Heavy Mineral Placer Sand Deposits of Kontiagarh Area,Ganjam District,Orissa, India

The Kontiagarh placer deposit in the Ganjam district, Orissa, India extends in northeast direction having a width of 700–1000 m. A total of 187 samples were collected meterwise from 55 bore holes in a grid pattern from beach, frontal, intermediate and back dunes covering an area of approximately 1 km². Light minerals decrease in size from the beach to the back dunes, whereas the size distribution of heavy minerals in the beach and dunes is more or less uniform. The average heavy mineral content in the beach and dunes vary from 9.38% to 24.20%. The heavy minerals are ilmenite, garnet, sillimanite, rutile, monazite, and zircon with trace amounts of magnetite, hornblende, diopside, sphene, tourmaline, and epidote. Heavy minerals are mostly less than 350 µm in size, with a peak distribution in the range between 180 and 125 µm. Ilmenite shows exsolution intergrowth with hematite. Mineral chemistry of ilmenite, hematite, leucoxene, magnetite, monazite and sillimanite are examined by EPMA. Leucoxene is lower in Fe and higher in Ti, Al, Cr and V than ilmenite. The litho‐units of the Precambrian Eastern Ghats Mobile Belt, comprising primarily khondalite, charnockite, calc‐silicate granulite and gneiss, are the source of heavy minerals for this deposit. The bulk sample has 7.30% ilmenite, 5.24% sillimanite, 9.16% garnet, 0.18% rutile, 0.14% monazite, 0.06% zircon and 0.52% other heavy minerals. The deposit has good potential for economic exploitation of ilmenite, rutile, sillimanite, monazite, zircon and garnet.     

Extreme Sea Levels Associated With Severe Tropical Cyclones Hitting Orissa Coast of India

Extreme sea levels associated with severe cyclonic storms are common occurrences along the east coast of India. The coastal districts of Orissa have experienced major surges in the past. The recent Paradip super cyclone is one of the most severe cyclones, causing extensive damage to property and loss of lives. Extreme sea levels are major causes for coastal flooding in this region. Damages can be minimized if the extreme sea levels are forecast well in advance. In the present study, we develop a location specific, fine resolution model for the Orissa coast on the lines similar to that of IIT-D storm surge model (Dube et al. 1994). The model runs on a personal computer. The bathymetry for the model is extracted from very fine resolution naval hydrographic charts for the region extending from the south of Orissa to south of West Bengal. A simple drying scheme has also been included in the model in order to avoid the exposure of land near the coast due to strong negative sea surface elevations. An attempt was made in this study to simulate extreme sea levels along the Orissa coast using the data of past severe cyclones. The model results reported in the present study are in good agreement with available observations or estimates.     

热带森林覆被的时空动态评价——以印度Malkangiri district of Orissa为例

Tropical forests have been recognized as having global conservation importance. However,they are being rapidly destroyed in many regions of the world. Regular monitoring of forests is necessary for an adaptive management approach and the successful implementation of ecosystem management. The present study analyses the temporal changes in forest ecosystem structure in tribal dominated Malkangiri district of Orissa,India,during 1973-2004 period based on digitized forest cover maps using geographic information system (GIS) and interpretation of satellite data. Three satellite images Landsat MSS (1973),Landsat TM (1990) and IRS P6 LISS III (2004) were used to determine changes. Six land cover types were delineated which includes dense forest,open forest,scrub land,agriculture,barren land and water body. Different forest types were also demarcated within forest class for better understanding the degradation pattern in each forest types. The results showed that there was a net decrease of 475.7 km2 forest cover (rate of deforestation = 2.34) from 1973 to 1990 and 402.3 km2 (rate of deforestation = 2.27) from 1990 to 2004. Forest cover has changed over time depending on a few factors such as large-scale deforestation,shifting cultivation,dam and road construction,unregulated management actions,and social pressure. A significant increase of 1222.8 km2 agriculture area (1973-2004) clearly indicated the conversion of forest cover to agricultural land. These alterations had resulted in significant environmental consequences,including decline in forest cover,soil erosion,and loss of biodiversity. There is an urgent need for rational management of the remaining forest for it to be able to survive beyond next decades. Particular attention must be paid to tropical forests,which are rapidly being deforested.     

Mode of Occurrence and Characteristics of Mn-ore Bodies in Iron Ore Group of Rocks, North Orissa, India and Its Significance in Resource Evaluation

Abstract. Several meso‐scale manganese ore bodies, scattered within Jone's horse‐shoe shaped synclinorium, in Bonai‐Keonjhar region of north Orissa are well known in the mineral map of India. Different grades of manganese ores are being exploited from this region by various agencies over a few decades. However, deceptive nature of ore bodies and complexity in control of mineralisation greatly confuse the exploration geologists for evaluation of these resources. In a recent study, the authors have classified Mn‐ore bodies of this region into three broad categories such as stratiform, stratabound (‐replacement) and lateritoid types based on mode of occurrence and their other chemical characteristics. Mn‐ore bands occur in close association with BIF and iron ores. Volcaniclastic shale in large geographic extension encloses these ore bodies. In the stratiform category of ore bodies (BMnF, analogous of BIF), manganese and shale bands, in variables thickness, alternate with each other and extend to a great depth. Such ore bodies generally constitute marginal to low‐grade ores, are characterised by low Mn/Fe ratio (～2) and have relatively lower abundance of trace (1500 to 2500 ppm) and relatively higher REE constituents. The stratabound‐replacement types of ore bodies are of intra‐stratal nature, occurring within tuffaceous shale. These are mostly shear‐controlled ore bodies extending along a zone of certain width. Increase in average Mn/Fe ratio (～6) and trace content (5000 to 8500 ppm) by 5 to 2.5 order of magnitude respectively or more above stratiform category are characteristic of these deposits. The lateritoid ore bodies have limited depth persistency. Such deposits are usually very low in Mn/Fe ratio (<1), trace (<2000 ppm) and REE contents. Different methods of exploration techniques are suggested for various categories of Mn‐ore bodies. In this context, the above findings would be the database for the exploration geologists to evaluate the potential of newer/existing Mn‐ore resources in this part of north Orissa.