THE UTILISATION OF 2-D RESISTIVITY AND INDUCED POLARIZATION (IP)

METHOD TO DETERMINE THE IRON ORE BODIES FROM THE MAGNETIC

SURVEY RESULT AT KAMPUNG MELAKA, KUALA LIPIS, PAHANG

Adreina Shamelia SH1, Fathin Nur Amirrah MN1, Kasdi Nata S1, Dr Mohd Rozi2

1PERMATApintar® National Gifted Center, Universiti Kebangsaan Malaysia2School of Environment and Earth Science, Faculty of Science and Technology,

Universiti Kebangsaan Malaysia

ABSTRACT

In Malaysia, on mineral that has high potential to be explored is iron ore. To identify the iron ore

bodies, 2-D resistivity is used in this study whereas Induced Polarization (IP) method is used to

differentiate between iron ore deposits and ground water beneath the ground. A small current was

injected into the ground by the electrodes and the resulting voltage difference between the electrodes

was determined which will present the resistivity measurement. By using the 2- D resistivity method,

iron ore can be detected by its low resistivity. Meanwhile, high resistivity indicates the presence of

ground water, residual soil, fresh rocks and weathered rock. A total of three survey lines with a total

length of 600 m is divided into three different lots, each has a total length of 200m. The study was held

at Kampung Melaka, Kuala Lipis, Pahang, Malaysia. Magnetic survey result was used to gain the

result from the collected data. The result shows that the iron ore underlying the surface from the depth

of 5m down until 30m was mostly located at lot 1 and 2 based on their low resistivity. The first lot

consisted of iron ore from 20% until 25%. The second lot indicated the existence of iron ore for about

30% to 35% whereas third lot only point out the existence for about 15% to 20% over each 200m

survey line.

KEYWORDS: Iron ore; 2-D Resistivity; Induced Polarization (IP) method; Survey lines

INTRODUCTION

The most common element in the Earth’s crust are oxygen, silicone, aluminium and iron at the

fourth place. Iron is mostly found in combination with other elements such as oxygen, and also in the

form of iron oxide minerals such as magnetite (Fe3O4) or hematite (Fe2O3) and other compounds.

Resistivity survey is a method used to find the subsurface resistivity distribution based on the

measurements made on the surface of the ground. The real resistivity of the subsurface can be

assumed from the measurements ( Loke, 2001). The resistivity of material is defined as the resistance

in ohms between the opposite faces of a unit cube of the material (Kearey et al., 2002).

The presence of Induced Polarization (IP) method in the instrumentation for magnetic surveys

has been the most advance system. The inversion of IP data can be done with the RES2DINV, a

computer program. Generally, there are two mechanisms for IP which are membrane polarization and

the electrode polarization effects. The clay minerals consist in the rock or sediment is responsible to

cause membrane polarization effect whereas the conductive minerals in rocks cause the electrode

polarization ( Loke, 2001)

LITERATURE REVIEW

Iron ore can be categorized into low-grade and high grade ore depending on the percentage of

the presence of iron compound. High-grade ore contains more than 60% of iron and perhaps, comes

from deposits of massive hematite formed by in situ enrichment of iron, usually a banded iron

formation. Low-grade iron ore, on the other hand, commonly contains 25-30% of iron and it naturally

forms iron-rich rock. Most of iron ore deposits in the world contains low-grade iron because of the

presence of other minerals, mainly silica. Demand of iron ore is increasing yearly among industry

players and iron ore is an important commodity besides gas, oil and gold (Rosli Saad et al, 2012).

Electrical survey method is currently the preferred method and requires taking measurement

on the ground surface in order to find the subsurface resistivity distribution. Various geological

parameters such as minerals, underground water and porosity are related to ground resistivity. To

measure the resistivity, current is injected through two electrodes which are planted into the ground

and the resulting voltage difference at two potential electrodes are then taken. An apparent resistivity

value can be measured from the current (I) and voltage (V) values,

pa=kV / I

where k is the geometric factor which depends on the order of four electrodes. Resistivity meters

normally show a resistance value, so apparent resistivity is measured by

pa=kR

To find out the original subsurface resistivity, an inversion of the calculated apparent resistivity values

using a software in the computer must be carried out which is RES2DINV (Loke, 1999).

"Induced polarization (IP) is an electrical geophysical method to measure the effect on current

flow of charge storage beneath ground" (Rosli Saad et al, 2012). IP can identify disseminated

minerals. Overvoltage, the basic concept, occurs because of the characteristic of ground which plays

the part as capacitor when DC current is turned off, voltage calculated does not immediately drop to

zero from two potential electrodes but takes finite time to rot with time. Then, DC current is turned on

and voltage calculated takes same finite time to achieve steady value (Milson, 2003).

The most important parameter to be obtained from the IP method is chargeability of minerals

and rocks. Chargeability is defined as the ratio of the area under the decay curve to the potential

difference calculated before turning the current off. Real chargeability is the ratio of the secondary

voltage, Vs, or the over- to the observed voltage, Vo (Seigel, 1959)

METHODOLOGY

The 2-D resistivity and IP are the two electrical imaging methods that is used to conduct this

study. The 2-D resistivity method is responsible to determine the ore bodies from the contrast of

resistivity value but the IP method is utilized to secernate the chargeability of the subsurface between

ground water and iron ore. Two survey lines of about 100m each are used for every 3 lines which

make a total of 600m. The electrode spacing for the pole- dipole array used is about 5m. The software

used to process the data was the RES2DINV.

Study Area

The study area is situated at Kampung Melaka, in Kuala Lipis, Pahang. This site covers the

land area of 400 acres (Figure 1) and is located about 10 km away from Kuala Lipis town. Some 200

magnetic data were collected at the study area. The magnetic survey points were marked as KML

which refers to Kg. Melaka in our survey reference. The GPS reading was saved with the label

KML01A as for the first point at the first line. Each line has 3 points to be taken its location. The tags

are being continued until the last point for the third line. All these 3 points are situated in 3 different

places with different remarks.

The Instrument

The main instrument used for this magnetic survey were ABEM SAS1000 resistivity meter

and ABEM LUND ES464 electrode selector system. This system was laid out in a straight line where

41 stainless steel electrodes were connected with multi- core cable. Only three active electrodes were

selected to be taken their measurements. The spacing between each electrodes was 5 metres apart for a

length of about 200m and about 30m in depth, based on Wenner spacing electrode array.

Figure 1: Resistivity meter and electrode selector system used in magnetic survey

RESULT AND DISCUSSION

Line 1

Figure 2: Line 1

Figure 2 above shows Line 1from KML01A to KML01B, covering the distance of 100m,

between KML01A and KML01B. Similarly, the distance from KML01B to KML01C is also

equivalent to the distance between the first two points..

Figure 3: The resistivity section (right side) and IP section (left side) of KML01 survey line.

From Figure 3, it is observed that the higher the number of the chargeability of the section, the

higher the abundance of the iron ore body. Result for Figure 3 shows the abundance of the quality iron

ore body is little. This is shown by the various colours of the diagram. The orange to purple part

means the soil of the site; whereas the blue to green part shows the abundance of the iron ore body on

the site. The red part of the Figure 3 indicated high quality iron ore. Figure 3 above shows the

resistivity test on Line 1. Based on the results of the test that had been carried out on Line 1, there are

obviously more soil and rock than the iron ore bodies itself. The iron ore that are abundance in the this

figure show its number near 100m and there are only small part of the iron ore shows the part of the

dark blue part of iron. There are a lot more non-quality iron ore than the quality iron ore itself. Most of

the section is filled with residual stone. It covers almost 50% of the diagram.

For resistivity section for Line 1, Figure 3 shows the abundance of iron ore body, including the

one with the mixed iron, which had been bonded with other element; such as silica. The resistivity of

the iron ore is used to the section of the iron ore on the site. The most accurate result is the

chargeability section. For Line 1, as the colour goes up, there less abundance of the iron ore body.

Line 2

Figure 4: Line 2

Figure 2 shows Line 2 which consist of 3 points. The distance between these points is about

100m each. That means that it is 100m from KML02A to KML02B, and also the same for KML02B

to KML02C.

Figure 5: The resistivity section (left side) and IP section (right side) of KML02 survey line.

The result for the resistivity at Line 2 shows that the potential iron ore is situated under the

weathered rock and followed by fresh rock. This is based on the colour of the graph as the blue part

indicates the presence of potential iron ore. As it also means that there are plenty of iron ore if the

number of the chargeability of the section is superior. Based on the results of the test, it seems obvious

that the iron ore at Line 2 is more than other two lines as it covers almost 60 meters from each side

with the depth of 15 meters from the bottom. The fresh rocks fill the depth for about 10 meters at the

first 80 meters length and the next 80 meters with a gap of 40 meters. This is because the orange and

brown parts are both show the fresh rocks while the green and yellow parts indicate the weathered

rock.

The profile of the IP result shows that it is covered by a thick soil with chargeability value of 10.3

– 93.3 msec. The pure iron ore which has chargeability value of ¿0 .02 msec is found to be at the

depth of from the surface until 20m downwards.

Line 3

Figure 6 : Line 3

This is a picture of Line 3 which consist of 3 points that have been taken from Google Earth

based on their coordinates. The coordinates were taken while the research was conducted. The

distance between these points are about 100m each which means that it is 100m from KML03A to

KML03B and also the same for KML03B to KML03C.

The survey line three is located at the highest place among the three survey lines. There was a

construction during the period of our research. The length of survey line is 200 m with 5.0 m spacing

for each electrode. The interpretation from the resistivity survey shows that the subsurface profile for

the line survey three consists of boulders as the main component (309−762Ωm) . The dark blue

shows that there are small amount of quality iron ore in this profile (50 .8−125Ωm). The potential

iron ore is found at the start and the end of the line survey about 40 m long. The centre of the profile is

fulled with weathered rocks and small parts of fresh rocks. Their thickness is about 10 m depth.

The IP result shows that the profile is covered by a thick soil with chargeability value of

12 .2−71. 2msec . Pure iron ore with chargeability value of ¿0 . 02 msec is expected to lies at 13.4-

21.5 m depth.

Figure 7 : The resistivity section (left side) and IP section (right side) of KML03 survey line.

CONCLUSION

The iron ore at all three lines are shown to be about 15 - 35%. There is not much potential iron ore at

these lines. Line 1 came out to have average potential iron ore of about 20-25% while at Line 2, it has

the highest amount of potential iron ore which about 30 – 35%. As for Line 3, the estimated iron ore is

about 15-20%.

REFERENCES

Griffith, D.H. and Barker, R.D., 1993. Two dimensional resistivity imaging and modeling in areas of complex geology. Journal Applied Geophysics, 29:211-226.

Hutchinson, 2009. Geology of Malaysia, Geological Society of Malaysia

Keary, P., Brooks M. and Hill i., 2002. “An Introduction to Geophysical Exploration,” 3rd edition, Blackwell Science, :183-203.

Keller, G.V. and Frischknecht F.C. 1996. Electrical Methods in Geophysical Prospecting. , Oxford: Pergamon Press Inc.

Lindgren and Waldemar, 1933. Mineral Deposits, 4th Edition, New York:McGraw-Hill.

Loke, M. H. 1994. The inversion of two-dimensional resitivity data. Unpubl. PhD thesis, University Of Birmingham

Loke M.H. and Barker R.D., 1996. Rapid Least-squares Inversion of Apparent Resistivity Pseudoction using a Quasi-Newton Method, Geophysical Prospecting, 44:131-152.

Milsom, J., 2003. “Applied Geophysics,” 3rd edition, John Wiley & Sons Ltd., :83-126.

Telford, W.M. and R.F. Sheriff, 1990. Applied Geophysics, 2nd Edition, Cambridge University Press.

Wait, J.R., 1958. Discussions on a Theoritical Study of Induced Electrical Polarization, Geophysics, 23:144-154.

Zonge, K.L., Sauck, W.A. and Sumner, J.S., 1972. Comparison of Time, Frequency, and Phase Measurements in Induced Polarization, Geophysical Prospecting, 20:626-648.