ORIGINAL PAPER

Application of integrated geoelectrical methods in Marand(Iran) manganese deposit exploration

Hamidreza Ramazi & Kamran Mostafaie

Received: 4 October 2011 /Accepted: 8 February 2012# Saudi Society for Geosciences 2012

Abstract This paper addresses the application of integratedgeoelectrical methods including induced polarization (IP),resistivity (RS), and self-potential (SP) for exploration andevaluation of the Marand (Iran) manganese deposit. The SPmethod was used for reconnaissance, in which five profileswere designed and surveyed with a reference electrode thatwas placed in a distance of at least 800 m far from themeasurement points. For the conduct of RS and IP, a newarray proposed by Ramazi (2005a), named combined resis-tivity profiling and sounding (CRSP) was used along nineprofiles that made it possible to do sounding survey andproduce apparent resistivity pseudo-sections. Some anoma-lies were detected by means of SP surveys along the profilesand some other were located from IP and RS pseudo-sections, and there was good consistency between anoma-lies detected by IP and RS and SP method. To check theefficiency of CRSP and in comparison with dipole–dipolearray, in the location of profile no. 6, a profile with thedipole–dipole array was designed and surveyed. Finally,by integration of the results from the geoelectrical methods,some locations were suggested for borehole drilling. Afterdrilling in those locations, cores were studied and comparedwith the results obtained from the geoelectrical methods thatresulted in confirmation of the geoelectrical findings. The

results obtained by the CRSP array have a match better thanthe drilling results.

Keywords Integrated geoelectrical methods . CRSP array .

Manganese deposit . Marand . Iran

Introduction

Manganese is one member of the ferrous metals group withincreasing importance in recent years, due to the expansionof steel industry that led it to be considered as a strategicmetal. Its application is increasing especially in metallurgi-cal engineering for production of various alloys that resultedin deprivation of its shallow and high-grade deposits andencouraged prospecting and exploration of its deep and low-grade deposits.

Exploration of manganese, especially sedimentary typedeposits, accompany with many problems (Hood 1979).Because of deferent behavior of manganese in various geo-chemical environments, the application of geochemicalmethods in manganese deposit exploration is accompaniedwith limitations (Force and Maynard 1991). However, thereis no standard geophysical method for manganese (Mn)deposit exploration. Due to these problems, new applicablemethods especially geophysical methods have been of in-terest for mineral prospectors.

Aeromagnetic survey can be used to define broad terrainspermissive for the presence of this deposit type. Because ofan association between some sedimentary manganesedeposits and iron formation, most iron formation has adistinct, positive magnetic contrast with surrounding rock(US Geological Survey and Corporación Venezolana deGuayana, Tecnica Minera 1993). For example, airborneelectromagnet was used in the exploration of the Groot

H. Ramazi :K. Mostafaie (*)Department of Mining & Metallurgical Engineering,Amirkabir University of Technology (Tehran Polytechnic),Tehran, Irane-mail: Kamran_m@aut.ac.ir

K. Mostafaiee-mail: k.mostafaei@gmail.com

H. Ramazie-mail: Ramazi@aut.ac.ir

Arab J GeosciDOI 10.1007/s12517-012-0537-2

Island Mn deposit (Richard and Harald 2000). Geoelectricalmethod is less applicable for the exploration of Mn deposits;nevertheless, the self-potential (SP) method proved success-ful in suitable environments (Force et al. 1999). The appli-cation of geophysical methods in the exploration ofmanganese can be related to Jensen (1954), Bhimasankaram

and Rao (1958), Rao and Sinha (1957), Brown and Evans(1989), Morey (1990), Goankar et al. (2001), and Murthyet al. (2009).

In Iran, magnetometry methods were applied as tradition-al method for the exploration of Mn deposits, and othergeophysical methods were not widely used in Mn prospec-ting. There are few investigations about the application ofgeophysical methods in exploration of manganese in Iran.For example, we can refer to the study of Yosefi and Ramazi(1992) and Samadi and Mehrabi (2004).

In all discussed studies, geoelectrical methods are usedeither as subsidiary methods or not used. Due to mentioneddebates in this paper, we present the application of integra-tive geoelectrical methods including resistivity, self-potential, and induced polarization in the exploration ofMn deposits. The aim is to check the applicability of thementioned methods to obtain some information about exis-tence, shape, and depth of the mineral bodies.

Study area

The study area is located in the northwest of Iran, easternAzerbaijan, and 17 km north of the Marand City. The centralpoint of area could be assigned by 45°42′40″ E and 38°35′40″ N coordinates (Fig. 1).

From regional geological point of view, the study area isin a magmatic zone named the Uremieh–Dokhtar volcanicbelt. The area is composed of several geological formationsof tuffs and pyroclastics in the southwest and west, sand-stone with marls in the west, gypsiferous marls in the center,moderately consolidated conglomerates with volcanic peb-bles in the north, and limestone in the northeast. Mineral

Fig. 1 Location and geological map of the study area in Iran

Fig. 2 Map locations of surveyprofiles

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bodies (mainly sulfides) occurred as veins and dikes. In thecentral part of the area, the geological formations are par-tially covered by gravels and soils (Fig. 1). From topograph-ical point of view, the area could be divided into two parts.The northern part is more or less flat and the other parts aremountainous with complex topography.

Geophysical methods

Integrated geophysical methods are commonly used in min-eral exploration to obtain qualified results (Gautneb andTveten 2000). Uncertainties of the occurrence, association,depth, shape, and quality which are usual with metamorphicdeposits have led to the application of geophysical methods(Murthy et al. 2009). Selection of geophysical method(s) tobe applied in a mineral deposit exploration depends on thephysical properties of the target and its accompanied rocks,geological setting, and even its topography. An integrationof a few methods is necessary in many cases in order toachieve more certain result.

In the Marand manganese deposit, due to geologicalsetting, the topography of the area and low resistivity of

the mineral bodies, an integration of geoelectrical methodsincluding SP, induced polarization (IP), and resistivity (RS)were used.

Survey design

As mentioned before, the goal of this study was to test theapplicability of the mentioned methods in the exploration ofmineral bodies. In this manner, a profile (the first profile,P1) was assigned for SP surveying along a direction onwhich several small outcrops of the mineral bodies exist(Fig. 2). In the first step, SP was surveyed along this profilewith interval points of 5 m. The length of this profile wasabout 350 m. A reference electrode (N electrode) was em-bedded in limestone outcrops expecting a value low of theSP, 400 m far from the profile.

After surveying this profile, the acquired SP data wereprocessed and interpreted. The results show that in the outcroppositions, the magnitude of SP value (negative) is high, and insome cases, it increases to more than −250 mV (Fig. 3).

On other words, the recorded SP anomalies have a goodaccordance with the mineral body outcrops. It means that theSP method could be used to detect the manganese minerals, asa primary tool. From this point of view, we decided to surveysome other SP profiles. Accordingly, four other profiles weredesigned and surveyed in the western part of the study area(Fig. 2). The purpose of these surveys was to evaluate theapplicability of SP method in the detection of probable hiddenanomalies in this area. Measuring point intervals was 5 m inall profiles. Totally, 350 points were surveyed.

Nine profiles were designed for resistivity and inducedpolarization surveying (Fig. 2). Profile nos. 1, 4, 6, and 7(P1, P4, P6, and P7 in Fig. 2) were considered along themineral vein outcrops and/or positions with high SP values.The other profiles were surveyed in geologically potentialpoints of mineral vein existence.

To compile resistivity and chargeability pseudo-sectionalong the assigned profiles, we used combined resistivity

Fig. 3 SP variation along profile 1

Fig. 4 Survey point in CRSParray

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sounding and profiling (CRSP) electrode array (Fig. 4). Thisarray was introduced in 2005 by Ramazi. By this array, threevertical electrical soundings are surveyed by a set of spreadingcurrent electrodes which normally is used for one VES. In thisarray, the distance of measuring points is equal to spacing ofthe potential electrodes (Q2p20P2P10P1Q1, Fig. 4).

The CRSP array has successfully been applied to manymineral deposit exploration and site investigation projects.Some of them are as follows: geoelectrical study in the DehHossain aquiriferous silica deposit in Arak (Ramazi 2005b);the application of geoelectrical methods in the Khonik(Ghaen, Iran) copper deposit exploration (Ramazi andMostafaie 2010); application of geoelectrical methods in theNarestan (Saveh, Iran) copper deposit exploration (Ramaziand Mostafaie 2011); and the application of geoelectricalmethods for underground sinkhole detection in foundationsof the Sattary U turn bridge in Abshenassan Highway, Tehran(Ramazi et al. 2010).

The data obtained by this array could be processed andinterpreted as sounding curves and/or data required forcompiling pseudo-sections simultaneously. This array pro-vides continuous data laterally and in dip direction. Incomparison to pseudo-sections which resulted from the oth-er arrays such as dipole–dipole, geological bodies, especial-ly high angel ones, are identified more clearly.

In the profiles P1, P2, P4, P6, and P7, measuring pointintervals were assigned 5 m for current electrode distances(AB) from 25 to 150 m. For AB shorter than 25, the distanceof each couples of the potential electrodes was decreased to2 m, and each one of the sounding point was separatelysurveyed. In the profiles P3, P5, and P8, electrode spacingwas 10 m. In the CRSP array; electrode spacing was select-ed identical to vein dimensions. Moreover, electrode spac-ing of 10 m was used in profile nos. 3, 5, and 8. Most of theprofiles selected were coincident on outcrops. The positionand shape of the surveyed IP and RS profiles were shown inFig. 2. This system has the ability to simultaneously surveyIP and RS in a point.

The distance of survey points is equal to the spacing ofpotential electrodes, and for all current lines, the electrodespacing for potential electrodes remains constant. For ex-ample, with receiver electrodes spacing of 5 m in thismethod, the current line of 25 to 150 m has been usedsuccessfully to study a silica dike. In comparison with otherarrays such as the dipole–dipole, this array has a smallerarray index that will reduce the error of calculated resistivityvalue and makes it possible to investigate more depth. Also,to check the efficiency of CRSP and comparison with dipole–dipole array, in the location of profile no. 6, a profile withdipole–dipole array was designed and surveyed.

Self-potential data

The SP data were processed and the results are presented as SPvariations along the profiles in Figs. 3, 5, 6, 7, and 8. Toidentify sharp anomalies, the SP magnitudes less than−150 mV have been taken into account. Of course, SP valuesless than −100 mV could be considered as detected anomalies.

SP1 The results extracted from profile SP1 is presented inFig. 3. As it is shown in the figure, five SP anomalieshave been recorded. Two of them are very sharp (less

Fig. 5 SP variation along profile 2

Fig. 6 SP variation along profile 3

Fig. 7 SP variation along profile 4

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than −250 mV) and the others are more or less sharp.One of the very sharp anomalies is located in a dis-tance of 40 m, and the second one is situated in a 190-m distance from the beginning of the profile.

SP2 Variation of self-potential along this profile is illus-trated in Fig. 5. There is not any mineralized bodyoutcrop along this profile. As it could be distin-guished in Fig. 5, no considerable anomaly is

recorded in this profile and SP changes are in therange of background of various rocks.

As could be found in Fig. 5 and in other SP figures,in a few cases, the recorded SP is plus (+). It meansthat the reference electrode has been placed in alocation on which SP is not zero.

SP3 This profile was surveyed along a nearly W–E direc-tion in the southwest of the study area (Fig. 3). Also inthis profile, there is no outcrop of the mineralizedbodies. The obtained results are presented in Fig. 6.As it is apparent in this figure, although few incon-siderable anomalies were detected, no important SPanomaly has been recorded along this profile.

SP4 This profile was surveyed nearly in the central part ofthe study area (Fig. 2). In this profile, there is nooutcrop of the mineralized bodies. The results areillustrated in Fig. 7. As shown in the figure, SPvariation is in a range of the background and noconsiderable SP anomaly has been recorded alongthis profile.

SP5 This profile was surveyed in the northwestern part ofthe area, along a S–N direction, and crosses the pro-files of SP4, SP2, and P9 (Fig. 2). A graph of the SPchanges along this profile is presented in Fig. 8. As

Fig. 9 Pseudo-section no. 1prepared in the line P1

Fig. 8 SP variations along profile 5

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could be seen in this figure, SP is in the range ofbackground values and no any anomaly is observed.

To check the results of SP studies for the possibility ofexistence of the mineralized veins, some short profiles (e.g.,P9, Fig. 2) were designed to be surveyed by the IP and RSmethods. Results of the IP and RS studies did not lead torecord any remarkable anomaly.

Evaluation of SP studies

As it was mentioned, the aim of the SP surveys was toevaluate the applicability of this method to detect probablehidden Mn anomalous.

A review of the results extracted from SP measurementsshows that all of the existed ore bodies were detected by themethod. In other words, all mineralized zones have

Fig. 10 Pseudo-section no. 4prepared in the line P4

Fig. 11 Pseudo-section alongP6 by CRSP array (IP)

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produced large values of SP less than −150 mV. On the otherhand, in locations with low SP magnitude, no anomaly wasrecorded by RS or IP surveying.

Some moderate magnitudes of SP which seems to belongto thin and very thin geological bodies were recorded. But,these anomalous were not detected by RS or IP measure-ments. It can be due to two reasons: first, the existence ofvery thin veins, too thin to be detected by the applieddistance of potential electrodes in IP and RS surveys, andsecond, SP noises or false anomaly.

The evaluation of SP surveys leads to conclude: SPmethods can successfully be used in this type of manganesedeposit exploration. Of course, it is understood that SPmethods are applied as primary methods to get some generalidea about the targets. This general idea can be used tooptimize the design of RS and IP profiles. High velocityof SP surveys, low expenses, and easy processing andinterpretations are also the other advantages of this method.

Resistivity and induced polarization

As it was mentioned, resistivity and induced polarizationmethods were applied to get some information about exis-tence, depth, and shape of the probable ore bodies.

Therefore, in accordance with the SP results, a few profileswere designed and surveyed by these methods (Fig. 2). TheRS and IP data were processed and appropriate pseudo-sections were compiled (Figs. 9, 10, and 11). For the inves-tigation of several locations for mineral veins and theirspread and depth, IP and RS profiles were designed andsurveyed (Figs. 9, 10, and 11).

Data obtained from these surveys were processed and IPand RS pseudo-section in length survey profiles was com-piled. The important problem in this case is to distinctboundaries of anomalies that needed geological considera-tions and experiences. After compilation of several types ofdata such as drilling and geology, the model was preparedfor individual anomalies. Values higher than 18 mV/V wereconsidered as anomaly. Values higher than 24 were consid-ered as good anomaly and values lower than 18 were con-sidered as background. This IP values are in correlation with5–10 and 10–15 in resistivity.

Description some of the IP and RS pseudo-section

Pseudo-section no.1 This pseudo-section was prepared inline P1 by length of 15 mm and strike of N–S. This line waslocated on one outcrop of the deposit and its strike was

Fig. 12 Pseudo-section alongP6 by dipole–dipole array (IP)

Fig. 13 Pseudo-section alongP6 by CRSP array (RS)

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perpendicular to the veins. As it is shown in Fig. 9, a vein inthe middle of profile can be distinguished with IP value upto 18 mV/V. In the depth of 20 to 30 and in depth lower than45 m, the IP value in the core of these veins may reach to24 mV/V that is regarded as a good anomaly and indicatethat vein has high-grade interbeds. This anomaly was some-what obvious in RS pseudo-section.

Pseudo-section no. 4 This pseudo-section was prepared inline P4 by 15 m length and maximum current line of 100 m.In this profile, there is a limestone outcrop but mineraliza-tion does not occur in this location. In this pseudo-section,an anomaly in the depth of 20 m in the middle of the profilecan be distinguished (Fig. 10).

Pseudo-section no. 6 This pseudo-section was prepared inline P6 with length of 60 m and maximum current line of100 m and strike of NE–SW. As can be seen in Fig. 11, threeanomalies are distinguishable with high IP value. The sharp-est one belongs to a mineralized body that has a smalloutcrop on the surface. These anomalies are demonstratedin RS pseudo-section by resistivity of about 10 to 15 4

(Fig. 13). Four shallow boreholes were drilled in this area to

investigate the geophysical anomalies that are shown withsymbol B on this profile (Fig. 15). Along other profiles, areasof mineralization were detected as anomalous by IP and RSmethods. To compare the results obtained by CRSP array withthe results of dipole–dipole array, the profile 6 was alsosurveyed by the dipole–dipole array. The obtained results bythese two arrays are compared in Figs. 11, 12, 13, and 14.

IP and RS evaluation

The IP results in this area were promising and favorable. Thismethod separated background and anomaly values very welland detected major veins and their interbeds. This method israther sensitive to ore mineralization and grade than to otherfactors such as ore weathering and fracturing. As mentionedbefore, the results of this method were confirmed by thedrilling. Although the results of RS are not promising as theIP, its finding can be worth full along with the IP results.However, RS results depend on other geological factors(e.g., oxidation and/or the presence of pyroclastics that haslow resistivity and occurs among limestone layers that do havenot manganese and their IP values are low).

Fig. 14 Pseudo-section alongP6 by dipole–dipole array (RS)

Fig. 15 Result of drilling alongP6

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Drilling results

After the termination of geophysical operation and interpre-tation, and integration of the obtained data with geologicinformation, 13 boreholes were drilled in the study area(Fig. 16). These boreholes were drilled by a drill wagondown to a depth of 10 m. Some of them were drilled near tothe outcrops and others on the anomalous localities detectedby the geophysical pseudo-section. Along all boreholes,powders were sampled and analyzed. In the most cases,the results of sampling confirmed the geophysical anomaliesespecially the IP anomalies. For example, in the boreholeB1 (Fig. 11) in the depth of about 1 m and lower, the gradeof Mn was significantly high. A sharp anomaly of IP (andSP) was recorded in this location. The result of drillingalong profile no. 6 is shown in Fig. 15.

Conclusion

In the outcrops, the SP method shows remarkable anoma-lies. However, some SP anomalies do not relate with min-eralization. SP can be used in the first stage of explorationfor optimization of other geophysical methods because oflow cost and high speed of SP surveying.

Induced polarization method proved to be accurate in theseparation of limestone layers from background and separa-tion of manganese interbeds from limestone. In some of thepseudo-sections, manganese veins were clearly separatedfrom background and this was confirmed by the drillingresults.

The results of resistivity methods in most cases are incoordination with the IP results; however, in some cases,

this coordination is reduced because of RS dependence onother factors of manganese mineralization. These factorsmay be related to the presence of pyroclastics that havelow resistivity and occurs among limestone layers that donot have manganese and their IP values are low.

In comparison to other arrays, the CRSP provided greateraccuracy and speed and led to much better results especiallyin high angle mineralized veins. On the other hand, readingerror is much less than other arrays due to its array factors,and this helps to study deeper anomalies than other arrayssuch as the dipole–dipole.

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