Abstract: The present study is an attempt to understand the mineralogical and geochemical characteristics of iron formations especially, the ferried group of elements and their significance in the origin to selected iron formations of northern districts of Tamil Nadu. Fourier Transform Infrared (FTIR) spectroscopy and ore microscopic investigation reveals that, the banded magnetite quartzite samples consist of magnetite and quartz as major minerals with hematite, grunerite, hornblende, hypersthene, goethite and chlorite as accessory minerals. About 36 magnetite quartzite samples were analyzed for the ferride group of elements of study regions. The results of chemical analyses of ferride group elements like Mn, Ni, Ti, Co, Cr and V in the iron formations of different regions are presented and interpreted. Lower concentration of these elements in the iron formations indicate that source of materials derived from weathering of landmasses. Further enrichment of Ti and Cr compared to other elements suggest the BIF’s are of metasedimentary in origin.
INTRODUCTION
The important magnetite quartzite deposits of Tamil Nadu occur in Tirthamalai, Kanjamalai, Godumalai, Vellalagundam, Kollaimalai and Tattayyangarpettai, Tiruvannamalai and Thirthamalai hill regions in the northern districts of Tamil Nadu. These iron formation consist magnetite and quartzite and associated with charnockite, granites, pegmatite, garnetiferous pyroxene granulite, amphibolites, basic intrusive and hornblende-gneisses. The iron ore formations of parts of Tamil Nadu were studied by Krishnan and Aiyangar (1944), Saravanan (1969), Anjaneya and Krishna Rao et al. (1970), Dymek and Klein (1988) and Ali and Robert (2005). Saravanan (1969) stated ore deposits of Kanjamalai, Salem are of meta-sedimentary origin. He stated that, the iron-formations represent original non-clastic and oxidate sediments and regarded that the iron and silica were derived due to weathering of land masses. The present study deals the petrological and ferried group elements concentration and their significance in the origin of iron formations of northern districts of Tamil Nadu, India.
MATERIALS AND METHODS
The study area including Tirthamalai, Godumalai, Vellalagundam, Tattayangarpettai, Kanjamalai hill regions falls between north latitude 78°00’ to 79°00’ and east longitude 11°00’ to 12°00’ in the high-grade granulite terrain of northern districts of Tamil Nadu State (Fig. 1). The study area is situated 360 km southwest of Chennai and 170 km east of Coimbatore. The study area has mainly salubrious climate due to Shevaroy hills. Here, the iron formations are highly deformed and occur at an elevation of 400-700 m above MSL within the gneisses and granulites.
| Fig. 1: | Geology of the study area (Geological Survey of India, 1984) |
To study the petrological and geochemical characters of the iron formations of the study regions, about 36 samples of banded magnetite quartzite were collected during June 2007 in the study area subjected for petrological studies. The Fourier Transform Infrared (FTIR) is carried out at CSIL Laboratory Annamalai University during August 2007 and the elements were determined by ICP-MS at Activation laboratory, Canada by August 2007.
GEOLOGICAL SETTING AND PETROGRAPHY
In field, the iron formations show long dark and glistering bands. They are highly foliated, deformed and metamorphosed. The banded magnetite quartzites samples are fine to course grained, highly magnetic, banded in nature with alternative quartz and magnetite bands. The thickness of bands varies from 2-3 cm. These are almost completely made up of white quartz and dark magnetite with little amount of grunerite and goethite. The individual grains are flattened parallel to the banding and vary in sizes from 2-12 mm.
Thin section study of iron formations reveal the presence of quartz, magnetite, hematite, goethite, grunerite, hornblende, hypersthene, pyroxene, chlorite and apatite (Fig. 2). Magnetite is dark and isotropic and sometimes it shows brushed extinction. The hematite is formed due to oxidation of magnetite along the fractures and cleavages. The lensoidal quartz in the iron formations are built by magnetite grains and minor quantities of grunerite. Grunerite is a typical ferromagnesian silicate mineral seen as rounded grains and needles. It occurs as, independent grains and also as interstitial grains showing optically sharp boundary. The grains are subhedral and do not appear to replace pyroxene and later than magnetite and quartz. It shows peleochroism in shads of pale green to pale brown. The cleavages are distinct and intersecting at angles of 56° and 124°. It exhibits extinction angle of Z^C = 18°. Repeated twinning is observed in all gains. Hypersthene and diopside are present in minor amounts and occur as coarse, subhedral to anhedral grains. Hypersthene contains the inclusion of magnetite. The accessory minerals identified in these formations are chlorite, hornblende and apatite. The apatite grains are laths shaped with high relief. It is unevenly distributed and concentrated in some quartz bands. Chlorite shows the spherulitic structures and formed over quartz domains. It exhibits faint pleochroism in shades of yellow, light and dark brown.
| Fig. 2: | Photomicrograph showing the bands of magnetite,
quartz and grunerite (32X, Crossed polars) |
| Fig. 3: | FTIR spectrum of banded magnetite quartzite of the study area |
Fourier Transform Infrared Spectroscopy (FTIR)
The Fourier transform infrared spectroscopy is a powerful research tool
in mineralogy when used in conjunction with X-ray diffraction and other techniques
for identification of minerals. FTIR spectra of iron oxides (Fe3O4)
are well established. In situ FTIR study on the dehydration of natural
goethite shows the peak position for the stretching mode around 3150 cm-1
and in plane deformation mode it is about 890 cm-1. The shorter wavelengths,
the optical and infrared (0.4 to ~ 2.5 mm), the resulting spectrum are most
sensitive to iron (oxides, oxyhydroxides) and alteration cations of water, hydroxyl
and carbonate bearing minerals. FTIR spectrum of magnetite samples of the study
regions exhibit strong absorption bands at 570-1. FTIR spectrum of
the study area magnetite quartzite exhibit absorption frequencies for magnetite
(570-1), quartz (1081-1), hematite (466-1),
goethite (794-1) and hornblende (505-1) (Fig.
3) and is similar to the study carried out by Ishii and Nakahira (1972).
FERRIDE GROUP ELEMENT GEOCHEMISTRY
The concentrations of ferried group elements Mn, Ni, Ti, Co, Cr and V in the iron formations of the study area samples are given in Table 1. Minimum and maximum values of these BIF’s are given in Table 2. The samples of Tirthamalai region show the range of Mn (201-627 ppm); Ni (20-50 ppm); Ti (54-444 ppm); Co (1-12); Cr (20-20 ppm) and V (5-17 ppm) (Table 2). The values of this region are low and highly variable compared to other regions.
The samples of Godumalai region shows the concentration of elements in the range of Mn (225-488), Ni (-20-62), Ti (30-564), Co (1-5), Cr (20-102) and V (-5-20), respectively (Table 1). The results show that the all samples exhibit low concentrations. The Tattayangarpettai region shows the range of concentration of ferried group elements as (217-705), (-20-138), (60-1067), (-1-11), (-20-144) and which shows the similar trend with the samples of Godumalai region (Table 1). The Vellalagundam region shows the range of concentration as, Mn (186-366), Ni (-20-41), Ti (60-1635), Co (-1-8), Cr (-20-41) and V (-5-57), respectively. The concentration of ferried group elements of this region is in Table 1. In which few samples have very poor concentrations compared to the samples of other regions. The Kanjamalai region shows the concentration of elements in the range of Mn (140-31); Ni (72-8); Ti (500-10); Co (21-4); Cr (202-41); and V (32-16) and their concentrations are given in Table 1. The average concentrations of ferried group elements of iron formations of northern district of Tamil Nadu. The results of interpretation of samples of all regions show not much variation and exhibit similar trends. The low concentration of these elements indicates the source of materials derived from weathering of land masses and not from any volcanic sources (Table 2).
| Table 1: | Results of analyses of Ferried Group Elements (in ppm) of Tirthamalai, Godumalai, Tattayangarpettai, Vellalagundam and Kanjamalai regions |
| *TM: Tirthamalai, GU: Godumalai, TA: Tattayangarpettai, V: Vellalagundam, SR: Kanjamalai | |
| Table 2: | The minimum, maximum and average values of ferried group elements in ppm for banded magnetite quartzites of the study area |
| Table 3: | The average concentrations of ferried group elements of iron formations |
These BIF’s are later metamorphosed. Among these elements the Ti and Cr are enriched compared to other elements indicating that BIF’s of the study area are of meta-sedimentary origin (Saravanan, 1969). It is suggested the low concentration of these elements in many iron formations of central Sweden indicating sedimentary origin.
The average concentrations of ferried group elements of study regions are also compared with other iron formations of Kemmangundi, Ongole and Central Sweden (Table 3). The samples of the study regions show similar trends with the other regions of the world indicating meta-sedimentary origin (Anjaneya and Krishna, 1970).
CONCLUSIONS
The iron formations of northern districts of Tamil Nadu consist of long dark and glistering bands. They are, highly foliated, deformed and metamorphosed. They are composed of quartz, magnetite, hematite, goethite, grunerite, hornblende, hypersthene, chlorite and apatite. The Fourier Transform Infrared (FTIR) spectrum of samples of study region shows the absorption frequencies for individual minerals as magnetite (570-1), quartz (1081-1), hematite (466-1), goethite (794-1) and hornblende (505-1). The concentration of ferried group elements in the iron formations of study regions indicates to meta-sedimentary origin. The average concentrations of elements show similar trends with other iron formations of meta-sedimentary origin in Kemmangundi, Ongole and Central Sweden.
ACKNOWLEDGMENTS
The authors are thankful to Act lab (Canada) for providing chemical analyses of the samples by ICP-MS. The financial supports provided by University Grants Commission, New Delhi and Department of Science and Technology, New Delhi (Projects: GEMIORD No. SR/FTP/ES-01/2000 and SPECSIGNS No. NRDMS/11/1153/06) are gratefully acknowledged. The authors are also thank the CSIL Laboratory, Annamalai University for providing Fourier Transform Infrared (FTIR) analyses.