GEOPHYSICS (ELECTROMAGNETIC SKEMANG)

Question 1

based on the response f the ground to the propagation of EM fields (Alternating Electric intensity and Magnetizing force)

Answer 1

Electromagnetic Survey

Question 2

an instrument use to primary or inducing field generated by passing an alternate current through a coil/loop or wire placed over the ground

Answer 2

Transmitter Coil

Question 3

IN the presence of a conducting body, the MAGNETIC COMPONENT og an EM field penetrating the ground induces this type of secondary alternating currents to flow within the conductor

Answer 3

Eddy Currents

Question 4

How can the anomaly be measured?

Answer 4

By meauring the difference between the Primary Field (Transmitted) and Secondary Field (received) induced by Eddy Current

Question 5

What information ca the EM anomaly give about a conductor?

Answer 5

3D Perspectives of Mineral Bodies: Geometry and Electrical Properties

Question 6

The depth of penetration in EM Surveys is inversely dependent on

Answer 6

Frequence of EM
Conducitivty of the medium

Question 7

represent the maximum depth at w/c a conductor mau still produce an EM anomaly

Answer 7

Effective Depth of Penetration

Question 8

Used in locating Massive sulfide Boies

Answer 8

Fixed Source Vertical Loop Method

Question 9

EM Method with uses poweful RADIO Transmitters as used in long range communication in which Depth Penetration is low

Answer 9

Very Low Frequency (VLF)

Question 10

This methos uses a natural EM field induced by thunderstorm and enables deeper pentration due to high frequency waves

Answer 10

Audio Frequence Magnetic Method (AFMAG)

Question 11

What is the terms used to denote Ntural EM field caused by thunderstorms?

Answer 11

Sferics

Question 12

Measurement of the secondary field in the absence of the primary field wherien the eddy currents defuse aroung the boundary of a highly conductive subsurfac body and decay slowly when the inducing field is removed.
Rate of decay of Eddy Current can be measured to locate anomalous conducting bodies
Primary Field is non-continuous

Answer 12

Time Domain EM (TDEM)

Question 13

Uses magnetic components of the EM Field so that there is no need for physical contact with the ground for either transmitter and receviever and can be used at much faster speed

Answer 13

Non Contacting Conductivity measurement

Question 14

Widely used during Reconnaissance for traget detection due to its high speed approach to cover vast areas in shortest time making it cost effective

Answer 14

Airborne EM Survey

Question 15

airborne survey when only the receiver is airborne

Answer 15

Passive

Question 16

Both the Transmitter and the receiver are mobile and use where areas of difficult ground access

Answer 16

Active Systems

Question 17

A type of Active Airborne system that use a large transmitter sling between tail and wings and receiver is towed from a cable of about 150 m behind the airfraft. Due to uncotrolled height and direction during flight movement, only the PHASE difference between primary and resultant fields caused by a conductor can be measured

Answer 17

Quadrature System

Question 18

A type of Active Airborne Systemw here the transmitter and coils are mounted either on thwe wings of an aircraft at ground clearance 100-200m or on a beam fixed beneath a helicopter flown at an elevation of 20m maintaining Fixed Separation and height

Answer 18

Fixed Separation System

Question 19

Airborne TDEM

Answer 19

INPUT (Induced Pulse Transient)

Question 20

Flight pattern

Answer 20

To and Fro
E-W/W-E
N-S/S-N

Question 21

Mining and Econ Geol

Answer 21

?Metallic ore, Massive Sulfides
?VMS Deposits
?Locating abandoned mineshafts, crown pillars and subsidence features
?Identifying Bedrock an Mineralization Discontinuities
?Identifying sources of contamination in mining complexes

Question 22

Structural

Answer 22

?Delineating faults, shear zones with thin metallic veins , Facture zones and contacts

Question 23

Hydrogeol

Answer 23

?Hydrogeological Studies

Question 24

Environmental and Engg

Answer 24

?Determination of past land fill sites
?Mapping of Soil types, Land utilziation and Land drainage pattern

Question 25

Archaeology

Answer 25

Buried objects

Question 26

large scale low frequency natural magnetic fields w/in and around earth (Natural EM Fields)

Answer 26

Magnetotelluric field

Question 27

Natural Alternating Electric Currents flowing within and around earth

Answer 27

Telluric Currents

Question 28

The onlye electrical technique capable of penetrating to depths of interest to the OIL INDUSTRY in which potential differences are monitored using NON Polarizing electrodes or plates

Answer 28

Telluric Methods

Question 29

Used in the investigation of crust and upper mantle and is more complex than telluric since both electric and magnetic fields must be measured that provides info about the subsurface

Answer 29

Magnetotelluric Surveying

Question 30

Physical Properties

Answer 30

All boies w/ high electrical conductivity have strong EM Fields
Some which contain insulartors may produce secondary EM Fields if conductive accessory minerals are suffieicient

Question 31

Most conductive VMS

Answer 31

Chalcopyrite and Pyrrhotite

Question 32

Weak Conductors

Answer 32

Sphalerite and barite

Question 33

Profilinvs vs Sounding

Answer 33

Takig a series of reading ALONG A LINE using a fixed configuration of coils or electrodes (Moving but fixed set up ng electrodes)

Sounding only one lcocation with several coil spacing and orientations (Stationary but different setup)

Question 34

Max depth for Groun surveys

Answer 34

500 m

Question 35

Max depth for Airborne

Answer 35

50 m