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Hardrock


Hardrock a term used loosely for igneous and metamorphic rock, as distinguished from sedimentary rock. These are consolidated rocks like granite or marble. An unlimited reserve of hard rock consisting of granodiorite, quartzdiorite and gneiss of the Pre-Cambrian has been discovered at a shallow depth of 128 m in Maddhapara in the Dinajpur district. Pegmatite, pyrite, chalcopyrite and siderite have been observed in the vicinity of granodiorite, quartzdiorite and gneiss. Hard rock deposits are also recorded in Ranipukur and Pirganj inRangpur district at a depth of 171 m and 265 m respectively, and from Bogra, Joypurhat-Jamalgonj, and Kansat of Rajshahi district at depths of 2,150 m, 600'667 m and 615 m respectively (Rahman,1997). Besides these, there are surface deposits of construction materials such as boulders, gravels etc. at Tetulia-Panchagarh in Dinajpur district; Kaptai-Alikadam-Ukhia-Teknaf-St. Martin's Island in greater Chittagong district and some other places in greater Sylhet district.

Thus the hardrocks of Bangladesh are categorized as (i) Maddhyapara subsurface hardrock, (ii) Bholaganj-Jaflong hardrock concretions, (iii) Tetulia-Patgram-Panchagarh hardrock concretions, and (iv) Chittagong-Chittagong Hill Tracts sedimentary concretions.

Maddhyapara subsurface hardrock In 1974-75 the geological survey of bangladesh (GSB) drilled six wells in and around Maddhyapara and confirmed the existence of Precambrian hardrock at very shallow depths. In these wells the Precambrian hardrock was encountered between depths of 128m and 154m. Techno-economic feasibility study of the Maddhyapara hardrock project was carried out by SNC (Surveyor Nenniger and Chenvert), a Canadian consultancy firm. Finally, the Government of Bangladesh approved the project in 1978. However, the project started working formally from early 1994, following the signing of two international contracts for the Barapukuria Coal Mine Development Project and for the Maddhyapara Hardrock Mining Project between CMC of China and petrobangla, and NAMNAM of the Democratic Republic of Korea and Petrobangla respectively. Maddhapara Granite Mining Company Limited (MGMCL) a company of Petrobangla under the Ministry of Power, Energy and Mineral Resources, and Government of the People's Republic of Bangladesh was incorporated on August 04, 1998 Maddhapara Granite Mining Company Ltd. Was established with multifold responsibilities of production of hardrock with daily production capacity of 5,500 M. tons from the underground mine, marketing and selling of the produced hardrock to different Government entities.

Salient Features of Maddhapara Hardrock Mining Project:

1. Depth of rock 124 meter from the surface.
2. Reserve & mine area Reserve in the mine area of 1.0 km × 1.2 km =1.2 km2 is 174 million tons.
3. Annual Production 1.65 million tons.
4. Life of the mine Project analysisbased on 41 years (including development period) but mine operation life may be extended for more than 70 years.
5. Method of mine Room & Pillar/ Sub-Level Drift Stopping Method.
6.

Mode of Entry
(Length & dia. of shafts)

Two Vertical shafts (The length of the skip shaft is 380m & cage shaft 330 m. Inner dia of both shafts is 5.0 m. and distance between two shafts is 85 m).

7.

Investment cost
(TK. In lakh)

Total Local FE
1024998.31 33110.06 69388.25
($ 197.889 m.) ($ 57.086 m.) ($ 140.803 m.)

8.

Estimated production cost

TK. 702 / ton ($12.095 / ton)

(a) after completion of the Project Annual payment to Govt. Exchequer(TK. In lakh)

Total -5552.50

(b) annual foreign exchange saving

TK. 13879.00 lakh ($ 23.925m)

Maddhyapara Granite Mining Company Limited (MGMCL), finally went into production 25th may 2007 after missing several deadlines in about a decade.

Hardrock has been extracted upto April 2007 a sum of total amount of 459,283.98 metric ton 392030.78 m ton of hardrock have already been sold to different organisations. These rocks are used as construction materials for Housing apartments, Commercial buildings, Roads and Highways, Bridges, Dams, River Dykes, Embankments, Flood control, Railway ballast and sleepers, Decoration pieces, Tiles, etc.

And the possible users of this hard rock are the authorities of Bangladesh Railways,Roads and Highways, Water Development Board, Power Development Board, and the Sea Ports, Housing and Settlement, and Local Government and Engineering departments.

Gravel deposits Wide areas of northern and northeastern parts of Bangladesh are covered with gravel beds. In the north, the gravels are well exposed at Dahagram-Angorpota, Patgram, Dalia, Chapani, Kaliganj in greater Rangpur and Tetulia, Vazanpur, Boalmari, etc in greater Dinajpur. These gravels are quite large (maximum recorded elongation is 30 cm) and are alternated with very coarse to medium sand. They are quite fresh and well rounded, with a smooth surface haviung quartz, quartzite, granite, gneiss and schist as their dominant lithologies. These gravel beds are grouped together as the Panchagarh sandy-gravel beds belonging to the Upper Pleistocene series. During the last glacial maximum (ie 18,000 years BP) the Himalayas were quite high and were glaciated. The glaciers extended up to the foothills. Dry climatic conditions prevailed during that time and the melt water was flowing over the Bengal plain through some narrow and deeply incised river systems. At the end of the last glaciation (upper part of Upper Pleistocene) monsoon rainfall was quite prominent and the glacier also started melting. The melt water plus the amplified monsoon water flowed over the Bengal plain. The narrow river systems were over-loaded and surplus water flowed over the barind tract. These enormous water flows carried the gravels up to the Panchagarh-Dahagram-Dalia area and were deposited as some piedmont deposits.

On the other hand, the gravels of the northeastern part of Bangladesh are well exposed in the Jaintiapur-Bholaganj area in greater Sylhet district. Here the gravel beds are divided into two lithostratigraphic sub-units: older sub-unit (high terrace) and younger sub-unit (low terrace). The older sub-unit in the Jaintiapur area and Binda Tila that caps the hill tops have been named the 'Sona Tila Gravel Bed'. Similarly, the younger sub-unit of the Bholaganj area and the river bed deposits of the present river system have been named the 'Bholaganj Gravel Bed'.The Sona Tila Gravel Bed is equivalent to the Lower Pleistocene series and belongs to the Madhupur Clay formation while the Bholaganj Gravel Bed is equivalent to the Upper Pleistocene to Holocene series. They are made up of river borne deposits.

Apart from these, numerous hill streams also deposit gravels on the streambeds of the hill ranges and in the plains close to these ranges. These hill ranges are mostly located in the Sylhet, Chittagong and Chittagong Hill Tracts region. Also in the Teknaf-Cox's Bazar sea beach seven separate occurrences of gravels are present between Moderbunia chhara and Rajar chhara. These gravels are of sedimentary origin and mostly belong to the Surma and Tipam Group of sediments. [Sifatul Quader Chowdhury and Sanzida Murshed]