FULLERENES IN MID PROTEROZOIC CUDDAPAH BASIN, INDIA

FULLERENES IN MID PROTEROZOIC CUDDAPAH BASIN, INDIA

Synopsis

Background:

The ~2.0 Ga intra-cratonic crescent shaped Cuddapah Basin is located in the eastern part of the Dharwar Craton and occupies an important place in Indian Geology. It extends over a length of 440 km and trends in NNE-SSW in the north and NNW-SSE in the south through N-S in the middle. It has a maximum width of 145 km in the middle and occupies nearly 44,550 sq.km. The Basin hosts rich deposits of barytes, (vein and bedded), limestone, dolomite, asbestos, basemetals, clay, slates, uranium etc., Diamondiferous, kimberlites, conglomerates, gravels are known from the Basin. Recently methane gas shows are also reported. The recent discovery of the presence of fullerenes in a few black tuff samples from the Mangampeta area of the Cuddapah Basin, analysed at the Stanford University (Sreedhar Murty 2005) added a new dimension to the mineral wealth, of the Cuddapah Basin and called for immediate attention.

What are Fullerenes?

Fullerene is a pure carbon molecule composed of at least 60 atoms of carbon and exhibits a bucky ball structure as shown in Fig.1. The discovery of C60, C70, the carbon cage molecules popularly known as fullerenes, named after the famous Architect, Buckminister Fullerene (Kroto et al 1985), opened new and vast vistas in understanding these curious molecules. The fullerenes, like artificial diamonds, can be synthesized from carbon.

Fullerene Applications:Fullerenes, their derivatives and carbon nano tubes have a number of interesting properties due to their unusual structures and sizes. The size of the individual fullerene molecules makes them ideal building blocks for use in designing molecular units that find application in nanotechnology. The fullerene family of carbon molecules possesses a range of unique properties. A fullerene nano-tube has tensile strength, about 20 times that of high-strength steel alloys, and a density half that of aluminum. Carbon nano-tubes demonstrate superconductive properties, for commercial applications, including computer memory, electronic wires. Fullerenes can be used in the construction of aerospace vehicles because of the substantial performance gains. Its molecular nano-technology improves the existing launch vehicle designs. They are very cost-effective compared to the present materials being used. Several fullerene derivatives have interesting pharmacological properties such as anti-Alzheimers activity. The fullerene family of carbon molecules thus belonging to a unique class of strategic minerals, hold a great promise in a wide spectrum of fields including future micro-electromechanical systems (MEMS), nanotechnology, solar energy technologies, superconductivity, computer memory, aerospace vehicle technology, designing and building of atomically precise programmable machine assemblies that could conceivably adjust to any environmental conditions.

Natural Fullerenes:

Synthesis of fullerene from carbon in the laboratories is complex and expensive, while the reported occurrences of fullerene in nature are rather scanty. The natural fullerenes when they were detected first during early eighties were originally thought to be brought from space since these were found to be constituting an important carrier phase for noble gases in carbonaceous chondrite meteorites. Though the natural fullerenes were thought to be mainly of extra-terrestrial origin, subsequent studies showed their existence in the terrestrial rocks as well. Its first reported occurrence in natural terrestrial rocks was in shungite, a ~2.0 Ga. old Proterozoic Formation from Karelia, Russia, containing highly carbonified carbonaceous matter (Buseck et al 1992). This paved the way for subsequent studies on natural fullerenes (Buseck 2002, Jan Jehlicka et al., 2003, etc.). Fullerenes were reported particularly from those lithologies that experienced high energy events such as lightning (Daly et al 1993), wild fires associated with K-T boundary (Heyman et al 1994 a, b, 1995, 1996, 1998) or meteoritic impacts (Becker et al 1994). Occurrence of fullerenes was also reported from the litho-units corresponding to mass extinction boundaries of the Cretaceous-Triassic boundary event (250m.y) as also from the well-established Cretaceous-Tertiary boundary (65 m.y) corresponding to the Dinosaur extinction period. Similarly, fullerenes were also reported from Triassic-Jurassic (T-J) boundary, volcano-sedimentary sequences, in carbonaceous chondrite meteorites and breccia samples from the meteorite impact craters, in fulgurite in coal samples, and impact craters of NASAs Long Duration Exposure Facility (LDEF) space-craft. In India too, occurrence of fullerene is reported from the Cretaceous rocks at the K-T boundary in Rajasthan and in black tuff samples of the Pullampet Formation Proterozoic Cuddapah Basin. Occurrence of Fullerenes in Cuddapah Basin:

Five black tuff samples from the Mangampeta area of the Cuddapah Basin, analysed at the Stanford University (Sreedhar Murty 2005) indicated presence of C60, C70 and C84, suggesting the presence of naturally occurring fullerenes in this part of the world. Fig.2 shows the location map of fullerene occurrence in the Mangampeta, Cuddapah district, Andhra Pradesh.

Encouraged by such convincing results and realizing the vast application potential of this very important and strategic mineral, the Andhra Pradesh Mineral Development Corporation (APMDC), Government of Andhra Pradesh, has come forward to support further studies in this area under a research project and entrusted the responsibility of executing the same to M/s. Geo Resources and Technologies Private Limited (GRTC).

The main objectives of the project are to ascertain the extent of fullerene occurrence, its nature and distribution, the associated geological and physicochemical conditions, the subsurface model of the investigated area and to visualize a model for the genesis.

Summary of The Work done:

Against the above background the present project was implemented by M/s. GRTC during 2008-2009. Under this programme, integrated geoscientific investigations including geological, geochemical, geophysical studies in the Mangampeta barytes mine were conducted.

Representative rock samples collected were subjected to detailed analysis using different analytical methods like High Performance Liquid Chromotography (HPLC), Mass Spectrometry, X-Ray Diffraction in different laboratories both in India and U.S.A. The results clearly brought out presence of fullerene in several tuff samples examined, in significant quantities, much higher than those reported earlier, from different parts of the world. These results suggest viability of fullerene for exploitation.

Geophysical results have brought out a well defined NW-SE trending linear zone of high electrical conductivity and polarizability cutting across the mining area This is interpreted to be representing a deep fracture zone presumably related to the volcanic activity believed to be responsible for the genesis of the barytes mineralization of this area.

Based on the studies, a model is proposed for the genesis of Fullerene in this area. The model postulates that the volcanic activity, supposed to have been associated with the origin of barytes in the area, played a significant role in creating suitable thermal conditions and environment conducive to the transformation of the existing hydrocarbon material into higher order allotropes of carbon representing the family of Fullerenes.

Alternately the magmatic origin model envisaged for barytes may also hold good for fullerenes as well since the tuff and barytes as also the tuff and fullerenes are intimately associated and formed in, more or less, identical conditions.

Future studies:The study has established the presence of significant amounts of fullerenes C60 as well as C70 in Mangampeta barytes mine. This valuable nano material with its molecular closed case structural arrangement of atoms has very special physical applications including delivering drugs by the Pharmaceutical R&D sector, improving the efficiency of the solar panels and increasing the output of oil in reservoirs. Considering their high market value and their immense application potential, the next phase of the activity is logically related to commercial exploitation of this deposit. Since this is a unique occurrence it automatically gets focus from various quarters of the world and prompts search for possible presence of natural fullerenes in similar geological conditions in A.P, and elsewhere in the country and outside. In order to take advantage of the findings of the present study, it is indeed necessary that the Mangampeta deposit be exploited immediately before the strategic importance of this unique find is diluted or lost.

Accordingly, conversion of the present findings of fullerene into a viable deposit warrants expeditious action and foresight in the form of extensive efforts to extract and evaluate the resource followed by, viability studies including setting up of a pilot plant and then finally entering into exploitation. In view of the non availability of the complex technology and expertise in the country to achieve the above envisaged goals, it becomes imperative to go in for international collaboration.

I. Introduction:

The intracratonic Proterozoic Cuddapah Basin, ~2.0 Ga old, located in the eastern part of the Dharwar Craton (fig.1), occupies an important place in Indian geology and tectonics. The Basin hosts a wide spectrum of rich mineral resources like barytes, asbestos, basemetals, diamond, uranium, limestone, etc., even methane gas shows are also reported in the south western region of the Basin.

Further, recent studies on analysis of rock samples from the Cuddapah Basin have added a new dimension to the mineral wealth, that the Cuddapah Basin holds. Five black tuff samples from the Mangampeta area of the Cuddapah Basin, analysed at the Stanford University (Sreedhar Murty 2005) indicated presence of naturally occurring fullerenes C60, C70 and C84 in this part of the world, which is unique. It is not an isolated occurrence, unlike in the case of several reports from different parts of the world. Encouraged by such convincing results and realizing the vast application potential of this very important and strategic mineral, the Andhra Pradesh Mineral Development Corporation (APMDC), a Government of Andhra Pradesh Enterprise, has come forward to support further studies under a research project and entrusted the responsibility of executing the same to M/s. Geo Resources and Technologies Consultants Private Limited (GRTC), Hyderabad.

The main objectives of the project are to examine the nature, distribution and extent of fullerene occurrence, the associated geological and physicochemical conditions, etc., in the Mangampeta Barytes mine. Accordingly the GRTC has undertaken systematic investigations using integrated geological, geochemical and geophysical studies.

The present efforts under this project thus aim at examining some representative rock samples from this Proterozoic Cuddapah Basin and subject them to systematic analysis for investigation and detection of possible presence of fullerenes. Since some of the institutions like IICT, M/s. Alkali Metals, ILS at the HCU in India and other institutions abroad such as the Stanford University, M/s. NANO-C at Boston, USA, have the required laboratory facilities like the HPLC, Masspectrometry, X-Ray Diffraction, etc., the cooperation of these institutions was sought to conduct analysis on a few rock samples to look for possible presence of fullerene. Besides examining the geological conditions and collecting representative rock samples and carrying out the analysis for presence of fullerene, efforts were also made to conduct geophysical studies in order to understand the subsurface conditions of the study area. Based on such an integrated approach, the present study brought out several positive signatures to show occurrence of natural fullerenes, in the Pullampet sediments of Mangampeta area of the Cuddapah Basin. Fullerene is a pure carbon molecule composed of at least 60 atoms of carbon and exhibits a bucky ball structure as shown in Fig.1. The discovery of C60, C70, the carbon cage molecules popularly known as fullerenes, named after the famous Architect Buckminister Fullerene (Kroto et al 1985), opened new and vast vistas in understanding these curious molecules. The fullerene family of carbon molecules belong to a unique class of strategic minerals that hold a great promise in a wide spectrum of fields including future micro-electromechanical systems (MEMS), nanotechnology, solar energy technology, enhanced oil recovery, superconductivity, computer memory, aerospace vehicle technology, designing and building of atomically precise programmable machine assemblies that could conceivably adjust to any environmental conditions.

The artificial fullerenes, like artificial diamonds, can be synthesized from carbon using elaborate, complicated and expensive techniques. But the natural fullerenes when they were detected during early eighties were originally thought to be brought from space since these were found to be constituting an important carrier phase for noble gases in carbonaceous chondrite meteorites. Though the natural fullerenes were thought to be mainly of extra-terrestrial origin, subsequent studies showed their existence in the terrestrial rocks as well. Fullerene in shungite, a ~2.0 Ga. old Proterozoic formation from Karelia, Russia, containing highly carbonified carbonaceous matter was the first reported occurrence in natural terrestrial rocks (Buseck et al 1992) which paved the way for subsequent studies on natural fullerenes (Buseck 2002, Jan Jehlicka et al., 2003, etc.). Fullerenes were reported particularly from those lithologies that experienced high energy events such as lightning (Daly et al 1993), wild fires associated with K-T boundary (Heyman et al 1994 a, b, 1995, 1996, 1998) or meteoritic impacts (Becker et al 1994). Occurrence of fullerenes was also reported from the litho-units corresponding to mass extinction boundaries of the Cretaceous-Triassic boundary event (250m.y) as also from the well-established Cretaceous-Tertiary boundary (65 m.y) corresponding to the dinosaur extinction period. Similarly, fullerenes were also reported from Triassic-Jurassic (T-J) boundary section of Queen Charolotte Islands, British Columbia, in solid bitumen samples from neo Proterozoic (585 Ma) volcano-sedimentary sequence of the Bohemian Complex in Mitov area of Czech Republic (Jan Jehlicka et al 2003), in carbonaceous chondrite meteorites and breccia samples from the meteorite impact craters like Sudbury in Canada, Gardnos in Norway and Ries in Germany (Elsila et al 2005), in fulgurite in coal samples from China and impact craters of NASAs Long Duration Exposure Facility (LDEF) space-craft.

In India too, there have been a few reports on the occurrence of fullerene - one in the Cretaceous rocks at the K-T boundary in Rajasthan and the other, in black tuff samples of the Proterozoic Cuddapah Basin (Parthasarathy et al 1998, Misra et al 2007, Sreedhar Murthy 2005). Following is a brief account of the Cuddapah basin and that of the Mangampeta baryte mine area where from fullerene was reported.II. Cuddapah Basin:

The Cuddapah Basin (Fig.1) is a crescent shaped mid-Proterozoic Basin and has more than six kilometers thick sedimentary pile and rests over a granite gneiss and schist basement with a profound unconformity. The sedimentary pile is broadly classified into a lower Cuddapah Supergroup and an upper Kurnool Group.

Studies on the geology and tectonics of the Cuddapah Basin were first carried out by King (1872) and are continued by several workers even today, though intermittently. Stratigraphically, the Cuddapah Basin is divided into Papaghni, Chitravathi, Nallamalai Groups and Srisailam Quartzite. The Basin comprises mainly ortho-quartzite-carbonate suite and basic to acid volcanics and sills in the lower part and siliceous shales/tuffs with quartzite interbands in the upper part (Nagaraja Rao et al 1987). Revised strategraphy of the Cuddapah Basin is given in Table I.

Resting unconformably over the Cuddapah sediments, the Kurnool Group sediments are exposed in two isolated tracts, in the central (Nandyal depression) and north-eastern (Palnad depression) parts of the Cuddapah Basin. Both these sub-basins are separated by the Nallamalai rocks and Srisailam plateau. (Fig .1 & 2).

The Cuddapah sediments were laid under quiet and submergence conditions. The craton around the Cuddapah Basin (except in the east) was the source for the Cuddapah (barring the Nallamali Groups) and Kurnool rocks and the Nallamalai Group from the Eastern Ghats terrain.

The Cuddapah Basin has progressively evolved through the formation of a series of sub-basins, viz., the Papaghni and Chitravathi Groups in the western sub-basin, Nallamalai sub-basin in the eastern sub-basin, Srisailam Quartzite in the Srisailam sub-basin and the Kurnool and Palnad Groups in the Kurnool/Palnad sub-basins.

TABLE - I

Revised Stratigraphy of the Cuddapah Basin and

Adjoining Crystallines

(After GSI, 1981 )

Kurnool

sub-basinPalnad

sub-basin

K

U

R

N

O

O

L

G

R

O

U

PNandyal Shale50-100m30- 50m

Koilkuntla Limestone15-50m10-30m

Paniam Quartzite10-35m. 5-40m

----------Regression or Local Disconformity--------

Owk Shale10-15m 3 5m

Narji Limestone100-200m 300-350m

Banganapalli Quartzite10-57m70m

----------------Unconformity----------------------

C

U

D

D

A

P

A

H

S

U

P

E

R

G

R

O

U

P Srisailam Quartzite Iglapenta Quartzite 200m

Tapasipenta Siltstone100m

Krishna Quartzite320 (+) m

----------------Unconformity----------------------

Nallamalai GroupCumbum (Pullampet) Formation-

shale /phyllite, quartzite/dolomite

2000m3500m (+)

Bairenkonda / (Nagari) Quartzite-

quartzite & shale1500/4000m

--------------Disconformity----------------------

Chitravati GroupGandikota Quartzite 1200m Depth to basement at Muddanuru 6000m (+/-)

Tadipatri Formation- shale & tuff, lava flows, sills, etc.,

4600m

Pulivendla Quartzite 1200m

--------------Disconformity----------------------

Papaghni

GroupVempalle Formation-

dolomite and shale with flows Gulcheru Quartzite1500m

--------------Non-conformity----------------------Dharwar crystallinesGranite, Gneiss, Schists, etc.,

Six phases of igneous activity were recognized in the Cuddapah Basin. These are basic volcanism during Vempalle times; basic and acidic volcanism during Tadipatri deposition; dolerite, gabbro and picrite sills during post Tadipatri period; acid volcanism during Pullampet/Cumbum Formation; basic intrusive activity during Nagari Quartzite Formation; and granitic intrusion into the Cumbum Formation along the eastern margin of the Nallamalai Fold Belt (Nagaraja Rao et al 1987). The acid volcanic activity during the Pullampet/Cumbum times, represented by tuffs rich in barium, magnetite are by far the most important from the point of fullerene.

Cuddapah Basin is a north plunging asymmetric synchronism comprising a non-folded western limb and an intensely folded, overturned and thrusted eastern limb (Narayanaswami, 1966). Four morphological sub-basins, concomitant with the depositional sub-basins were recognized. Several linears running for several kilometers in EW, ENEWSW and NW/NNW SE/SSE were identified. Among these, the Chelima-Zangamrajupalle- Mangampeta fracture is considered very significant, as it might have facilitated movement of exhalatives and /or ejection of tuff material rich in barium, etc.

Based on Rb Sr, Sm Nd and Pb Pb isotopic ages the oldest age given to Cuddapah Basin is 2170Ma while the youngest is around 1000 m. y. Lampriotes intrusive into the Cumbum sediments have given an age range between 1090 and 1380Ma. The fullerene bearing tuffs of Mangampeta are, therefore considered older than 1380Ma.

The Cuddapah Basin abounds in a variety of economic minerals and include asbestos, barytes (vein and bedded), basemetals, cement chemical and flux grade limestones, dolomite, clay, slates, uranium, fullerene, etc.

More details on the stratigraphy, sedimentation, basin evolution, igneous activity, structure, geochronology, mineral wealth, etc., of the Cuddapah Basin are given in Appendix-A for better comprehension and understanding.

III. Mangampeta Barytes Field (MBF):

Mangampeta (14 05 ' N : 79 19 'E ) area, being a part of the Nallamalai sub-basin, is located in the southern horn of the Cuddapah Basin (see fig.2), and mainly forms the upper parts of the Pullampet Formation. The world famous barytes deposit of the Mangampeta Barytes Field (MBF) is located at the Mangampeta village and occurs confined to the Pullampet Formation. In the following paragraphs, a semi detailed account of various genetic studies carried out for barytes is given as fullerenes is closely associated with tuffs associated with the barytes.

III.1. Geology: Pullampeta Formation around Mangampeta Barytes Field:

The Pullampet Formation comprises predominantly tuff with interbands of quartzite and dolomite. King included Pullampet Shale as a part of the Cheyair Group and considered it to be older to Bairenkonda Quartzite Formation. But the work by Nagaraja Rao et al (1987), has shown that Pullampet Formation is a part of the Nallamalai Group and overlies the Bairenkonda (Nagari) Quartzite. In the Pullampeta hill range, the Pullampet Formation grades into Cumbum phyllites/slates/shales along the strike and the dip and hence Cumbum and Pullampet Formation are stratigraphically one and the same and are referred to as Cumbum Formation in the northern part and Pullampet Formation in the southern part. Thus, as per the latest classification (GSI 1981), the Pullampet Formation is shown as time equivalent of the Cumbum Formation belonging to the Nallamalai Group.

Studies carried out by Karunakaran (1974 & 1976) and Kurien et al (1976) on the rocks in and around Mangampeta area have brought out volcanogenic nature of the barytes and the associated rocks (mainly black tuff). Extensive field and petrographic studies carried out in the adjacent areas in the strike continuity of the MBF for a length of over 30km has led to the conclusion that a major part of the Pullampet sequence, lithologically described by the earlier workers as shale, quartzite and dolomite with the exception of dolomite, is perhaps volcanogenic. A band of magnetite tuff with silica and carbonate rich flows and bands is recorded from near the base of Pullampet Formation, near Cheyair river valley along Rajampeta - Rayachoti Road (GSI News, 1977).

Detailed field and petrographic studies in the Mangampeta area have led to identification of a predominantly volcanogenic sequence of rocks comprising vitric crystal tuff (tuff) with intercalations of quartz-crystal tuff. In thin sections, the tuffs show fine grained groundmass made up of chlorite and carbonaceous dust. Here tuff refers to a combination of altered glass and crystal (quartz) fragments or a mixed one. The tuff and the associated quartzite beds exhibit excellent sedimentary structures, like graded bedding, ripple marks, cross-bedding, convolute laminations, etc. On the basis of petrographic studies, diverse types of tuff have been identified. These include glass tuff, quartz crystal tuff, quartz pyrite lapilli tuff, barytes lapilli tuff, etc. Interbedded with these tuffs occur flows extremely rich in barium sulphate. The rocks met within the MBF are thus comprised of mixed tuff (mixture of vitric and crystal tuff). Crystal tuff and dolomite with numerous quartz veins cut across all the lithounits. Pyrite is present as thin stringers and small lenses, knots and disseminations and at places it is associated with minor amounts of chalcopyrite.

Tuff:

It is earthy white, cream, buff, purple, gray and black in colour and is thinly bedded and well cleaved. Outcrops are generally weathered and at places they are clayey and ochreous in nature. Pyrite associated with this rock is limonitised in the weathered profile. These rocks are weathered to varying depths depending upon the penetration of the circulating waters. These are weathered to a maximum depth of about 40m. The rock is fine grained and argillaceous. The black colour of the rock is due to the presence of carbon. The specific gravity of this rock varies from 2.4 to 2.9, the weathered tuff being lighter. The rock underwent mild metamorphism of green schist facies and has become slaty.

In thin sections, the rock is extremely fine grained and contains gray to greenish gray argillaceous matrix with angular to sub angular, subhedral to anhedral grains of quartz. Fine acicular grains of sericite are also found admixed with the matrix. At places, quartz grains show dark encrustations, which could be carbon. Plagioclase feldspar, pyrite, tourmaline, zircon are the associated minerals. At places presence of secondary carbonates is recognized. Plagioclase is fine to medium grained, subhedral in shape and is at places highly kaolinised and sericitised. Pyrite grains are anhedral and limonitised. Fibrous rim of quartz is generally present around pyrite grains.

Crystal tuff:

It occurs as interbands within tuff and varies in thickness from less than a centimeter to 50cm. Thicker bands usually occupy tops of linear edges. There are two type of crystal tuff. The predominant one is extremely fine grained, compact, massive and has cherty /flinty appearance and exhibits sub conchoidal fracture. The other type of crystal tuff, relatively less common, is gritty in appearance and consists of medium sized, rounded to sub rounded grains of quartz set in siliceous matrix. At places, it is calcareous and ferruginous. Occasionally it exhibits colour banding suggesting thinly bedded nature. Outcrops are seen in the area north and east of Mangampeta. The rock is traversed by thin veins of quartz. Pyrite occurs as lenses, nodules, clots and disseminations.

Under the microscope the rock comprises angular to sub angular grains of quartz, plagioclase feldspar, sericite, secondary carbonate, pyrite and tourmaline. In general it is fine to medium grained and shows inclusions of fine dust. At places the rock exhibits sutured and embayed margins. Undulose extinction of the quartz grains is common. Occasionally fine grains of barytes and anhedral grains of carbonates are found replacing quartz grains along their periphery. Pyrite is also found to replace both quartz and carbonates. Unidirectional growth of fibrous quartz on secondary pyrite crystals is observed at places. Frosting of quartz grains is observed occasionally. Sub- rounded to elliptical grains of tourmaline are present which at places occur as inclusions within in the quartz grains.

Dolomite:

The rock is gray, extremely fine grained, massive, ramified with irregular veins of quartz, calcite and occasionally barytes. It is cherty and siliceous at places and occurs as lenses and intercalations vary in thickness from about a metre to 10m within the tuff. Outcrops are seen in and around Mangampeta and North West of Rajampeta, etc.

Impure dolomite occurring generally along the fringes of the lenses is flaggy and exhibits crude banding whereas the pure dolomite occurring in the central parts of the dolomite bands is massive. At places the rock is tuffaceous. It is more prevalent in the middle and upper parts of the Pullampet succession. Vein barytes is mostly confined to this rock and mined at places.

In thin section the rock mainly consists of fine, equigranular grains of carbonates (mainly dolomite) and presents a mosaic texture. The grains are usually subhedral to anhedral and at places show sub rhombohedral outline. The associated minerals are quartz, pyrite (mostly limonitised) and feldspar. The rock is frequently traversed by veinlets of quartz and carbonates and rarely barytes. At places the rock carries bands of tuffceous material (fine grained argillaceous material).

III.2. Structure:

The rocks trend in a general NNW-SSE direction with gentle to moderate dips varying from 10 to 30 towards ENE. Variations in strike and reversal of dip due to folding and swerving is common.

Primary structures noticed in the tuff and crystal tuff are ripple marks, current bedding and graded bedding. Stray oscillatory and interference types of ripple marks suggest a current direction from SSW to NNE. Intraformational conglomerate and breccia are seen in dolomite and crystal tuff. Chert nodules, geode fillings and stylolites are seen in crystal tuff and barytes. Penecontemporaneous deformation is not uncommon in tuff and occasionally in barytes.

The rocks are folded into a series of gently plunging anticlines and synclines over NNW-SSE axes plunging at 10 -15 towards NNW. Generally the folds are open and symmetrical type. Another set of folds trending ENE-WSW are represented by gentle and open warps. These folds are found to be progressively more open from west to east. The major folding has resulted in the development of NNW-SSE trending axial plane cleavage in the tuffs. The cleavage plane dips consistently towards ENE at steeper angle than bedding. The beds are generally right side up except at a few places where overturning is seen.

Minor faults of dip-slip type with displacement between 2 to 4 metres are observed. Brecciation, silicification and slicken slide surfaces are the manifestations of the faulting.

In the MBF, the structure of the Northern lens is a cross-folded doubly plunging asymmetrical syncline (Neelakantam 1987). At places the tuff beds are overturned very tightly as seen in the mines. These overturned beds are crossed folded subsequently, lending a cylinder-like appearance at places. Quartz vein/veinlets are found to occupy the dilation zones in the black tuff as could be seen from the figure3.

III.3. Mangampeta Barytes Deposit:

The Mangampeta barytes deposit occurs in the form of two lensoid bodies within the tuff sequence of the Pullampet Formation. Fig.4 shows the location of the Managampeta Barytes mine. The barytes body occurring at Mangampeta village is called Northern lens and is bigger of the two. The other one is located about 700m south of the Northern lens is called Southern lens. From the study of the structural data and lithological variations it is surmised that the Southern lens is a separate body and occurs stratigraphically below the Northern lens.

a) Northern Lens:

The Northern lens occupies an area of about 0.81 sq.km. It is 1220m long and 900m wide. Maximum thickness of barytes is 40m in the central part. It has an overburden of black tuff varying in thickness from 0m to 181m. The Northern lens is estimated to contain a probable reserve of over 74million tonnes of barytes of all grades. It is the single largest and thickest known deposit containing about a quarter of the known barytes reserves of the world (Neelakantam, 1987).

The generalized lithological succession of the beds in the Northern lens is as follows:

Quartz veins, stringers & veinlets of barytes Contains pyrite and chalcopyrites as pods and stringers

Carbonaceous tuff (partly weathered)2 to 180m

Carbonaceous tuff with quartz rosettes/ lapilli0 to 6m

Tuff with quartz and barytes lapilli/rosettes0.2 to 3m

Lapilli/rosette barytes0.23 to 22m

Granular barytes 1.2 to 35m

Carbonaceous tuff2 to 76m

Dolomite with black tuff bands>50m

Alternate gray and black tuff with thin dolomite bands>4 to 15m

Dolomite> 68m

b) Southern Lens:It has a strike length of about 300m and maximum width of 70m with steep dips towards ENE. It has an area extent of 0.0059 sq.km and average thickness of 9.78m (Neelakantam,1987). Barytes from this lens is completely mined out.

Granular, lapilli/rosette, vein and replacement are the four genetic types of barytes found in MBF, the first two being economically significant. Lapilli barytes invariably overlies the granular barytes beds. The granular barytes is a product of exhalative volcanic action and the lapilli/rosette barytes represents the pyroclastic phase of the same volcanism. Vein barytes occurs in the form thin stringers cutting the barytes and tuff beds and is considered to be hydrothermal. Barytes replacing quartz and pyrite grains is observed in thin sections only (Neelakantam, 1987). Generalized geological succession of beds in Southern lens is as follows:

Litho UnitThickness range (m)

Soil0.50 - 2.00

6.Tuff (partly weathered)2.00 - 51.62

5.Tuff with quartz-pyrite lapilli 1.58

4. Tuff with barytes rosettes 4.55

3.Granular barytes 1.15 - 12.38

2. Tuff with barytes rosettes 0.20

1. Carbonaceous tuff > 11.30

c) Major Element analysis:

During the course of detailed exploration for barytes by GSI in Mangampeta area, Neelakantam (1987) analysed several samples of tuff for their major element content. The major element constituents R2O3, Fe2O3, SiO2 and Loss on Ignition (LOI) are in the ranges, 2.27-11.7%, 0.85-7.34%, 04.65-50.85% and 0.73-10.59%, respectively. It is observed that SiO2, R2O3, Fe2O3 and LOI content are higher in tuff than in barytes. It has also been established that there exists an inverse linear relationship between BaSO4 content and each of the major element constituents, thereby suggesting homogenous nature of the tuff material associated with the barytes.

Three samples of black tuff (folded sample-6, S-12 OB (bottom) and S-15 OB-3 were analysed for ascertaining their major element chemistry and their results are shown in Table.2. Results of black and weathered tuffs analysed for the project geochemistry of gray and black tuff overburden on the Mangampeta Barytes deposit are given alongside for comparison. The range of major element constituents in the tuff by GSI is also shown.

Table 2

Major element Chemistry of Black tuff and Weathered tuff

Name of the elementConcentration (ppm)*Samples. S.No. 2,3 and 4 analysed by XRF in IICT, Hyderabad for GRTC

S.No. 5and 6 by Dr.V. Sudarshan, Dept of Applied Geochemistry, Osmania University, Hyderabad

*S-12 OB (bottom)*S-15 OB-3*Folded sample-6Black tuffWeathered tuff

123456

SiO2Al2O3Fe2O359.2

16.7

4.655.7

15.10

5.135.0

22.0

18.863.71

15.05

5.8166.5

16.07

6.83

MgO

CaO

Na2O

K2O6.2

6.6

0.6

4.97.4

10.1

0.5

4.813.9

2.9

0.3

3.23.42

2.58

0.78

3.171.55

0.15

037

3.15

TiO2P2O5MnO

SrO0.6

0.1

-

-0.6

0.2

-

0.01-

1.5

-

-0.45

0.12

0.02

-0.58

0.08

0.06

-

NiO

ZrO20.01

0.050.08

0.040.2

--

--

-

S0.40.51.5--

The above XRF analysis results indicate that the sample Nos. S-12 OB (bottom) and S-15 OB-3 are alumious sediments rich in MgO (6.2 and 7.4 %) and CaO (6.6 and 10.1 %). This is perhaps due to proximity to dolomite material. In fact, these samples could be classified as dolomitic tuff. High concentration silica (55.7 and 59.2 %) is mostly due to presence of quartz. The presence of S (0.4 to 1.5 %) is perhaps due to presence of sulphides. Neelakantam and Kopresa Rao (1980) have established presence of elemental sulphur in the barytes beds underlying the black tuffs.

The XRD analytical results more or less compare well with those of XRF. It may be noted that the analysis of both black tuff and white or weathered tuff compare well, suggesting derivation from the same source. Minor variations in the Fe2O3, MgO, CaO, etc., are due to presence of dolomitic material and /or sulphides.d) Trace Element analysis: Several black and weathered tuff samples were analysed by GSI and Applied Geochemistry Dept., Osmania University for their trace element content and the results are given in Table 3.

Concentration of Cu, Pb, Zn, Co, Ni, Mn, Bi, Sb, Ge are of same order in both weathered and black tuffs, suggesting derivation from the same source. The concentration of Mn, Ni, Co, Cu, V, Zr and Ti are significantly higher than normal background values for similar rocks. Presence of Rb, Ce, La and Li are detected in very low levels. The trace element analysis suggests that weathered and black tuffs are one and the same and the former resulted from the surface weathering and alteration of the latter. Higher than normal background values of Mn, Ni, Co, Cr, V and Ti coupled with the presence of Rb, Ce, Nb, La and Li is suggestive of derivation from igneous/magmatic source (Neelakantam, 1987).

These results indicate the trace element contents are of the same order in the black and weathered (white/cream) tuffs, except for Cu, Pb and Zn in weathered tuffs. The low content of Cu, Pb and Zn in weathered tuff when compared to the black tuff may be due to oxidation of chalcopyrite, galena and sphalerite and subsequent removal by the weathering agents and surface circulating waters. Anomalous concentration of Pb, Zn,

Table.3

Trace element analysis of Black tuff and Weathered tuff

Name of the elementConcentration (ppm)Remarks

*Black tuff** Weathered

tuffBlack tuffWeathered tuffBlack tuff

1234567

Be

Cr

Co

Ni

Cu

Zn

Ge

Sr

Y

Pb

Ga

Rb

Sc

V

Zr

Nb

Cs

Hf

Ta

Th

U

La-

50-100

5

10-100

50-100

-

10

-

-

20-100

5-100

-

-

10

50-150

-

-

-

-

-

-

--

100

5-10

75

5-10

-

100

-

-

10-50

10-20

-

-

10

50-100

-

-

-

-

-

-

--

183

15

92

69

82

-

59.81

26.7

89.35

27

218

20

221

250

6

17

7.5

0.3

-

-

--

147

5.7

39

36

44

-

59.66

28.48

25.41

28

220

21

220

301

28

13

9.2

1.1

-

-

-0.869

-

14.792

-

-

-

1.889

-

-

-

11.889

-

-

-

367.603

12.449

3.148

9.614

1.171

19.198

3.072

37.778* average of 14 samples

** average of 4 samples

AAS/Spectrographic analysis given in columns 2 & 3 is by GSI. (Neelakantam, 1987)

ICP-MS analysis in column 6 by GSI

(Misra, 2007)

XRD analysis given in column 4 and 5 are by Sudarshan, (2007)

Rb, Zr, Hf, Ni, V is perhaps attributable to their magmatic origin. ICP-MS analysis of the black tuff by GSI (Misra 2007) has also shown presence of 37.778 ppm La, 8.894 ppm Pr, 32.183ppm Nd, which is suggestive of igneous origin. Uranium mineralisation is nown from the granite-gneiss basement of the Cuddapah Basin and hence high Th (19.198 ppm) and U (3.072 ppm) contents are expected.

Six samples of black tuff with sulphide (pyrite/chalcopyrite) disseminations and knots and pods of sulphide, were analyzed for their basemetal and noblemetals and the results are shown in Table 4.Table.4

Results of analysis of Base and noble metals in TuffsSample No.Carbon%Copper ppmNickel ppmGold ppmPlatinum

ppbPalladium ppbRhodium

ppb

14.0844720.04