Questions and Answers of Geophysics For The Mineral Exploration

What is the difference between absolute and relative measurements? What is a gradient measurement?
Give a practical definition of noise in a geophysical context. Describe some common types of non-geological environmental noise.
A data series comprises 1001 evenly sampled data values spaced 10 m apart. (a) What is the longest wavelength(lowest frequency) fully represented in the data series; (b) what is the shortest
What is levelling? Give examples of typical levelling artefacts.
Describe how data values can be manipulated to create coloured pixel images on a computer screen.
Describe techniques for separating the longer-wavelength regional field and shorter-wavelength local variations in a data series.
How can the strike extent and attitude of an anomaly source be estimated using a contour display of geophysical data? How do changes in depth to the source affect the display?
What is meant when a model is described as 1D, and as 2.5D?
Explain equivalence and the phenomenon of non-uniqueness. How are they related?
What is the difference between forward and inverse modelling? Describe the advantages and disadvantages of both.
Explain why gravity responses are monopoles and magnetic responses dipoles.
Explain induced magnetism, remanent magnetism, total magnetisation and the Konigsberger ratio. How does magnetic susceptibility affect all of these parameters?
Explain how a change in survey height (or depth to the source) affects gravity and magnetic responses. Sketch the various anomalies.
What are the benefits of gravity and magnetic gradiometer measurements over conventional field measurements?
Contrast the sequence of reductions applied to gravity and magnetic survey data.
Sketch in the principal meridian plane the magnetic field of a sphere and the induced magnetic anomaly above it for magnetic inclinations of +90°, +45° and 0°. How do these differ in the opposite
Describe four data processing techniques you would use to assist in the analysis of low-latitude TMI data.
What are horizontal and vertical derivatives, the tilt derivative and the analytic signal? What benefits do they provide over the TMI and gravity field measurements?
Describe the magnetic properties of magnetite. How does grain size influence magnetic properties?
Serpentinisation is an important control on rock magnetism and density – discuss.
Describe an appropriate workflow for the analysis of a set of magnetic susceptibility measurements.
What is Euler deconvolution?
How might magnetic data be used during greenfields exploration for gold deposits in Archaean greenstone belts?
What is meant by the terms half-life and Compton scattering, and why are these important for radiometric surveys?
Compare and contrast individual channel values and channel ratios. How can they be used in the interpretation of radiometric survey data?
Describe how the radiometric element concentration of igneous rocks varies as rock chemistry varies from ultramafic to ultrafelsic.
Describe the nature and distribution of K, U and Th in overburden material.
Give some examples of mineral deposit types which may be directly detected by radiometric surveys.
What is disequilibrium and why is it important?
What is the difference between a scintillometer and a spectrometer? Explain stripping ratios and how they are determined.
Calculate the statistical measurement error for the following count levels measured over one second: 10, 40, 100, 400 and 1000. How does the error change with count level and how can it be reduced
Describe the circle-of-investigation and how this can be used to select the most appropriate survey height.
What is the source of atmospheric radon gas and how are its effects removed during reduction of radiometric survey data?
What are the two main ways in which electric current flows through rocks?
Why is the presence of a conductive overburden so significant for electrical and EM methods?
What are thought to be the main causes of self-potential anomalies?
What factors should be considered when selecting an electrode array for a resistivity/IP survey?
Explain how a pseudosection is created for one of the common electrode arrays. Why does this lead to ‘pants-legs’anomalies?
Explain how the depth of investigation can be varied in electrical and EM methods.
Describe the relationship between the primary and secondary magnetic fields.
What is meant by the terms ‘step response’ and ‘impulse response’ in EM methods?
How would you recognise the response from a confined conductor in time domain electromagnetic data?
How would you differentiate between in-hole and off-hole responses in downhole electromagnetic data?
What factors control the depth penetration of an electromagnetic field?
What kind of electrical and EM surveys would be most suitable for detecting the following kinds of nickel mineralisation? (a) Disseminated sulphide; (b) massive sulphide; (c) lateritic.
Describe what is meant by the terms wavefront, ray and Fresnel zone, and explain their relationship to each other.
Explain the principle of geometric spreading. By how much do the energy and amplitude of body waves and surface waves change when the wavefront expands to double, and four times, its radius?
Describe the main controls on variations of velocity and acoustic impedance across the three main rock classes.
Describe the effects of metamorphism, serpentinisation and weathering on seismic velocity and acoustic impedance.
Describe the process of stacking seismic reflection data. What assumptions are made about the seismic properties of the subsurface, and how might they affect the results in an area of complex geology?
How is a synthetic seismogram produced and how can it be used in the interpretation of seismic data?
Describe the fundamental phenomenon that controls the resolution of seismic reflection data.
Compare and contrast the seismic refraction and reflection methods describing the strengths and weaknesses of both methods.
What type of seismic survey would you use (a) to map the thickness of the sediments in a palaeochannel, (b) to detect massive sulphide mineralization between drillholes and (c) to map a coal seam