| Limestone a sedimentary
rock consisting chiefly of calcium carbonate, primarily in the form of
the mineral calcite and with or without magnesium carbonate. Common minor
constituents include silica, feldspar,
clays,
pyrite and siderite. Organic or inorganic processes form limestone. Much
limestone is highly fossiliferous and clearly represents ancient shell
banks or coral reefs. It is the chief raw material for cement. It is also
used in the preparation of paper, steel, sugar, glass and lime.
In Bangladesh there are surface and sub-surface deposits of
limestone. The surface to near surface deposits are at st
martin's island of Cox's Bazar district and Bhangerghat-Lalghat-Takerghat
of Sunamganj district. The subsurface deposit is present at Joypurhat
of Joypurhat district. The limestone at the St Martin's Island
is Late Pleistocene and the other limestone is of Eocene age.
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Limestone,
Sitakunda |
In Bangladesh the limestone deposit was first discovered
at St Martin's Island in 1957. Later, Geological Survey of Pakistan (GSP)
surveyed the area in 1958 and found 1.8 million ton of shelly and coralline
limestone in an area of 0.60 sq km. However, these limestones are not
of good quality. In the years between 1951 and 1957 small pieces of limestone
were found at Takerghat area of Sunamganj district. Later, GSP drilled
66 holes in the area in 1961 to know the extent of the limestone. It was
found that the limestone is extended in the Bagalibazar-Takergaht-Bhangerghat
area of the district. At Bagalibazar it is 30m to 100m below the surface.
The average thickness is 152.2m and reserve is 17 million tons covering
an area of 0.77 sq km. In Lalghat the limestone is 6m to 10m below the
surface. The thickness varies from 22m to 76m and the reserve is 9.8 million
tons in an area of 0.25 sq km. In Takerghat the limestone is 7m to 57m
below the surface. The thickness varies from 2.8m to 44m and reserve is
2.2 million tons in an area of 0.42 sq km and in Bhangerghat the limestone
is 29m below the surface. The thickness varies from 6m to 37m and reserve
is 1.0 million ton in an area of 0.0013 sq km. In 1982 geological
survey of bangladesh (GSB) drilled 5 more holes in the area
and expected more deposits of limestone at shallower depth.
Exploitation of limestone from Takerghat area started in 1965 by East Pakistan Industrial Development Corporation when the supply of limestone for Chhatak Cement Factory from Meghalaya stopped due to the Indo-Pak war. About 0.612 million tons of limestone was extracted from the area from 1972 to 1993. At present the reserve is almost replenished. Besides small deposit of limestone (up-thrown block) at the Dauki river of Sylhet district is also present. This deposit is also almost replenished due to extraction by local people. The deposit of sub-surface limestone
was first discovered at a depth of 1967m below the surface at Kuchma of Bogra district when Standard Vacuum Oil Company was drilling for oil. Later, in 1964 GSP (under UNPAK mineral survey project) investigated detail geological and geophysical surveys in the area and found Eocene limestone in the region. Drilling in this area confirmed the limestone at 330m below the surface at Patnitala of Naogaon district, 495m at Paharpur of Joypurhat district and 517m to 548m at Joypurhat-Jamalganj area. In 1966 Fried Krupp Roshtoff of Germany completed the feasibility study of the mining of limestone and found the mine economically feasible. In 1969 Paul Dofrin Technical Service of UK re-evaluated the project and the government took the project for mining. In 1974 Government of Bangladesh approved the exploration of limestone from the depth by shaft sinking
employing freezing method.
In 1978 GSB drilled two more holes in the proposed mine
area and by analysis of all the data they calculated the reserve of 270
million tons of limestone of which 100 million ton is mineable from an
area of 6.7 sq km. Cementation Mining Ltd of UK calculated the underground
temperature of the mine area and found that the temperature is little
higher than the general depth gradient temperature of the area. They opined
that the freezing cost of the mineshaft will be higher and as a result
the mine will not be economically feasible. According to their opinion
the project for extraction of limestone from Joypurhat area was abandoned.
GSB in the years 1996 and 1997 drilled two more holes to get the limestone
at shallower depth but these were not successful. [QM Arifur Rahman]
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