2-D Resistivity and Induced Polarization (IP) Methods for Iron Ore Exploration

2-D Resistivity and Induced Polarization (IP) Methods for Iron Ore Exploration

Rosli Saad Senior Lecturer (Dr.), Geophysics Section, School of Physics, Universiti Sains  Malaysia, Penang, Malaysia; email: email: [email protected]

Ahmad Sayful Mohamad Undergraduate Student, Geophysics Section, School of Physics, U niversiti Sains  Malaysia, Penang, Malaysia; e-mail: e-mail: [email protected]

Imran Adli Undergraduate Student, Geophysics Section, School of Physics, U niversiti Sains  Malaysia, Penang, Malaysia; email: email: [email protected]

ABSTRACT 2-D Resistivity and Induced Polarization (IP) methods are some of the few geophysical methods applied in subsurface study to assess the potential of iron ore exploration. Four survey lines with a total length of 4km were conducted using Pole-dipole array with minimum 5m electrode spacing. Results are presented in resistivity and chargeability inversion models form. The results of the study showed that the area is underlain by thick colluviums with resistivity and chargeability values of 10-300 Ωm and 0.1-3msec respectively. The result also suggests that the colluviums were expected to cover a depth of up to 150m.

KEYWORDS: KEYWORDS:

2-D Resistivity; Induced Polarization; Iron ore; Chargeability

INTRODUCTION In general, the study area covered by colluvium of Jurrasic - Triasic age with arenaceous and argillaceous beds predominates. According to Bashforth (1973), a deposit of iron ore can be defined as a mineral body with sufficient size, iron content, chemical composition, physical and economic characteristic that will allow it to be a source of iron, either immediately or potentially. Iron ore can only be considered to be an iron ore if the total cost of extracting iron from it is comparable with the cost of extracting iron from other ores. This will be governed by many factors, such as iron content, the nature of the impurities and the location of the deposit (Hussain, 1985).

- 2973 -

Vol. 17 [ 2012] , Bund. U

2974

THEORY OF 2D RESI STI VI TY The resistivity method is used in the study of horizontal and vertical discontinuities in the electrical properties of the ground, and also in the detection of three-dimensional bodies of anomalous electrical conductivity. It is routinely used in engineering and hydrogeological investigations to investigate the shallow subsurface geology (Kearey, 2002). The resistivity value for each type of rocks are different for example, igneous rocks tend to have highest resistivity value while sedimentary rock tend to have highest conductive value due to high porosity content. On the other hand, metamorphic rocks have intermediate but overlapping resistivity value. Table 1 shows the resistivity values of some of the typical rocks and soil materials (Keller and Frischknecht, 1996). Table 1: Resistivity values for common rocks and soil mineral (Keller and Frischknecht, 1996). Resistivity (ohm-m) Material 10 to 800 Alluvium 60 to 1000 Sand 1 to 100 Clay 10 to 100 Groundwater (fresh) 8 - 4 x 103 Sandstone 3 20 - 2 x 10 Shale 3 50 – 4 x 10 Limestone 5000 to 1,000,000 Granite

There are many configuration uses in resistivity method such as Wenner, Schlumberger and Pole-dipole configuration. Theoretically, Pole-dipole configuration is an interesting configuration since it ability to providing a large scale of reading. However, the noise that accumulates from the large numbers of reading are also large which make it difficult in processing. Figure 1 shows the configuration for Pole-dipole array (Milsom, 2003).

V

I

∞

Figure 1: Pole-dipole configuration (Milsom, 2003).

Vol. 17 [ 2012] , Bund. U

2975

THEORY OF INDUCED POLARIZATION (IP) IP surveys are perhaps the most useful of all geophysical methods in mineral exploration, being the only ones responsive to low-grade disseminated mineralization. There are two main mechanisms of rock polarization and three main ways in which polarization effects can be measured. The results obtained by the different techniques are equivalent, but there are practical differences (Milsom, 2003). IP equipment is similar to resistivity, but uses a current about 10 times that of a resistivity spread; it is also rather more bulky and elaborate. Theoretically, any standard electrode spread may be employed but in practice the Dipole-dipole, Pole–dipole and Schlumberger configurations are the most effective. Electrode spacing may vary from 3 to 300m with the larger spacing used in reconnaissance surveys. To reduce the moving current electrodes and generator, several pairs of current electrodes may be used, all connected via a switching device to the generator. Traverses are made over the area of interest plotting the IP reading at the mid-point of the electrode array (Kearey, 2002). The most commonly measured parameters use in IP method is chargeability. Table 2 shows the chargeability of common minerals and rocks (Telford et al., 1976).

Table 2: Charging and integration times of 3 sec and 0.02 - 1.0 sec, respectively (Telford et al., 1976). Material Type Pyrite Chalcocite Copper Graphite Chalcopyrite Bornite Galena Magnetite Malachite Hematite

Chargeability (ms) 13.4 13.2 12.3 11.2 9.4 6.3 3.7 2.2 0.2 0.0

STUDY AREA o

The study area is located at north peninsular Malaysia with latitude of 5   40’ 08.31” and longitude 100o 34’ 17.69”. Most of the area is planted with oil palm and rubber plantation. A total of four survey lines were carried out on the survey area with the total length of 4000m (Figure 2). Lines L1 - L3, were carried out with the orientation of north-west to south east and line L4 was carried out with the orientation of north to south.

Vol. 17 [ 20 12] , Bund. U

297 6

Figure 2: -D resistivity and IP su rveys at stu y area.

METH ODOL GY The study w s carried out with two electrical m thods whic were 2-D resistivity a d Induced Polarization (IP) methods. The sur eys were us ed Pole-dipo le array with 5m minimum electrode spacing. A total of 41 electrodes ere used. The survey us ed four smart cables whi h 100m length eac , ABEM S S4000 syst m and ES1 0-64. Processing was pe rformed usi g Res2 inv softwar .

RES LTS A D DI S CUSSI N The resistivit   result of L1- L4, Figu e 3-6 (top) suggest the area is und rlain by thi k collu iums with r sistivity valu e of 10-300 m. The colluviums can e expected t  cover a depth of up to 150m. The colluviums can be divided into two ones. The fi st zone is ha rd layer whi h the r sistivity val e of 800-1500Ωm while the second zone is boul ders or hard  material with resistivity value 1500Ωm. The bedrock lies between 30-150m d epth with resistivity val e of >8 0 Ωm.

The IP result f L1- L4, Fi ure 3-6 (bottom) suggest the area is un derlain by thick colluviu s with hargeability value of 0.1 3msec. The colluviums a re covering  depth of up to 150m. T e bedrock lies between 30-150m epth with c argeability v alue of >5ms ec.

Vol. 17 [ 20 12] , Bund. U

297 7

Figure 3: Pseudosection f L1; top is resistivity s ection and ottom is ch rgeability section.

Figure 4: Pseudosection f L2; top is resistivity s ection and ottom is ch rgeability section.

Vol. 17 [ 20 12] , Bund. U

297 8

Figure 5: Pseudosection f L3; top is resistivity s ection and ottom is ch rgeability section.

Figure 6: Pseudosection f L4; top is resistivity s ection and ottom is ch rgeability section.

Vol. 17 [ 2012] , Bund. U

2979

CONCLUSI ON As conclusion, the IP result suggests the area is dominated with colluviums with chargeability rate of <5msec which high potential for iron ore mining. The chargeability values of 3-5msec could indicate an average grade of 10 -20% and 0.1-3msec could indicate an average grade of 2040% of iron ore.

REFERENCES 1. Asrarullah and Hussain. A. (1985) "Marble Deposits of North West Frontier Province", Pakistan: Geological Survey of Pakistan Information Release, No. 128. 2. Bashforth, G.R. (1973) "The Manufacture of Iron and Steel", Vol. 1, Bbmbay, B. I. Publishers, pp 137. 3. Keller G.V. and Frischknecht F.C. (1996) "Electrical Methods in Geophysical Prospecting", Pergamon Press Inc., Oxford. 4. Kearey P., Brooks M. and Hill I. (2002) "An Introduction to Geophysical Exploration", Third Edition, Blackwell Science Ltd., pp 183-204. 5. Milsom J. (2003) "Field Geophysics", Third Edition, John Wiley & Sons Ltd., pp 83-126. 6. Reynolds J.M. (1997) "An Introduction to Applied and Environmental Geophysics", John Wiley & Sons Ltd., pp 415-522. 7. Telford, W.M., Geldart, L.P., Sheriff. R.E, and Keys, D.A. (1976) "Applied Geophysics", Cambridge University Press.

© 2012 ejge