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J. Ind. Geophys. Union ( July 2009 )Vol.13, No.3, pp.149-161

Geophysical exploration for manganese-some first handexamples from Keonjhar district, Orissa

B.V.S.Murthy, B.Madhusudan Rao, A.K. Dubey and Srinivasulu,Centre of Exploration Geophysics, Osmania University, Hyderabad – 500 007

E-mail: bvs_murthy_2006@yahoo.co.in

ABSTRACTManganese ores in India are being exploited since the past hundred years. Continuous exploitationof shallower and massive deposits led to searching for further occurrences and also necessitatedapplication of geophysical methods. Geological survey of India since 1940s, has been exploring formanganese deposits in various parts of the country employing different geophysical methods(Ganokar, Das & Srirama 2001).

The authors of this paper had opportunity to conduct geophysical surveys comprising gravity,magnetic and electrical resistivity methods in some selected blocks in the JAMDA-KOIRA belt ofKeonjhar District, Orissa. Manganese ore, mainly psilomelane and pyrolusite occur in this belt assmall lenses/lumps discontinuously and, in general under cover of laterite. These ore occurrencesappear to be confined to near NW-SE or N-S belts and associated with shales/phyllitic shales belowwhich are occurring occasionally brecciated conglomerates with chert and cherty quartz. Thebasement is Banded Iron Formations, mainly BHJ and BHQs.

In the first block, which is about 300mx300m size, magnetic, gravity and electrical resistivityprofiling and soundings were conducted. The geophysical signatures, though feeble, showed thetrends and alignments of ore bodies and the intervening faults/ fractures associated with ironconcentrations. Based on these results two more blocks (Block – II about 89hectares and Block –III about 24 hectares) were covered by magnetic mapping, electrical resistivity profiling and soundingand gravity survey on selected traverses. The geophysical anomalies in these two blocks also arecharacteristic in delineating the probable alignments of manganese bodies. Critical analysis of,essentially, the magnetic contour maps and resistivity and magnetic profile data helped visualizingpockets of likely occurrence of manganese ore.

INTRODUCTION

Manganese ores in India are being exploited well overthe past hundred years. These ores are mainly ofsecondary origin and are associated with the olderArchean metasedimentaries. The deposits in Indiawere originally classified as three fold (Fermor, 1909),which were subsequently modified as four fold (GSINews 1973; Krishnaswamy 1979). They are asmentioned here under :

(a) Syngenetic Gonditic deposits associated withhighly metamorphosed Sauser series of rocks as inCentral and Western India, (b) Syngenetic reef depositsassociated with the Khondalite sequences of EasternGhats, (c) Replacement deposits in the Banded IronFormations as in Singhbhum, Karnataka and Goaregions and (d) Lateritoid deposits and supergeneenrichments associated with all the above three.

Uncertainties of the occurrence, association,

depth, shape and quality which are usual withmetamorphic deposits, have led to application ofGeophysical methods. Since the initial investigationsby M.B.R.Rao in Mysore state in the late 1930s,development of Geophysical techniques andavailability of improved and modern technology led tofurther deployment of geophysical techniques in thesearch for manganese ores. Geological survey of Indiais the pioneer in this respect, followed by differentinstitutes academic, research and professional. Thefirst hand experiences of the authors in certainlocations in the Jamda-Koira belt of the singhbhumcomplex are discussed in the following.

GEOLOGICAL SETTING OF THE REGION

Manganese deposits in peninsular India occur inPrecambrian rocks and are confined to several discretebelts. The Jamda-Koira belt of north Orissa is

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manifested by the Iron ore series and is associatedwith Banded Iron Formation (Fig.1). Trace elementstudies on manganese of the Barbil area suggest aprobable non-volcanogenic origin (Ajmal 1990).

The older metamorphics are highly folded anderoded prior to the deposition of the iron ore series.At the interface between these two an unconformityis marked by the occurrence of conglomerates andquartzites. These are overlain by shales/phyllites andBHQs. The shales contain deposits of manganese ore(pyrolusite and psilomelane) derived possibly from theshales themselves. The BHQs have an over allthickness of about 300m forming isoclinally foldedridges and capped by very high grade hematite. Theyinclude alternating layers of chert, Jasper andhematite. These formations indicate depositions inquiet waters far from shore. The surface having beenexposed to long duration of intensive weathering, hasthe cover of goethite, limonite and laterite withoccasional occurrence of siderite.

These iron ore series are intruded sporadically bybasic lavas and at certain places by ultrabasic rocks.The manganese deposits of Keonjhar area amidst thelateritic iron ores are due to concentration near thesurface by meteoric water. The ores, in general, areof irregular shapes confined to the zone of weathering.In addition to psilomelane and pyrolusite, wad andlimonite also occur. They are mostly of low to averagegrades, though occasionally rich pyrolusite bands areseen. They are also associated with considerableamount of iron. Drilling and mining information fromnumerous working mines in Barbil-Joda belt suggestthat the manganese occurs as discontinuous lensoidbodies confined between shales at the bottom andBHQs, BHJ, laterite sequence on the top. Howeverthe orientation of these lensoid bodies are highlyaltered due to intensive folding and structuraldeformations of the region. Each of the manganeseoccurrences may be of about a meter to over 5mthickness, a few meters to over 100m in length and a

Figgure 1. Jamda-Koira Belt- Regional Geology Map (After Krishna swami, 1979)(*Location of Blocks Studied).

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Geophysical exploration for manganese-some first hand examples from Keonjhar district, Orissa

few meters to 20 to 30 m in depth extent. Theoverburden cover may be varying from a fewcentimeters to a few meters.

Basis of Manganese exploration through Geophysics

Earliest geophysical surveys in India for mineraldeposits were perhaps by late M.B.R.Rao in the 1930sunder Mysore geological survey. He employedmagnetic and electrical resistivity methods (Rao &Sinha 1957) for manganese.Later Jenson (1954)reported electrical equipotential survey for manganesein Central India. Bhimasankaram & Rao (1958)conducted magnetic and electrical resistivity surveysin the Garividi area of Eastern Ghat region. Since late1940s Geological Survey of India has been exploringfor manganese deposits in various parts of the countryemploying different geophysical methods like gravity,magnetic, electrical resistivity, S.P. (Dash,Venkateswarlu & Reddy 1978, Gaonkar, Das &Srirama 2001). Unconventional approach of helicopterborne electromagnetic (HOISTEM) survey wasconducted by LEME research group (Meyers 2003) in

Pilbara region of western Australia where 1.6 milliontones of conductive manganese ore of hydrothermalorigin associated with resistive dolomite was discovered.

Selection of Geophysical methods dependsessentially upon the possibility of prevalence ofdetectable geophysical anomalies. These, in turn aregoverned by the physical property contrast between themineral ores of interest and the host rocks. Underfavorable conditions of massive, shallow occurrenceof deposits in a geological environment of minimumnoise the geophysical methods will become directtools. Sometimes when the mineral occurrence is ofsmaller size located at larger depths and has lowcontrast in physical property with the host rocksgeophysical methods may be used as indirect tools.That is, the search will be for other associatedminerals, or structural, or lithological configurationswhich can lead towards the mineral of interest.

In Table 1 are presented the physical properties ofManganese ores and other minerals and host rocksrelevant to the geological setting of the Jamda-Koiraregion. These values are collected and consolidatedfrom available published literature including text books.

Table 1. Physical properties of Manganese ore and country rocks

Ore (origin) / Chemical Mn Density Mag.Suc. Elec.Resis Dielectric rock Composition Content (g/cc) Micro CGS Ohm-m constant

Pyrolusite MnO2 63% 4.70-5.00 Paramag. 5x10-3-10 2101(secondary)

Psilomelane MnOMn2OH2O 3.70-4.70 4.5x103 2977(secondarycolloidal)

Braunite Mn2O3Mn6O2 64.3% 4.75-4.82 0.16-1.2x103-7

(Secondary (colloidal)(or) Primary)

Rhodochrostie MnCO3 47.8% 3.40-3.60 100 6.8(primary or sec.)

Rhodonite MnSiO3 41.8% 3.40-3.6 Paramag. 5x1010 13-30Water saturated

Jacobsite MnFe2O4 4.95 200-3000

Haematite Fe2O3 70% 4.90-5.30 100-300 10-3-106 25

Limonite Fe2O33H2O 59.9% 3.60-4.00 50-150 106-108 3.2-5.9

Goethite Fe2O3H2O 62.9% 4.00-4.40 40-2000 11.7

Gabro 2.79-3.11 33-7650

Dolerite 2.89-3.28 Vary with Fe

Shales 2.50-2.70 100-10000

Phyllites 2.40-2.50 Vary as percomposition

Laterite 2.30-2.70 50-500

BHJ/BHQs 2.72-3.10 100-200

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From the table of physical properties it is clear thatthe manganese ores pyrolusite and psylomelane havesignificantly high density values compared to laterite,phyllite, shale or BHJ/BHQ. Iron ores namelyhematite, limonite or goethite show higher densityvalues comparable to manganese. In the case ofmagnetic properties manganese (pyrolusite &psylomelane) show paramagnetic (antiferro magnetic)responses comparable to that of hematite. Howeveramidst the environment of phyllite, shale,conglomerate or quartzites the manganese ores can beexpected to show detectable magnetic responses. Theintergranular pore spaces in the manganese ores andtheir shallow occurrence in the region make themrelatively conductive compared to the BHJ/BHQs orlaterite. The difficulty is however, in distinguishingmanganese ores from the phyllites and shales. In viewof these physical properties information and theexperience of the earlier scientists in other areas wehave chosen magnetic method as the primary toolwhich is given support by electrical resistivity andgravity. Cost effectiveness and ease of conducting field

surveys were also given due weight in the selectionof geophysical methods and their sequence.

Present Geophysical Investigations

The scientific interest of the present authors and theeconomic interest of private lease holders in differentblocks of the Jamda-Koira belt have led the authorschoosing three blocks (marked in fig.1) for the presentgeophysical investigations. In view of the limited sizesof occurrence of manganese deposits in these areas analmost uniform network of 10mx20m size formagnetics was chosen. Electrical resistivity profilingpoints with two spacings of AB/2 = 10m and 30m,soundings with AB/2 up to 90m and gravityobservations were located along related traverses ineach block. The instruments used are protonprecession magnetometer of IGIS & Terra Sciencemake, Resistivity meters Aqua Meter–Pune and DDR–III of IGIS and Lacoste–Romberg Gravimeter (ModelG1106). Elevation and position location data wereobtained using Total Station.

Figure 2. Block-1 Layout of Geophysical Survey Net.

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BLCOK-1

This block is nearly in a square shape spreading forabout 25 hectares. The topography of the area is in afashion that is elevated towards SE with a relief ofabout 60meters. The surface is covered by thickforest. From east to west the area is marked by lateritecapping; BHJ, BHQs in the central elevated portionsand gradually thickening soil cover towards west andsouthwest.

Though number of boreholes were drilled earlierin the area by a private mining company, no geologicallog about the occurrence or otherwise of manganeseat depth was available to the present authors.However, a rough idea of the surface distribution ofsome pockets of manganese lumps/lensoids with orwithout the association of iron and/or laterite isavailable from the lease companies.

Geophysical traverses (mainly magnetic) were laidin the West to East direction at 25m traverse intervalalong which stations were located at 10m interval. Tohave more control, additional traverses were laid inthe N-S direction with a view to map the response ofore bodies and also to detect and demarcate theirboundaries. Additional stations were laid at 5m

interval on majority of the traverses with a view totrace the lateral spread of ore lenses. In total about650 magnetic observations, 193 resistivity profilingpoints, 38 schulmberger soundings and 140 gravityobservations were made in the area. The layout ofgeophysical observations is shown in Fig 2.

Correction for the diurnal variation of magneticfield was effected through maintaining a secondinstrument at local base.

The magnetic map (Fig.3) interestingly is distinctand characteristic in revealing changes in themagnitudes of anomalies, trends and alignmentsattributable to known and unknown surface andsubsurface geological situation. The magneticvariations shown at 25 nT contour interval correspondwell with the trends of manganese ore distributed inlumps/lensoid form. These anomalous zones areshowing alignments in NW–SE, N–S and E–Wdirections. In the SW part of the Block, the highintensity anomaly closures are related to theoccurrence of iron ores or iron rich BHJ/BHQs. Atplaces manganese associated with iron is also showinglocalized magnetic anomaly closures like in the southand also in the north. Magnetic anomalies in lateriticzones are also of low order variation. Low order

Figure 3. Magnetic Total Field Map of Block-1 : (Contour Interval: 25n T).

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elongated magnetic closures in the NW-SE directionand the cross trends in the NE-SW direction broughtout especially with the 5m interval stationscorroborated well with the known distribution ofmanganese lumps and thus helped identifying possiblenew occurrences also. The magnitudes of magneticanomalies due to manganese ore and/or its contactwith the host rocks are of the range 100 to 250 nT.However, these anomaly magnitudes depend upon thedepth and width of the manganese ore and the natureof the host rock. Besides, the magnitude, sharpvariation in character and dipolar nature of anomalyover the contacts are additional criteria in identifyingthe probable locations of manganese lensoids. On aqualitative study of different magnetic profiles fromthe area, electrical resistivity profiling data wereobtained as stated earlier, along 3 traverses, two ofwhich are in N-S and another in the E-W directions.The first traverse is passing through the major closure

in magnetic contour map (i.e., E–2400), another oneis passing through E-2500 and the third one in an E-W direction, is through N-2000.

Resistivity data obtained along these 3 traverses areeffectively corroborating with the evidences ofoccurrence of manganese brought out in the magneticpicture. Manganese zones exposed are occurring atshallow depths in elevated areas and are marked byhigh resistivity zones relative to the surroundings.Larger AB/2 revealed decrease in resistivity thoughmaintaining relative high over the surrounding. Thesituation reverses when the manganese is occurringin low lying areas. The correspondence between boththe geophysical data is remarkable, especially inrevealing the pockets of manganese occurrence, zonesof Iron concentration, lateritic zones and soil coveredareas. Structural features like faults, fractures andcontacts between different lithologic units are alsonoticeable. The geoelectric section prepared from

Figure 4. Block-1 Gravity Map.

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electrical soundings along NS-III line (E2400) shownin Fig (4) suggests a schematic litho cum structuralconfiguration of the shallow subsurface and thereforefavorable zones for manganese occurrence.

The gravity anomaly contour map prepared for thisblock (Fig.4) has excellent agreement with themagnetic map especially in showing the zone ofmanganese ore occurrences (from NW-SE) and thepockets of Iron concentration. Pockets of manganeseoccurrence eventually are revealed by relative gravityhighs of the order 0.10 to 0.25mgal. The contourtrends also reveal structural trends like faults andfractures and the discontinuities in the occurrence ofmanganese lenses. The gravity map shown is preparedat 0.05 mgal contour interval and is referred to a localbase and therefore the appearance of positive and

negative anomaly closures. Though the topography isrelatively gentle, at a few places like along N-2050 andE-2175 the appearance of sharp closures in gravitymight be indicating terrain effects, correction forwhich is not feasible in the absence of detailedelevation data beyond the borders of the block.

Based on the study of the magnetic, electricalresistivity and gravity data a geophysical anomaly trendmap has been prepared and projected on to the surfacemineral occurrence map (Fig. 5). In the geophysicalsection prepared along Traverse E-2400in block –I withall three types of geophysical data and the geoelectricsection from Schluberger VES shown in Fig.6, thecriteria for visualizing causative sources can be easilyimagined. The central high resistivity zonecorresponding to the gravity low and flanked by sharp

Figure 5. Block-1 Trends From Geophysical (Gravity & Magnetics) Data.

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magnetic fault/dyke like anomalies on either sideappear to be due to a major fold, the flanks on eitherside are the likely seats of manganese occurrence asat VES-II to VES-6 (N-1925 to N-1950) and VES-8 toVES-7 zones (N-2025 to N-2075). The correspondenceamong these geophysical signatures facilitatesformulating and streamlining the geophysicalmethodology for manganese prospecting in theseregions. Based on these inferences a few locations inthe block were suggested as at around E-2450, N-1875for possible occurrence of manganese.

Block – II

This block is about 89 hectares in area, spread innearly rectangular shape and is mostly covered by thick

forest. Topography is highly undulatory representingthe north – northeast sloping limb of a hill rangeextending in a NE-SW direction. Places of the hillslocated in the south east are up to 680m a.m.s.l.,whereas the minimum elevation are about 550ma.m.s.l. located in the NW of the block. NE – SWtrending valleys also are there draining the areatowards NE to form almost perennial streams.

The geological formations are similar to that of theearlier block, with exposures of shales/phylllites,laterite, BHQs and limonite and goethite. In this blockalso manganese ore is associated with laterite and ironand at places covered under soil. The sizes ofmanganese occurrences as seen in some test pits byindustry are relatively small compared to the sizes oflaterite and iron exposures. Though no standard

Figure 6. Geophysical Section along Traverse-E2400 of Block-I.

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Figure7. Magnetic Total Field Map of Block-II.

Figure 8. Geophysical Section along Traverse -10 of Block-II.

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Figure 9. Block-III Total Field Magnetic Map.

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correspondence 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 – III

This 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 in

small 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.

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CONCLUSIONS

Prospecting manganese is still a puzzle despite thelarge number of geophysical investigations conductedby earlier researchers. This is because of the variedtypes of origin and occurrence controlled by theregional geology. In the Jamda-Koira belt of Singhbhumregion manganese occurs as small lensoids/lumpslocated between highly folded structurallydisturbed phyllitic shales and BHJ/BHQs of Ironore series. The magnetic, electrical resistivity andgravity surveys conducted in 3 blocks suggestedscope for analyzing and assigning causative sources

for the anomalies and identifying criteria forlocating manganese either directly or indirectlycontrolled by lithology.

The geophysical study presented in this paperforms the first level of investigation. The inferencesmade out of the present qualitative study needs to bestrengthened through first hand physical propertystudies on rocks and the ores from the field,conducting further detailed gravity and magneticinvestigations in identified pockets of the blocks andquantitative interpretation and estimations throughverification drilling or pitting at one or two locationsin each block.

Figure.10. Geophysical Section along Profile –II of Block-III.

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Revised accepted 2009 June 20; Received 2008 November 19)

ACKNOWLEDGMENTS

The authors are thankful to the private companieswho have shown interest in geophysical explorationand sponsored the work. Constructive criticism andvaluable comments by the unknown referees aregratefully acknowledged.

B.Madhusudan Rao, A.K. Dubey and Srinivasuluare thankful to Osmania University for providing theresearch facilities. The authors are also thankful toSri M.B.S.V. Rao, Ms.Laxmi Prasanna and othermembers of the field team for their participation inthe data collection and processing.

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Fermor, L.L., 1909. The manganese ore deposits of India.Memories of Geol. Surv. Of India. 1, 37PP.

Goankar, S.G., Das, A.K. & Srirama, B.V., 2001. Geophysicalsignatures of manganese deposits in differentGeological environments and strategy for theirexploration. Geol.Surv.india/Spl.pub.No.64, 459-467

GSI NEWS : GIVE REFERENCEJensen, K.D., 1954.Geo Electrical investigations of

Manganese ore bodies in India, J. Pure and AppliedGeophysics, 28 (1), 91-108

Krishnaswamy, S., 1979. India’s mineral resources Oxford& IBH Publishing Co.

Meyers Jayson, 2003. Discovering manganese ore undercover using ‘hoistem’. Hoistem: 2003 News & EventsCRC LEME (CO-operative Research centre for Landscape Environments and Mineral exploration) Australia.

Rao, M.B.R. & Sinha, S.C., 1957. Magnetic surveys for theexploration of manganese ores in India, Methods andcase histories in mining Geophysics 6th. Commonwealth Mining & Metallurgical congress. Ottawa,Canada, 301-311.

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