On the Occurrence and Mineralogy of the Manganese Ore Bodies of Eklingji, Udaipur District, Rajasthan

ON THE OCCURRENCE AND MINERALOGY OF THE MANGANESE ORE BODIES OF EKLINGJI, UDAIPUR DISTRICT, RAJASTHAN

BY M. A. KHAN (Department of Geology, Aligarh Muslim University, Aligarh) Received April 11, 1964 (Communicatedby ProfessorL. Rarna Rao, F.A.SC.) ABSTRACT The occurrence of manganese ore det3osits of Eklingji, a locality situated about 14 miles NNE of Udaipur Town, is recorded here for the first time. The country rocks in which the ores occur are Aravalli phyllite, quartzite and limestone striking NE-SW to N-S. Workable ores are generally found occupying the joints, bedding planes and breceiated portions of the country rocks. There are also some instances of concentration of ores in pockets and cavities within the host rocks. Hard and massive ores are more common than soft and powdery ores. Generally the ores are fovnd in botryoidal, mamillated and various other forms usually having colloform bandings. Ore-microscopic study of the ores revealed the presence of cryptomelane, manganite and pyrolusite. Often the ores have concentric or linear banded texture of colloidal origin. Crystalline pyrolusite (polianite) and manganite either occupy vugs and small cavities within colloform ores or are radially arranged on their surfaces. The paragenetic sequence of the ore-minerals has been suggested on the basis of their textural relationship. The origin of the ore-minerals has been attributed to solidification and crystallization of a colloidal manganese 'gel' that mineralised the country rocks along planes of weakness at a low temperature. INTRODUCTION THE material, on which this paper is based, was collected by the author recently from a few localities close to Eklingji (24 ° 45':73 ° 43'), Udaipur District, Rajasthan. The area forms a part of the topographical sheet No. 45H/10.

Eklingji is situated about 14 miles NNE of Udaipur on way to Nathdwara and Ajmer. B7 155 156 M.A. KHAN

Heron (1953) in his report on the geology of Central Rajasthan has described the occurrence of Alwar quartzites and grits of Delhi system over- lying Aravalli phyllites and quartzites from near Eklingji. He suspected a faulted zone extending from Udaipur City (24 ° 35':73 ° 41') up to Eklingji on the north. Most of the manganese ores of the area under investigation, are associated intimately with a brecciated rock composed largely of fractured quartzites and vein quartz which extend in a N-S direction. B. C. Roy (1957), reporting on the potentialities of the manganese ores of Udaipur, recorded some manganese ore workings from near Udaipur Town and Nathdwara, but none from Eklingji area. There is no previous published work on the occurrence of manganese ores of Eklingji. The present investigation is a part of the detailed work undertaken by the author on the manganese ores of Rajasthan.

OCCURRENCE OF MANGANESE ORES

The area under consideration, includes three localities just south of Eklingji, viz., Chhoti Hat (24 ° 42': 73 ° 43'), Bari Har (24 ° 43':73 ° 44') and Nagda (24 ° 44' : 73 ° 43'), where there are several small workings of manganese ore, all of which were found associated with AravaUi pl~yllite, qu~tzite and limestone trending N-S (Text-Fig. 1.)

Locwr,,o.v op ~vE ~KLs, v6.,,S MAHL~ANES~ owe ~rmos UD ,wIS~ U R RRJA~ THAH

7"0 V~Iv~

TExT.FIo. 1. Occurrence and Mineralogy of Manganese Ore Bodies of Eklingji 157 Chhoti 1-Iar In Chhoti Har, which is about 4 miles south-east of Eklingji, the manganese ores occur mostly on hill tops and slopes in association with cherty quartzite and limestone striking NE-SW. Some of the quartzite outcrops show well-preserved ripple marks. The ores were found distributed sporadi- cally along fractures, joints and bedding planes of the country rocks. A kind of network ore having innumerable unreplaced fragments of brecciated quartzite is of common occurrence (P1. IX, Fig. 1). The deeper workings have a greater concentration of better quality of ores, mostly in the form of lense s and narrow elongated bodies of different sizes, disposed both along and across the strike of the host rocks. Generally the ores are hard, massive and compact. There are four quarries in the area, the largest of which measures 200' x 200' × 20'. Bari Har Several small trial pits and trenches have been sunk on ridge slopes and hillocks just north of Bari Har, the biggest one being 100' x 40' x 45'. The country rock is quartzite striking NE-SW. Here the manganese ores generally occupy small pockets and cavities within the quartzite. There are also some instances of partial replacement of the host rock by manganese ore. Generally the ores are soft, massive and powdery. Yellow and red ochres were seen in frequent association with the softer manganese ores.

Nagda The ore workings of Nagda are in the form of several small trenches and pits, sunk on the western slopes of the hillocks facing Nagda which is about one mile S-W of Eklingji. The manganiferous rocks of this locality appears to be at least 3 miles long and 2 miles wide. The biggest quarry in the area is about 70',x20'x 30'. The manganese ores are associated with quartzite, phyllite and limestone striking more or less N-S, and dipping almost vertically. The host rocks are locally mineralized largely along their bedding planes, joints and fissures. There are also some instances of concentration of ores in small pockets and cavities within the country rocks.

MINERALOGY OF THE ORES The ores are composed largely of cryptomelane and pyrolusite with some wad and most of them exhibit mamillary, botryoidal and often stalactitic forms. Crystalline pyrolusite (polianite) and manganite arc subordinate in amount. 156 M.A. KHAN

The ore-microscopic study of carefully selected polished sections of manganese ores from tke different workings of the Eklingji area revealed the presence of the following manganese minerals : Cryptomelane, Pyrolusite and Manganite. Cryptomelane Cryptomelane constitutes the bulk of the manganese ore-minerals of the area under investigation. It occurs as hard, compact and massive mineral, commonly in various colloform masses such as mamillary, botryoidal, kidney-shaped, etc., along with some crystalline pyrolusite and manganite. Some cryptomelane also occurs in finely acicular form. The colour of the mineral under reflected polarized light is greyish-white to bluish-grey. Reflecting power is moderate. Pleochroism is distinct. Anisotropism is fairly strong in shades of grey. Etch reactions : Positive: HNO8 .. Stains light brown HCI .. .. Stains permanent brown H~O~ + H2SO4 .. Turns sooty black SnCI~ (Sat.) .. Blackens Negative: H2SO4, KCN, KOH, etc.

Note.--Work is in progress to confirm the identification of this mineral as Cryptomelane by X-ray studies. Pyrolusite Pyrolusite is next to cryptomelane in abundance. It occurs in massive as well as in crystalline (polianite) forms. The massive pyrolusite is generally associated with colloform cryptomelane and occurs as linear bands or con- centrie rings alternating with the, latter, It was also seen filling shrinkage cracks in some colloform ores. Crystalline pyrolusite occurs either in micro-vugs in colloform ores or on their surfaces in a radiating pattern. Generally, the pyrolusite crystals are coarse-grained and euhedral in form having well-developed cleavage. In reflected light, colour of the mineral is white with a yellow tint to grey white. Reflectivity power is moderately high. Anisotropism is strong in yellowish-brown and grey colours. Pleochroism is distinct in oil, greyish- white to pale yellowish-white. Prismatic cleavage (one set) is well developed, Occurrence and Mineralogy of Manganese Ore Bodies of Eklingji 159

Etch reactions : Positive: H20~ .... Effervesces, no stain H~O~ + H~SO4 .. Etches black SnCI~ (Sat.) .. Turns black instantaneously Negative : HCI, HNOa, KOH, KCN, etc. Manganite Manganite is intimately associated with crystalline pyrolusite and in a large majority of cases, it has suffered pseudomorphic alteration into the latter. In partly altered manganite crystals, pyrolusite was seen replacing the former along their cleavage planes. Manganite occurs in prismatic 'crystal aggregates lining the boundaries of colloform ores along with pyrolusite. Under reflected light the colour is dark grey to dark brownish-grey. It is strongly anisotropie in shades of bluish-grey eolours and moderately pleo- chroie from greyish-white to brownish-grey. Reflecting power is low. One- directional prismatic cleavage is often seen in the coarser needles.

Etch reactions: Positive: HC1 (cone.) .. Produces etch cleavage H20~ + H~SO4 .. Darkens slightly SnC12 (Sat.) .. Etches heavily and corrodes the grains Negative : HNOs, HzO2, KOH, KCN, etc.

TEXTURAL RELATIONSHIP OF THE ORE MINERALS AND THEIR PARAGENESIS The manganese ores of the area under review, are formed largely of colloform cryptomelane and pyrolusite with some colloidal silica. Crystalline pyrolusite (polianite) and manganite are subordinate in amount. Most of the colloform varieties of ores are characterised by their distinctly banded texture. The colloform banding is either concentric or linear. In some ores the thinly laminated colloform bands with sharply contrasting colours are very prominent (P1. IX, Fig. 2). These lineally banded ores are generally bounded by laths of pyrolusite and manganite, developed perpendicular to their free surfaces. The concentrically banded ores (P1. IX, Fig. 3) are, however, more prevalent than the ores having linear bands. Often veins of p)'rolusit¢ 160 M.A. KHAN

follow the shrinkage cracks in colloform ores. Manganite and pyrolusite generally occur together as crystalline aggregates occupying vugs or cavities in colloform ores or radiating from their outermost surfaces (PI. IX, Fig. 4). Manganite has been replaced pseudomorphically by pyrolusite to a considerable ~xtent. From their textural study it appears that ;most of the ore-minerals origi- nated from a low temperature colloidal gel of manganese which, after solidification and crystallization, deposited almost contemporaneously cryptomelane ~nd pyrolusite in various colloidal forms and also the crystalline manganite and pyrolusite (polianite) as acicular and lath-shaped crystals in the vugs and cavities or on the younger surface of the massive minerals (see Edwards, 1960). Therefore, the formation of the two crystalline ore-minerals apparently continued slightly beyond that of the colloform minerals (see Roy, S., 1961). On the basis of the above discussion, the paragenetic sequence of the ore-minerals of the Eklingji area is suggested as follows: 1. Colloform cryptomelane and pyrolusite. 2. Manganite. 3. Pyrolusite (polianite).

CONCLUSION The manganeseores of Eklingji are closelycomparable to those of several other localities around Udaipur such as Debari, Kanpur, Panda, Lakawas and Nathdwara, described by B. C. Roy 0957), as far as their physical characters and mode of occurrence are concerned. There is adequate evi- dence to believe that the ore-bearing solutions oT manganese attacked the country rocks largely along their planes of weakness such as joints, fractures, bedding planes, brecciated zones, etc., in the post-Aravalli times. To some extent the host rock is also mineralisedas a result of metasomatic replacement by manganese ores, which are generallyfound in the form of lenticular or irregular replacementbodies. The ores are, therefore, of secondary origin. However, the original source of the ore-solutioncannot be ascertained before a detailed survey of the country around all the manganesedeposits of Udaipur ig made. ACKNOWLEDGEMENT

The author is greatly indebted to Dr. S. H. Rasul, ph.D., F.G.S., Atigarh Muslim University, Aligarh, for his kind guidance, valuable suggestions and going through the manuscript. The author acknowledges 3I. A. Khan Proc. Ind, Acad. Sci,, B, Vol. LX, PI. IX

FIGS. 1-4 Occurrence and Mineralogy of Manganese Ore Bodies of Eklingji 161 with gratitude the facilities and help provided by Professor G. V. Damle, Head of the Geology Department, M.B. College, Udaipur, and Shri L. N. Panday, a manganese ownor working in the area, during his fieldwork.

REFERENCES

Edwards, A. B. .. Textures of the Ore Minerals and Their Significance, Mel- bourne, Australia, 1960, pp. 20-21. Heron, A. M. .. "The Geology of Central Rajputana," Mem. GeoL Surv. Ind., 1953, 79, 302-08. Roy, B. C. .. "The manganese ore deposits in Udaipur and Banswara, Rajasthan," Bull. Geol. Surv. Ind., 1957, Series A, No. 14. Roy, S. .. "Mineralogy, texture and paragenesis of the manganese ores of Gumgaon-Ramdongri mine area, Nagpur District, Maharashtra, India," Proc. Nat. Inst. Sci. Ind., 1961, 27A (2), 113. Schouten, C. .. Determination Tables for Ore Minerals, New York, 1962. Short, M. N. .. "Microscopic determination of the ore-minerals," Bull. Geol. Sum., U.S. Department of Interior, U.S.A., 1940, No. 914.

EXPLANATION OF PLATE ]X

FIG. 1. A hand specimen of manganese ore showing some unreplaced fragments of brecciated quartzite, × about ½ nat. size. Fro. 2. Polished section of manganese ore exhibiting linear colloform bands of ore-minerals and gangue, × about 3 nat. size. Fro. 3. Polished section of concentrically banded ore of manganese, × 14. FxG. 4. Polished section of colloform manganese ore in which pyrolusite and manganit¢ crystals radiate from its free surface, × 14.