CHAPTER- VI PETRO-MINERLOGICAL CHARACTERIZATION OF HOST ROCKS AND ORE MINERAL ASSEMBLAGES

Transcription

1 CHAPTER-VI

2 139 CHAPTER- VI PETRO-MINERLOGICAL CHARACTERIZATION OF HOST ROCKS AND ORE MINERAL ASSEMBLAGES The chapter includes the detailed petrography of the basement Bonai granite and overlying quartz-pebble conglomerates (QPC) and Iron Ore Group(IOG) quartzites. It also includes the study and identification of various radioactive phases in radioactive quartz-pebble conglomerates. Detailed mineralogical characterization of radioactivebearing and associated minerals have been studied using microscopy coupled with image analyzer, SEM-EDS, EPMA, CN-film studies etc Sampling and Methodology: Systematic sampling was carried out from different QPC occurrences exposed along western margin of Bonai granite in and around Bagiyabahal, Birtola village and north of Darjing and also north of Balisura village in Phuljhori Pahar. Similarly, from the above locations, samples of IOG quartzites with which QPC are associated and the basal Bonai granite were sampled. The samples include the surface samples mainly from outcrops, nala cuttings, road cuttings, trenches and along river banks. Polished thin sections were prepared and studied using Nikon Microscope-model EL-600 attached with image analyzer at Petrology Laboratory of AMD, DAE, Jamshedpur. Radiometric survey as well as their radio-elemental analysis indicated radioactive nature of QPC (Chapter-V, Table 5.3), hence, only QPC samples were subjected to cellulose nitrate (CN-film) film autoradiography for characterizing the radioactive phases in them. Quartzites and Bonai granite being non-radioactive in nature were not taken up for CN-film study. Various characteristic features of different lihounits and radioactive phases were obtained using Image analysis of Mutech and Biovis 1.5 version software at Petrology Lab., AMD, Jamshedpur. Radioactive grab QPC samples were also investigated for the presence of secondary uranium minerals with the help of ultraviolet (UV) lamp the reason is, under UV light, secondary uranium minerals show fluorescence. In a few samples, UV lamps indicated presence of secondary uranium mineral/s by showing bright greenish to pale-greenish fluorescent color.

3 140 Scanning Electron Microscopy with Energy Dispersive Spectrometry (SEM-EDS) was also conducted for selected QPC samples at Presidency University, Kolkata using SEM-TESCAN VEGA attached with OXFORD EDS to characterize minerals along with their electron images and EDS spectra. Radioactive QPC were also studied for minerals chemistry using Electron Probe Micro-Analyzer (EPMA) at AMD, DAE, Hyderabad with the help of Model SX-50, CAMECA, France. It has three vertical and one inclined linear focusing wavelength dispersive spectrometers fitted with LIF, PET, TAP and pseudo crystals (PC1 & PC2) diffracting crystals. The system is controlled on and off line by Sun Micro-System under UNIX environment. The laboratory undertakes non-destructive micro-domain (1 micron diameter) near surface, qualitative and quantitative analyses of elements with atomic number 5 (Boron) and above with detectable limits generally of 0.01%. Elements like U, Th, Pb, Si, Ca, Ti, Y and other RE 2 O 3 were analyzed in uraninite, monazite, zircon, pyrite and galena grains. Microscopic Study Besides petrographic characters of QPC, associated quartzite and the basal Bonai granite samples were also studied microscopically. Petrography of Boani granite followed by IOG quartzites and finally QPC are presented below Bonai granite Bonai granite is ubiquitously present in the Singhbhum-Orissa Craton is an important Archean granitic suite (700 sq.km. area) (Saha,1994) and the QPC lenses occur all along the granitc body, both along its eastern and western margin (Kumar et al., 2011a).The Bonai granite is generally medium to coarse grained and show hypidiomorphic texture. It consists mainly of quartz, feldspar and mica [Fig. 6.1(1, 2,3)]. Quartz grains are smaller in size (0.40 mm- 1.2mm, rarely 2.0 mm) than feldspar (0.48 mm- 1.68mm) which are sub-hedral and show moderate undulose extinction. Feldspar minerals are represented by both K- and plagioclase. K-feldspar is mainly micro-perthite and microcline (0.64 mm-1.44 mm) and is partly sericitized [Fig. 6.1(4, 5, 6)]. On the other hand, plagioclase grains (0.48 mm-1.68 mm) occurs as lath shape which are highly sericitized retaining their shape and twinning [Fig.6.1(5, 6)].

4 141 Mineralogy of Basement Bonai Granite Perth Micrl Alt Plg Biot Micrl Fig. 6.1(1). Bonai granite showing hypidiomorphic texture and alteration of plagioclase laths (sericitisation)(alt Plg), Sundargarh dist of Orissa. Note subhedral grains of microcline (Micrl), anhedral to subhedral quartz () with undulose extinction and biotite flakes(biot), TL, air, 2N. Fig. 6.1(2). Bonai granite from Brahmni River section showing hypidiomorphic texture and presence of Subhedral grains of quartz,(), altered plagioclase feldspar (alt-f), microcline (Micrl), biotite (Biot) and little amount of muscovite (Mus). TL, air, 2N. Micrl Alt-Plg Micrl Alt-Plg MI Fig. 6.1 (3). Hypidiomorphic textute in Bonai granite showing subhedral grains of quartz ()),altered plagioclase( Alt-P), fresh microcline (Micrl), TI, air, 2N. Fig.6.1(4). Fresh microcline (Micrl) and sericitized plagioclase (Alt-Plg)in Bonai granite,note myrmekitic intergrowth(mi) and relict twinning in plagioclase feldspar, Quartz is strained (),TI, air, 2N. K-F Micrl Epi Alt. Plg. Mus Fig.6.1(5).Microcline-microperthite (K-F) rich portion of Bonai granite, Barghat area, Sundergarh dist, Orissa, TL, air, 2N. Fig. 6.1 (6).Microcline (Micrl) and altered plagioclase (Alt. Plg) rich portion of Bonai granite with muscovite flakes(mus)and fine epidote grains (Epi) as inclusion with plagioclase,barghat area, Sundergarh dist, Orissa, TL,air, 2N.

5 142 Both muscovite and biotite are present in the granite but biotite exceeds muscovite. The higher amount of biotite is responsible for the grey color of the granite in the area. Muscovite flakes are larger than biotite and are feebly deformed. Biotite occurs as small flakes and shows light to deep brown pleochroism [Fig. 6.1(7)]. Biot Mus Zir Alt. Plg Fig. 6.1(7). Biotite (Biot) rich part of Bonai granite. TI, air, 1N. Fig. 6.1 (8). Euhedral zoned zircon (Zir) as inclusion within altered plagioclase feldspar (Alt. Plg) in Bonai granite. TL, air, 2N. is quartz, Mus.- Muscovite. Biotite is bleached and also chloritized [Fig.6.1 (9, 10)]. Both bleached biotite and biotite with one set of perfect cleavage are noted in Bonai granite [Fig.6.1 (13)]. Euhedral and zoned zircon [Fig.6.1 (8) ] and also a few epidote grains are noted as inclusions within biotite [Fig.6.1 (13, 14)] and altered plagioclase feldspar [Fig.6.1 (7, 8)]. Opaque grains are very few. Perth Micrl Chl Alt- Biot Biot Chl Plg Fig.6.1(9). Bonai granite showing alteration of biotite (Biot) into chlorite (Chl), Dahichor area, Sundergarh dist of Orissa. Few feldspar grains (Plg and Micrl) are also seen TL, air, 2N. Fig.6.1(10). Bonai granite from Dahichor area, Sundergarh dist of Orissa showing alteration of biotite (Biot) into chlorite (Chl). Quartz () and few feldspar grains (Plg and Micrl) seen, TL, air, 2N. The main alterations noted in Bonai granite are chloritization of biotite and sericitization and feebly epidotization of plagioclase feldspar. Alteration of magnetite/hematite to goethite is also observed [Fig. 6.1(12, 16)]. Presence of

6 143 myrmekitic intergrowth [Fig. 6.1(4)] is evidence of its possible magmatic origin which is noted along the contact of fresh microcline and plagioclase laths. Mu Micr Mt G Fig.6.1(11).Pegmatite showing coarse grained microcline (Micrl), muscovite flakes (Mus) and strained quartz (), Gopna bridge, NH-215, Sundergarh dist, Orissa., TL,air,2N. Fig. 6.1(12) Subhedral grain of grey colour magnetite (Mt) altering into brownish red colour goethite (G) along its border in Bonai granite, RL, Oil. Bld biot Epi Epi Qt Cleav Biot Fig.6.1 (13). Bleached biotite (Bld biot) in Bonai granite containing inclusions of epidote (Epi). TL,air, PPL. Cleaved biotite Cleav biot) has one set perfect cleavage. Fig.6.1(14). Biotite in Bonai granite conataining inclusions of epidote (Epi).TL, air, 2N. Mt Mt Chl G Fig.6.1(15).Alteration of biotitie to chlorite and magnetite into goethite in Bonai granite, TL, air, PPL. Fig.6.1(16). Relict magnetite (Mt) altering into goethite in Bonai granite, RL,oil.

7 IOG QUARTZITES IOG quartzites are well exposed in a series of hill ranges along western margin of Bonai granite near Gurundia, Bhaludungri, Bagiyabahal-Tikiyatpali, Lodhani and north of Darjing in Phuljhori Pahar. They are known here as Gurundia quartzite. Under microscope, they appear as fine grained quartz-arenite to ortho-quartzite assemblages consisting mainly of quartz, few muscovite /sericite flakes, rare opaques and accessory minerals like sphene, zircon, and magnetite. The rock show clastic to foliated nature. The quartz grains are sub-angular to elongated, deformed showing moderate to strong undulose extinction at places. The grain size of quartz ranges from 0.30 mm to 0.90 mm. The matrix component of the rock is mainly made up of sericite. Alignment of quartz and sericite / muscovite flakes imparts foliation to the rock. Rounded to well rounded quartz grains as pebbles are also observed in the rock indicating that the original rock was sandstone which later on metamorphosed to quartzite. Fig.6.2(1). IOG quartzite, Siyalkudar area overlying QPC, western margin of Bonai granite, Sundargarh district, Orissa., TL, air, 2N. Fig. 6.2 (2).IOG quartzite, Siyalkudar area. Note the presence of coarse grained and strained quartz rich portion within fine grained quartz. TL air, 2N. Stretched quartz Fig.6.2(3).IOG quartzite as siltstone, Siyalkudar area overlying Bonai granite. Note the presence of clastic nature in fine quartz and sericite matrix. TL, air, 2N. Fig.6.2(4). IOG quartzite, Siyalkudar area, Sundargarh district, Orissa. Note the stretching of quartz grains. TL, air, 2N.

8 145 Recrystallization of quartz has resulted into the welding of the quartz grain boundaries and hence provided hardness to it. Mica flakes also show bending of their cleavage suggesting post-depositional deformation. Opaques are included with mica flakes. Sphene is fine sized, euhedral [(Fig.6.2(7)] whereas zircon[(fig.6.2(5), 6.2(6) ] which is up to 0.09 mm size is zoned and euhedral in nature and both are included in quartz grains suggesting their possible igneous source. In some samples, chalcopyrite is also noticed as inclusion within quartz. [Fig. 6.2 (7)]. Zir Zir Pebble Fig.6.2(5).Fractured zircon grain (Zir) with rounded boundary in tectonized IOG quartzite, Sundergarh district, Orissa.TL, air, 2N. Fig.6.2 (6). Rounded zircon grain in matrix part of IOG quartzite, Siyalkudar area, Sundergarh district, Orissa.. TL air, 2N. Zir Sph Seri Cpy Fig. 6.2 (7). Sphene (Sph) and zircon (Zir) as heavy minerals in tectonized IOG quartzite, Sundargarh district, Orissa.. Quartz () is highly strained.tl, air, 2N. Fig.6.2 (8). Inclusion of chalcopyrite (cpy) in quartz (qtz) in IOG quartzite, Siyalkudar area overlying QPC, western margin of Bonai granite, Sundargarh district, Orissa. RL. air, Seri - sericite matrix.

9 Metabasic rocks: Metabasic rocks occur as small lensoidal bodies just above IOG quartzites north of Bhaludungri, Birtola and Phuljhori Pahar. They are light green in color, fine grained and are comprised of tremolite and actinolite within chlorite-rich mass. Accessory amounts of muscovite, sericite and rare grains of tourmaline are also observed. Chlorite appears as an alteration product of actinolite. It has been identified as quartzactinolite-chlorite schist [(Fig. 6.3(1, 2)]. Fig. 6.3(1). Metabasic (Actinolite schist), western margin of Bonai granite, TL, air, PPL. Fig. 6.3(2). Metabasic (actinolite schist) from western margin of Bonai granite showing laths of plagioclase feldspar and green colored actinolite flakes.,tl, air, 2N QUARTZ-PEBBLE CONGLOMERATES (QPC) QPC is an important litho-units identified in the area because of its radioactive nature, which occur as lensoidal bodies either inter-bedded with IOG quartzites or as basal conglomerate just below IOG quartzite near Baratangra, Bagiyabahal and Balisura in PhuljhoriPahar. QPC consists mainly of quartz pebbles and granules, rare chert and quartzite set in mainly arenaceous, argillaceous and ferruginous matrix. Quartz pebbles from Phuljhori Pahar range in size from 1.36 mm to 5.20 mm whereas the size of pebbles from Brahmni River vary from 1.04 mm to 2.4 mm, rarely 3.6 mm. In some samples of QPC from Phuljhori Pahar, bimodal distribution of quartz pebbles have been noted, the larger one from 2.4 mm to 8.8 mm and smaller one is 0.88 mm to 1.44 mm. Both ash grey color smoky and white vein quartz have been noted in QPC.

10 147 Quartz and sericite matrix Overgrowth in quartz Elongated quartz pebble Corroded quartz pebble margin Fig. 6.4(1) QPC from Brahmni River Section, West of Bagiyabahal, Note elongated as well as subrounded qtz pebbles.quartz rich matrix.tl, air, 2N. Fig. 6.4 (2).Overgrowth in quartz pebble in QPC from Brahmni River Section, West of Bagiyabahal. Quartz rich matrix. TL, air, 2N. Biot and seri Siliceous Matrix matrix Fig. 6.4 (3). General view of conglomerate shows crude directional orientation of quartz pebbles with fine quartz (), sericite(seri) and biotite (Biot) as matrix, PhuljhoriPahar area, TL, air, 2N. Fig. 6.4(4) Oligomictic QPC with rounded quartz pebbles ( ) within siliceous matrix from Bagiyabahal area, TL, air, 2N. Qt seri Fig.6.4(5).QPC from west of Bagiyabahal, right bank of Brahmni River,fine grained recrystallised quartz () and subrounded and elliptical quartz pebbles,tl,air, 2N. Fig.6.4 (6). Sheared QPC from Bagiyabahal area with minor amount of sericite in matrix.tl, air, 2N. The matrix component of QPC is mainly made up of fine sized quartz grains [Fig.6.4 (8)] which is sub-rounded and well sorted than clast components. In addition, chlorite [Fig. 6.4(9, 10,11)] is another important matrix material in QPC.

11 148 Sericite [Fig. 6.4(1, 3, 6)] and minor biotite [Fig.6.4(3,10)] are also present in the matrix. In most of the samples, goethite, limonite and minor hematite are invariably seen which are responsible for brown to red coloration to the rock [Fig. 6.4(11,12)]. Aren. Mat Quartz pebble Fig.6.4(7).Pebble and granules set in arenaceous matrix in QPC, PhuljhoriPahar, Sundargarh dist., Orissa. TL, air, 2N. Fig.6.4(8).Chloritic matrix (Chl) in QPC, with elliptical unzoned zircon (Zir), Birtola area, Sundergarh district, Orissa. TL, air, 1N. Biot Chl Chl Fig.6.4(9). Fine sized chlorite flakes (Chl) as matrix around grain boundaries of quartz pebbles (), TL, air, 1N. Fig.6.4(10).Fine sized biotite flakes (Biot) and chlorite (Chl) matrix encircling quartz clasts () in QPC, Birtola area, Orissa,TL,air, 1N. Pebble Chl Epi FM G Pebble Fig.6.4(11).Green chloritic (Chl) and brown colour goethitic (G) matrix of QPC, Birtola area, Sundergarh dist., Orissa,TL,2N. Fig.6.4(12).Dark brown colour ferruginous material (FM) in QPC, Birtola area, Sundergarh dist., Orissa,TL, air, 2N.Note presence of an epidote grain (Epi). Biotite, sericite and few muscovites are also observed as matrix component in QPC from the study area. Most of the quartz pebbles are monocrystalline though some are few polycrystalline in nature. Clast is generally sub-angular to sub-rounded to partly

12 149 elongated showing moderate undulose extinction suggesting mild deformation [Fig.6.4(1,2,3,4,5,6,7)]. The detrital components or heavy minerals in the QPC matrix are mainly zircon [Fig.6.4(8,14a,14b],tourmaline[Fig.6.4(13)], sphene [Fig.6.4(15)], anatase, rutile [Fig.6.4(16a,16b)], magnetite [Fig.6.4(17a,17b)] and chromite[fig.6.4(18a,18b)].euhedral zoned zircon to sub-rounded zircon are commonly seen in the matrix. Grains of sphene, zircon, tourmaline and aggregates of epidote form the accessory minerals. Zir Tour Fig.6.4(13).QPC from Brahmni River Section, presence of tourmaline (Tour) in matrix.tl, air, 2N. Fig.6.4(14a). Highly fractured zircon grains (Zir) show altered grain boundary, TL, air, 2N. Zir Sph Fig.6.4(14b). Detrital fractured zircon grain in QPC matrix, Birtola area, Orissa. TL, air, 2N. Fig.6.4(15). Brownish pink coloured sphene (Sph) alongwith chlorite in QPC. TL, air, 1N. Rut Rut Fig.6.4(16a).Subrounded rutile grain(rut) as inclusion within quartz in sheared QPC, Bagiyabahal area,tl, air,1n. Note very high relief. Fig.6.4(16b). Rutile grain in QPC matrix, TL, air, 2N.

13 150 Mt Mt Fig.6.4(17a). Rounded magnetite grain in QPC sericitic matrix. TL, air, 1N. Fig.6.4(17b). Rounded magnetite grain in QPC sericitic matrix. In fig.6.4(17a) RL, air, 1N. Chl Mt Mt Fig.6.4(18a).Rounded fractured magnetite grain(mt) in QPC chloritic matrix, Birtola area, TL, air, 1a. Fig. 6.4(18b).Rounded fractured magnetite grain (Mt) in fig. 6.4 (18a), Birtola area, RL, air, 1N. Py Py Fig.6.4(19a).Sub-rounded to irregular shaped pyrite grain(py) in QPC matrix, Bagiyabahal area RL, air. Fig.6.4(19b). Two rounded pyrite grains (Py) in QPC matrix, Bagiyabahal area. RL, air,

14 151 Presence of pyrite, chromite, monazite and rutile has been confirmed by SEM-EDS study as well. Electron image and EDS spectra of monazite [Fig. 6.4 (26, 27, 28)], chromite [Fig. 6.4(29)], rutile [Fig. 6.4(30)] and pyrite [Fig. 6.4(31)] confirms the presence of heavy minerals that are usually associate with paleoplacer QPC occurrences. Amongst them, monazite is the main phosphate mineral phase. Ubiquitous presence of quartz as pebbles along with rare chert and quartzite is suggestive of oligomictic nature of quartz-pebble conglomerates from study area. Ore mineralogy: Ore microscopic study of polished thin sections under reflected light microscope reveals the presence of pyrite, goethite, limonite, magnetite, ilmenite and chalcopyrite in QPC. Pyrite is the dominant sulfide mineral and is subrounded to irregular shaped. Minor amounts of chalcopyrite as specks and galena are also observed as sulfide minerals in these conglomerates. Fine sized sub-rounded - rounded anhedral grains of pyrite [Fig. 6.4(19a, 19b)] and chalcopyrite [Fig.6.4(21)] grains are observed in QPC. Very fine inclusions of pyrite grains are noted as disseminated grains throughout carbonaceous lump and along the grain boundary of monazite [Fig. 6.4(20)]. Among oxides, goethite, chromite, magnetite, limonite, hematite, rutile and ilmenite are the ore minerals observed in QPC. Py Cpy Py Fig.6.4(20). Fine inclusions of pyrite (Py) in carbonaceous lump in sheared QPC, Bagiyabahal area, RL air. Fig.6.4(21).Pyrite (Py) and chalcopyrite (Cpy) in sheared QPC, Bagiyabahal area, Sundergarh dist, Orissa, RL,air. Alteration Features in QPC: Alteration is not very conspicuous in the radioactive QPC; however a few grains are showing the tendency of alterations. Limonitization of pyrite and goethite, chloritization of biotite, muscovite from sericite and alteration of magnetite to

15 152 limonite, goethite and hematite and leucoxenisation of ilmenite are some of the alteration features noted. Presence of mainly mono-crystalline quartz pebbles with few polycrystalline inclusions of zircon in quartz and also as derital grains and presence of tourmaline, are suggestive of derivation of QPC from felsic igneous provenance. Post-Depositional Changes : Post-depositional changes in QPC are manifested in the form of (i) fracturing of quartz and magnetite grains [Fig. 6.4(20,21,22)], (ii) minor bending of mica flakes [Fig.6.4(23)], (iii) alignment of quartz pebbles [Fig. 6.4(1,3,4,5,9)], (iv) elongation in quartz pebbles [Fig.6.4(24,25)], (v) dissolution of quartz pebble margins [Fig.6.4(31)], recrystallization of fine quartz along quartz pebble grain boundary [Fig. 6.4(25)] and (vi) overgrowth in quartz pebbles [Fig. 6.4(2)]. The alignment of pebbles in a crude directional orientation with minor degree of pre-diagenetic micro-fractures, healed with fine grained granular quartz is noteworthy. Bagiyabahal area show conspicuous directional orientation. The micaceous minerals like biotite, muscovite, chlorite and sericite form thin flakes which are elongated. Fine sized chlorite flakes, biotite and sericite also heal the micro-fractures in goethitized magnetite. All these samples are marked by biotite, dark brown in color which shows minor alteration to chlorite and many flakes are curved and bent. Thus, alignment of quartz pebble mirco-fractures in pebbles and curved and bent nature of mica flakes favor minor deformation, alterations suffered by QPC after deposition. Overgrowth in quartz and irregular grain boundary in quartz pebbles appears due to dissolution of silica due to post-depositional diagenetic nature. Formation of secondary uranyl minerals along cleavage of mica flakes and adsorption of uranium over ferruginous material are some of the evidences noted in favor of post-depositional activity and alterations in QPC. Post- depositional deformations have also been observed in IOG quartzites with which QPC lenses are associated. Elongation in quartz grains [Fig.6.2 (1,4)], alignment of quartz and sericite flakes [Fig.6.2 (3)], moderate to strong undulose extinction in quartz [Fig.6.2 (7)], bending and fracturing of zircon grains [Fig.6.2

16 153 (5)], and recystallization of fine quartz along quartz grain boundary, bending of color bands due to green colored fuchsite [Fig.6.2 (3)], are some of the evidences observed in IOG quartzites from study area supporting post-depositional deformation. SEM-EDS study confirmed the presence o, monazite [Fig.6.4 (28, 29)], rutile, [Fig.6.4 (30)], chromite [Fig.6.4 (31)], pyrite [Fig.6.4 (32)] and secondary U minerals [Fig.6.4 (33,34,35)]. Most of the secondary uranium minerals are U-phosphate. Presence of secondary U indicates dissolution of uranium due to oxidation after deposition and their complexing with phosphate.

17 154 Microscopic Observations of Post-Depositional Changes within QPC Fracture in quartz pebble healed by fine quartz Op Biot Fine quartz and sericite matrix Sec. Fig.6.4 (22).QPC from Phuljhori Pahar showing presence of strained and Stretched quartz pebbles in siliceous and sericitic matrix. Tl, air. 2N. Fig. 6.4 (23). Biotite (Biot) and sericite (Seri) flakes and secondary quartz (Sec. )healing the microfractures in magnetite in QPC matrix, TL, 2N. R Microfracture Fig. 6.4 (24). Fine grained quartz () and sericite (Seri) seen around pebbles of quartz () and also healing microfractures in QPC, Phuljhori Pahar, TL, 2N. Fig.6.4 (25). Elongated pebbles of quartz () with fine grained recrystallised quartz (R) around the quartz clasts, TL, 2N. + seri Recrystallise d quartz Fig. 6.4 (26). QPC with large pebbles of quartz () set in fine sized quartz, sericitic and chloritic matrix. Note the presence of recrystallised quartz along grain contact of quartz pebble., TL, 2N. Fig.6.4(27).Pebble of quartz () with microfractures healed with fine grained granular quartz in QPC, TL, 2N.

18 155 SEM-EDS STUDY Spectrum 1 O La Si P C Ca La Nd Nd La Th S Th Ca Th Th Ca La Nd La Nd Nd La La Nd La La Nd Nd Fig.6.4(28). BSE image of monazite grain within carbonaceous mass in QPC Full Scale 794 cts Cursor: (33 cts) kev EDS spectra of monazite grain Fig. 6.4 (28). Element Weight % Atomic % C K O K Si K P K S K Ca K La L L Nd L Th M Total 100 EDS analysis of monazite grain Fig. 6.4 (28). Spectrum 1 O La Si P C Ca La Nd Nd La Th S Th Th Ca Th Ca La Nd La Nd Nd La La Nd La La Nd Nd Full Scale 794 cts Cursor: (33 cts) kev Fig.6.4(29). BSE image of monazite grain in QPC matrix. EDS spectra of monazite grain in QPC in Fig. 6.4(29).

19 156 Spectrum 1 Ti Ti O Cr Ti Cr EDS spectra of rutile in fig30. Cr Full Scale 1362 cts Cursor: (8 cts) kev EDS spectra of Rutile in fig. 6.4 (30). Fig. 6.4(30). BSE image of anhedral rutile in QPC. Element Weight % Atomic % OK Ti K Cr K Total 100 EDS analysis of Rutile in 6.4 (30). O Cr Spectrum 1 Fig.6.4 (31). BSE chromite in QPC image of rounded Fe Zn Al Re Re Re EDS spectra Crof chromite grain in fig Full Scale 1620 cts Cursor: (28 cts) kev EDS spectra of Chromite grain in fig.6.4 (31). Element Weight % Atomic % O K Al K Cr K Fe K Zn K Re M Total EDS analysis of Chromite grain in fig.6.4 (31). Cr Fe Fe Re Re Zn S Spectrum 4 Fe Fe Full Scale 1799 cts Cursor: kev Fe Fig.6.4(32). BSE image of subrounded pyrite grain (10micron) in QPC. EDS spectra of pyrite grain in fig. 6.4 (32). Element Weight % Atomic % S K Fe K Total 100 EDS analysis of pyrite grain in fig. 6.4 (32).

20 157 Ti O P Spectrum 2 C Ca Si Th S U U Th Ca U Th U Ca Ti Th U Ti Full Scale 370 cts Cursor: (17 cts) kev Fig. 6.4 (33). BSE image of U-phosphate in QPC EDS spectra of U-phosphate in fig. 6.4(33) possibly euxenite(y,,u,th)(nb, Na,Ti) 2 O 6. Euxinite is commonly partially amorphous due to radiation damage (metamictisation). O La Spectrum 1 C La La Al P La La La La La La Full Scale 1332 cts Cursor: (10 cts) kev EDS spectra of REE-phosphate in fig.6.4(34). Fig. 6.4 (34). BSE image of REE-phosphate in QPC Fig. 6.4 (35). BSE image of U-Pb- Y-Cu sulphide phosphate in QPC Element Weight % Atomic % C K O K Al K Si K P K S K Cu K Y L Pb M U M EDS analysis of U-Pb-Y-Cu sulphide phosphate in QPC in fig. 6.4 (35).

21 CELLULOSE NITRATE FILM STUDY OF RADIOACTIVE QUARTZ- PEBBLE CONGLOMERATES Radiometric verification with hand held scintillometer in the field areas and their subsequent radiometric assay for U and Th has indicated that only QPC are radioactive and IOG quartzites are non-radioactve in nature. Hence, only radioactive QPC samples were subjected to CN-film auto-radiographic study for identification and location of radioactive phases. Polished thin sections of radioactive QPCs were taken and then indicator made up of powdered uraninite grain mixed with red color nail polish were placed on the four corners of slide. In the mean time, cellulose nitrate film(cn-film) of variety CN-85( Colorless) cut into thin section size were taken and placed over the section so that indicator on drying will make its impression on the CN-film. Later on, another glass slide of same size was taken and kept over the section under study and tightened the both ends with the help of rubber band so that the CN-film will be in close contact with the polished thin section of the rock samples. The section with CN-film was kept for about 72 to 144 hours for exposure depending on its order of radioactivity recorded on the exposures. Then the CN-film was taken out and kept in 10 % NaOH solution for etching, dried in oven at 45 0 C temperature and then film is taken out. The film is now ready for alpha track study which becomes visible under optical microscope. The alpha tracks on CN-film are then matched with the polished thin sections for location of radioactive phases. Once located, then the optical properties under both transmitted and reflected light have been studied and then the mineral responsible for radioactivity have been characterized. The CN- film study indicates that most of the radioactivity in QPC is contributed by adsorbed U over goethite [Figs.6.5(1), (2), (3)] and veins of ferruginous material [Fig.6.5(4)] secondary uranyl mineral [Fig.6.5(13), (14), (15), (16), (17), (18)], grains of monazite [Fig.6.5 (5) & (6)], zircon, rarely allanite and xenotime.

22 159 Petrographic study of QPC including CN-film autoradiography followed by their Electron microscopic study indicated the presence of discrete uraninite grains in QPC. The uraninite grains are muffin [Figs.6.5 (9) & (10)] to sub-rounded [Figs.6.5 (11) & (12)] in shapes which register very high density alpha tracks on cellulose nitrate film. This is the first report of discrete uraninite grains in QPC from the study area and published in Kumar et al. (2012). Secondary uranyl mineral from Balisura has been identified as uranophane (Saxena et al., 1994). Monazite has also been identified in SEM-EDS study. SEM-EDS study also indicated the presence of other U-phosphate mineral which contain U,, Nd and Ca but not Th [Figs. 6.4(33),(34) and (35)]. G Fig. 6.5(1). Radioactive grain of goethite (G) in QPC matrix. TL. air, 1N. Fig. 6.5(2). Low to moderate density alpha tracks (I) due to radioactive grain of goethite (G) in QPC matrix. TL. air, 1N. T T Epi G G Fig. 6.5(3). Radioactive vein of goethite (G) in QPC matrix and corresponding alpha tracks (I). TL. air, 1N. Fig. 6.5(4). Alpha tracks (as small dots) due to adsorbed uranium over ferruginous material (dark colour) and a grain of epidote in QPC of Birtola area. TL, air, 2N.

23 160 M M Fig. 6.5(5). Monazite (M), fractured and rounded in QPC, located at the centre of the photograph, Bagiyabahal area. TL, air, 2N. Fig. 6.5(6). Grains of monazite (M) in QPC matrix with alpha tracks as dots. TL. air, 2N. Fig. 6.5(7).Medium density alpha tracks over carbonaceous material with inclusions of monazite grains and pyrite in sheared QPC, Bagiyabahal area, Sundergarh dist, Orissa, Fig. 6.5(8).SEM image of monazite within carbonaceous matter in perforated portion in sheared QPC,of fig.5.1.5(7). Op U Fig. 6.5 (9). Bean shaped partly altered uraninite grain (U) in QPC matrix nearby opaque grain (Op). TL, air, 1N. Fig. 6.5(10).Alpha tracks of corresponding radioactive phase in fig.6.5 (9), Bagiyabahal sheared QPC, TL, air, 1N.

24 161 Py Py U U T Fig. 6.5(11). Anhedral uraninite grain (U) in QPC matrix and corresponding high density alpha tracks (T). TL, air, PPL. Fig. 6.5(12). Subrounded grain of brecciated uraninite (U) with corresponding dense alpha track in sheared QPC, east of Bagiyabahal, RL, air,1n. RP RP Alpha tracks Fig. 6.5(13a). Grey color radioactive phase (RP) in sheared QPC, East of Bagiyabahal near Tikiyatpalli, condenser in, RL, air. Fig.6.5(13b).Alpha tracks over grey color radioactive phase in fig.6.5(13a), East of Bagiyabaha lnear Tikiyatpalli, PPL,air, condenser in.

25 162 SU T Fig.6.5(14a). Green flakes of secondary uranium mineral (SU) in QPC matrix. TL, air, PPL. Fig. 6.5(14b). Corresponding high density alpha tracks (T) due to green flakes of secondary uranium mineral (SU) in QPC matrix in fig 6.5 (14a). TL,air, SU AT SU Fig..6.5(15a).Greenish-yellow colour secondary uranyl mineral (SU) in QPC, Phuljhori Pahar, Orissa, TL, air, PPL, condenser in. Fig. 6.5(15b). High density alpha tracks (AT) due to secondary uranyl mineral in fig.6.5(15a), Phuljhori Pahar, Orissa, TL, air, PPL, condenser in. SU Op Fig. 6.5(16a). Encrustation of light green to brown colour secondary uranium (SU) associated with muscovite and opaque (Op) in QPC of Phuljhori Pahar. TL. air, PPL. Fig. 6.5(16b). High density alpha tracks due to encrustation of secondary uranium associated with muscovite and opaque in QPC of Phuljhori Pahar in fig.6.5(16a). TL. air, PPL.

26 163 Table 6.1: Petrographic characters of different QPC lenses exposed along western margin of Bonai granite Location- Brahmni R. Bagiyabahal Birtola Phuljhori Pahar Balisura Properties Nature Oligomictic Oligomictic Oligomictic Oligomictic Oligomictic Occurrence Basal Basal to interbedded interbedded Interbedded Basal Clast White qtz >smoky qtz White qtz >smoky qtz White qtz >smoky qtz Matrix Siliceous + sercitic and Siliceous and sericitic Siliceous, sericitic, ferruginous ferruginous and minor chloritic White qtz >smoky qtz Siliceous, sericitic, ferruginous and minor chloritic White qtz >smoky qtz Siliceous, sericitic, ferruginous Dimension 50m X m 630m x m 28m x m 48m x m and 15m x 25m x m m Pebble size mm Upper-12 to 30mm mm mm 15-80mm Basal-25 to 75mm Matrix mineral Zircon, goethite,altered magnetite, pyrite, tourmaline Zircon, monazite, goethite, pyrite, ilmenite, magnetite, chromite, rutile, uraninite Zircon,monazite, xenotime, altered magnetite Monazite, goethite,pyrite, tourmaline Goethite, tourmaline, pyrite and galena Adsorbed U over Monazite, rare uraninite Monazite, Monazite, xenotime, Secondary Uranyl goethite, altered grain, adsorbed U over xenotime, adsorbed adsorbed U over mineral along magnetite goethite, carbonaceous U over ferruginous ferruginous veins and muscovite flakes, material veins,hematite, and allanite adsorbed U over goethite U 3 O 8 <5ppm to 0.011% <5ppm to % 11 ppm to 0.022% <0.010 to % 10ppm to % Radioactive phase/s ThO 2 17ppm-0.017% <10 ppm to % 10ppm to % 13 ppm to % 16 ppm to %

27 164 Thus, petrological characterization indicates oligomictic nature of QPC consisting mainly of quartz pebbles. The matrix component is arenaceous (Fine quartz) to argillaceous (sericitic, chloritic, Biotite) and ferruginous in character. Heavy minerals are represented by zircon, tourmaline, pyrite, magnetite, ilmenite, chromite, monazite and uraninite. Radioactive phases are in the form of uraninite, secondary uranyl minerals, adsorbed uranium with goethite, limonite, ferruginous material and monazite grains. QPC have undergone mild deformation after deposition.