Precambrian Stromatolitic Phosphorites of Udaipur, Rajasthan, India

D. M. BANERJEE Department of Geology. University of Delhi, Delhi-7, India

ABSTRACT which are shown in Table 1. Resting on the basement of the Banded Gneissic Complex, the Study of the origin of phosphorite in the Pre- Debari Formation of the present scheme was cambrian Aravalli metasediments has involved designated by Heron (1953) as Debari Quartz- stratigraphic analyses of the Aravallian rock se- ite and considered by him to be the equivalent quences around Udaipur, petrography of the of the Alwar Quartzite of the Delhi System. phosphatic minerals, chemical analyses of rep- Study by the author has shown that such postu- resentative samples and reconstruction of the lation is not valid. A major fault postulated by environment of deposition. The role of Heron between the quartzites of Debari and Stromatolitic algae in the formation of the sedi- phyllites of Udaipur valley does not exist. Fol- mentary phosphorite has been clearly demon- lowing the code of stratigraphic nomenclature, strated. Evidence suggests that the in this paper the Aravalli System of the earlier phosphorites of the Udaipur area were depos- workers has been given the status of Group ited in shallow waters where luxuriant growth which has been subdivided into three Forma- of Stromatolitic algae helped in trapping and tions. precipitating phosphorus from the basin waters. The phosphorite-bearing horizons are confined to the Matoon Formation and phos- INTRODUCTION phate minerals are especially abundant in the The discovery of sedimentary phosphorite in brecciated cherty rocks and bluish-gray dolo- the Precambrian Aravalli rocks of Rajasthan has mite, interbedded with these rocks or found as awakened keen interest in the study of the concentrations along Stromatolitic columns. genesis of Indian phosphorites. Such study is They also occur as disseminated grains in dolo- particularly important in view of the unique mite or as small nodules and intraclasts. association of phosphorites with the stromato- Five modes of occurrence of phosphorite can lites, a high PaOs content, and their occur- be recognized in the Udaipur area: rence in Precambrian metasediments. 1. Columnar algal (Stromatolitic) phosphorite showing concentration of phosphatic PREVIOUS WORK material in the algal columns. Phosphate miner- Phosphorite in the Precambrian Aravalli als also accompany the stromatolites as pellets limestone near Kanpur was discovered by a and intraclasts in a nonphosphatic dolomitic team of geologists of the Geological Survey of matrix (Figs. 5,8). India in early 1967. Muktinath (1967), Muk- 2. Laminar algal phosphorite, occurring as tinath and Sant (1967), Muktinath and others phosphatic laminae comformable with the bed- (1969), Chatterjee (1968), and Sethi (1969) ding of the dolomitic host rock. The laminae gave summaries of the work done in various rarely cut across the bedding (Fig. 4). phosphorite deposits of Rajasthan. However, 3. Reworked silicified conglomeritic or brec- no attempt has been made to analyze various ciated phosphorite showing fragments of geological, chemical, and physical factors that stromatolites set in a cherty and quartzose ma- controlled the origin of Precambrian phosphor- trix (Fig. 7). ites of Rajasthan. 4. Massive-bedded phosphorite with thin nonphosphatic pelitic interlayerings and quart- STRATIGRAPHY zose laminations. Systematic mapping by the author in the 5. Disseminated and nodular phosphorite set Udaipur area, including the areas of Kanpur, in bluish-white nonphosphatic dolomitic matrix Matoon, Sisarma-Neemuch Mata, andjhamar- (Fig. 8). kotra-Sameta, has revealed a succession of rocks Based on the percentage of P2Os content in

Geological Society of America Bulletin, v. 82, p. 2319-2330, 9 figs., August 1971 2319

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TABLE 1. STRATIGRAPHIC SUCCESSION AT UDAIPUR

Lithic quartzite, flaggy quartzite, and current-bedded orthoquartzite UDAIPUR FORMATION Sandy phyllite, graywacke, and "wild flysch" Sandy phyllite, calcareous phyllite, biotite schist, and carbon phyllite

Orthoquartzite, brecciated calcareous o quartzite, marble, and carbon phyllite et CD Impure marble, dolomitic limestone with rolled and rewashed fragmental phosphorite with biohermal phosphorite MATOON FORMATION Sandy phyllite and schist Orthoquartzite, brecciated quartzite, dolomite, marble, rolled fragmental phosphorite, and biohermal phosphorite Impure marble, carbon phyllite with small specks of garnet and manganiferous dolomite intruded by post-Aravalli(?) aplo-granite

Buff to reddish-brown orthoquartzite with intercalated phyllite and chlorite schist DEBARI FORMATION Metaconglomerate and petromictic arkose Meta-arkose Metaconglomerate and fel spathic quartzite -Local Shears- •Faults

Banded Gneissic Complex Gneisses, granites, mica schist, marble, dolomite, and quartzite (Bhilwara Group)

the rock, three main groups of phosphorites can northern part of Matoon, Dakan Kotra, Nee- be differentiated: much Mata, and Badgaon deposits are of this A. Very rich phosphorite with PiO^ content type. varying between 35 and 37 percent. This type is found in a. major part of the Jhamarkotra and LITHOLOGIC SETTING OF ARAVALLI Sameta deposits. PHOSPHORITES B. Rich phosphorite with P2O? content The lithological setting, structure, and distri- varying between 25 and 35 percent. A major bution of various phosphorite deposits of Udai- part of Jhamarkotra, Matoon, and Kharbaria Ka pur district are illustrated in Figures 1 and 2. Gurha deposits are of this type. The Neemuch Mata and Badgaon deposits oc- C. Poor phosphorite with PzOs content cur in a younger horizon than that of the others. varying from 10 to 25 percent. The Kanpur, In the Matoon hill (Fig. 2), the phosphorite

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bed pinches and swells along the strike of the tional nature of phosphorite-quartzite contact formation. The richest portion of the deposit represented by a 20-m-thick zone of admixed ( > 30 percent ?2O5) is confined to the central pebbly rocks, can be very clearly seen in the part of the arcuate hill and is composed of brec- various adits driven into the Matoon hill by the ciated, conglomeritic, and pelletal phosphorite, Geological Survey of India. The phosphorite gradually becoming fine grained and stromato- bed dips 50° to 70° toward the west, conforma- litic toward both the north and the south. Cur- ble with the inclination of the country rock. rent-bedded orthoquartzite underlies the In the Kanpur area, the phosphorite is phosphorite and is laterally replaced by dolo- confined to the dolomitic columns of Minjaria mite and current-bedded dolocalcarenite in the and Collenia. The broad structure is a doubly northern part of the deposit (Fig. 2). The transi- plunging antiform with two smaller synforms.

GEOLOGICAL MAP OF ARAVALLIS NEAR UDAIPUR. RAJASTHAN

Based on Heron (1953) D.M. Boner Jee Figure 1. Geological map of the Aravallis near Udai- thoquartzite; (5) sandy phyllite and biotite schist; (6) pur, Rajasthan, based on Heron (1953) and modified by arkose and metaconglomerate; (7) gneisses, granites, the author. The insert shows the location of the area in quartzites, and basic rocks; (8) aplitic granite (position India. (1) Phyllite and graywacke; (2) dolomite and lime- controversial); (9) dip of bedding; (10) vertical bedding; stone with phosphorite; (3) carbon phyllite; (4) or- (11) fault.

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D.M. Bonerjee

Figure 2. Detailed geological map of three phos- and ripple-creased orthoquartzite; (5) brecciated quartz- phorite deposits near Udaipur, Rajasthan, India, based ite and silicified phyllite; (6) phosphorite; (7) carbona- on the author's systematic mapping: (1) dolomite, lime- ceous phyllite; (8) dip of bedding; (9) vertical bedding; stone, and marble; (2) current-bedded calcarenite and (10) foliation with dip; (11) joint; (12) fold axis with calcareous grit; (3) sandy phyllite; (4) current-bedded plunge; (13) fault; (14) inferred contacts. The phosphorite-bearing stromatolitic beds be the folded extension of the Matoon deposit. have been folded along with the country rock, In Dakan Kotra, the stromatolitic phosphor- and therefore roughly follow the trace of the ites are associated with siliceous dolomite and major fold. While the phosphatic material is occur close to a vast gneissic mass. A thin or- concentrated in the algal columns, the inter- thoquartzite bed occurs discontinuously below columnar spaces are mainly dolomitic (Figs. 5, the phosphorite. Toward the west, the sandy 9). Medium-grained orthoquartzite underlies phyllite occurring above the phosphorite the phosphorite-bearing beds in the east and is grades into a graywacke type of rock. overlain by sandy phyllite in the west. Near Jhamarkotra and Sameta, the lentiform The Kharbaria Ka Gurha deposit appears to phosphorite-bearing horizon extends for more

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than 16 km in length, with thickness varying from 1 to 25 m. Since it is the southern extension of the Matoon deposit, the lithological setting is similar. The deposit forms a broad arcuate belt that is bordered on the southern side by the craton of the Banded Gneissic Com- plex. A very thick orthoquartzite and cherty rock underlie the phosphorite, and impure dolomite overrides them. The significant fea- tures of this deposit are: 1. The columnar stromatolitic phosphorites and layered stromatolitic variety occur at the two extremes of the belt, while the central portion is made up of reworked, conglomeritic, and brecciated phosphorite containing angular and rounded fragments of algal stromatolites. 2. The columnar algal phosphorites are de- formed and display elliptical tops aligned in an east-west direction. The Neemuch Mata-Badgaon-Sisarma belt is located west of Udaipur adjacent to Pichola and Fatehsagar Lakes and extends as discontinu- ous beds in dolomites for more than 5 km. The dolomitic stromatolite-bearing phosphorite grades laterally into quartzose rocks. These Figure 3. Tops of stromatolitic columns showing deposits are located on the margins of a huge concentration of phosphatic materials (darker parts) granitic mass. near the wall margins and along the laminae of the in- dividual column. Locality: Neemuch Mata deposit. SIGNIFICANCE OF STROMATOLITE-PHOSPHORITE ASSOCIATION These Precambrian Aravalli phosphorites are closely associated with the stromatolites Col- lenia, Baicalia, and Minjaria (Banerjee, 197 la, 1971b; see also Figs. 3, 4, 5), and it is therefore tempting to suggest genetic connection of phosphorite with the stromatolites. It is well known now that the stromatolites were formed by benthonic algae occurring in shallow waters in sublittoral to littoral environments. Collenia and Oncolites have been reported from the phosphorite-bearing Sinian rocks of China and in Figure 4. Laminated algal phosphorite (Collenia sp.) some parts of the U.S.S.R. (Bushinskii, 1964, showing broad open laminated structure with concentration of phosphatic minerals (dark) in the laminae. 1969; 1970, personal commun.). Singh (1969) Lighter shades are dolomite. Locality: Dakan Kotra and Valdiya (1969a) have recorded phosphor- deposit. ite-dolomite association in stromatolite-bearing horizons of Gangolihat Dolomite Formation of sociated with clastic arenaceous dolomite and the Calc Zone of Pithoragarh, which has been are almost always underlain by orthoquartzite. correlated with the Middle Ripheans of the Rocks of the Debari Formation and the Udai- U.S.S.R. and Sinians of China (Valdiya, pur Formation are devoid of any phosphorite- 1969b). bearing horizon. In the Matoon and Jhamarkotra areas, manganiferous limestone ASSOCIATION OF DETRITAL and quartzite, dolomite, slate, and calcareous DOLOMITE, ORTHOQUARTZITE, phyllite commonly occur below, above, and AND CARBONACEOUS PHYLLITE within the phosphorite beds. The close prox- These phosphorites are characteristically as- imity of marine carbonaceous phyllite to the

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Figure 5. Negative print of a thin section of phos- with clastic carbonate and fine quartz (darker hue). phatic Baicalia sp. Phosphorite (lighter tone) alternates

phosphorite horizon of Matoon and Jhamarko- of tourmaline, zircon, and garnet occur as tra is significant. Similar conditions and litho- heavy minerals (Fig. 6). logical association have been noted by The stromatolitic phosphorite is composed of Bushinskii (1969) in all the rich phosphorite- angular, elongated to wedge-shaped fragments bearing beds of Karatau and Kunyang in the of stromatolites (0.1 to 2 mm) which are par- U.S.S.R. and Tien Shan ranges of the U.S.S.R. tially replaced by cellophane, francolite, or da- and China, except that the algal remains occur hallite, which occur in a matrix of crystalline only rarely in these deposits. carbonates with minor amounts of subangular to subrounded quartz grains and very little PETROGRAPHY OF PHOSPHORITE clayey material. The algal fragments are par- tially made up of and also replaced by phos- The term "cellophane" has been used here phatic minerals. Quartz pellets are also noted. to describe the crypto and microcrystalline apatite of variable composition. Cellophane (8 to CHEMICAL COMPOSITION 18 ju,), quartz (0.29 to 0.009 mm), dolomite Chemical analyses of phosphorite samples (1.76 to 0.38 mm), calcite (1.18 to 0.30 mm), from Aravallis are given in Table 2. The ana- dolomicrite (0.05 to 0.006 mm), and clays are lyses were carried out in various laboratories the principal mineral constituents of phosphor- under different analytical conditions; therefore ite of Udaipur. Quartz is the dominant gangue not all of the components can be compared. mineral in fragmental phosphorite, while cal- The F:P2O5 ratio is variable. In the majority of cite and dolomite constitute the chief gangue in cases, the ratio tends to be low. This lower the stromatolitic phosphorites. Carbonaceous value is possibly due to analytical error or may matter is commonly present, but the amount is be due to substitution of other anions and OH less than 1 percent in certain varieties of phos- for F. Chlorine content is generally low, and it phorite from Matoon. Secondary limonite and is absent in many samples. X-ray studies have limonitized pyrite occur sporadically in Matoon indicated that the most common mineral is car- and Jhamarkotra phosphorites. Rounded grains bonate fluorapatite. X-ray and infra-red studies

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Figure 6. Negative print of a thin section of phos- (very dark tone) fills a fracture plane on the lower right phorite from Matoon. A complete hexagonal crystal of side. Other phosphatic minerals occur as ovules, sub- fluorapatite on the right side is for the most part re- rounded fragments, and small poorly developed hexa- placed by carbonates (darker tones). Secondary quartz gonal sections.

of Kanpur and Matoon samples (Chowdhury appear to be related to facies changes of argilla- and others, 1968) has shown that the strontium ceous and silico-argillaceous shale and phyllite occurs as SrSO4 and that free calcite and quartz into dolomite or orthoquartzite; these strata ap- are present. These authors have concluded that pear to have been deposited close to the area of the phosphatic minerals are formed as a result abrupt shallowing of the basin. This period of of substitution of carbonate and hydroxyl shallowing was accompanied by the formation groups in the fluorapatite lattice. Carbonate and of intraformational conglomerate and breccia oxides of manganese occur sporadically in brec- composed of rounded pebbles and angular ciated brown limonitized quartzite and phyllite. fragments of stromatolitic phosphorite, quartz- Manganiferous sediments are also interbedded ite, and occasional dolomite. The basis of this with the phosphorite. They occur also as fillings postulation of abrupt shallowing is the occur- in the fracture planes of hard massive phosphor- rence of load-casted, convolutely laminated, ites of Matoon. It was noticed that increase of shaly horizon superimposed directly over the the manganese content in the neighboring sedi- current-bedded, pebbly orthoquartzites, fol- ments has served as an indicator for the pres- lowed by algal dolomitic phosphorite. Presence ence of phosphorite. Aravalli phosphorites are of these benthonic calcareous algae clearly indi- characteristically inactive as evident from radi- cate a shallow to very shallow condition. Occur- oactivity measurements; these deposits demon- rence of quartzite and phosphorite pebbles and strate a sharp contrast with most of the other large-scale cross bedding indicate wave move- deposits of the world. It is interesting to note ments at the site of deposition. Paleocurrent that workable deposits of uranium at Umra and studies by the author have suggested a uni- Udaisagar occur in carbonaceous phyllite, only formly westerly current direction. Imperfect a few kilometers from the Matoon and Jhamar- orientation of elongate grains suggest deposi- kotra deposits. tion of the phosphatic particles by currents, ENVIRONMENT OF DEPOSITION since the orientation produced by postdeposi- tional processes, such as compaction, would be The phosphorite-bearing strata of Udaipur more uniform. Facies changes of phosphorite

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TABLE 2. CHEMICAL ANALYSIS OF PRECAMBRIAN PHOSPHORITES OF UDAIPUR, RAJASTHAN

Locality No. 'A SiO, CaO MgO C02 F Cl sos L.O.I. Mois- C02 F Al^ ture

Ma toon 1. 26.12 20.93 3.02 40.28 4.03 2.01 - 0.39 0.07 0.15 0.07 deposit 2. 35.46 10.56 1.18 47.75 0.28 0.94 1.60 tr 0.21 1.66 0.02 0.04 -- -_ 3. 28.60 17.50 2.79 43.80 3.32 1.55 - 2.40 5.8__9 0.11 0.04 4. 35.62 12.30 1.53 29.35 __ 8.10 1.71 - 0.03 __ 0.22 0.04 5. 31.60 12.65 2.72 46.74 -- 1.26 1.85 — 1.68 1.95 0.11 0.04 0.059 6. 29.35 17.89 3.58 42.89 — 3.30 1.85 — 0.30 4.42 1.35 0.11 0.06

Kanpur 7. 12.66 8.20 0.90 39.60 9.65 24.77 1.65 tr 0.21 27.32 __ 1.95 0.13 deposit 8. 20.57 3.60 2.36 43.50 7.77 20.05 0.85 - __ 20.45 0.09 0.09 0.04 9. 13.81 1.26 1.98 43.25 8.30 28.41 0.75 — — 28.59 0.08 2.05 0.05

Jhamar- 10. 37/21 3.02 1.25 53.36 1.46 2.03 — 1.80 2.4 0.3 0.03 0.05 Kotra 11. 19.50 2.20 4.28 43.80 6.20 20.85 1.50 — — 22.79 1.87 1.07 0.07 deposit 12. 37.32 2.63 1.48 53.56 1.80 4.50 -- not call:ulated 0.12 — 13. 35.63 3.85 2.86 51.29 1.66 3.90 2.04 - 0.04 5.76 0.08 0.10 0.05

Neemuch-Mata 14. 12.50 24.81 4.85 33.75 4.42 16.80 1.50 - 1.18 17.17 0.28 1.3 0.12

Sisarma 15. 3.86 26.75 0.98 26.74 11.17 28.85 0.72 — - 29.56 0.06 0.13 0.19

Dakan Kotra 16. 5.08 7.73 0.30 39.34 9.83 23.60 0.73 - ~ 0.22 0.05 4.6 0.14

Kharbaria 17. 26.79 14.73 1.03 46.00 1.00 9.10 1.32 — 0.10 0.05 0.34 0.05 ka Gurha

Nos. 1. and 7. Muktinath and others (1969); Nos. 2. and 3. Muktinath (1969, Geol. Survey India Rept.); No. 4. Banerjee (1970); Nos. 5, 6, 8, 9, 10, 11, 14, 15. Adhia (1969); No. 12. Sethi (1969); No. 13. Banerjee (1970); Nos. 16, 17. Muktinath and others (1969).

with quartzose rocks also indicate shallow- Aravallis were not totally related to marine water conditions. transgressions, but coincided in major part with Reworking of the phosphorite and quartzite the intraformational lacunae, which were con- is indicated by irregular orientation of the algal nected with the evidences of shallow basin ac- fragments and quartzite pebbles, which indi- cumulations. cates a high-energy movement of water in a shallow environment. A high-energy condition ROLE OF ALGAL STROMATOLITES is also evident from the predominance of sand- IN THE FORMATION OF sized quartz grains and the near absence of PHOSPHORITES clayey matter in the majority of phosphorite Sedimentological evidence presented above samples. Slump breccia of chert and phosphor- clearly demonstrates that the basin of phosphorite indicate the presence of submarine relief ite accumulation was indeed a shallow one. This and gliding over the paleoslope. was indicated by the occurrence of algal phos- Occurrences of lacunae in the sedimentation phorite and also nonphosphatic Collenia, and is indicated by a sharp decrease in thickness and the like, in all of the deposits of Udaipur. Logan even wedging out of the phosphorite beds in and others (1964) and Monty (1965) are of the the direction of strike. These phosphorites ap- opinion that the algal stromatolites are charac- pear to have been formed in a somewhat re- teristic of the intertidal and shallow sublittoral stricted basin of deposition, occupying arms of zones. It was suggested by Charles (1953), pre-existing seas and perhaps developed on the based on the experimental work of Riviere neritic shelf areas of the Aravalli geosyncline. (1941), that the accumulation of phosphorus The older Precambrian gneissic basement com- on the sea floor by flourishing benthonic algal plex would have provided a land area from growth might cause phosphorite formation in which phosphorus was chemically eroded and the euphotic zone. Ubiquitous occurrence of transported into the adjacent sea. Along the benthonic phosphatic algal stromatolites in all shallow regions of the sea, algal stromatolites, of the phosphorite deposits of Udaipur clearly growing luxuriantly in a warm sunny environ- indicates that the phosphorus accumulation was ment, were perhaps instrumental in trapping restricted to the zone of photosynthesis. A sig- and precipitating the dissolved inorganic phos- nificant aspect of this association is that only the phorus from the sea water. algal stromatolitic columns are markedly phos- All of these factors indicate that the forma- phatic (Fig. 9), the intercolumnar spaces are tion of rich layers of bedded phosphorites of always made up of nonphosphatic dolomite.

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Figure 7, Photomicrograph of a reworked fragmen- regular broken fragments set in a clastic carbonate ma- tal phosphorite. Phosphatic minerals (darker tone) are trix. Fractures are filled with dolomite and quartz and fractured and occur as crude hexagonal forms and ir- chert. Crossed nicols.

The laminated form of the phosphorite also in- Another significant aspect of this association dicates concentration of phosphatic minerals is that the form and nature of the stromatolitic only in the laminar parts of the broadly lami- laminae were controlling factors in phosphate nated stromatolites (Fig. 4). The fragmental accumulation. Collenia columnaris, with little or stromatolites occur as angular to rounded no intercolumnar spaces, tight packing, and nodular bodies amidst nonphosphatic to weakly stout growth, did not favor the precipitation of phosphatic dolomitic limestone. Fragmental phosphatic material; however, the assemblage phosphoritic stromatolite cemented by the of Baicalia, Minjaria, Collenia symmetrica, and cherty and quartzose material (Figs. 7, 8, 9) the like, with very large intercolumnar spaces, indicates fragmentation and brecciation of branching stems, and sparsely arranged highly columnar stromatolites by wave action, and convex laminae, served as ideal hosts for the subsequent recementation in situ by siliceous phosphatic sediments (Banerjee, 197 la, solutions. The possibility of biogenic origin of 1971b). silica cannot be ruled out. Brecciation of Luxuriant growth of photosynthesizing algal stromatolitic phosphorite may also have been stromatolites in the shallow waters might have caused by the removal of the calcareous matrix depleted the basinal water with CO 2 content, by connate waters, resulting in the collapse and which would cause increase of pH of the water, fragmentation of the phosphatized stromatolitic resulting in precipitation of carbonate minerals. columns. In waters saturated with CaCOs and P ions, a

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co-precipitation of carbonate and phosphate will take place with increasing pH. Ames (1959) suggested that phosphate reaction with calcite was commonly a replacement process with good structure duplications. The process was presumably one of an exchange of a phosphate ion for a carbonate radical brought about by molecular diffusion. Stromatolitic voids were lined with phosphates and the original carbonate was removed by solution (Fig. 5). Massive-bedded phosphorites associated with the stromatolitic variety appear to have originated during simultaneous sedimentation of pelitic and phosphatic sediments. It is possi- ble that at a later date some of the phosphatic material was differentiated from the sedimentary pile and formed isolated phosphatic nodules, which occur as disseminated phosphorite in a dolomitic or pelitic matrix. ACKNOWLEDGMENTS I am thankful to S. P. Nautiyal and Muk- tinath for giving me the opportunity to work in the Aravalli ranges of Rajasthan and to V. N. Sam, S. L. Mehra, and V. K. Agarwal for help during the course of field investigations. To A. G. Jhingran, I owe my gratitude for providing laboratory facilities for me. I am also grateful to K. S. Valdiya for critically reading the manuscript and for making many valuable sugges- Figure 8. Negative princ of a thin section of a disseminated and nodular phosphorite. Left half of the tions. print shows the composition of the matrix as microcrystalline dolomite and clastic quartz (darker tone). On the right side, there are the phosphatic minerals occurring as rounded to subrounded fragments, ovules and pellets. REFERENCES CITED

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