Precambrian Stromatolitic Phosphorites of Udaipur, Rajasthan, India
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D. M. BANERJEE Department of Geology. University of Delhi, Delhi-7, India Precambrian Stromatolitic Phosphorites of Udaipur, Rajasthan, 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) phosphor- ite 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 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/82/8/2319/3443454/i0016-7606-82-8-2319.pdf by guest on 27 September 2021 2320 D. M. BANERJEE—PRECAMBRIAN PHOSPHORITES, INDIA 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 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/82/8/2319/3443454/i0016-7606-82-8-2319.pdf by guest on 27 September 2021 LITHOLOGIC SETTING OF ARAVALLI PHOSPHORITES 2321 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. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/82/8/2319/3443454/i0016-7606-82-8-2319.pdf by guest on 27 September 2021 2322 D. M. BANERJEE—PRECAMBRIAN PHOSPHORITES, INDIA 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 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/82/8/2319/3443454/i0016-7606-82-8-2319.pdf by guest on 27 September 2021