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AGE811S - ADVANCED GEOPHYSICS - 2ND OPP - JULY 2022 |
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NAMIBIA UNIVERSITY
OF SCIENCE AND TECHNOLOGY
FACULTY OF HEALTH, APPLIED SCIENCES AND NATURAL RESOURCES
DEPARTMENT OF NATURAL AND APPLIED SCIENCES
QUALIFICATION : BACHELOR OF SCIENCE HONOURS
QUALIFICATION CODE: 08BOSH
LEVEL: 8
COURSE CODE: AGE811S
COURSE NAME: ADVANCED GEOPHYSICS
SESSION: JULY 2022
DURATION: 3 HOURS
PAPER: THEORY
MARKS: 100
SUPPLEMENTARY/ SECOND OPPORTUNITY EXAMINATION QUESTION PAPER
EXAMINER(S) | Prof Benjamin Mapani
MODERATOR: | Mr. Robert Mwanachilenga
ANSWER QUESTION ONE (1) AND ANY OTHER THREE (3)
THIS QUESTION PAPER CONSISTS OF 4 PAGES (Including this front page)
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QUESTION 1: Compulsory
1.1 Name any 4 branches of Geophysics and the relevant rock physical property
on which each branch relies.
[5]
1.2 What are the units that we use in magnetic and gravity surveys?
[5]
1.3. Name four (4) major applications of geophysical methodology.
[10]
1.4. Name the arrays commonly used in resistivity and IP
surveys for sounding and profiling.
[5]
QUESTION 2.
2.1 Write the general formula which expresses the form and amplitude of a
gravity (or magnetic) anomaly. Briefly explain the effect on an anomaly
of each of the parameters in the formula and outline possible ambiguities.
[10]
2.2 Show, with the aid of a sketch, the effect on a magnetic anomaly of taking
readings at too coarse a spacing. Discuss how this will affect interpretation?[5]
2.3. Of the two effects on a magnetic (or gravity) anomaly that happens as one buries
its source at progressively at deeper depths, use a sketch to show how the gravity or
magnetic profile will look at (i) shallow depth, (ii) intermediate depth and (iii) very deep
levels.
[4]
2.4. Show three differences between a gravity and magnetic anomaly
[6]
QUESTION 3
3.1 Name the reductions that need to be applied to observed gravity data
in order to produce a Bouguer anomaly map.
[4]
3.2 The magnetic data is normaly produced in Total Magnetic intensity anomalies.
From this is calculated the First Vertical Derivative and Analytical Signal. List the
benefits, and drawbacks, of doing so in each case.
[9]
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3.3 What is meant by the terms:
magnetization and magnetic coercivity
induced
magnetization;
remanent
[6]
3.4 Sketch a gravity anomaly across the given ore bodies in Figure 1 below. Give a brief
explanation outlining why the anomaly shapes differ.
[6]
gulsums 2)
150
100
50
k eS-—a—!—4km
6.8 —
10.2 —
$L== 1085kkg/mm?
25.5
34.0 kr
- LENP GTHP =13§k=m160 kg/m ¢ f |///s/j!/j~8km — a
DENSITY= 2700 kg/m?
gulsums)
150
100
50
6=40kg/m>
L= 8.7 km
0.0
8.5
17.0
255
ian4 aA 7
Treg t,t,
a
NGTH=4k4r
6.8
10.2
—
—
28km
L$E=NG2T7H0=kg/9mk3m
= 40 kg/m:
DENSITY= 2700 kg/m?
C
Figure 1a and b.
34.0km
QUESTION 4
a. Explain the following terms and their usefulness in data filtering: (i) first vertical
derivative (FVD); (ii) analytic signal (AS).
[10]
b. Sketch the Wernner and Schlumberger arrays and state what the main difference
between the two is.
[5]
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c. Name the elements/minerals that we can explore for using radiometrics, and state
the name one of the instruments used in this method.
[5]
d. For deeper ore bodies, which method would give us the best result between
gravity and magnetics? Explain your answer.
[5]
QUESTION 5
5.1. Discuss the usefulness of radiometrics in the exploration of mineral deposits and
give an example of one such mineral/element/material.
[9]
5.2. Explain in some detail the differences on how gamma spectrometers and
scintillometers actually obtain data.
[8]
5.3. In the case of borehole spectrometer surveys, discuss the methodology and the
material we use to cover the borehole probe, giving details why this is necessary. You
may use a suitable sketch to illustrate your answer.
[8]