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AGE811S - ADVANCED GEOPHYSICS - 1ST OPP - JUNE 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: JUNE 2022
DURATION: 3 HOURS
PAPER: THEORY
MARKS: 100
FIRST OPPORTUNITY EXAMINATION QUESTION PAPER
EXAMINER(S) | Prof Benjamin Mapani
MOpERATOR: | 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
[25]
1.
Indicate the primary geophysical (potential field) method/s that can be used in
the following applications: give a brief explanation why that is the most suitable
(the use of diagrams appropriately will attract marks):
(a) Exploring a gneiss for massive sulphide mineralisation
(5)
(b) reconnaissance exploration of iron deposits on a large scale of
100 km x 100 km (Magnetite and hematite combined).
(5)
(c) Investigating for a subsurface salt dome.
(5)
(d) Identification of pollution/pollutants of fresh ground water ona
municipal landfill or waste disposal site.
(5)
(e) Screening a mining area for acid mine drainage solutions
from the oxidation of pyrite from their tailings dam.
(5)
QUESTION 2
[25]
2.(a) Write the general formula which expresses the form and amplitude ofa
(10)
gravity (or magnetic) anomaly. Briefly explain the effect on an anomaly
of each of the parameters in the formula and outline possible ambiguities.
(b) 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)
(c) What are the two effects on a magnetic (or gravity) anomaly of burying its
source at progressively deeper depths?
(4)
(d) Show three differences between a gravity and magnetic anomaly.
(6)
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QUESTION 3
[25]
(a) Discuss the corrections applied to gravity data in order to produce
a Bouguer anomaly map.
(4)
(b) 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)
(c) What is the function of a base station in magnetics and gravity surveys? How
would Sunspot activity affect your surveys and what time of the day would be best
suited to carry a magnetic survey.
(2, 2, 2)
(d) Sketch a gravity anomaly across the chromite ore body in Figure 1 below. Give a
brief explanation outlining why the anomaly shapes differ.
(6)
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Figure 1.
QUESTION 4
[25]
(a) Figure 2 shows a simple pendulum, suspended by a mass less rod, | and a weight
M. Given the parameters in the diagram, |, M, g and the angle y, derive a formula
for the swing of a pendulum. Find the kinetic energy and velocity of the
pendulum with L =30 cm, and m = 500 g. Use g = 9.81 m/s?.
(15)
(b) Discuss what would happen to the value of g, if different values of M were used, and
explain why. What does this simple experiment tell us about gravimeter
calibrations.
(S)
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(c) Derive the expression for Newton’s universal gravitational law, and equate it to the
formula: F = ma. Discuss the resultant expression and its fundamental usefulness.
(5)
Figure 2.
QUESTION 5
[25]
(a) IP and resistivity are useful in the vertical sounding and profiling methodology.
To do this we need to assess the resistivity or conductivity of the given area.
State three areas where we can use this methodology, in each case state the
relative conductivity/resistivity of the sought after material compared to the
host rock/soil.
(6)
(b) Draw a configuration of the Wenner and Schluberger array. State the differences
between the two and give any advantages if any of one array over the other. (2, 4)
(c) Ifwe need to see or go much deeper in our investigations, which set of electrodes
(voltage or current) do we need to shift and in which fashion relative to the current
or voltage electrodes?
(4)
(d) Discuss the usefulness of radiometrics in the exploration of mineral deposits and
give an example of one such mineral/element/material.
(5)
(e) Distinguish between gamma spectrometers and scintillometers.
(4)
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