ISSN 0579-4706 © Govt. of India PGSI. 340 Controller of Publication 700-2011 (DSK-II) GEOLOGY AND MINERAL RESOURCES OF THE STATES OF INDIA ⁄FFfi∂F ÇÅW fiF°‹FXk ÇÅF ⁄F[PÊF£FFŒF JÊFk äFPŒF°F ıFkıFFÕFŒF GEOLOGICAL SURVEY OF INDIA Miscellaneous Publication No. 30, Part XIX – SIKKIM ⁄FFfi∂FU‹F ⁄F[ÊFY£FFPŒFÇÅ ıFÊFWaáFμF PÊFPÊFÕF “ÇÅFËFŒF ıFk -30 ⁄FFçF XIX Published by order of the Government of India 2012 © INDIA, GEOLOGICAL SURVEY (2012) Compiled by the officers of Sikkim Unit, Operation: WSA Processing and editing of the manuscript by S/Sri Subhra Suchi Sarkar, Md. Amjad Ali and Smt. Gargi Bhattacharya Senior Geologists under the supervision of S/Sri Pradip De , Bikash Chandra Roy and K.V.Nambiar Directors, Publication Division, Geological Survey of India, Eastern Region and under the overall supervision of Shri I. K. Khan, Deputy Director General Geological Survey of India, Eastern Region Price: Rs. l30 $ 7 £ 4 Published by the Director General, GSI, 27 J. L. Nehru Rd. Kolkata 700016 and printed at M/s Arunima Printing Works, 81 Simla Street, Kolkata 700006, Phone: 91-33-22411006, E-mail: [email protected] Foreword detailed account of Geology and Mineral resources of Sikkim has been prepared in order to publish the volume in the form of Miscellaneous APublication 30 series for the first time. The present write up gives a summarized account of information on the geology, structure and mineral resources to be used by earth science fraternity, administrators, entrepreneurs and also common man. The climate of Sikkim is favourable for medicinal herbs and plants. The temperature of the state ranges between 4°-35°C in lower altitudes and 1°-25° C in higher altitudes. The state houses one National Park and five wild life sanctuaries. All these factors contribute to the setting up of tourism and pharmaceutical industries in years to come. The Himalayas in Sikkim has been divided into linear geotectonic belts with distinct geological characteristics. Beginning from south these are Sub-Himalayas, Lesser Himalayas, Trans Himalayas and Higher Himalayas. The Main Boundary Thrust separates the Siwaliks of the sub-Himalayas domain from the Lesser Himalayan Belt and the Main Central Thrust separates the lesser Himalayas from Higher Himalayas. The rocks of the area ranges in age from Proterozoic (undifferentiated & Meso) to Ordovician followed by Permo-Carboniferous Gondowana rocks overlain by Triassic sequence of sandstone, shale and limestone and culminating in Upper Pleistocene- Holocene (variegated clay, fine to medium sand and pebble bed) sediments. Due to highly deformed nature of rocks the area is susceptible to landslides and the recent earthquake of September, 2011 has warranted a detailed study of structural data of the terrain for taking up remedial measures and also for handling various geotechnical projects. The state is endowed with rich mineral resources. This includes asbestos, base metals, coal, dolomite, graphite, limestone, marble, sillimanite, talc, topaz, tungsten & vermiculite. The details of individual mineral regarding the mode of occurrences, grade and reserves has been dealt in depth in the manuscript. Kolkata Dated, 14th December, 2011 iii iv vi CONTENTS I INTRODUCTION 1 Climate 1 Agriculture 1 Fauna and flora 1 Physiography and drainage 2 Lakes of Sikkim 3 Glaciers of Sikkim 4 Hot Springs 5 II GENERAL GEOLOGY 6 Stratigraphic classification 6 CENTRAL CRYSTALLINES 6 Chungthang Formation Kanchenjunga Gneiss/Darjeeling Gneiss (Undifferenciated) 7 Banded / Streaky gneisses / Migmatites 7 Augen bearing biotite gneiss with//without Garnet, Kyanite, Sillimanite 8 Sillimanite Granite Gneiss 8 DALING GROUP 11 Gorubathan Formation 12 Reyang Formation 13 Buxa Formation 13 LINGTSE GRANITE-GNEISS 15 MOUNT EVEREST PELITIC FORMATION 16 MOUNT EVEREST LIMESTONE FORMATION 16 GONDWANA SUPERGROUP 17 Rangit pebble slate 17 Damuda Formation 18 Lachi Formation 19 Chho Lhamo (TSO Lhamo) Formation 21 Intrusive Granites 22 Syenitic Rocks 23 Sesela Formation 24 vii STRUCTURE AND TECTONICS 25 METAMORPHISM 28 SEISMICITY AND EARTHQUAKES 30 III MINERAL RESOURCES 32 Asbestos 32 Base metals 32 Lead 40 Calcareous Tuffa 40 Coal 40 Dolomite 42 Graphite 43 Kyanite 44 Limestone 44 Marble 45 Silica and silica sand 46 Sillimanite 47 Talc 47 Topaz 47 Tungsten 47 Uranium mineralization 47 Vermiculite 47 IV LOCALITY INDEX 48 V REFERENCE 48 viii MISC. PUB. NO. 30(XIX) 1 I. Introduction Sikkim or Sikhim is a name derived from the Places with an altitude of 6065 m and above are Sanskrit word Shikhim meaning ‘Crested’. In all of snowbound and places as low as 3002m come within the Sikkim there is not a single kilometer of ‘flat land’. With snowline in the winter. The temperature in the lower an area of 7096 sq km, measuring 113 km from north to altitudes fluctuates between 4°-35°C and places with south and 64 km from west to east, the state has moderate height (around 1829 m) such as Gangtok elevations ranging from 240 to 8484 meters above mean temperature varies between 1°C and 25°C. In the high sea level. The State of Sikkim is located in the southern altitude area (above 3993 m), the temperature never rises mountain ranges of Eastern Himalayas between Northern above 15°C and slides down to the freezing point in winter. Latitudes 27°05and 28°08 and Eastern Longitudes Agriculture 88°10 and 88° 55. Sikkim is the 22nd State of the Indian Union, which came into existence with effect from 16th Agriculture accounts for one third of Sikkim’s gross May; 1975. Sikkim is bounded by Nepal in the west, domestic product. More than 64% of the population Bhutan in the east, Tibet in the north and state of West depends on agriculture for livelihood. Products such as Bengal in the south. The state has been divided into four rice, wheat, maize, finger-millet, barley, buckwheat, and districts, viz. East, West, North and South districts and pulses like ricebean, rajmah, fieldpea, cowpea and each district has further been subdivided into two sub- clusterbeans and oil seeds like rapseed, mustard, divisions for administrative purposes. soyabean and sunflower are grown in the area. Of late there is a thrust on planting medicinal herbs, which Climate : abound the natural vegetation. The State is reported to The climate of the State has been roughly divided have more than 424 species of the medicinal plants. into the tropical, temperate and alpine zone. For most part of the year, the climate is cold and humid. Most part of the state receives heavy rainfall throughout the Fauna and flora year. It is only in the month of October-March that the Sikkim is enriched in forest resources. The total area State remains comparatively drier. The extreme northern under the administrative control of Forest, Environment parts, adjoining Tibet, however, receive very little and Wild Life Department is 5765.10 sq km which rainfall. The mean annual rainfall is minimum at Thangu accounts for 81.24% of the total geographical area of the (82 mm) and maximum at Gangtok (3494 mm). An state. The State has one national park (Kangchenjunga isohyatal analysis of these data reveals that there are National Park) and five wildlife sanctuaries. Names of two maximum rainfall areas (i) South-east quadrant principal endangered species of Sikkim are bharal, including Mangan, Singhik, Dikchu, Gangtok, Rongli, clouded leopard, fishing cat, golden cat, himalayan thar, etc. (ii) South-west corner including hilly terrain. In leopard cat, red panda, marbled cat, musk deer, nayan of between these two regions, there is a low rainfall area great Tibetan sheep, pangolin, serow, snow leopard, (around Namchi). There is an area in north-west Sikkim spotted lingsang, Tibetan antelope, Tebetan Fox, Tibetan which receives less than 4.9 mm of rainfall. Rainfall is gazzelle, Tibetan wild ass, tiger, Tibetan wolf. Important heavy and well distributed during the months from May birds are black necked crane (migratory), blood pheasant, to early October. July is the wettest month in most of peafowl, Tibetan snow cock, tragopan pheasant, snow the places. partridge, and siberian crane (migratory). 1 2 GEOL. SURV. IND The dominant flora in temperate zone is oak, cuherry, crow fly distance towards north. Siwaliks starts at 153 alurel, chestnut, maple, birch and rhododendron and the m and ends at 823 m. Dalings continues up to 1220 m dominant flora in the southern part of Sikkim is plantains, and then Darjeeling Gneiss starts. On the eastern side bamboos, tree ferns, walnut, sal and oak. Cimbidiums, Siwalik ends at 732 m, Dalings at 1376 m. At the central vanda, cattaleya, hookeriana, farmeri, dendrobiun- part of the area, i.e. in Tista Dome the height is in general amoenum and noble orchid are the most popular flora. between 1200 to 2500 m though the summit point is on 3233 m. As soon as the Daling rocks are crossed the Physiography and drainage height increases sharply from average 1800 m to 3000 The State encompasses parts of Lesser Himalaya, m in the lower reaches, 3000 m to 4500 m in the middle Higher Himalaya, and the Trans Himalaya and hosts reaches and 4500 m to 6700 m in the upper reaches of some of the highest mountain peaks of the Himalaya. the dome. The rocks north of South Tibetan Detachment The elevation ranges from 300 to 8586 m with increasing System(STDS) are in general occurring above 4200 m elevation from south to north. In Sikkim-Darjeeling to 7300 m. Himalaya, the Lesser Himalaya starts from Kalijhora (in Darjeeling) in south/west and continues up to Singhik The Tista Rangit water divide is the main N-S water (in Sikkim) in north/east. The low grade metamorphic divide within the Sikkim-Darjeeling Himalaya. This rocks of Lesser Himalaya start at as low as 300 m and water divide takes an E-W swing after crossing the continue up to 3050 m (Mount Mainak).