BHUTAN - ESCAP Repository

ATLAS OF MINERAL RESOURCES

OF THE ESCAP REGION

Volume 8

BHUTAN

EXPLANATORY BROCHURE

UNITED NATIONSECONOMIC AND SOCIAL COMMISSION FOR ASIA AND THE PACIFIC IN CO-OPERATION

WITH THE DEPARTMENT OF GEOLOGY AND MINES OF BHUTAN

1991

ATLAS OF MINERAL RESOURCES OF THE ESCAP REGION SERIES

(Separate booklets prepared by the secretariat of the United Nations Economic and Social Commission for Asia and the Pacific in co-operation with national geological agencies)

Volume 1. MALAYSIA (ST/ESCAP/339)

United Nations publication, non-sales, 1985. Explanatory brochure in English, 16 pp. with 3 atlas sheets in a back pocket, comprising the Geological Map and Mineral Resources Map of Peninsular malaysia, the Geological and Mineral Resources Maps of Sarawak and Sabah at 1: 2,500,000 scale and the legend.

Volume 2. SOLOMON ISLANDS (ST/ESCAP/392)

United Nations Publication, non-sales, 1985. Explanatory brochure in English, 35 pp. with 2 atlas sheets in a back pocket, comprising the Mineral Resources Map of Solomon Island at 1: 2,000,000 scale and the legend.

Volume 3. REPUBLIC OF KOREA (ST/ESCAP/481)

United Nations publication, non-sales, 1987. Explanatory brochure in English, 51 pp. with 3 atlas sheets in a back pocket, comprising the Geological and Mineral Resources Maps of the Republic of Korea at 1:1,000,000 scale.

Volume 4. NEW ZEALAND (ST/ESCAP/561)

United Nations publication, non-sales, 1988. Explanatory brochure in English, 28 with 5 atlas sheets in a back pocket, comprising the Geological Maps of North and South Islands, the Mineral Resources Maps of North and South Islands and the legend.

Volume5. SRI LANKA (ST/ESCAP/718)

United Nations publication, 1989. Explanatory brochure in English, 45 pp, with 3 atlas sheets in a back pocket, comprising the Geological, Metamorphic and Mineral Resources Maps of Sri Lanka at 1:1,013,760 scale. Sakes No. E. 89.II.F.14, ISBN 92-1-119541-1, ISSN 1014-5451. Price US$ 12.00

Volume 6. VIET NAM (ST/ESCAP/831)

United Nations publication, 1990. Explanatory brochure in English, 124 pp, with 2 atlas sheets in a back pocket, comprising the Geological and Minerals Resources Maps of Viet Nam at 1: 1,500,000 scale. Sales No. E. 90. II.F. 10, ISBN 92-1-119559-4, ISSN 1014-5451. Price US$ 19.00

Volume 7. LAO PEOPLE’S DEMOCRATIC REPUBLIC (ST/ESCAP/929)

United nations publication, 1990. Explanatory brochure in English, 19 pp, with 2 atlas sheets in a back pocket, comprising the Geological and Mineral Resources Map of Lao PDR at 1 : 1,500,000 scale. Sales No. E.90.II.F.14, ISBN 92-1-119572-1, ISSN 1014-5451. Price US$ 12.00

ECONOMIC AND SOCIAL COMMISSION

FOR ASIA AND THE PACIFIC

Bangkok, Thailand

ATLAS OF MINERAL RESOURCES

OF THE ESCAP REGION

Volume 8

BHUTAN

EXPLANATORY BROCHURE

UNITED NATIONS New York, 1991

ST/ESCAP/1056

UNITED NATIONS PUBLICATION

Sales No.E.92.II.F.7

ISBN: 92-1-119596-9

ISSN: 1014-5451

The designation employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Secretariat of the United Nations concerning the legal status of any country, territory, city or area of its authorities, or concerning the delimitation of its frontiers or boundaries.

Mention of any firm or licensed process does not imply endorsement by the United Nations.

This publication has been issued without formal editing.

PREFACE

This volume aims to show the distribution of mineral deposits and occurrences in the Kingdom of Bhutan, irrespective of their current economic significance, and to provide information on their contained commodities, reserves, geographic locations, their relation to the geological environment and other characteristics. The publication consists of this explanatory brochure and two atlas sheets, viz. a geological and a mineral resources map at a scale of 1: 500,000.

The explanatory brochure gives a broad overview of the tectonic framework of the Bhutan Himalaya and short descriptions of the underlying lithologies and of the associated mineral occurrences, giving an up-to-date account of metallic, non-metallic and coal deposits in the Kingdom. Also included is an index, some information on production levels and a review of the status of mineral imports and exports, followed by expected future trends.

The information contained within this brochure is mainly based on work by the Geological Survey of India (Bhutan Unit, Samchi), on fieldwork and publications by the Geological Institute of the University of Zurich, Switzerland, and on reviews and field investigations of the Department of Geology and Mines, Thimphu, Bhutan, followed by discussions and close cooperation among staff of the Department of Geology and Mines and representatives of the ESCAP Mineral Resources Section, culminating in this compilation.

The current status of development in the Kingdom of Bhutan in general, and of its Department of Geology and Mines in particular, which is still in an early stage of growth, provides the background against which to consider the information provided in this volume. The maps should be viewed as sketch maps, both from a geographical and a geological point of view, but provide sufficient information to gain the valued attention not only of the professional reader, but of the interested layman as well.

The ESCAP secretariat trusts that the present volume will indeed create interest in the mineral resources of Bhutan, both from within the Kingdom and from other member countries and beyond, while at the same time stimulating a systematic approach to the establishment and improvement of a reliable database on geology and mineral resources, of which the current maps and accompanying text are modest but adequate beginnings.

iii

Explanatory Notes

In the absence of a reliable map base, the 1 : 500,000 map had to be adjusted to geographical coordinates. Correct spacings between meridians were determined to approach a conical projection, after which the Landsat-derived drainage pattern as published by Gansser (1983) was fitted to these geographical coordinates. When checked against reductions of existing 1: 50,000 topographic sheets, the result was found to be a reasonable topographic base map. Nevertheless, after these reductions became available, it was decided to use these after all, to avoid confusion in some of the border areas, notably in the southeast.

The geology as shown is a mixture if not a patch work of different sources, the two main ones being the work of the Geological Survey of India (Bhutan Unit) covering the south and the centre, and the work by Gansser (1983), which was mainly followed in the north and northwest. A third map, a compilation supplied by the Department of Geology and Mines, was followed only when information on the other two maps was absent or contradictory.

The stratigraphy is the result of lengthy deliberations among DGM and ESCAP staff, as many different versions had been published and were in use simultaneously. The result again is a compromise between different sources: the GSI, the DGM, and some individual authors like Jangpangi (1978) and Gansser (1983).

Data on mineral resources were compiled mainly from the GSI (1984) publication “Geology and Mineral Resources of Bhutan” and “Geology and Mineral Resources of the Kingdom of Bhutan” by DGM geologist Shivaraj Gurung, and is largely left untouched. Some minor input from other scattered sources has been incorporated in a computer database, which forms the basis of the Index as found in the brochure.

Brian Shaw’s “Bhutan: Physical and Social Geography” (1990) supplied some of the general background data, whereas the information on imports and exports of industrial minerals was collected by Dr. D.N.S. Dhakal of the DGM in Thimphu.

iv

CONTENTS

v

Preface ............................................................................................................................................................................................. iii

Explanatory Notes........................................................................................................................................................................ iv

I. BACKGROUND INFORMATION.............................................................................................................................. 2

II. GEOLOGY OF BHUTAN ................................................................................................ ........................................... 3

A. Major Geotectonic Units ........................................................................................................................................... 3

B. Distribution of Rocktypes in Bhutan ....................................................................................................................... 7

C. Regional Metamorphism in Bhutan ........................................................................................................................ 9

III. MINERAL DEPOSITS.................................................................................................................................................... 12

A. Metallic Minerals.......................................................................................................................................................... 12

B. Non-Metallic Minerals................................................................................................................................................. 21

C. Mineral Fuels................................................................................................................................................................. 37

D. Index of Mineral Deposits .......................................................................................................................................... 41

IV. MINERAL PRODUCTION, IMPORTS AND EXPORTS ................................................................................ 43

A. Production of Industrial Minerals in Bhutan.......................................................................................................... 43

B. Imports, Exports and Trends ..................................................................................................................................... 43

LIST OF TABLES

1. Lithostratigraphy of the 1 : 500,000 Geological Map of Bhutan ............................................................................ 10

2. Bhurkhola West Block: Reserves down to a vertical depth of 90m ........................................................................ 15

3. Bhurkhola West Block: Reserves between 90m and 200m vertical depth............................................................. 15

4. Bhurkhola West Block: Reserves for the entire Block............................................................................................... 15

5. Summary of Reserves Estimate for the Gongkhola Copper Deposit....................................................................... 17

6. Copper Occurrences in the Samchi District, Bhutan.................................................................................................. 18

7. Lead-Zinc Mineralization in the Jemena Area............................................................................................................. 20

8. Chemical Composition of the Kalesor Dolomite Bands............................................................................................ 24

9. Dolomite Reserves and Grades, Bhutan ....................................................................................................................... 26

10. Khepchishi Hill Graphite Reserves................................................................................................................................ 27

11. Gypsum Reserves and Grades, Bhutan......................................................................................................................... 29

12. Reserves of the Khanko Limestone Deposit................................................................................................................ 32

13. Limestone Reserves and Grades, Bhutan...................................................................................................................... 34

14. Talc Occurrences of Bhutan ........................................................................................................................................ 35

page

CONTENTS (Continued)

15. Coal Reserves and Grades, Bhutan................................................................................................................................. 38

16. Mineral Production in Bhutan......................................................................................................................................... 43

17. Mineral Exports and Imports in Bhutan, 1988 ............................................................................................................. 43

18. Summary of Metallic Mineral Resources of Bhutan ................................................................................................. 47

19. Summary of Non-Metallic Mineral Resources of Bhutan......................................................................................... 50

LIST OF FIGURES

I. Geotectonics of the Wider Himalaya Region .............................................................................................................. 4

II. Regional Cross-Section from Shillong, India Through Bhutan to Lhasa, Tibet..................................................... 5

III. Structural Map of the Bhutan Himalaya....................................................................................................................... 6

IV. Subrecent Tectonics at the Hatisar Embayment........................................................................................................... 7

V. Metamorphic Zoning in the Bhutan Himalaya ............................................................................................................ 11

VI. Geological Map with Tungsten Mineralization of the Dholpani-Bhurkhola Area, Geylegphug District ........ 13

VII. Localities of Copper Mineralization in the Samchi District...................................................................................... 19

VIII. Occurrence of Phosphorite in Mauree, Kalikhola Area.............................................................................................. 22

IX. Graphite Occurrences in Bhutan .................................................................................................................................... 28

X. Limestone Occurrences in the Nganglam Area, Samdrup-Jongkhar District, Bhutan ....................................... 31

XI. Coal-bearing Strata of the Area between Deo River and Jomo River, SE Bhutan................................................ 37

vi

page

1

INTRODUCTION

Historically, Bhutan has not been a notable producer of minerals, although there are traces of ancient iron ore mining, providing material for the manufacture of weapons, artifacts and chains for suspension bridges. Remnants of lead and zinc smelting have also been found. And then there is the occasional reference to gold nuggets said to occur in the largely inaccessable Black Mountain region of Central Bhutan.

Being a land-locked country of some 46,000 km2 and with a population of currently around 0.6 million1, Bhutan’s economy is largely based on agriculture. Having improved and enlarged the road system, constructed power lines and established telecommunication networks as well as scheduled flights to neighbouring countries, Bhutan is embarking on a programme of controlled industrial development, including minerals, while emphasizing the need to safeguard the environment. The country’s main natural resources are water (which is used to produce cheap and

clean electric power), forestry (presently being developed in a more systematic way) and various mineral resources.

Largely with the valued assistance of the Geological Survey of India, deposits of limestone, dolomite and gypsum have been identified in varying detail, along with some base metals and an insignificant amount of iron ore. Concerning energy resources: although Bhutan has ample hydropower and some scattered coal (and graphite) deposits, the country has to import all the hydrocarbons it needs for its development. However, following positive indications to that effect, the possibility of petroleum occurring in the southern border areas with India is being investigated. Clearly, both the need and the potential for further exploration exists.

The physiography of Bhutan of course continues to have its impact on exploration activities, with conditions varying between extremes: from the hot and humid south to the inaccessable snow-covered and barren Great Himalayas of the north.

1 Official figure for 1990, as quoted by the Royal Government of Bhutan.

2

I. BACKGROUND INFORMATION

Bhutan with its 46,000 square kilometers is the smallest independent nation on the Asian continent. The nearest seaport is Calcutta in India, 750 km by road from the Bhutanese bordertown of Phuntsholing. From there, the capital Thimphu is 175 km by road to the north. The country’s international airport is situated in the Paro valley, about two hours by road from the capital.

The terrain is some of the most rugged in the world, rising from altitudes close to sea level to over 7000 m, in some areas within distances of less than 100 km. The highest Bhutanese mountain, covered with eternal snow is Mount Chomolhari at 7314 m (the Kula Kangri with its 7554 m being just outside of its territory). This rough terrain is well dissected by numerous rivers and their tributaries, most of which originate in the so-called Greater Himalayas and flow southward through narrow gorges and ravines before entering the Duar plains to finally drain into the Brahmaputra. From west to east are the Jaldhaka, Amo Chu, Wang Chu, Mo Chu, Mangde Chu (Tongsa), Bumthang and Dangma Chu (Manas). The broad valleys of Paro, Thimphu, Punakha and Bumthang make up the economic and cultural heartland of the country. A significant feature in Central Bhutan are the north-south ranging Black Mountains, which have significant impact on climatic conditions.

Bhutan has perhaps the greatest variety of climates of any country its size, ranging from hot and humid tropical conditions to the glaciers and eternal snow of the north. The most important climatic factor is the southwest monsoon which lasts from mid-June to September, bringing 60-90 per cent of annual precipitation, depending on the region. Average rainfall ranges from about 2500 mm in the south (5000 mm locally) to 500 mm to 1000 mm in the inner valleys, and to less than 500 mm at elevations above 4000 m. The monsoon is particularly strong in the west but its impact in the east is diminished by the rainshadow effect of the Black Mountain range. Average daily temperatures in the (sub) tropical south vary from 15° to 30°C. At about 1500 m the climate becomes cool and misty for much of the year. In the inner valleys the climate is rather

variable but tends to be temperate and distinctly seasonal. At around 3500 m the climate becomes increasingly severe and dry: short cool summers and long cold winters.

Despite its small size, population density is rather low, and the largest urban area is the capital Thimphu, which has perhaps grown to 20,000 inhabitants. Labour, particularly skilled labour is hard to come by and relatively expensive, which explains why large numbers of workers have traditionally been imported, particularly in construction. The economy of Bhutan is essentially agrarian, with an estimated 93 per cent of the economically active population engaged in agriculture and livestock raising, with 9 per cent of the land under cultivation, and with agriculture contributing at least a third of the gross domestic product.

The expenditure on industry and mining during the current (6th) Five Year Plan was around Nu. 1,553.6 million or 16.4 per cent of the total, based on exploitation of mineral and forest resources, agricultural produce and inexpensive power. Private enterprise has so far mainly taken the form of small-scale industries. The 6th Plan however, put considerable emphasis on the formulation of a strategy for a faster expansion of export-orientated industries. The hydroelectric project is expected to stimulate growth in the industrial sector.

The Penden Cement factory in southern Bhutan began operating in 1981 and earned Nu. 130 million in 1988. A second cement plant, at Nanglam is to be completed by 1991. Yangzom Cement Industries is a private undertaking. A calcium carbide plant at Pasakha, near Phuntsholing, was set up with assistance of the World Bank, and commercial production began in 1988. In addition, small industrial estates have been established at Phuntsholing, Geylegphug and Samdrup-Jongkhar, producing a variety of consumer goods and industrial products.

A Japanese-constructed satellite station in Thimphu is now operational and capable of direct high quality telecommunications access, such as by fax, to third countries.

3

II. GEOLOGY OF BHUTAN

As Bhutan covers a small portion of the mighty Himalayan Range south of the main watershed, which provides a natural boundary with Tibet to the north, its geology can best be observed in a regional context before homing in on the local situation (Figure I).

A. Major Geotectonic Units

To put things in such a regional perspective, Gansser (1964, 1983, etc), looking at the problem with the eyes of an Alpine geologist, observed that the Himalayas are made up of a sequence of major geotectonic units which express themselves geomorphologically as the Sub-, Lesser (or Lower) and Higher (or Greater) Himalayas, separated from each other by major faults or thrusts. From S to N these units are the:

* Main Frontal Thrust or MFT, locally observed to separate the basement rocks of the Indian Shield from the

* Siwalik Belt with molasse type rocks of the Sub- Himalayan foothills, separated by the

* Main Boundary Thrust or MBT from the metasedimentary series and crystalline sheets of the Lower Himalayas. These in turn are overridden by the

* Main Central Thrust or MCT sheet, which in most published geological sections through the Himalayas finds itself at the base of the Higher Himalayas, frequently represented by isolated “klippen”. Going upward through these main thrust sheets, their sequence tends to end conformably with the overlying

* Tethyan or Tibetan basin sediments.

Figure II adds a third dimension to this rather simplified geotectonic framework.

Since in Bhutan we are nearing the eastern end of the Himalaya, presumably somewhat removed from the main centres of geotectonic stress that formed the basis of the orogenesis, one could envisage the main Himalayan thrusts to either splice out or to have a diminished movement along them, or both. Either of these phenomena could account for the reluctance by some authors reporting on Bhutan to identify unequivocally the MCT (e.g. Gokul, 1976/1982) while on the other hand many different, smaller thrustplanes have been recorded. However, opposing views exist, that stress the importance of thrust-tectonics to the understanding of the geology of the Bhutan Himalaya (e.g. Jangpangi, 1978).

Presently, the traditional classification in Sub-, Lesser and Higher Himalaya is now seen in Bhutan as being just morphological as the three main geotectonic units that can be recognized have indeed been found to cut across the earlier subdivision. These tectonostratigraphic units are:

(1) the Frontal Belt, making up the foothills and part of the Lesser or Lower Himalaya,

(2) the Central Crystalline Belt, occupying portions of the Lesser and Higher (or Greater) Himalaya, and

(3) the Tethyan Belt, covering the Higher Himalaya and isolated but large portions of the Lesser Himalaya.

At least three successive cycles of deformation have affected these three belts. The first, main phase operated under a N-S stress field, producing tight, E-W striking, overturned folds with the generally north-dipping axial plane cleavage which is the most prominent planar structure in the area. The intensity of this type of deformation decreases towards the north, however. During the final stages of main phase folding, extensive tectonization, shearing and (over) thrusting took place, a.o. resulting in the Main Central Thrust (MCT) and translation of rocks from north to south. The second deformation phase, still under a N-S stress regime, resulted in upright open folds, associated with the formation of the Main Boundary Fault and the thrusting of Paleozoic rocks over the Tertiary Siwalik Group of rocks. A third phase of deformation, operating under an E-W stress orientation, resulted in N-S trending, round-hinged, upright open folding affecting earlier planar structures and thus creating the peculiar north-pointing “spurs” of the major thrust contacts, as seen in Sikkim and the Kuru Chu area of Bhutan (see figure III).

In the southern foothills, warped and tilted river terraces are evidence of Quaternary to subrecent morphogenic uplift. In one instance this has even resulted in terraces having been affected by overthrusting (Nakata, 1972), which led to the recognition of the Main Frontal Thrust or MFT (see figures I and IV).

Even younger tectonic activity in the form of pronounced NS-striking faulting and fracturing overprints all previous deformations and can easily be detected on satellite images (see figure III). In the Bhutan Himalaya this fault pattern is interpreted as a reactivation of the old structural grain of the Indian Shield. Seismic activity appears to be related to this youngest fracture pattern and its intersection with the MFT (Gansser, 1983). Unfortunately, records on earthquake history and locations of epicentres are scarce in Bhutan, although sizeable earthquakes have occurred in the vicinity. Clearly, Himalayan uplift is an on-going activity and is proceeding at a unique rate of about 5 mm per year (Yang and Liu, 1974)!

Turan

Figure I. Geotectonics of the Wider Himalaya Region (Gansser, 1983).

The boundaries and names shown on this map do not imply official acceptance or endorsement by the United Nations

Arabian Sea

Bay of Bengal

Tarim

BHUTAN

DeccanTrap

Al

Helmond

Figure II. Regional Cross-Section from Shillong, India Through Bhutan to Lhasa, Tibet. Gansser (1983).

Indian Shield

5

Crystalline sheets

Kingdom of Bhutan

metasedim

ents

Siw

aliks molasse

Shilong Brahmaputra


sz

Tethyan sediments

Transhimalayan Pluton

NB

Kangdese(Lhasa

km10

0

10

20

30

40

50

60

70

■80

SUTUREFlysch Belt

ZONEYomdrok Tso

Platform Sed. Puma Tso

Masang Kang Anti-form

KankarpunzumTongsaMCTMBTMFT

SA

km10

0

10

20

30

40

50

60

70

80

Structural Map of the Bhutan Himalaya

Os

Figure III. Detail of Figure I: Structural Map of the Bhutan Himalaya.

Note: Sikkim and Kuru Chu “spurs” of the Main Central Fault Line (MCT); after Gansser (1983).

Abbr

D ' DarjeelingG : Gengtok Ch : Chomolhari KK: Kunla Kangri MK: Masang Kang Pa : ParoPh : PhariP : Phuntcholing

Ta : Tashigang T : Thimphu To : Tongsa

1980 A. GansserSCALE

20 km100

LEGEND

Tethyan sediments

Metasediments of Lesser Himalaya

Cryst. Sheets i Migmatites and granit gneisses,incl. Indian Shield basement

Cryst. Sheets ; Pre-Cambr. metasediments

Quaternary

Siwalik Molasse Leuco. granite 10-25 my

Main thrustsMFT : Main Frontal Thrust MBT : Main Boundary Thrust MCT : Main Central ThrustFault and fracturesFold axis incl. some major lineations, dip<30°, dip> 30° General dip and strike direction


7

MBT : Main Boundary Thrust

MFT : Main Frontal Thrust

Figure IV. Subrecent Tectonics at the Hatisar Embayment (Geylegphug district, Bhutan).

B. Distribution of Rocktypes in Bhutan

+++ Rocks of the Frontal Belt +++

1. Recent deposits

The foothill terraces of southwest and south-central Bhutan mentioned above are composed of sand, gravel and boulders and occur to about 300 m above sea level.

2. The Siwalik Group

The Frontal Belt consists of sedimentary and metasedimentary rocks, extending in an E-W direction while dipping to the north. Along its southern margin, two narrow strips of the autochtonous Siwalik Group of sedimentary rocks are present: one in central Bhutan extending from east of the Raidak river to west of Sarbhang town, the other in eastern Bhutan stretching from east of the Manas river to the eastern boundary with the Indian state of Arunachal Pradesh. River sections expose three divisions: Lower, Middle and Upper Siwaliks, ranging in age from Mio- to Pleistocene.

The grey-green claystones of the Lower Siwaliks contain occasional limestone nodules and highly fractured hard sandstones. They are well developed along a section of the Samdrup-Jongkhar-Deothang road in eastern Bhutan, are highly folded and merge into the Middle Siwaliks without any visible break.

The friable sandstones of the Middle Siwaliks show a decrease in clay beds when going upwards in the sequence.

Finally, a thick conglomeratic horizon with boulders and pebbles of quartzite and jasper in a sandy matrix constitutes the Upper Siwaliks.

The Siwaliks are thrown into transverse, broad open folds which are likely to result from the third phase deformation with its E-W compressional movements. They are generally overlain by the allochtonous Buxa Group of metasedimentary rocks of presumed Mid-Paleozoic age. This fault contact is the Main Boundary Thrust or MBT.

3. The Damuda and Diuri Formations

In the southeastern part of the Frontal Belt (and to a lesser degree in the southwest) a narrow strip of allochtonous Damuda (Gondwana) rocks of lower Permian age, comprising sandstone, shale and coal seams, overlie the Siwalik rocks along the MBT and are then in turn overlain by the Buxa Group. These Damudas resemble those of peninsular India but are more indurated and tectonized. The coal seams are confined to the southern (lower?) zone of coarse-grained feldspathic sandstones with pyrite nodules intercalated with carbonaceous shales. The overlying northern zone consists of a sequence of grey quartzitic sandstone and carbonaceous shale with fossil plant remains characteristic of the lower Gondwana.

Next, the Diuri Formation (at times considered part of the Damudas) follows with grey boulder slates, which are made up of pebbles of quartzite, phyllite, dolomite and gneiss in a slaty matrix. In the absence of pebbles, the slates are carbonaceous. A possible glacial origin has been suggested for these tilloid rocks (Bhatia & Kanwar, 1975).

4. The Buxa Group

Wherever both Damudas and Diuris are missing, which is likely to happen along strike, the Buxa Group directly overlies the Siwaliks by means of the Main Boundary Thrust. Starting up from the MBT, we first encounter the quartzites and conglomerates of the Lower Buxa or Thungsing (previously Thungshing) Formation. Next follows the Middle Buxa or Phuntsholing Formation with variegated phyllites and quartzites, in turn overlain by the dolomites and quartzites of the Manas Formation (Upper Buxa). The terms “Lower” to “Upper” should not be taken too literally, as boundaries are gradational and appear merely to reflect facies changes within the original basin of sedimentation. This may even be valid for the Shumar Formation, which structurally overlies the Buxa Group, mainly in the southeast of Bhutan.

5. The Shumar Formation

The Shumars represent another assemblage of metasedimentary phyllite, quartzite and thin marble bands

Source : Hakata, T. 1972

Alluvial fill

Mam terraces

Tethyan Sedments

Tilted and faulted terraces

Siwaliks

8

of presumably Precambrian to Mid-Paleozoic age. The green micaceous quartzites are often flaggy and occasionally associated with banded iron formation, while the phyllites are both calcareous and carbonaceous, containing thick limestone and dolomite beds of potential economic interest. Some of the phyllites are host to beds and lenses of gypsum, often of considerable thickness (Khothakpa a.o.). Some repetition of lithologies within the Shumar Formation is the effect of EW-striking normal faulting. The proximity of major thrusting (MCT) is borne out by the fact that while the Thungsing Formation is only mildly deformed, the Shumars show mylonitization. The rocks have been affected by regional metamorphism to chlorite grade, with incipient biotite growth, i.e. locally at higher elevations.

+++ Rocks of the Central Crystalline Belt +++

Two main lithological groups have so far been recognized within the metamorphic thrust sheets of this bell; they are currently known as the Thimphu and Paro Formations.

6. The Thimphu Formation

Also known as the Thimphu Gneissic Complex, this formation is characterized by migmatites and biotitegranite-gneisses with thin beds of quartzite, quartz-mica schists, calc-silicate rocks and marbles, etc.

Symptoms of thrusting such as the above-mentioned mylonitization was not always as clearly in evidence. In southwestern Bhutan, the Thimphu gneisses directly overlie the rocks of the Shumar Formation. These phyllites and schists pass more or less gradually into a garnetiferous micaschist and finally into the overlying Thimphu gneisses without any sudden stratigraphic, metamorphic or tectonic break. The resulting apparent inversion of metamorphic grades prompted Gansser’s interpretation of an enormous overturned fold, culminating into a thrust (MCT?), with subsequent metamorphic overprinting obscuring the actual thrust plane itself. Similar conditions prevail elsewhere along strike of this tectonic contact.

7. The Paro Formation

Also referred to as the Paro Group, this formation is characterized by quartz-mica schists, quartzites, calc-silicates, marble and thin beds of graphitic schist, and shows only minor migmatization. In fact, the Paro and Thimphu lithologies are said to differ mainly in their ratios of crystalline vs. metasedimentary rocks. They otherwise show stratigraphic, structural and metamorphic continuity between them, with the Thimphu gneisses being considered the granitized equivalent of the Paro (and other) rocks. This interpretation may have to be revised however, as recent indications point to a much younger, i.e. Paleozoic age of the Paro rocks. This could lead to a rehabilitation of the “Paro Window” (Jangpangi, 1978 and Gansser, 1983)

and the associated thrust- or napper-tec tonics such as are well established in other parts of the Himalaya.

+++ Rocks of the Tethyan Belt +++

As mentioned earlier, the metamorphic and granitized contact of the Tethyan rocks with the underlying Thimphu Gneissic Complex is gradational. There are two principal areas where these rocks of presumed Precambrian to Cretaceous age are exposed: the extreme north of the country with its rim of largely undifferentiated sedimentary rocks, and the central area of the Black Mountains and their surroundings. Rocks in the latter area are currently subdivided as follows. The lowermost Tirkhola Formation is overlain by the Black Mountain Group, which in turn is followed by the Shodug Formation and finally the formations of the Lingshi “Basin” in the Northwest - all mutually separated by unconformities.

8. The Tirkhola Formation

Previously described as the Mao Khola Group, the Tirkhola Formation (late Precambrian to Cambrian?) consists of thickly bedded quartzites and phyllitic quartzites, locally with thin bands of phyllite, quartzite and limestone (previously the Hara Chu Formation). Tirkhola rocks are underlying large parts of Central and Eastern Bhutan.

9. The Black Mountain Group

This rock series of supposedly Ordovician to Lower Carboniferous age starts with the quartzite and conglomerates of the Nake Chu Formation, and is overlain by the Mane Ting Formation with its flagstone, metavolcanics and slates. Higher up in the sequence we encounter the limestones and calcareous phyllites of the Wachi La Formation. Next in line are the slates and limestones of the Tang Chu Formation, although the exact position of these rocks in the sequence is obscured by the fact that their only reported occurrence is north of the Black Mountain “Basin”, presumably with a tectonic contact.

10. The Beli, Barishong and Shodug Formations

The Beli Formation is described as a thick series of grey quartzite, slate, white to cream sandstone, dark grey pyritiferous slate, siltstone, calcareous quartzite and friable buff to cream sandstone. Upper Gondwana and Lower Cretaceous ammounites are found in the claystone and slates. The formation apparently overlies the Black Mountain Group, albeit unconformably. The same can be said of the slates and pebbly slates of the Shodug Formation, which for the time being provides the only link with the Lingshi Basin of the Northwest.

There, the current situation has not been clearly resolved either, although considering both the stratigraphic descriptions of GSI publications and the relatively detailed mapping carried out by Gansser in the area, two major

9

lithostratigraphic units are in evidence: first the Barishong Formation, starting off with quarztites and phyllites, before becoming increasingly calcareous with limestones and calcareous phyllites (previously featuring as the limestone facies of the Chekha Formation). The Barishong Formation is then overlain by the Shodug Formation, as mentioned mainly a series of locally pebbly slates.

The remainder of the Tethyan sediments exposed in the extreme Northwest and North of Bhutan, have so far not been differentiated and are represented as such on the map.

11. Intrusive Rocks

Tourmaline-bearing granites and pegmatites, in the form of dykes, sills, laccoliths and larger intrusions affect the Central Crystalline Belt and the Tethyan rocks. These Chomolhari leucogranites occur all along the Bhutan Himalaya with a remarkably constant composition. However, the larger intrusive bodies are concentrated in the northern ranges.

Petrological work and field relationships suggest a history of different phases of acid to intermediate magmatism. Composition of these granitic rocks varies from adamellite to granodiorite and trondhjemite (Chuzom granite-gneiss).

The granite-gneisses contained within the Shumar and Buxa rocks of Southeastern Bhutan are represented by several larger bodies extending for several kilometers and are thought to be either related to anticlinal uplifts or to internal fault and thrust zones. Both continue eastwards into Arunachal Pradesh. They consist of muscovite-biotite granites and granite gneisses with a more or less porphyritic texture. The contacts are tectonized with no signs of contact metamorphism.

An overview of the various rock units described is given in table 1.

C. Regional Metamorphism in Bhutan

The Buxa and Shumar rocks are characterized by chlorite-grade metamorphism and pass gradually into schists with incipient growth of biotite, followed by a zone of garnetiferous mica schist and finally into gneisses. Although narrow, these zones nevertheless provide continuity from low-grade metasediments in the south to overlying gneisses in the north. Only these Thimphu gneisses contain recorded high-grade metamorphic minerals. So there is an apparent inversion of metamorphic zones.

In West-Central Bhutan, the metasediments (both Black Mountain and Paro rocks) generally belong to the greenschist facies of metamorphism, passing into almandineamphibolite facies and higher grades of the Thimphu gneisses,

from which staurolite, kyanite and sillimanite have been recorded.

In Central Bhutan, the metasediments show biotite and garnet grade metamorphism. A thin zone of staurolitebearing quartz-mica schist occurs within the garnet zone, which grades into gneisses by way of a zone of feldspathization. The Thimphu gneisses of Wangdiphodrang and Tongsa Districts display high grade index minerals such as kyanite and sillimanite.

In Northern Bhutan, Tethyan metasediments display a very low degree metamorphism, nowhere exceeding chlorite grade. In the centre however, where the black Mountain rocks underlie the Beli and Shodug Formations, there appears to be a transitional granitized contact with the Thimphu gneisses. Biotite porphyroblasts have also been recorded and are considered typical for these Tethyan rocks in Central Bhutan.

For the time being, figure V results from an attempt by Gansser (1983) to map the distribution of metamorphic zones in the Bhutan Himalaya, a complicated orogen which exposes old (Late Precambrian) crystalline basement with its related metasediments, later bioitite granites and subsequently overprinted by a conspicuous and much younger progressive Himalayan metamorphism. The old Central Belt rocks of the Himalaya have been fully recrystallized by this Neogene Himalayan metamorphism, which is mostly syn- to post-orogenic.

The metamorphic grades discussed represented primarily the latest Himalayan phase and not the proceeding Precambrian metamorphism. This is in contrast to the structure, which in various places still retains the older trends or reflects a reactivation of an older structural grain.

Study of the three major rock groups: (1) carbonates, (2) pelites and (3) migmatites and granitized rocks with the youngest products of anatexis, the leuco-granites, give us the generalized map with metamorphic isograds presented here as figure V. Although of an interim nature, the main trends shown are reasonably representative of the distribution of metamorphic grades in Bhutan. Three items complicate the matter however, and merit future attention. Firstly the syn- to post-kinematic age of the metamorphism, secondly the fact that isograds can be either parallel or discordant to major tectonic trends, and thirdly the above-mentioned reverse metamorphism noted in many sections. Various explanations have been proposed (Frank el al., 1973/1977; Le Fort, 1975), none of which has so far been able to solve this (but particularly the latter) problem.

Apart from the regional metamorphism, the young (10-20 Myrs) leucogranites have locally produced a pronounced contact metamorphism.

10

Table 1. Lithostratigraphy of the 1 : 500,000 Geological Map of Bhutan

Rocks of the Tethyan BeltNorth

Beli Formation:

Shodug Formation:

Barishong Formation:

Tang Chu Formation: Wachi La Formation: Mane Ting Formation: Nake Chu Formation:

Tirkhola Formation:

quartzite, (pyritiferous) slate, siltstone, sandstone

slates, pebbly slates and diamictites

quartzites, phyllites to limestone and calcareous phyllites

slates and limestonelimestone and calcareous phyllitesflagstone, metavolcanics and slatesquartzites and conglomerates

bedded quartzites and phyllitic quartzites, locally limestone

Black Mountain Group:

Rocks of the Central Crystalline Belt

Paro Formation:

Thimphu Formation:

quartz-micaschists, quartzites, calc-silicates, marble with thin beds of graphitic schist, with minor migmatization

migmatites and biotite-granite gneisses with thin beds of quartzite, micaschist, calc-silicate rocks and marbles

Rocks of the Frontal Belt •

Buxa Group

Shumar Formation:

Manas Formation: Phuntsholing Formation Thungsing Formation:

Diuri Formation:

Damuda Formation:

phyllite, green micaceous quartzite and thin marble bands, some BIF

dolomite and quartzitesvariegated phyllites and quartzitesquartzites and conglomerates

grey tilloid boulder slates and carbonaceous slates

sandstones, shale and coal seams, to feldspathic quartzites and carbonaceous shales

SiwalikFormation

Upper Siwaliks:Middle Siwaliks:Lower Siwaliks:

Alluvium:

thick conglomerates with quartzite/jasper boulders in sandy matrix friable sandstone with few claybedsgrey-green claystones with limestone nodules and hard sandstone

terrace deposits of sand, gravel and boulders

Intrusive Rocks

Chomolhari Granite:Dhansiri Gneiss:Chuzom Granite-Gneiss:

tourmaline leucogranites and pegmatitesmuscovite-biotite granitcs/gneisses with some porphyritic texture granodiorite-adamellite gneiss

South

LOWER GREENSCHIST FACIES

HIGHER GREENSCHIST FACIES

BIOTITE PORPHYROBLAST FACIES

LOWER AMPHIBOLITE FACIES

HIGHER AMPHIBOLITE FACIES

SILLIMANITE - GRANULITE FACIES

ZONES OF GRANITISATION

LEUCOGRANITES

) TETHYAN SEDIMENTS

Figure V. Metamorphic Zoning in the Bhutan Himalaya. Sketch map as presented by Gansser (1983); geological boundaries no longer as shown.

Metamorphic Map of the Bhutan Himalaya

50 kmshowing isogrades and locations of analysed samples . 129

Ch: CHOMOLHARIDa: DARJEELINGGa: GANGTOKPa: PAROMK: MASANG KANG

KK: KUNLA KANGRITa: TASHIGANGTh: THIMPHUTo: TONGSA


12

III. MINERAL DEPOSITS

A. Metallic Minerals

1. Iron and Ferro-Alloy Minerals

Iron (Fe)

Occurrences of iron ore are known near Mauree village on the left bank of the Sunkosh river. The area exposes rocks of the Siwaliks group comprising grey micaceous sandstone, siltstone and ferrugenous clay striking S70°W and with northerly dips of 20° to 70°. Two bodies of iron ore are found within the micaceous sandstone. The ore bodies are bedded, hard, compact, massive and at places laminated and highly jointed. The massive ore is steel-grey in colour with a cheery-red streak while the laminated ore is brown with a dirty brown to cherry-red streak. Iron content of the ore varies from 25 per cent to 46 per cent Fe.

Two small bodies (Eastern and Central) were selected for grade and reserve estimation:

The ore returns the following assay values:

BlockPotential Ore

Ore type OutcropArea (m2)

Av. Grade (% Fe) Reserve (Ml)

EAST Laminated 9,900 32.46 1.63350

Massive 3,300 48.54 0.63525

CENTRAL Laminated 4,600 31.20 0.70840

TOTAL 2.97715

SiO2

6.84%

Al2 O3 18.72%

Fe2O3 44.20%

P2°5 2.30%

CaO 1.20%

MgO 2.93%

TiO2

9.90%

MnO 0.33%

n2o 0.12%

k2o 0.03%

LOI 12.90%

This low grade iron ore could well be mined on a small scale to supply future local industries.

Tungsten (W)

Tungsten mineralization occurs in skarn rocks near the contact of Thimphu gneisses and Shumar metasediments in the Dholpani and Bhurkhola areas of the Geylegphug district. The mineralization in the area is unique as it is the first of its kind reported in the Himalayas.

The area around Dholpani and Bhurkhola, where the Phuntsholing, Manas, Shumar and Thimphu formations are exposed, lies in the Lesser Himalayan tectonic belt. Here, the Tethyan formations are in juxtaposition with the sub-Himalayan formations along a major thrust fault. In the Bhurkhola section, the Buxa group, represented by a thick dolomite horizon is absent. Except for the Thimphu formation which consists of garnetiferous quartzmica schist, calcareous quartzite, calc-gneiss and tourmaline granite, the rest of the formations are represented by low grade metasediments consisting of phyllites, quartzite, dolomite and narrow lenticular patches of crystalline limestone or marble.

The most prominent planar structure in the Thimphu as well as in structurally underlying formations is a schistosity which is parallel to the compositional layering, trending ENE-WSW and having north-westerly dips varying from 40 to 60 . Figure VI shows the geology of the tungsten mineralization in the Dholpani-Bhurkhola areas.

As the skarns have developed at the expense of calc-silicate rocks, they are basically very similar to the calc-silicates but differ in the relative prevalence of its different mineral constituents. The skarns show greater development of garnet, epidote and opaques and are usually very coarse-grained, especially the massive variety.

The Dholpani and Bhurkhola skarns are very different from typical skarn deposits as they are banded and deficient in iron, pyroxenoids and idocrase. The common mineral assemblage in the skarns comprises quartz, clinopyroxene, hornblende, biotite, garnet, epidote, carbonate and feldspar. Sulphide minerals are pyrrhotite, pyrite, chalcopyrite and arsenopyrite in order of abundance. Rare sphalerite and molybdenite also occur. Magnetite is absent.

Field and laboratory studies indicate that skarn formation in the area was distinctly separated in time from regional metamorphic events. Very coarse-grained garnet, glomeroblastic aggregates forming irregular and discontinuous patches, and associated sulphides suggest that the skarn was dominated by metasomatic processes in which sulphide-rich fluids took part. Absence of magnetite indicates low oxygen fugacity. The presence of tourmaline granite nearby and of tourmaline granite/pegmatite in the calc-silicates suggests that the formation of skarn may be related to post-tectonic emplacement of tourmaline granite

13

Figure VI. Geological map with tungsten mineralization of the Dholpani-Bhurkhola area, Geylegphug District.

LOCATION MAP

CHINA

BHUTAN

Thimphu

PhuntsholingBhurkhola

DholpaniGeylegphug

INDIA

SARBHANG

SCALE

O 1 2 3 4 km

Strike and dip of bedding

Thrust

Road

Indo-Bhutan boundary

LEGEND

RECENT

MANAS

Alluvium /Colluvium/Talus

Dark grey dolomite

Green-Purple phyllite with purple quartzite bands.

Interbeded green phyllite and quartzite

Marble

Granite gneiss

Garnetiferous schist with gneissic skarn rock with scheelite mineralization bands

PHUNTSHOLING

SHU

MA

RTH

IMPH

U

B

A

D

C

A

SKARN2000

1000

SECTION A-B (Dholpani)

B

SKARN

D

SECTION C-D (Bhurkhola)

C

2000

1000


14

in the promixity. No evidence is yet available to identify the source of the fluid responsible for skarn formation.

With regard to controlling factors, the skarn-type tungsten mineralization occurs within calcareous metasediments associated with garnetiferous mica-schists of the Thimphu formation. The calcareous metasediments hosting the mineralization comprise coarse-grained marble, banded calc-silicate rocks and calc-quartzite. The skarn shows a crude to well developed banding parallel to sub-parallel to the dominant bedding plane schistosity. The scheelite grains are arranged parallel to the banding. This along with the general disposition of the skarn parallel to the general trend of the host rocks and the absence of any shearing etc. suggest that the bedding plane schistosity has primarily controlled the scheelite mineralization.

The chemical composition and nature of the host rock have played a major role in localizing scheelite mineralization. Thus, in the calcareous host rock, better mineralization is confined to impure marble/siliceous marble and its related calc-silicates. Poor mineralization is seen in calc-quartzite and in highly siliceous rocks. Minor scheelite mineralization is also seen in the calcareous part of the bordering micaschists and gneisses at the hanging- and foot-wall sections.

Dholpani Deposit

The mineralized skarn zone in the Dholpani area occurs over a strike length of about 450m with widths varying from 6 m to 8 m. The skarn is developed along the contact of marble with the tourmaline-bearing granite. The area is divided into three blocks: Dholpani East, Dholpani West and the Gurung Khola Blocks.

An area of 0.27 km2 was covered by a detailed drilling survey; 19 boreholes were drilled totalling 1,399.30 m. Results of the three blocks are as follows:

Blocks It No. of holes Results/Remarks

Gurung Khola 3 Not encouraging

Dholpani West 2 Intersected mineralized zones4 Barren

Dholpani East 10 5 series I:5 series II: Mineralized

Exploration work in the Dholpani area has been completed and details on reserves and grades are as follows:

A bulk sample sent to the Indian Bureau of Mines (IBM, Nagpur) for bench-scale beneficiation tests showed that the tungsten ore is susceptible to both physical and

chemical beneficiation. The result showed a high grade scheelite concentrate of 67.09 per cent WO3 with 38.90 per cent recovery and a low grade concentrate of 35.86 per cent WO3 with 10.40 per cent recovery. Overall recovery was 49.30 per cent WO3. This high grade scheelite concentrate was said to be suitable for use in the tungsten carbide industry while the low grade concentrate may be used in the production of ammonium paratungstate (APT).

It is worth noting that besides scheelite, the test also returned a copper concentrate of 21.09 per cent Cu with 66.90 per cent recovery (wt per cent yield = 0.65) and 7.81 per cent Zn. This copper concentrate may be suitable for copper smelting after blending with copper concentrates of low zinc content. In any case, in view of the low WO3 (0.10 per cent) and Cu (0.22 per cent) contents in the initial feed assay, such high recoveries are remarkable.

Bhurkhola Deposit

The skarn mineralization in the Bhurkhola area extends over a strike length of 1.20 km from Seti Khola in the west to Bhurkhola in the east. The width of the mineralized zone ranges from a few metres to up to 50 m. The area is divided into a Bhurkhola West and a Bhurkhola East Block with strike lengths of 480 m and 380 m respectively. Field observations show that grades and widths of the scheelite mineralization in the skarn are best in the westernmost part of the Western Block.

Tungsten mineralization in the Bhurkhola area occurs in the form of scheelite disseminations associated with calc-silicate skarn rocks. Both banded and massive varieties of skarn are present and show highly variable mineral compositions. The banded variety shows strong scheelite mineralization and is generally poor in sulphides, whereas the massive variety has appreciable amounts of very coarse-grained garnets, pyroxene and sulphides with scheelite occurring in a train of discrete individual grains along the interface of garnet-rich laminae. Within the skarn, the distribution of scheelite varies from traces to over 1 per cent WO3.

Detailed mapping, trenching and channel sampling over a strike length of 1.2 km from Seti Khola to Bhurkhola was carried out to delineate the scheelite-bearing skarn. Analyses of channel samples at 100 m intervals showed an average content of 0.30 per cent WO3>

The Eastern Block shows poor mineralization and does not appear to be promising.

In the Western Block however, based on encouraging surface results, detailed exploration by drilling was undertaken. So far, 18 boreholes have been completed at 100 m spacings in three series so as to intersect the skarn at 30 m, 60 m and 90 m vertically below surface outcrops. All boreholes drilled in the Western Block intersected the economically significant mineralized zone. Noteworthy is the intersection of tin mineralization in borehole BK-4A.

Earlier detailed work in the Bhurkhola area has shown probable reserves of 1.35 Mt of tungsten ore with an

Cut-off Reserves Reserves GradeGrade (% WO3) Mt Category (% wo3)

0.12 0.349 (down to Probable0.15 0.335 75 m depth) under 1.0 m : 0.250.20 0.200 stoping :

width. :

15

average grade of 0.48 per cent WO3 at 0.25 per cent WO3 cut-off grade and down to a dept of 90 m. Based on currently available data, the tungsten mineralization at the western block of the Bhurkhola area appears to have economic potential. From available surface and subsurface data, the mineral potential of the Bhurkhola West Block has been categorized and listed in the following tables below (Tables 2, 3 and 4).

Table 2. Reserves down to a vertical depth of 90 m (open-cast mining)

Tonnage (in Mt)

Av. Grade (in % wo3)

Av. Width (in m)

Strip WO ContentRatio (tonnes)

RESERVES (>0.3% WO3) Conditional

0.476 0.470 3.81 1:5.53 2 237

RESOURCES (0.1-0.3% WO3) Entire Width

1.027 0.150 3.71 1:3.28 1 562

of Skarn 2.700 0.180 14.03 1:1.10 4 801

Table 3. Reserves between 90 m and 180/200 m vertical depth (below open-cast mine)

Tonnage (in Mt)

Av. Grade (in % WO3)

Av.Width (in m)

WO3 Content (tonnes)

RESERVES (>0.3% WOp Conditional

0.800 0.447 4.20 3 576

RESOURCES(0.1-0.3% WO3)

0.440 0.150 4.01 664

Table 4. Reserves for the entire Block (leaving top 15m as ‘back of the mine’ in

underground mining)

Tonnage (in Mt)

Av. Grade(in %WO3)

Av.Width (in m)

WO3 Content (tonnes)

RESERVES 1.380 0.450 3.81 6210(>0.3% WO3) ConditionalRESOURCES 1.420 0.157 3.44 2 229(0.1-0.3% WO3) RESOURCES(.05-, 1 % WO3) 0.660 0.063 2.41 416

The detailed drilling survey in the western extension of the Western Block (i.e. the Seti Khola Block) is in progress. Detailed geology of the area shows that the skarn body extends further west to the confluence of Gurung Khola and Khaja Khola. Hence total probable reserves for the area are likely to increase considerably after completion of the evaluation.

In order to ascertain the susceptibility to beneficiation of the Bhurkhola tungsten orc, bulk samples were sent to IBM (Nagpur) and NML (National Metallurgical Laboratories, Jamshedpur, India). Two samples, one low grade and the other high grade (0.13 per cent and 1.10 per cent

WO3 respectively) were subjected to beneficiation studies by NML. Their results indicated that the ore is not very amenable to physical beneficiation. The final tungsten concentrate was only 15.4 per cent WO3 with a 42.70 per cent recovery. However, by chemical leaching of the ore, it was possible to obtain a recovery of more than 85 per cent WO .

3

Similar beneficiation tests (combined gravity, floatation and Mozley separation) conducted by IBM however, returned a tungsten concentrate of 69.70 per cent WO3 with 60.40 per cent recovery (wt per cent yield = 0.36 per cent). Tungsten concentrates analysing 65-70 per cent would meet market specifications for scheelite.

Although contrasting results are achieved by NML and IBM despite using similar methods of beneficiation, IBM studies did establish beyond doubt that the ore is indeed susceptible to physical beneficiation. Chemical leaching as conducted by NML is adopted only when physical beneficiation would fail to yield a concentrate of higher grade.

The Bhurkhola scheelite has an average grade of 0.34 per cent WO3 and hence falls in the “average ore category”. As per the classfication proposed by the Department of Mines, Ministry of Steel and Mines (1987, India), the Bhurkhola scheelite ore falls in the reserve category where WO3 content is more than 0.30 per cent. At the present status of exploration, probable reserves at Bhurkhola stand at 1.38 Mt having an average grade of 0.45 per cent WO3, with metal content (WO3 content) amounting to 6210 tonnes.

The skarns in the Bhurkhola West Block have been found to continue further west to the Sethi Khola area where surface values of tungsten are encouraging. The recent find of a new skarn body downstream of the Bhurkhola- Gurung Khola confluence has heightened the likelihood of the skarn body continuing further west of the Dholpani area. Detailed investigations to scan the area between Dholpani and Bhurkhola prospects are under way.

2. Base Metals

Copper (Cu)

Copper mineralization is reported from a number of places in Bhutan. The various occurrences known to date are described here briefly:

Gongkhola

The Gongkhola copper deposit is situated at 40 km map distance from Geylegphug. Access is by a 48 km long mule track from Surey. The deposit is divided into three blocks: the Eastern, Central and Western Blocks, with strike lengths of 2100 m, 500 m, and 800 m respectively; the Nobji Chu sector has a strike length of 200 m. The width of the mineralized zones varies from 1 to 2 m but wider zones of up to 12.5 m were occasionally intersected

16

in boreholes. The grade varies considerably along both strike and dip.

Copper mineralization in the form of chalcopyrite occurs within the crystalline mangano-siderite rock at the contact of carbon phyllite and quartzite belonging to the Mane Ting formation (Black Mountain group). In addition to mineralization in the main quartz-carbonate rock (Lode 1), significant zones of mineralization are recorded within the footwall quartzite, associated with thin quartz-carbonate veins (Lode 2). The average strike of the rock units is NE-SW with dips of 55° to 65° towards NW, while the orebodies are generally conformable with their host rocks.

The Gongkhola copper deposit was discovered in 1976. Preliminary investigations were carried out during the field seasons 1976-1977 and 1977-1978. Detailed mapping of the area showed that the copper mineralization extends over a strike length of 3.6 km. Drilling started in February 1979. By November 1987, 10,808 m had been drilled in 102 boreholes, covering an area of 2.6 km2. A total of 5,675 samples from the ore zone were analysed for copper, 558 core samples were submitted for gold assay and 106 samples for rock-geochemical analysis.

Detailed geophysical work including induced polarization, resistivity, self potential and ground-magnetics was carried out in the Central Block, as earlier drilling had not explained the lack of correlation of subsurface mineralization with surface data. Results obtained so far from work carried out in all three blocks are discussed below:

Eastern block: 54 boreholes were drilled over a strike length of 2,100 m, proving the payable strike length to be 1,850 m. Two lode zones with most widths varying between 1.14-2.25 m (max. 12.29 m) were intersected. In one intersection (Lode 2), the copper content varies from 0.50 to 4.81 per cent Cu. Based on these results, total reserves of 1.89 Mt of ore with 1.53 per cent Cu were calculated, based on a 1 m stoping width and a cut-off grade of 1 per cent (Gupta and Augustine, 1984).

During the period October 1983 to September 1985, two deep boreholes (GE-56 and GE-57, 500 m apart) were drilled to intersect the ore zones at the 400 m level. Only borehole GE-57 intersected two zones of mineralization, having respective widths of 1.93 m with 1.05 per cent Cu (Lode 1) and 1.60 m with 1.75 per cent Cu (Lode 2). Three more deep boreholes (GE-59, -60 and -61) were drilled from October 1985 to March 1987. The drilling results arc summarized below:

Profile Borehole it Mineralized zones intersected

F-F’ GE-56 Nil to very poorI-I' GE-57 1.05% Cu over 1.93 m (Lode 1)

1.75% Cu over 1.60 m (Lode 2)O-O’ GE-59 0.82% Cu over 1.30 m (Lode 1)

0.92% Cu over 1.74 m (Lode 1)1.06% Cu over 1.19 m (Lode 1)

K-K’ GE-60 Nil to very poor (<0.50% Cu)G-G’ GE-61 Analytical results outstanding

This shows that no significant mineralization of any appreciable strike length has been proved by deep drilling at the 400 m level in the Eastern Block.

Central Block: 23 boreholes were drilled in this block. The payable zone extends over a strike length of 450 m with widths ranging between 0.50-5.08 m and grades varying between 0.53-1.87 per cent Cu, to a vertical depth of 120/130 m. Based on this result, a total reserve of 0.35 Mt of ore with 1.50 per cent Cu is calculated for both lodes 1 & 2. Since the first IV series boreholes did not intersect any quartz-carbonate rocks, two more IV series holes were drilled to test lode persistance at 200 m vertical depth. However, only a small zone of 0.98 m thick with 0.50 per cent Cu was intersected by these boreholes.

Data obtained from the initial stages of drilling did not correlate with surface indications, probably due to structural complexities in this part of the deposit. As a further check, a detailed geophysical survey was therefore carried out, employing induced polarization, resistivity, self potential and ground-magnetics. Results obtained from the integrated survey showed that payable ore extends over a strike length of 500 m in some parts of the block. The average width of Lode 1 varies from 0.84 m to 4.82 m and that of Lode 2 from 0.54 m to 7.92 m (occasionally 12.98 m). Lode 1 showed an average grade of 0.56- 1.87 per cent Cu and Lode 2 varied from 0.53 to 1.73 per cent Cu.

Western Block: 13 boreholes were drilled in this block over a strike length of 400 m. Initial results reflected a very low potential for payable ore and hence work was discontinued. However, subsequent discovery of mineralization in the Western Block along the northern contact of carbonaceous phyllite with quartzite, over a strike length of 800 m, called for renewed drilling, which was carried out from October 1983 to March 1987. Four holes (GWR- 1 to GWR-4) were drilled on the northern side al strike intervals of 200 m to test the ore at 50 m depth. Results did not indicate any significant zones of mineralization. Two more boreholes were drilled: GWR-5 at the southern contact of the carbonaceous phyllites and GWR-6 100 m further east, but the latter failed to intersect quartz-carbonate rock. Borehole GWR-5 did intersect three minor zones of mineralization however, with 1.12 per cent Cu over 0.55 m (in the hanging wall of the carbonaceous phyllites), with 0.48 per cent Cu over 1.69 m and 0.77 per cent Cu over 0.90 m within the quartz-carbonate. These zones do not appear to have any appreciable strike length and may just represent minor lenses. In view of these indications however, the Western Block does appear to have at least some economic significance.

Probable reserves for the Eastern and Central Blocks, to a vertical depth of 120/130 m, and subject to three alternative cut-off grades and stoping widths, are as follows:

17

Grade % Cu

StopingWidth (m)

Cut-off % Cu

Probable Reserves (in Mt)

1.52 1.00 2.24371.35 1.50 1.00 2.12811.40 2.00 1.9004

1.29 1.00 3.22531.24 1.50 0.80 3.15251.22 2.00 2.7319

1.04 1.00 5.25161.01 1.50 0.50 5.22310.97 2.00 5.2439

Based on the exploratory work carried out so far in the Gongkhola copper prospect, the following conclusions may be drawn:

1. Out of the three blocks, only parts of the Eastern ( 1,850m) and Central Blocks (450 m) look promising. Both Lode 1 and Lode 2 in these blocks show persistance at depth down to 120/130 m, but widths and grades vary considerably, both along strike and dip.

2. Probable reserves computed over a total strike lengthof 2300 m (1850 m in the Eastern and 450 m in the Central Block) is 2.24 Mt with 1.52 per cent Cu, based on a stoping width of 1 m and a cut-off grade of 1 per cent Cu.

3. In the absence of complete figures on the Central Block, total reserves based on a 1 per cent cut-off and a 1 m stoping width are likely to be around 2.50 Mt at 1.50 per cent Cu. If all proposed deep boreholes intersect the mineralized zones, tentative reserves of 10.0 to 12.0 Mt of copper ore become a distinct possibility, which would make the deposit economically viable.

4. Investigations into the association of gold with copper in the Gongkhola area revealed a gold content of 0.20 g/tonne in the Eastern Block.

5. Mangano-siderite, containing up to 9 per cent MnO and 50 to 55 per cent Fe2O3, occurs in crystalline form as a principle gangue mineral. Its potential in the production of steel and for other industrial uses, merits further study.

6. Average characteristics of ore zones at the Gongkholacopper deposit for various cut-off values of grade, width and accumulation (grade x width) indicate that parts of the deposit contain good ore, which occurs as narrow and impersistent lenses at various levels. Continuity of individual lenses (at a sample cut-off grade of 1 per cent Cu) appears to be around 300 m, whereas persistence at depth may be limited to about 50 m. More than 77 per cent of the ore intersections of these lenses have widths of less than 200 cm.

Unless significant amounts of other associated valuable metals prove to be recoverable along with copper ore, exploitation of the deposit does not seem feasible at this stage.

In June 1986, Hindustan Copper Limited (HCL), after thorough study of exploration data, reported on the commercial possibilities of the Gongkhola copper prospect. The data examined showed wide variation in the values of observed width and accumulation. Widths of the individual intersections vary from 31 cm to 12.29 m, whereas accumulation values range from 1.00 to 1.917 per cent Cu. The study stated that the prospect may turn economically viable provided widths and grades are found to be around 3.5 m and 1.70 per cent Cu respectively. Though the orebody does not meet these requirements in the explored area (Table 5), it is pointed out that a number of zones approaching the required grade were intersected in some sections of the deposit.

Table 5. Summary of Reserves Estimate for the Gongkhola Copper Deposit based on Various Cut-off Values.

Accumulation cut-off values (cm %Cu) 100 150 200

Cut-off width (cm) 150.00 200.00 150.00 200.00 150.00 200.00

Cut-off grade of ore zones (%Cu) 0.67 0.50 1.00 0.75 1.33 1.00

0.50% cut-off Av. tonnage/unitBlock (Kilolonnes)

84.00 92.00 67.00 71.00 57.00 59.00

Total tonnage (mill, tonnes)

3.44 3.77 2.75 2.91 2.34 2.42

Av. in-situ grade (% Cu)

1.06 0.97 1.14 1.09 1.17 1.14

1.00% cut-off Av. tonnage/unitBlock (Kilolonnes)

34.00 50.00 36.00 41.00 22.00 24.00

Total tonnage (mill, tonnes)

1.76 2.06 1.48 1.68 0.90 0.98

Av. in-situ grade (% Cu)

1.40 1.19 1.51 1.32 1.60 1.45

Constraints : Unit Block size explored : 100 m (strike) x 50 m (depth).Estimated only for 41 Unit Blocks.

18

From the available borehole data, the HCL team estimated in-situ reserves of 528,300 tonnes of ore with an average grade of 1.69 per cent Cu and 8,947 tonnes of contained copper in a small block of 400 m strike length in the Eastern Block. Using different parameters, the team considered that the prospect studied could reach a production of 70 to 150 tonnes a day and a mine life of 12.5 years. Based on HCL recommendations, drilling to a depth of 400 m was proposed to establish persistance of the orebody at depth in the Eastern Block. Detailed work by the Geological Survey of India (Bhutan Unit) in the Gongkhola area is nearing completion.

The Jongda Copper Occurrence

The mineralized zone is located at Yor Chu, 3.5 km NNE of Jongda village. The sparse sulphide ore occurs in massive amphibolite bodies intruding the garnetiferous feldspathic biotite gneiss of the Thimphu formation. One such amphibolite body measures 2 km in length and 800 m in width. Pegmatite and quartz veins intruding the amphibolite bodies are mineralized with chalcopyrite, pyrite, pyrrhotite and magnetite. The mineralized zones contain 0.20 per cent to 0.30 per cent Cu and 75 ppm to 125 ppm Ni.

The Samchi Copper Belt

Copper mineralization is reported from several places in the Samchi district (Figure VII). The ore occurs in quartz veins intruding the quartz-sericite-chlorite phyllite of the Phuntsholing formation. The host rocks strike NW- SE with a 30° to 35° dip towards NE. Mineralized zones are characterized by reddish-brown stains and limonitic gossans. Associated minerals are chalcopyrite, bornite, azurite, pyrite, pyrrhotite and galena. A summary of the various occurrences in the Samchi Copper Belt is given in table 6.

Munga Khola Occurrence

This is located in Munga and Sarbhang Khola, 12km north of Sarbhang. The ore occurs in thick ultrabasic sills intruding the quartzite at the contact of the Thimphu and Phuntsholing formations. The mineralization is in the form of sparse disseminations of chalcopyrite, pyrite, pyrrhotite and marcasite along a 240 m x 8 m zone. Average copper grade is about 0.1 per cent Cu.

Tirkhola Occurrence

Sporadic occurrences of copper mineralization are found on the western and eastern banks of the Jiti river in the Tirkhola area. The ore occurs in veins and veinlets of quartz, traversing quartzites associated with slates and schists. The minerals associated are chalcopyrite and malachite. Average content is about 50 ppm Cu.

Gomchu Occurrence

This occurrence is about 2km NNW of Khaling village (130 km post on the Samdrup Jongkhar-Tashigang road). The ore is found in quartz-carbonate veins within the quartz-biotite-chlorite phyllites of the Shumar formation and occurs over a strike length of 2.2 km from Gomchu Nala towards the east. About 0.50 Mt of copper ore, containing 0.5 per cent to 0.6 per cent Cu and 1 per cent Pb- Zn are estimated for the area.

Kharungla Occurrence

This is located SSW of the Kharungla Pass (between the 107 km and 111 km posts along the Samdrup Jongkhar-Tashigang road). The sparse copper mineralization occurs in quartz veins traversing the quartzites and calcareous phyllites of the Shumar formation, with chalcopyrite and

Table 6. Copper occurrences in Samchi district, Bhutan

Occurrence Location Width & Strike Length of Mineralised Zones

Grade (% Cu)

Bungthing 3.5 Km N Chengmari 4.00 m x 125 m 0.34

Chunpatang 200 m N Nainatal 3 m x 210 m 3.21

Saureni 9 Km SE Samchi 40 cm x 4 m 0.75

Chiuri Bote 7 Km NE Samchi 30 cm x 10.5 m 0.35

Dhau Khola 1 Km SE Chiuri Bote 1.8 m x 6 m -

Lamitar-Rambagar NE Chengmari 1 m x -? 1.80

Dham Dhum 1 Km NW Samchi 0.80 sq. Km -

Athais Khola 2 Km N Saureni 6 m x 95 m 1.20

Sundari Khola 4 Km E Golatar 1.27 m x 300 m 0.81

Dzonsa Dzong19

Golatar

Shunderi/KholaLoti khoJa

Figure VII. Localities of copper mineralization in Samchi District

Sochukha

Chundwar Fort

Athais khola

SaureniSamchi

Dham Dhum

Bunthing

Chunpatang

COPPER OCCURRENCE

LOCATION MAP

THIMPHU

BHUTAN

SAMCHIPhuntsholing

8370m

.7569 m

2076 m

6240m

5982

2868 m

20

bornite being the principal ore minerals. The width of the mineralized zone is about from 5 to 20 cm and average Cu content is about 50 ppm.

Lead-Zinc (Pb-Zn)

Genekha Deposits

The Pb-Zn deposits of the Genekha area are located at Romegang Ri, Chakula and Tashisheka at altitudes from 3,000 to 3,700 m. Access is by a 20 km 4 WD road from Sisina.

The Pb-Zn mineralization in the area occurs as concordant, tabular to lenticular and “pod”-like bodies and as disseminations, stringers and fracture fillings with the crystalline limestones of the Paro formation. The common ore minerals are heminorphite, zincite, galena, sphalerite, smithsonite, cerussite with subordinate amounts of pyrite, pyrrhotite, magnetite, chalcopyrite, franklinite, tetradymite, covellite and chalcocite. Gangue minerals are calcite, dolomite, quartz, tremolite, baryte and micas. The Pb-Zn ore is oxidized to varying degrees, both at the surface and at depth.

Romegang Ri: There are eleven lodes located at Romegang Ri out of which five are of economic interest. The mineralization is hosted within the top 100 m to 130 m of the crystalline limestone. The width of the partings between the adjacent lodes varies between 5 m and 15 m. The five significant lodes occur within a depth range of 50 to 75 m from the surface and the orebody has a strike length of 750 m.

Estimated probable reserves of the Romegang Ri deposit based on three cut-off grades are as follows:

Cut -off Grade (Pb+Zn)

Reserves (Mt)

Average Grade (%)Pb+ZnPb Zn

1.00% 1.196 1.99 2.41 4.402.50% 0.585 3.46 3.90 7.364.00% 0.356 4.95 5.48 10.43

Chakula Deposit: The Chakula deposit consists of eight ore lodes occurring within the limestone. The lodes extend over a strike length of 1,100 m.

Estimated total reserves for the Chakula deposit amount to 3.116 Mt with an average grade of 1.03 per cent Pb, 6.33 per cent Zn and 7.36 Pb+Zn.

Tashisheka: This occurrence finds itself about halfway in between the Chakula and Romegang Ri deposits. As surface sampling results were not encouraging, no further work such as drilling was carried out, but the possibility of fresh sulphide ore occurring at depth has yet to be investigated, e.g. using geophysical methods.

Jemena Pb -Zn Occurrence

The Jemena occurrence is located 300 m north of Jemena village in Thimphu district and can be reached by a 10 km long road from Khasardrapchu.

The Pb-Zn mineralization occurs in coarse-grained limestone of the Paro formation. The ore minerals are partially to completely oxidized at the surface as well as at depth. Principal ore minerals are galena, sphalerite, hemimorphite, cerussite and smithsonite. Gangue minerals include calcite, secondary iron oxides, carbonates and calc-silicate minerals. The ore minerals occur as disseminations, stringers, pockets of lenses, “pods” and as fracture fillings. Magnetite occurs both as disseminations and as bands reaching widths of up to 15 m. The coarse crystalline limestone in which the mineralization occurs forms the top-most stratigraphic horizon of the Paro formation in the area. The underlying rock types are graphitic schist, quartzite, quartz-mica schist, and calcareous quartz schist.

In all, 0.10 km2 of the area has been mapped in detail. Seven boreholes totalling 381.95 m have been drilled, but only three of these intersected the mineralization. Details of the mineralized zones are summarized in table 7. Based on these data, Pb-Zn mineralization in the Jemena area appears to be of limited potential, though further work is required to truly assess its economic significance.

Table 7. Lead-zinc Mineralization in the Jemena area.

BH #From (m)

Mineralized Zones To (m) Thickness (m) %Pb

Average Grade of Ore %Zn %Pb+Zn

JBH-1 0.00 1.30 1.30 1.29 Tr. 1.298.70 8.90 0.20 2.41 Tr. 2.41

JBH-5 4.45 5.25 0.80 1.34 8.01 9.355.90 8.20 2.30 0.52 1.69 2.21

JBH-6 1.55 1.90 0.30 Tr. 2.31 2.314.00 4.10 0.10 2.59 39.10 41.694.50 4.80 0.30 2.96 7.59 10.556.40 7.30 0.90 11.43 9.13 20.56

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Ratepani-Gombadara

In this area (Sarbhang), galena has been found occurring as veins, stringers, and disseminations within highly brecciated/mylonitized limestone. Solid chunks of ore have also been reported from below some limonitized zones. The mineralization can be traced over a strike length of 50 m. Patches of gossan with very fine-grained pyrite have also been located. Detailed investigations to further delineate and assess the extent of the mineralization are foreseen.

3. Light Metals

Beryllium (Be)

Beryl - Scattered Occurrences

Notable occurrences of beryl are reported from a number of places in Bhutan, but always associated with the Thimphu formation. Crystals of beryl, ranging in size from 0.5 cm to 4 cm are reported from Chirang, Dung Dung-Khosala(Tongsa district), Nobang (Wangdi-Phodrang) and Radi (Tashigang), where they occur in pegmatite and quartz veins. No reliable quantitative data are as yet available.

4. Precious Metals

Gold (Au)

Green-schist belts, carbonaceous rocks and I-type granites of the Thimphu formation are considered favourable host rocks for gold mineralization. River terraces, fossil placers and Siwalik sediments are also considered promising factors in the search for gold. A preliminary search for gold was done in a few selected areas. Although results so far are erratic and inconclusive, detailed and systematic exploration for the mineral is warranted.

Gongkhola

Potential gold content in the Gongkhola copper prospect was studied by analyzing borehole samples. Results indicated overall gold values ranging from 0.40 to 0.80 ppm (g/tonne). Borehole samples from the central block showed high arsenic values (>1000 ppm As) and gold values ranging from 0.20 to 1.20 ppm Au. Similar assay results from the Eastern Block showed an average of 0.2 ppm Au. The feasibility of extracting gold from the copper lodes as a by-product has yet to be studied in detail.

Kuru Chu

Alluvial deposits of gold are reported from the sands and gravels of the Kuru Chu in the Monji area (Lhuntshi district). Indications are pointing to a widespread distribution of fine and flaky gold with values ranging from 0.001 to 0.25 g per 764 m2 (1524 kg) of sand

in the area. Besides gold, heavy minerals such as magnetite, ilmenite, garnet, pyrite, zircon, zoisite, epidote, tourmaline, hornblende, diopside, leucoxene and rutile are also concentrated in the sand.

Since the Kuru Chu is a fast flowing river, auriferous sand and gravel is limited but systematic sediment sampling further upstream should provide clues as to the primary source of the alluvial gold.

Dholpani-Bhurkhola

Tungsten is a mineral closely associated with gold. Borehole samples analyzed from the Dholpani-Bhurkhola tungsten prospect have also returned appreciable quantities of gold. Full analysis of the samples is still outstanding.

Gurung Khola

Gold mineralization is also reported from carbonaceous phyllite occurring al Gurung Khola (Geylegphug). Fire assay of grab samples returned gold values as high as 10 ppm Au. Subsequent channel sampling of the host rock showed analysis of gold to be less than 0.10 ppm. Only one channel sample analysed 3.99 ppm of gold. A thorough detailed re-investigation of the Gurung Khola gold occurrence is warranted to get a clearer understanding of the extent of gold mineralization in the area. Other occurrences of carbonaceous phyllites within the Thimphu formation also need to be examined for evidence of gold mineralization.

B. Non-Metallic Minerals

1. Chemical and Fertilizer Minerals

Phosphate (P)

In the course of detailed investigations for Rare Earth Minerals (IRE Ltd., 1977) in the Mauree-Kalikhola area, an about 20 m thick zone of phosphorite was located within the black ironstone shale/carbonaceous phyllite. The mineralized zone extends over 820 m along strike. Detailed geological mapping (Figure VIII) outlined a distinct band of more than 25m mineralized shale, sandwiched between the Gondwana-Siwaliks contact (thrust).

Analysis of channel samples of the mineralized shale indicates a 6.75-20.76 m thick phosphorite horizon with 0.43-23.9 per cent P2O5 (av. 13.24 per cent). A systematic search for similar phosphate occurrences at the Siwalik-Gondwana contact may prove worthwhile.

Pyrite (Py)

Pyrite occurrences are reported from the Dangling Ri in the Belfai area (Tashigang) and from Dhanese in the Geylegphug district.

Figure VIII. Occurrence of phosphorite in Mauree, Kalikhola area.22

LEGEND

ALLUVIUM

RIVER TERRACE

SIVALIKS

DAMUDAS

PHUNTSHOLINGS

MANAS

PHOSPHORITE HORIZON

THRUST

MAIN BOUNDARY FAULT

INTERNATIONAL BOUNDARY


SCALE

i km0.5o

23

Dangling Ri

This occurrence is located near the 134 km post on the Sampdrup Jongkhar-Tashigang road, where pyrite occurs mainly as disseminations and stringers along the bedding of grey chert-quartzite. The mineralization is characterized by reddish brown stains and crusts of brownish yellow limonitic gossan at the surface. The lenticular body has a strike length of 7 m with thickness ranging from only 1 cm to 80 cm, averaging 35 cm.

Pyrite forms the bulk of the ore.. The grains are euhedral to subhedral and contain inclusions of quartz. Gangue minerals include mainly quartz with minor amounts of chlorite, epidote, limonite and zircon.

About 9 tonnes of pyrite ore are estimated for the area to a depth of 2.0 m and with sulphur contents varying from 3.21 to 15.58 per cent.

Dhanese

This pyrite occurrence is located near Dhanese village, about 25 km north-north-west of Phipsugaon. Nodules of pyrite are found sparsely disseminated in the carbonaceous slaty phyllite interbedded with the dolomite. The nodules vary in diameter from a few millimeters to 5 cm. The mineralization is characterized by red stains and coatings of gossaniferous material on the slaty phyllites. Sulphur content of the ore varies between 0.28 and 12.50 per cent.

2. Ceramic and Refractory Minerals

Clays (Cly)

Clay occurrences are located near Khelkha (Wangdiphodrang) and at Wang Paon (Thimphu). Khelkha is 32 km from Wangdiphodrang on the road to Tongsa and Wang Paon is 5 km from Sisina on the Sisina-Chakula road.

Khelkha

The clay here occurs as a lensoidal body of about 50 m long and 2 m thick. It is masive as well jointed and often present in pockets within the host rock. Detailed mapping and channel sampling found both its quantity and quality insignificant, though the clay may still serve local users.

Wang Paon

The clay here is in the form of a tabular to lensoid body associated with the metapelites of the Paro formation. The occurrence is about 2,400 m long and 4 m thick. The clay has moderate plasticity and can be easily moulded. It may find application in ceramics and bricks industries or as a drilling mud.

Dolomite (Do)

Bhutan has inexhaustible reserves of dolomite all along the foot-hill region. Most of the deposits are accessible by 4WD vehicles. The largest of the dolomite deposits occur between the Manas river in the east and Samchi in the west, over a distance of more than 240 km. A summary is presented in Table IX at the end of this section.

Dolomite occurs as bands of various dimensions and are associated with the Manas formation of the Buxa group. The bands are frequently intercalated with phyllite, slaty phyllite and quartzite. In some occurrences, the dolomite grades into low grade limestone.

Samchi-Khanabharti-Sarkitar

The dolomite occurs here as continuous bands from the left bank of the Khanabharti Khola to the right bank of Pagli Khola over a strike length of more than 9 km. This deposit is being quarried at Khanabharti and Khagra Jhora sections where the bands are 600 m and 250 m thick respectively. Another 100 m thick band is located at the confluence of Sangla Khola and Sukti Khola. The 300 m band north-west of Gomtu continues up to Sarkitar village on the right bank of Pagli Nala. Further east, the deposit is overlain by the floodplain gravels of the Pagli Nala. Over its entire length the deposit forms a NW-SE trending craggy ridge, rising to an altitude of 700 m.

The dolomite is of good quality with high MgO and CaO, and is low in alumina and insolubles. Random chip sample analyses from different portions of the deposit indicate an average of 20 per cent MgO, 30 per cent CaO, 1.9 per cent A12O3 and less than 2 per cent insolubles. Assuming an average width of 200 m over the entire strike length of 9 km, the deposit holds inferred reserves of 102 Mt down to a depth of 30 m. This dolomite is suitable for use as a fluxing agent and for refractory purposes.

Uare-Deergaon

This deposit extends over a strike length of about 8 km from Uare village on the left bank of the Khanabharti Khola in the west to Deergaon on the right bank of Pagli Nala in the east. The dolomite band has a uniform thickness of 50 m almost throughout its strike length. A 1 km portion around trigonometric point 0.879 (near Uare village) is 150 m wide.

Chip samples collected at this point indicate an average of 20.5 per cent MgO, 30 per cent CaO, 1.5 per cent A12O3 and 2 per cent insolubles, while chip samples from Sukti Nala gave 20 per cent MgO, 28 per cent CaO, 5 per cent R2O3 and 4 per cent insolubles. Assuming an average thickness of 50 m over the entire strike length, estimated reserves for this deposit are 29 Mt to a depth of 30 m.

24

Khanabharti North-Pagli-Titi-Hauree

This dolomite band stretches from east of Dalamthan (near Bukay Dham) in the west, to the right bank of the Hauree Nala south-west of Tadingaon in the east, covering a strike length of about 16 km. The dolomite of this area is fine to medium-grained, cream to light grey in colour, hard and highly fractured.

A detailed drilling survey of a block of 1.1 km strike length and 280 m width, carried out in this area proved total reserves for this block to be 31.04 Mt. Assuming an average width of 250 m, estimated reserves for the entire strike length of the deposit are 388 Mt to a depth of 30 m. The dolomite is of good quality, analysing 20 per cent MgO, 30 per cent CaO, 1.5 per cent R2O3 and less than 2 per cent insolubles.

Titring-Kalesor

This grey coloured dolomite stretches from Titring in the west to the Torsa river in the east. It strikes NE-SW and dips streply towards NW. Dolomite also occurs on the south-west slope of the Sunkanti-Kalapani hill. Based on surface data, total reserves of 529 Mt are estimated for this area.

Kalesor

Four bands of dolomite with a total thickness of 330 m are exposed on the southern flank of the Kalesor hill over a strike length of 5.25 km. These bands are separated by about 20 m of phyllite. Towards the northern slope of the hill, only two bands are exposed, separated by a 30 m thick phyllite.

Analytical results (Table 8) show little variations for all four bands. The dolomite is of good quality and could be used for refractory purposes or as a fluxing agent. Estimated reserves of the Kalesor dolomite are 2,500 Mt assuming a specific gravity of 2.68 and a 25 per cent deduction because of solution cavities.

Mohakal-Baikinza-Piping-Hasinigaon

Several bands of dolomite occur in these areas. The general trend of these bands is ENE-WSW, dipping 40° to 60° towards NNW. At Piping, the bands strike NNW and dip towards the east, forming steep cliffs. The bands at Basinigaon, Lebrong and Deoraligaon are each about 20 m thick. The Baikinza band is about 60 m thick, increasing to about 100 m towards the east. The Pabjigaon dolomite band is 80 m thick while the Piping band has a maximum thickness of 500 m. A dolomite band at Mahakal village is about 270 m thick.

In all of these deposits, the dolomite occurs as darkgrey to greyish-white crystalline bands with partings of thin layers (upto 1 m) of light-dark-grey and purple phyllites. The dolomite is generally highly jointed and fractured.

The table below lists chip sample analyses from different parts of the deposit.

Locality % MgO % CaO % A.I. Remarks

1 Dhanese ridge

21.14 29.19 3.42 average 2 chip samples

2 DhaneseSth ridge

20.95 28.79 4.60 1"

3 SarbhangKhola

20.56 29.05 4.94 1"

Surface data led to estimated potential reserves of 730 Mt for this area.

Kakulang

Massive dolomite bands with thin partings of carbonaceous phyllite are exposed all along Taklai, Sukuntaklai and Kakulang river sections. The sub-parallel Kanamakura- south and Kanamakura-north bands trend roughly eastwest.

The Kanamakura-south band occurs between the Sukuntaklai river in the west and the Kakulang river in the

Table 8. Chemical composition of the Kalesor dolomite bands

Band Area % MgO % CaO % A.I. Remarks

I Northern slope 21.35 29.80 1.60 41 chip samplesII -do- 21.14 29.73 2.61 65 -do-

I Southern slope 21.35 29.90 2.68 28 -do-II -do- 21.38 29.97 1.50 16 -do-III -do- 21.15 29.38 2.47 37 -do-IV -do- 21.16 29.87 2.02 24 -do-

25

east over a distance of about 12 km with a maximum width of 800 m, exposed on the western bank of the Kanamakura river and forms ridges as high as 200 m.

The Kanamakura-north band extends for over 20 km from east of Thewargaon in the west to the eastern bank of the Kakulang river in the east and may extend further. The dolomite band attains a maximum thickness of 2 km in the Taklai and the Kakulang rivers and forms numerous ridges rising to a height of 300 m. A sequence of sericitechlorite, phyllite and orthoquartzite occurs between the northern and southern bands.

The north and south Kakulang bands gradually merge with the carbonaceous phyllite and grey orthoquartzite in the west. The dolomite is grey to dark grey in colour with a fine angular grain mass and is closely jointed. Veinlets and lenses of fine-grained white calcite and pockets of calc-tufa are common in the dolomite.

The bulk of the dolomite deposits contains over 20 per cent MgO and less than 2.3 per cent SiO2. Tentative reserves of 2,900 Mt are estimated on the basis of reconnaisance surface data.

Manas

This dolomite band spans 35 km from Kakulang river in the west to the Dangme Chu in the east. The width of this dolomite band varies between 500 m in the Kakulang river section, 4 km in the Mangde Chu section between Pangkhar and the Lilang Chu, and about 4.5 km in the Nirang Chu section between Dagsa and Yongbari. The entire dolomite band is folded into a syncline and forms ridges up to 300 m high.

Dolomite chip samples collected from Dagsa and elsewhere show contents with up to 21 per cent MgO for this deposit. Assuming a strike length of 35 km and an average width of 2 km, tentative reserves of 5,985 Ml arc estimated to a depth of 30 m.

Dechhiling

The deposit extends over a strike length of 20 km in an east-west direction, west of Dechhling village. Chip sample analyses of the dolomite band show up to 21 per cent MgO. Assuming an average width of 2 km and a persistence at depth of 30 m, tentative reserves of 2,400 Mt of dolomite arc calculated.

Narphung-Khandame

Two thick bands of dolomite are present in this area. The NE-SW trending Narphung band extends over 9 km with thicknesses ranging from 1 km in the north to about 2 km in the south-western part. The Khandame band

trends NE-SW in the north and E-W in the south (folded?). The band has a strike length of 10 km and a thickness of 1.5 km. Both brown-grey and dark-grey varieties exist.

Chip sample analyses of the Narphung band show an average of 21.28 per cent MgO and 29.79 per cent CaO. Assuming an average thickness of 750 m and a down-dip continuity of 30 m, reserves of 135 Mt are tentatively designated to the Narphung band. Estimated reserves of 281 Mt apply to the Khandame dolomite band.

Graphite (Gr)

Khepchishi Hill

The Khepchishi Hill Graphite deposit is located in the Chilaila area, Haa district at an altitude of over 3900 m and remains snow-covered during the winter. The deposit can be reached by bitumen road either from Haa (26 km) or from Paro (60 km). Hashimara is the nearest railway station which is about 240 km away.

The graphite occurs in association with graphitic schist which forms concordant bands within quartzite, calcareous quartzite, calc-silicate rocks and dolomite. These rock units are all considered to be part of the Paro formation. Most of the graphite is cryptocrystalline although a lesser flaky variety also exists.

There are three bands of graphite-schist. They merge into a single composite band near the Latina spur and extend south-eastward into the Khepchishi peak. The composite band has a strike length of 1500 m and a width of over 30 m. The three individual bands continue over strike lengths of about 250 m with thicknesses ranging from 5 to 10m.

For the purpose of evaluation, the Khepchishi Hill graphite deposit has been subdivided into five blocks. Block I is the north-western part of the deposit, exposing two bands of graphite-schist. Block II exposes three bands which merge into a single composite band at the Latina spur. The blocks III, IV and V include the south-eastern extension of the composite band. Block IV is the most promising one. The ore to overburden ratio is about 1:1. Detailed geological mapping and drilling covering an area of 0.59 km2 was completed in 1983. In the first four blocks, 31 boreholes were drilled. In Bock V only surface sampling was carried out. Alltogether 34 trenches were excavated in the five blocks and 109 trench samples collected at 5 m intervals. These as well as core samples from all boreholes were analysed. The overlying crystalline limestone (dolostone?) was also systematically sampled and analysed to test its suitability for industrial use. The detailed work at Khepchishi Hill was completed in October 1983. The Khepchishi Hill graphite deposit has estimated total graphite ore reserves of 53.74 Mt. The ore reserves per block are given in table 10 below:

26

Table 9. Dolomite reserves and grades, Bhutan

LOCATION MODE OF OCCURRENCE STATUS OF INVESTIGATION RESERVE (mill. T)

RESERVECATEGORY

GRADE % MgO %CaO

Rehti-Sarkitar 9 km strike length 200 m av. thickness.-30.00 m depth.

Preliminary surface investigation. Chip sampling.

102.00 Estimated 20.00 30.00

Dare-Deergaon 8 km strike length 50 m thickness. -30.00 m depth.

Preliminary surface investigation. No sampling done.

29.00 Estimated — .......

Khanabharti-Nth. Pagli- Titi-Hauree

16 km srike length 250 m thickness. Cream & light-grey, hard & intensely fractured dolomite.

Detailed exploration by drilling.

31.04 Proved 20.50 30.00

Titirng-Kalesor Nth.

Grey dolomite Preliminary surface investigation. Channel sampling.

529.00 Possible —

Kalesor 5.25 km strike length 330 m max. thickness. White-grey dolomite

Systematic surface investigation.Channel sampling.

250.00 Probable 21.35 29.80

Mehakal- Paikinza- Piping- Pabjigaon- Basinigaon

20.00-500.00 m thick.Crystalline darkgrey dolomite.

Preliminary surface investigation.No sampling done.

—

Danese 600.00-700.00 m thick. Preliminary surface investigation. Random chip sampling.

730.00 Possible 20.95 22.73

Kakulang 32.00 km strike length 200.00-800 m thick. Massive grey with calcite veins.

Systematic surface investigation.Chip sampling.

2 900.00 Probable 20.00 —

Manas 35.00 km strike length2.00 km width.30.00 m av. depth.

Preliminary surface investigation.Random chip sampling.

5 985.00 Probable 21.00 —

Dechhiling 20.00 km strike length av. 2.00 km width.-30.00 m depth.


2 400.00 Probable 21.00 —

Narphung 9.00 km strike length av. 750.00 m thick.-30.00 m depth.Brown-dark grey.


135.00 Probable 21.23 —

Khandame 10.00 km strike length av. 1.50 km thikckness.-30.00 m depth.


281.00 Probable 21.33 29.60

27

Table 10. Khepchishi Hill Graphite Reserves

Block I II III IV V

GraphiteReserves (Mt)

0.24 5.89 5.70 33.88 8.03

Category —— Proved —— Probable Inferred

Overburden (Mt) High 5.94 8.13 23.49 5.52

The graphite ore of Khepchishi hill returned the following analyses:

Non-carbonate carbonCarbonate carbonAsh

10 to 22% (occasionally 28%) traces to 3%70 to 85%

The Khepchishi ore underwent successive beneficiation studies by the National Metallurgical Laboratory (NML), the Patna Estate Graphite Corporation (PEGC) and in 1988, Austroplan. Tests carried out by PEGC indicated that the ore could be beneficiated to 90 per cent F.C. with 95 per cent recovery after six flotation cycles using HSD, pine oil and xanthanates in the ratio 2:2:1 respectively. Similar tests carried out by the Austroplan team showed that the graphite could be beneficiated to more than 90 per cent F.C. with three flotations. A techno- economic feasibility study on the Chilaila graphtie was also done by Austroplan (1989).

Donga Graphite Occurrence

This occurrence of a few bands of graphite-schist has recently been located (1989) at about 400 m south of Donga, in Chukha district and can be reached on foot from Makaibari (near the 63 km marker along the Phuntsholing- Thimphu highway) through Changkha and Toktokha or from Mebisa through Japchho and Toktap (Figure IX).

The graphite is associated with fine to medium - grained graphite-schist, grey quartzite and quartz-mica schist; the bands of graphite-schist underlie a gneissic assemblage and are in turn underlain by quartzite. The graphite-schist bands of the Donga area are associated with the Thimphu formation. They are flaky from fine to coarse, and occasionally grade into a fine granular type with quartzite and micaceous impurities.

The bands of graphite-schist are often exposed along sub-vertical scarps (average slope angle is roughly 70°) and the bands generally show a northerly dip of about 10°. The trend of the graphite-schist bands varies from NW-SE to N70°E - S70°W. The thickness of the exposed parts of the graphite-schist bands varies from 7 to 13 m. The contacts of the graphite-schist with both the underlying and overlying rocks are defined by zones in which fine laminations of graphite-schist alternate with the associated units. The middle portion of the graphite-schist bands are massive and homogenously made up of graphitic matter.

Layers and laminations of quartzite, mica schist and fuchsiteschist are abundant in graphite-schist. Ferruginous encrustations frequently occur parallel to the plane of schistosity.

Two bands of graphite-schist were traced for a cumulative strike length of about 600 m. Channel samples were collected at 1 m-intervals from the graphite band exposed along a scarp at about 150 m east of Donga. Chip samples at 1 m-intervals were also collected from the same band, at about 150 m N70°E from the channel sampling location. Chip samples were also collected from a band situated at about 60 m N15°W of Donga. Analytical results are not yet in hand. For the exposed part of the graphite-schist bands of the Donga area, roughly 0.22 Mt of ore is estimated to a depth of 20 m down dip. Grab samples of graphite from the Donga area show non-carbonate carbon more than 18 per cent C. Detailed mapping and sampling surveys have been proposed over the deposit.

Other occurrences of graphite-schist are present in the Chukha district, also at (a) Dapchhasa and (b) the Dorjomsa area east of Chimakoti, (c) the Takti Chu area, (d) the Duna (Dungna) area (non-carbonate carbon ranging from 14.18 to 23.10 per cent C) and (e) the Jemina area in Thimphu district (Figure IX).

These occurrences are associated with the gneisses of the Thimphu formation and the metasediments of the Paro formation. Detailed work has yet to start on these occurrences.

In grab samples of graphite-schist from the Dapchhasa- Dorjomsa area the weight percentage of carbonate carbon varies from 11.82 to 16.47 per cent, at an average of 14.62 per cent. Average ash content is about 84 per cent.

3. Other Industrial Minerals

Asbestos (Asb)

So far, only one occurrence of asbestos is known from Bhutan, near Thumkey, about 5 km east of Chengmari. It occurs as veins of varying thickness cross-cutting the epidiorite sills. The asbestos is of amphibole variety (anthophyllite, ferro-anthophyllite and amosite type) and occurs as slip fibres along foliations, joint planes, joints and fractures. Vein widths vary from 3 cm to 5 cm and lengths reach 3 m. The asbestos in this occurrence is brittle and splintery and hence the fibres cannot be spun. An area of 0.06 km2 was mapped in detail, covering the Thumkey occurrence. Indicated reserves are very small and insignificant.

Gypsum (Gy)

Deposits of gypsum are located at the Khothakpa area (Pemagatshel district) in eastern Bhutan. Khothakpa is connected with Thselingkher, which in turn is connected to Samdrup-Jongkhar by a 70 km long road. Other gypsum occurrences are located in Uri, Omsi Ri, Cherung Ri, Khar,

28

Takhtsong Monastery

Figure IX. Graphite Occurrences in Bhutan

THIMPHU

Chakula

Chuzom

JemenaPARO

Chilaila

CHAPCHA

HAA

LEGEND

Variegated Phyllites and Quartzites

THUNT SHOLING

Green Phyllite and Quartzite

SHUMAR

Quartzite, Quartz — mica Schist with GraphiticSchist & Marble bands. PARO

Migmatites, Biotite-granite Gneiss, etc.

THIMPHU

Granodiorite-adamellite Gneiss

CHUZOM

Marble bands

FAULTS

THRUST

GRAPHITE

Gedu

Mirchang

Tala

INDIA BHUTAN

Darga

DapchhasaDorfomsa

Omchu

DUNAM

29

Shali Sekar Brak, and Zeng Ri, all al short distances from Khothakpa.

Gypsum occurs as thick beds in intimate association with anhydrite within the Shumar formation. Generally the gypsum anhydrite beds are overlain by 25 m thick green phyllite and talus material. Commonly, the gypsumrich zones lie above the anhydrite zone. Both gypsum and anhydrite are white to grey, massive to bedded, and saccharoidal in texture. The gypsum-anhydrite beds are intercalated with thin bands of calcareous phyllite and carbonates.

Table 11 lists the various gypsum occurrences and their reserves and grades.

Uri Chu

This occurrence lies to the north of Nangkur village. The gypsum band is sandwiched between the overlying sericite phyllite and the underlying limestone. The bands extend for a strike length of about 1 km and range in thickness from 6 to 12 m. The gypsum is generally massive, rarely bedded, white and shows uniform saccharoidal texture.

Khar

Eight small lenticular bands of gypsum are located at Khar area near Rinthang (3 bands), Bros Khola (2 bands), and Up Ri (3 bands). These bands are overlain by sericite phyllite and underlain by limestone. They are generally massive, sometimes bedded, white and uniformly saccharoidal. Intercalated lenses of greenish calc-slate and limestone are present within the gypsum bands. The strike lengths of these bands vary from 20 to 132 m and widths range from 1 to 5 m.

Cherung Ri

Gypsum and anhydrite are associated with slaty phyllite, calcareous phyllite, green phyllite and limestone

in the Cherung Ri area. The anhydrite zone underlies the gypsum band, which is always intercalated with phyllite and calcareous quartzite partings. The band has its maximum thickness in the north-east, gradually diminishing towards the south-east. Thickness of overburden ranges from 3 to 25 m. A detailed drilling survey was carried out over the Cherung Ri deposit (1968-1973); 43 holes were drilled, out of which 39 intersected gypsum bands.

Khothakpa

Work on the Khothakpa gypsum deposit has been completed; PCA is currently mining Khothakpa gypsum for use in the manufacture of cement.

Limestone (Ls)

Limestone deposits are widespread in southern Bhutan. Several bands of limestone of mineable quantity exist near Pagli-Titi, Kalesor and Khanabharti in south-western Bhutan and in the Nganglam area to the east. These limestone deposits are easily accessible by surfaced roads connected to the various railway stations in India. Mappable bands of crystalline limestone occur within the Thimphu and Paro formations. Details on these deposits follow and are summarized in the accompanying table 13.

Pagli-Titi

This occurrence stretches for about 3.3 km from Pagli Khola in the west to about 1.3 km east of Titi Khola in the east. It is associated with the grey phyllites and quartzites which constitute the Manas formation of the Buxa group. 66 boreholes totalling 5,186 m were drilled in three blocks: Pagli Western, Eastern and Titi blocks. The Eastern block alone contains proven reserves of 5.45 Mt of portland cement grade limestone with an average grade of 46.52 per cent CaO, 2.78 per cent MgO, 11.6 per cent A.I. and 2.29 per cent R2 03 .

Reassessment of the Pagli Western Block by the Geological Survey of India (GSI) in 1975 established total reserves at 6.04 Mt of cement grade limestone averaging

Table 11. Gypsum reserves and grades, Bhutan

NAME OF THE DEPOSITSRESERVES (mill. T)

RESERVECATEGORY % SO, % Gyp.

GRADE % Anhy. % CaCO3 % lmp.

REMARKS

Cherung Ri(i) With phyllite intercalation 69.036 Proved 33.86 48.67 18.90 73.31 18.63

(ii) Without phyllite intercalations 56.448 Proved 41.12 58.22 23.30 10.20

(iii) With CaSO4.H20~83.65 % 55.942 Proved — — .... ----- ----- This type of gypsum is used in Sindri Fertiliser Plant.

Uri 13.600 Inferred ...... 91.63 1.26 ---- -----

Khar 0.034 Probable — 87.87 1.18 ...... ......

Omsi Ri 8.830 Inferred ...... 91.00 — ---- ----

30

44.8 per cent CaO, 2.42 per cent MgO, 8.99 per cent A.I., and 2.42 per cent R2O3, in addition to 1.18 Mt of marginal cement grade limestone with an average grade of 38.44 per cent CaO, 3.12 per cent MgO, 18.20 per cent A.I., and 3.06 per cent R2O3. The Western block is being mined by the Penden Cement Authority, having started in 1980.

Further work by the GSI in 1987 revealed four additional bands of limestone in the Pagli mine area. These bands are the western extension of the Pagli Western block. Detailed mapping and drilling is in progress on this extension. Based on available surface and subsurface data, estimates of total reserves arrive at 1.64 Mt for this area.

Estimated reserves of 1.50 Mt of cement grade limestone are likely to be available from the eastward extension near Pagli Khola. In total, potential reserves of 9.14 Mt of cement grade limestone are listed for the Pagli- Titi area. The average grade of this limestone is given as 40 per cent CaO, 2.75 per cent MgO, and 12 per cent R2O3.

Nganglam Area

Several bands of high cement grade limestones are located in the Nanglam area (Figure X).

Marung Ri

This band occurs within the quartzites and phyllites of the Buxa group and stretches for 7.5 km. Detailed drilling proved a total of 18.71 Mt of cement grade limestone over a strike length of 7 km and an average grade of 46.04 per cent CaO, 4.87 per cent MgO and 4.07 per cent A.I.

Kurung Ri

This limestone has a strike length of 6 km and a thickness of 30 m. Surface data suggest inferred reserves of 14.5 Ml of cement grade limestone averaging 47.41 per cent CaO, 0.74 per cent MgO, 12.72 per cent A.I. and 1.71 per cent R203 for the Kurung Ri area. As the MgO content at Marung Ri is somewhat high (average 4.87 per cent), Kurung Ri limestone could serve as a sweetener to the Marung Ri limestone in the manufacture of cement.

Gachari

This limestone band spans a strike length of 3 km while its thickness varies from 5 to 22 m. Detailed work on the western part of the Gachari limestone indicates probable reserves of 1.09 Ml with an average grade of 33.83 per cent CaO, 2.64 per cent MgO, and 26.53 per cent A.I.

Kangrizhe

Here, a long band of limestone stretching for 700 m with an average thickness of 60 m is found. Based on surface data alone, tentative reserves of 7.0 Mt of cement grade limestone down to a depth of 100 m are estimated.

The limestone has an average composition of 45.61 per cent CaO, and 0.88 per cent MgO. A detailed drilling survey is in progress.

Mirchang-Tala

This deposit is located between the Mirchang ridge to the west and the western bank of the Raidak river to the east. It can be reached on foot by way of a 10 km long track starting at the 44 km post along the Phuntsholing-Thimphu highway.

The deposit consists of three lenses of limestone interbanded with garnetiferous schist and quartzite. The biggest lens, exposed around Badina village, is 950 m long and 50 to 70 m thick. The lens surfacing at Mirchang village is 350 m long and 30 m thick. The third lens, exposed 1 km north of Mirchang village has a strike length of 900 m and a 70 to 80 m thickness.

Based on surface and subsurface data, overall reserves are estimated at 6.5 Mt of limestone to a depth of 30 m down dip. Chip sampling indicated an average composition of 44.51 per cent CaO, 0.5 to 4 per cent MgO and 0.36-4.3 per cent R203 . The limestone is banded and suit-

r able for use as building or ornamental stone.

Khanku

This limestone deposit in the Paro district occurs 1.5 km south-west of Paro township on the western bank of the Paro Chu and on the ridge below which Khanku village is located. Paro is connected to Phuntsholing by a 166 km long bitumen road and Phuntsholing is only 20 km from the nearest railway station at Hashimara, India.

The limestone of the Khanku area constitutes part of the Paro formation and consists of three bands, separated by mica-schists and quartzites. The upper band is 1300 m long and 7-37 m thick; the middle band extends for 1500 m with a 34-54 m thickness. Drilling established reserves of 42.03 Mt of limestone of different grades as shown in table 12.

Kalesor-Titi

The limestone deposit of Kalesor occurs about 4.5 km NW of Phuntsholing. It is exposed along the right bank of the Torsa river on the lower slope of the Kalesor hill. It extends for a strike length of 3.25 km with thicknesses ranging from 5 to 50 m.

The limestone in the Titi area, north of the Bhoyani Khola is exposed on the southern slope of the Kalma Duars. The limestone is intercalated with slaty phyllite and quartzite of the Buxa group.

A total of 1.42 Mt of limestone with an average 44.47-52.58 per cent CaO, 0.44-3.93 per cent MgO, 0.70- 2.46 per cent R2O3 and 2.45-23.44 per cent A.I. has been estimated in the Kalesor area. Tentative reserves of high grade limestone with CaO more than 50 per cent reach

31

SCALE

o 1 2 3 4 km

Dichhiling

Marung Ri Limestone

Kurung Ri Limestone

LOCATION MAP

BHUTAN

Ngonglam

Beringma Limestone

Gachari Limestone

Congezi Limestone

Nganglam

Phyllite

Sandstone/Slate

Fault

Strike and Dip

Quartzite

Limestone

Dolomite

Siwalik

Damuda

Diuri

Buxa

Thrust

LEGEND


Figure X. Limestone occurrences in the Nganglam area, Samdrup-Jongkhar District, Bhutan.

32

Table 12. Reserves of the Khanko limestone deposit

GRADE RESERVES (MILLION TONNES) A.I% R2O3 CaO% MgO %PROVED POSSIBLE TOTAL

Grade I(over 50% CaO) 3.309 8.940 12.255 4.70 0.83 50.94 1.36

Grade II(over 48% CaO) 6.107 16.378 22.485 5.67 1.00 50.09 1.51

Grade III (over 53% Cao < 4% MgO) 10.547 25.113 35.659 7.54 1.20 48.10 2.05

Grade IV (over 35% Cao < 8% MgO) 12.43 29.411 42.030 11.37 2.58 40.47 4.98

about 74,000 tonnes assuming a depth of 10 m. About 0.2 Mt of limestone analysing 38.82 per cent CaO and 9.58 per cent MgO have been estimated for the Titi block.

Tokaphung

This limestone deposit is located near Tokaphung village and can be reached by means of a 3 km long mule track from Wamrong. The crystalline limestone occurs within the basal phyllite member of the Shumar formation. Ils content ranges from 45 to 50 per cent CaO for the lop 10 m. MgO and R2O3 contents for the whole deposit are less than 2 and 3 per cent respectively. Assuming an 80 per cent recovery and a 30 m average thickness, probable reserves for the deposit are 30 Ml.

Khanabharti

The limestone extends for 1.4 km with thicknesses ranging from 1 m to 26 m. Preliminary surface investigations covering an area of 0.8 km2 indicate a reserve of 0.26 Mt of limestone with an average composition of 44.44 per cent CaO, 4.44 per cent MgO, 2.4 per cent R2O3 and 8.96 per cent A.I. A mini-cement plant has been set up using this limestone.

Khaling

Here, a bedded 2 m-wide limestone stretching for 1.8 km is associated with the Shumar formation. Preliminary surface work covering 1 km2 indicates inferred reserves of 0.31 Mt, partly cement grade and partly blast furnace grade limestone.

Chilungkha

The crystalline limestone in this area forms part of the Paro formation in Haa district. Detailed work has led to estimated reserves of 1.4 Mt of carbide grade limestone over a strike length of 500 m to a depth of 50 m.

Tintala-Noonpani

These bands of limestone are associated with gneisses in this area of Samchi district. Drilling has shown that these bands do not extent at depth.

Haurie Khola

Four major bands of limestone occur here, about 10 km south-west of Phuntsholing. The strike length of the bands vary between 160 and 480 m. Detailed drilling has indicated probable reserves of 0.114 Mt of chemical grade limestone down to a depth of 20 m, in addition to 16.7 Mt of cement grade limestone. The chemical grade limestone al Haurie is currently being mined by BCCL for the production of calcium carbide.

Genekha

High grade crystalline limestone occurs at the Pb- Zn prospect of Genekha area in Thimphu district. The limestone shows variegated colours, is intensely fractured, and crossed by secondary calcite veins. Surface and subsurface data indicate an estimated reserves of 0.9 Mt of carbide grade limestone down to a depth of 30 m downdip with an average composition of 52 per cent CaO and 1.4 per cent MgO.

Haa Wangcha

Here, an area of 0.36 km2 was investigated by detailed mapping and channel sampling, resulting in tentative reserves of 5 Mt of chemical grade limestone with 52 per cent CaO and 2 per cent MgO. Drilling to prove the reserves was discontinued for the time being.

Rong Ri

The Rong Ri limestone deposit occurs discontinuously for about 4.5 km from south of Torme village in the

33

west to Katledara in the east. Two distinct limestone bands are exposed on both sides of the Rong Khola and occur within the interbedded sequence of phyllites and quartzites of the Shumar formation. The limestone bands vary in thickness from 7-15 m to 15-32 m respectively, are separated by 5-25 m phyllite partings and can be traced over a strike length of 500 m in the explored area.

The limestone is hard, compact and crystalline in nature, fine to medium-grained and grey to light grey in colour with thin intercalations of phyllite/carbonaceous phyllite. Disseminations and stringers of pyrite are present locally.

An area of 0.12 km2 has been explored in detail. Seven boreholes have been drilled totalling 546.40 m. Surface and core sample analyses indicate that the Rong Ri limestone is of chemical grade. Total in-situ reserves of limestone in Block A (strike length 124.5 m) and Block B (strike length 150 m) down to 80 m and 60 m below surface level work out to 1.11 Mt and 0.83 Mt respectively. A total of 1.94 Mt of limestone with a weighted average grade of 50.35 per cent CaO, 2.52 per cent MgO and 3.90 per cent A.I. is available from both blocks. Estimated reserves of chemical grade limestone in the two blocks is 0.85 Mt with a weighted average grade of 51.40 per cent CaO, 2.00 per cent MgO and 2.85 per cent A.I. This is based on assumptions that grade and thickness of drillhole insersections persist at depth. The limestone/wasterock ratio for both blocks is 1:1.71.

Chaibar

This limestone consists of several bands associated with the Shumar formation. It is of cement grade with 40.2 to 50.7 per cent CaO and 0.26 to 1.2 per cent MgO. Lower grade limestones also occur as pockets within the cement grade limestone. Surface data indicate probable reserves of 0.70 Mt of cement grade limestone in the area.

Dholpani-Bhurkhola

Bands of low to cement grade limestone occur in the Dholpani and Bhurkhola areas in association with phyllite and quartzite of the Buxa group. These bands range in strike lengths from 50 m to 450 m with thicknesses ranging from 7 to 25 m. The limestone has an average composition of 41.08 to 42.06 per cent CaO and 1.87 to 2.24 per cent MgO. Inferred reserves of 0.206 Ml of limestone are indicated for this area.

Mica (Mi)

Mica-bearing pegmatite veins intruding the gneisses of the Thimphu formation have been located in Chirang, at Lamidara, and near Damphu and Darachu in the Chirang district. The mica is in the form of books of variable dimensions and is highly strained, full of inclusions and commonly stained. This poor quality mica is of little economic importance.

Quartzite (Si)

Quartzite occurs as an important rock in all formations of the Bhutan Himalaya e.g. the Paro and Thungsing formations contain dominant beds of quartzite. The following deposits have been studied in some detail for their suitability as raw material in the manufacture of glass, ferro-silicon and calcium silicide. These deposits occur in the Tintali area, Samchi district, the Kamjee area, Chukha district, and in Burichu, Chirang district.

The Tintali quartzite occurs as a thickly bedded sequence with chlorite schist intercalations and epidiorite sills within the Shumar formation.

The Kamjee quartzite also occurs as a thickly bedded sequence interbanded with micaceous quartzite and mica schist laminations. The quartzite is white, massive and commonly jointed. Quartzite at Burichu occurs along with quartz-mica schist and belongs to the Tirkhola formation.

Tintali

This quartzite is coarse-grained, snow-white to greenish/greyish white, hard, compact and well jointed. Impurities include iron oxides, chlorite and mica flakes. The thickness of the bed ranges from 4 to 42 m.

An area of 0.08 km2 was explored by drilling. Based on these data and chemical analyses, reserves of 3.49 Mt of quartzite with an average chemical composition of 97.54 per cent SiO2, 1.06 per cent A12O3, and 0.28 per cent Fe2O3 are indicated, apparently suitable for the manufacture of ferrosilicon and calcium silicide.

Kamjee

Here, the quartzite is medium to coarse-grained and thickly bedded with regular joints. Flaky mica is commonly present along the bedding planes. The thickness of this bed varies between 36 to 62 m.

Preliminary work on the Kamjee quartzite indicates sizable reserves of quartzite. Chip sample analyses show 85.0 to 89.0 per cent SiO2 and Fe2O3 ranging from 0.36 to more than 1.0 per cent. This grade of quartz may not be suitable for the manufacture of glass. However, more detailed work is necessary to assess both quality and quantity of this deposit.

Burichu

The quartzite in this area is associated with mica schist. Six grab samples of quartzite show 94.40 per cent SiO2 and 0.2 to 0.5 per cent Fe2O3. This grade of quartzite may find use in the manufacture of colourless window glass and containers. More work is needed for a total assessment of the deposit.

34

Table 13. Limestone reserves and grades, Bhutan

LOCATION MODE OF OCCURRENCE

STATUS OFINVESTIGATION

RESERVES (mill. T)

RESERVE CATEGORY

GRADE REMARKS%CaO %MgO

Pagli West Bedded Lst. intercalated with phyllites - Buxa Group.

Detailed expleration by drilling.

6.040 Proved 40.60 2.70 Leased to PCCL for use in the manufacture of calcium carbide.

Pagli West Extension

--------- idem...... —— ............--idem-............ 1.600 Inferred Cement Grd.

Titi --------- idem--------- ----------- idem---------- 1.500 Inferred Cement Grd.

Tala/Mirchang

Bedded crystalline Lst. - Thimphu Fm.

Surface & exploration by drilling.

8.500 Estimated Cement Grd. Leased to BCCL

Khanku Bedded crystalline Lst. - Paro Fm.

Surface & exploration by drilling

12.44029.590

ProvedProbable

Cement &Carbide Grd.

Kalesor-Titi Bedded Lst. interca- alated with phyllites - Buxa group.

Preliminary surface investigation.

1.600 Inferred Cement Grd.

Kurung Ri --------- idem--------- Preliminary surface investigation.

14.500 Estimated 48.47 0.69

Marung Ri --------- idem--------- Detailed exploration by drilling.

18.710 Proved 46.04 4.87

Gachari --------- idem-.......— ----------- idem---------- 1.090 Probable 88.83 2.51

Kangrizhe --------- idem............ ----------- idem---------- 1.259 Estimated 15.54 0.68

Khanabhati Bedded Lst. intercalated with slaty phyllites-Buxa Gp.


0.260 Inferred 44.44 4.44

Khaling Bedded crystalline Lst. - Shumar Fm

............. -idem-............ 0.310 Inferred Cement & B.F. Grd.

Chilungkha Bedded crystalline Lst. - Paro Fm.

Detailed exploration by drilling.

1.400 Estimated 52.50 ......

Haurie Khola Grey Lst. interbedded with phyllites- Buxa Group.

----------- idem---------- 16.7000.114

ProbableProbable

Cement Grd.Chemical Grd.

Leased to BCCL.

Genekha Crystalline Lst. hosting Pb-Zn ore.

...... ........ idem---------- 0.900 Probable 52.00 1.40

Haa Wangcha Bedded crystalline Lst. - Paro Fm.

Surface investigation. Exploration by drilling discontinued.

5.000 Probable 52.00 2.00

Rong Ri Crystalline Lst.bands - Shumar Fm.

Surface investigation.Exploration by drilling.

1.940 Proved 50.35 2.52 Leased to BCCL.

Katie Dara Crystalline Lst.- Shumar Fm.

Surface Investigation. 0.110 Tentative 52.69 2.33

Chaibar Crystalline Lst. - Shumar Fm.

Surface Investigation. 0.700 Probable 45.50 0.70

Dholpani-Bhurkhola

Bedded Lst. intercalated with phyllites-Buxa Group.

Surface Investigation 0.206 Inferred 41.67 2.05

TOTAL 121.186 million tonnes.

35

Talc (Te)

A number of talc occurrences are reported from the foot-hill regions of Bhutan. They extend from Samchi in the west, to Sarbhang in South Central Bhutan, and can all be reached by 4WD vehicle.

Talc occurs as thin lenses, films, pockets and bands associated with quartzite, phyllite and calcareous quartzite of the Buxa group. The thicknesses of the talc bands range from a few centimetres to 40 m. Surface investigations to trace the strike extent of the talc bands were conducted over most of the occurrences in the Samchi area. Chemical analysis of grab and channel samples were also carried out, mainly in the east.

The individual talc occurrences with their reserves and grades are shown in table 14.

Pa Chu-Seti Khola

This occurrence, located al the Pa Chu and Seti Khola confluence can be reached from Phuntsholing along an 8 km track. A description of the two lenses follows:

Lens Strike length Thickness Depth S.G. Reserves (t)

I 90 m 5 m-12 m 10 m 2.7 10,000II 300 m 13 m-40 m 10 m 2.7 10,000,000

The talc is white, pale green, dark-grey to greenish- grey in colour. Inclusions of quartzite, phyllite and dolomite are common. Nevertheless, this talc deposit is suitable for economic exploitation.

Khampa

This occurrence is located along a nala in a landslide zone near Khampa village. Eight lenses are present in this occurrence ranging in size from 7 m x 3 m to as large as 48 m x 20 m. The talc is white, pale green to grey in colour, and is foliated. Reserves of 12,500 tonnes of talc are inferred for this area.

Thunuwa

This occurrence is located on the west side of Thunuwa village. There are four lenses, varying in length from 30 to 70 m and in thickness from 5 to 40 m. The talc is light to dark green in colour and is intercalated with quartzite and phyllite. About 3,600 tonnes of low grade talc is inferred for this area.

Pagli-Sarkitar

This occurrence, located near Pagli, consists of three lenses of talc. Green and white varieties are present and the talc is semi-transparent. As the grade is low, no reserves have been calculated.

Malabanse

This occurrence is located close to the Pagli-Sarkitar occurrence. There are three lenses of talc with a maximum length of 170 m. The talc is of a schistose type with quartzite intercalations, green to white in colour and semitransparent. Potential reserves of 5,300 tonnes of talc are estimated.

Table 14. Talc occurrences of Bhutan

LOCATION DESCRIPTION OF THE OCCURRENCEESTIMATEDRESERVE (T) TALC GRADE REMARKS

Pa Chu-Seti Khola

30 km strike length, 9 m thickness, 10 m depth. White to greenish colour.

110,000 Medium-high grade

Workable deposit.

Khàmpa 5.00-8.00 m depth.As small lenses. Siliciousnature

12,000 Medium grade

Thunuwa As small lenses. 3,600 Low grade

Pagli- Sarkitar

As small lenses. 1,900 Low-medium grade

Malabanse 5.00-8.00 m depth. As small lenses. Silicious nature.

4,300 Low-medium grade

Lapchekha As small lenses. 4,200 Low grade

Sukti Khola As small lenses. 2,300 Low grade

Budheni As small lenses. 1,800 Low grade

Lhoring As small lenses. Steatite grade

36

Lapchekha

This talc occurrence is situated at about 24 km ENE of Samchi. There are five lenses of a grey to light green soapstone variety in this area. Potential reserves of 4,200 tonnes of soapstone are estimated.

Sukti Khola

The talc here occurs about 1 km east of the confluence of Sukti and Sangle Khola. The talc lenses are small and thin in this area with estimated reserves of only 2,300 tonnes.

Budheni-Tin Doban

Small lenses of white, grey and green varieties of talc, often sheared and impure, are associated with quartzite and phyllite in this occurrence. About 1,800 tonnes of low quality talc is estimated for this area.

Lhoring

This occurrence is located at Khare Dara and Gumba Dara and can be reached on foot from Sarbhang. The talc is light cream in colour and occurs as lenses within the sheared dolomite bands.

Chemical analysis shows the talc to be of good quality (Steatite grade) but further detailed study will be needed to determine if economically exploitable reserves exist. For the time being, reserves of 20,000 tonnes of talc are estimated, based on surface data.

Calc-tufa (Tuf)

The calc-tufa of the Kalapani area (Samchi district) occurs as 20 isolated deposits stretching for 8 km from north of Aneri village to the east bank of the Khanabharti river (Rheti khola). The area is linked with Dalgaon Railway station by a 15 km long dirt road.

The calc-tufa is confined mainly to the low lying areas and occurs as tabular and blanket-type deposits without any overburden. The average thickness of the deposits ranges from 1 to 7 m but may reach 21 m locally. Areal extent of individual thicknesses range from 23,000 m2 to 34,700 m2. Lime content varies from 39.87 to 48.16 per cent CaO.

Detailed work on 11 of the deposits indicate probable reserves of 1.04 Mt with average compositions of 44.88 per cent CaO, 2.83 per cent MgO, 2.43 per cent R2O3 and 9.45 per cent A.I. The deposits have yet to be subjected to an economic assessment.

About 509,014 tonnes of calc-tufa is of better quality and could be used for sweetening the relatively low grade limestone while the rest of the material could be used directly in the manufacture of cement. The Penden Ce

ment Authority is indeed currently mining the calc-tufa for that purpose.

Marble (Mar)

Bands of marble are associated with all three tectonostratigraphic belts of the Bhutan Himalaya. Prominent among them are those associated with the Buxa group (Manas formation) and with limestones listed in the previous section. Some of the important marble deposits of Bhutan are found in the Pagli-Titi, Marung Ri, Khanabharti, Khanku, Bunakha-Chapcha, Mirchang, Genekha, and Gida- Jemena areas.

Pagmmli-Titi

Bands of marble are intimately associated with limestones of the Pagli-Titi area.

Marung Ri

Bedded deposits of marble and limestone occur at Marung Ri in the Nganglam area. MgO content of the marble is around 4.87 per cent.

Khanabharti

Several bands of marble are associated with the low grade limestone of the Khanabharti area in Samchi district. Their MgO content is around 4.44 per cent.

Khankhu

The marble bands here are intimately associated with the limestone of the Paro formation. This marble, being banded and medium-grained is suitable for decorative purposes.

Bunakha-Chapcha

Some surface sampling and detailed mapping was carried out over two marble bands in this area. These bands are about 40 to 50 m thick and have considerable strike length.

Mirchang-Tala

These bands of marble vary in thickness from 30 to 80 m and have strike lengths of 350 to 950 m. The marble is banded and suitable for use as building stone.

Genekha

The elliptical body of marble in the Romegang Ri Pb-Zn prospect extends over a strike length of over 1,150 m with its thickness ranging from 75 to 166 m. This marble is also banded and suitable for building material.

37

Gid a

Medium to coarse-grained white, banded crystalline marble with a thickness ranging from 4.5 to 8.0 m and a strike length of about 800 m occurs in this area. Channel sampling showed the marble to be quite pure with more than 90 per cent CaCo3 content. The total volume of marble estimated for the area is 0.841 million cubic metres, assuming a 25 per cent loss because of fractures or cavities within the crystalline marble. At a specific gravity of 2.6, this amounts to 2.186 Mt of marble available in the Gida area.

The Gida marble is being mined by the Bhutan Marble and Minerals Limited (BMML) for use as ornamental slabs, tiles and marble chips. The marble is also mined for use by BCCL in the manufacture of calcium carbide.

Jemena

Medium to coarse-grained white, banded and dark grey crystalline marble occurs as a sequence interbedded with quartzite, graphitic schist and mica schist of the Paro formation. Both pure and impure (dolomitic) marbles are present in the area. The marble bands vary in thickness from 10 to 65 m.

Surface and core sample analyses indicate that the marble in the area is of chemical grade with a weighted average of 50 per cent CaO for the entire deposit. Geological reserves of 12.01 Mt of pure marble are estimated for the area.

Slate (Sia)

The three major slate deposits in Bhutan arc Sha Bhel (Bonsegeoma), Kobja (Wangdi) and Pemagatshel.

The Bhel deposit is connected with Wangdi Phodrang by a 20 km long road leading to Peleta. The Khobja deposit is about 65 km from Wangdi Phodrang and 20 km from Nobding. The Bhel and Khobja slates occur as thickly bedded deposits intercalated with clay and sandstone within the Tang Chu formation of the Black Mountain group. The deposits are overlain by impure slates and underlain by

sandstones. At Pemagatshel, the slate occurs as slaty phyllite and forms part of the Shumar formation.

Bhel-Khobja

This deposit has a strike length of 5 km and an average thickness of 650 m. About 100 m of the slate has been identified as a workable deposit. The slate in this area is dark in colour with distinct cleavage planes and well spaced joints. It is free from impurities and has the required physical characteristics for commercial use.

Pemagatshel

These slates or rather slaty phyllites occur at Pang Thang and Pemagatshel east and cover an area of 0.026 km2 and 0.052 km2 respectively. They are light-to steelgrey in colour, soft, thinly laminated with wide joint spacings. Sandstone lamina are present within the slaty phyllite. The Pemagatshel slate is of poor quality but would still be suitable for roofing purposes on a local scale.

Based on surface investigations, reserves of 16 million cubic metres of good quality slate is indicated for the Bhel and Khobja areas to a depth of 30 m. Because of its poor quality, no reserve estimates have been made for the Pemagatshel deposit.

C. Mineral Fuels

Coal (C)

The coal occurrences of Bhutan are restricted to the foothills of Eastern Bhutan and are located in the Samdrup Jonkhar district, near the Indo-Bhutan border, along a 65 km long bell between Deo Nadi in the west and Leshang Ri in the cast (Figure XI). Access is by dirt road or footpath.

Coal occurs as thin seams within the sandstone and shale of the Damuda (prev. Lower Gondwana) sequence near the Main Boundary Fault. Their thickness is mostly less than 2 m and only rarely exceeds this (maximum 10.0- 12.0 m). The strike extent of most of the coal seams is less than 100 m with only a few cases continuing over more than 500-600 m.

Figure XI. Coal-bearing strata of the area between Deo River and Jomo River, South-East Bhutan.

1. Siwaliks2. Damudo3. Diuri Boulder Slate4. Louri Phyllite

ThrustCoal - bearing

LOCATION MAPINDIA

BHUTAN

TIBET

38

The coal is highly crushed, sheared and tectonised and therefore always powdery or flaky. Lumpy coal is rare. On account of tectonism, the seams are intersected by closely spaced faults or shear planes, resulting in frequent changes in the trends of the seams. The 65 km belt contains a number of individual coal deposits (also summarized in table 15).

Jagartala Area

This coal occurrence is located near Bukti village in the Samdrup Jongkhar district. It is accessible by a 12 km long footpath along the bank of the Jaibar Nadi from Okhaldunga, a village in the foothills near the Indo-Bhutanese border. Okhaldunga is connected to Rangiya Railway Station by a 60 km long dirt road. During the monsoons, the Jaibar Nadi frequently floods and the area becomes inaccessible.

There are three occurrences in the Jagartala area: the Land Slide Occurrence, the Jaibar Nadi Eastern Bank and the Jaibar Nadi Western Bank Occurrence.

Of these three, the Landslide Occurrence shows maximum exposure over an area of about 300 m x 100 m. There are 38 coal seams in the area with strike lengths ranging from 15 to 150 m and thicknesses from 0.5 to 2.5 m (maximum 10.0 m).

The Jaibar Nadi Eastern Bank occurrence lies al about 165 m NE of the Tirki Khola-Jaibar Nadi confluence. A sandstone-coal seam sequence is exposed in an area of about 600 m x 16 m. There are 7 coal seams with

strike lengths varying between 4.0 and 16.60 m and thickness between 0.3 and 2.80 m.

The Jaibar Nadi Western Bank occurrence is situated at about 240 m north of the Tirki Khola-Jaibar Nadi confluence. There are 4 coal seams which are 4.6 - 80.0 m long and 0.2 - 0.8 m thick in this occurrence. The coal of these areas is soft, flaky and powdery in nature. It has an average of 24.5 per cent volatile matter and 47.0 per cent fixed carbon, is bituminous, poorly caking and has a fuel ratio ranging from 0.60 to 2.10.

Gerua Occurrence

A detailed drilling survey is now in progress at Gerua and the Diamalakhola area on the Bhantar-Deothang road, where two coal seams are exposed, over 2 m thick each.

Diglai Nadi Occurrence

This occurrence is about 7.5 km at N80°E from the Jaibar Nadi Occurrence. Access is by a 10 km long footpath from Diwali to Dalim village. Diwali is connected with Tangla Railway station by a 45 km long dirt road passing through Penari, Phunti-achang and the Orangajuli tea garden of Assam. During monsoons, the area remains inaccessible. The coal seams are associated with feldspathic sandstone and carbonaceous shale and are exposed as small, isolated, lenticular bands on both banks of the Diglai Nadi for about 1 km, from 0.5 km north of its confluence with the Tiklai Khola. A total of 34 lenses have been mapped on the right bank and 6 on the left bank.

Table 15. Coal reserves and grades, Bhutan

Total Known Coal Reserve 1.96546 million tonnes based on surface data alone.

OCCURRENCENO. OF SEAMS

THICKNESS (m)

STRIKELENGTH

(m)DIP EXT. RESERVE

(m) ( tonnes)

Jagartala 38 0.70-2.8 13-150 20 1,030,000 (upto 30 m

depth)

Gerua-Dimla 2 -2.0 -----KholaDiglai Nadi 40 0.7-2.1 11-500 20 86,500

Chamrang Nadi

32 1.0-4.5 10-175 20 72,600

Kalapani 33 1.0-12.0 5-150 20 178,310

Nunai Nadi 4 0.9-1.7 30 .........

BhorilaRash Ri

36 0.6-6.0 20-320 25 303,650

Nagor Khola 5 1.0-2.5 34-600 30 52,000

Khaurang-Leshing Ri

5 1.0-6.0 ........ 270,000

Deothang 12 0.5-3.5 ......... - .........

....... ...... Investigation in progress............... -........ -.........

Possible ....... 11.4-34.8 22.5 32.4-69.0 52.5

Possible 6.2-43.4 22.5 6.6-35.4 27.0 29.6-64.8 43.0

Possible 19.1-43.7 34.5 7.2-29.9 21.5 29.8-47.6 41.5

— 16.4-65.7 5.8-14.5 .... 24.3-68.9 ....

Possible 11.5-48.5 24.2 11.4-48.8 26.9 20.9-63.8 40.1

Possible 13.8-47.9 26.0 8.5-33.0 26.5 34.0-64.9 41.0

Possible 16.3-35.7 .... 3.2-27.5 .... 56.4-55.2 ....

— 5.6-43.3 .... 21.9-35.1 .... 20.1-55.2 ....

RESERVE CATEGORY

% ASH % VOLATILES % F.C.

Range Av. Range Av. Range Av. REMARKS

Inferred 13.1-50.0 31.0 18.0-27.0 23.0 33.5-56.0 46.0

39

The total strike length between the left and right bank exposures is about 500 m. In general, the coal of the Diglai Nadi occurrence is soft, powdery and flaky; lumpy coal is absent. The coal ranks as sub-bituminous to semi- bituminous with fuel ratios ranging from 2.05 to 2.65. Both low-volatile and high-volatile varieties are present. It is poorly caking to non-caking, although some lenses contain coal with fairly good caking properties.

A total reserve of 86,500 tonnes of coal has been estimated for this occurrence, down to a depth of 20 m.

Chamrang Nadi occurrence

This coal-bearing Gondwana horizon continues from the Pagla Khola (Kalapani Nadi Coal Mine) westward, and crops out along the hill slopes on both sides of the Chemrang Nadi. Eight coal seams and lenses, ranging in thickness from 1.0 to 4.50 m and extending from 10 to 175 m along strike are located on the east bank.

These occurrences can be reached by way of a 6 km long footpath from the Kala Nadi coalmine colony. The latter is reached by a 40 km long dirt road from Tangla Railway Station on the Ranghia-Tezpur line. During the monsoons, the occurrence becomes inaccessable. The coal is sub-bituminous in rank with fuel ratios between 1.42 and 1.72. At places, it is also anthracitic. Assuming a persistence at depth of 20 m, a total of 72,660 tonnes of coal has been estimated for this occurrence.

Kalapani Nadi Occurrences

A number of coal occurrences are noted in the Kalapani Nadi, about 4 km north of the coal mine colony. This colony is reached by a 45 km long dirt road from Tangla Railway Station; during monsoons, the area becomes inaccessible. These occurrences are divided into three areas on the basis of seam distributions: the Kalapani Mines area, the Kalapani East Landslide area and the Pagli North area. The Kalapani Nadi coal is sub-bituminous to bituminous with fuel ratios of 1.22 to 2.00.

Kalapani Mines Area: Seven coal lenses are located on the left bank of the Pagla Khola, about 100 m upstream from its confluence with the Kalapani Nadi. Maximum thickness of one lens is about 10 m and the strike extent is about 112 m. The thicknesses of the remaining 6 lenses vary from 2 to 5 m, with strike extent of 30 to 100 m.

The coal contains 20.6-24.2 per cent volatile matter, 37.5-43.7 per cent ash and 33.4-35.8 per cent fixed carbon. Reserves of 76,290 tonnes of coal have been estimated down to a depth of 20 m along dip.

Kalapani East Landslide Area : This locality is about 1.3 km east of the Kalapani Mines area. There are 15 coal seams of 1-12 m thickness and 5-95 m strike lengths

covering an area of 300 m x 200 m. The coal contains an average of 21.5 per cent volatile matter, 34.5 per cent ash and 41.5 per cent fixed carbon. It is non-caking to poorly caking. Reserves of 43,000 tonnes of coal have been estimated to a depth of 20 m.

Pagli North. Area: This area is located on the left bank of the Pagli Khola, about 200 m NW of the Kalapani river. Fourteen lenses of coal (1 m to 6 m thick, 10 m to 50 m strike extent) have been located here. The coal has an average of 25.0 per cent volatile matter, 33.5 per cent fixed carbon and 30.0 per cent ash.

Nunai Nadi Occurrence: Access to this coal occurrence is by a 45 km long dirt road via Bhuttiachang, Orangajuli and Nunai Paro Tea gardens from Tangla Railway station. Part of the road becomes inaccessible during monsoons. On the left bank of the Nunai river, the coalbearing strata, having a width of 500 m, contain four coal seams showing pinch-and-swell structures both along their strike and dip.

The coal is powdery and flaky in nature. The seams are 1.2 m, 1.0 m, 0.9 m and 1.7 m wide respectively, each having a strike length of about 30 m. The coal is semi- bituminous, has an average of 25.0 per cent volatile matter, 30.0 per cent ash, 33.5 per cent fixed carbon and a fuel ratio of 2.76-5.69. No reserves have been estimated as the seams are narrow and impersistent.

Bhorila Rash Ri Occurrence: The coal occurrence of the Bhorila Rash Ri section can be reached by a 40 km long dirt road from Tangla Railway station. These occurrences can be divided into three blocks, viz. the Bhorila Block in the east, the Khasdim Block in the centre, and the Rash Ri Block in the west. In the Bhorila Block, 23 outcrops of coal over a strike length of 650 m can be grouped into 5 seams. The seams range in length from 100 to 370 m and in width from 0.5 to 20 m. In the Khasdim Block there are 8 outcrops which can be grouped into 4 seams. The seams range in length from 50 to 120 m and in width from 0.6 to 2.0 m. In the Rash Ri Block, there are 29 outcrops which can be grouped into 6 seams ranging in length from 80 to 290 m and in thicknesses from 0.75 to 6.0 m.

The coal has an average of 26.89 per cent volatiles, 24.16 per cent ash and 40.14 per cent fixed carbon. In all three blocks, reserve have been estimated from the exposed and inferred strike lengths of the various outcrops down to a depth of 25 m along dip. A total of 303,650 tonnes of coal have been estimated for the area of which 101,300 tonnes are from the Bhorila Rash Ri Block, 17,480 tonnes from the Khasdim Block and 184,870 tonnes from the Rash Ri Block.

Nagor Khola Occurrence: This is located at about 5 km due N80° of Kherkheria. Access is by a 44 km long dirt road from Tangla Railway station. A 12 km long stretch of the road from Ayodhyapur to the coal occurrence becomes inaccessible during the monsoon.

40

In the eastern part of the area, there are seams having strike lengths of 42 m, 34 m, and 1.7 m respectively and widths of 1.7 m, 1.0 m, respectively. In the western part, two seams of 1.0-2.5 m width and about 60.0 m strike length are present. The coal has an average of 26.5 per cent volatile matter, 26.0 per cent ash and 41.0 per cent fixed carbon. It is bituminous with fuel ratios of 1.00-2.00. Total reserves of about 52,000 tonnes of coal may be available from this area, down to a depth of 30 m.

Khourang-Leshing Ri occurrence: There are a few exposures of coal along the Kharkheria-Lauripa footpath towards Lauri village. They can be approached by a 44 km long road from Rangiya. They can also be reached by way of a 13 km long road from Rangiya, or by taking a 13 km long footpath from Diapham along the Diapham Khola. The area becomes inaccessible during the monsoon season.

Three coal seams of 1-6 m thickness are intermittently exposed over a strike length of 500 m in Khaurang Nadi, south of Kherkheria Lauripa footpath. Two coal seams of less than 1 m thickness are also exposed in the Leshing Ri section, north of the Kherkheria-Lauripa footpath. In addition, several other coal seams of less than 0.5 m thickness have been noted in the Khaurang and Leshing Ri sections. The coal is powdery and flaky and ranks bituminous to anthracitic. It has 31.5-27.51 per cent volatile matter, 16.25-35.65 per cent ash and 56.43-76.93 per cent fixed carbon. Total estimated reserves of 270,000 tonnes of coal have been designated to this area.

Deothang occurrence: This coal-bearing horizon, occurring about 3 km south-west of Deothang has a strike length of 2.25 km. It has a width of 60-70 m containing 10- 12 coal seams of 0.5-3.5 m thickness.

The coal contains 21.85 per cent volatiles, 5.6-20.1 per cent ash and 20.1-55.2 per cent fixed carbon.

Summarizing the work carried out on coal: In the Jagartala area a detailed drilling survey was carried out

over an area of 0.6 km2, which was mapped in detail. In all, 37 boreholes were drilled totalling 5,357.65 m. Drilling in the Gerua-Dimala Khola area is in progress. All other occurrences were explored by detailed mapping, trenching and channel sampling. Based on this work, the following appraisal can be given:

1. Detailed exploration in the Bhangtar Central Block has been completed and a quantitative assessment will be made as soon as results of coal analyses are obtained. Presently four potential blocks along the Deothang-Bhangtar road are designated for detailed evaluation by drilling.

2. Potential for mining Bhutanese coal, especially of the Bhangtar area has been studied. Considering the unusual nature and disposition of the coal exposures, it is assumed that coal mining may be possible in patches only by open cast methods with limited mechanization. In most places, the seams have an unfavourable coal to overburden ratio. Beneficiation tests carried out indicated that the ash content of the coal can be reduced by screening through 0.5 mm mesh to 25 per cent.

3. The coal seams are crushed, friable and powdery in nature, with intercalations of sandstone and shale in varying proportions, which may cause deterioration of the quality of the seams. The ash in the coal samples is probably due to impregnation of extraneous material during tectonic flow. The coal seams are significantly high in ash content varying from a minimum of 13.1 per cent to a maximum of 49.9 per cent. The moisture and volatile matter on an airdried basis vary from 0.8 to 2.8 per cent and from 14.9 to 34.0 per cent respectively. The Bhangtar prospect generally can be classified as low to medium volatile bituminous coal. Total sulphur, as well as the phosphor content is low, varying from 0.1 to 1 per cent and 0.013 to 0.22 per cent respectively. The coals are weakly caking with a caking index of 8 to 9.

41

D. Index of Mineral Deposits and Occurrences of Bhutanalphabetical reference to the 1:500,000 Map

MapNo.

AppoximateLongitude

CoordinatesLatitude

Name of Locality District Commodity Proven Reserves

(I)

Probable Reserves

(I)

Possible Reserves

(D

Grade or Quality

4 89° 08'E 26° 55'N Athais Khola Samchi Copper 1.20% Cu36 89° 48'E 26° 46'N Baikinza Chukha Dolomite low quality37 89° 48'E 26° 57'N Basinigaon Dagana Dolomite not sampled

101 91°57'E 26° 55 'N Bhorila Rash Ri Samdrup-Jongkhar Coal 303650 40.1% fixed C2 90° 24'E 26° 58'N Bhurkhola Geylegphug Tungsten 1380000 2700000 0.45% - 0.18% W03

87 89°05'E 26° 55'N Budheni Samchi Talc 900 poor quality80 89° 32'E 27° 08'N Bunakha-Chapcha Chukha Marble

5 89°03'E 26° 58'N Bungthing Samchi Copper 0.34% Cu84 90° 05 'E 27° 05'N Burichu Chirang Quartzite 94.40% SiO260 91°22'E 26° 59'N Chaibar Pemagatshel Limestone 700000 45.5% CaO 0.7% MgO20 89° 37'E 27° 17'N Chakula Zn-rich soil Thimphu Lead-Zinc 141000 0.28%Pb 1.06% Zn20 89° 37'E 27° 17'N Chakula (Genekha) Thimphu Lead-Zinc 3116000 1.03% Pb 6.33% Zn

102 91°49'E 26° 56'N Chamrang Nadi Samdrup-Jongkhar Coal 72660 43% C 27% volatile61 89° 19'E 27° 21'N Chilungkha Haa Limestone 1400000 52.5% CaO25 90° 08'E 27° 00'N Chirang Chirang Beryllium 7

83 90° 07'E 27° 02'N Chirang Chirang Mica poor quality6 89° 09'E 26° 57'N Chiuri Bote Samchi Copper 0.35% Cu7 89° 01'E 26° 57'N Chunpatang Samchi Copper 3.21% Cu

32 91° 34'E 27° 13'N Dangling Ri Tashigang Pyrite 9 3.21%- 15.58% S53 89° 40'E 27° 08'N Dapchhasa-Dorjormsa Chukha Graphite 14.6% fixed C38 91° 13'E 26° 55 'N Dechhiling Samdrup-Jongkhar Dolomite .24E+10 up to 21 % MgO

103 91°3O'E 26°51'N Deothang Samdrup-Jongkhar Coal 20.1%-55.2% fixed C8 89° 05 'E 26° 55'N Dham Dhum Samchi Copper 7

39 90° 05'E+ 26° 50'N+ Dhanese Chirang Dolomite .73E+09 21% MgO 29% CaO33 90° 05 'E 26° 50'N Dhanese Chirang Pyrite 0.28%- 12.50% S

9 89° 10'E 26° 56'N Dhau Khola Samchi Copper 7

10 90° 17'E 26° 57'N Dholpani Geylegphug Copper 7

3 90° 17'E 26° 57'N Dholpani Geylegphug Tungsten 349000 0.25% WO362 89° 19'E 26° 56'N Dholpani-Bhurkhola Geylegphug Limestone 206000 41.6% CaO 2.0% MgO

104 91°46'E 26° 55'N Diglai Nadi Samdrup-Jongkhar Coal 86500 52.5% C 22.5% volatile54 89° 37'N 27° 00'N Donga Chukha Graphite 217360 > 18% fixed C26 90° 37'E 27° 19'N Dung Dung-Khosala Tongsa Beryllium 7

63 91° 13'E 26° 52'N Gachari (Nganglam) Samdrup-Jongkhar Limestone 1090000 33.8% CaO 2.6% MgO105 91° 38'E 26° 52'N Gerua-Dimala Samdrup-Jongkhar Coal sub-bituminous

81 89° 34'E 27° 24 'N Gidakhom (Jemena) Thimphu Marble dim.st & carb.grade21 89° 34'E 27° 24 'N Gida-Jamdo Hom Thimphu Lead-Zinc <4000 ppm Zn & Pb11 91° 36'E 27° 08'N Gomchu Tashigang Copper 500000 0.6% Cu + 1% PbZn12 90° 26'E 27° 10'N Gongkhola Tongsa Copper 2243700 10000000 1.52% Cu 0.2 ppm Au29 90° 26'E 27° 07 'N Gongkhola Tongsa Gold 0.2 - 1.2 ppm Au64 89° 17'E 27° 22 'N Haa Dzong Haa Marble 7

64 89° 17'E 27° 23 'N Haa Wangcha Haa Limestone 5000000 52.0% CaO 2.0% MgO65 89° 17'E 26° 50'N Haurie Khola Samchi Limestone 16700000 52.0%CaO 2.0% MgO

106 91°41'E 26° 54'N Jagartala-Jabair Nadi Samdrup-Jongkhar Coal 1030000 47% C + 24.5% volatile22 89° 32'E 27° 26 'N Jemena Thimphu Lead-Zinc 2.69% Pb+4.34%Zn13 90° 30'E 27° 36 'N Jongda Tongsa Copper 0.25% Cu40 90° 40'E+ 26° 50'N+ Kakulang Geylegphug Dolomite .29E+10 20% MgO <2.3%SiO297 89° 07'E 26° 49 'N Kalapani Samchi Calc-Tufa 1040000 44.9% CaO 2.8% MgO

107 91° 51 E 26° 56'N Kalapani Nadi Samdrup-Jongkhar Coal 119290 37.1% fixed C41 89° 20'E 26° 52'N Kalesor Samchi Dolomite .25E+10 21%MgO30% CaO66 89° 20'E 26° 52'N Kalesor-Titi Samchi Limestone 1600000 cement grade14 89° 27'E 26° 53'N Kamjee Chukha Copper low85 89° 27'E 26° 53 'N Kamjee Chukha Quartzite 85-89% SiO267 91° 14'E 26° 52'N Kangrizhe (Nganglam ) Samdrup-Jongkhar Limestone 1250000 45.6% CaO 0.9% MgO68 90° 26'E 27° 06 'N Katie Dara Geylegphug Limestone 110000 52.7% CaO 2.3 % MgO69 91° 35'E 27° 11 'N Khaling Tashingang Limestone 310000 cement & BF grade88 89° 19'E 26° 55’N Khampa Samchi Talc 12500 7

70 89° ITE 26° 52'N Khanabharti Samchi Limestone 260000 44.4% CaO 4.4% MgO70 89° 11'E 26° 52’N Khanabharti Samchi Marble 4.44% MgO42 89° 11'E 26° 50'N Khanabharti Sarkitar #Samchi Dolomite . 10E+09 20% MgO 30% CaO43 89° 14'E 26° 51'N Khanabharti-Pagli etc Samchi Dolomite .38E+09 20% MgO 30.0% CaO

42

MapNo.

Appoximate Longitude

CoordinatesLatitude

Name of Locality District Commodity Proven Reserve.

(l)

Probable y Reserves

(l)

Possible Reserves

(I)

Grade or Quality

44 91° 31'E 27° 00'N Khandame Tashigang Dolomite .28E+09 21% MgO 29.8% CaO71 89°25'E 27° 25 'N Khangkhu Paro Limestone 12440000 29590000 cement/carbide grade71 89° 25'E 27° 24 'N Khangkhu Paro Marble decorative stone57 91° 20'E 26° 59 'N Khar Pemagatshel Gypsum 34000 87.87% CaS04.2H2015 91° 31'E 27° 15'N Kharung La Samdrup-Jongkhar Copper 50 ppm Cu

108 92° 02'E 26° 55'N Khaurang Leshing Ri Samdrup-Jongkhar Coal 270000 56.4%-76.9% fixed C34 90° 05 'E 27°31'N Khelkha Wangdi-Phodrang Clay local use55 89° 20 'E 27°23'N Khepchishi Hill Haa Graphite 11830000 33880000 8030000 <22% fixed C58 91°24'E 27°01'N Khothakpa Pemagatshel Gypsum 69036000 48.67%CaS0 .2HO98 90° 13'E 27° 37'N Kobja Wangdi-Phodrang Slate 8000000 high quality30 91°03'E 27° 42 'N Kuru Chu alluvium Lhuntshi Gold 1ppm - 0.2 ppm Au72 91° 17'E 26° 53 'N Kurung Ri (Nganglam) Samdrup-Jongkhar Limestone 14500000 48.7% CaO 0.7%MgO89 89° 13'E 26° 55'N Lapchekha Samchi Talc 4200 soapstone90 90° 14'E 26° 55'N Lhoring (Khare Dara) Sarbhang Talc good qualtiy91 89° 12'E 26° 50'N Malabanse Samchi Talc 5300 ?45 91° 01'E 26° 55 'N Manas Samdrup-Jongkhar Dolomite .59E+10 21% MgO73 91° 16'E 26° 55 'N Marung Ri (Nganglam) Samdrup-Jongkhar Limestone 18710000 46.0% CaO 4.9 MgO73 91° 12'E 26° 54'N Marung Ri (Nganglam) Samdrup-Jongkhar Marble 4.8% MgO

1 89° 51'E 26° 46'N Mauree Dagana Iron 2977150 25%-46% Fe31 89° 54'E 26° 46'N Mauree-Kalikhola Dagana Phosphate 0.43%-23.9% P20574 89° 25'E 26° 55 'N Mirchang-Tala Chukha Limestone 6500000 44.5%CaO < 4%MgO74 89° 26'E 26° 56'N Mirchang-Tala Chikha Marble building stone46 89° 38'E 26° 44'N Mohakal Sarbhang Dolomite low quality16 90° 16'E 26° 55 'N Munga Khola Sarbhang Copper 0.10% Cu

109 91° 59'E 26° 53'N Nagor Khola Samdrup-Jongkhar Coal 52000 41.0%C 26% volatile47 91° 31'E 27° 00'N Narphung Tashigang Dolomite . 13E+09 21.3% MgO 29.8 CaO27 90° 12'E 27° 28 'N Nobang Wangdi-Phodrang Beryllium ?

110 91° 53'E 26° 56'N Nunai Nadi Samdrup-Jongkhar Coal 33.5% fixed C92 89° 22'E 26° 55 'N Pa Chu-Seti Khola Samchi Talc 220000 economic grade48 89° 47'E 26°45'N Pabjigaon Sarbhang Dolomite ?75 89° 15'E 26° 51'N Pagli West Samchi Limestone 6040000 1640000 46.5% CaO 2.8 MgO93 89° 12'E 26° 49'N Pagli-Sarkitar Samchi Talc poor quality75 89° 15'E 26° 51'N Pagli-Titi Samchi Marble ?99 91°27'E 27° 00'N Pemagatshel Pemagatshel Slate local use49 89° 44'E 26° 44'N Piping Sarbhang Dolomite low quality28 91° 40'E 27° 20 'N Radi Tahigang Beryllium ?50 89°09'E 26° 50'N Rethi South-Sarkit Samchi Dolomite23 89° 37'E 27° 17'N Romegang Ri (Genekha) Thimphu Lead-Zinc 514000 3.74% Pb+4.46% Zn76 89° 37'E 27° 17'N Romegang Ri (Genekha) Thimphu Limeston 900000 52.0% CaO 1.4% MgO76 89° 37'E 27° 17'N Romegang Ri (Genekha) Thimphu Marble building stone77 90° 26'E 27° 06 'N Rong Ri Geylegphug Limestone 810000 51.3% CaO 1.6% MgO82 90° 43'E 27° 40 'N Sapchi Thang Bumthang Marble ?17 89°08'E 26° 54'N Saureni Samchi Copper 0.75% Cu

100 90° 11 'E 27° 33 'N Sha Bhel (Bansegoema) Wangdi-Phodrang Slate 8000000 high quality94 89° 12'E 26° 50'N Sukti Khola Samchi Talc 2300 ?18 88° 57'E 27° 02 'N Sundari Khola Samchi Copper 0.81% Cu24 89° 37'E 27° 19'N Tashisekha (Genekha) Thimphu Lead-Zinc <1.0% Pb+Zn56 89° 05'E 26° 57 'N Thumkey Samchi Asbestos low quality95 89° 16'E 26° 55 'N Thunuwa Samchi Talc 3600 ?

86 88° 58'E 27°01'N Tintala Samchi Quartzite 3490000 97.54% Si0278 88° 58'E 27°01'N Tintala-Noonpani Samchi Limestone 114000 chemical grade96 89° 10'E 26° 55 'N Tin-Doban Samchi Talc 900 poor quality19 90° 16'E 27° 02 'N Tirkhola Geylegphug Copper 50 ppm Cu75 89° 15'E 26° 51'N Titi Samchi Limestone 1500000 cement grade51 89° 21'E 26° 51'N Titring-Kalesor North Samchi Dolomite .52E+09 ?

79 91° 35'E 27°05'N Tokaphung Tashigang Limestone 30000000 47.5% CaO <2% MgO52 89° 09'E 26° 51'N Uare-Deergaon Samchi Dolomite 29000000 20% MgO 28% CaO59 91° 22'E 26° 59'N Uri Chu Pemagatshel Gypsum 13600000 91.63% CaS04.2H2035 89°35'E 27° 19'N Wang Paon Thimphu Clay 20000 ceramic grade

43

IV. MINERAL PRODUCTION, IMPORTS AND EXPORTS

A. Production of Industrial Minerals in Bhutan

Although most of the information on reserves is contained within the Index, the scarce production figures are best represented in a separate table, as given below:

Table 16. Mineral Production in Bhutan

MineralCommodity

Area orLocality

Cumulative Production

m3

Annual Average Production

3 m

Calc-tufa Kalapani 113,544 12,616Gypsum Shumar 145,146 20,735Dolomite Kalesor 298,311 33,145Dolomite Pagli 294,182 32,686Dolomite Khagrakhola 267,323 29,702Dolomite Singye, Durpani 234,750 26,083Dolomite Chunaikhola (Pagli) 509,221 72,745Limestone Pagli 1,059,563 132,445Limestone Beci, Pasakha 12,230 6,115Limestone Durpani, Somchi 16,959 5,653Slate Wangdi 5,010,637 sq.ft 501,063 sq.ftCoal Samrang, Bhagta 137,660 15,296

Table 17. Mineral Exports and Imports in Bhutan, 1988

Material

EXPORTS IMPORTS

Quantity Value Quantity Value

1 Boulders 1,154,000 381,000 — —2 Stone Chips 17,290 6,000 942 3,0003 Sand 1,885 1,000 28,755 52,0004 Marble

slabs - - 8,858 26,000powder - - 44Mt 17,000chips 170Mt 8,000 215Mt 215,000

5 Limestone 8.4Mt 2,000 39,533 3,816,0006 Gypsum 536,346 5,722,000 1,008 10,0007 Dolomite

slabs 513,128 1,056,000 13,348 8,000chips 5,088,706 8,889,000 25,097 24,000powder 2,389 4,111,000 37Mt 14,000

8 Soapstone 18Mt 59,000 0.87Mt 10,0009 Coal 4,672Mt 1,012,000 18,245Mt 7,105,000

10 Bentonite - - 2Mt 4,000

Source: OTI, 1989

B. Imports, Exports and Trends

1. Import and Export Figures

Bhuan imports as well as exports many types of non-metallic mineral products. Transportation cost from one part of the Kingdom to another is one of the reasons. The imports are, however, smaller in value and in quantities as compared to the exports. For 1988, the details regarding imports and exports for industrial minerals and coal are given in table 17.

2. Future Trends

Exports of boulders are expected to rise once the trade agreement with Bangladesh comes into effect. The DGM is putting together a proposal for a private entrepreneur to export 30,000 Mt of stone lumps per annum to Bangladesh.

Exports of marble products will rise in the future with the expansion of mining activities of Bhutan Marbles and Minerals Ltd., located at Gidakom area in Thimphu valley, after 1991.

Dolomite exports will rise with the expansion of dolomite markets in India. Bhutan’s dolomite is primarily used as fluxing agent in Indian steel plants. India is in the process of expanding steel production, expecting to double its output by the year 2000.

Bhutan’s coal is of an inferior quality and considering the way the reserves are distributed, is not amenable to “scientific” mining either. Coal imports will rise in the future with the expansion of coal consuming industries in Bhutan.

The general trend will be an expansion of mineral exports, while keeping the imports stagnant, if not at a complete stop, for most mineral products.

Blank page

Page blanche

Annex I

SUMMARY OF MINERAL RESOURCES OF BHUTAN

Blank page

Page blanche

47

Table 18. Summarry of Metallic Mineral Resources of Bhutan

MINERAL LOCATION MODE OF OCCURRENCESTATUS OF

INVESTIGATIONRESERVES (mill. T)

RESERVE CATEGORY GRADE REMARKS

COPPER Gongkhola

Jongda

Network of veinlets, stringers, disseminations, fracture/ breccia fillings.

Sulphide mineralisation in massive amphibolite bodies intruding gametiferous-feldspathic-biotite gneiss.

Detailed exploration by drilling is complete.


2.50 under 1.0% cutoff & 1.0m stopping width.10.00 to 500m depth.

Probable (upto 120m depth).

Estimated

1.55% Cu.

1.50% Cu.

0.20-0.30% Cu.

A block of 500 m length detai led exploration by deep drilling & exploratory mining.

Bungthing 4m x 125m zone of mineralization in the quartz veins intruding the quartz-sericite chlorite phyllites of Phunt- sholing Fm.


0.34% Cu. The occurrences from Bungthing to Dham Dhum forms a continuous belt - The Samchi Copper Belt.

Chunpatang 3m x 210m zone of mineralization.

Saureni 40cm x 4m zone of mineralization.

Chiuri Bole 30cm x 10.5m zone of mineralization.

Lamitar-Rambagar

Im x - - ? zone of mineralization.

Athais Khola 6m x 95m zone of mineralization.

Sundari Khola

1.27m x 300m zone of mineralization.

Dhau Khola 1.8m x 6m zone of mineralization.

Dham Dhum 0.08 sq.km area of mineralization.

Munga Khola

240m x 8m mineralized zone in the ultrabasic sills intruding the quartzites of Thimphu Fm.

Tirkhola Sulphide mineralization in the veins & veinlets of quartz traversing the quartzites of Cheka Series.

Gomchu Sulphide mineralization in the quartz-carbonate veins traversing the grey quartzbiotite-chlorite phyllites of Shumar Fm. Mineralized zone extends over 2.20 km.

Kaurungla 5-20cm mineralized zone in the stringers and veins of quartz traversing the calcareous phyllites and quartzite of Shumar Fm.

LEAD-ZINC Romegang Ri

Carbonate hosted epigenetic & stratiform ore occurring as lensoids. There are five mineralized lodes which are partially oxidised.

3.21% Cu.

0.75% Cu.

0.35% Cu.

1.80% Cu.

1.20% Cu.

0.81% Cu.

0.10% Cu.

50ppm Cu.

0.50-0.60%Cu.1.0% Pb+Zn.

50ppm Cu.

3.74% Pb4.46% Zn

0.50 Estimated

0.514 Probable

--------idem............

--------idem - ----- -

.......... idem............

.......... idem------- -

.......... idem - ----- -

--------idem---------

.......... idem............

.......... idem----- - -

--------idem............

.......... idem---------

--------idem - ----- -

.......... idem............

Detailed exploration by drilling completed.

48

Table 18. (Continued)



RESERVE CATEGORY GRADE REMARKS

Chakula Similar mode of mineralization as in Romegang Ri. There are eight mineralized lodes which are completely oxidised.

Detailed exploration by drilling completed

3.116 Proved 1.03% Pb6.33% Zn

— Metal rich soils. — 0.141 Inferred 0.28% Pb1.06% Zn

Jemena Pb-Zn mineralization localised in coarse grained crystalline Lst. - Paro Fm. Mineralized as disseminations, stringers, fracture fillings, small pockets, lenses & pods of massive ore.

Detailed exploration by drilling seven boreholes totalling 381.95 m.

---- Not estimated------ 3.22% Pb11.31% Zn

The average value of mineralized zones intersected by 3 boreholes. Further work necessary for final assessment of the deposit.

Ratepani-Gombadra

Galena mineralization in the form of veins, stringers and disseminations within brecciated Lst. Mineralized oyer 50m strike length.

Surface indication only. Detailed investigation for the area being done by GSI (Samchi).

TUNGSTEN Dholpani As disseminations in the skarn rocks associated with Thimphu Fm.


0.3490.12% cutoff0.3350.15% cutoff0.2000.20% cutoff

Probable

(upto 75m depth & Im slopping

0.25%WO3 Beneficiation test show that the ore is amenable to beneficiation (IBM, see text).

Bhurkhola ----------idem----------- Detailed exploration by drilling in progress. 18 boreholes completed.

2.7000.10% cutoff1.3300.30% cutoff

Probable (upto 90m depth).Probable (upto 180/ 200m depth).

0.18% WO3

0.45% WO3

Exploration by drilling in progress. Final assesment of reserve is likely to be much higher.The ore is amenable to beneficiation (IBM, see text).

Pho Chu Indication of scheelite mineralizations in calc- silicate sediments in river terraces & beds.

Preliminary investigation by river sediment sampling.

— Detailed field investigation recommended to locate the source rock.

IRON MaureVillage

Bedded massive & laminated ore bodies in grey micaceous sandstone of the Siwalik Group.


3.000 Estimated 37.40% Fe (av. of the range 25-46% Fe).

Reserve estimated for only two small selected blocks from East & Central blocks.

PYRITE Dangling Ri Disseminations & stringers along bedding planes of grey chert quartzite - Shumar Fm. About 7m strike length & av. 35cm thick.


9.00 tonnes Possible (to down depth of 2m).

3.21-15.58% sulphur (S).

Dhanese Disseminated pyrite nodules in the carbonaceous slates


— 0.28-12.50% sulphur(S)

GOLD Gongkhola Associated with copper mineralization in the quartz - carbonate rocks al the contact of carbonaceous phyllite & quartzite of the Mane Ting Fm.

Analysis of the selected borehole samples.

0.20-1.20 PPM.

Borehole sample analysis from the Central Block show very high arsenic values (1000 ppm - 2.67% As).

Kuri Chu Placer gold in the sands and gravels.

Preliminary study by stream sediment sampling-gold extraction by panning.

-------------0.001-0.15 (per 0.764 cu.m/1524 Kg sand)

Systematic stream sediment & soil sampling further upstream may prove conclusive.

49

Table 18 (Continued)



RESERVECATEGORY GRADE REMARKS

Dholpani-Bhurkhola

Gold associated with scheelite mineralization in the calc-silicate rocks.

Analysis of the borehole sample.

Gold analysis to be collected from G SI.

Gurungkhola Gold mineralization associated with pyrite & chalcopyrite in the carbonaceous phyllites.

Preliminary surface studies. 37 channel samples collected & analysed by AAS.

0.10-3.99 PPM.

Grab sample analysis by fire assay yielded 10 PPM of gold. Resampling and analysis by fire assay reccomended.

50

Table 19. Summary of Non-Metallic Mineral Resources of Bhutan


INVESTIGATIONRESERVES

(mill. T)RESERVE

CATEGORY GRADE REMARKS

COAL Jagartala As thin discontinuous Surface investigation. 1.030 Inferred Sub-bitum.seams along lower part Detailed exploration (upto 30mof Gondawana sequence. by drilling started. depth).38 seams of 0.70-2.8mthickness exposed along13-150m strike length.

Gerua- Two seams of ~2.00m Detailed investigation — Sub-bitum.Dimala thickness. in progress.Diglai Nadi 40 seams of 0.70-2.10m Surface investigation. 0.0865 Possible Sub-bitum.

thickness along 1 l-500mstrike lengths.

Chamrang 32 seams of 1.00-4.50m --------idem---------- 0.0726 Possible Sub-bitum.Nadi thickness exposed along

10-175m strike length.Kalapani 33 seams of 1.00-12.00m --------idem---------- 0.17831 Possible Sub-bitum.Nadi exposed over 5-150m to bitum.

strike lengths.Nunai Nadi 4 seams of 0.90-1.70m Surface investigation. — Sub-bitum. Coal seams are too thin

thickness exposed over and impersistent.30m strike length.

Bhorila 36 seams of 0.60-6.00m Surface investigation. 0.30365 Possible Sub-bitum.Rash Ri thickness exposed over

20-320m strike length.Nagor Khola 5 seams of 1.00-2.50m Surface investigation. 0.05200 Possible Sub-bitum.

thickness exposed over34-600m strike length.

Khaurang- 5 seams of 1.00-6.00m Surface investigation. 0.27000 Possible Bituminous-Leshing Ri thickness exposed over anthracitic

500m strike length.Deothang 12 seams of 0.50-3.50m Surface investigation. — Sub-bitum. Coal seams are too thin

thickness exposed over and impersistant.2.25 km strike length.

GRAPHITE Chilaila Crypto-crystalline to Detailed exploration by 11.83 Proved 10-22% N.C.amourphous / flaky type drilling completed. Ben 33.99 Probablewithin the graphite eficiation tests & feas- 8.03 Inferredschist. About 30-90in ibility studies havethick band on the sout- been conducted.hem slope of the Khep-chishi Hill.

Donga Fine-coarse flaky graph- Preliminary surface 0.21736 Estimated 18.20% N.C. Systematic mapping &ite associated with the investigation by chip (upto 20m (Average) detail exploration bygraphitic schist of Thim- and channel samplings down depth) trenching &drillingphu Fm. over a strike length proposed.

600m.

GYPSUM Cherung Ri White to grey, massive/ Detailed exploration by 151.426 Proved 53.45% Gyp. Reserve include with/bedded with saccharoidal 43 boreholes drilled, 21.10% Anhy. without phyllite inter-texture. Gypsum asso- 39 intersected the gyp- 37.50% SO3 calations. The assaydated with anhydrite & sum bands. 73.31% CaCO3 values are rough averagecommonly intercalated with overall impurities +with calcareous phyl- NaCl of 14.41%.lites and carbonates.

Uri -------- idem............. Surface investigation by 13.600 Inferred 91.63% Gyp.6 - 12m bands extending pitting, trenching and 1.26% Anhy.over 1 km strike length. systematic sampling.

Khar Eight small lenticular Surface investigation 0.034 Probable 87.87% Gyp.bands of 1.0-5.0m thick- by pitting, trenching 1.18% Anhy.nesses & 20-132m strike & systematic sampling.lengths. Intercalatedwith greenish limestone& greenish calc-silicate.

Dapchhas Dorjomsa Taktichu Duna Jemena

Graphite associated with graphitic schists of Paro and Thimphu Formations.

Occurrences noted during recconnaissance mapping.

Systematic mapping reccomended for tracing these occurrences.

51




(mill. T)RESERVE


Omsi Ri Bands of gypsum with variable thicknesses intercalated with calcareous phyllites and carbonates.

Systematic surface sampling.

8.830 Estimated 91.00% Gyp. Occurrences of gypsum are also located in the near-by Sakar Brak and Zeng Ri areas.

LIMESTONE Pagli West

Pagli West Extension

Bedded deposit associated with grey phyllites and quartzite - Buxa Group.

--------idem----------

Detailed exploration by drilling completed. Reassessment done in 1975 - GS1.Detailed exploration by drilling in progress.

6.040

1.640

Proved

Inferred

46.52% CaO2.78% MgO

Cement Grd.

Currently being mined by the Penden Cement Authority.

1’iti Block ........... idem--------- Detailed exploration by driling in progress.

1.500 Inferred Cement Grd.Carbide Grd.

Exploration by drilling is in progress for assessing.

Tala/ Mirchang

Khanku

Crystalline Lst. interbanded with gametiferous schist & quartzites. Three bands with 30-80m thicknesses & 350-950 strike lengths.Crystalline Lst. associated with quartzites - Paro Formation.

Detailed exploration by drilling completed. Chip samples analysed.


6.500

42.030

Estimsted

Probable

44.51% CaO 0.50-4.00%

MgO.

40.47-50.91%CaO.

1.36-4.98%

Mined by BCCL.

Kalesor-Titi

Kurung Ri

Bedded Lst. intercalated with phyllites & quartzite - Buxa Group

Bedded Lst. within the phyllites & quartzites of the Buxa Group. The Lst. band is 30m thick & 6 km in strike extension.

Preliminary' surface investigation.


1.694

14.500

Estimated

Inferred

38.82-52.52% CaO 0.44-3.93% MgO.48.47% CaO

0.69% MgO

About 74,000 tonnes of high grade Lst. (CaO> 50%) has been estimated for the area.

Ma rung Ri

Gachari

Kangrizhe

Khanabharti

Khaling

--------idem---------- 7.5 km in strike extension

--------idem.............5-22m thick band & 3 km in strike extension........... idem----------Average thickness of 60m over strike extension of 700 m.Bedded Lst. intercalated with phyllites & quartzite - Buxa Group. 1.0-2.6m thick bands over 1.40 km strike extension.Bedded crystalline Lst. - Shumar Fm. Upto 2.0m thickness & 1.8 km in strike extension.

Exploration by drilling completed.

........... idem---------

--------idem----------



18.710

1.090

7.000

0.260

0.310

Proved

Probable

Estimated

Inferred

Inferred

46.04% CaO4.87% MgO

33.83% CaO2.64% MgO

45.61% CaO0.88% MgO

44.44% CaO4.44% MgO

Cement Grd.B.F. Grd.

The Kurung Ri Lst. can be used as a sweetener to this limestone in cement manufacture.

Chilungkha Bedded crystalline Lst. -Paro Fm. Upto 500m strike extension.


1.400 Estimated 52.0-53.0% CaO.

Reserve & grade for two bands of carbide grade limestone.

Hauree Bedded grey Lst. interbedded Detailed exploration 16.700 Probable Cement Grd. Currently being pocketKhola with phyllites & quartzite -

Buxa Fm. 160m-480m strike extension.

by drilling completed. 0.114 Probable Chemical Grd. mined by BCCL for carbide grade Lst.

Genekha Bedded crystalline Lst. hosting oxidised Pb-Zn mineralization. Paro Fm.

Exploration by drilling concurrent with exploration for Pb-Zn. Groove sampling.

0.900 Probable 52.0% CaO1.4% MgO

Carbide grade limestone.

Ha Wangcha Thick bedded crystalline Lst. - Paro Fm. Occurs over an area of 0.36 sq. km.

Surface investigation. Exploration by drilling discontinued.


Detailed exploration by drilling (DOM) discontinued upon instruction by MTIF.

52




(mill. T)RESERVE


Rong Ri

Katie Dara

Bedded crystalline Lst. -Upper Part of Shumar Formation.

-------- idem----------

Surface investigation.Exploration by drilling.

Surface investigation.Groove sampling.

1.940

0.850

0.110

Proved

Proved

Tentative

50.35% CaO2.52% MgO

51.40% CaO2.00% MgO

CaO >51.0% MgO < 2.33%

Leased to BCCL for use in the manutacture of calcium carbide.

Groove sample analysis show 51.00-54.29% CaO & 0.33-4.33% MgO.

CALC-TUFA

Kalapani Associated with limestone/ phyllites of Buxa Fm. There are 20 isolated occurrences with av. thickness varying from l-7m (max. 21.03m) & areal extents ranging from 2300 to 34700 sq.km.

11 of the occurrences were explored by drilling.


About 0.51 mill. tonnes of better quality tufa can be used as sweetener. The deposit is exploited by PCA for use as sweetener.

MARBLE Khanku

Gida- Jemena

Genekha

Mirchang-Tala

Marung Ri

Chaibar

Dholpani- Bhurkhola

Tokaphung

Associated with the crystalline Lst. - Paro Fm. Medium - coarse grained, banded & white varieties.White coarse crystalline marble associated with mica schist & quartzites of Paro Fm.Banded marble extend over 1.25 km & 75-166m thick.

Three bands of medium grained banded marble of 30-80m thickness & 350- 950m strike extension.Bedded deposit of crystalline marble associated with limestone.----- idem..........

Bedded Lst. intercalated with phyllites & quartzites. Buxa Group. Bands range from 7-25m thick & 50-450m strike extension. Bedded crystalline Lst. within the basal phyllite member of the Shumar Fm. Av. of 30m thickness.


Surface investigation al Gida. Exploration by drilling completed al Jemena.Detailed exploration by drilling concurrent with exploration for Pb-Zn mineralization.Detailed exploration by drilling comleted.

.......... idem.............

Surface investigation.Groove sampling.

Surface investigation.Channel sampling.

Surface investigation.

42.030 Probable MgO < 4.0%

Marble at Gida is being mined by BCCL and BMML.

Suitable for ornamental building material.

Mined by BCCL.

— MgO < 1.4%

MgO < 4.0%

4.87% MgO

CaO < 50.70%MgO < 1.20%

CaO < 42.06%MgO < 2.24%

CaO < 50.00%MgO < 2.00%

0.700

0.206

30.000

Probable

Inferred

Probable

There are pockets of interior quality Lst. within the cement grade Lst. The grade ranges from 40.20- 50.70% CaO and 0.26- 1.20% MgO.

Tintale- Noon pan i

Ri tan g

Tashi Bhel

Singhi Chu Pachu Bimetar Sankhey. Bunakh- Chapcha

Thin bands of crystalline Lst. within gneisses of Thimphu Fm.Crystalline Lst. of the Thimphu Fm. 2 bands of 40-45m thick extending over long distance.Biochemical type Lst. associated with dolomites.

Detailed exploration by ......................................... drilling completed.

Preliminary surface .........................................investigation.

Preliminary surface ....................................- -investigation.

-------------- Results to be collected from GS1.

36.0-46.0% CaO. 0.8-1.2% MgO.

30.6-41.1%CaO.11.9-21.2%MgO.

Bands of crystalline marble of 40-50m thickness extending over 1 km.

Occurrence noted during ------ - - - - -.................the course of regional or systematic mapping.

Preliminary surface .........................................investigation.

43.0% CaO

53




(mill. T)RESERVE


Khanabharti

Pagli-Titi

Ha Wangcha

Several banus of marble associated with low-grade limestones.-------- idem - -- -----

Thick bands of while crystalline marble extending over 1 km.


Detailed exploration by drilling on course of exploration for Lst.Surface investigation.

4.44% MgO

2.75% MgO

2.00% MgO

DOLOMITE Rebti - Sarkitar

Uare-Deer-gaon

Bands of dolomite intimately intercalated with phyllite, slaty phyllite & quartzite associated with Manas Formation of the Buxa Group. Av. 900m thick & striking for 9.0 km.-------- idem----------Av. 50m thick & striking for about 8.0 km.

Surface investigation. Chip sample analysis.


102.000

29.000

Estimated

Estimated

20.00% MgO30.00% CaO

20.50% MgO30.00% CaO

Khanabharti Nth. Pag- li Titi- Hauree

Titring- Kelesor Nth.

--------idem----------Extends over a strike length of 16 km & av. width of 250m. Dolomite is fine to medium grained, creamlight grey, hard & highly fractured.-------- idem----------Grey dolomite.

Surface investigation & exploration by drilling on pari of the area.

Surface investigation. Channel sampling.

398.00

529.00

Estimated

Possible

20.50% MgO30.00% CaO

21.35% MgO29.80% CaO

A block of the deposit with av. width of 280m & strike length of 1.10 km has been explored by drilling & a reserve of 31.04 mill. tonnes is proved in the area.

Kalesor -------- idem----------Four bands of dolomite with cumulative thickness of 330m & strike length of 5-25 km. While io grey dolomite.

Systematic surface channel sampling.

2500.00 inferred 21.35% MgO29.80% CaO

The grade of the dolomite varies from 21.14- 21-38% MgO & 29.38- 29.97% CaO for the entire deposit.

Mohakal- Baikinza- Piping- Pabjigaon- Basinigaon

Dhanese

Kakulang

........... idem---------Crystalline & dark grey dolomite inierbanded with thin bands of dark grey & purple phyllites. Thickness varies from 20-500m. --------idem---------- Three very thick bands of dolomite of 80-700m thickness.Massive grey dolomite with calcite veins. 200-800m thickness over 32 km strike length.

Preliminary' surface investigation.


Systematic surface chip sampling.

730.00

290.00

Probable

Probable

20.95% MgO28.78% CaO

20.00% MgO2.30% SiO 2

No sampling is done for the deposit.

Mamas Very thick band of dolomite. Width of the band ranges from 0.50-4.50 km and extends over 35.0 km.

Preliminary random chip sampling.

5985.00 Probable 21.00% MgO Largest dolomite band in Bhutan. Assumed depth continuity of 30m.

Dechhiling Average width of 2.0 km over 20.0 km strike length.

Priliminary random chip sampling.

2400.00 Probable 21.00% MgO Assumed depth continuity of 30 m.

Narphung Average thickness of 750m over 9.0 km strike length. Brown-grey & dark grey varieties of dolomite.

Preliminary' random chip sampling

135.00 Probable 21.28% MgO29.79% CaO

Assumed depth continuity of 30 m.

Khandame Average thickness of 1.5 km over 10.0 km strike length.

Preliminary random chip sampling.

281.00 Probable 21.33% MgO29.80% CaO

Assumed depth continuity of 30 m.

QUARTZITE Tintale Thick bedded sequence with interbands of chlorite schist & epidiorite sills - Shumar Fm. The quarizite is coarse gr./snow white to greenish-greyish/ well jointed & hard, thickness ranges from 4 to 42 m.

0.08 sq.Km of the area explord by drilling

3.49 Proved 97.54% SiO21.06% A12O.0.28% Fe2O3

May be suitable for the j manufacture of ferrosili

con & calcium silicide.Reserve for the entire area will be much larger.

54




(mill. T)RESERVE


Kamjee Thickly bedded fine-medium grained, well jointed white quartzite with inclusions of mica schist laminations & quartz-mica schist. Thickness ranges from 36 to 62m.


Very large — 85.0-89.0%SiO2 0.36-1.00% Fe2 O3.2 3

May be suitable for low qauality glass manufacture.

Burichu Bedded quartzite with quartz-mica schist inclusions. Tir Khola Fm.

Preliminary surface investigations.

94.40-96.91%SiO2. 0.20-0.50%Fe2°3-

May be suitable for the manufacture of colourless glass & containers.

Other areas Thickly bedded quartzites associated with Thimphu, Paro & Thungsing Fm.

Preliminary recconnaissance studies.

Systematic investiqations may lead to delineation of high quality quartzite.

SLATE Sha Bhel- Kobja

Thick beds of slate intercalated with claystones & sandstones. Av. thickness of 650m & strike of over 5 km.

Detailed surface investigation.

16.00 mill.cubic metre

Estimated Good Grd. The slate is black with well delined cleavages & very little jointing. It is being quarried for use as roofing sheets, slabs & tiles.

Pemagatshel Thinly laminated soft steel- Preliminary surface grey slaty phyllites with wide investigation.joint spacings occurs overan area of 0.078 sq.km.

Not estimated

Low Grd. The slaty phyllite (slate) is of poor quality. It is being locally quarried for roofing purposes.

MICA Lamidara- Damphu- Darachu

Books of mica within the pegmatite veins intruding gneisses of Thimphu Fm.

Surface investigation& sampling.

Not estimated

Low Grd. The mica is highly stained & full of inclusions.

TALC Pa Chu-Seti Khola

Two lenses of talc (5-12m & 13-40m thicknesses; 90m & 300m strike lengths respectively) occurring within low grade metasediments of Buxa Group.

Surface investigation. 0.110 Estimated Med-High Grade.

Assumed depth persistance of 10m. Contains quartzitic impurities. The talc is white, dark grey & pale greenish to greenish- grey in colour. This deposit is workable one.

Khempa 8 small lenses of 3-20m thick & 7-48m lengths.

Surface investigation. 0.012 Estimated Low-Med.Grade.

The talc is white, pale green & grey in colour, foliated and grades into quartzite.

Thunuwa Four lenses of 5-40m thi- icknes & 30-70m lengths.

--------idem---------- 0.0036 - - idem - - Low Grd. Light-dark green talc intercalated with quartzite & phyllites.

Pagli-Sarkitar

Three lenses of talc with quartzitic/phyllitic intercalations.

--------idem---------- 0.0017 - - idem - - Low-Med.Grade.

White & green coloured semitransparent varieties are present.

Malabanse Three lenses with maximum length of 170m.

--------idem---------- 0.0043 - - idem - - Low-Med.Grade.

White/green semitransparent & schistose varieties. Contains silicious impurities.

Lapchekha Five lenses. --------idem---------- 0.0042 - - idem - - InferiorGrade.

Grey-light green soapstone variety talc.

Sukli Khola As small lenses. --------idem---------- 0.0023 - - idem - - Low Grd. Contains quartzitic impurities.

Budheni-Tin Doban

--------idem............. --------idem---------- 0.0018 - - idem - - Low Grd. White, grey & green varieties talc. Highly impure & sheared.

Lhoring As small lenses within the dolomite bands.

---- - - idem-------- High Grd. The talc is ligth cream in colour & of Steatite grade.

CLAY Khalkha Occurs as a lensoidal body of 50m x 2m non-foiliated massive & well jointed clay associated with Mao Khola group rocks.

Channel sampling. The clay is impure & the reserve is of insignificant quantity.

Wang Paon Tabular to lensoidal body (2400m x 4m) of clay associated with the metapelites of Paro Fm.

Surface investigation. 0.070 Estimated The clay has moderately good plasticity & hence mouldable.

55




(mill. T)RESERVE


ASBESTOS Thumkay Occurs as veins of varying thicknesses (3-50 cm & upto 3m long) intruding the epidiorite sills associated with quartzite & phyllites of Buxa Group.

Surface investigation of 0.06 sq.km area.

— The asbestos fibres are brittle & splintery. Reserve is considered too small.

PHOSPHATE Maure-Kalikhola

Mineralized within the black ironstone shales & carbon phyllites. 7-21m horizon extending over 820m strike length. The occurrence is at the contact of Siwalik & Gondwana.

Preliminary surface investigation. Channel sampling.

0.43-23.9%P2O5

The mineralized shale has max. thickness of 25m. A 10.45m thick horizon has an av. of 13.24% P2O5 at 10% P2O5 cutoff grade.Search for similar occurrence along Siwalik- Gondwana-Buxa sequence is considered highly desirable.

56

BIBLIOGRAPHY

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6. Gansser, Augusto (1983): "Geology of the Bhutan Himalaya”. Band 96, Denkschriften der Schweizerischen Naturforschenden Gesellschaft, Birkhauser Verlag Basel Boston Stuttgart, 181pp ISBN 3-7643-1371-4

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9. Karan, Pradyumna P. (1967): "Bhutan - A Physical and Cultural Geography". University of Kentucky Press, Lexington, Library of Congress Catalogue Card No. 67-17842, ESCAP Libriry No 915.413.1 KAR. B.

10. Le Fort, P. (1975): "Himalayas, the Collided Range - Present Knowledge of the Continental Arc”, American Geological Sciety 275-A, pp 1-44

11. Nakata, T. (1972): " Geomorphic History and Crustal Movement of the Foot-Hills of the Himalayas”, Scientific Report, Tokoku University, 7th Ser. 22, 1, pp 39-177

12. Nautiyal, S.P., Jangpangi, B.S. et al. (1964): "A Preliminary Note on the Geology of Bhutan Himalaya" proceedings of the International Geological Congress, 22nd Session, India, 1964, pp 1-14

13. Reddy, K.P. & Jayaram, S. (1983): "W-Mo-Sn-Cu-Zn Mineralization in Skarn Rocks, Dholpani Area, Gaylegphug District, Bhutan", Proceedings of the Workshop on MAWAM, 1979, published as Special Publication of the Geological Survey of India, No. 13, 1983, pp 125-129

14. Shivaraj Gurung (1990): "Geology and Mineral Resources of the Kingdom of Bhutan”, DGM Report, with Appendix “Summary of Metallic (Table I) and Non-metallic (Table II) Mineral Resources of Bhutan” (Dec. ’90 update)

15. Thinley Dorji (1990): "Progress Report for Spring 1990" , DGM Report, with Appendix A: “Geology of Bhutan”, and Appendix B: “Mineral Resources of Bhutan”

16. Yang, L & Liu, T. (1974): "Neotectonic movements of Mount Qomolangma District", Scientia Geologica Sinica, Vol. 3, pp 209-220

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United Nations PublicationSales No. E.92.II.F.7ISBN 92-1-119596-9ISSN 1014-5451ST/ESCAP/1056

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