Sands along Brahmaputra River of Bangladesh have long been considered to be a source of heavy minerals (HMs) since it traversed a long way through various terrains. An attempt has been made under this research work to determine the kinds and amounts of heavy minerals in the sands sourced from the river system. Samples from 14 locations along Brahmaputra River covering 30 km distance from upstream to downstream of the river are found to contain different heavy minerals concentration with a range of 7.92 - 25.16 weight% with the remaining of the sample comprising silicate and aluminosilicates. Mineral characterization from peak positions in diffractogram of X-ray Diffraction (XRD) evaluate quartz, feldspar and mica are major categories light mineral while rutile, magnetite, illmenite, zircon, monazite, garnet, uranium arsenide and uranium fluoride are the major types heavy minerals. Ilmenite and rutile are main contributors of total heavy mineral (THM). Titanium bearing minerals ilmenite and rutile contributes 26.22% - 31.01% and 14.57% - 23.50% of THM. In the present study area, most of the sands are found to be fine and medium grained as obtained from the particle sizes analysis using 18- to 230-mesh.
Minerals are the composite of different elements and occur naturally as crystalline inorganic substances in sediments. Mineral sediments, sands and mud are weathered from mountain belts, transported by rivers, glaciers or wind and deposited. Minerals are classified into two types on the basis of its density such as light minerals (specific density less than 2.9/103 kg·m−3) and heavy minerals (specific density greater than 2.9/103 kg·m−3) [
The Brahmaputra River originating in Tibet and flowing through Tibet and the north-eastern part of India enters Bangladesh in Kurigram District. The immense amount of sediment carried by the Brahmaputra River, derived from intense erosion of the Himalayas (in the north), is delivered to the Bay of Bengal. During transportation sandy materials laid down on the bed of the river, forming sand bars. The thickness of sand deposits up to gravel bed is 44 m [
Heavy minerals, having higher specific gravity, occur in all sands. Some sands contain large enough concentrations of valuable heavy minerals to serve as commercial sources of these minerals. The kinds and amounts of heavy minerals occurring in Brahmaputra River are of great interest to warrant commercial exploitation. An attempt has been made through this study to know the heavy minerals concentration together with individual heavy mineral quantification along Brahmaputra River in Bangladesh.
The present study area covers Kurigram sadar, Ulipur and Chilmari Upazila of Kurigram district which is traversed by Brahmaputra (Jamuna) river (25˚48'26"; 89˚45'09" - 25˚33'32"; 89˚41'01"). The study area covers stable sand bars in an area of 30 km × 4 km from upstream to downstreamof the Brahmaputra River in the Kurigram district, north-eastern Bangladesh (
The present study covers about 30 km × 4 km area from which 14 successive locations were selected and numbered as DK1-DK14. From each location two samples were collected from sand bar (“chars”) and river bed found in the study area. The sample locations were recorded in terms of degree-minute-second (latitudinal and longitudinal position) using a hand-held global positioning system (GPS) (Model: Magellan-Map-410) unit. Each location is separated by a distance of approximately 2 km (approximately 1 minute in co-ordinate system). The samples were collected at the depth of 0 - 5 cm by plastic spade during summer period of 2014 and collected samples were packed in polyethylene bags. Each sample has the weight of about 2 kg. The collected samples were air dried at room temperature in open air.
Preparation and preliminary analysis of sediment samples were carried out as per the procedure given in Carver [
For mechanical separation 10 kg raw sand samples were dried in the sun to remove moisture. Separation of heavy and light minerals was carried out depending on specific gravity/density of the minerals using laboratory shaking table. For each sample, heavy minerals fraction obtained after density separation dried in burner. Magnetite, ilmenite, rutile and zircon mixed with others were separated using Induced Roll Magnetic Separator (IRMS) applying fixed magnetic intensity at 0.5 amp, 2.5 amp, 5.5 amp, and 7.5 amp condition, respectively.
Powder X-ray Diffraction (XRD) is a versatile technique that can be used to identify any crystalline substances, such as most minerals. It can also be used to quantify the proportions of different minerals or indeed many other substances when they are present in a mixture. Powder X-ray diffraction analysis is seemingly the perfect technique for crystalline-mixture analysis, since each component of the mixture produces its characteristic pattern independently of the others, making it possible to identify the various components by unscrambling their superposed patterns. An X-ray beam of known wavelength is focused on a powdered sample and X-ray diffraction peaks are measured using a detector. In the present study X-ray diffraction technique has been utilized to discern these properties. The phase identification was performed using Philips X’Pert Pro multipurpose X-ray diffractometer which uses copper Kα radiation. X-ray generator operated at 40 kV and 30 mA, and all scans were run at a speed of 2˚ per minute, from 10˚ to 70˚, with a continuous step size of 0.02.
The heavy mineral separation analysis has been carried out to know the total heavy mineral (THM) weight percentage in the present samples. Weight percentage of separated heavy minerals in most of the samples varied from 8% to 15%, while in one sample it reaches to 25%; similar THM value is reported for Brahmaputra river sand [
Average THM value in the sand samples of the study area is 12.40% while low (within10%) THM percentage is encountered in four locations. These values of THM are higher than the other river of Bangladesh as observed in someshari river [
Granulometric analysis has been carried out to know the content of sand, silt and clay (%) in the present sediments. Percentage of sand, silt and clay (%) content of the samples are presented in
X-ray diffraction is a unique analytical tool for the analysis of geological samples. It is the most important and informative technique for identification and characterization of minerals in the sediments. The XRD spectra were recorded for all the sediment samples to determine the mineralogical composition. A representative diffractogram is shown in
The XRD pattern (
The Brahmaputra drains the Tibetan Plateau of China and is dominated by upland tributaries originating in the Himalayas. The Brahmaputra flows through various rock types including Precambrian metamorphics (high-grade schists, gneisses, quartzites, metamorphosed limestones), felsic intrusives, and Paleozoic-Mesozoic sandstones, shales and limestones [
Heavy Mineral | Wt% | |||
---|---|---|---|---|
60-mesh | 120-mesh | 200-mesh | Pan | |
Ilmenite | 8.79 - 25.72 | 54.76 - 63.27 | 13.50 - 19.45 | 5.33 - 8.02 |
Rutile | 11.33 - 55.82 | 36.03 - 62.42 | 7.12 - 22.00 | 1.00 - 4.26 |
Zircon + others | 15.25 - 53.03 | 42.21 - 73.41 | 4.51 - 11.00 | 0.10 - 0.40 |
mainly Lesser Himalayan and Indo-Burman Ranges with having little influence of Himalayan tributaries and north Himalayan [
The heavy fractions of sands along the Brahmaputra River are primarily the source of the iron titanium and iron oxide minerals magnetite and ilmenite. Most of the heavy minerals are in the 60- to 200-mesh size range. Most of the samples have between 8 and 15 percent heavy minerals. Ilmenite ranges from about 4 to 9 percent and rutile ranges from about 3 to 5 percent. Such percentages are much higher than those of Someshari river sands of Bangladesh. Considering the high heavy mineral concentration in river sands, the possibility of commercial utilization of the heavy minerals in sands along the Brahmaputra River is quite a burning issue at the present time.
The authors are thankful to local Administration and people of the study area for their assistance during field work. The authors are also grateful to laboratory staffs of Nuclear Minerals Unit of Atomic Energy Research Establishment for their assistance in laboratory analysis. This work is financed by the Ministry of Science and Technology, Government of The People’s Republic of Bangladesh under the Special Allocation program 2014- 2015.
Md. IbrahimKhalil,Md. Nazrul IslamKhan,Md. ZafrulKabir,Ratan KumarMajumder,Md. IdrisAli,DebasishPaul,Syed Mohammad AzharulIslam, (2016) Heavy Minerals in Sands along Brahmaputra (Jamuna) River of Bangladesh. International Journal of Geosciences,07,47-52. doi: 10.4236/ijg.2016.71005