Sharif Hossain Khan, Md. Sakawat Hossain and SM Mahbubul Ameen
The Financial Express, 06.03.2012
Our media has been publishing reports for last few days the finding ‘deposit’ of iron in Atrai riverbed in Dinajpur. The overenthusiastic reports attracted thousands of curious people to rush to Khansama Upazila of Dinajpur to physically check the presence of ‘iron deposit’ there. In the meantime some of the locals suggested the presence of iron rich hillocks in the middle of the river. Some suggested mysterious presence of hillocks covered with iron rich sand in the middle of Atrai River at Bhabki Union of Khansama Upazila, Dinajpur.
Further confusion arose as ‘experts’ of soil science department of Haji Dannesh Science and Technology University, Dinajpur hinted potential iron ore deposit in the area.
As Dinajpur has a number of proven coal and basement rock deposits and two underground mines for coal and construction rocks have been developed to extract resources, people positively react to new addition to mineral deposits in the district. It is indeed a positive reaction of the people who aspire to change their fate with new findings of valuable mineral resources under their land. But any finding of commercially viable mineral deposit should be assessed by the geoscientists prior to declaration of their potential development opportunities. Geologists should primarily survey and collect samples from the potential mineral body, assess its qualitative and quantitative state. Subsequently the experts should assess techno-economic feasibility of the resource and recommend for further studies for development.
The rumour of finding iron ore deposit in the riverbed of Khansama, Dinajpur naturally attracted attention of the students and the faculty members of Geoscience Department of Jahangirnagar University. A reconnaissance team headed by the authors was sent to the area on 2 March 2012 to physically investigate the area and collect sample from the ‘iron rich hillocks’ in the riverbed which have primarily attracted people.
It is revealed that the area of attraction is located at the left bank of Atrai River (facing down stream) of Agra village, of Bhabki Union of Khansama Upazila, Dinajpur. The spatial dimension of the apparently iron rich deposits is very small and the deposits are not continuous. Field investigation further reveals that there are three major discontinuous blocks with variable length, thickness and width in exposed condition in the left bank of the river bed. Total spatial dimension of the deposits is approximately 300m in length, approximately10m in width and 3m in thickness.
Since the iron containing mineral bodies are found in the river Atrai at Khansama, Dinajpur, it is useful to look into the Atrai River and its flowing history. The Atrai River originates at approximately 10km northeast of Shiliguri town of West Bengal in India. Then it flows west of the river Brahmaputra. It is the westernmost distributaries of the Brahmaputra. It changes its name from Karatoya to Atrai near Khansama Upazila of Dinajpur district. It flows through the eastern part of Dinajpur town and enters West Dinajpur of West Bengal after passing through Bhusir Bandar and Samjia Ghat. The river then flows south to Manda Upazila through the Barind Tract near Naogaon district of Bangladesh. It flows further south and turns southeast, then continues through Chalan Beel and meets the Hurasagar River. Atrai River meets the river Jamuna near Baghabari through Hurasagar. Total length of this river is approximately 240 miles (390 km). Maximum depth of river is 99 feet (30 m). The Atrai was formerly one of the great rivers of north Bengal by which the waters of the river Teesta discharged into the Ganges systems. In 1787, however, the river Teesta broke away from its ancient bed and cut for itself a new and capacious channel by which it found its way into the river Brahmaputra. Since then the Atrai has lost its importance and has now few traces of its former greatness.
The river Atrai deposited its sediments as alluvial fan in the region. These sediment generations, transportation and deposition are controlled by the on set of humid monsoon climate during the late Pleistocene to Holocene time (approximately 10,000-20,000 years back). These alluvial sediments might be rich in iron bearing minerals (like hematite, goethite, limonite etc.) and have been concentrated at the present site to form isolated and sporadic alluvial placers. The humid climatic conditions are prevailing since their deposition which causes the leaching of labile minerals (unstable minerals continually undergoing chemical, physical or biological changes) leaving the resistant minerals in-situ. The authors inferred that the deposits are at the initial phase of laterisation (ultimate stage of weathering) and may bear characteristics of iron bearing minerals of lateritic conditions (intense weathering) such as hematite, goethite, limonite and bauxite.
However, from the very first observation it is found that the iron concentration in the so called ‘brownish hillocks’ in the Atrai riverbed at Khansama is very low. Their spatial extent is very small and the rocks are of very young age. To form an iron deposit of economic value, it needs millions of years from river transported iron bearing placer deposits. Also, any commercial deposit should have a sizable volume of iron rich ore deposit. From our first site investigations we found that the Khansama findings do not have the required volume or concentration of iron rich mineral ore presence. Therefore, from initial observation, it can be concluded that the iron containing sand in river Atrai cannot be considered as mineral deposit. The sacrificial extent of the iron like deposit in the Khansama Upazila cannot be taken as an iron ore deposit at this stage. Further investigation if unveils subsurface deposition of mature ore body rich in minerals of commercial importance may carry interest for further study.
The writers, Professor Dr. Sharif Hossain Khan, Md. Sakawat Hossain, Assistant Professor, and SM Mahbubul Ameen, Assistant Professor are faculty members of Department of Geosciences, Jahangirnagar University