B.V.S.Murthy, B.Madhusudan Rao, A.K. Dubey and Srinivasulu - IGU

More documents

Recommendations

Info

$Bed Rock investigation by Seismic Refraction Method - A case ... - IGU$

B.V.S.Murthy et al.Figure 9. Block-III Total Field Magnetic Map.158
Geophysical exploration for manganese-some first hand examples from Keonjhar district, Orissacorrespondence is noticeable between manganeseoccurrences and the topography, the manganese bodiesappear to be located on the hill slopes to go undersoil cover thickening towards NW.In this block also magnetic data were collected, asstated earlier, at the grid specification of 10mx20mwith the traverses laid in an E-W direction with a totalnumber of 4374 stations. A magnetic contour mapwas prepared at 25nT contour interval (Fig.7). Themagnetic picture is very interesting with the two foldcharacter of concentration and alignment of magneticclosures and relatively magnetically smooth and plainregions. The clusters of magnetic closures with a widerange of fluctuating intensities appear to be in twoNE-SW extending bands in the major part of the areaand a cluster of closures in the western corner of thearea. Topography and the location of old mine pitscorrespond well with the first feature that NE-SWaligned magnetic contour closures reveal theoccurrence of manganese ores along with associatediron. The second feature viz., the cluster of magneticclosure located in the west of the area has to beattributed to presence of magnetic iron. Possibility ofoccurrence of manganese here in association with ironcan not be ruled out. The two parallel bands ofmagnetic closures in the NE-SW direction mightrepresent the two limbs of a fold with its axis alignedin that direction.Electrical resistivity and gravity surveys werecontemplated in this block. In Fig.8 also the behaviorof geophysical magnetic and electrical resistivityvariations identified in block –I (Fig.6) can be seenespecially around station 90 on this Traverse-10.Therefore the zone between stations 85 and 95 is ofinterest in terms of manganese occurrence. The zonebetween stations 120 and 140 where high gradientmagnetic values correspond to high resistivity atshallow depth may be latarite with iron or iron ore.VES data to prepare a geoelectric section would helpdrawing more reliable inferences.Block – IIIThis block elongated in a NW-SE direction is almostof a parallelogram shape. It occupies about 24 hectaresarea in the Jamda – Koira belt and is covered by notso dense a forest. Topography suggests a NW-SEtrending ridge, (probably an anticlinal fold) with thesloping eastern limb and southern apex portionappearing in the area of study. Elevation relief is about30m in the area with the highest and lowest valuesbeing 640m and 610m. Geologically the area is coveredwith Quartzites, Laterite, and Alluvium. Manganeseoccurs in some places in the form of lumps and insmall pockets. Iron ore, mostly lateritic and haematite,appear in the NW border aligned in a NW-SE direction.There is only one pit dug for manganese, located inthe eastern edge of the area.Following the usual specifications as earlier,magnetic data were collected from the block.Considering the alignment of the ridge and also themagnetic map, additional traverses were laid in thisblock in the SW-NE direction (7 traverses) and NW-SE direction (2 traverses) along which the magneticstations were located at 5m interval. Electricalresistivity profiling and soundings were conductedalong three of the SW-NE traverses. Totally about 1102magnetic observations were made to prepare themagnetic map. Electrical resistivity profiling pointsnumbering 542 and soundings 28 were made in thisblock.The magnetic anomaly map (Fig .9) is slightlydifferent from that of the earlier two blocks inreflecting the magnetic signatures of the subsurface.The elevated ridge like NW-SE feature with exposuresof BHQs and Quartzites and partly covered byAlluvium and laterite is moderately magnetic. Againalong the eastern border of the area in the downwardslope direction magnetic response is slightly active.The central portion between these two zonesextending in the NW-SE direction is magneticallyrelatively calm. However, there are recognizable trendsin the NW-SE direction and in the SW-NE directionsimilar to those observed in Block – I. Most of thehigh intensity magnetic closures are correspondingwith known occurrence of (lateritic) Iron ore. Theclusters of magnetic closures in the NE of the areaare probably revealing the occurrence of Iron ores.Manganese being moderately magnetic, the trends andcross trends of magnetic anomaly features andlocalized closures of moderate values adjacent to thehigh intensity closures are of interest in the contextof manganese exploration.As in the case of Block – I, electrical resistivityprofiling data, geoelectric section prepared form VESdata and the magnetic field along three SW-NEtraverses were studied. Fig. 10 shows one such sectionrevealing the correspondence between the electrical andmagnetic data and the inferred geoelectric subsurfacesection. It is interesting that the quartzites and BHQsare revealed by high resistivities and smooth magneticvariations. Lateral changes in lithology in the shallowsubsurface are also prominently brought out. It islikely that the subsurface configures as an anticlinalfold between VES-4 and VES-7 followed by a synclinebetween VES-8 and VES-10. The sloping limbs ofthese folds are of interest in terms of manganeseoccurrence as in the case of Block-I.159
Page 1 and 2: J. Ind. Geophys. Union ( July 2009
Page 3 and 4: Geophysical exploration for mangane
Page 9: Geophysical exploration for mangane

B.V.S.Murthy, B.Madhusudan Rao, A.K. Dubey and Srinivasulu - IGU

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?