Contribution of Geophysics to the Study of Barite Mineralization in … · profile of Fig. 9j, the...

자원환경지질, 제53권, 제3호, 259-269, 2020Econ. Environ. Geol., 53(3), 259-269, 2020http://dx.doi.org/10.9719/EEG.2020.53.3.259

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Contribution of Geophysics to the Study of Barite Mineralization in the

Paleozoic Formations of Asdaf Tinejdad (Eastern Anti Atlas Morocco)

Dakir Ibrahim1, Benamara Ahmed2, Aassoumi Habiba1, Ouallali Abdessalam1 and

Ait Bahammou Youssef3

1Lab: environmental geology and natural resources, Cartography and Digital Technologies team, Department ofGeology, Faculty of Science, Abdelmalek Essaadi University, Tetouan. Morocco2Applied Geophysics and Modeling in Geoenvironment Department of Geology, Faculty of Science and Techniques,Errachidia Moulay Ismail University3Laboratory of Geophysics and Natural Risks Department of Geology, Faculty of Sciences, Rabat, Mohammed VUniversity(Received: 26 October 2019 / Revised: 28 October 2019 / Accepted: 04 June 2020)

The use of the geophysical method in mining prospecting has been studied in the Asdaf region (South-East of

Morocco). The objective of the study is to examine the aptitude of the electrical technique, in this case induced polar-

ization (IP) and electric tomography, combined with the electromagnetic method (VLF), in the exploration of barite . The

result obtained by the pseudo-sections of electrical tomography and that of KH filtration highlighted anomalies of resistant

contact (greater than 400Ω.m) and of high charge chargeability (5mV / V). These contacts are hosted in less resistant

Devonian age shale and sandstone. The resistivity response obtained at their level is characteristic of the venous structures

associated with barite mineralization. The direction of the mineralized veins is parallel to the direction of the fractured

zones (NE-SW), which indicates that the mineralization in place is due to the tectonic movements of the Hercynian orog-

eny (from Devonian to Permian). These veins are aligned with the locations of abandoned mine shafts and with surface

mining areas. Geophysical technique therefore seems to play a key role in barite mining exploration.

Key words : electrical method, electromagnetic method, Eastern Anti Atlas, Paleozoic, resistant anomaly, mineralized

veins, barite

1. Introduction

The region of Asdaf is located southwest of the

town of Tinejdad in the extreme north of the Ougnat

massif. The region is a depression, characterized

as a whole by the outcrop of Quaternary formations

that cover the Silurian and Devonian formations.

The measurement procedure consists of the

introduction of an electrical tomography whose

purpose is to highlight an image of the subsoil

according to sections of electrical resistivity. In order

to confirm the location of the different contacts

encountered, we also provided measurements in

induced polarization (IP). The depth of the soil

prospected by the measurement profiles is about

57 m approximately, in order to confirm the passage

of the mineralized zones, we realized electric

trainings, and electromagnetic profiles, which will

be used for the realization of the maps at the level

of the prospected area. Resistivity and chargeability

are well-known geophysical methods, and are

traditionally applied to mineral exploration (Dakir

et al. 2019; Djroh S.P. 2014; Florsch N. et al.

2017) and in environmental studies, is often used

260 Dakir Ibrahim et al.

to delineate contaminant plumes and geological

boundaries (Elis V. R. et al. 2016; Aristodemou and

Thomas-Betts 2000; Baines et al. 2002; Bernstone

et al. 2000; Blondel 2014). The VLF-EM method

is widely used for the detection of buried conductive

targets, including Ait Bahammou et al. (2019)

aquifer faults systems. This method is applied in

the Mining Prospective (Fisher 1983) and (Usman,

A.O 2014).

2. Geological Context

The study area is part of the Eastern Anti-Atlas

which is limited to the East by Hamada of Guir, to

the South by that of Kem-Kem, to the West by the

basin of Tazzarine and to the North by Cretaceous

and Tertiary basins of Errachidia Boudenib and

Ouarzazate. The axis of this chain is occupied by

lands of Saghro and Ougnat.

The study area is a depression formed mainly by

Quaternary soils, this zone is limited to the north

by the outcrop of Carboniferous formations (Jbel

Asdaf) and by the Ordovician formations to the

South (Fig. 1).

The structure of this region was made during the

early Paleozoic and then during the Hercynian

cycle. It constitutes the foreland of the Hercynian

chain. Thus, the formations of the study area are

affected by a set of faults (Fig. 2) of direction

generally EW to NE-SW inherited periods of rifting

Fig. 1. Geological map of the study area (Dainelli P. et al., 2007).

Fig. 2. The structural map of the Eastern Anti-Atlas (Charles Robert-Charrue 2006).

Contribution of Geophysics to the Study of Barite Mineralization in the Paleozoic ... 261

(Cambro-Ordovician, Devonian middle-upper) and

which were reactivated in inversion during the

Hercynian Orogeny. The corresponding reefs in

recess or in reverse fault are at the origin of the

generally open folds that one meets in the Paleozoic

cover of the massif (Baidder et al., 2011).

3. Methodology

3.1. Electrical Method

The electrical method is based on the injection

of a direct current into the ground and the measure-

ment of the electrical potential generated between

two receptor electrodes located on the surface. To

characterize the structure of the subsoil, it is

necessary to measure the electrical resistivity and

chargeability. The device used is Winner’s (Fig. 3).

The electrical resistivity and the chargeability

are calculated by the two formulas (1.1) and (2):

(1.1)

With K is the geoelectric coefficient that depends

on device used

(1.2)

(2)

3.2. Electromagnetic Method

The electromagnetic method makes it possible

to measure the conductivity of the medium by the

use of electromagnetic fields. Direct contact with

the soil is not necessary: this method is quick to

implement and can cover large areas (McNeill 1980).

The very low frequency electromagnetic method

(VLF-EM) is based on the use of radio waves

between 15 and 30 kHz (Müller et al., 1984). The

primary magnetic field Hp emitted by the VLF

stations can be captured by the VLF instruments

(Fig. 4). When a conductive element is traversed

by an electromagnetic field Hp, an induced current

(eddy current) passes through it and produces a

secondary magnetic field Hs phase-shifted with

Hp, oriented in any direction (McNeill and Labson,

1991). The two components are calculated by the

two equations (Saydam 1981).

(3)

(4)

In order to have effective electromagnetic measure-

ments, we used two filters using KHFFILT software:

The Karous and Hjelt (KH) filter that applies to

the real component. This filter makes it possible to

establish apparent current density cross-sections

showing the driver’s response at depth (Karous

and Hjelt 1983). Qualitatively, it is possible to

distinguish the conductive anomalies from the

resistances by using a cross-section of the apparent

current density (Karous et al. 1977), where a high

positive value corresponds to a conductive structure

and low negative values corresponds to a resistant

structure (Benson et al. 1997; Sharma and Baranwal,

2005).

The Fraser filter has also been applied to the real

component and presented as a contour map. As a

ρa KΔV

I--------=

K2π

1

AM---------

1

BM---------–

1

AN--------

1

BN--------+–

-----------------------------------------------=

m1

V0

------ Vt t( ) td

a

b

∫=

τ Re Hp⁄=

ε Im Hp⁄=

Fig. 3. Principle of winner device.


result, the real filtered component will always have

a positive peak above an anomaly zone (Fraser1969).

4. Results and Discussion

To achieve the objective of highlighting the

different heterogeneities of the soil prospected and

to determine the location of the mineralized veins

(barite), we realized 2 profiles of electrical tomogra-

phy (induced polarization and electrical resistivity),

4 horizontal electrical profiles and 10 electromagnetic

lines, which are located on the map of (Fig. 5).

4.1. Electrical prospecting

The profiles are made over a length of 320 m

and are oriented slightly in a NW-SE direction.

The results of the study are presented in the form

of inverse models of electrical pseudo-sections (2-

D). These resistivity models generally have mean

square errors (RMS) varying from 0.1 to 2%,

which reflects the degree of adjustment between

the calculated data and those obtained in the field,

and subsequently improves the use of these models

to analyze and interpret them later. The models

representing the abnormally high resistivity and

Fig. 4. Principle of low frequency and near field electromagnetic methods (Chouteau M. and Giroux B. 2008).

Fig. 5. location of the geophysical profiles made on the map extracted by Google Earth.


chargeability contacts were distinguished from the

rest of the zones investigated. Their resistivity

varies from 300 to more than 500 Ωm. Figure 6

represents the typical inverse model of these

identified anomalies. In fact, two large resistant

anomalies in symmetrical mound form (> 500 Ωm)

were located to the northwest and southeast of the

pseudo-section. These two resistant anomalies are

Fig. 6. Model 1 in pseudo-correlative sections of chargeability results a) and those of apparent resistivity b).

Fig. 7. Model 2 in pseudo-correlative sections of chargeability results a) and those of apparent resistivity b).


located at distances of 80 and 240 m respectively

from the start of the profile, with a depth of 30 to

32 m and an average thickness of around 3 m. The

base of the structure extends beyond 34 m, which

probably suggests the continuity of the mineralization

at depth. These resistant contrasts present gradual

variations in the color scale linked to a zonation

probably distinct from the mineral content. This

response reflects the presence of a vein-like structure

to which the mineralized barite veins have been

assigned. Figure 7 shows the presence of a resistant

contact anomaly (500 Ωm), of chargeability greater

than 5mv / v, located in the middle of the profile,

it probably corresponds to the passage of another

possible mineralized vein.

The map of Fig. 8 reveals the presence of two

faults located in the northern part of the east map

and having a general direction NE-SW, and suggests

the presence of three deferent zones: The first one

appeared resistant is situated in the NNW part of

the map, this zone is characterized by important

values of the resistivity around 350 Ohm-m, these

values are attributed to the outcrop of the sandstones

and the passage of the veins in barite. The second

zone is located in the middle of the map, the values

of the resistivity vary between 100 and 200 Ohm-m,

these values are explained by the establishment of

quaternary alluvium which becomes thicker towards

the SE part of the map. And the third zone with

low resistivity located in the SSE part of the map,

with a value of less than 100 Ohm-m due to the

thickening of quaternary alluvial formations and

the presence of a water accumulation zone.

Fig. 8. Apparent resistivity map at the Asdaf area.


4.2. VLF Data Filtering and Qualitative

Interpretation

The pseudo sections of Fig. 9a and Fig. 9b show

that the terrain appeared very homogeneous and

slightly resistant, the current density value is varied

between -10 and 10. The appearance of the pseudo-

section Fig. 9c suggests significant variations, in

the middle at a distance of 300m the ground appeared

resistant (below -10) this zone is continuous at

depth up to 60m at the end of profile, at a distance

Fig. 9. Apparent Current density cross section plots of real component data against distance, from all VLF line.


of 450m a conductive zone is encountered due to

the passage of a fractured zone. For the profile of

Fig. 9d which appeared heterogeneous shows the

presence of a zone of fracture anomaly at the

beginning of profile at a distance of 10m this

fracturing is limited in surface. The pseudo section

Fig. 9e highlights 3 conductive anomalies the first

is spotted at a distance of 100 meters this anomaly

is becoming more important at depth (60m), the

second anomaly is located deep at a distance of

300m from the beginning of the profile and the last

conductive zone is located on the surface. For

Fig. 9f and Fig. 9g, the profiles show significant

variations in apparent current density, the ground

is marked by 4 conductive zones (greater than 40)

which are successively located at 50m, 150m, 250m,

and 400m, these zones are probably attributed to

the passage of fractures, this profile also suggests

resistant zones located in the middle of the profile

which will be attributed either to the barite vein or

to sandstone formations of Devonian and Silurian

age. For the profile of the Fig. 9h appears hetero-

geneous, the shape of this profile will allow us to

identify 4 zones of conductive anomalies that are

located successively at a distance of 100m, 200m

350m and 500m these anomalies are observed on

the surface. With regard to the pseudo-section of

the (Fig. 9i) it signs the presence of 5 zones of con-

ductive anomalies which are marked successively

at a distance of 75m, 125m, 300m, 350m and 400,

these values are always attributed to the passage

accumulations of alluvial formations. For the last

profile of Fig. 9j, the latter shows a strong hetero-

geneity, the values of the apparent current density

are negative and positive, for the negative resistance

encountered at the beginning and in the middle of

the profile is really related signal of the sandstone

formations and the passage of a mineralized zone,

then for the positive anomalies they are attributed

to the passage of the fracturing. Finally, after

appreciating the qualitative interpretations of the

pseudo-sections obtained in the Asdaf zone, the

latter allowed the resistant zones attributed to the

passage of the baryte veins and the conductive

zones that are attributed to the passage of the zones

to be well located. fractured.

The structural analysis of geophysical anomalies

allowed us to identify a set of faults crossing the study

Fig. 10. Fraser filtered contour map of real component from 10 VLF lines.


area. The stereographic processing of geometrical

properties of these structures has highlighted two

major fault families; NE-SW (N30-50) and ENE-

WSW (N60-90), in addition to some N-S direction

of fractures and ESE-WNW (Figure 11a), their dip

is vertical to sub-vertical (Figure11b) .The majority

of mineralized veins identified by geophysics,

whose dip is also almost vertical (Figure 12b) have

an EW orientation along the fault planes. The

other veins are slightly NE-SW and ESE-WNW

oriented. This trend is confirmed by the stereographic

projection of all the alignments of the resistant

geophysical anomalies (Figure 12a).

Mineralization occurred and developed at the level

of deep faults under the effect of hydrothermal

movements in relation to the Hercynian orogeny.

The relatively conductive areas located in their

vicinity are attributed to the presence of superficial

secondary fractures occupied by conductive alte-

rations.

5. Conclusion

The combination of electrical methods and the

VLF electromagnetic method has proven to be

more effective and more suitable for characterizing

the importance and the placement of mineralized

veins in relation to the structural system in the

Asdaf region.

The geophysical study highlighted the presence

of resistant (300 to 500 Ω.m) and loadable (greater

than 8mV / V) electrical anomalies, the average

Fig. 12. A. Directional rosette of the veins. B. Associated stereogram.

Fig. 11. A. Directional rosette of faults. B. Associated stereogram.


depth of which can reach up to 30 m. The anomalies

identified are attributed to the barite mineralized

veins whose alignment is oriented in direction E-

W to NE-SW parallel to the faults that affected the

anti-Oriental Atlas. Their development depends on

the degree of alteration of the structures in place.

The deep filling of these barite faults occurred by

the circulation of hydrothermal fluids during the

Hercynian orogeny and after the host formations.

These veins are aligned according to the locations

of the mining shafts which are either abandoned or

still in operation and exploited by artisanal open-

cast miners. This therefore confirms the importance

that the technique can play in orienting and improving

the cost of barite exploration and extraction.

Conflict of Interest Statement

On behalf of all authors, the corresponding author

states that there is no conflict of interest.

Data Availability

The data used to support the findings of this

study are available from the corresponding author

upon request.

Disclosure

This research did not receive any financial support.

References

Ait Bahammou, Y., Benamara, A., Ammar, A. and Dakir, I.(2019) Fracture zones detection for groundwater explo-ration integrating Resistivity Profiling and Very LowFrequency electromagnetic methods (Errachidia basin,Morocco). Contributions to Geophysics and Geodesy,v.49/2, 2019 p.181-194.

Aristodemou, E. and Thomas-Betts, A. (2002) DC resis-tivity and induced polarization investigations at a wastedisposal site and its environments. Journal of AppliedGeophysics, v.44, n.2-3, p.275-302, 2000. Baines et al.

Baidder, L., Michard, A. and Saddiqi, O. (2011) New geo-logical and mining guide books of Morocco. Notes andMemoirs of the Geological Service, v.2, p.47-111.

Baines, D., Smith, D. G., Froese, D. G., Bauman, P. andNimeck, G. (2002) Electrical resistivity ground imaging(ERGI): a new tool for mapping the lithology and geom-etry of channel-belts and valley-fills. Sedimentology,v.49, n.3, p.441-449.

Benson, A. K., Payne, K. L. and Stubben, M. A. (1997)Mapping groundwater contamination using DC resis-

tivity and VLF geophysical methods–A case study.Geophysics, v.62, n.1, p.80-86. doi: 10.1190/1.1444148.

Bernstone, C., Dahlin, T., Ohlsson, T. and Hogland, H.(2000) DC resistivity mapping of internal landfill struc-tures: two pre-excavation surveys. Environmental Geol-ogy, v.39, n.3-4, p.360-371,

Blondel, A. (2014) Development of electrical geophysicalmethods for the characterization of sites and soils pol-luted with hydrocarbons [doctoral thesis], UniversityMichel de Montaigne.

Chouteau, M. and Giroux, B. (2008) Applied GeophysicsII: Electromagnetic Methods, Lecture Notes. Polytech-nic School of Montreal.

Dakir, I., Benamara, A., Aassoumi, H., Ouallali, A. and AitBahammou, Y. Application of Induced Polarization andResistivity to the Determination of the Location of Met-alliferous Veins in the Taroucht and Tabesbaste Areas(Eastern Anti-Atlas, Morocco) Hindawi. InternationalJournal of Geophysics Volume 2019. Article ID 5849019,11 pages https://doi.org/10.1155/2019/5849019.

Dainelli, P., et al. (2007) DIR. GEOL. MAROC. Geologicalmap of Morocco at 1 / 50.000 Taroucht Explanatorynote. Notes and Mem. Serv. Geol Morocco NH-30-XIX-2d.

Djroh, S. P. (2014) Geophysical studies of the copper-nick-eliferous platinum-Samapleu deposit. 3D modeling testby interpretation of magnetic and electrical data. Thesisof Doct., Univ. Félix Houphouet-Boigny, Ivory Coast,176p.

Elis, V. R., Ustra, A. T., Hidalgo-Gato, M. C., Pejon, O. J.and Hiodo, F. Y. (2016) Application of induced polar-ization and resistivity to the environmental investigationof an old waste disposal area. Journal of EnvironmentalEarth Sciences, v.75, n.20, article 1338.

Florsch, N., Feras, A., Bonnenfant, J. and Camerlynck, C.(2017) Induced polarization, a geophysical tool for thespatialisation of slag clusters for the estimation of ironand steel production. Arche-Sciences, v.2, n.41-42,p.23-33, 2017.

Fischer, G., Le Quang, B. V. and Muller, I. (1983) VLFGround Surveys, a Powerful Tool for the Study of Shal-low 2-D Structures. Geophys. Prosp., v.31, p.977-991.

Fraser, D. C. (1969) Contouring of VLF-EM data. Geo-physics, v.34, n.6, p.958-967. doi: 10.11 90/1.1440065.

Karous, M. and Hjelt, S. E (1977) Determination of appar-ent current density from VLF measurements: report.Department of Geophysics, University of Oulu, Finland,Contribution No.89, p.19.

Karous, M. and Hjelt, S. E. (1983) Linear filtering of VLFdip-angle measurements. Geophys. Prosp., v.31, n.5,p.782-794. doi: 10.1111/j.1365-2478. 1983.tb01085. x.

McNeill, J. D. (1980) Electromagnetic terrain conductivitymeasurements at low induction numbers. – TechnicalNote, TN-6. Geonics Ltd.

McNeill, J. D. and Labson, V. F. (1991) Geological map-ping using VLF radio fields. In: Nabighian M. C. (Ed.):Electromagnetic Methods in Applied Geophysics: Volume2, Application, Parts A and B. Society of ExplorationGeophysicists, 521-640. doi:10. 1190/1.9781560802686.ch7.

Mûller, I., Gibert, J. and Laurent, R. (1984) Application ofgeophysical, electromagnetic VLF (Very Low Fre-quency) and micro-seismic methods to the study of the


karst of Dorvan Cleyzieu (Southern Jura, France)). Bul-letin of the Hydrogeology Center, 5, 3, University ofNeuchâtel, Center for Hydrogeology, 145-162 (in French).

Robert-Charrue, C. H. (2006) Structural Geology of theEastern Anti-Atlas, Morocco [doctoral thesis], NeuchâtelUniversity.

Saydam, A. S. (1981) Very low frequency electromagneticinterpretation using tilt angle and ellipticity measure-ments. Geophysics, v.46, 1594e1606.

Sharma, S. P. and Baranwal, V. C. (2005) Delineation ofgroundwater-bearing fracture zones in a hard rock area

integrating very low frequency electromagnetic andresistivity data. J. Appl. Geophys., v.57, n.2, p.155-166.doi: 10.1016/j.jappgeo.2004.10.003.

Usman, A. O., Omada, J. I. and Omali, A. O (2014) Appli-cation of Vlf-Em Geophysical Method in DelineatingPb-Zn Mineralization in Ishiagu Area, Ebonyi State,Nigeria, IOSR Journal of Applied Geology and Geo-physics (IOSR-JAGG), e-ISSN: 2321-0990, p-ISSN:2321-0982. Volume 2, Issue 4 (Jul-Aug. 2014), PP 38-46.

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