canada (GSC) and Association Nationale de la Recherche Technique (ANRT) reference standard rock samples. For detailed procedure and accuracy, see Balaram et al., (1988, 1990). 4.6 Tabulation of Analytical Data ; The analytical data on Kudremukh BIF under study are tabulated through table 4-7. Data on major and trace element of CBIF and SBIF (including amphibolite) are tabulated in table 4 and 5 respectively while the rare earths of CBIF and SBIF (including amphibolite) are tabulated in table 6 and 7 respectively. 46 TABLE 4 : MAJOR AND TRACE ELEMENT COMPOSITION OF THE KUDREMUKH CHERTY BANDED IRON FORMATION Element G02 G03 GOT G012 G013 G014 G017 G018 (wt.%) Major(Wt%) Si02 61.48 44.77 49.51 34.09 41.09 50.24 52.08 37.08 Fe203 (T) 30.72 52.48 48.28 55.75 55.21 42.73 45.05 57.17 FeO 13.32 16.20 15.24 16.48 16.48 23.20 12.92 18.08 Ti02 0.01 0.01 0.01 0.01 0.01 0.04 0.01 0.01 AI2O3 0.19 0.09 0.06 0.16 0.27 1.94 0.02 0.12 MnO 0.22 0.01 0.03 0.09 0.02 0.12 0.04 0.05 MgO 0.82 0.78 1.29 3.80 2.01 2.10 1.00 0.09 CaO 4.32 1.60 0.85 5.45 0.78 1.39 1.54 5.19 Na20 0.02 0.01 0.08 0.27 0.32 0.38 0.04 0.02 K2O 0.02 0.01 0.01 0.10 0.07 0.14 0.01 0.06 P2O5 0.02 0.04 0.04 0.28 0.03 0.01 0.04 0.01 Trace(ppm) Sc 1.78 5.49 1.65 1.47 2.78 2.58 2.24 5.08 V 2.82 2.02 1.65 3.09 4.88 3.79 9.64 6.83 Cr 8.71 3.76 2.23 3.54 3.44 3.62 3.48 4.22 Co 27.63 28.40 23.35 14.69 23.81 31.46 33.19 16.90 Ni 12.97 6.01 0.21 15.98 1.88 7.65 2.42 16.62 Cu 51.42 34.57 2.81 14.23 16.46 5.88 3.94 11.01 Zn 25.94 20.00 9.77 20.68 21.09 21.92 9.16 12.25 Ga 1.00 0.80 0.45 0.76 1.21 1.08 0.56 1.52 Rb 7.63 1.37 0.65 7.38 22.81 8.47 2.15 7.73 Sr 74.18 75.13 22.80 110.11 17.95 24.08 32.37 82.13 Y 4.45 2.40 2.90 7.68 3.12 4.96 3.22 7.67 Zr 5.98 2.45 3.36 2.91 4.45 7.66 3.67 11.55 Nb 0.41 0.20 0.15 0.19 0.47 0.27 0.24 0.38 Ba 62.11 22.27 20.01 414.93 13.98 9.75 82.29 24.05 Hf 0.26 0.14 0.42 0.38 0.24 0.02 0.05 0.57 Ta 0.20 0.26 0.48 0.48 0.20 0.16 0.25 0.14 Si02/Fe203 2.00 0.86 1.03 0.61 0.74 1.18 1.16 0.65 Rb/Sr 0.10 0.02 0.03 0.07 1.27 0.35 0.07 0.09 Cr/Ni 0.67 0.63 10.62 0.22 1.83 0.47 1.44 0.25 Zr/Y 1.34 1.02 1.16 0.38 1,43 1.54 1.14 1.51 47 Table 4 (contd.. .) Element G021 G024 GO3 0 G03 8 G058 G073 GO9 0 GO103 (wt.%) Major(Wt%) Si02 47.29 78.87 42.13 34.25 48.23 37.81 57.34 66.36 Fe203 (T) 48.78 20.53 52.83 59.73 48.86 49.91 37.63 28.02 FeO 13.20 17.00 24.36 31.40 19.48 20.64 11.16 9.84 Ti02 0.01 0.01 - 0.01 0.01 1.49 0.01 0.01 AI2O3 0.05 0.07 - 0.23 0.11 1.37 0.12 1.20 MnO 0.05 0.07 0.06 0.06 0.03 0.29 0.04 0.02 MgO 1.66 0.01 2.40 2.51 1.37 2.49 1.65 0.99 CaO 2.02 0.01 1.36 1.20 1.23 4.38 2.54 0.01 Na20 0.05 0.31 0.21 0.21 0.04 0.58 0.09 0.6 2 K2O 0.02 0.01 0.03 0.01 0.04 0.42 0.02 0.06 P2O5 0.05 0.01 — 0.01 0.04 - 0.07 - Trace(ppm) Sc 0.55 2.87 0.69 1.29 1.15 2.13 0.80 2.23 V 2.33 3.71 2.93 6.27 1.74 17.89 48.06 21.63 Cr 8.18 3.72 1.86 2.52 2.66 32.19 42.25 11.67 Co 30.84 28.08 32.39 8.92 27.01 12.79 55.69 148.05 Ni 33.17 13.89 5.18 0.57 3.90 13.73 5.05 6.27 Cu 14.98 29.27 29.53 7.22 14.99 8.40 46.27 64.92 Zn 38.30 26.20 59.18 35.17 25.34 37.38 22.32 175.81 Ga 0.42 0.79 1.20 2.50 0.75 3.49 0.65 3.58 Rb 8.89 1.65 0.50 0.57 0.39 61.94 1.36 5.56 Sr 74.43 70.00 14.14 29.19 24.97 48.22 77.53 28.10 Y 4.81 3.49 6.10 4.35 4.26 5.13 4.17 4.00 Zr 1.87 5.84 0.80 1.91 1.74 23.27 0.92 1.18 Nb 0.20 0.18 0.20 0.86 0.23 1.07 0.29 0.03 Ba 64.21 479.10 1.16 3.86 5.45 147.78 6.12 38.57 Hf 0.09 0.21 - 0.09 0.19 0.56 0.24 - Ta 0.20 0.22 0.43 0.09 0.18 0.27 0.46 0.46 Si02/Fe203 0.97 3.84 0.80 0.57 0.99 0.76 1.52 2.37 Rb/Sr 0.12 0.02 0.04 0.02 0.02 1.29 0.02 0.20 Cr/Ni 0.25 0.27 0.36 4.42 0.68 2.35 8.37 1.86 Zr/Y 0.39 1.67 0.13 0.44 0.41 4.54 0.22 0.30 tsi n 133 en i^mcD2;NK:c/3»Qis)oann I—' VO CAJOOI—'(—'I—'UJ (—' U) 4^ (JO (-1- H^ O O O ooc3-\oa^*x>*x)Kjuio.*a.aiK)uioi—I OOtOMOOOl—'OOIO O a I c» >xi o cr> NJtococritooa>o-JNJ>xiOJO(—'--jco OOOo^COUlCOOCTlt—' O 00 fO CTl LnLn*>.criVDto>fe-ootoo -J CO K) I—' -ON>l-'i-'>(^l-' OJ U1 CO o 4i> U) h^ O OOh-'h-'(-'4i.~J*>.ljO|—'lOtOOOOO-lNJ OOMtOOh-'t—'UntOOO o I VO to 00 ^J I—'touio*>.ooo^ix>oo U1 tsj -^ (oO C»OVOa\(-'VDOOcTv--J 00 I—' ^ en O O O I—' 00-~401-'tO-~JNJO»X>UJU1UJNJ OOOCOOOOO^I—'U) o (Tl *» O U) toojMMoo^JNj^^uiwN)!—'a^^—I OOOOOUlOOOUl**^ -J NJ (Jl O *>'h-'-^H-'l-'-J00H-'tOU100 NJ Ln M ^ M -J h-' en *k O M O O OO--JOOK>--JK)OOV0tv)00*X> I—' K) Un CTi 1—' U1 a O I—' O h-' OOH-'Oh-'tO*ih-'OCnOOOOODI—'OlO OOOOOOOO00iX>00 o (-• ^ UJ O Ul OOOVOOOOOOI—'h-'00 cri to CO o a\t-' (-"tuoototoi—'a\ui>^ en to 4:^oj un t-'iotoi—' to 4^ *» 4^ H-' O O oo,fe.t—'.;i.(J^a^ototooo^>>^U)^to o *k|—'OOOunLn>ti o 1 • I ^J^ I—' CJ> on >Ci o h-' o o o h-'OOOOl—iOOOoOO 00 *» on roooootooov^i—' o O h-' O *• oo •IS. o 1 • • • . I I h-J lO NJ o •Cil—'tnot—'»fc.Ln-~Jon to 00 to CD oo *>• o CO oo CTi 00 VD to OA ^^y—cotooo^cico^o o a^ U1 OJ OJ to M O h-' I—' o Table 4 (contd...) Element G018 2 G0194 GO208 G0211 G0227 G0229 GO230 G0231 (wt.%) Major(Wt%) Si02 45.66 40.27 58.05 47.58 74.14 41.07 58.23 50.48 Fe203 (T) 38.91 48.75 35.35 50.45 23.63 52.19 39.42 37.09 FeO 15.40 8.68 31.24 15.80 7.28 17.52 6.60 17.60 Ti02 0.99 1.34 0.43 0.01 0.01 0.01 0.01 0.98 AI2O3 1.07 0.59 0.31 0.15 0.10 0.21 0.11 0.65 MnO 0.37 0.25 0.02 0.16 0.04 0.10 0.02 0.22 MgO 1.36 2.00 2.04 0.55 0.14 1.78 0.60 2.78 CaO 7.66 3.77 1.58 0.10 1.69 4.11 0.70 3.96 Na20 0.36 0.41 0.09 0.30 0.10 0.32 0.01 0.38 K2O 0.57 0.13 0.48 0.03 0.02 0.06 0.01 0.39 P2O5 — — — 0.03 0.02 0.10 0.04 - Trace(ppm) Sc 2.21 2.67 1.64 1.38 0.64 1.42 0.40 0.36 V 133.00 11.83 22.38 99.31 3.42 4.69 55.45 23.68 Cr 27.72 18.43 11.44 13.72 5.13 9.31 12.17 94.01 Co 43.12 66.14 24.10 47.96 68.66 22.69 63.89 36.28 Ni 18.26 17.01 13.28 0.23 21.67 17.41 11.53 29.52 Cu 11.56 30.01 20.10 10.91 4.89 4.98 8.33 52.80 Zn 70.26 17.03 39.90 19.21 13.93 14.56 52.89 100.65 Ga 4.41 2.08 4.46 1.44 0.28 1.07 0.37 2.38 Rb 104.89 140.72 10.51 10.56 4.16 7.83 1.51 6 0.54 Sr 59.74 34.68 34.43 5.06 38.78 49.67 20.65 40.11 Y 7.44 7.10 9.54 3.63 1.47 4.04 2.85 6.11 Zr 21.87 10.63 14.68 3.48 1.28 4.22 0.94 17.68 Nb 0.85 0.61 0.91 0.61 0.31 0.37 0.25 0.69 Ba 170.80 95.40 24.51 34.38 15.54 51.40 13.47 116.86 Hf 0.33 0.18 0.24 0.12 0.05 0.28 0.19 0.27 Ta 0.63 0.86 0.36 0.37 0.52 0.16 0.34 0.65 Si02/Fe203 1.17 0.83 1.64 0.94 3.14 0.79 1.48 1.36 Rb/Sr 1.76 4.06 0.31 2.09 0.11 0.16 0.07 1.51 Cr/Ni 1.52 1.08 0.86 59.65 0.24 0.54 1.06 3.19 Zr/Y 2.94 1.50 1.54 0.96 0.87 1.05 0.33 2.89 Table 5 : MAJOR AND TRACE ELEMENT COMPOSITION OF THE KUDREMUKH SHALY BANDED IRON FORMATION AND INTERLAYERED AMPHIBOLITE (SAMPLE NO. GO-85) Element GO-X G017A G071 GOBS G0129 G0132 GO150 G02 23 G0233 (wt.%)1 Major•(Wt% ) Si02 31.12 46.27 37.44 61.43 40.05 52.60 44.32 46.02 51.19 Fe203 (T) 46.79 42.30 51.86 4.32 39.93 24.14 18.78 42.41 18.34 FeO 31.32 26.44 30.64 1.48 25.68 10.28 9.92 19.76 8.08 Ti02 4.42 3.09 0.31 0.37 0.01 4.58 0.32 0.18 0.55 AI2O3 5.24 3.11 4.16 14.40 9.48 9.09 6.44 3.54 8.43 MnO 0.54 0.36 0.10 0.02 0.01 - 0.04 0.10 0.04 MgO 2.23 2.11 2.33 0.56 2.85 2.18 13.64 1.52 5.08 CaO 5.23 0.11 0.14 1.17 - - 1.48 1.77 4.11 Na20 0.47 0.34 0.60 1.69 0.53 0.56 0.19 1.08 0.12 K2O 2.35 1.22 2.20 2.92 4.65 3.32 2.72 0.76 4.00 P2O5 — — 0.03 0.12 - — 0.01 — 0.07 Trace (ppm) Sc 6.10 5.16 6.87 4.50 14.96 4.97 37.89 1.55 34.94 V 87.25 15.77 44.91 42.71 148.69 4.95 210.03 6.29 349.35 Cr 32.87 93.11 34.14 10.09 228.93 11.10 1709.65 83.56 Co 12.38 24.16 13.11 46.86 38.44 25.81 86.24 31.97 66.63 Ni 22.88 21.65 23.82 6.74 81.86 3.65 687.30 7.85 124.04 Cu 364.36 4.72 48.29 17.58 35.12 34.56 2.19 9.40 89.06 Zn 324.50 66.10 63.63 42.55 94.02 82.47 62.78 53.16 154.66 Ga 10.69 2.65 8.77 17.44 13.22 9.57 8.70 2.77 19.98 Rb 438.35 275.80 500.07 163.55 953.37 742.50 421.99 151.38 419.33 Sr 45.82 5.05 32.92 261.13 12.58 8.58 33.19 68.27 287.80 y 23.95 2.79 7.05 26.05 2.45 20.05 1.00 2.84 23.60 Zr 108.09 52.55 134.30 179.81 57.81 412.38 16.42 3.40 19.76 Nb 5.10 3.97 7.16 20.03 2.38 14.49 0.71 1.21 4.36 Ba 672.99 388.09 194.65 996.24 562.59 729.47 124.63 370.90 441.08 Hf 2.15 0.72 1.93 4.97 1.04 7.96 0.57 0.02 0.54 Ta 0.88 0.80 0.43 3.54 0.45 2.74 0.12 0.54 0.26 Si02/:Fe20 ^i 0.67 1.09 0.72 14.22 1.00 2.18 2.36 1.09 2.79 Rb/Sr 9.57 54.61 15.19 0.63 75.79 86.54 12.71 2.22 1.46 Cr/Ni 1.44 4.30 1.43 1.50 2.80 3.04 2.49 - 0.67 Zr/Y 4.51 18.84 19.05 6.90 23.60 20.57 16.42 1.20 0.84 48 TABLE 6 : RARE EARTH ELEMENT ABUNDANCES IN THE KUDREMUKH CHERTY BANDED IRON FORMATIONS Element (cone. G02 GO 3 G07 G012 G013 G014 G017 G018 in ppm) La 1.74 4.30 8.95 10.43 3.5L 5.07 3.06 3.34 Ce 8.42 3.48 6.55 21.15 4.88 2.42 1.77 6.51 Pr 0.75 0.37 0.81 2.17 0.55 0.22 0.16 0.74 Nd 2.59 2.77 3.05 9.00 1.52 1.06 0.65 1.89 Sm 0.79 0.57 1.39 2.97 0.46 0.28 0.24 0.49 Eu 0.18 0.37 0.64 2.18 0.24 0.19 0.11 0.83 Gd 0.98 0.43 1.16 2.73 0.52 0.25 0.30 0.84 Tb 0.13 0.09 0.22 0.46 0.07 0.05 0.04 0.12 Dy 0.76 0.39 1.37 2.85 0.45 0.32 0.26 0.76 Ho 0.17 0.09 0.33 0.56 0.11 0.08 0.06 0.18 Er 0.45 0.23 0.89 1.55 0.32 0.23 0.18 0.48 Tm 0.07 0.03 0.13 0.23 0.05 0.04 0.03 0.08 Yb 0.40 0.20 0.83 1.26 0.35 0.27 0.21 0.48 Lu 0.05 0.04 0.12 0.20 0.03 0.05 0.04 0.09 La/Sc 2.64 2.12 14.66 19.18 3.41 5.31 3.69 1.78 La/Lu 3.48 11.62 8.06 5.64 12.65 10.96 8.27 4.01 Nd/Yb 2.28 4.88 1.30 2.52 1.53 1.38 1.10 1-40 LREEN/HREEN 1.65 2.88 1.70 1.75 2.26 2.72 2.07 1.55 IIREE 17.48 13.36 26.44 57.74 13.06 10.53 7.11 16.83 49 Table 6 (con td. . .) Element (cone. G021 G024 GO30 G038 G058 G07 3 GO9 0 GO103 in ppm) La 4.35 3.95 5.27 0.35 0.78 7.89 1.64 4.78 Ce 2.20 6.49 6.23 0.74 1.95 10.49 2.36 1.35 Pr 0.22 0.72 0.65 0.10 0.24 1.01 0.15 0.16 Nd 0.97 3.09 2.97 0.50 0.92 4.25 0.92 0.77 Sm 0.38 0.46 0.56 0.23 0.27 0.84 0.46 0.08 Eu 0.17 0.49 0.38 0.13 0.21 0.23 0.35 0.14 Gd 0.20 0.57 0.97 0.36 0.48 1.09 0.32 0.12 Tb 0.04 0.10 0.16 0.07 0.08 0.15 0.05 0.02 Dy 0.26 0.49 0.95 0.38 0.46 0.91 0.32 0.18 Ho 0.06 0.09 0.22 0.08 0.10 0.22 0.08 0.06 Er 0.15 0.19 0.55 0.20 0.26 0.58 0.22 0.24 Tm 0.02 0.02 0.08 0.03 0.04 0.09 0.04 0.05 Yb 0.13 0.11 0.49 0.16 0.21 0.56 0.24 0.49 Lu 0.03 0.02 0.13 0.03 0.04 0.11 0.04 0.13 La/Sc 21.38 3.72 20.64 0.74 1.84 10.01 5.54 5.79 La/Lu 15.68 21.36 4.38 1.32 2.11 7.75 4.43 3.98 Nd/Yb 2.63 9.89 2.13 1.09 1.55 2.67 1.35 0.55 LREEN/HREEN 3.68 3.61 1.58 0.58 0.93 2.42 1.55 1.82 Z.REE 9.18 16.79 19.61 3.36 6.04 28.42 7.19 8.57 ^ t-< z; tr< tr^ (-• K H- .—~ W >-3 M W CL OJ Cu c rr D a M 0) 0 m cr W» Ww K wf CO\ 'V D 3 h-' wz cr c o 'V 0 0) (D \ 3 • 3 K rt w w 2w; P CL NJ to h-' 1—' UJ -^ OOOOOI—'Ol—'Oh-'l>JO-J>0 0 U o ui OJ o^ *> O h-'--Jh-'~JtONjNJLOL*JOUJOOUJ^ (^ h-' ~J O u: Ul^oto(J10ovDh-'•^to^h-'O^Jto h-- -J I—' t-- M to tsj OOOOOOOOOOh-'OOJtO o to NJ 4^ 00 10 OJ:iO^h-'Cnh-'cr\OCri00UJ0JJ^ U3 Ijn 10 1X> CO >X>Ui^U>U1LnOU)Lnv£)h-'^>X>h-' 4^ 00 -J Ui h-i h-" to OOOOOOOOOOh-'OtOM o •~J to *. O vU OOOOOI-'OU14**»--JUI«»0 •-J to LO *» l£) l-'Ulh-'COOO h-' h-' h-' l_n h-' o COh-'CT\h-'Ln OOOOOOOOCDOOOh-'O o h-' ^ 10 10 t/l ^ OOOOOh-'Oh-'Oh-'OOh-'UJU) ui VO --J O CTi CO h-'Ulh-'-^U)ChUJ>X)-J4:i00UlCDlO h-' U1 U> h-' ^ h-' 1X> O OOOoOOOOOOOOh-iVD CI ^ h-* 00 O VO OOOh-'OtOOh-'OI—'^^OtOh-" o U1 OJ 4^ O CO tO00tOh-''*^h-'4^h-'00U1tO00|sj-J h-" CJ> to to h-' to Ol -vj OOOOOOOh-'OOIOOCOUl CD O O 00 O O to h-'UlOuitO^Dh-'CDh-'^COOOh-'Ln 00 o o U) Ln toh-'Ooootocncri^coo>^~J--Joo 4^ *» h-' to to %fc> OOOOOOOOOOOOh-'h-' o 00 *i h-- O to 4^ OOCDOOOOC5CDOC50H-'h-' o cr. -^ >-D 00 O Oh-'Oh-'Oh-'Oh-'004i.tO-JUJ o h-- UJ LO -J h-* 4^ ai-^IO0J.ta.4itOtOi-DVD^C3V£>CD 00 o M 2 t-l f nmDi-3Citxicoz^T30t-' 1-^ M W c cr '- N> h-' -«J h-' K) U1 h-" OOOOOh-^Oh-iOO^OOCT^ o o 00 ^O ^O U1 O h-iuih-'a>N)h-'N>ouna-iaiix>^(Ti NJ -J U) 00 CTi NJ oji^ouicr^ooh-'^oo-Juii-nvxi o 00 CD vx> h-" M ro (jj OOOOOOOOOOh-'OOJh-' o *> *». Ui 00 h-' OU)ON>h-'(jOOUnh-'*»^U)~-JOl tn a^ -~j ^ N) m KJ >ti <0 >l^ OOOOOOOOOOh-'ONJO o 00 NJ h-' NJ O Oh-'Oh-'ONJOtsJtOK>M(sJOi.D K) h-' *». 4i. 00 to h-'h-'NJCOCni(i*'Oi*>--J*^l/1h-'Ln 00 h-' h-i OJ tvJ OOOOOOOOOOh-'OOOh-' o 00 *» 00 h-" h-" 0(jOOU)h-'*»Oit^h-'CAjU1UJ4^h-' K) N) O lU -J IX) J^OU^Oh-'U^-~Jh-'00oo^a^L^u^ NJ VD VDa\0 Element (cone. GO-X G017A G071 G085 G0129 G0132 GO150 G0223 G0233 in ppm) La 22.38 13.66 3.97 49.30 3.56 106.30 1.19 3.84 7.98 Ce 37.84 18.66 24.38 308.68 6.90 178.23 3.15 6.32 15.46 Pr 3.78 1.81 3.13 38.28 0.93 17.47 0.44 0.63 2.00 Nd 17.29 7.03 11.03 128.42 4.75 70.80 1.99 2.42 9.56 Sm 2.95 1.05 2.37 24.03 0.96 10.06 0.60 0.39 2.23 Eu 1.39 0.42 0.48 3.42 0.42 1.74 0.05 0.19 1.12 Gd 3.81 1.25 1.98 18.95 1.25 9.81 0.43 0.47 2.82 Tb 0.77 0.21 0.18 2.23 0.18 1.25 0.07 0.08 0.55 Dy 4.56 1.18 0.99 9.06 1.06 6.84 0.36 0.40 3.35 Ho 1.01 0.24 0.21 1.52 0.23 1.40 0.07 0.08 0.68 Er 2.70 0.63 0.54 3.35 0.60 3.38 0.18 0.18 1.87 Tm 0.42 0.09 0.08 0.43 0.09 0.46 0.03 0.02 0.22 Yb 2.53 0.49 0.46 2.77 0.53 2.58 0.13 0.12 1.38 Lu 0.36 0.08 0.05 0.42 0.07 0.40 0.04 0.01 0.21 La/Sc 9.92 7.16 1.56 29.61 0.64 57.81 11.77 6.70 0.62 La/Lu 6.72 18.46 8.87 12.69 5.50 28.73 3.22 41.52 4.11 Nd/Yb 2.41 5.05 8.45 16.32 3.16 9.66 5.39 7.10 2.45 LREEj^/HREEf^ 1.85 3.81 3.91 5.49 1.64 5.65 2.09 3.90 1.29 HREE 101.79 46.80 49.85 590.86 21.53 410.72 8.73 15.15 49.43 50 CHAPTER V GEOCHEMISTRY 5.1 General Statement; The major, trace and rare earth elements (REE) characteristics of the BIFs and associated amphibolite layer from Kudremukh schist belt are discussed in this chapter. The chemical data (Tables 4-7, Chapter IV), are plotted on various geochemical variation diagrams and the chondrite normalized REEs are plotted on Masuda-Coryl diagram to understand the genesis of the banded iron formation from the studied area. BIFs are essentially chemical sediments and mainly consists of Fe203{T) and Si02 but it is drastically affected by clastic input. 5.2 Major Element; The major element composition of the analysed samples are shown in the variation diagram (Fig. 5). On the basis of their SiO-;,, AI2O3 and Fe203 content, the samples analysed are grouped as Cherty Banded Iron Formation (CBIF), Shaly Banded Iron Formation (SBIF) and amphibolite (Sample No. G085). CBIF contains more than 15% f'^o'^l ^""^ ^^^ rest is Si02, SBIF contains more than 15% Fe20o and more than 2% AI2O3, whereas amphibolite contains less than 5% FeoO-, and more than 14% Al20o. Almost all major element constituents exhibit a large scale variation in their abundances in SBIF. CBIF for a major part is made up of Si02 and Fe203{T). Alkali content (K20+Nd20) of all the CBIF is less than 1.0%, where 51 Pj Os L 4J'lr'?i.°_* TiOz : -! t ^£-*: ^._a_D K20 CaO C ' MgO '• D D • ••• • " AI2O3L: • • ••• • • iJ°n.4. ° FejOj Si02 1 1 3E .01 .1 1 10 100 Wt% Figure 5. Major element distribution in the sample analysed. Solid circle = cherty BIF; empty square = shaly BIF (amphibole bearing, AI2O3 enriched); empty circle = amphibolite layer within cherty BIF. Same symbols are used in all the illustrations. 52 as all the SBIF and the amphibolite layers have more than 1.0% alkali content. AI2O2 and Ti02 appears to be the most diagnostic constituents of the different varieties of iron formation of the belt. MnO and P2'-'5 ^^^ °^ very low abundance and exhibit an overlap between the two varieties. Tables 4-7 and Fig. 5 show significant variation in iron and silica content and consequent scatter in 5102/^^203 molar ratio depending upon the thickness of the meso and micro bands present in the sample. Presence of thin layers of the amphibolites in BIF is reflected in the AI2O3, CaO, MgO and K2O content of the samples. Calcite is present in most of the analysed samples which is reflected in the CaO content (ranging upto 12.34%). CaO in sample No. G012 is present as calcite along with specks of amphiboles, especially actinolite. A large scatter from 0.02 to 9.48% is found in AI2O3 content of CBIF and SBIF. The AI2O3 content of most of the samples is below 2%, whereas 8 samples contain AI2O3 between 2-9.48%. The amphibolitic layer has 14.48% of AI2O3. Actinolite is a fairly abundant silicate in the BIFs, their relative abundance in the samples is reflected in the variation of MgO from 0.01 to 13.64%. Both Na20 and K2O are relatively enriched in the samples where biotite is present. Ti02 concentration is high (upto 4.58%) in the SBIF as compared to CBIF where both Ti02 and AI2O3 are extremely depleted (Fig. 6). Among major elements AI2O3 and Ti02 content and their mutual relationship in BIF constitute the most significant feature. Ewers and Morris (1981) suggested that increasing concentration of these oxides rdflect progressively higher inputs of clastic components. Linear relationships between AI2O3 and 53 100 Ti 02 Figure 6. AI2O3 vs. Ti02 plot shows enrichment of AI2O3 and Ti02 ir^ SBIF and depletion in most of the CBIF, indicating mixing of con tinental debris along with the chemical precipitation of FeO and Si, especially in SBIF. 54 TiOn of S macrobands has been observed by several workers (Laajoki and Saikkonen, 1977; Trendall and Pepper, 1977; Ewers and Morris, 1981). Manikyamba et al. (1991) have also observed the crude linearity at an elevated concentration of AI2O2 and Ti02. Thus the AI2O3 and Ti02 abundances in the BIFs of the present investigation indicate that clastic sedimentation from various sources has occurred simultaneously with chemical precipitation of Fe and Si02; the source and quantity of the clastic input has been responsible for the observed compositional variation in Kudremukh BIFs. A good positive correlation between AI2O2 and K2O is visible in Fig. 7. A simultaneous increase of AI2O3 along with K2O is noticed in the total population of the samples. Both AI2O3 and K2O are higher in SBIF than CBIF, thereby indicating that terrigenous component has been a very significant source of contamination in these otherwise chemical sediments. The evidence for the contribution from basic volcaniclastic and terrigenous components for SBIFs and amphibolite layer is much more convincing in the trace element abundances and ratios as discussed below. 5.3 Trace Elements: The trace element content of the CBIFs and SBIFs, though shows a gradation, is distinct for the two groups as the CBIFs are depleted in all elements except Fe and Si whereas SBIFs are relatively enriched in Rb, Sc, Zr, Y, Cr, Ni, Hf, V, and other elements as can be seen from Tables 4-7 and Fig-.-8. Gradation between cherty and shaly BIFs from very low to high content of these element is clearly reflected in given Tables and Figures. A 55 100 r O 10 (gP # a O I CsJ • • 0-1 J-t •• 0-01 0-1 10 K20 Figure 7. AI2O3-K2O variation diagram, demonstrat ing AI2O3 and K2O differences between cherty and shaly BIF. 56 Sc • .... •«•;»« V** AllD D O P V •P • •• • • jr^ • • Cr Co n • «V« »* n » ^ Ni Cu I • • • •• • *M^ vn? Zr Ga •••• :•••. .1 •.- • • ••• • • D • • Rb ;•: . • • Sr (? Y OrT'.V..V. °a Zr ^_ ^ .V. :.!_LeL!_ _!_'_25 *•!_ ^ 5? _ ? ' •*•*• • • 0 n NbiL. •• .' ••:••. On O . • • • ° , D O Ba 3r" •^^."cr j_.* o^ ^gp 3J,. • ••• • o rf^ o Vi Ta .1 10 100 1000 10000 ppm Figure 8. Trace element distribution in Kudremukh 5IFs. 57 good positive correlation between Rb and K2O is exhibited in Fig.9. This correlation between Rb and K2O breaks down at a very low K2O and Rb content of CBIF. This distinction between the shaly and cherty BIFs is not reflected in the Sr and CaO ratios as CaO is mainly present in interstitial carbonate in CBIFs. In SBIF, CaO is present in amphiboles. The systematic increase of Sr abundance along with CaO can be seen in CBIFs except in sample G024 and GO103 {Fig. 10). Two samples of the SBIF have different Sr/CaO ratio, whereas the amphibolite being enriched in Sr, is having a distinct and different Sr/CaO ratio. The Sr and CaO content of the CBIF is indicative of significant carbonate precipitation along with the ferric hydroxide. This aspect is also reflected in the scatter of Rb and Rb, Sr ratio in the cherty BIF (Fig.11). The SBIF have very high Rb content compared to CBIF though the Sr content is almost similar. Sc and Al20o also show distinct behaviour in the BIFs, rich in amphiboles from those that are poor in amphiboles (Fig.12). The CBIFs which are depleted in AI2O3 are also depleted in Sc but show a great scatter. However, Zr and Sc in CBIF show positive interdependence on each other but the relationship is reverse in SBIF (Fig.13). Zr enrichment of the order of 410 ppm in sample G0132 which contains 24.14% Fe203 and 3.32% K2O is difficult to explain unless terrigenous clay was also deposited along with iron oxide and Si02- Similar difference in the compositional characteristics of CBIF and SBIF can be seen in Zr/Y behaviour (Fig.14). Furthermore the elevated concentration of Hf and Zr in SBIF and depletion with large scatter of these elements in CBIF clearly demonstrates that SBIF 58 lOOOr D D t 100 cr 0-01 0-1 I 10 — K20 Figure 9. Rb vs. K2O plot showing a very good positive correlation at an elevated Rb-K20 content. 59 10000 1000 o 100 - • • CO D 10 - c 0-01 0-1 10 CaO Figure 10. Sr vs. CaO plot showing a scatter in CBIF and SBIF. This is typical of Sr and CaO precipitation along with ferric hydroxide and mixing of shaly material. 60 1000 r- .D So a D o 100 t 10 (r. • •u. I - • •. 0-1 10 100 1000 Sr Figure 11. Rb-Sr variation diagram, demonstrating Rb enrichment due to contribution from continental source. 61 1000 r- 100 a o 10 CO • • cP° L •..••A*. • • > 0-1 [ O'OI 0-1 10 AU2^O 3 Figure 12. SC-AI2O3 variation diagram showing a crude positive correlation. Sc and AI2O3 content are high in amphibole rich SBIF. 62 lOOOi- 9) 100- ff M B 10 - 0 0-1 10 100 Sc Figure 13. Zr-Sc variation diagram showing a positive interdependence in CBIF and reverse relationship in SBIF. This variation in Zr content is due to the deposition of terrigenous clay along with chemical precipitates. 63 000 o Q c I 100 D © a M n 10 0 I I l_^J. II M II 2 6 10 K 18 22 26 Y Figure 14. Zr vs. Y plot demonstrating the behaviour of zr and Y in CBIF and SBIF. 64 is enriched in Zr and Hf , due to terrigenous input (Fig.15) as both Zr and Hf are more abundant in continental rocks. Chromium content of the SBIF and CBIF shows a great scatter with a weak sympathetic correlation between Cr and MgO (Fig. 16). Sample GO150 which constitutes more than 13% MgO and 19% Fe20o contains about 1700 ppm Cr. This undoubtedly indicates that volcaniclastic material may also have been deposited along with the chemical precipitates and terrigenous clays. The large scatter in the abundance of Cr and MgO (Fig.16) demonstrates that volcaniclastic contribution has been quantitatively and qualitatively inconsistent. Similar scatter or a low order sympathetic correlation is seen in Cr and Ni content (Fig.17). Both Cr and Ni content of the SBIF are very high compared to CBIF. Similarly weak but positive correlation between Cr and Co also substantiates that volcaniclastic material also has contributed to the composition of the BIF (Fig.18). Inspite of a great scatter in Ni:Co ratio the contribution of volcaniclastic debris to the basin in which BIFs were deposited cannot be missed (Fig. 19). Hydrothermal solution and sea water, both are extremely depleted in these elements and so is the case with the terrigenous sediments (Beukes et al., 1990). Therefore only the contribution of volcaniclastic activity within the basin can explain the enrichment in Cr, Ni and Co. Cr and Zr show a low order antipathetic relationship among the samples of SBIF (Fig.20). SBIF samples which are enriched in Cr are depleted in Zr . This relationship, however, breaks down to a scatter in CBIF. The mixing of the terrigenous and volcaniclastic material 65 1000 H f Figure 15. Zr vs. Hf plot show a sympathetic increase in CBIF and SBIF at higher concentration, but at lower level it breaks down. However, Zr and Hf are more enriched in SBIF than CBIF, indicating contribution from terrigenous input. 66 lOOOOr- GO 150 I 1000 Q o 100 10 - 60 24 . # • l_ 1 0-01 0-1 i 10 100 MgO —i Figure 16. Cr content of the SBIF and CBIF showing a great scatter with a weak positive correlation between Cr and MgO. High Cr and MgO content in some samples is indicative of volcaniclastic contribution along with chemical precipitates and terrigenous clay. 67 lOOOOi- 1000 ! o o '00'" Dm 10 OCT VI i 0-1 10 100 1000 Ni Figure 17. Cr vs. Ni plot showing a low order sympathetic correlation. Cr and Ni content is low in CBIF but in most of SBIF, it is high. 68 10000- D t lOOOh o D OOi- D • • ©• . . • • ••. 1 I I I I I 1 I I I I I I I 0 20 60 100 — Co Figure 18. Cr vs. Co plot showing variation between CBIF and SBIF. 69 1000 D 00 Q 10 kl O 9 0-1 I M I I I I I I I I I I I I 0 40 80 120 Co Figure 19. Ni vs. Co plot showing variation between CBIF and SBIF. 70 0000 r- 000 o 00 6 ° & 0 • • • OD t • • • 0 10 00 000 Zr Figure 20. Cr vs. Zr plot depicts antipathetic relationship between Cr and Zr in SBIF but in CBIF it breaks down to a scatter. It is indicative of volcaniclastic contribution along with chemical precipitates and terrigenous clay. 71 for the shaly precursors pf the SBIF and even some CBIF- is very clearly demonstrated by the plots of Ni+Cr+Co content against Zr (Fig.21). Zr/Y ratio when plotted against Zr concentration show positive sympathetic relationship of high order for both SBIF and CBIF (Fig.22). As demonstrated from AI2O3, Ti02/ K2O, Rb, Zr, Y and other data discussed above, fine grained continental detritus and volcaniclastic material has certainly contributed substantially towards the bulk composition variation of BIF. The observed concentration of the elements characteristics of divergent sources can be explained only when terrigenous and volcaniclastic material is provided to the basin when chemical precipitation of Si02 and iron was taking place. This clastic material produced interbedded shales which have been metamorphosed to various types of amphibole bearing rocks. The source of the iron and silica was most probably hydrothermal as indicated by REE data. 5.4 Rare Earth Elements; The REE patterns of the BIFs are shown in Fig.23-29. The 41 samples analysed for REE concentration have been divided into 6 groups. Group one consists of sixteen samples which contain depleted to moderate £REE (including La) , LREE/HREE s=-l, Nd/Yb-^1, and weak to strong positive Eu anomalies. These patterns are illustrated in Figs. 23 and 24 as the presentation of sixteen samples in one illustration was difficult and confussing. Group two, comprising of 3 samples (Fig. 25), shows depleted to moderate ZREE, Moderate La enrichment, weak to positive Eu 72 1000 o 00 D 1 a D M 10 0 n 0-1 1 1 0 00 1000 10000 Cr + Co + Ni — Figure 21. Zr vs. (Cr+Co+Ni) plot clearly shows the antipathetic relationship between the terrigenous and volcaniclastic contribution, suggesting mixing of these material along with the deposition of chemogenic sediments. 73 00 >- D D n D 0- M o D • 2* D 0-1 u 0-1 10 100 000 Zr Figure 22. Zr/Y vs. Zr plot shows a clear sympathetic correlation. 74 La Ce Pr Nd Sm Eu Gd Tb Oy Ho Er Tm Yb Lu Figure 23. REE pattern of 8 CBIF samples with strong positive Eu anomalies and low total REE content, indicating a hydrothermal source for iron and silica. 75 100 X Go 90 V Go 149 # Go - 180 fl Go - 182 0 Go - 208 • Go • 227 • Go - 229 + Go - 231 0-1 La Ce PI- Nd Sm Eu Gd Tb Oy Ho Er Tm >fb Lu Figure 24. REE pattern of 8 CBIF samples with strong positive Eu anomalies and low total REE content, indicating a hydrothermal source for iron and silica. 76 o-il I I I I I i I 1 I 1 i I I I La Ce Pr Nd Sm Eu Gd Tb Oy Ho Er Tm Yb Lu Figure 25. CBIFs with weak to positive Eu anomalies and moderate La enrichment. 77 anomalies including LREE/HREE greater than one and Nd/Yb i^^ 1. Six samples belonging to Group three (Fig.26) have depleted SLREE, strong La enrichment, weak to strong positive Eu anomalies including high La and LREE/HREE ratios. Also a very large variation from 0.55 to 6.20 is seen in Nd/Yb ratios. Shape from Ce to Sm also shows a big change from one sample to another, same is the case from Gd to Lu. Group four (Fig.27) consists of seven samples which show moderate to slightly enriched HREE, no Ce enrichment, very weak to strong negative Eu anomalies, LREE/HREE^ 1, Nd/Yb ^::s^l. All the above four groups belong to CBIF in which AI2O3 is less than 2%. Group five (Fig.28) is made up of five samples of SBIF which are enriched in 2 REE, shows no La enrichment compared to Ce and Nd, LREE/HREE are considerably greater than one, Nd/Yb are also more than one. Most of the samples show weak positive Eu anomalies, fractionated patterns of REEs from La to Lu are a significant feature. Though the abundance of REEs are little less but the overall pattern resembles with PAAS. Group six (Fig.29) consists of four samples including one sample G085 of amphibolite and three samples of SBIF. These samples show moderate to very high order enrichment in "£REE, very high LREE/HREE and Nd/Yb and weak to strong negative Eu anomalies. These patterns correspond to that of acid volcanics especially sample G0132. Sample GOBS (an amphibolite), in addition to highest LREE and 1.REE, contains a positive Ce anomaly. Sample G071 of SBIF also show slight positive Ce anomaly. The variations in the total REE content and in La enrichment together with the magnitude and nature of Eu anomalies in CBIF and SBIF is extremely 78 La Ce Pr Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Figure 26. REE pattern of 6 CBIF showing moderate to strong Eu anomalies with high La enrichment indicating mixing of hydrothermal solution with ambient oceanwater. 79 100 r D U(j \)i a Go 164 * Go 178 V Go 2V. • ijO - 2 0-1 J 1 L J I 1 L J I I I La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yt Lu Figure 27. Negative Eu anomalies in 7 CBIF samples. 80 100 r La Ce PC Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Figure 28. SBIF samples showing moderate enrichment in REE, with moderate positive Eu anomalies. o Go - 71 X Go - 85 La Ce Tb Dy Figure 29. REE pattern of 4 samples including sample G085 (amphibolite layer) , showing enrichment in REE with strong negative Eu anomaly. These plots suggest mixing of hydrothermal solution with ambient sea water. significant. Fig.30 shows that generally the REE content of "the Al203-rich shaly (amphibolitic) BIF is significantly higher than those of low AI2O2 CBIF. This clearly reveals that REE enrichment is caused by clastic input. HREE and LREE increases simultaneously and this ratio is also found to increase in the shaly (amphibolitic) BIF (Fig. 31). BIF samples with a higher total REE also show higher abundance of Zr (Fig.32). The differences and the variations in the Nd/Yb ratios of the CBIF and SBIF are shown in Fig.33. Variation in the La content at very low level of Lu may be seen in Fig.34. La and Sc exhibit a large scatter (Fig. 35). These binary relationships indicate the independence of La enrichment with respect to other elements. Ce also does not show any correlation with Fe203 (Fig. 36) or with any other element. Pronounced Ce depletion is not observed in the samples from Kudremukh as has been found in the BIFs of Sandur and Chitradurga (Manikyamba et al.,1991; Gnaneswar Rao,1991). Absence of Ce anomalies has been recorded from other Archaean BIFs (Shimizu, et al.,1990; Derry and Jacobsen,1990). 5.5 Enrichment of ZREE, Eu anomaly and anomalous behaviour of La; BIFs of Kudremukh schist belt show an enrichment in REE from CBIF to amphibolite layer through SBIF. The REE characteristics of sediments during diagenesis (Fleet, 1984) and during low grade metamorphism (Taylor and McLennan, 1985) are not changed. Therefore, the clastic input is the only parameter to affect the abundance and pattern of REEs. According to Derry and Jacobsen (1990), the overall pattern of REEs in BIFs are as 83 0000 O 000 D LU D D 100 an w ••r •. Q y D 0 J 0-0! O'l I 10 — AI2O3 -^ Figure 30. SREE vs. AI2O3 plot show that REE content increases with clastic input as most of SBIF have higher EREE than those of CBIF. 84 10000 r 1000 o a bJ D CC 100 a 10 10 100 1000 HREE Figure 31. LREE vs. HREE plot show sympathetic relationship. This ratio increases from CBIF to SBIF. 000 r- a O D 100 D D D • •• n 10 M ••D • • • • • 0-1 I 10 100 1000 10000 ^REE Figure 32. Zr vs. EREE plot show sympathetic relationship, both are high in SBIF as compared to CBIF. 86 000 o 100 D 10 D D vt^ 0-1 0-01 01 I 10 Yb - Figure 33. Nd vs. Yb plot show sympathetic correlation. 1000 I- 100 D T ;5io- ••..° ••:. • ::°o. a: 0-1 0 01 0-1 Lu ) Figure 34. La vs. Lu plot showing a scatter, both in CBIF and SBIF. 38 1000 r- a o A 100 - a D • % D o 10 - •• i"^:-.- • •• D 0 J 0 10 100 Sc Figure 35. La vs. Sc plot showing a great scatter in CBIF and SBIF, indicating mixing of volcaniclastic and terrigenous material along with the deposition of chemogenic sediments. 89 10000 r- 1000 o D 100 h- D D 10 • V D 01 J \ J \ I 1 I 0 20 40 60 80 Fe203 - Figure 36. Ce vs. Fe203 plot show scatter suggesting no relationship between the two. 90 similar as of oxide facies BIF formed by precipitation of Fe oxyhydroxides from sea water with a REE pattern similar to modern ocean (with exception of Eu and Ce). It may be concluded that variation in REE of Kudremukh BIFs have resulted from the mixing of clastic component and the chemical precipitates. The REEs are a group of 14 elements characterized by very similar chemical properties. Their ionic (+3) radii decreases from La to Lu. They are usually trivalent, however, cerium (Ce) and europium (Eu) can also occur in tetravalent and divalent states, respectively. Under oxidizing condition tetravalent Ce which is exceedingly insoluble will be fractionated from the trivalent REE, resulting in negative Ce anomaly. Therefore in oceans Ce is rapidly incorporated in bottom sediments like Mn nodules. Likewise, Eu will be fractionated from REE under reducing condition resulting in negative Eu anomaly and under oxidizing condition all Eu will change to Eu-^"*" state resulting in positive Eu anomaly. Behaviour of Eu is very complex. The presence of positive Eu anomaly in chemical sediments older than 1900 Ma indicates that a considerable proportion of the Eu must have been present as Eu , rather than totally as Eu during deposition of REE in these chemical sediments (Fryer, 1977a). In order to produce a positive Eu anomaly in a chemical sediment, europium must be mobilized as Eu . According to Graf (1978), the positive Eu anomalies in BIFs indicate an input of strongly reducing hydrothermal solutions into the waters from which the BIFs precipitated. The aqueous geochemistry of europium in different oxidation states at elevated 91 temperatures and pressures is unknown (Sverjensky, 1984). At low temperature near earth surface conditions the Eu is mostly in trivalent state. However, at temperatures greater than about 250°C, Eu^"^ should predominate. Eu-^"*" is not stable at elevated temperatures (Shul'gin and Koz'min, 1963, Sverjensky, 1984). Consequently, hydrotherraal solution which are reducing in nature should have Eu . An Eu anomaly could have been imparted to the solution either by fractionation of REE during partitioning between the solution and host or source rocks or by preferential alteration of an anomalous rock phase such as feldspar (Graf, 1977) . Modern sea water does not typically display an Eu anomaly except near hydrothermal vents. Present day hydrothermally active regions in East Pacific Rise (EPR) and Mid Pacific Rise (MPR) are characterized by low REE abundances, extreme positive Eu anomalies and LREE enrichment (Michard et al., 1983, Michard and Albarede, 1986; Campbell et al., 1988; Michard, 1989; Barrett et al., 1990, Derry and Jacobsen, 1990). The hydrothermal Eu anomaly is lost immediately following the discharge of hydrothermal solutions into sea water (Klinkhammer et al., 1983). The Eu anomaly is also absent in metalliferous sediments from various ridge related sites in the eastern Pacific (Ruhlin and Owen, 1986). This anomaly is not transmitted in modern oxidized open oceans because of rapid oxidation of hydrothermal Eu^"*" to Eu^"*" in the water column; any precipitates formed also strongly absorb sea water REE that lack a positive Eu anomaly. However, if Archaean oceans were relatively reducing, transmittance of a positive Eu 92 anomaly away from its hydrothermal source seems plausible (Barrett et al., 1988). Apart from the positive Eu anomalies, which are characteristics of BIF all over the world (Laajoki, 1975; Laajoki and Saikkonen, 1977, Fryer, 1977a, 1977b; Barrett et al., 1988; Dymek and Klein, 1988; Beukes and Klein, 1990; Derry and Jacobsen, 1990; Gnaneswar Rao, 1991; Khan et al., 1991; Manikyamba et al., 1991), most important and significant aspect of the REEs from the BIFs of Kudremukh schist belt is La enrichment (Fig.25 and 26). La enrichment is also reported from Chitradurga schist belt (Gnaneswar Rao, 1991), Sandur schist belt (Manikyamba et al., 1991) and from Archaean greenstone belt of Canada (Barrett et al., 1988). Barrett et al., (1988) have interpreted that La enrichment is caused by the La spiking from hydrothermal solutions. It is a feature inherited from high-temperature hydrothermal solutions, although there is no obvious reason why La should be preferentially extracted from source rocks. The chemical precipitates in the Red Sea deeps also show distinct La enrichments (Courtois and Treuil, 1977). 93 CHAPTER VI DISCUSSION AND CONCLUSION As mentioned in the previous chapters, the source of iron, silica and oxygen has been an extremely debated aspect of the genesis of BIF (Cullen, 1963; Lepp and Goldich, 1964; Naqvi, 1967; Trendall and Blockley, 1970; Cloud, 1973; Goodwin, 1973; Holland, 1973; Drever, 1974; Gross, 1980; Gole and Klein, 1981; Mel'nik, 1982; Fryer, 1983; Morris and Horwitz, 1983; Trendall and Morris, 1983; Miller and O'Nions, 1985; Simonsen, 1985; Carey, 1986; La Berge, 1986; Morris, 1986; Garrels, 1987; Holm, 1987; Barrett et al., 1988; Dymek and Klein, 1988; Jacobsen and Pimentel-Klose, 1988; Stanton, 1989; Beukes et al., 1990; Derry and Jacobsen, 1990; Nealson and Myers, 1990; Carrigan and Cameron, 1991; Gnaneswar Rao, 1991; Khan et al., 1991; Manikyamba et al., 1991). The debate about the source of iron in iron formations has gained great inputs from the REE data available on MOR vents, oceanic metalliferous sediments, ocean water and river water (Klinkhammer et al., 1983; Michard et al., 1983; Koski et al., 1984; Bowers et al. , 1985; Goldstein and Jacobsen, 1988; Derry and Jacobsen, 1990) . The average chemical composition of Archaean (>2.5 Ga) and early Proterozoic iron formations are similar (Gole and Klein, 1981; Davy, 1983) perhaps indicating a common source of dissolved iron, derived either from a continental or a marine source 94 (Carrigan and Cameron, 1991). There are different interpretation as to the source of iron within the marine environment, with opinion divided between reduction of detrital Fe and a volcanic hydrothermal component. A direct volcanic source of iron for the Hamersley iron formations was rejected by Holland (1973) , who favoured the reduction of detrital ferric iron minerals to soluble ferrous iron in the deep anoxic ocean. However, it is now known that submarine hydrothermal systems can release substantial amounts of iron (Bowers et al., 1988). Since the present day hydrothermal Fe flux appears insufficient to supply Fe to the BIFs, either the concentration of Fe in hydrothermal waters or the mass flux of hydrothermal waters, or both, were higher in the Archaean if the main source was hydrothermal water (Jacobsen and Pimentel-Klose, 1988). Higher heat production in the Archaean earth almost certainly implies a higher Archaean surface heat flow which in turn should result in high sea-floor production rates. A substantial proportion of the Earth's heat flow is dissipated by the passage of seawater through ocean ridges. The higher heat flow of Archaean time would thus have led to a high flux of water through ridges and other centers of submarine volcanism. The chemical composition of the solutions from the experiments carried out at 375°C closely resembles that of the natural hydrothermal vents. The results of Seyfried and Janeck (1985) suggest a strong increase in the concentration of Fe with increasing temperatue. Hydrothermal solutions are extremely depleted in REE but have a strong positive Eu anomaly. Away from the vent sites this 95 positive Eu anomaly vanishes both vertically and laterally. The metalliferous deposits just at the vent site also show depleted SREE and positive Eu anomalies (Ruhlin and Owen, 1986). Present day ocean water has an extremely depleted pattern of REE with no Eu enrichment and most of the ocean flux is provided as the dissolved load to the ocean {Goldstein and Jacobsen, 1988). Red Sea hydrothermal solutions and metalliferous sediments in addition to depletion in EREE have positive Eu anomalies (Barrett et al., 1988). Miller and O'Nions (1985) reported Nd isotopic compositions of Precambrian BIFs and concluded that the Fe were supplied by continental weathering, and in this respect the water masses in which the iron-formation formed were analogous to the modern oceans. However, the £jq^ data (Cjq^j = Nd/ '*Nd) of the BIF from Hamersley basin (Western Australia) and Michipicoten basin (Ontario, Canada) (2.7-2.9 Ga) show that the solutions which provided iron and Nd were derived from the mantle as theC»7J is closer to mantle and varies between 0 to +4 (Jacobsen and Pimentel-Klose, 1988). These studies very clearly suggest that REEs, Fe and Si of the BIF are derived from mantle through hydrothermal solutions (Derry and Jacobsen, 1990). A mix of 1:100 of hydrothermal solutions with the modern oceanic water is able to produce the magnitude of positive Eu anomalies found in BIFs (Beukes and Klein, 1990). Submarine hydrothermal systems provide means for both providing a large supply of dissolved iron and to help buffer the sulphate content of anoxic waters to sufficiently low levels that the transport of iron is not limited by its precipitation close to 96 the source as sulphide. Cameron (1982) on the basis of his studies on isotopic fractionation of sulphur has argued that increase in oceanic sulphate approximately coincided with the greatest tectonic milestone in geological history; the change from a highly mobile Archaean crust to a Proterozoic regime of stable continental mass. The Archaean/Proterozoic boundary seems to mark a change from a regime of rapid plate formation to a slower one {Dewey and Windley, 1981) that would, in turn produce a lower rate of exchange between reduced mantle material and the hydrosphere/atmosphere. This change in the history of the earth resulted in depletion in amount of Fe concentration in ocean water and the entry of significant amount of free oxygen into the atmosphere. The data from the present study also shows that the pure CBIFs are depleted in REE, with variable La and Eu enrichment. The hydrothermal source for Fe, Si and REEs is also supported by a plot of (Cu+Co+Ni) vs. 2REE for the Kudremukh BIF (Fig.37). Most of our pure CBIFs lies within well defined field, labelled "Hydrothermal Deposits". Some samples of CBIF and SBIF lies outside the field suggesting that the hydrothermal solutions were mixed with continental debris and volcaniclastic material at the time of chemical precipitation of BIF. The mixing with ambient sea water and the clastic input from divergent sources explain the variation in the magnitude of La, Eu, REE enrichment. From the study of microorganisms (microfossils) it can be inferred, for instance, that photosynthesis, possibly oxygenic, 97 10000 Hydrogtnoui 4 D»*p-»»o Dtpoallt 1000 -•- •''I Hy4reth«rmol / \ o Deposits / ^"^ o / \ + o o lOOh a "^mrn.^ a • ) 'v. 10 J. 10 100 1000 5REE ^ Figure 37. (Cu+Co+Ni) vs. £REE plot show most of the samples within well defined field of hydrotherraal deposits. Some samples lies outside this field indicating mixing of continental debris and volcaniclastic material with hydrothermal solutions, fields of hydrothermal deposits and deep-sea deposits are after Klein and Beukes (1989). 98 occurred at the time corresponding to the geological age of these particular fossils. Furthermore, if independent geochemical data indicate that a reducing atmosphere prevailed at the time, the fossils may represent anoxygenic precursors of oxygenic cyanobacteria, or they may represent the time of emergence of oxygenic cyanobacteria. After the discovery of the microfossil in the Gunflint chert (Barghoorn and Tyler, 1965), it is widely believed that change of the anaerobic atmosphere to aerobic is a consequence of biological photosynthesis mainly by different types of algae (Cloud, 1983; Towe, 1990). Current thinking based on some fossil finds is that first life, whatever their form, could have originated as early as 3.5 Ga ago (Schopf et al., 1983). Cloud (1985) argues that geochemical interpretation is consistent with the presence of life back to the oldest known sediments, the 3.76 Ga old metasediments of the Isua region of southeast Greenland. One fossilized form of well developed cellular life in the form of mat of filamentous organisms has been found in chert of the Warrawoona Group in Pilbara block of western Australia {~3.5 Ga old) (Lowe, 1980; Walter et al., 1980). Slightly younger microfossils (3.3 - 3.5 Ga old), resembling cyanobacteria have been found in the early Archaean Apex Basalt and Towers Formation of the Warrawoona Group (Schopf and Packer, 1987). Some other stromatolites of approximately similar age have been reported from limestone in the Fort Victoria greenstone belt of the Rhodesian Archaean Craton within Zimbabwe (Orpen and Wilson, 1981). Stromatolites of late Archaean age have been reported from Dharwar Craton also (Srinivasan and Naqvi, 1990). Early Proterozoic 99 granular iron-f.ormations from several localities have yielded micro-fossils of photosynthetic bacteria. Although the BIF contain considerable quantities of organic matter, morphology of the microfossils is generally not preserved in them. Enormous amount of silica precipitation has taken place along with iron in the absence of silica secreting bacteria during Archaean (Heinen and Ochler, 1979). Precipitation of silica is also difficult to explain because to bring silica into solution alkaline environment is needed and to precipitate it rhythmically acidic environment is essential (Mel'nik, 1982). In view of this difficulty some authors like La Berge (1973; 1986) believe that even silica has been precipitated by biological process. So far neither microfossils nor stromatolites have been discovered from Archaean BIFs (Schopf and Walter, 1983; Walter and Hofmann, 1983) except from the black cherts of Donimalai, Sandur schist belt (Naqvi et al. 1987). It has remained an extremely attractive and provocative hypothesis to suggest that biological activity has played major role in the precipitation of BIFs. Since often very large quantities of organic matter are found to be interbedded with these rocks, this speculation is very convincing. In the absence of recognisable morphological convincing record, the isotopic and trace element data is the only alternative to suggest BIF genesis. Such data from Kudremukh iron-formation, as discussed above, indicate that the concept of biological mediation for the precipitation of iron of oxide facies BIF is plausible. However, Stanton (1989) has suggested that cherts of BIFs were originally deposited as products of sea floor hydrothermal 100 exhalation, as a hydrous . form of Si02, probably a gel. With diagenesis and ageing this material dehydrated and transformed, in situ, to quartz. Metamorphic heating then induced variable grain growth and coarsening. The bedded iron oxide forms and develops during sedimentation and diagenesis, limonite is the precursor mineral and magnetite is the final product. The BIF of Kudremukh belonging to Bababudan Group are mainly associated with mafic and acid volcanic rocks which occur below and interbedded with thin current bedded quartzites. These BIFs especially of Kudremukh region are of mixed oxide, silicate, and carbonate facies (MOSCF) and significantly differ from those of Chitradurga, Shimoga and Sandur schist belts which are associated with stromatolites, manganese formation, carbon phyllites in addition to metavolcanics (Manikyamba et al.,1991). Kudremukh BIFs based on the data presented above are classified into cherty and shaly types. Their geochemical and petrological characters presented above indicate that three processes namely hydrothermal/fumarolic activity, volcaniclastic debris settling and terrigenous sedimentation simultaneously have contributed to the formation of Kudremukh BIF. The high MgO content of several samples indicates that volcaniclastic material most probably ash has also settled along with chemical precipitation of Fe20^ and Si02. La enrichment, positive Eu anomalies and depleted character in total REE content suggest that iron and silica were provided by hydrothermal and fumarolic activity (Michard and Albarede,1986; Barrett, et al.,1988; Dymek and Klein,1988; Klein and Beukes,1989; Michard,1989). Significant enrichment in AI2O3, K2O, enriched and 101 fractionated REE pattern, Zr and Rb enrichment and also in few cases negative Eu anomalies indicate terrigenous contribution which settled as extremely thin layers between the chemogenic precipitates of silica and iron. The hydrothermal solutions would have brought iron in ferrous state and its precipitation in Fe-rhythmites could have been possible only if the ambient ocean had an intermittent oxygenated atmosphere. There are two major models for the precipitation of BIFs. One model which has been applied to Hamersley basin where BIFs are considered to be evaporites and the fine grained laminations are believed to be varves (Trendall, 1983). The other model envisages that oxygen was provided through photoautotrophy to precipitate ferrous iron as ferric iron in hydrated form (Cloud, 1973; Schopf et al.,1983). Evidence of existence of photosynthetic bacteria has not so far been found in Kudremukh region; nor stromatolites or microfossils or even carbonates are present there. Neither is there evidence for evaporites or desiccation. Therefore, it is tentatively concluded that the oxygen was produced in some other shallower part of the basin which has been eroded and destroyed. The iron and silica rich hydrothermal solutions were probably put into the ambient ocean in its deeper part and due to upwelling (Holland,1973; Drever,1974) moved towards the shelf region. 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