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INTRODUCTION

The ancient Indians were the first in the world to take notice of the mineral diamond for its beauty and hardness. Diamond was discovered by the Indians in the eighth century B.C. They used to collect diamonds from its secondary sources i.e., the quaternary gravel beds and gravel bars in the sediments. Despite this ancient tradition, the primary sources of diamonds (kimberlite, lamproite, and other kimberlite clan rocks) have been found in India only after its Independence (except the Majhgawan pipe).The diamondiferous Majhgawan pipe has operated as India's only significant primary diamond mine with a grade of about 10 carats per hundred tonnes.

Diamond occurrences in India are quite widespread. Information on the ancient diamond mines and geology of the diamond bearing strata is available from the writings of the medieval period European travellers traders and Portuguese and British officials and geologists of the Geological Survey of India (GSI). Systematic geological details are obtained from the investigations carried out for diamonds since, 1950's, mostly by the GSI, which were at peak in 1980s with implementation of National Diamond Project, aimed at assessing the diamond potentials of different known host rocks. Subsequent works were oriented towards locating primary host rock for diamond and many kimberlite bodies in the already known areas and new kimberlite/lamproite fields in virgin areas were discovered.

The known areas of occurrences of diamond source rocks are broadly grouped into three diamond provinces, namely the South Indian Diamond Province (SIDP), the Central Indian Diamond Province (CIDP) and the East Indian Diamond Province (EIDP). Each of these Provinces extends approximately over an area of 100,000 sq. km and includes both primary (Kimberlites/Lamproites) and secondary source rocks (conglomerates and gravels) for diamond. The SIDP is confined to the Dharwar Craton in the states of Andhra Pradesh, Karnataka and Maharastra, the CIDP to the Aravalli Craton in the states of Madhya Pradesh, Rajasthan and Uttar Pradesh and the EIDP to the Bastar and Singhbhum Cratons in the states of Maharastra, Chhattishgarh, Orissa, Jharkhand and Madhya Pradesh.

Considering the Cratons and presence of diamonds and the source rocks, areas have been prognosticated for kimberlite search in India.They are: (1) South Indian Diamond Province (SIDP) including East Dharwar Craton and adjoining Dharwar Mobile Belt; (2) West Dharwar Province; (3) East Bastar Craton including parts of Eastern Ghat Mobile Belt (EGMB); (4) West Bastar Craton; (5) Southern part of Bundelkhand Aravalli Craton ; (6) North of Central Indian Suture (CIS); (7) Southern part of Singhbhum Craton including Singhbhum Mobile Belt; (8) Raigarh Mobile Belt; (9) Structural Corridor of Son Narmada rift zone; (10) Structural Corridor of Tapti Lineament Zone; (11) Mahanadi Gondwana Graben and (12) Godavari Gondwana Graben.

The SIDP consists of both primary and secondary source rocks of diamond. The kimberlites localised within the Eastern block of the Dharwar Craton are grouped into three fields, namely Wajrakarur Kimberlite field, (WKF), Narayanpet kimberlite Field (NKF) and Raichur Kimberlite Field (RKF). The major lamproite dykes occurring along the eastern margin of the Craton i.e. within the Nallamalai Fold Belt (NFB) and close to the north eastern margin of the Cuddapah basin are included in the Chelima Lamproite Field (CLF) and Jaggayyapeta Lamproite Field (JLF) respectively. Until now, only the WKF is found to contain diamondiferous pipes. Besides, the SIDP is well known for several diamondiferous conglomerates in the Banganapalle conglomerate/sandstone horizons of which the late Proterozoic Banganapalle conglomerate, occurring at the base of the Kurnool Group of rocks

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was extensively mined in both Kurnool and Palnad basins. Old workings are also found in the middle Proterozoic Cumbum pebbly sandstone older to the Banganapalle conglomerate, occurring in the Kolluru area in the north-eastern corner of Cuddapah basin. Though this diamond occurrence is rather localised, it assumes significance, in that, many of the world famous diamonds were reportedly recovered from gravels of the area. Another localised occurrence of old mining activity confining to the Mesozoic /Tertiary (?) sandstone is around Mallavelli to the east of Vijaywada and south-eastern side of the Eastern Ghat Mobile Belt. The gravels mainly of Krishna river along with those of the Pennar river, Sagileru, Kundair, Hundri and Ramileru yielded large quantities of diamonds. Diamond occurrences in the Godavari gravels are sporadic.

The CIDP also consists of primary and secondary source rocks. The NE-SW trending Panna Diamond belt with established ancient mining activity is located within this province. This is the only belt where active mining for diamond is presently carried out in the country. The National Mineral Development Corporation Ltd is exploiting Majhgawan kimberlite/lamproite, the only diamond producing mine.A little amount of diamond is being recovered from placer occurrences. The kimberlites/ lamproites (-1100Ma) intruding into the Kaimur Group of rocks are found along the western margin of the Vindhyan basin adjoining the Bundelkhand granite and are included in Majhgawan Kimberlite/Lamproite Field. Kimberlitic rocks discovered in this province are only a few and sporadic and are reported from the Bundelkhand granite terrain. The Vindhyan Supergroup of rocks host a major share of diamonds produced from the Panna Diamond Belt in the form of three diamondiferous conglomerate horizons associated with the Itwa sandstone, Jhiri shale, and Gahadra sandstone Formations of the Rewa Group of rocks of late Proterozoic age. Diamondiferous alluvial gravels are found mostly along the banks of the Ken-Ranj-Baghain rivers and lateritic gravels over the Baghain and Gahadra Sandstone Formations.

The EIDP is known for ancient diamond mining activity at a few places only viz., Wairagarh area in Maharastra, and Hirakud area in Orissa and Koel-Sankh river areas in Jharkhand. Kimberlite discoveries in the province are very recent and investigations carried out in different parts of the Bastar Craton led to identification of two new kimberlite fields (1) Mainpur kimberlite Field (MKF) and (2) Tokapal Kimberlite Field (TKF), both in the state of Chhattisgarh. The kimberlites of the MKF intruded into the Khariar group of rocks and those of TKF into the Indravati group of rocks of late Proterozoic age. Some of the kimberlites in the MKF are known to be diamondiferous. The recent discovery of kimberlitic / lamproitic rocks in Nuapada district of Orissa has opened a new area of primary source rocks for diamond. A few lamproite dykes have been discovered recently in adjoining Bargarh district, Orissa. A few of the Cretaceous lamproites intruding into the Gondwana sediments of the Damodar valley coalfields and South Rewa Gondwana basin show similarities to that of lamproitic rocks. Diamonds are also reported in the gravels of Maini, Ib, and Mand rivers in Chhattishgarh and Tel-Mahanadi rivers in Orissa. The ancient workings in Wairagarh area appear to be in the conglomerates as well as gravels. The conglomerates and grit are associated with either the middle Proterozoic Sakoli group or the early Proterozoic Dongargarh Group of rocks.

The Peninsular India with several Archaean-Proterozoic nuclei is cris-crossed by many deep-seated fractures. These nuclei,underlain by.thick lithospheric mantle roots, have witnessed different events of kimberlite,lamproite magmatism. The NW SE trending fractures and /or their intersections with NE-SW to ENE-WSW trending fractures appear to be major loci for emplacement of kimberlites/lamproites. High level (crater facies) kimberlites and lamproites are generally expected in the Aravalli and Bastar Cratons in view of their emplacement into the platformal sediments. However, occurrences of large pipes cannot be ruled out in Cuddapah

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basin and even in highly eroded granite-greenstone terrain in the Dharwar Craton where 20 to 60 ha size diamondiferous kimberlite pipes have been found.

Until 1980, the kimberlite-exploration efforts by various exploration agencies were rather limited and were not properly coordinated. However, in last 15 years India saw the discovery of a number of kimberlites/lamproites in Chhattishgarh, Andhra Pradesh, Karnataka and Orissa, some of which are diamondiferous.(Fig. 1)

Meaningful prospecting and exploration for diamond and kimberlites depend much on the right type of prognostication. Prognostication for mineral search is essential at different stages of prospecting from regional operations over large areas to detailed operations over narrowed down target areas.

DIAMOND RESERVE AND PRODUCTION IN INDIA

Diamond has been the most priced among the gems since more than 2000years.The price of diamond depends upon its weight, quality, shape and flawlessness. Diamond has a high refractive index and strong dispersion which gives it that exciting brilliance when cut as facetted stone. Gem diamonds are transparent and colourless or show faint shades of different colours. The transparent water clear diamonds are known as " of first water" or "blue white". When yellowish tinge is present, they are termed as off-colour stones. Diamonds with green, blue or red shades are rare but are most valuable gems.

Flawless stones of good colour are employed in gem trade while off colour, flawed and defective stones, chips and cutting as well as small grains and dust are used industrially.

RESOURCES:

DIAMOND FIELDS OF INDIA ARE GROUPED INTO 3 REGIONS:

1. South Indian tract of Andhra Pradesh, comprising parts of Anantapur, Cuddapah, Guntur, Krishna, Mahboobnagar and Kurnool districts

2. Central Indian tract of Madhya Pradesh comprising Panna belt and 3. Eastern Indian tract of mostly Chhattisgarh and Orissa, lying between Mahanadi and Godavari

valleys.

As per the records from the Indian Mineral Year Book-2001, the recoverable reserves of diamond as on 1.4.1995 are placed at 981,515 carats. In addition to the above, there are conditional resources of about 1.9million carats. Recoverable reserves of diamond by grades and states, are given in table below:

RESERVES OF DIAMOND (BY STATES/GRADES) (IN CARATS) State/Grade Recoverable reserves (As on 1.4.1995) Proved Probable Possible Total India(Grade: Unclassified)

851156 - 130359 981515

By States Andhra Pradesh 5465 - - 5465 MadhyaPradesh 845691 - 130359 976050

PRODUCTION & STOCKS

Production of diamond at 57,406 carats in 2000-2001 registered an increase of 40% over the

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previous year. There are two reporting mines both in public sector located in Panna district of Madhya Pradesh. Of these, one mine, owned by National Mineral Development Corporation Ltd (NMDC) contributed as much as 99% to the total output of diamond and the remaining 1% was by the Department of Geology & Mining, Govt of Madhya Pradesh.

Of the total output, gem variety covering only rough and uncut constituted 29% and industrial 71% covering off colour and dark brown varieties. Mine head stocks of diamond at the end of the year were 11360 carats as against 6095 carats in the beginning of the year. The average daily employment of labourer during 2000-2001 was 360 as against 389 in 1999-2000.

PRODUCERS OF DIAMOND, 2000-2001

Location of Mine Name and address of producer. State District

National Mineral development Corporation. Ltd. 10-3-311/ A, Castle Hills, Masab Tank, Hyderabad- 500028, A.P.

Madhya Pradesh Panna

Director of Geology & Mining, Government of Madhya Pradesh, Panna, Dist Panna, Madhya Pradesh

Madhya Pradesh Panna

PRODUCTION OF DIAMONDS, 1998-99 TO 2000-2001 (By States) (Quantity in Carats; Value in Rs. 000)

State 1998-99 1999-2000 2000-2001 Quantity Value Quantity Value Quantity Value India 34580 216506 40956 213985 57406 276837 Madhya Pradesh

34580 216506 40956 213985 57406 276837

PRODUCTION OF DIAMOND 1999-2000 & 2000-2001 (By Sector / state / district / states) (Qty. in carats; value in Rs.000)

1999-2000 2000-2001 Quantity Quantity

State/ District No.of

Mines Gem Indus-trial

Others Total Value No.of

Mines Gem Indus-trial

Others Total Value

India 2 11938 29017 40956 213985 2 16466 40940 - 57406 276837 Public Sector

2 11938 29017 40956 213985 2 16466 40940 - 57406 276837

Private Sector

- - - - - - - - - - - -

Madhya Pradesh

2 11938 29017 40956 213985 2 16466 40940 - 57406 276837

Panna 2 11938 29017 40956 213985 2 16466 40940 - 57406 276837 * Covers off colour and dark brown

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MINE-HEAD STOCKS OF DIAMONDS, 2000-2001

(By state / Grades) (Qty. in carats) State At the beginning of the year At the end of the year

Gem Rough & Uncut

Industrial* Others Total Gem Rough & Uncut

Industrial* Others Total

India 2324 3771 - 6095 3489 7871 - 11360 Madhya Pradesh 2324 3771 - 6095 3489 7871 - 11360

* Covers off colour and dark brown

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PART I

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DETAILED INFORMATION ON DIAMOND IN MADHYA PRADESH, CHHATTISGARH, MAHARASTRA AND ORISSA

DIAMOND PROSPECTS IN MADHYA PRADESH

PANNA DIAMOND BELT

Introduction

The diamond belt occurs on the northern fringe of the Vindhyan plateau in Panna and adjoining districts of Madhya Pradesh in Central India. The belt is 80km long and 6 - 10 km wide and trends ENE WSW. The area bounded by N.Latitude 2430': 2500' and E.Longitudes 8000': 8045' covers about 4000 sq.km. Sporadic diamond mining has been going on in this belt for nearly 400 years. Diamonds occur in recent gravels, conglomeratic horizons in the Vindhyan Supergroup of Proterozoic sediments and in two kimberlite/lamproite pipes intrusive into the above sediments. Even lateritic caps over sandstone are diamond bearing. The diamonds are largely of gem variety and off colour.

Accessibility

Panna, a small town and district headquarters is in the western part of the belt. It is well connected by road, 70km from Satna on Allahabad Bombay section of Central Railway and 200 km from Jhansi on Delhi-Madras trunk section. The nearest airport, Khajuraho, is at a distance of 40 km and is connected to Delhi and Varanasi. The western part of the diamond belt is in the Panna National Park and is normally not available for exploration.

Geological setup:

The area is represented by basement rocks comprising Bundelkhand Granites (2400 Ma approx.) with enclaves of older metamorphics such as sericite quarzite, banded magnetite quartzite, quartz--hornblende schist, garnetiferous mica schist and amphibolites.

Bundelkhand granite is a composite mass of different phases of granite, composition ranging from granite to tonalite and minor diorite variants. The bulk of the granite consists of coarse grained pink porphyritic granite, medium grained pink non-porphyritic granite and grey granite. The granites and older metamorphics are traversed by numerous dolerite, olivine-dolerite, basalt, olivine-basalt, gabbro, pyroxenite, peridotite, lamprophyre and possible kimberlite dykes. Syenite, micro-granite, pegmatite, aplite and quartz veins have also been recorded from granites.

The Upper Proterozoic Supergroup of rocks overlies the basement with an unconformity. The Vindhyans are represented by a sequence of sandstone, shale and limestone. They have been divided into Semri, Kaimur, Rewa and Bhander group of rocks respectively in order of younging. The Gahadara Sandstone surface is dotted by outliers of Deccan Trap basalt (60-110Ma approx.) and laterites.

The Vindhyans host a major share of diamonds of the Panna Diamond Belt because of the Majhgawan and Hinota diamondiferrous kimberlites/ lamproites and the diamondiferous conglomerates towards top of the Itwa sandstone, at the base of the Jhlri shale and, towards top of the Gahadara Sandstone.

Lithostratigraphic succession of the rocks of the diamond belt is presented In Table 1.

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Table-1

LITHOSTRATIGRAPHIC SUCCSESSION OF THE ROCKS IN PANNA DIAMOND BELT

Age Super Group Group Formation Member Lithology Alluvium with diamondiferous gravel beds at the base

Recent to Quaternary

Diamondiferous and non-diamondiferous lateritic gravel veneer

60-110 Ma Deccan Trap Two basaltic flows, partly lateritised Cretaceous (?)

(?) Infra-trappeans

Purple and white sandstone

----------------- ------------------ unconformity --------------------------------------------

Gahadara Sandstone

Pink and white, medium grained sandstone with diamondiferous conglomerate

Jhiri Shale Green and yellow shale and siltstone

with diamondiferous conglomerate at the base and as interbeds

Rohania Sandstone

White, medium grained sandstone with diamondiferous conglomerate

Pindhra Shale Chocolate and green shale Bhulwa Limestone

Limestone, chert

Itwa Sandstone

Banbiha Sandstone

Greenish, glauconite sandstone

Lower to Middle Palaeozoic

Rewa Group

Panna Shale Chocolate and grey calcareous shale and siltstone.

KIMBERLITE DIATREMES Baghain Sst. White, medium grained sandstone. 974-1120 Ma Kaimur Group Pipartola Cong.

Reddish conglomerate with jasper. Palkawan Shale Black, grey, yellow and white shale. 1250 Ma

VIN

DH

YA

N SU

PER

GR

OU

P

Semri Group Pandwafall Sst.

Greenish glauconite sandstone. ------------------ ----------------- ------------------ Unconformity --------------------------------------------

Intrusives Basalt, dolerite, gabbro, pyroxenite, lamprophyre and kimberlite (?) dykes. Aplite, microgranite and quartz reefs.

Granites

Multiphased granite intrusives (grey granite, pink porphyritic granite and pink medium grained granite).

2400 Ma

BU

ND

ELK

HA

ND

G

RA

NIT

ES

Older metamorphics

Sericite-quartzite, banded magnetite-quartzite, muscovite schist, garnetiferous mica schist, amphibolite gneiss and ultramafites.

Exploration:

The Geological Survey of India (G S I) carried out regional exploration over a large part of the belt and detailed exploration of the two pipes, and two conglomeratic blocks at Hatupur and Sahidan. The adjoining cratonic area of Bundelkhand has also been examined and a few ultrabasic and basic bodies appeared interesting.

The diamond bearing lamproite pipe at Majhgawan is being mined by National Mineral Development Corporation Limited (NMDC), with an average annual production of 16,000 carats. The lamproite pipe at Hinota has low diamond incidence and is not worked. NMDC also took up mining of a large gravel block at Ramkheria but abandoned the work due to operational difficulties. The extension of Hatupur conglomerate block has been explored by MECL. Rest of diamond mining in the Panna area is

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done by the unorganised sector. The State Government collects 20% royalty on sale of diamonds from this sector. . '

The occurrence of diamonds over such a long belt viewed in the light of only two known diamond bearing pipes at one end of the belt strongly point to contribution of diamonds from more pipes. A strong magnetic anomaly exists along the length of the diamond belt. Drilling at three places over this anomaly has revealed presence of ultrabasic rocks below the sedimentary cover.

A geological map of the belt and a status map on the work carried out in Panna area are enclosed.

As a result of GSI's work several prospective blocks have been identified for further investigation. Such blocks are listed below and short description on their status is enclosed. .

A. LAMPROITE/ KIMBERLITES

A.1 MAJHGAWAN KIMBERLITE/LAMPROITE DIATREME

Geographic data: Location : Majhgawan, Panna district. Coordinates : Lat.: N. 24039' ; Long. E.: 80002' ; Toposheet no. 63 O/2 Extent : 515 x 330 m diatreme. Access : Majhgawan pipe is located about 20 km south-west of Panna, the district

headquarters. Since Majhgawan pipe is a diamond producing mine, it is connected to Panna by an all weather road.

Topography: The pipe intrudes into the Baghain sandstone, which forms a flat geomorphic surface with a height of 360m to 400m above MSL. At present, the mine is approximately 80m deep with a number of benches.

Surface water : NMDC has constructed a small reservoir just to the south of the mine wherefrom it uses water for its treatment plant.

Ground water : The water table is approximately 20 m below the surface. The mine requires draining of water with the help of pumps.

Geological setup:

The Majhgawan kimberlite diatreme identified as lamproite by a few is a downward tapering, cone shaped body measuring about 515 x 330 m in plan. The contact with the host rock dips at fairly constant angle of 700 inwards. The contact between the kimberlite diatreme and the Baghain sandstone is normally sharp. In the western and southern periphery, however, the kimberlite is highly sheared and traversed by a network of calcite veins.

The diatreme contains both cognate and accidental xenoliths, the former predominating over the later. The accidental xenoliths include black porcellanite, purple shale and the Baghain sandstone.

The yellow and blue ground are well developed with a capping of 5 to 6m of soil. The contact between the yellow and the blue ground is at an average depth of 14 m from the surface.

There are five varieties of kimberlite:

1. Basaltic kimberlite with phlogopite. 2. Basaltic kimberlite without phlogopite.

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3. Kimberlite breccia with phlogopite. 4. Kimberlite breccia without phlogopite and 5. Kimberlite breccia with abundant phlogopite

Three distinct phases of emplacement of kimberlite could be recognised from the study of matrix and cognate xenoliths of the kimberlite breccia.

Exploration :

It is to be emphasised at the outset that the Majhgawan kimberlite is the only commercially exploited kimberlite in the country. NMDC which has been mining the deposit for many years possess data on incidence, average weight and types of diamonds and aspects related to its mining, treatment and marketability of diamonds. However, the exploration programme was aimed at: (1) establishing offshoots of the kimberlite diatreme, (2) deciphering the geometry of the body and study of different petrographic varieties at depth and (3) establishing incidence of diamond in the 'extended arm' of kimberlite on the basis of surface sampling with the help of deep pits.

A total of 2943.70 metres of drilling in 25 boreholes was done to study the pipe. During shallow drilling, two prominent offshoots were delineated upto a depth of 40 m and an additional reserve of kimberlite (0.14 Mt) has been established upto a depth of 40 m. To study the behaviour of the Majhgawan kimberlite at depth, 5 boreholes were drilled from outside the pipe area. The drilling has established the extension of pipe to a vertical depth of 330 m). The wall of the pipe indicates an inward dip of about 700 to 800. As against the diameter of the pipe, which is about 330 m on surface, it reduces to about 125m at a depth of 330m. The pipe continues to further depth. Treatment of about 1643.71t of kimberlite (Table 2) from offshoot yielded 14 diamonds weighing 7.20 ct indicating an incidence of 0.43 cpht as against 10 cpht in the main pipe.

Table- 2

Details of excavation, treatment and diamond recovery in Majhgawan kimberlite Block Total Diamonds Gem Off. Colour Industrial Pit

No. Depth (m)

Excavation (cu m)

Treatment (t) No. Wt (ct) No. Wt (ct) No. Wt (ct) No. Wt (ct)

1 7.50 46.87 68.82 - - - - - - - - 1A 8.30 51.87 130.70 4 1.67 1 0.33 1 0.51 2 0.83 2 28.50 178.13 471.90 3 1.80 2 1.41 1 0.39 - - 3 41.80 261.25 665.27 4 2.08 2 1.02 - - 2 1.06 4 7.50 46.87 - - - - - - - - - 5 10.00 62.50 139.70 3 1.65 2 1.02 - - 1 0.63 6 12.00 75.00 159.32 - - - - - - - - 7 6.50 40.63 - - - - - - - - - Total 763.12 1643.71 14 7.20 7 3.78 2 0.90 5 2.52

The different petrographic varieties of kimberlite and their daimond content are given in table 3.

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Table- 3

Comparison of incidence of diamonds in different varities of kimberlite by Haldar (1972) and Ghosh.

Petrographic variety Diamond Incidence (cpht) (Haldar 1972)

Diamond Incidence (cpht) Ghosh (1982)

i) Kimberlite breccia without phlogopite 5.70 - 24.80 ii) Kimberlite breccia with phlogopite . 4.77 - 9.04 22.05 - 30.09 iii) Basaltic kimberlite without phlogopite 3.70 - 25.82 iv) Basaltic kimberlite with phlogopite 7.00 -18.02 11.45 - 13.90 v) Kimberlite breccia with abundant phlogopite 12.94 -13.35

It can be observed that there are wide variations in the incidence of diamonds in the same variety of kimberlite. The ratio of gem, off colour and industrial diamonds from the Majhgawan pipe is 38:40:22. (as per NMDC data).

Recommendations:

For increasing the indigenous production of diamonds in the country, the Majhgawan kimberlite prospect can provide following support :

1. With the help of suitable mining methods, the production can be raised considerably. 2. At present there is no method for recovery of micro-diamonds (less than 0.5mm in size) from

kimberlite. A method to this effect has to be worked out.

A.2 HINOTA KIMBERLITE DIATREME

Geographic data Location : NNW of Hinota Village, Panna district Coordinates : Lat. N.: 24040' ; Long. E: 80001' Toposheet no. 63 D/2 Extent : 200 x 180 m diatreme. Access : Hinota kimberlite diatreme is located about 20 km WSW of Panna, the district

Headquarters.

Topography : The pipe is emplaced into the Baghain sandstone which forms a flat geomorphic surface with a height of 360m to 400m. The pipe forms a topographic depression.

Surface water : The area is surrounded by small ephemeral streams. A few small ponds (100 m diameter) are found in a radius of about 2.5 km from the pipes.

Geological setup : The Hinota diatreme is emplaced into the Baghain Sandstone Formation of the Kaimur Group (Vindhyan Supergoup). On surface, the diameter of the pipe is 200 x 180 m with a slight NW-SE elongation. On the aerial photographs, the pipe is recognised by its high density of vegetation and negative topography. It is well recognised on satellite imageries also. The pipe was discovered as a result of magnetic and electrical resistivity surveys by GSI.

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The drilling in the Hinota pipe indicated top 2.5m of detrital material, followed by about 25 m of earthy yellow and greenish clayey matter and then blue ground upto a depth of 60 to 75m ending up in hard kimberlite. The diatreme comprises massive basaltic and micaceous kimberlite grading into autolithic kimberlite breccia. Chemical analysis of Hinota kimberlite is presented in table 2.

Exploration :

a. Regional mapping on 1:50,000 scale. The study was aided by aerial photo-interpretation. b. Large scale mapping: About 120 sq.km on 1:12,500 scale for sedimentological studies, plotting

of conglomerate horizons and diamondiferous gravel horizons. c. Detailed mapping: About 0.5 sq.km on 1:1,000 scale, grid sampling, demarcation of different

lithounits, drilling and shaft sinking. d. Geophysical studies: Magnetic, electrical resistivity and gravity surveys to understand its

geophysical characteristics. e. Drilling: During 1968-70 and again during 1984-86, the drilling was done in the Hinota pipe to

know its geometry at depth and petrochemical characters. During 1984-86, a total of 631.65 m of drilling was done in 3 boreholes, which indicated that the body extends beyond 160m in depth.

f. Shaft Sinking: One 18.50m deep shaft was sunk in the pipe.

Following is the summarised log of the shaft. 00.00 - 01.20 m

01.20 - 02.20 m 02.20 - 07.00 m 07.00 - 11.50 m 11.50 -13.50 m 13.50 -18.50 m

Black clayey soil Black clayey soil with concretions Weathered kimberlite Basaltic kimberlite Weathered, serpentinised, carbonated kimberlite Kimberlite breccia and yellow ground

(g) Processing: A total of 228.40 tonnes of material from the shaft was treated and only two diamonds weighing 1.71 ct were recovered, which shows a very low incidence of diamond. Earlier studies by NMDC and GSI also indicated its low diamond content.

Recommendations : As diamond incidence is low, further investigation in this pipe is unwarranted.

Caution : The Hinota pipe falls in the Panna National Park area and to obtain prospecting lease, and to carry out large scale operations or even preliminary surveys, a prior permission from the Ministry of Environment, Government of India, is necessary.

B. CONGLOMERATES

B.1 HATUPUR BLOCK

Geographic data: Location : Hatupur, Panna district. Coordinates : Lat.: 24048'; Long.: 80025' ; Toposheet no. 63 D/5 Extent : Hatupur block is 3 km x 3 km in extent; Hatupur, Rakhel and Damulua

villages are located within the block. Access : The block is located about 23 km ENE of Panna on Panna-Paharikhera

Road. Topography : The block fringes at Gahadara sandstone scarps in the southeastern part of the block, with an elevation difference of about 70m .There is a small hill in the eastern part of the block with a height of 440m.

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Surface water : The area is drained by small ephemeral streams. A comparatively large stream exists in the western part of the block. There are two large tanks in the north. Water table : On the basis of drill hole data, the water table is recorded at about 15m below the surface. Geological setup :Following is the lithostratigraphic sequence of rock units on the basis of regional and large scale mapping and drilling.

Gahadara Sandstone Formation (Upper Rewa sandstone) Jhiri Shale Formation with a basal conglomerate Itwa Sst. Formation with diamondiferous conglomerate towards top. Rewa Group Panna Shale Formation

Kaimur Group Baghain Sandstone Formation (Upper Kaimur Sandstone.)

Palkawan Shale Formation Semri Group Pandwall Sandstone Formation.

--------------------------------------------- Unconformity ------------------------------------ Bundelkhand granite with enclaves of older metamophics.

Jhiri Shale : The Jhiri shales are exposed on the surface in the entire block. At the base of the Jhiri shale, a diamondiferous conglomerate horizon (Jhiri conglomerate), varying in thickness from 4 cm to 54 cm, exists. The Jhiri shale is underlain by Itwa Sandstone Formation. Towards the top of (but not at the top) the Itwa Sandstone Formation, another diamondiferous conglomerate horizon (known as Itwa conglomerate) exists. The Jhiri and Itwa conglomerates are separated by 2 to 3 m thick sandstone horizon. The Itwa Sandstone Formation and Jhiri Shale Formation (with conglomerate) show very gentle dip towards SSE. The gradient is 1.5 to 2 m per 100 m.

Itwa Conglomerate : It is an ill sorted conglomerate and comprises subangular to subrounded granules, pebbles and cobbles of white sandstone (Baghain sandstone), green glauconitic sandstone (Semri), yellow and white shale fragments (Semri) , vein quartz, jasper and chert (from basement). The pebbles do not show preferred orientation. The matrix is arenaceous. The thickness of conglomerate varies from less than 5 cm to 2m. Drilling indicated frequent variation in thickness of conglomerate. During shaft (2 x 2m) sinking, these conspicuous variations have been observed. On an average, the thickness is about 50 cm.

Jhiri Conglomerate : It is also a thin blanket type of conglomerate, thickness of which varies from 2 cm to 70 cm. It is composed of subrounded to rounded well sorted granules and small pebbles of vein quartz, jasper, chert, Pandwall sandstone and platy fragments of shale set in a fine glauconitic silty matrix. Exploration : Large scale mapping The area has been mapped on 1:12,500 scale to demarcate conglomerate

horizons, diamondiferous lateritic and alluvial gravels. Detailed mapping About 5 sq.km on 1 :2000 scale. Drilling For the sake of convenience, the Hatupur Block was divided into two sub-

blocks. In the western block the grid was laid at 200m intersection and in the eastern block at 250 m intersection. A total of 3345.95 m of drilling was done in 108 boreholes. The drill hole data revealed that the thickness of the Jhiri conglomerate ranges from about 1 cm to 70 cm. The depth of conglomerate varies from 4.55m to 36.35m.

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The Itwa conglomerate is separated from the Jhiri conglomerate by a non-diamondiferrous shale / sandstone horizon, the thickness of which varies from 2 to 4 m. The thicker conglomerate horizons also carry sandstone interbeds. The thickness of Itwa conglomerate varies from 1 cm to 2.42m and depth from surface varies from 3.42 m to 62.28m. Core loss has also been recorded in a few drill holes. In view of this, much thicker horizon of conglomerate is expected in the pits than in boreholes.

Isopach map for the Jhiri and the Itwa conglomerates indicates irregular distribution of conglomerate. Both the conglomerates are thicker along palaeochannels than adjoining parts. The palaeochannels are oriented along NE-SW and E-W directions. Isolated patches of thick conglomerate are also recorded. The stratum contour plan of the base of the Itwa conglomerate horizon shows uniform and conspicuous south-easterly gradient.

Shaft Sinking: 36 shafts (2.5 x 2.5m) , ranging in depth from 5m to 34.75m, were sunk on a grid varying from 100 to 250m to excavate the conglomerates. At the bottom of the shaft, where the Itwa conglomerate was encountered, two east-west oriented drives (1.8m height, 2.1m width and 6m length on each side) were driven to win the requisite quantity of conglomerate. The average thickness of conglomerate in shafts worked out to be 60 cm, varying from 17cm to 1.40m. A total of 4746.92 t of conglomerate was obtained from 6494.50 cu m. of excavation, which was treated at NMDC plant, Majhgawan.

Dimensions of explored prospects :

i) Sub-block A The sub-block (area 0.3 sq.km) was proved to contain conglomerate reserves of about 0.45 Mt with a diamond incidence of 27.91 cpht. This block is open at both ends, indicating the possibility of its further extension towards east and towards south-west. MECL has drilled in the eastern extensions of the block, the results of which are yet to be received.

ii) Sub-block B This sub-block measures 750 x 500m. Proved reserves of pure and diluted conglomerate estimated are 0.53 Mt and 1.49 Mt, respectively. Treatment results of the samples drawn are not available so far. The depth of the Itwa conglomerate varies from 20.95m to 29.10m

iii) Sub-block C The block is along a NW-SE trending channel defined by drill holes 43A, 43B, 46A, 46C, 47, 47A, 47B, 47C, 48, 48B, 50, 50C, 51 and 51C. Thickness of the Itwa conglomerate ranges from 1.14 to 1.80m and depth varies from 6.45 to 21.65m. On the basis of the data of three pits (P-28, P-35 and P-36) and drives, about 0.31 Mt of undiluted and 0.74 Mt of diluted conglomerate of proved category have been estimated. Probable reserves of 0.60 Mt of undiluted conglomerate and 2.72 Mt diluted conglomerate have been estimated on the basis of drill hole data. The treatment results are not yet available.

iv) Sub-block D It is a small block located in the northeastern corner of the Hatupur block and defined by drill holes 56-A, 57B and 61 C. The thickness of the Itwa conglomerate varies between 22 and 30 cm and depth varies from 8 to 8.5 m. Probable reserves of the conglomerate have been estimated at 0.106 Mt. for the undiluted and 0.742 Mt for the diluted categories.

v) Sub block E It is 1 km long, trending N-S and defined by drill holes 50A, 50B, 55, 55A, 55B and 60C. The thickness of Itwa conglomerate varies from 10 to 77cm and depth from 12.70 to 25.15m. No pits have been sunk in this sub block. On the basis of the drill hole data, probable reserves of the conglomerates have been estimated at 0.378 Mt of undiluted and 1.49 Mt of diluted conglomerate.

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vi) Sub-block F It has a dimension of 500 x 500m and is a south-easterly extension of the subblock C. Drill holes 49A and 54 and pit No.37 are located in the block. The depth of the Itwa conglomerate varies from 23.40 to 26.05m and thickness from 29 cm to 1.70m. On the basis of the drill hole and pit data, proved and probable reserves of diluted conglomerate have been estimated at 0.247 Mt and 0.495 Mt respectively.

Diamonds:

The percentage of gem quality of diamonds is very high (55%). Off-colour and industrial diamonds constitute 19% and 26% of the total diamonds. The largest sizes of diamonds recovered so far, during the exploratory operations, are 3.38 ct (industrial variety), 2.27 ct (gem quality) and 1.68 ct (off colour). Average size of gem, off-colour and industrial varieties is 0.6 ct, 0.45 ct and 0.63 ct, respectively.

B.2 SHAHIDAN BLOCK

Geographic data: Location : 2.5 Km NE of Panna, Panna district. Coordinates : 24044': 80012' ; Toposheet no. 63 D/2 Extent : 2700 X 700 m Topography : Gently rolling terrain. Access : Panna is well connected by road from different places. The block is easily

approachable by metalled road to Paharikhera. Janakpur village is at the centre of the block.

Geological setup: Jhiri conglomerate occurs at the base and as interbeds within the JhiriShale and siltstone of the upper part of the Rewa Group. It forms escarpment to the SW and NE of Panna. The conglomerate is coarse, pebbly or granular, with subrounded granules of jasper, chert, sandstone and shale. It is rather well sorted with a sandy matrix.

Exploration: Shahidan area has the record of best and larger size diamond recovery. Data computed from the operations of one of the large and systematically managed mines in Shahidan area during 1919-1925, indicated diamond incidence of 43 cpht. During 1972-74, GSI drilled 20 boreholes which indicated that the cumulative thickness of conglomerate to the SSE of Janakpur is above 30 cm. During 1980-85, mapping (on 1:5000 scale) and drilling (62 boreholes by MECL) was done. Drilling showed an average thickness of 20 cm of conglomerate. Drilling was spaced at 300m apart along the strike of the formation (N72 E - S 72 W) and at 200m apart along dip direction (S 18 E). 10 pits sunk at drill hole sites indicated, on an average, 1.7 times greater thickness of conglomerate.

The northern part of the area has a number of old workings which are upto 15m deep and water logged, causing seepage problem. The large tank (Lokpal Sagar) at the SW part of the block may also cause seepage problem. A part of the northern section is in reserve forest, while the southern part is under cultivation.

B.3 GANJA - SHAHPUR BLOCK

Geographic data:

Location : Near Ganja - Shahpur village, Panna district. Toposheet : 63 D/5 Topography: Gently rolling terrain.

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Geological Set up

Both Itwa and Jhiri conglomerates are encountered in the area. The Jhiri conglomerate is both matrix as also clast supported. The clast supported conglomerate has 50% to 70% of clasts embeded in an argillaceous matrix. The clasts comprise mainly of grey, white, cream and pink coloured quartzite, vein quartz, red and brown jasper, green shale, yellow chert, greenish sandstone and BHJ. The matrix supported conglomerate has 15% to 40% of clasts set in an argillaceous groundmass. The clasts are generally of granule size. These include white quartzite, vein quartz, grey quartzite, green shale, cream quartzite, jasper, pink quartzite and chert.

Exploration: 16 holes drilled in the area encountered Jhiri conglomerate at a depth of 12.15m in the northwest and at 49.30m in the southeast, down the dip. This is in conformity with the regional dip of the formation.

The Itwa conglomerate is intersected at a depth of 13.48m in the northwest and 50.50m in the southeast. Thickness of Itwa conglomerate varies from 6 to 70 cm.

Drill hole data also indicated that there is a rapid variation in the number of bands of Jhiri conglomerate from 1 to 6. The Itwa conglomerate has generally one or two bands, except for southwestern side where 5 bands are recorded. .

Reserve: On the basis of drill-hole data, indicated reserves of the Jhiri conglomerate is about 6.74 Mt and that of the Itwa conglomerate about 4.44 Mt

C. RIVER GRAVELS

Geographic data: Location : Itwa, Brijpur, Ramkheria villages, Panna district. Coordinates : N.Lat.: 24047'- 24049'; E.Long.: 80023'- 80030'; Toposheet no. 63 D/5 Extent : Gravel zone extends from Ramkheria (24049': 80027') in the east to Itwa (240

47' : 800 23') in the west. Access : The area lies about 20 Km ENE of Panna and an all weather road between

Panna and Paharikeria runs through the entire length of gravel zone.

Topography The area is practically flat, with the Baghain River incising into the flood plain deposits.

Surface water The Baghain river is perennial and flows towards ENE. Ground Water The water table shows high fluctuations and is very shallow during

rainy season and early winter. Exploration :

Regional mapping (1:50,000):

Systematic mapping of alluvial zone was done as part of regional mapping

Large scale mapping: The area around and along the Baghain river was mapped on 1 : 12,500 scale as a part of delineation of diamondiferous gravel zones

Geophysical Survey: Geophysical survey of the gravel along the entire river section in Itwa-Ramkheria section was done during 1970s and the depth of bed rock was demarcated by taking cross traverses.

Dimension of the prospect The area covers a length of approximately 15 km and width of 1 to 2

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km.Diamondiferous gravel is restricted to the basal part of the alluvial pile and its thickness varies from 30 cm to 4 m. It comprises boulders and pebbles of sandstone, shale and laterite, set in sandy matrix.

Diamond Incidence : Diamondiferous alluvial gravel of Ramkheria has been worked since historical past. Bulk sampling by the GSI in 1956 in the gravel indicated an incidence of 26 cpht. The exploration by NMDC proved a resource of about 1,15,000 ct with incidence of about 16 cpht.

Recommendations : Ramkheria gravel deposits indicate higher diamond incidence than the Majhgawan kimberlite. Moreover the percentage of gem quality diamonds is more than that from the Majhgawan mine. In such context, this prospect appears to be quite promising provided prior exploration is done in the gravel. A few areas were delineated on the basis of photogeological studies for detailed exploration along the Baghain River.

D. BUNDELKHAND BASEMENT

Several ultrabasic bodies are found in the Bundelkhand granite massif. Many of them seem to have been emplaced after or along with the granitic rocks. Preliminary exploration revealed diamonds from the area. The bodies are small in size. However, in view of their possible regional relevance in the emplacement of diamond bearing pipe rocks, short descriptions are given below.

D.1 ANGOR AND BANDHA ULTRABASIC BODIES

Geographic Data:

Location : 0.5 km north of Angor Village Prospect : Angor Ultramafic prospect District : Chhattarpur district. Coordinates : 24044'; 79025' Toposheet no.54 P/6. Access : Angor is a village on the Sagar-Chhatarpur state Highway, being about 40

km south of Chhatarpur, which is the district headquarters and 130 km SW of Panna. The nearest railhead is Harpalpur on Jhansi Manikpur broad gauge section.

Topography The granitic country is flat Water Sources: Water supply is possible from nearby seasonal streams; scarcity may

exist during summer. Groundwater is limited Geological setup The ultramafic rocks are found in Bundelkhand granites. The body

is exposed mainly on the eastern side of the road but much of it has been levelled off to form cultivated land.

Exploration : : Geophysical surveys indicate a 450 m long and 200m

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wide body, trending in NNW-SSE direction. Another 170m long and 30m wide body is located 0.5 km NW of the first body. Drilling indicates top 7 -12m weathered zones, underlain by brecciated carnbonated pyroxenite, underlain by harzburgite. The body dips 450 towards east. 7 boreholes totalling 792.35m were drilled in the main body, which continues beyond 289m depth. Six large pits reaching to a depth of 10m were put and two diamonds totalling 0.2 carats were recorded after treating 937.40 tonnes of excavated material. In course of another excavation, 311.80 tonnes of treated material yielded five diamonds weighing 3.52 carats. NMDC treated 1000 tonnes without any recovery of diamond. A similar body occurs near Bandha (240 39/:790 19'; 54 P/6) to the southwest of Gulganj. It is a dyke-like body, about 10m wide and covered by soil at both ends. 86 tonnes of material treated yielded two diamonds weighing 1.62 ct (one gem 0.57ct and one industrial 1.05 ct).

. Recommendations In view of the diamond incidence, both the bodies could be subjected to further investigation.

D.2 DONGRAHA ULTRABASIC ROCK

Geographic data: Location : East of Dongraha, Panna district. Coordinates : 24051'; 80008' Extent : 10m long and 50cm to 1m wide; trends N 30 E - S 30 W.

Geological setup: The rock is intensely weathered, black in colour and porphyritic with phenocrysts of altered olivine. Groundmass contains calcite and dusty opaques like ilmenite, magnetite and possibly perovskite.

Exploration: No exploration was carried out.

D.3 ULTRABASIC ROCKS OF HARSA

Geographic data: Location : 1.5 km north of Harsa village, Panna district. Toposheet : 63 D/1 Coordinates : 24046' ; 80006' Extent : The outcrop measures 1 m long and 50 cm wide. Access : Harsa can be approached from Madla on Chhatarpur -Panna Road. Madla

lies on the eastern bank of Ken river.

Geological set up: The outcrop shows sharp contact with prophyritic pink granite; the other side is covered by residual soil, rich in carbonate kankars. The rock is massive, greenish, hard, compact and shows porphyritic nature. The xenocrystic grains are rounded. Second generation olivine grains are euhedral.

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The groundmass is a turbid mass of calcite. Serpentine, magnetite and opaques are also present. The rock has been identified as lamprophyre.

Exploration: No exploration for recovery of diamond was carried out.

D 4 ULTRABASIC DYKE NEAR BARIARPUR BARRAGE

Geographic data: Location : East bank of Ken river, north of Barrage. Panna district Coordinates : 24051' ; 80006'. Toposheet no.63 D/1. Extent : A dyke-like body, 5m to 10m wide and more than 1 km long, ends covered

under soil. Access : Bariarpur village is 20 km by forest road from Madla. It is also approachable

from Ajoygarh, a sub-divisional town of Panna district. Geological set up : The body occurs like a dyke, trending N 50 E -S 50W. It is well exposed in the west bank canal of the barrage, varying in thickness from 5 to 10m. The rock is grey, green to greenish brown, showing olivine, reddish mica and opaques. The body cuts through Bundelkhand granite and shows contact metasomatism. The rock is traversed by serpentine, carbonate and quartz veins. It continues under soil cover for 600m, as proved by drilling three holes, spaced 200m apart; further extension possible.

Two pits were sunk in the eastern bank of the Ken river and treatment of 138 tonnes of material from one of the pits yielded one diamond (off-colour) weighing 0.44 ct.

Recommendation: In view of large strike extension and diamond incidence, the body should be further investigated.

D.5 BASALTIC KIMBERLITE OF BIHARPUR AREA

Geographic data: Location : 0.7 km WNW of Biharpur, Panna district. Coordinates : 24057' : 80031' - Toposheet no. 63 D/9 Extent : 600m long and 1 to 5m wide. Access : Biharpur is situated to the north-east of Kohari which lies on Panna-Kalinger

road and is about 70 km from Panna. The area is just south of the well known Kalinger Fort.

Geological setup: An olivine bearing porphyritic dyke traverses granite intermittently for about 600m. It trends ENE-WSW. Olivine is altered and the groundmass is light brown glass, showing spherulitic structure and a colourless mineral showing fibrous habit.

Exploration: Two boreholes, aggregating 298.43m, were drilled. No kimberlite was intersected in any of the holes and it appears that this dyke pinches off at very shallow depth. About 33 cu m excavation was done, and 55 tonnes of material treated but no diamonds were recovered.

PROSPECTS IN CHHATTISGARH

The Chhattisgarh State forms a part of Bastar Craton extending on west to Maharashtra and on east to Orissa. It is of great significance that the Raigarh Mobile Belt, located between the Bastar Craton on south-west and the Singhbhum Craton on north-east, is manifested by the

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presence of diamond in all the streams of Ib, Maini, Mand and Sankh and their tributaries. The Archon of Bastar Craton is bordered by Protons of Raigarh Mobile Belt and Eastern Ghat Mobile Belt and this tectonic scenario is important in regional prognostication for diamond and kimberlite is Bastar Craton. In Bastar Craton there has been no major thermal activity after 2000 Ma. Hence, the Proterozoic platformal belts over the cratonic area have been selected as first priority blocks for investigation of kimberlite.

The eastern and central parts of the craton are priority areas because they represent the low heat flow and high permeability zones. The area is marked by presence of platform cover sediments which protects the kimberlite diatremes from erosion. The prominent Proterozoic basins are Chhattisgarh basin, Pairi-Khariar basin, Ampani basin, Indravati basin, Sabri basin and Albaka basin.

Considering all the positive features, the following target areas have been prognosticated in search for kimberlites.

a) The Pairi-Khariar basin and surrounding granitic terrain, b) the Indravati basin and adjoining gneissic complex on west and south, c) the Sabari basin and adjoining gneissic complex, d) Saraipalli area comprising rocks of Chhattisgarh basin and the adjoining granitic terrain, e) the Albaka and Abujhmar basins, f) the southern part of Chhattisgarh basin and adjoining granitic terrain, g) the Raigarh Proterozoic crystallines bordering the Bastar Craton.

A total of 14 priority target blocks have been demarcated of which 11 are in Chhattisgarh and three in Madhya Pradesh. The area of each block has been tentatively kept at 5000 Sq. Km.

In the Chhattisgarh State, so far, two Kimberlite fields have been identified which are Mainpur Kimberlite Field in Raipur district and Tokapal Kimberlite Field in Bastar district.

A. MAINPUR KIMBERLITE FIELD (RAIPUR DISTRICT)

The Mainpur Kimberlite Field (MKF) is one of the three established diamond bearing kimberlite fields in Peninsular India, the other two being Panna in northern Madhya Pradesh and Wajrakarur (including Chigicherla and Kalyandurg kimberlites) in Andhra Pradesh. MKF is located in the south-eastern part of the Raipur district of the state of Chhattisgarh in Central India, 135km SE of Raipur city. Exploration activities by the GSI and the State Government have led to the identification of five kimberlite pipes (including three diamondiferous pipes) and more than 40 kimberlitic indicator anomaly zones in the MKF, which are likely to be associated with kimberlitic bodies.

Tectonic Setting:

The Mainpur Kimberlite Field is located within the Bastar Craton (BC) close to its contact with the granulite terrain of the lower to middle Proterozoic Eastern Ghat Mobile Belt (EGMB) in the east. This contact is also marked by occurrences of middle to late Proterozoic alkali syenite complexes, the nearest being at Khariar in Orissa. The Archaean granite-greenstone of BC is overlain by late Proterozoic platform sediments of Chhattisgarh Supergroup deposited in different sub basins. The kimberlites of MKF are intrusive within the platformal sediments of the Pairi sub basin.

Discovery of five kimberlitic diatremes (Payalikhand-I & II, Bahradih, Jangra and Kodomali) has led to the establishment of Mainpur Kimberlite Field in southeastern part of Raipur district in Chhattisgarh state.

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The area under investigation falls in Survey of India Toposheet Nos 64L/4 and L/8 and is confined to the cratonic part. The kimberlitic diatremes have been emplaced over the Bastar craton close to the Bastar craton-Eastern Ghat Mobile Belt contact.

The area falls in the Mahanadi major basin in the water divide zone between the Tel river sub-basin and the Pairi-Sondur river sub-basin. The eastern part of the area is characterized by high plateau with steep scarps (Khariar plateau) and the western part is characterized by rugged undulating topography comprising isolated hills with elevations of more than 700m.

The regional tectonic set-up in the Mainpur Kimberlite Field includes three distinct units viz. the Bastar Craton, the Eastern Ghat Mobile Belt (EGMB) and the Proterozoic sedimentary sequences. The Archaean rocks include a group of gneissic complex (quartzo-felspathic-biotite-hornblende gneiss, banded iron formation and pyroxenites). These rocks have been intruded by gabbroid rocks and further engulfed by multiphase granitoid rocks (Bundeli granitoid). The Eastern Ghat group of rocks constitute high grade granulite facies charnockite, two pyroxene garnetiferous granulities and leptynite. Younger dolerite intrusives occurring as swarms trend mostly NW-SE and ENE-WSW.

Late Proterozoic sedimentary rocks over the crystalline basement formed the Khariar syneclise. These cover sedimentary rocks are included in Pairi/Khariar Group and have been lithostratigraphically equated with the Singhora group of rocks occupying a NNE-SSW tract north of Khariar basin at the eastern fringe of the main Chhattisgarh basin. The sedimentary rocks include sandstone, shale, chert and limestone.

Regional Structure:

The cratonic area is characterized by NW-SE trending fractures extending for hundreds of kilometers and E-W fractures both marked by extensive doleritic intrusion and silicifications. The EGMB set up mainly exhibits N-S to NNE-SSW trending fractures. The cover sediments are horizontally disposed and show N-S to E-W trending faults and fractures. At the junction between Bastar Craton and EGMB, N-S trending intrusives of alkaline rocks have been reported (Mahadevan et al., 1989). Many of the fracture lineaments are characterized by the presence of basic-ultrabasic intrusives.

Kimberlitic rocks: their occurrence and distribution

: Five kimberlitic diatremes have been located in a linear span of 12.5 km in the Mainpur kimberlite field. The kimberlitic diatremes are Payalikhand-I (100m x 100m), Payalikhand-II (50m x 50m), Jangra (>50m across), Kodomali (300m across) and Bahradih (300m x 200m). Most of the diatremes are circular in plan while Bahradih diatreme is elliptical. Amongst the diatremes only kodomali exhibits fresh rock exposures. While others have been weathered to green earth at the surface.

The broad regional stratigraphy of MKF belt is as follows:

Recent-Sub Recent - - Soil, alluvium, laterites (?)

Upper Proterozoic Chhattisgarh Super Group, Khariar Group and Ampani Group

- Shale,limestone,quartzite, arenites and conglomerate

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Lower Proterozoic Budeli Granitoids - Alkali granites, porphyritic granite, granodiorite and sheared granite gneiss with pegmatites

- Bilari Group - Lakhadabri acid volcanics, Arangi basic volcanics.

- Disconformity - - - - Arjuni formation Phyllite, BIF,

metagreywacke with subordinate volcanics and polymict conglomerate

- Sonakhan Group - Uncorformity - - Bagmara Formation Pillowed metabasalt, acid

volcanics, shale, chert, pebbly schist.

- Uncorformity - - Eastern Ghat Group - Khondalite, charnokite

and mafic granulite Archaean To Proterozoic

Baya Gneissic complex Peninsular Gneiss

- Amphibolite, biotite gneiss, tonalite-granodiorite gneiss and migmatite.

- Tonidongar Group - Metaultramafites and basics, high grade metasediments, banded magnetite quartzite and fucschitic quartzite.

A. 1. PAYALIKHAND DIATREMES

Geographical data:

Location Payalikhand village, Raipur district Coordinates Lat 20010/10//; Long 82021/00//, Toposheet No:

64 L/8 Access 169 km from Raipur Topography 460m above MSL

Geological Set up:

The Payalikhand area comprises a complex lithological assemblage represented by metavolcanics and metasedimentary sequences of Sonakhan Group, rocks of Baya Gneissis Complex, khondalite and charnockite suite of rocks of the Eastern Ghat Mobile Belt, intrusive Bundeli granitoid and the sedimentary cover sequences of Pairi and Ampani Groups and Chhattisgarh Super Group.

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Exploration:

This includes reconnaissance/large scale mapping, pitting/trenching, geochemical and bulk sampling, petro mineralogical studies, shallow drilling and also inputs from geophysical surveys and photogeological and remote sensing studies. Two diatremes have been located along the slope of a foothill of the Khariar plateau.

Characteristics of the diatremes:

Number and name of kimberlite body

Dimension Trend Emplacement control

Outcrop characteristics

Diamond contents/Heavy minerals

MKF Field

Payalikhand -I

100m x 100m

Circular Within granitoid rocks (64L/8)

Expressed as a break in slope, highly altered kimberlitic rock (green earth) diatreme facies

Diamondiferous and garnet, spinel, clinopyroxene

Payalikhand- II

50m x 50m

Circular Within granitoid rocks 64L/8

Along break in slope, highly altered kimberlitic rock as green earth.

Diamondiferous`

A. 2. BAHRADIH DIATREME

Geographical data

Location Bahradih village, Raipur district Co-ordinates Lat: 20012/ 30// : Long 82012/ 00//, Toposheet

no 64L/4 Access 12 Km northwest of Payalikhand Topography Approx 300m above M.S.L Geological Set up The geological set up is same as that of

Payalikhand Block. The kimberlite pipe located at Baharadih is elliptical in shape. Presence of xenoliths of consolidated shale and sandstone within the weathered kimberlite indicate post Khariar age of diatremes. Since the kimberlite pipe does not crop out above the Khariar cover sediments, it is therefore, presumed that it has only intruded part of the sequence.

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Exploration:

This includes reconnaissance/large scale mapping, pitting/trenching, geochemical sampling, bulk sampling, shallow drilling, inputs from the geophysical surveys, remote sensing and photogeological studies.

The Bahradih diatreme is located in an ampitheatre like depression created by the second order nala. The amphitheatre is surrounded by resistant granitoid rocks. Bahradih diatreme surfaces at an altitude of 560m from MSL.

Characteristics of the diatreme:

Name of kimberlite body

Dimension Trend Emplacement control

Outcrop characteristics

Diamond contents/Heavy minerals

Bahradih 300m x 200m

Sub circular Within granitoid rocks (64L/4)

Ampitheatrical depression, highly altered kimberlitic rock (green earth), diatreme facies

Diamondiferous and garnet, spinel, clinopyroxene, orthopyroxene, phlogopite

A. 3. JANGRA DIATREME

Another pipe has been located near Jangra (200 08 30: 820 19 40 ). The Jangra diatreme is also located in an ampitheatre like depression created by a first order drainage. Like the Bahradih diatreme, at Jangra also the ampitheatre is surrounded by resistant granitoid rocks. Jangra diatreme surfaces at an altitude of 500m from MSL.

Characteristics of the diatreme

Name of kimberlite body

Dimension Trend Emplacement control

Outcrop characteristics

Diamond contents/heavy minerals

Jangra 50m x 50m Circular Within granitoid rocks 64L/8

Ampitheatrical depression within granitoid

Not known/ garnet and spinel

A. 4. KODOMALI DIATREME

Kodomali ( 20 0 11/ 10// : 820 14/ 08// ) kimberlite exposes as a dyke with an WNW-ESE trend and is the only diatreme with rock exposure visible at the surface, amongst the five known diatremes in Mainpur Kimberlite Field. Like other diatremes, this diatreme is also surrounded by the granitoids. The near surface alteration as green earth is not much as compared to other diatremes.

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Characteristics of the diatreme

Name of kimberlite body

Dimension Trend Emplacement control

Outcrop characteristics

Diamond contents/ heavy minerals

Kodomali 300m x 300m Circular Within granitoids 64L/8

Fresh rock exposed with calcretes and patchy development of near surface green earth

Diamondiferous and garnet, spinel, clinopyroxene, ilmenite and olivine

Kimberlites of Mainpur kimberlite field have been classified into three volcanic facies, viz. crater, diatreme and hypabyssal. Crater facies material has been preserved as xenoliths within Payalikhand-I and -II diatremes. Bahradih, Payalikhand I and II and Jangra diatremes have been classified as diatreme facies rocks. Only Kodomali rocks are classified as hypabassal facies

Recommendation: The MKF has scope for further work to establish more kimberlite pipes and evaluation of their diamond potentiality.

B. TOKAPAL KIMBERLITE FIELD (BASTAR DISTRICT)

The discovery of diamondiferous kimberlitic diatremes in Proterozoic sedimentary basinal area of Pairi-Khariar group, led to further search of kimberlites in similar geotectonic conditions in parts of Sabari and Indravati basinal areas in Bastar district of Chhatisgarh state. The regional search for kimberlites in Indravati basinal area has located kimberlite clan rocks in Tokapal, Duganpal, Bhejripadar and Parpa-Parakot areas and the Tokapal Kimberlite Field was established. The kimberlitic rocks are confined within the upper Proterozoic Indravati sediments and the upper parts (tuffs) are highly oxidized and are manifested by lateritised sub-domal morphostructures. The area is occupied by the Archaean-Proterozoic rocks of Bastar Craton. The kimberlitic pipes have intruded along NW-SE trending fracturers, which are exhibited by mafic dyke swarms in the area. The NW-SE trending dyke swarms as well as major lineaments and faults possibly indicate reactivated mantle permeable zones along which the kimberlitic pipes have been emplaced within the Proterozoic cover sediments.

Regional Geology and tectonics:

The Bengpal and Sukma group include amphibolite and granulite facies gneiss, metasedimentary and meta igneous complex showing polyphase deformation and metamorphism. The Bailadila Group and equivalents include lower amphobilite facies, BIF dominated, metasedimentary and metaigneous rocks. The Kotri supergroup includes bimodal acid and basic volcanics, ultramafics, sediments and shallow level intrusive granites. The Abujhmar group includes basalt, gabbro, conglomerates, sandstone and shale. The Indravati and Sabari group of sediments constitute the lower clastic facies and the upper carbonate facies.

The regional tectonics set-up in the Indravati basinal area includes three distinct units viz. the Archaean assemblage of Bastar Craton, the Eastern Ghats Mobile Belt (EGMB) and the

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Proterozoic sedimentary sequences of Indravati and Sabari Groups. The Indravati basinal area forms the east central part of Bastar Craton.

The Tokapal, Duganpal and Parpa-Parakot kimberlitic rocks probably indicate multiple intrusions from a single or multiple feeders covering an area with 5km length and 1 km width. The borehole core samples indicate multiple intrusions at different levels with deposition of tuffs in the upper part.

The Bastar kimberlites exhibit small domal morphostructurers within regional domal morphostructures. Sub-aerial effusive activity has also been preserved because of minor erosion in this area, which is very rare. The crater facies pyroclastic rocks have been well preserved in the area. This is the first and rare example in the Bastar cratonic area where kimberlitic pipes are surrounded by the remnants of tuff rings.

The Bastar kimberlites are in the crater facies, without much erosion. It is also interesting to note that in Baster, there are kimberlitic flows in phases overlain and underlain by Indravati sediments.

B.1. TOKAPAL KCR (KIMBERLITE CLAN ROCK) BODY

The Tokapal rock is exposed in pit section and the rock is greenish in colour and shows typical kimberlitic clast-matrix texture and flowage structure. The rock shows crude banding and top portion is lateritised and covered by black soil horizon.

Characteristics of the pipe

Tokapal Kimberlite Field, Indravati Basin

Place Trend Dimension Control Characteristics Diamond content

Tokapal KCR body

Not established

Not known Within sediments (Jagdalpur Formation) in the form of flows,65E/16)

Manifested by sub-domal morphostructure with laterite and black soil cover. The rock is exposed in pit sections only.

Not known

B. 2. DUGANPAL KCR BODY

The Duganpal kimberlitic rock is exposed in the Duganpal nala section and the tuffs are exposed in the Bahar nala section. The tuffs and pyroclastic rocks are lateritised and manifested by highly oxidized subdomal morpho-structures. The pyroclastic rocks of Duganpal area constitute pyroclastic breccias and tuffs. The pyroclastic rocks belonging to the crater facies include the basal breccia overlain by the purely stratified coarse pyroclastics and well notified tuffs. The pyroclastic breccia contains angular to rounded clasts (>25%) of red and purple shale, limestone and siltstone ranging from few mm to 0.5m. These fragments, including phlogopite olivine spinel rich mantle xenoliths, are cemented.by pyroclastic materials similar to that of

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overlying tuffs. The soil and stream sediment samples over the body are highly dominated by spinels and ilmenites. The body has been exposed by drilling.

Characteristics of the pipes

Tokapal Kimberlite field, Indravati Basin

Place Trend Dimension Control Characteristics Diamond content

Duganpal KCR body

Not established Not established, may be westward extension of Tokapal body

Within sediments (Jagdalpur Formation) in the form of flows,65E/16

Manifested by sub-domal morphostructure and highly oxidized tuffs with kimberlite clan rocks of crater facies.

Not known

B. 3. BHEJRIPADAR KCR BODY

The Bhejripadar kimberlitic body is located near village Bhejripadar (65 E/16). The body is exposed within the sandstone unit of Tirathgarh Formation. The body is also characterized by a domal morphostructure with bouldery exposures of greenish yellow kimberlite in the sloping ground. The rock is highly altered and preserves typical kimberlitic clast-matrix texture. It contains xenoliths of shale, sandstone and altered ultramafic nodules.

Characteristics of the pipe

Tokapal Kimberlite field, Indravati Basin

Place Trend Dimension Control Characteristics Diamond content

Bhejripadar Not established

Not established

Emplaced into the sediments

The body exhibits a sub-domal morpho-structure. Bouldery outcrops are exposed in the slopes. The body is mostly covered by sediments and lateritic soil.

Not known

:

B. 4. . PARPA PARAKOT KCR BODY

The kimberlitic rock in Parpa Parakot sector was observed from the borewell cores drilled by the State Agricultural Department. The crater facies rocks are concealed under the soil and laterite cover of >20m. The borehole data show the presence of kimberlitic tuffs and pyroclastic rocks below 19.87m from the surface upto 36.67 m. From 36.67m to 62.69m greenish black massive kimberlite was observed. These kimberlitic rocks may be part of the Tokapal body, which needs to be confirmed by geophysical investigation.

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Characteristics of the pipe

Tokapal Kimberlite field, Indravati Basin

Place Trend Dimension Control Characteristics Diamond content

Parpa-Parakot KCR body

Concealed under soil, laterite and sediments revealed by drilling

Not established, may be eastward extension of Tokapal body

Emplaced into the sediments

Nil Not known

Ultrapotassic and ultramafic rocks have also been reported within the lower clastic facies of Indravati Group of rocks..The ultrapotassic rocks may be compared with the group III type of ultrapotassic rocks as described by Foley et al (1987). The rock shows different types viz. a high potassium silica undersaturated, low potassium silica saturated and silica over-saturated types. The ultramafic rocks intrusive into the Tirathgarh Formation are composed of Mg rich chlorite and ortho-pyroxenes (mostly enstatite) with carbonates and opaques. So, the emplacement of kimberlite clan rocks was preceeded by ultrapotassic and ultramafic magmatism during the deposition of clastic sediments of Indravati group.

Petrographic studies reveal that the Bastar kimberlites are very much altered. Olivine pseudomorphs are dominated as serpentine, antigorite with fine-grained carbonates and spinels. At places, radiating, rounded grains of chlorite are observed in the matrix. Typical bronze yellow coloured phlogopites are observed in the groundmass. In some sections the country rocks mainly of shale fragments are oval shaped and its margins are highly digested and embayed due to the interaction with kimberlitic magma.

C.EXPLORATION FOR KCR IN RAIGARH MOBILE BELT

The exploration for KCR was also conducted in the Tapti Lineament Zone (TLZ) in parts of Raigarh and Surguja districts of Raigarh Mobile Belt from 1994 to 2000 on the basis of reported diamond incidences in the river gravels of Ib, Maini, Mand, Utial and Talda drainages. A total of 6000 sq km area was covered by PGRS studies and stream sediment sampling, but no primary source of diamond has been located except one grain of chromite falling in the edge of kimberlite field.

D. SARANGARH SECTOR

The Sarangarh area falls in the north eastern part of Chhattisgarh basin. A major part of the area forms a part of Bardwar sub basin of Chhattisgarh supergroup. Stream sediment sampling in the area revealed presence of kimberlitic pyrope garnet which are found to be G-9 type of lherzolitic derivative. In addition G-5 garnet has also been discovered from stream sediment samples. Detailed sampling in this area is recommended.

PROSPECTS IN MAHARASTRA

Indicator mineral survey carried out in the western part of Bastar craton, falling in Chandrapur and Garchiroli districts of Maharastra has revealed chrome diopside and G5 garnet

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in 5 drainage area. The chrome pyroxenes show some similarity with the pyroxenes from the Monastry kimberlite field., South Africa, in terms of their Ca/ (Ca + Mg) and Mg/(Mg + Fe) ratio with chromium.

Results of the Indicator Mineral Survey:

Preliminary indicator mineral survey carried out in the western parts of Bastar Craton covering Chandrapur and Garchroli districts, in Maharastra has shown chrome pyroxenes in 12 out of 60 samples, from five drainage areas viz. Andhari and its tributaries in Mul-Sindewahi area southeast of Saoli and north of Awalgaon, all in Chandrapur district and Deorighat nala a tributary of Sati nadi, east of wairagarh and Karwapa nala south of Chatgaon, Garhchiroli district. Besides one garnet grain having a composition close to G5 garnet (high magnesian almandine, Dawson, 1980) was recovered along with chrome pyroxenes (MgO-6.9%, TiO2O.03% and Cr2O3-0.06%)

Detailed indicator mineral survey carried out in two blocks viz. Andhari river and southeast of Saoli has confirmed the presence of G5 garnet and chrome diopside in seven samples. The chrome diopsides include both calcic and subcalcic varieties. In general, the chrome dipside population is calcic with Cr2O3 in the range of 0.12 to 0.55%. The G5 garnets have MgO in the range of 6.42% to 10.65%. ,FeO 23.69%, SiO2 37.63% to40.17%, Al2O3 21.03% to 23.15%, TiO2 - 0.01% to 0.12% and Cr2O3 0.04% to 0.12%

The chromium pyroxenes of the area comprise three types viz., low chrome diopside, low to high chrome, sub-calcic diopsides and sub-calcic chromian augite/salite. By and large the population is sub-calcic with high Fe and A12O3. The plots of Cr2O3 with Ca/Ca+Mg and Mg/Mg+Fe of the chrome diopsides indicate some similarity to the chrome diopsides from the Monastery Kimberlite field, South Africa. (Mitchell 1986) and Letseng la terae kimberlite, Lesotho, particularly with the samples of high Ca/Ca+Mg ratio of the study area.

The recovery of chrome diopside is considered to be important, particularly when recovered with other indicator minerals. This particularly true, as similar chrome-pyroxenes can also be found in many alkaline rocks such as minette, alkali basalts, nephelinite etc. (Mitchell 1986). As there is no reported occurrence of any such rocks in the present area, and considering the presence of G5 garnet coupled with pyroxenes, the indicator minerals may probably, be kimberlitic. This is in conformity with the regional survey and indicates the source area of the indicator minerals, narrowing down the search area. Though traverses during the study have not shown any kimberlites and lamproites in the area, test pitting in selected areas may be required to examine the possibility of these rocks.

PALEOPLACER DIAMONDS OF WAIRAGARH, MAHARASTRA:

Diamond incidence is known from conglomerates of Wairagarh area in Maharastra (Tavernier 1676). A brief account of the diamond incidence in Wairagarh area is as follows:

The Wairagarh area exposes a narrow stretch of (10km x 6km), NNW-SSE trending low grade, highly deformed meta sedimentary belt within the terrain occupied by Archaean Amgaon Gneiss and forms a part of the western part of Bastar Craton. The metasediments comprise framework supported polymictic conglomerate, gritty and pebbly arenaceous units, quartzite and quartz-mica schist. Polymictic conglomerate is made up of bizarre assemblage of clasts of different composition and size set in a well-foliated quartz sericite matrix. Quartzite dominates the clast population accounting nearly for 80%, and the remaining includes gneiss, vein quartz, ferruginous quartzite, and metabasics. The deformed clasts display high degree of flattening and

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the rock records variable (sub horizontal to steep) stretching lineation. The conglomerate grades laterally in to gritty quartzite and mica schist. The ductile shear zone occurring along the eastern margin of Sakoli Fold belt passes through the sediments resulting strong deformation of the basement cover rocks.

The Wairagarh metasedimentary unit (WMS) appears to have been deposited over the gneissic basement. The Dongargarh granite dated 2465-2270 Ma by Sarkar 1994, occurs along its eastern margin. A narrow lensoidal body of granite occurs within the WMS towards its southcentral part. The lensoidal body of granite does not show any strain evidence. Younger cover rocks of platformal facies of probable Pakhal rocks (mid to late Proterozoic) and lower Gondwana affinity (Talchir) occur to the western and northwestern part respectively. The stratigraphic status of WMS is still not clear. The total absence of granite clasts in the WMS and the undeformed nature of granite as compared to the strained nature of the WMS suggest that the granite may be intrusive, which may assign an early Proterozoic age to the WMS.

From the available records it is known that mining in Wairagarh area was prevalent since the early part of 15th century. Farishta in 1425, Garcvia daorta in 1565 and Abul Fazal in 1590 (Ball, 1984) described the richness of the mines and the quality of the diamonds. From the distribution of the old workings and abundant dumps it can be assumed that the entire area was scanned for diamonds, including alluvial, colluvial, weathered bed rock and even the laterite profile developed over the conglomerate. It appears that the clast rich portion was selectively mined, as good crop of heavy minerals are associated with such coarse clastics. The workings having a general size of 25m-40m diameters are seen spread throughout the area. Study of the old dumps and stacks suggest that the old miners have removed the clasts at the site of pits itself and the matrix was crushed to 1cm and 5mm size for recovery of diamonds.

An octahedral diamond (3.5mm long and 2.5mm wide, 0.15 carat) recently recovered during the GSI investigations of the conglomerate unit of WMS shows a light greenish tint with well developed crystal faces. The octahedra edges show stepped surfaces and twinning noticed is of spinel law, having a triangular shape in plan. A black coating, noticed in a cavity on one face, appears to be graphite inclusion. Along with diamond other heavy assemblages identified include ilmenite, garnet (G-5 garnet, almandine, grossular and andraditic garnets), pyroxenes, amphibole, staurolite, chrome spinel and rare tourmaline. The chrome pyroxenes are low chrome variety. The Ca/(Ca+Mg) and Mg/Mg+Fe ratios of the pyroxenes do not indicate any kimberlite/lamproite affinity.

The discovery of diamond in an older conglomerate of probable early Proterozoic age points to much older diamondiferous intrusion in the western part of Bastar Craton. The source rock of diamond probably of Archaean age may be difficult to locate due to complex geological processes the terrain has undergone, which include granite intrusion, regional metamorphism followed by deposition of younger proterozoic and Gondwana rocks. This find has opened up new vistas of diamond search in similar geological milieu in the western Bastar Craton.

PROSPECTS IN ORISSA

In order to locate more kimberlite/lamproite bodies within and adjacent to Mainpur Kimberlite field in the eastern part of Bastar Craton, multisensor Twin otter aero-geophysical survey were carried out by the Airborne Mineral Survey and Exploration Wing (AMSE Wing) of Geological Survey of India during 1994-98 along E-W flight lines at intervals of 500m with a mean terrain clearance of 80m covering an area of about 27,850 sq. km. from Mainpur-

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Payalikhand area in the south to Raigarh-Sundergarh area in the north around Chhattishgarh-Orissa border. The vast amount of this aero geophysical data was utilized for search of kimberlite.

Near Sakri village, Bargarh district, Orissa NE-SW trending olivine lamproite dyke cross cutting a NW-SE trending dolerite dyke has been discovered. Recently some more small lamproite bodies have been discovered in the adjoining areas.The lamproite in Sakri confirmed by SEM/EDX studies has olivine (altered), titaniferous phlogopite, and carbonates (dolomites and calcites) besides zinc bearing chrome spinels, clinopyroxene, monazite and high Fe-Ba potash feldspars(sanidine?). Discovery of this lamproite has raised hopes of finding more such dykes and main lamproite bodies along the ideal setting of the contact of Bastar Craton and Eastern Ghat Mobile Belt. It may be mentioned here that this present setting is similar to the Krishna lamproite field (KLF) on the eastern margin of Dharwar Craton just outside the NE horn of Cuddapah basin in Andhra Pradesh.

Discovery of a lamproite dyke on the margin of Bastar Craton and Eastern Ghat Mobile Belt and incidence of several kimberlite indicators in Mainpur-Gariaband and Khariar road-Paikamal area prove that the integrated strategy is well founded and worth continuing further to utilize the vast amount of aero-geophysical data available with GSI pertaining to this area. Recently State DGM has recovered diamond from a pipe in Kalmidadar.

Analytical results:

Determinative analytical techniques such as SEM-EDX, EPMA were pursued for suspected heavies to identify indicator minerals. Deep red garnets recovered from samples drawn from the north of Mahasingh in southern faulted contact zone of Gondwana with cratonic gneiss in Ib basin are identified to be magnesian almandine by SEM-EDX with MgO around 7%. Garnets from stream sediments of Motur nala, a tributary to Tel river to south of Dharamagarh were identified as magnesian almandine by SEM-EDX with MgO around 13%. Suspected garnets from Indravati river basin are identified as magnesian almandine by SEM-EDX with MgO around 9%. MgO, FeO, CaO% of these garnets from all the three river basins when plotted on Dawson-Stephens diagram, fall in G-5 field.

The Cratonic domain of western Orissa lying in tectonic juxtaposition with circum cratonic EGMB is a promising regional target of primary diamond exploration due to its lofty age old diamond panning records and recent discovery of kimberlite diatremes in adjoining state of Chattisgarh having identical geological milieu.

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PART - II

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DETAILED INFORMATION ON DIAMOND IN ANDHRA PRADESH & KARNATAKA

DETAILED PROSPECTS IN ANDHRA PRADESH

South India is known from antiquity, for its most beautiful, famous and large size diamonds. The ancient diamond mining activity was concentrated mostly along the alluvial tracts of the Krishna River in the modern State of Andhra Pradesh. Many celebrated diamonds like the Great Moghul (787 ct), the Koh-i-noor, Pitt/Regent (41 ct), Nizam (440 ct), Hope (67 ct), Orloff, Darya-i-noor etc. are known to have been recovered from the mines along the alluvial tracts of the Krishna River, perhaps aptly referred to as diamond river by Ptolemy. Having a place of pride for the ancient diamond mining as trade, Andhra Pradesh is bestowed with both primary (kimberlites and lamproites) and secondary (conglomerates and gravels) sources of diamond.

Geologically, this historically world-famous diamond province occurs in the Southern Indian Shield which is divided into Dharwar Craton and Southern Granulite Terrain based on the gross lithological assemblages (Ramakrishnan. 1993). The Dharawar Craton exposes a granite-greenstone ensemble composed predominantly of granitoids, gneisses and greenstone (schist) belts and late to post-tectonic granites (Closepet Granite and its equivalents) which were intruded by mafic dyke swarms. This dyke infested Archaean granite-greenstone terrain is unconformably overlain by sediments of Meso-to-Neo Proterozoic intracratonic sedimentary basins (Radhakrishna 1990, Drury et al, 1984). The granite-greenstone terrain and sediments in the north and northwestern part are covered by Cretaceous-Tertiary lava flows of the Deccan Trap. The cratonic granite gneiss assemblage concealed below the lava flows perhaps extends upto the Son Narmada Lineament in the north. The Craton is bounded by the Eastern Ghats Mobile Belt in the east, the rifted continental margin a result of fragmentation of the Gondwana Land in the west, the Godavari Graben in the northeast and the Palghat Cauvery Shear System in the south.

Dharwar Craton remained free of any orogenic movements since 2500 Ma.. The Southern Granulite Terrain, on the other hand, shows imprints of Pan African (600 500 Ma) remobilization marked by the EW to WNW ESE trending shear belts (Ramakrishnan , 1993). These major geological events in the South Indian Shield were followed by the fragmentation of the Gondwana Land, northward drifting of the Indian Plate and widespread lava flows of the Deccan Traps under the influence of a mantle plume activity.

The South Indian Peninsular Shield is endowed with both kimberlites and lamproites. The known kimberlites are distributed in two major fields, namely Wajrakarur Kimberlite Field (WKF) and the Narayanpet Kimberlite Field (NKF) within the granite-greenstone terrain, while the lamproites are distributed in two fields, namely the Nallamalai fold belt of the Cuddapah basin and the Jaggayyapeta Lamproite Field or Krishna Lamproite Field (JLF/KLF) within the Peninsular Gneissic Complex.

The South-Indian diamond province is confined to the south of Pranhita Godavari rift zone, essentially consisting of four main geotectonic units namely (1) Western block of Dharwar Craton (WDC), (2) Eastern block of Dharwar Craton (EDC) (3) Eastern Ghat Mobile Belt (EGMB) and (4) Southern Granulite Terrain (SGT). These kimberlites and lamproites are known

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to occur only from the Eastern Dharwar Cratonic block mainly falling in Andhra Pradesh and minor parts in adjoining Karnataka.

A.KIMBERLITES AND LAMPROITES

Kimberlites and lamproites are located in about 270